HYBRIDIZATION PROBES AND METHODS
The present invention relates to compositions and methods for detection, analysis, and treatment of nucleic acids. In particular, the present invention relates to compositions and methods for generating and using hybridization probes.
This application is a continuation application of and claims priority to U.S. patent application Ser. No. 14/938,240, filed Nov. 11, 2015, and claims priority to U.S. provisional patent application Ser. No. 62/078,252, filed Nov. 11, 2014, each of which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTIONThe present invention relates to compositions and methods for detection, analysis, and treatment of nucleic acids. In particular, the present invention relates to compositions and methods for generating and using hybridization probes.
BACKGROUNDFISH (fluorescence in situ hybridization) is a cytogenetic technique that is used to detect and localize the presence or absence of specific DNA sequences on chromosomes. FISH uses fluorescent probes that bind to only those parts of the chromosome with which they show a high degree of sequence complementarity. Fluorescence microscopy can be used to find out where the fluorescent probe is bound to the chromosomes. FISH is often used for finding specific features in DNA for use in genetic counseling, medicine, and species identification. FISH can also be used to detect and localize specific RNA targets (mRNA, lncRNA and miRNA) in cells, circulating tumor cells, and tissue samples. In this context, it can help define the spatial-temporal patterns of gene expression within cells and tissues.
Human genomic DNA is a mixture of unique sequences and repetitive sequences that are present in multiple copies throughout the genome. In some applications, it is desirable to generate hybridization probes that anneal only to unique sequences of interest on a chromosome. Preparation of unique sequence probes is confounded by the presence of numerous classes of repetitive sequences throughout the genome of the organism (Hood et al., Molecular Biology of Eucaryotic Cells (Benjamin/Cummings Publishing Company, Menlo Park, Calif. 1975). The presence of repetitive sequences in hybridization probes reduces the specificity of the probes because portions of the probe bind to other repetitive sequences found outside the sequence of interest. Thus, to ensure binding of hybridization probes to a specific sequence of interest, probes lacking repetitive sequences are needed.
Recent contributions have addressed this question by inhibiting hybridization of the repetitive sequences with the use of unlabeled blocking nucleic acids (U.S. Pat. No. 5,447,841 and U.S. Pat. No. 6,596,479). Use of blocking nucleic acids in hybridizations is expensive, does not completely prevent hybridization of the repetitive sequences, and can distort genomic hybridization patterns (Newkirk et al., “Distortion of quantitative genomic and expression hybridization by Cot-1 DNA: mitigation of this effect,” Nucleic Acids Res. vol 33 (22):el91 (2005)). Thus, methods that prevent hybridization of repeat sequences without the use of blocking DNA are desirable for optimal hybridization.
One means to achieve this is to remove unwanted repeat segments from the hybridization probes prior to hybridization. Techniques involving the removal of highly repetitive sequences have been previously described. Absorbents, like hydroxyapatite, provide a means to remove highly repetitive sequences from extracted DNA. Hyroxyapatite chromatography fractionates DNA on the basis of duplex re-association conditions, such as temperature, salt concentration, or other stringencies. This procedure is cumbersome and varies with different sequences. Repeat DNA can also be removed by hybridization to immobilized DNA (Brison et al., “General Methods for Cloning Amplified DNA by Differential Screening with Genomic Probes,” Molecular and Cellular Biology, Vol. 2, pp. 578-587 (1982)). In all of these procedures, the physical removal of the repetitive sequences will depend upon the strict optimization of conditions with inherent variations based upon the base composition of the DNA sequence.
Several other methods to remove repetitive sequences from hybridization probes have been described. One method involves using a cross-linking agent to cross-link repetitive sequences either to directly prevent hybridization of repetitive sequences or to prevent amplification of repeat sequences in a PCR reaction. (U.S. Pat. No. 6,406,850). Another method uses PCR assisted affinity chromatography to remove repeats from hybridization probes (U.S. Pat. No. 6,569,621). Both of these methods rely on the use of labeled DNA to remove repeat sequences which makes these processes complex and difficult to reproduce. Further, both methods are time consuming, requiring multiple rounds of repeat removal to produce functional probes suitable for use in fluorescent in situ hybridization (FISH) or other hybridization reactions requiring high target specificity.
Thus, methods for removing repetitive sequences from probes are desired.
SUMMARY OF THE INVENTIONThe present invention relates to compositions and methods for detection, analysis, and treatment of nucleic acids. In particular, the present invention relates to compositions and methods for generating and using hybridization probes.
Embodiments of the present technology provide compositions, kits, and systems for generating and using probes selectively generated or synthesized to exclude sequences of disinterest and/or include sequences of interest (e.g., substantially repeat-free nucleic acid probes). For example, in some embodiments, the present invention provides a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences (e.g., free of repeats, non-conserved sequences, conserved sequences, GC rich sequences, AT rich sequences, secondary structure, or coding sequences) of the nucleic acid of interest that are at least 100 bp in length (e.g., at least 100, 200, at least 300, or at least 400) and optionally no more than 20% different in length from each other (e.g., 20% or less, 10% or less, 5% or less, 4% or less, 3% or less, 3% or less, 1% or less, or identical lengths); and b) generating (e.g., via amplification, cloning, synthesis, or a combination thereof) a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence. In some embodiments, the method further comprises one or more of the steps of c) fragmenting the probe-containing nucleic acids to generate probes; and d) further amplifying a subset of the probes to generate probes substantially free of undesired sequences (e.g., ISH probes lacking, for example, undesired repeat sequences). In some embodiments, the method further comprises the step of d) separating probes based on size. In some embodiments, the separating is conducted using chromatography or electrophoresis. In some embodiments, the method further comprises the step of isolating a subset of the probes. In some embodiments, the subset is based on size of the separated nucleic acid. In some embodiments, the probes are attached to nucleic acid adaptors. In some embodiments, the adaptors are amplification primers. In some embodiments, the amplification primers are functionalized for downstream applications (e.g., by the addition of labels, binding sites, or restriction sites). In some embodiments, the probes are separated and a subset of the probes ais isolated. In some embodiments, the amplification is PCR. In some embodiments, regions substantially free of undesired sequence are identified using computer software and a computer processor. In some embodiments, the of probe-containing nucleic acids are fragmented by sonication (although any of a variety of other chemical, physical, or other approaches may be used). In some embodiments, the separating is by electrophoresis or chromatography. In some embodiments, the fragments are from about 100 to 500 bp in length, although other lengths may be used. In some embodiments, the probes are labeled (e.g., with a fluorescent label). In some embodiments, probes are 85% , 90% , 91% , 92% , 93% , 94% , 95% , 96% , 97% , 99% , or 100% free of undesired nucleic acid sequences.
In some embodiments, the present invention provides a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; c) fragmenting the probe-containing nucleic acids to generate probes; d) attaching adaptors to the probes; and optionally e) further amplifying a subset of the probes.
Further embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; c) fragmenting the probe-containing nucleic acids to generate probes;; and optionally d) further amplifying a subset of the probes.
Additional embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences, wherein the undesired region is, for example, repeat sequence, non-conserved sequences, conserved sequences, GC rich sequences, AT rich sequences, secondary structure, or coding sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; and c) fragmenting the probe-containing nucleic acids to generate probes; and optionally d) further amplifying a subset of the probes.
Yet other embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; c) fragmenting the probe-containing nucleic acids to generate probes; d) separating the probes by size; e) isolating a subset of the probes; and optionally f) further amplifying a subset of the probes.
Still other embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; c) fragmenting the probe-containing nucleic acids to generate probes; d) separating the probes by size; e) isolating a subset of the probes, wherein the subset comprises nucleic acids of 80 to 300 bp in length (e.g., approximately 150 bp in length); and optionally f) further amplifying a subset of the probes.
Additional embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; and c) fragmenting the probe-containing nucleic acids to generate probes; optionally d) further amplifying a subset of the probes generate a probe set; and e) performing a hybridization assay (e.g., ISH assay) with the probe set.
Further provided herein are a set of nucleic acid probes (e.g., hybridization probes (e.g., in situ hybridization (ISH) probes)) free of undesired sequences generated by the aforementioned methods and kits and systems comprising the probes. The present disclosure is not limited to a particular assay or target. In some embodiments, probes detect expression of an oncogene or chromosomal aneuploidy.
Additionally provided herein are methods of performing a hybridization assay, comprising contacting a target nucleic acid with a probe (e.g., an ISH probe) generated by the aforementioned method.
Also provided herein is the use of any a probe (e.g., a ISH probe) generated by the aforementioned method in a hybridization (e.g., ISH) assay.
Additional embodiments are described herein.
As used herein, the term “substantially free of undesired nucleic acids” refers to a nucleic acid that is substantially free (e.g., 85% , 90% , 91% , 92% , 93% , 94% , 95% , 96% , 97% , 99% , or 100% free) of undesired nucleic acids. Undesired nucleic acids include, but are not limited to, repeated nucleic acids, non-conserved sequences, conserved sequences, GC rich sequences, AT rich sequences, secondary structure, or coding sequences
As used, the terms “substantially repeat free nucleic acid sequence” or “nucleic acids free of repeats” refer to a region of nucleic acid that is substantially free (e.g., 85% , 90% , 91% , 92% , 93% , 94% , 95% , 96% , 97% , 99% , or 100% free) of repeated nucleic acid sequence.
As used herein, the term “sample” is used in its broadest sense. In one sense, it is meant to include cells (e.g., human, bacterial, yeast, and fungi), an organism, a specimen or culture obtained from any source, as well as biological samples. Biological samples may be obtained from animals (including humans) and refers to a biological material or compositions found therein, including, but not limited to, bone marrow, blood, serum, platelet, plasma, interstitial fluid, urine, cerebrospinal fluid, nucleic acid, DNA, tissue, and purified or filtered forms thereof. Such examples are not however to be construed as limiting the sample types applicable to the present invention.
The term “label” as used herein refers to any atom or molecule that can be used to provide a detectable (preferably quantifiable) effect, and that can be attached to a nucleic acid or protein. Labels include but are not limited to dyes; radiolabels such as 32P; binding moieties such as biotin; haptens such as digoxgenin; luminogenic, phosphorescent or fluorogenic moieties; and fluorescent dyes alone or in combination with moieties that can suppress or shift emission spectra by fluorescence resonance energy transfer (FRET). Labels may provide signals detectable by fluorescence, radioactivity, colorimetry, gravimetry, X-ray diffraction or absorption, magnetism, enzymatic activity, and the like. A label may be a charged moiety (positive or negative charge) or alternatively, may be charge neutral. Labels can include or consist of nucleic acid or protein sequence, so long as the sequence comprising the label is detectable. In some embodiments, nucleic acids are detected directly without a label (e.g., directly reading a sequence).
As used herein, the term “nucleic acid molecule” refers to any nucleic acid containing molecule, including but not limited to, DNA or RNA. The term encompasses sequences that include any of the known base analogs of DNA and RNA including, but not limited to, 4-acetylcytosine, 8-hydroxy-N6-methyladenosine, aziridinylcytosine, pseudoisocytosine, 5-(carboxyhydroxylmethyl)uracil, 5-fluorouracil, 5-bromouracil, 5-carboxymethylaminomethyl-2-thiouracil, 5-carboxymethylaminomethyluracil, dihydrouracil, inosine, N6-isopentenyladenine, 1-methyladenine, 1-methylpseudouracil, 1-methylguanine, 1-methylinosine, 2,2-dimethylguanine, 2-methyladenine, 2-methylguanine, 3-methyl cytosine, 5-methylcytosine, N6-methyladenine, 7-methylguanine, 5-methyl aminomethyluracil, 5-methoxyaminomethyl-2-thiouracil, beta-D-mannosylqueosine, 5′-methoxycarbonylmethyluracil, 5-methoxyuracil, 2-methylthio-N6-isopentenyladenine, uracil-5-oxyacetic acid methylester, uracil-5-oxyacetic acid, oxybutoxosine, pseudouracil, queosine, 2-thiocytosine, 5-methyl-2-thiouracil, 2-thiouracil, 4-thiouracil, 5-methyluracil, N-uracil-5-oxyacetic acid methylester, uracil-5-oxyacetic acid, pseudouracil, queosine, 2-thiocytosine, and 2,6-diaminopurine.
As used herein, the term “hybridization” is used in reference to the pairing of complementary nucleic acids. Hybridization and the strength of hybridization (i.e., the strength of the association between the nucleic acids) is impacted by such factors as the degree of complementary between the nucleic acids, stringency of the conditions involved, the Tm of the formed hybrid, and the G:C ratio within the nucleic acids. A single molecule that contains pairing of complementary nucleic acids within its structure is to be “self-hybridized.”
The term “primer” refers to an oligonucleotide, whether occurring naturally as in a purified restriction digest or produced synthetically, which is capable of acting as a point of initiation of synthesis when placed under conditions in which synthesis of a primer extension product which is complementary to a nucleic acid strand is induced, (e.g., in the presence of nucleotides and an inducing agent such as DNA polymerase and at a suitable temperature and pH). The primer is preferably single stranded for maximum efficiency in amplification, but may alternatively be double stranded. If double stranded, the primer is first treated to separate its strands before being used to prepare extension products. Preferably, the primer is an oligodeoxyribonucleotide. The primer should be sufficiently long to prime the synthesis of extension products in the presence of the inducing agent. The exact lengths of the primers will depend on many factors, including temperature, source of primer and the use of the method. For example, in some embodiments, primers range from 10 to 100 or more nucleotides (e.g., 10-300, 15-250, 15-200, 15-150, 15-100, 15-90, 20-80, 20-70, 20-60, 20-50 nucleotides, etc.).
In some embodiments, primers comprise additional sequences that do not hybridize to the nucleic acid of interest. The term “primer” includes chemically modified primers, fluorescence-modified primers, functional primers (fusion primers), sequence specific primers, random primers, primers that have both specific and random sequences, and DNA and RNA primers
The term “amplifying” or “amplification” in the context of nucleic acids refers to the production of multiple copies of a polynucleotide, or a portion of the polynucleotide, typically starting from a small amount of the polynucleotide (e.g., as few as a single polynucleotide molecule), where the amplification products or amplicons are generally detectable. Amplification of polynucleotides encompasses a variety of chemical and enzymatic processes. The generation of multiple DNA copies from one or a few copies of a target or template DNA molecule during a polymerase chain reaction (PCR), rolling circle amplification (RCA), or a ligase chain reaction (LCR) are forms of amplification. Amplification is not limited to the strict duplication of the starting molecule. For example, the generation of multiple cDNA molecules from a limited amount of RNA in a sample using reverse transcription (RT)-PCR is a form of amplification. Furthermore, the generation of multiple RNA molecules from a single DNA molecule during the process of transcription is also a form of amplification.
As used herein, the term “solid support” is used in reference to any solid or stationary material to which reagents such as antibodies, antigens, and other test components are attached. Examples of solid supports include microscope slides, wells of microtiter plates, coverslips, beads, particles, cell culture flasks, as well as many other suitable items.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTIONThe present invention relates to compositions and methods for detection, analysis, and treatment of nucleic acids. In particular, the present invention relates to compositions and methods for generating and using hybridization probes.
Embodiments of the present technology provide compositions and methods for generating probes substantially free of undesired sequences (e.g., FISH probes lacking undesired sequences, such as repeat sequences) that solve the limitations of existing methods of removing undesired sequences from probes by providing multistep or otherwise burdensome methods.
Embodiments of the present invention are illustrated for use in generating repeat free ISH probes. One of skill in art understands that the disclosed methods can also be applied to other undesired sequences and other probe applications.
The presence of repeat sequence in FISH probes leads to background signals in other loci containing similar repeats. Additionally it increases the bulk of the FISH probe unnecessarily, leading to wasted material. Finally, regardless of the repeat sequence, FISH probes are typically prepared from DNA generated directly from BAC sequences over 100 kb in length. The methods provided herein allow selection of non-repeat sequence, specific to the genomic region of interest, circumventing potential issues with availability of BACs covering the genomic region of interest and overcomes disadvantages of existing methods of generating repeat-free probes (See e.g., Rogan et al., Genome Research 11:1086-1094, 2001; Commercially available probes from Kreatech, Durham, N.C.; Sealey et al. Nuc. Acid. Res. Volume 13 Number 6 1985; Dorman et al., Nucleic Acids Research, 2013, Vol. 41, No. 7; Boyle et al., Chromosome Res. 2011 October; 19(7):901-9; and Craig et al., Hum Genet (1997) 100 : 472-476).
The probes described herein provide the following advantages over existing probes: decrease in interference from repeat sequence; eliminates the need for human DNA blocker; faster hybridization times; higher hybridization temperature (e.g., easier probe removal and more uniform hybridization temperatures), resulting in faster hybridization times; preparation via amplification (e.g., PCR) gives faster, less expensive, more reliable manufacture; and, once made, the template finds use in scale up and manufacturing applications.
I. Generation of ProbesExemplary methods of generating probes substantially free of undesired sequences are described below. Embodiments of the present invention are illustrated for use in generating ISH (e.g., FISH) probes. One of skill in art understands that the disclosed methods can also be applied to other undesired sequences and other probe applications.
Embodiments of the present technology provide compositions, kits, and systems for generating and using probes selectively generated or synthesized to exclude sequences of disinterest and/or include sequences of interest (e.g., substantially repeat-free nucleic acid probes). For example, in some embodiments, the present invention provides a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences (e.g., free of repeats, non-conserved sequences, conserved sequences, GC rich sequences, AT rich sequences, secondary structure, or coding sequences) of the nucleic acid of interest that are at least 100 bp in length (e.g., at least 100, 200, at least 300, or at least 400) and optionally no more than 20% different in length from each other (e.g., 20% or less, 10% or less, 5% or less, 4% or less, 3% or less, 3% or less, 1% or less, or identical lengths); and b) generating (e.g., via amplification, cloning, synthesis, or a combination thereof) a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence. In some embodiments, the method further comprises one or more of the steps of c) fragmenting the probe-containing nucleic acids to generate probes; and d) further amplifying a subset of the probes to generate probes substantially free of undesired sequences (e.g., ISH probes lacking, for example, undesired repeat sequences). In some embodiments, the method further comprises the step of d) separating probes based on size. In some embodiments, the separating is conducted using chromatography or electrophoresis. In some embodiments, the method further comprises the step of isolating a subset of the probes. In some embodiments, the subset is based on size of the separated nucleic acid. In some embodiments, the probes are attached to nucleic acid adaptors. In some embodiments, the adaptors are amplification primers. In some embodiments, the amplification primers are functionalized for downstream applications (e.g., by the addition of labels, binding sites, or restriction sites). In some embodiments, the probes are separated and a subset of the probes ais isolated. In some embodiments, the amplification is PCR. In some embodiments, regions substantially free of undesired sequence are identified using computer software and a computer processor. In some embodiments, the probe-containing nucleic acids are fragmented by sonication (although any of a variety of other chemical, physical, or other approaches may be used). In some embodiments, the separating is by electrophoresis or chromatography. In some embodiments, the fragments are from about 100 to 500 bp in length, although other lengths may be used. In some embodiments, the probes are labeled (e.g., with a fluorescent label). In some embodiments, probes are 85% , 90% , 91% , 92% , 93% , 94% , 95% , 96% , 97% , 99% , or 100% free of undesired nucleic acid sequences.
In some embodiments, the probes are approximately 50 to 1000 bp in length. For example, in some embodiments, probes are 50 to 900 bp, 50 to 800 bp, 50 to 700 bp, 50 to 600 bp, 50 to 500 bp, 50 to 450 bp, 50 to 400 bp, 50 to 350 bp, 50 to 300 bp, 50 to 250 bp, 50 to 200 bp, 50 to 150 bp, 50 to 100 bp, 80 to900 bp, 80 to 800 bp, 80 to 700 bp, 80 to 600 bp, 80 to 500 bp, 80 to 450 bp, 80 to 400 bp, 80 to 350 bp, 80 to 300 bp, 80 to 250 bp, 80 to 200 bp, 80 to 150 bp, 80 to 100 bp, 100 to 900 bp, 100 to 800 bp, 100 to 700 bp, 100 to 600 bp, 100 to 500 bp, 100 to 450 bp, 100 to 400 bp, 100 to 350 bp, 100 to 300 bp, 100 to 250 bp, 100 to 200 bp, 100 to 150 bp, 150 to 900 bp, 150 to 800 bp, 150 to 700 bp, 150 to 600 bp, 150 to 500 bp, 150 to 450 bp, 150 to 400 bp, 150 to 350 bp, 150 to 300 bp, 150 to 250 bp, 150 to 200 bp, 150 to 150 bp, or 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141 ,142, 143, 144, 145, 146, 147, 148, 149, or 150 bp. In some embodiments, probes are 85% , 90% , 91% , 92% , 93% , 94% , 95% , 96% , 97% , 99% , or 100% free of undesired nucleic acid sequences.
In some embodiments, the present invention provides a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; c) fragmenting the probe-containing nucleic acids to generate probes; d) attaching adaptors to the probes; and optionally e) further amplifying a subset of the probes.
Further embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; c) fragmenting the probe-containing nucleic acids to generate probes;; and optionally d) further amplifying a subset of the probes.
Additional embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences, wherein the undesired region is, for example, repeat sequence, non-conserved sequences, conserved sequences, GC rich sequences, AT rich sequences, secondary structure, or coding sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; and c) fragmenting the probe-containing nucleic acids to generate probes; and optionally d) further amplifying a subset of the probes.
Yet other embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; c) fragmenting the probe-containing nucleic acids to generate probes; d) separating the probes by size; e) isolating a subset of the probes; and optionally f) further amplifying a subset of the probes.
Still other embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; c) fragmenting the probe-containing nucleic acids to generate probes; d) separating the probes by size; e) isolating a subset of the probes, wherein the subset comprises nucleic acids of 80 to 300 bp in length (e.g., approximately 150 bp in length); and optionally f) further amplifying a subset of the probes.
Additional embodiments provide a method of generating a probe to a nucleic acid of interest, comprising: a) identifying regions of the nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length; b) generating a plurality of probe-containing nucleic acids corresponding to the regions substantially free of undesired sequence; and c) fragmenting the probe-containing nucleic acids to generate probes; optionally d) further amplifying a subset of the probes generate a probe set; and e) performing a hybridization assay (e.g., ISH assay such as FISH) with the probe set.
Further provided herein are a set of nucleic acid probes (e.g., ISH probes) free of undesired sequences generated by the aforementioned methods and kits and systems comprising the probes.
Additionally provided herein are methods of performing a hybridization assay, comprising contacting a target nucleic acid with a probe (e.g., a ISH probe) generated by the aforementioned method.
Also provided herein is the use of any a probe (e.g., a ISH probe) generated by the aforementioned method in a hybridization (e.g., ISH) assay.
Exemplary methods of generating probes are described in detail below.
A. Probes
The present invention provides, in some embodiments, methods of generating probe libraries. In some embodiments, probes are between approximately 100 and 400 bp in length (e.g., between 100 and 300 bp in length).
In some embodiments, libraries of probes are generated that are complementary to different regions of a target sequence. In some embodiments, all of the probes in a library are of similar length (e.g., within 1% , 2% , 3% , 4% , or 5% , 10% , 20% or identical in length).
Probes can comprise any number of modified bases, modified backbones, inclusion of minor groove binders, and labels (e.g., as described in more detail below). Examples of such analogs include, without limitation, phosphorothioates, phosphoramidates, methyl phosphonates, chiral-methyl phosphonates, 2′-O-methyl ribonucleotides, and peptide-nucleic acids (PNAs).
B. Identification of Undesired Sequences
The present invention is not limited to a particular type of undesired sequences. In some embodiments, undesired sequences are, for example, repeat sequence, non-conserved sequences, conserved sequences, GC rich sequences, AT rich sequences, secondary structure, and coding sequences. In some preferred embodiments, repeat-free sequences are removed in order to optimize probe binding.
In some embodiments, substantially repeat-free or other undesired segments of genomic DNA in a region of interest are first identified. In some embodiments, contiguous repeat-free segments of genomic DNA in a region of interest are identified by bioinformatics methods. The present invention is not limited to a particular bioinformatics method. In some embodiments, commercial software packages such as, for example the RepeatMasker function of UCSC Genome Browser (available from The National Cancer Institute's Center for Biomedical Informatics and Information Technology) are utilized, although other commercial or non-commercial software packages are specifically contemplated.
In some embodiments, the Repeat-Masker function of Genome Browser is used to distinguish repeat from nonrepeat portions by presenting repeat sequence in lower case and nonrepeat in upper case, and the sequence downloaded. External software programs or manual examination of sequence information are used to remove the repeat portion of the sequence and to present the stretches of contiguous nonrepeat sequence in order of their length. The shorter stretches (usually less than 300 bp) are discarded, and a number of the longer stretches are identified such that their combined sequence length is sufficient to prepare a probe with acceptable labeling intensity for the intended use.
C. Generation of Probes
Following identification of undesired sequences, probes are designed that are substantially free of undesired sequences. Probes may be generated using any suitable method. In some embodiments, probes are amplified using the method described below.
In some embodiments, libraries of probes are synthesized. In some embodiments, synthetic probes comprise a region of complementarity to the target sequence and a label region that is not-complementary to the target sequence (See e.g.,
In some embodiments, oligonucleotides for use in amplification methods or probe generation are synthesized. Exemplary methods for oligonucleotide synthesis are described herein. To obtain the desired oligonucleotide, the building blocks are sequentially coupled to the growing oligonucleotide chain in the order required by the sequence of the product. The process has been fully automated since the late 1970s. Upon the completion of the chain assembly, the product is released from the solid phase to solution, deprotected, and collected. Products are often isolated by high-performance liquid chromatography (HPLC) to obtain the desired oligonucleotides in high purity. Typically, synthetic oligonucleotides are single-stranded DNA or RNA molecules around 15-25 bases in length.
In some embodiments, the selectivity and the rate of the formation of internucleosidic linkages is improved by using 3′-O-(N,N-diisopropyl phosphoramidite) derivatives of nucleosides (nucleoside phosphoramidites) that serve as building blocks in phosphite triester methodology. To prevent undesired side reactions, all other functional groups present in nucleosides are rendered unreactive (protected) by attaching protecting groups. Upon the completion of the oligonucleotide chain assembly, all the protecting groups are removed to yield the desired oligonucleotides.
Exemplary protecting groups and nucleoside phosphoramidite building blocks include, but are not limited to, acid-labile DMT (4,4′-dimethoxytrityl) protecting groups. Thymine and uracil, nucleic bases of thymidine and uridine, respectively, do not have exocyclic amino groups and hence do not require any protection.
Although the nucleic base of guanosine and 2′-deoxyguanosine does have an exocyclic amino group, its basicity is low to an extent that it does not react with phosphoramidites under the conditions of the coupling reaction. However, a phosphoramidite derived from the N2-unprotected 5′-O-DMT-2′-deoxyguanosine is poorly soluble in acetonitrile, the solvent commonly used in oligonucleotide synthesis. In contrast, the N2-protected versions of the same compound dissolve in acetonitrile well and hence are widely used. Nucleic bases adenine and cytosine bear the exocyclic amino groups reactive with the activated phosphoramidites under the conditions of the coupling reaction. By the use of additional steps in the synthetic cycle or alternative coupling agents and solvent systems, the oligonucleotide chain assembly are carried out using dA and dC phosphoramidites with unprotected amino groups. In some embodiments, exocyclic amino groups in nucleosides are kept permanently protected over the entire length of the oligonucleotide chain assembly.
The protection of the exocyclic amino groups is generally orthogonal to that of the 5′-hydroxy group because the latter is removed at the end of each synthetic cycle. The simplest to implement and hence the most widely accepted is the strategy where the exocyclic amino groups bear a base-labile protection. Most often, two protection schemes are used.
In some embodiments, Bz (benzoyl) protection is used for A, dA, C, and dC, while G and dG are protected with isobutyryl group. More recently, Ac (acetyl) group is often used to protect C and dC.
In the second, mild protection scheme, A and dA are protected with isobutyryl or phenoxyacetyl groups (PAC). C and dC bear acetyl protection, and G and dG are protected with 4-isopropylphenoxyacetyl (iPr-PAC) or dimethylformamidino (dmf) groups. Mild protecting groups are removed more readily than the standard protecting groups. However, the phosphoramidites bearing these groups are less stable when stored in solution.
In some embodiments, the phosphite group is protected by a base-labile 2-cyanoethyl group. Once a phosphoramidite has been coupled to the solid support-bound oligonucleotide and the phosphite moieties have been converted to the P(V) species, the presence of the phosphate protection is not mandatory for the successful conducting of further coupling reactions.
Non-nucleoside phosphoramidites are the phosphoramidite reagents designed to introduce various functionalities at the termini of synthetic oligonucleotides or between nucleotide residues in the middle of the sequence. In order to be introduced inside the sequence, a non-nucleosidic modifier has to possess at least two hydroxy groups, one of which is often protected with the DMT group while the other bears the reactive phosphoramidite moiety.
Non-nucleosidic phosphoramidites are used to introduce desired groups that are not available in natural nucleosides or that can be introduced more readily using simpler chemical designs.
Oligonucleotide synthesis is carried out by a stepwise addition of nucleotide residues to the 5′-terminus of the growing chain until the desired sequence is assembled. Each addition is referred to as a synthetic cycle and consists of four chemical reactions:
Step 1: De-blocking (detritylation)
The DMT group is removed with a solution of an acid, such as 2% trichloroacetic acid (TCA) or 3% dichloroacetic acid (DCA), in an inert solvent (dichloromethane or toluene). The orange-colored DMT cation formed is washed out; the step results in the solid support-bound oligonucleotide precursor bearing a free 5′-terminal hydroxyl group. Conducting detritylation for an extended time or with stronger than recommended solutions of acids leads to depurination of solid support-bound oligonucleotide and thus reduces the yield of the desired full-length product.
A solution of nucleoside phosphoramidite (or a mixture of several phosphoramidites) in acetonitrile is next activated by an acidic azole catalyst, 1H-tetrazole, 2-ethylthiotetrazole, 2-benzylthiotetrazole, 4,5-dicyanoimidazole, or a number of similar compounds. The mixing is usually very brief and occurs in fluid lines of oligonucleotide synthesizers while the components are being delivered to the reactors containing solid support. The activated phosphoramidite in 1.5-20-fold excess over the support-bound material is then brought in contact with the starting solid support (first coupling) or a support-bound oligonucleotide precursor (following couplings) whose 5′-hydroxy group reacts with the activated phosphoramidite moiety of the incoming nucleoside phosphoramidite to form a phosphite triester linkage. The coupling of 2′-deoxynucleoside phosphoramidites is very rapid and requires, on small scale, about 20 s for its completion. In contrast, sterically hindered 2′-O-protected ribonucleoside phosphoramidites utilize longer times to be coupled in high yields. The reaction is also highly sensitive to the presence of water, particularly when dilute solutions of phosphoramidites are used, and is commonly carried out in anhydrous acetonitrile. Generally, the larger the scale of the synthesis, the lower the excess and the higher the concentration of the phosphoramidites is used. In contrast, the concentration of the activator is primarily determined by its solubility in acetonitrile and is irrespective of the scale of the synthesis. Upon the completion of the coupling, any unbound reagents and by-products are removed by washing.
The capping step is performed by treating the solid support-bound material with a mixture of acetic anhydride and 1-methylimidazole or, less often, DMAP as catalysts and, in the phosphoramidite method, serves two purposes.
After the completion of the coupling reaction, a small percentage of the solid support-bound 5′-OH groups (0.1 to 1% ) remains unreacted and needs to be permanently blocked from further chain elongation to prevent the formation of oligonucleotides with an internal base deletion commonly referred to as (n-1) shortmers. The unreacted 5′-hydroxy groups are, to a large extent, acetylated by the capping mixture.
It has also been reported that phosphoramidites activated with 1H-tetrazole react, to a small extent, with the O6 position of guanosine. Upon oxidation with I2/water, this side product, possibly via O6-N7 migration, undergoes depurination. The apurinic sites thus formed are readily cleaved in the course of the final deprotection of the oligonucleotide under the basic conditions (see below) to give two shorter oligonucleotides thus reducing the yield of the full-length product. The O6 modifications are rapidly removed by treatment with the capping reagent as long as the capping step is performed prior to oxidation with I2/water.
The synthesis of oligonucleotide phosphorothioates (OPS) does not involve the oxidation with I2/water, and, respectively, does not suffer from the side reaction described above. On the other hand, if the capping step is performed prior to sulfurization, the solid support may contain the residual acetic anhydride and N-methylimidazole left after the capping step. The capping mixture interferes with the sulfur transfer reaction, which results in the extensive formation of the phosphate triester internucleosidic linkages in place of the desired PS triesters. Therefore, for the synthesis of OPS, it is advisable to conduct the sulfurization step prior to the capping step.
The newly formed tricoordinated phosphite triester linkage is not natural and is of limited stability under the conditions of oligonucleotide synthesis. The treatment of the support-bound material with iodine and water in the presence of a weak base (pyridine, lutidine, or collidine) oxidizes the phosphite triester into a tetracoordinated phosphate triester, a protected precursor of the naturally occurring phosphate diester internucleosidic linkage. Oxidation may be carried out under anhydrous conditions using tert-Butyl hydroperoxide or, more efficiently, (1S)-(+)-(10-camphorsulfonyl)-oxaziridine (CSO). The step of oxidation is substituted with a sulfurization step to obtain oligonucleotide phosphorothioates. In the latter case, the sulfurization step is best carried out prior to capping. In solid-phase synthesis, an oligonucleotide being assembled is covalently bound, via its 3′-terminal hydroxy group, to a solid support material and remains attached to it over the entire course of the chain assembly. The solid support is contained in columns whose dimensions depend on the scale of synthesis and may vary between 0.05 mL and several liters. The overwhelming majority of oligonucleotides are synthesized on small scale ranging from 40 nmol to 1 μmol. More recently, high-throughput oligonucleotide synthesis where the solid support is contained in the wells of multi-well plates (most often, 96 or 384 wells per plate) became a method of choice for parallel synthesis of oligonucleotides on small scale. At the end of the chain assembly, the oligonucleotide is released from the solid support and is eluted from the column or the well.
In contrast to organic solid-phase synthesis and peptide synthesis, the synthesis of oligonucleotides proceeds best on non-swellable or low-swellable solid supports. The two most often used solid-phase materials are controlled pore glass (CPG) and macroporous polystyrene (MPPS).
CPG is commonly defined by its pore size. In oligonucleotide chemistry, pore sizes of 500, 1000, 1500, 2000, and 3000 Å are used to allow the preparation of about 50, 80, 100, 150, and 200-mer oligonucleotides, respectively. To make native CPG suitable for further processing, the surface of the material is treated with (3-aminopropyl)triethoxysilane to give aminopropyl CPG. The aminopropyl arm may be further extended to result in long chain aminoalkyl (LCAA) CPG. The amino group is then used as an anchoring point for linkers suitable for oligonucleotide synthesis (see below).
MPPS suitable for oligonucleotide synthesis is a low-swellable, highly cross-linked polystyrene obtained by polymerization of divinylbenzene (min 60% ), styrene, and 4-chloromethylstyrene in the presence of a porogeneous agent. The macroporous chloromethyl MPPS obtained is converted to aminomethyl MPPS.
To make the solid support material suitable for oligonucleotide synthesis, non-nucleosidic linkers or nucleoside succinates are covalently attached to the reactive amino groups in aminopropyl CPG, LCAA CPG, or aminomethyl MPPS. The remaining unreacted amino groups are capped with acetic anhydride. Typically, three conceptually different groups of solid supports are used.
In a more recent, more convenient, and more widely used method, the synthesis starts with the universal support where a non-nucleosidic linker is attached to the solid support material. A phosphoramidite respective to the 3′-terminal nucleoside residue is coupled to the universal solid support in the first synthetic cycle of oligonucleotide chain assembly using the standard protocols. The chain assembly is then continued until the completion, after which the solid support-bound oligonucleotide is deprotected. The characteristic feature of the universal solid supports is that the release of the oligonucleotides occurs by the hydrolytic cleavage of a P—O bond that attaches the 3′-O of the 3′-terminal nucleotide residue to the universal linker as shown in Scheme 6. The critical advantage of this approach is that the same solid support is used irrespectively of the sequence of the oligonucleotide to be synthesized. For the complete removal of the linker and the 3′-terminal phosphate from the assembled oligonucleotide, the solid support 1 and several similar solid supports require gaseous ammonia, aqueous ammonium hydroxide, aqueous methylamine, or their mixture and are commercially available. The solid support utilizes a solution of ammonia in anhydrous methanol and is also commercially available.
In general, the 3′-hydroxy group of the 3′-terminal nucleoside residue is attached to the solid support via, most often, 3′-O-succinyl arm as in compound 3. The oligonucleotide chain assembly starts with the coupling of a phosphoramidite building block respective to the nucleotide residue second from the 3′-terminus. The 3′-terminal hydroxy group in oligonucleotides synthesized on nucleosidic solid supports is deprotected under the conditions somewhat milder than those applicable for universal solid supports. However, the fact that a nucleosidic solid support has to be selected in a sequence-specific manner reduces the throughput of the entire synthetic process and increases the likelihood of human error.
Oligonucleotide phosphorothioates (OPS) are modified oligonucleotides where one of the oxygen atoms in the phosphate moiety is replaced by sulfur. Only the phosphorothioates having sulfur at a non-bridging position are widely used and are available commercially. The replacement of the non-bridging oxygen with sulfur creates a new center of chirality at phosphorus. In a simple case of a dinucleotide, this results in the formation of a diastereomeric pair of Sp- and Rp-dinucleoside monophosphorothioates. In a n-mer oligonucleotide where all (n−1) internucleosidic linkages are phosphorothioate linkages, the number of diastereomers m is calculated as m=2(n−1). Being non-natural analogs of nucleic acids, OPS are substantially more stable towards hydrolysis by nucleases, the class of enzymes that destroy nucleic acids by breaking the bridging P—O bond of the phosphodiester moiety. This property determines the use of OPS as antisense oligonucleotides in in vitro and in vivo applications where the extensive exposure to nucleases is inevitable. Similarly, to improve the stability of siRNA, at least one phosphorothioate linkage is often introduced at the 3′-terminus of both sense and antisense strands. In chirally pure OPS, all-Sp diastereomers are more stable to enzymatic degradation than their all-Rp analogs. However, the preparation of chirally pure OPS remains a synthetic challenge. In laboratory practice, mixtures of diastereomers of OPS are commonly used.
Synthesis of OPS is very similar to that of natural oligonucleotides. The difference is that the oxidation step is replaced by sulfur transfer reaction (sulfurization) and that the capping step is performed after the sulfurization. Of many reported reagents capable of the efficient sulfur transfer, only three are commercially available:
3-(Dimethylaminomethylidene)amino)-3H-1,2,4-dithiazole-3-thione, DDTT (3) provides rapid kinetics of sulfurization and high stability in solution. 3H-1,2-benzodithiol-3-one 1,1-dioxide (4) also known as Beaucage reagent displays a better solubility in acetonitrile and short reaction times. However, the reagent is of limited stability in solution and is less efficient in sulfurizing RNA linkages.
N,N,N′N′-Tetraethylthiuram disulfide (TETD) is soluble in acetonitrile and is commercially available. However, the sulfurization reaction of an internucleosidic DNA linkage with TETD requires 15 min.
In the past, oligonucleotide synthesis was carried out manually in solution or on solid phase. The solid phase synthesis was implemented using, as containers for the solid phase, miniature glass columns similar in their shape to low-pressure chromatography columns or syringes equipped with porous filters. Currently, solid-phase oligonucleotide synthesis is carried out automatically using computer-controlled instruments (oligonucleotide synthesizers) and is technically implemented in column, multi-well plate, and array formats. The column format is best suited for research and large scale applications where a high-throughput is not required. Multi-well plate format is designed specifically for high-throughput synthesis on small scale to satisfy the growing demand of industry and academia for synthetic oligonucleotides. A number of oligonucleotide synthesizers for small scale synthesis and medium to large scale synthesis are available commercially.
Amplification methods are described below, although other methods may be used. Next, amplification (e.g., PCR) primers are designed to amplify stretches of sequence from the longest of the repeat-free segments identified using bioinformatics methods. In some embodiments, such segments are amplified using genomic or genome derived BAC DNA as an amplification template. In some embodiments, (e.g., in the case of longer stretches) multiple overlapping primer sets are used.
Illustrative non-limiting examples of nucleic acid amplification techniques include, but are not limited to, polymerase chain reaction (PCR), reverse transcription polymerase chain reaction (RT-PCR), transcription-mediated amplification (TMA), ligase chain reaction (LCR), strand displacement amplification (SDA), and nucleic acid sequence based amplification (NASBA).
In general, amplification methods utilize a DNA polymerase, a primer, and dNTPs. Exemplary DNA polymerases include, but are not limited to, phi29 DNA Polymerase, Taq DNA polymerase, DNA polymerase I, T7 DNA Polymerase, T7 DNA Polymerase, T4 DNA Polymerase, Pfu DNA Polymerase, and Bsm DNA Polymerase.
The polymerase chain reaction (U.S. Pat. Nos. 4,683,195, 4,683,202, 4,800,159 and U.S. Pat. No. 4,965,188, each of which is herein incorporated by reference in its entirety), commonly referred to as PCR, uses multiple cycles of denaturation, annealing of primer pairs to opposite strands, and primer extension to exponentially increase copy numbers of a target nucleic acid sequence. In a variation called RT-PCR, reverse transcriptase (RT) is used to make a complementary DNA (cDNA) from mRNA, and the cDNA is then amplified by PCR to produce multiple copies of DNA. For other various permutations of PCR see, e.g., U.S. Pat. Nos. 4,683,195, 4,683,202 and U.S. Pat. No. 4,800,159; Mullis et al., Meth. Enzymol. 155: 335 (1987); and, Murakawa et al., DNA 7: 287 (1988), each of which is herein incorporated by reference in its entirety.
Transcription mediated amplification (U.S. Pat. No. 5,480,784 and U.S. Pat. No. 5,399,491, each of which is herein incorporated by reference in its entirety), commonly referred to as TMA, synthesizes multiple copies of a target nucleic acid sequence autocatalytically under conditions of substantially constant temperature, ionic strength, and pH in which multiple RNA copies of the target sequence autocatalytically generate additional copies. See, e.g., U.S. Pat. No. 5,399,491 and U.S. Pat. No. 5,824,518, each of which is herein incorporated by reference in its entirety. In a variation described in U.S. Publ. No. 20060046265 (herein incorporated by reference in its entirety), TMA optionally incorporates the use of blocking moieties, terminating moieties, and other modifying moieties to improve TMA process sensitivity and accuracy.
The ligase chain reaction (Weiss, R., Science 254: 1292 (1991), herein incorporated by reference in its entirety), commonly referred to as LCR, uses two sets of complementary DNA oligonucleotides that hybridize to adjacent regions of the target nucleic acid. The DNA oligonucleotides are covalently linked by a DNA ligase in repeated cycles of thermal denaturation, hybridization and ligation to produce a detectable double-stranded ligated oligonucleotide product.
Strand displacement amplification (Walker, G. et al., Proc. Natl. Acad. Sci. USA 89: 392-396 (1992); U.S. Pat. No. 5,270,184 and U.S. Pat. No. 5,455,166, each of which is herein incorporated by reference in its entirety), commonly referred to as SDA, uses cycles of annealing pairs of primer sequences to opposite strands of a target sequence, primer extension in the presence of a dNTPs to produce a duplex hemiphosphorothioated primer extension product, endonuclease-mediated nicking of a hemimodified restriction endonuclease recognition site, and polymerase-mediated primer extension from the 3′ end of the nick to displace an existing strand and produce a strand for the next round of primer annealing, nicking and strand displacement, resulting in geometric amplification of product. Thermophilic SDA (tSDA) uses thermophilic endonucleases and polymerases at higher temperatures in essentially the same method (EP Pat. No. 0 684 315).
Other amplification methods include, for example: nucleic acid sequence based amplification (U.S. Pat. No. 5,130,238, herein incorporated by reference in its entirety), commonly referred to as NASBA; one that uses an RNA replicase to amplify the probe molecule itself (Lizardi et al., BioTechnol. 6: 1197 (1988), herein incorporated by reference in its entirety), commonly referred to as Qβ replicase; a transcription based amplification method (Kwoh et al., Proc. Natl. Acad. Sci. USA 86:1173 (1989)); and, self-sustained sequence replication (Guatelli et al., Proc. Natl. Acad. Sci. USA 87: 1874 (1990), each of which is herein incorporated by reference in its entirety). For further discussion of known amplification methods see Persing, David H., “In Vitro Nucleic Acid Amplification Techniques” in Diagnostic Medical Microbiology: Principles and Applications (Persing et al., Eds.), pp. 51-87 (American Society for Microbiology, Washington, DC (1993)).
In some embodiments, amplification is isothermal amplification. In some embodiments, amplification methods are solid-phase amplification, polony amplification, colony amplification, emulsion PCR, bead RCA, surface RCA, surface SDA, etc., as will be recognized by one of skill in the art. In some embodiments, amplification methods that results in amplification of free DNA molecules in solution or tethered to a suitable matrix by only one end of the DNA molecule are used. In some embodiments, methods that rely on bridge PCR, where both PCR primers are attached to a surface (see, e.g., WO 2000/018957, U.S. Pat. Nos. 7,972,820; 7,790,418 and Adessi et al., Nucleic Acids Research (2000): 28(20): E87; each of which are herein incorporated by reference) are used. In some cases the methods of the invention can create a “polymerase colony technology”, or “polony”, referring to a multiplex amplification that maintains spatial clustering of identical amplicons (see Harvard Molecular Technology Group and Lipper Center for Computational Genetics website). These include, for example, in situ polonies (Mitra and Church, Nucleic Acid Research 27, e34, Dec. 15, 1999), in situ rolling circle amplification (RCA) (Lizardi et al., Nature Genetics 19, 225, July 1998), bridge PCR (U.S. Pat. No. 5,641,658), picotiter PCR (Leamon et al., Electrophoresis 24, 3769, November 2003), and emulsion PCR (Dressman et al., PNAS 100, 8817, Jul. 22, 2003).
Examples of nucleic acid polymerases suitable for use in embodiments of the present invention include, but are not limited to, DNA polymerase (Klenow fragment, T4 DNA polymerase), thermostable DNA polymerases (Perler F. B. et al., Adv. Protein Chem. 1996, 48:377-435) identified and cloned in a variety of thermostable bacteria (such as Taq, VENT, Pfu, Tfl DNA polymerases) as well as their genetically modified derivatives (TaqGold, VENTexo, Pfu exo). Preferably the nucleic acid polymerase used for colony primer extension is stable under temperature at which the primer and template hybridization results enough specific to avoid incomplete or spurious amplifications of the template.
The amplification solution contains preferably, deoxyribonucleoside triphosphates, for example dATP, dTTP, dCTP, dGTP, naturally or non-naturally occurring, for example modified with a fluorescent or radioactive group. A large variety of synthetically modified nucleic acids have been developed for chemical and biological methods in order to increase the detectability and/or the functional diversity of nucleic acids. These functionalized/modified molecules (e.g., nucleotide analogs) can be fully compatible with natural polymerizing enzymes, maintaining the base pairing and replication properties of the natural counterparts, as recently reviewed (Thum O et al., Angew. Chem. Int. Ed. 2001, 40 (21): 3990-3993).
Other components of the amplification solution are added consequently to the choice of the nucleic acid polymerase, and they are essentially corresponding to compounds known in the art as being effective to support the activity of each polymerase. The concentration of compounds like dimethyl sulfoxide (DMSO), Bovine Serum Albumin (BSA), poly-ethylene glycol (PEG), Betaine, Triton X-100, or MgCl2 is well known in the prior art as being important to have an optimal amplification, and therefore the operator can easily adjust such concentrations for the methods of the present invention on the basis of the examples presented hereafter.
D. Fragmentation
In some embodiments, before or after amplification, the DNA is then fragmented (e.g., by sonication or other suitable method such as DNAse I) to lengths ranging from approximately 50 to 5000 bp (e.g., 50 to 4000, 50 to 3000, 50 to 2500, 50 to 2000, 50 to 1500, 50 to 1000, 100 to 5000, 100 to 4000, 1000 to 3000, 100 to 2500, 100 to 2000, 100 to 1500, 100 to 1000, or 100-500 bp), and the resultant repeat-free DNA library attached (e.g., via ligation, chemical, extension reaction, etc.) to adapters. In some preferred embodiments, probes are approximately 150 bp (e.g., 50 to 900 bp, 50 to 800 bp, 50 to 700 bp, 50 to 600 bp, 50 to 500 bp, 50 to 450 bp, 50 to 400 bp, 50 to 350 bp, 50 to 300 bp, 50 to 250 bp, 50 to 200 bp, 50 to 150 bp, 50 to 100 bp, 80 to900 bp, 80 to 800 bp, 80 to 700 bp, 80 to 600 bp, 80 to 500 bp, 80 to 450 bp, 80 to 400 bp, 80 to 350 bp, 80 to 300 bp, 80 to 250 bp, 80 to 200 bp, 80 to 150 bp, 80 to 100 bp, 100 to 900 bp, 100 to 800 bp, 100 to 700 bp, 100 to 600 bp, 100 to 500 bp, 100 to 450 bp, 100 to 400 bp, 100 to 350 bp, 100 to 300 bp, 100 to 250 bp, 100 to 200 bp, 100 to 150 bp, 150 to 900 bp, 150 to 800 bp, 150 to 700 bp, 150 to 600 bp, 150 to 500 bp, 150 to 450 bp, 150 to 400 bp, 150 to 350 bp, 150 to 300 bp, 150 to 250 bp, 150 to 200 bp, 150 to 150 bp, or 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97,98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141 ,142, 143, 144, 145, 146, 147, 148, 149, or 150 bp, etc.). In some embodiments, the adapted library is then fractionated (e.g., by electrophoresis, chromatography, or other separation method) to give a pool containing all the selected sequence at a variety of fragment sizes. Fractions (e.g., gel slices) corresponding to the desired fragment sizes are isolated.
E. Amplification
In some embodiments, fractions of the desired size are used as templates with amplification (e.g., PCR or another method described herein) primers corresponding to the adapters under preparatory amplification conditions.
All the chosen repeat-free sequence are represented in the amplified library. The probes (e.g., isolated after fragmentation or optional further amplification) are then labeled (e.g., with a fluorescent label, biotin, quantum dot label, or labels for colorimetric or silver stain detection) for use (e.g., as a FISH reagent).
In some embodiments, libraries of probes are cloned into expression vectors (e.g., one or more probes per vector). In some embodiments, such expression vectors find use in the future generation of libraries (e.g., via amplification or expression).
II. Uses of ProbesThe probes described herein find use in a variety of diagnostic, research, clinical, and screening applications. The described nucleic acid hybridization probes have broad utility for use in all forms of nucleic acid detection that is achieved by use of nucleic acid hybridization probes. The nucleic acid hybridization probes find use in detecting nucleic acid sequence targets in solution or bound to immobilized supports. Examples of applications where the composition and methods can be used to detect nucleic acid sequence targets in solution include PCR, real-time PCR, quantitative PCR, PNA clamp-mediated PCR and digital PCR. Examples of applications where the compositions and methods can be used to detect nucleic acid sequence targets immobilized to solid supports include northern blots, southern blots, dot blots, slot blots, microarrays, particle-based assays, In situ hybridization assays (ISH) such as, for example, chromagen in situ hybridization (CISH), RNA in situ hybridization (RISH), rapid FISH, Silver In Situ Hybridization (SISH), and FISH assays. Such applications are amenable to numerous fields, including medical diagnostics, molecular medicine, forensic science, specimen and organism cataloging, and microbial pathogen epidemiology.
The present invention is not limited to a particular target. The compositions and methods described herein find use in the detection of a variety of target nucleic acids (e.g., human or mammalian genomic nucleic acids), bacterial, viral, etc.
Probes may also be employed as isolated nucleic acids immobilized on a solid surface (e.g., nitrocellulose), as in aCGH. In some embodiments, the probes may be members of an array of nucleic acids as described, for instance, in WO 96/17958, which is hereby incorporated by reference it its entirety and specifically for its description of array CGH. Techniques capable of producing high density arrays are well-known (see, e.g., Fodor et al. Science 767-773 (1991) and U.S. Pat. No. 5,143,854), both of which are hereby incorporated by reference for this description.
A detailed description of the utility of the nucleic acid hybridization probes is presented below for FISH applications, although the probes find use in other applications.
FISH and other in situ hybridization methods may be performed on a variety of sample types. Example, include, but are not limited to formalin-fixed paraffin embedded (FFPE) tissue), fresh tissue, frozen tissue, cells (e.g., eukaryotic or prokaryotic cells); prepared using any suitable fixative. In some embodiments, touch prep or brushing (See e.g., Smoczynski et al., Gastrointest Endosc. 2012 January; 75(1):65-73) is utilized.
Touch prep specimens are generated by smearing or pressing onto a slide, applying pressure to the tissue, and fixing in ethanol under cool temperatures. In a specific embodiment the tissue is extracted surgically and smeared onto a glass slide by applying relatively weak pressure to tumor tissue and relatively strong pressure to normal tissue, followed by fixing in about 100% ethanol for approximately 10 minutes at about 4° C. In another specific embodiment, the samples to be analyzed by methods of the present invention are originally frozen in liquid nitrogen and stored at about −80° C.
For a typical ISH application, the following represents a typical procedure. Cells of a specimen are harvested, washed and pelleted. The cells of the pellet are usually washed in phosphate-buffered saline (PBS). The cells are suspended in PBS and re-collected by centrifugation. The cells can be fixed, for example, in acid alcohol solutions, acid acetone solutions, or aldehydes such as formaldehyde, paraformaldehyde, and glutaraldehyde. For example, a fixative containing methanol and glacial acetic acid in a 3:1 ratio, respectively, can be used as a fixative. A neutral buffered formalin solution also can be used, and includes approximately 1% to 10% of 37-40% formaldehyde in an aqueous solution of sodium phosphate. Slides containing the cells can be prepared by removing a majority of the fixative, leaving the concentrated cells suspended in only a portion of the solution.
The cell suspension is applied to slides such that the cells do not overlap on the slide. Cell density can be measured by a light or phase contrast microscope. The density of cells in these wells is then assessed with a phase contrast microscope. If the well containing the greatest volume of cell suspension does not have enough cells, the cell suspension is concentrated and placed in another well.
Prior to in situ hybridization, chromosomal probes and chromosomal DNA contained within the cell each are denatured. Denaturation process is performed in several ways. For example, denaturation can be effected with buffered solutions having elevated pH, with elevated temperatures (for example, temperatures from about 70° C. to about 95° C.), or with organic solvents such as formamide, ethylene carbonate, and tetraalkylammonium halides, or combinations thereof. For example, chromosomal DNA can be denatured by a combination of temperatures above 70° C. (for example, about 73° C.) and a denaturation buffer containing 70% formamide and 2×SSC (0.3M sodium chloride and 0.03 M sodium citrate). Denaturation conditions typically are established such that cell morphology is preserved. Chromosomal probes can be denatured by heat. For example, probes can be heated to about 73° C. for about five minutes.
After removal of denaturing chemicals or conditions, probes are annealed to the chromosomal DNA under hybridizing conditions. “Hybridizing conditions” are conditions that facilitate annealing between a probe and nucleic acid sequence target. Hybridization conditions vary, depending on the concentrations, base compositions, complexities, and lengths of the probes, as well as salt concentrations, temperatures, and length of incubation. The greater the concentration of probe, the greater the probability of forming a hybrid. For example, in situ hybridizations are typically performed in hybridization buffer containing 1-2×SSC, 50% formamide and blocking DNA to suppress non-specific hybridization. In general, hybridization conditions, as described above, include temperatures of about 25° C. to about 55° C., and incubation lengths of about 0.5 hours to about 96 hours. More particularly, hybridization can be performed at about 37° C. to about 40° C. for about 2 to about 16 hours.
Non-specific binding of chromosomal probes to DNA outside of the target region can be removed by a series of washes. Temperature and concentration of salt in each wash depend on the desired stringency. For example, for high stringency conditions, washes can be carried out at about 65° C. to about 80° C., using 0.2×SSC to about 2×SSC, and about 0.1% to about 1% of a non-ionic detergent such as Nonidet P-40 (NP40) or other suitable surfactant. Stringency can be lowered by decreasing the temperature of the washes or by increasing the concentration of salt in the washes.
Slides containing the samples are typically incubated in 2×SSC at 37° C. for 10-30 min. The slides are then incubated in 0.2 mg/ml pepsin at 37° C. for 20 min. Slides are subsequently washed twice in PBS at room temperature for 2 min. Cells are fixed in 2.5% Neutral Buffered Formalin at room temperature for 5 min. Slides are subsequently washed twice in PBS at room temperature for 2 min. The slides are subjected to dehydration by successive contact in solutions of 70% , 85% , and 100% ethanol at room temperature for 1 min. The slides are used immediately thereafter or stored at room temperature in the dark.
Hybridization can be performed with the HYBrite method or a conventional method. In the HYBrite method, a HYBrite™ system from Abbott Molecular (Downers Grove, Ill.) is used.
Conditions for specifically hybridizing the probes to their nucleic acid targets generally include the combinations of conditions that are employable in a given hybridization procedure to produce specific hybrids, the conditions of which may easily be determined by one of skill in the art. Such conditions typically involve controlled temperature, liquid phase, and contact between a chromosomal probe and a target. Hybridization conditions vary depending upon many factors including probe concentration, target length, target and probe G-C content, solvent composition, temperature, and duration of incubation. At least one denaturation step may precede contact of the probes with the targets. Alternatively, both the probe and nucleic acid target may be subjected to denaturing conditions together while in contact with one another, or with subsequent contact of the probe with the biological sample. Hybridization may be achieved with subsequent incubation of the probe/sample in, for example, a liquid phase of about a 50:50 volume ratio mixture of 2-4×SSC and formamide, at a temperature in the range of about 25 to about 55° C. for a time that is illustratively in the range of about 0.5 to about 96 hours, or more preferably at a temperature of about 32 to about 40° C. for a time in the range of about 2 to about 16 hours. In order to increase specificity, use of a blocking agent such as unlabeled blocking nucleic acid as described in U.S. Pat. No. 5,756,696 (the contents of which are herein incorporated by reference in their entirety, and specifically for the description of the use of blocking nucleic acid), may be used in conjunction with the methods of the present invention. Other conditions may be readily employed for specifically hybridizing the probes to their nucleic acid targets present in the sample, as would be readily apparent to one of skill in the art.
Upon completion of a suitable incubation period, non-specific binding of chromosomal probes to sample DNA may be removed by a series of washes. Temperature and salt concentrations are suitably chosen for a desired stringency. The level of stringency required depends on the complexity of a specific probe sequence in relation to the genomic sequence, and may be determined by systematically hybridizing probes to samples of known genetic composition. In general, high stringency washes may be carried out at a temperature in the range of about 65 to about 80° C. with about 0.2× to about 2×SSC and about 0.1% to about 1% of a non-ionic detergent such as Nonidet P-40 (NP40). If lower stringency washes are required, the washes may be carried out at a lower temperature with an increased concentration of salt.
Chromosomal probes can be directly labeled with a detectable label. Examples of detectable labels include fluorophores, e.g., organic molecules that fluoresce after absorbing light, and radioactive isotopes, e.g., 32P, and 3H. Fluorophores can be directly labeled following covalent attachment to a nucleotide by incorporating the labeled nucleotide into the probe with standard techniques such as nick translation, random priming, and PCR labeling. Alternatively, deoxycytidine nucleotides within the probe can be transaminated with a linker. The fluoropore can then be covalently attached to the transaminated deoxycytidine nucleotides. See, e.g., U.S. Pat. No. 5,491,224 to Bittner, et al., which is incorporated herein by reference. Useful probe labeling techniques are described in Molecular Cytogenetics: Protocols and Applications, Y. -S. Fan, Ed., Chap. 2, “Labeling Fluorescence In Situ Hybridization Probes for Genomic Targets”, L. Morrison et. al., p. 21-40, Humana Press, © 2002 (hereafter cited as “Morrison-2002”), incorporated herein by reference.
Attachment of fluorophores to nucleic acid probes is well known in the art and may be accomplished by any available means. Fluorophores can be covalently attached to a particular nucleotide, for example, and the labeled nucleotide incorporated into the probe using standard techniques such as nick translation, random priming, PCR labeling, and the like. Alternatively, the fluorophore can be covalently attached via a linker to the deoxycytidine nucleotides of the probe that have been transaminated. Methods for labeling probes are described in U.S. Pat. No. 5,491,224 and Molecular Cytogenetics: Protocols and Applications (2002), Y. -S. Fan, Ed., Chapter 2, “Labeling Fluorescence In Situ Hybridization Probes for Genomic Targets,” L. Morrison et al., p. 21-40, Humana Press, both of which are herein incorporated by reference for their descriptions of labeling probes.
Exemplary fluorophores that can be used for labeling probes include TEXAS RED (Molecular Probes, Inc., Eugene, Oreg.), CASCADE blue aectylazide (Molecular Probes, Inc., Eugene, Oreg.), SPECTRUMORANGE™ (Abbott Molecular, Des Plaines, Ill.) and SPECTRUMGOLD™ (Abbott Molecular).
Additional examples of fluorophores that can be used in the methods described herein are: 7-amino-4-methylcoumarin-3-acetic acid (AMCA); 5-(and -6)-carboxy-X-rhodamine, lissamine rhodamine B, 5-(and -6)-carboxyfluorescein; fluorescein-5-isothiocyanate (FITC); 7-diethylaminocoumarin-3-carboxylic acid, tetramethyl-rhodamine-5-(and -6)-isothiocyanate; 5-(and -6)-carboxytetramethylrhodamine; 7-hydroxy-coumarin-3-carboxylic acid; 6-[fluorescein 5-(and -6)-carboxamido]hexanoic acid; N-(4,4-difluoro-5,7-dimethyl-4-bora-3a, 4a diaza-3-indacenepropionic acid; eosin-5-isothiocyanate; erythrosine-5-isothiocyanate; 5-(and -6)-carboxyrhodamine 6G; and Cascades blue aectylazide (Molecular Probes, Inc., Eugene, Oreg.).
Probes can be viewed with a fluorescence microscope and an appropriate filter for each fluorophore, or by using dual or triple band-pass filter sets to observe multiple fluorophores. See, e.g., U.S. Pat. No. 5,776,688 to Bittner, et al., which is incorporated herein by reference. Any suitable microscopic imaging method can be used to visualize the hybridized probes, including automated digital imaging systems, such as those available from MetaSystems or Applied Imaging. Alternatively, techniques such as flow cytometry can be used to examine the hybridization pattern of the chromosomal probes.
Probes can also be labeled indirectly, e.g., with biotin or digoxygenin by means well known in the art. However, secondary detection molecules or further processing are then used to visualize the labeled probes. For example, a probe labeled with biotin can be detected by avidin conjugated to a detectable marker, e.g., a fluorophore. Additionally, avidin can be conjugated to an enzymatic marker such as alkaline phosphatase or horseradish peroxidase. Such enzymatic markers can be detected in standard colorimetric reactions using a substrate for the enzyme. Substrates for alkaline phosphatase include 5-bromo-4-chloro-3-indolylphosphate and nitro blue tetrazolium. Diaminobenzoate can be used as a substrate for horseradish peroxidase. Fluorescence detection of a hybridized biotin or other indirect labeled probe can be achieved by use of the commercially available tyramide amplification system.
One of skill in the art will recognize that other agents or dyes can be used in lieu of fluorophores as label-containing moieties. Suitable labels that can be attached to probes include, but are not limited to, radioisotopes, fluorophores, chromophores, mass labels, electron dense particles, magnetic particles, spin labels, molecules that emit luminescence, electrochemically active molecules, enzymes, cofactors, and enzyme substrates. Luminescent agents include, for example, radioluminescent, chemiluminescent, bioluminescent, and phosphorescent label containing moieties. Alternatively, detection moieties that are visualized by indirect means can be used. For example, probes can be labeled with biotin or digoxygenin using routine methods known in the art, and then further processed for detection. Visualization of a biotin-containing probe can be achieved via subsequent binding of avidin conjugated to a detectable marker. The detectable marker may be a fluorophore, in which case visualization and discrimination of probes may be achieved as described above for ISH.
In some embodiments, probes are designed to have labels placed at a common interval throughout the nucleic acid (e.g., one label group every 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12).
In some embodiments, a probe library comprises probes with different detectable labels (e.g., different colors of fluorescent signal).
Probes hybridized to target regions may alternatively be visualized by enzymatic reactions of label moieties with suitable substrates for the production of insoluble color products. A biotin-containing probe within a set may be detected via subsequent incubation with avidin conjugated to alkaline phosphatase (AP) or horseradish peroxidase (HRP) and a suitable substrate. 5-bromo-4-chloro-3-indolylphosphate and nitro blue tetrazolium (NBT) serve as substrates for alkaline phosphatase, while diaminobenzidine serves as a substrate for HRP.
In embodiments where fluorophore-labeled probes or probe compositions are used, the detection method can involve fluorescence microscopy, flow cytometry, or other means for determining probe hybridization. Any suitable microscopic imaging method may be used in conjunction with the methods of the present invention for observing multiple fluorophores. In the case where fluorescence microscopy is employed, hybridized samples may be viewed under light suitable for excitation of each fluorophore and with the use of an appropriate filter or filters. Automated digital imaging systems such as the MetaSystems, BioView or Applied Imaging systems may alternatively be used.
In array CGH, the probes are not labeled, but rather are immobilized at distinct locations on a substrate, as described in WO 96/17958. In this context, the probes are often referred to as the “target nucleic acids.” The sample nucleic acids are typically labeled to allow detection of hybridization complexes. The sample nucleic acids used in the hybridization may be detectably labeled prior to the hybridization reaction. Alternatively, a detectable label may be selected which binds to the hybridization product. In dual- or mult-color aCGH, the target nucleic acid array is hybridized to two or more collections of differently labeled nucleic acids, either simultaneously or serially. For example, sample nucleic acids and reference nucleic acids are each labeled with a separate and distinguishable label. Differences in intensity of each signal at each target nucleic acid spot can be detected as an indication of a copy number difference. Although any suitable detectable label can be employed for aCGH, fluorescent labels are typically the most convenient.
Exemplary methods of visualizing signals are described in WO 93/18186, which is hereby incorporated by reference for this description. To facilitate the display of results and to improve the sensitivity of detecting small differences in fluorescence intensity, a digital image analysis system can be used. An exemplary system is QUIPS (an acronym for quantitative image processing system), which is an automated image analysis system based on a standard fluorescence microscope equipped with an automated stage, focus control and filterwheel (Ludl Electronic Products, Ltd., Hawthorne, N.Y.). The filterwheel is mounted in the fluorescence excitation path of the microscope for selection of the excitation wavelength. Special filters (Chroma Technology, Brattleboro, Vt.) in the dichroic block allow excitation of the multiple dyes without image registration shift. The microscope has two camera ports, one of which has an intensified CCD camera (Quantex Corp., Sunnyvale, Calif.) for sensitive high-speed video image display which is used for finding interesting areas on a slide as well as for focusing. The other camera port has a cooled CCD camera (model 200 by Photometrics Ltd., Tucson, Ariz.) which is used for the actual image acquisition at high resolution and sensitivity. The cooled CCD camera is interfaced to a SUN 4/330 workstation (SUN Microsystems, Inc., Mountain View, Calif.) through a VME bus. The entire acquisition of multicolor images is controlled using an image processing software package SCIL-Image (Delft Centre for Image Processing, Delft, Netherlands).
In some embodiments, the present disclosure provides kits and systems for the amplification and/or analysis of nucleic acids. In some embodiments, kits include reagents necessary, sufficient or useful for analysis and detection of copy number or gene expression changes (e.g., primers, probes, anchors, solid supports, reagents, controls, instructions, etc.). For example, in some embodiments, kits comprise primers and anchors for amplification and sequencing of regions of interest and control regions. In some embodiments, kits include analysis software (e.g., to analyze sequencing data).
In some embodiments, kits comprise one or more containers that comprise reagents, primers, probes, anchors, solid supports, buffers, and the like. In some embodiments, each component of the kit is packaged in a separate container. In some embodiments, the containers are packed and/or shipped in the same kit or box for use together. In some embodiments, one or more components of the kit are shipped and/or packaged separately.
The assays and kits of the can be adapted or optimized for point of care assay systems, including Abbott's Point of Care (i-STAT™) electrochemical immunoassay system Immunosensors and methods of manufacturing and operating them in single-use test devices are described, for example in U.S. Pat. No. 5,063,081 and published U.S. Patent Application Nos. 20030170881, 20040018577, 20050054078, and 20060160164 (incorporated by reference herein for their teachings regarding same).
In some embodiments, systems include automated sample and reagent handling devices (e.g., robotics).
EXPERIMENTAL Example 1 Generation of ProbesUCSC Genome browser was used to identify sequence in the region of the HER2 locus with coordinates hg18 dna range chr17:35004678-35230380. This sequence was downloaded, coded such that regions identified by RepeatMasker were masked as lower case. The 225703 base sequence was treated with a software program that removed all sequence with more than 3 consecutive lower case letters, returning the stretches of repeat-free sequence along with their positions in the original sequence (
These sequences ranged in size from very small to 5615 bases. Only the longest fragments are selected for generating sequence library. A minimum length cutoff of1200 bp yielded 35 sequences containing 76904 bp of sequence. PCR amplification of each individual sequence is expected to give variable yields of subdomains of sequence depending on the length of the amplicon, therefore sequences were divided into multiple overlapping subsequence, 1200 bp each. All subfragments were designed to include at least 100 bp overlap with neighboring subfragments to accommodate variations in primer positions. This process generated 95 candidate sequences.
For each sequence a primer pair was designed with the web based program “BatchPrimer3” seeking generic primers to generate amplicons with Min 800, Opt 1200, Max 1200; primer length min22, opt 25, max 30; Tm min 65, opt 70, max 75. Primer sequences were downloaded as an xls file and copied into the spreadsheet for adjusting format to make it suitable for placing the order.
Primers were ordered from IDT as Mixed Forward and Reverse primers 12 nmole each dried in deep-well plate. To each well, 240 uL water (5 Prime 2900132) was added to give 50 uM each. Dilutions were prepared as needed for PCR.
PCR of genomic DNA yielded clean 1200mer product for only about half of the wells, therefore a preparation of BAC DNA containing the desired locus was used to generate a much higher success rate. BAC clones in E. coli covering the locus were obtained from Genome Systems, Inc. St. Louis, cultures grown and DNA isolated by “mini-prep.”
PCR Master Mix: A PCR kit containing Phire Hot Start II DNA Polymerase (Thermo F-122L) was used. It contained 400 uL 5×reaction buffer+40 uL 25 mM dNTP (Roche Diagnostics, Indianapolis, Ind.)+40 uL Phire polymerase+60 uL DMSO+1260 uL water+0.5 ug BAC DNA template.
PCR: To wells of a 96 well plate was added 2 uL each primer pair 5 uM+18 uL Master Mix; capped wells, placed on thermocycler with program 98 deg 30 sec, 30×(98 deg 8 sec, 72 deg 30 sec, 72 deg 2 min), 72 deg 10 min, 4 deg. At completion 5 uL of each reaction was sampled into 20 uL water with trace 6×DNA Loading dye (Thermo R0611), 20 uL was transferred to wells of an eGel 96 agarose gel (Life Technologies), and electrophoresed was 8 min. 94 of 96 wells show clean bands at expected MW (
Extend PCR to maximize yield. To each well containing the remaining 5 uL from electrophoresis sample, 10 uL of the same 5 uM primers+10 uL water+25 uL DreamTaq Green 2×perMM was added, and the tube was capped and placed on a thermocycler with program 10×(95 deg 30 sec, 55 deg 30 sec, 72 deg 2 min) 72 deg 6 min.
At completion, to each well 6 uL of (30 uL 1M MgCl2+192 uL 25 mM dNTP+378 uL water+100 uL DreamTaq Green 2×perMM) was added and the tube was capped and placed on thermocycler with program 6×(95 deg 30 sec, 55 deg 30 sec, 72 deg 2 min) 72 deg 10 min.
The contents of columns were combined to give 6 amplicon mixtures representing different loci of the genomic range, and the DNA isolated by precipitation with isopropanol and resuspended in water, yielding 100 uL solutions containing 52-75 ug DNA.
Fragmentation by sonication: Approx 180 ug DNA 1200-mers from PCR wells 1-48 and 49-96 were combined in tubes with water to give 400 uL, with sodium acetate at 300 mM. The tubs were placed in beaker of ice water in a sonicator cabinet, sonicated (sonicator Branson 450) output control 3, 30% duty cycle 16 min. The sonication products were precipitated with isopropanol and resuspended in 200 uL 600 mM NaCl in 20 mM Tris pH 8.2. The samples were fractionated by HPLC with MonoQ column (GE Life Sciences), BufferA =20 mM Tris pH 8.2; Buffer B=A+2.0M NaCl, 0.4 mL/min % B=40-50 over 32 min, collecting fractions. DNA elutes in a broad peak centered at about 15 min. Fractions were combined to give 7 pools for each. Electrophoresis on a 3% Agarose gel visualized with Ethidium Bromide shows fractions (labeled H15, H18, H21, H24, H27, H30, H33) ranging from about 80 bp to about 400 bp (
Amination of fragmented DNA: The pooled fractions were concentrated by isopropanol precipitation, resuspended in 20 uL water and denatured by heating lmin in boiling water. To the 20 uL denatured DNA was added 180 uL of a mixture of 1000 uL water, 600 uL trifluoroacetic acid (Sigma, St Louis MO) 348 uL ethylenediamine and 190 mg sodium metabisulfite, and the mixture incubated 20 min at 65 deg. The mixtures were then desalted by sephadex G25 and the desalted product concentrated by isopropanol precipitation and resuspension in water.
The aminated products were labeled with carboxytetramethylrhodamine using its NHS ester (Life Technologies C1171) by means well known in the art. Labeled product was isolated from residual unbound dye by ultrafiltration using 10kDa filters (Nanosep 10 Omega, Pall Corporation, Ann Arbor, Mich.), followed by filtration through 0.22u filters (Millipore UFC3OGV00, Billerica, Mass.).
Preparation of Probes via Adaptor Mediated PCRFragments of the desired size were also modified by ligating adaptors, and using the product as a template for PCR using primers corresponding to the adaptor sequence. This provides an efficient means of producing larger quantities of product of the desired size, as well as providing a means of coupling additional functional groups to the product. The process consists of modifying the fragments to give 5′ phosphorylated, blunted ends, followed by ligating adaptors of the desired sequence. The adaptors can be designed to contain restriction sites such that the dsDNA PCR product can be cleaved with appropriate restriction enzymes either to remove unwanted adaptor sequence or to reveal sticky ends suitable for ligating additional groups.
End repair of the fragments was by using the Thermo Fast DNA End Repair Kit K0771 according to directions, starting with 4 ug each fraction H18, H24, H30. Blunted products were isolated using spin columns (Invitrogen K310001) Treatment of 4 ug sonicated, fractionated DNA yielded approx 3.5 ug blunted product H18b, H24b, H30b, with respective concentrations 74, 66, 70 ng/uL.
An adaptor mix was prepared by combining each oligonucleotide G6a, G6b, Gc6a, Gc6b, BsPD, BsTB, BsPDc, BsTBc with 20 mM Tris pH 8.0 and 250 mM NaCl, the mixture heated lmin in boiling water and cooled to room temperature. T4 DNA Ligase (Invitrogen A13726, a kit containing the ligase at 5Units/uL, and reaction buffer) was used to ligate the adaptors to each blunted DNA fraction: to 10 uL blunted DNA fraction was added 5 uL adaptor mix, 2 uL 10×Ligase buffer, 2 uL 50% PEG4000 and luL, and the mixture left overnight at room temp. Adapted products were isolated using spin columns (Invitrogen K310001) eluting in 50 uL elution buffer, and labeled H18T, H24T, H3OT with respective concentrations 37, 39, 30 ng/uL.
PCR of adapted HER2 fractions was performed at 20 uL scale each using luL of the adapted template H18T, H25T, H30T, and a commercial PCR Master Mix (DreamTaq Green Thermo K1081). Each reaction contained a single primer G6a or
BsPD at 5 or 10 uM. Cycling conditions were 24×(95 deg 30 sec, 52 deg 30 sec, 72 deg 30 sec). Products were denatured by adding luL 1M sodium hydroxide to 4 uL product, and analyzed on 3% Agarose/EtBr gel. For all primers and primer concentrations tested PCR products show bands corresponding to the template sizes (
Products from the PCR shown in
Restriction digestion of PCR products to decrease adaptor portion: Restriction enzyme BspDI (New England Biolabs Ipswich MA) was used. To 260 uL water, 40 uL 10×CutSmart buffer BspDI (New England Biolabs Ipswich MA), 100 uL of the above PCR products H18B, H24B, H30B, and 10 uL 10U/uL BspDI was added, and the mixtures were incubated for 16h at 37 deg. Reactions were labeled H18R, H24R, H30R.
After a 16 h incubation, samples of each were taken for electrophoresis, comparing digested with undigested products. To wells of a PCR strip were added 8 uL 2×loading dye (Thermo Fisher Scientific), 0.6 uL (H18B, H24B, H30B), 2.4 uL (H18R, H24R, H3OR)+water to 10 uL; Each mixture was split to 2×5 uL each, to all added 4 uL water. To one of each added luL 1M NaOH and heated 95 deg 30 sec to denature. Five μL was loaded each to well of 3% Agarose/EtBr gel and electrophoresed. In the gel image “−” and “+” correspond to absence and presence of NaOH. All digestions show the smaller size and presence of end fragments expected for successful cleavage by BspDI (doublet probably from annealing fragment with residual primer). Denaturation by NaOH shows further decrease in size for both undigested and digested products. Higher MW smears from extended annealing of fragments are eliminated by denaturation.
The products H18B, H24B, H30B, H18R, H24R, H3OR were precipitated with isopropanol, resuspended in 20 uL water and subjected to amination and labeling with carboxytetramethylrhodamine by the procedure described above.
FISH Hybridization ConditionsThe targeting probes were hybridized to human chromosomal DNA in lymphocytes bound to glass microscope slides. In a typical experiment the reagent mixture consists of 74, of LSVWCP hybridization buffer (Abbott Molecular (Des Plaines, Ill.)) and 3 μL water containing 2000 ng sonicated human placental DNA, 500 ng COT-1 DNA (Life Technologies™ (Grand Island, N.Y.)), 50 ng of probe CEP17-SG buffer (Abbott Molecular (Des Plaines, Ill.)) and 100 ng of test probe.
The microscope slide was dehydrated by successive immersion in 70% , 85% and 100% ethanol, then air dried. The test solution (10 μL) was placed on the slide and covered with a 22×22mm slip, causing the solution to spread over the covered area. Rubber cement was applied to seal the edges and the slide placed in an instrument that controls the temperature. The temperature was raised to 70° C. for 5 min. to denature the DNA of both the sample and the reagent, then lowered to 45° C. lh to allow time for the reagent to hybridize to its target. After completion of the hybridization time, the rubber cement and slips were removed, and the slide washed 2 min. in a solution of 0.4×SSC and 0.3% NP40 at 73° C., then lmin in 2×SSC, 0.1% NP40 at room temperature, then air dried.
The slide was prepared for viewing by placing 10 uL of a solution of DAPI on the target area and covering with a slip. The slide was viewed with a fluorescence microscope equipped with filters suitable for the fluorophore of interest.
Fluorescence Microscopy of Rsultant Hybridization PatternsTen μL of DAPI-II (Abbott Molecular (Des Plaines, Ill.)) was placed on the slide at the position of the target, covered with a 22×22mm slip and viewed under fluorescence microscope equipped with filters that allow simultaneous visualization of DAPI, fluorescein (green) and TAMRA (orange) signals. The photograph (
Sequences used in adaptor modification and adaptor mediated PCR
Designs were carried out using model targets p53, HER2 and p16 based on available BAC probes for comparison. Genomic sequence corresponding to the targets, with repeat sequence flagged for removal, was identified with UCSC Genome Browser.
For PCR probes, computer applications were used to isolate the repeat-free portions of the sequence, and to identify fragments to target for preparation as “kilomers”. The web based application “BatchPrimer3” was used to generate primer sequences to amplify as much of each kilomer sequence as possible, and the identified primer sequences were synthesized by IDT in a 96-well format. For Oligo and Oligo-PCR hybrid probes, the repeat-free portions of sequence were further processed to identify fragments of specified size and GC content. Excel spreadsheets were used for such processes as appending common adaptor sequences, sorting and formatting the sequence lists for placing synthesis orders.
Bulk DNA, which ends up in the final probe, was generated either by oligo synthesis, Oligo-PCR hybrid, or by 1- or 2-step PCR. The 1-step PCR method is as follows: After PCR using BAC or genomic DNA template the products are combined and fragmented by sonication to give a product that can be chemically labeled by the same process used for BAC based FISH probes. FISH probes made this way are structurally identical to the AM BAC probes—the only difference is that the PCR probes exclude the repeat sequence and vector sequence present in BAC DNA. The 2-step method is as follows: The sonicated product is ligated to adaptors to make a single template mixture containing all the chosen targeting sequence. This template can then be used in a single PCR reaction using a single set of primers to generate bulk DNA for amination and labeling. In this case sonication is no longer needed since the amplified product is already the desired size. The template is prepared once, stored indefinitely and samples taken for each new preparation. The adaptor sequences are present at the 5′ and 3′ ends of the product. While they can be removed by restriction digestion, testing shows that their presence does not damage the performance in FISH assays.
Amine groups for attachment of fluorophore labels were introduced either byinclusion of aminoallyl dUTP in the PCR reaction, or by chemical amination. The chemical amination was performed by the bisulfite/TFA/ethylenediamine process used
with AM probes, but with the exception that a small amount of tetramethylethylenediamine was added after desalting the reaction mixture, but prior to ethanol precipitation. This displaces residual unlinked ethylenediamine that would otherwise compete for fluorophore in the labeling reaction.
Labeling the aminated DNA with fluorophore was done by a modification of an established process more suited to the numerous small scale reactions. In this modification the aminated DNA is combined with a reaction buffer of tetramethylethylenediamine and sodium chloride in 25% DMSO, the active fluorophore added and the mixture is incubated 2h at 60° C. The product is isolated by ethanol precipitation and subjected to 75° C. 72h formamide treatment standard.
HER2 PCR Probes:For HER2 PCR probes, three variants were generated, all using 76 kb of repeat-free sequence. For the simplest “1-step PCR” probe, the PCR generated DNA was treated the same as BAC DNA in conventional probes: fragmentation by sonication, followed by chemical amination and labeling. For the “2-step PCR” probe, the sonication fragments were ligated to adaptors to make a template. This template was amplified with a single primer to generate bulk DNA ready for amination and labeling. In the third format, “2-step PCR with aminoallyl dUTP”, this same template was amplified with a primer pair in the presence of aminoallyl dUTP to generate the aminated product, ready for labeling with any desired fluorophore.
Generation of repeat-free sequence in HER2 locus:
Sequence for the HER2 PCR format was identified using the locus defined by the P1 clones pVYS 174 C, E, H, I. These clones include 226 kb at hg18_dna range chr17:35004678-35230380. These coordinates were entered into UCSD Genome Browser, and the corresponding sequence presented using the Repeat Masker function to give the portions known to be repeat sequence in lower case. The upper case “unique” sequence portions were copied using an application to select out the upper case unique subsequences, retaining the position information of each. This yielded 35 sequences longer than 1200 bp (1234 to 5615 bp), totaling 76904 bp. These were processed with another application to break all the sequences into a total of 95 sequences, 1200 bp each, with at least 300 bp overlap. The 1200 bp sequences were entered into the web based application “BatchPrimer3”, with settings adjusted to give primers with Tm at least
- 65 deg, to include as much as possible (at least 800 bp) of each sequence in the amplicon.
The identified primer sequences were synthesized and placed as primer pairs in 96-well plate format. The primers were dissolved in water and prepared to give 5 uM each primer, while still in the 96-well plate format. PCR was in a 96-well plate in the same format as the primer pairs, using a master mix containing Phire polymerase, template consisting of a mixture of the P1 clones pVYS 174 C, E, H, I, and primers at 0.5 uM.
(Note, Genomic DNA can be used as template, but locus specific clones such as BACs and PAC's are preferred). The products were analyzed by 96-well eGel, and show strong clean bands for 94 of the 95 wells. When Taq polymerase was used only 87 of the 95 reactions showed product.
Fragmentation of HER-2 repeat-free sequence:
The contents of the PCR wells were combined and the DNA 1200mers were isolated by ethanol precipitation and PEG precipitation. The 1200mer mixture was sonicated by the same means used for fragmenting BAC DNA for other AM probes, and the sonicated product fractionated by HPLC with an ion exchange column to give narrow size fractions ranging from about 120 to about 400 bp. In some embodiments, the fractionation step is elminated
HER-2 probe from 1-step PCR process:
To prepare Probe 5/13-76A the fraction centered at 150 bp was aminated by a standard procedure and labeled with Spectrum Orange.
HER-2 probe from 2-step PCR process:
To prepare a HER-2 probe from the 2-step process, a portion of the same 150 bp HPLC fraction was treated with a blunting agent and ligated to adaptors. The adapted product was used as a template in a second PCR reaction, this time using only a single primer, with sequence corresponding to the adaptor. The use of a single primer to amplify the adapted template suppresses amplification of the shortest fragments via a stem-loop structure, and gives a product enriched in the longer fragments. The PCR product was aminated and labeled with Spectrum Orange, then subjected to 75° C. 72h formamide treatment.
HER-2 PCR probe via aminoallyl dUTP amination:
To prepare a HER-2 PCR probe via aminoallyl dUTP amination, the HPLC fractions of sonicated 1200mer were recombined (to simulate unfractionated fragments), treated with blunting agent and ligated to adaptors containing common 5′ end containing a BspQI restriction site. The adapted product was used as template in a second PCR reaction, this time using two primers corresponding to the adaptor sequences, and with aminoallyl dUTP replacing half of the dTTP. The PCR product was treated with the restriction enzyme BspQI to digest off the common ends, and the DNA product labeled with Spectrum Orange, then subjected to 75° C. 72h formamide treatment.
HER-2 Oligo probe:
Design of the HER-2 oligo probe started with the same repeat-free sequence as the HER2 PCR probes. An application was used to select non-overlapping 80-base portions of this sequence, all with approximately 50% GC content (G+C min =39, max
=41). A total of 401 such sequences were found. These were entered into the web application QuickFold with parameters Na+=0.05M, Mg++=0.001M, maximum of 1 Folding and the results copied as text and deltaG. The Find feature of Excel was used to flag sequences containing certain restriction sites for removal (to allow these sequences to be used in adaptors without interference with target sequence). The remaining sequences were sorted by deltaG, and the 288 (three 96-well plates) with lowest tendency to fold were selected for further processing and sorted by genomic location. The 80mer sequences were joined in pairs via a common 20 base connecting sequence and a different common 20 base was also added to the 3′ end of the pair, bringing the total to 200 bases to be synthesized. All 288 of the 80mers (Figure were represented in 144 separate “Forward” 200mers. The complements of the target 80mers and common 20mers were also calculated, and assembled the same way to give 144 separate “Reverse” 200mers. The assembly of these was designed such that upon mixing the sequences should duplex in a staggered fashion, giving long chains of annealed product.
Nucleic acids were chemically aminated by the procedure above, and labeled with Spectrum Orange. The labeled products were purified by gel electrophoresis to remove truncated synthesis products, and the full-length products combined to give the final probe.
Design of additional HER2 Oligo Probes started with the same sequence as for HER2 PCR probes, masking repeat sequences. Additional masking was introduced to flag for removal other undesirable subsequences: 5 or more consecutive “G” or “C” bases, and sequences corresponding to the BspQI restriction site “GCTCTTC” and “GAAGAGC”. The remaining sequence was processed to identify 60 base stretches with 55-65% GC. Very few acceptable sequences were found in the downstream 40 kb of the sequence, so only those in the range 1-180 kb were carried to the next stage. To the 3′ end of each sequence was added the bases “GGTTGAAGAG” polymerase using a complementary primer. The web based application “Zipfold” was used to determine the energy of folding. Of the 1027 60-mers assessed, the 960 with the lowest tendency to fold were retained. These were separated into 5 groups (192 members each =two 96-well plates) according to energy of folding, with each group sorted by position in the overall genomic sequence. The oligonucleotides were dissolved in water, and combined into groups according to folding tendency. Samples of each group were annealed with a primer containing sequence corresponding to the common 3′ end and Phire polymerase to elongate each to a blunt ended duplex mixture. These were purified by ion exchange HPLC to remove products of truncated oligomers..
p53 PCR Probes:Same as with the HER-2 probes, the p53 PCR probes were designed based on the sequence of the BAC for the corresponding BAC p53 probe. Kilomers were generated by PCR, combined and fragmented by sonication. For the 1-step PCR probe the sonication fragments were simply aminated and labeled. For the 2-step PCR variants the sonication fragments were blunted and ligated to adaptors to make the template. To generate bulk DNA for amination and labeling the template was amplified using primers corresponding to the adaptor sequences. Bulk DNA containing the amines for labeling was prepared from the same template but including aminoallyl dUTP in the reaction mixture. For an additional variant, the adaptor sequences were removed by digesting the PCR product with a restriction enzyme specific to a recognition site included in the adaptors.
Generation of repeat-free sequence in p53 locus:
Sequence for the p53 PCR format was identified using the locus defined by the BAC clone pVYS 173i. This clone consists of of 172 kb at hg18 dna range chr17:7435119-7606823. These coordinates were entered into UCSD Genome Browser, and the corresponding sequence presented using the Repeat Masker function to give the portions known to be repeat sequence in lower case. Table 1 below shows primer sequences.
The upper case “unique” sequence portions were copied as above to select out the upper case “unique” subsequences, retaining the position information of each. This yielded only 17 sequences longer than 1200 bp totaling 35930 bp. To these were added 13 fragments with lengths 800-1200 and 10 fragments 650-800 bp to give a final total of 55661 bp. The application “SeqChop3” was used on the first set to generate 1200-mers with 400 base overlap, yielding 65 sequences. The second set (800-1200) for 800mers with 200 base overlap gives 26 sequences. To complete a 96 well plate an additional 5 sequences in the 650-800 base region are accepted. The sequences so generated were adjusted to give primers with Tm at least 65 deg, to include as much as possible of each sequence in the amplicon. The primers were dissolved in water to give 5 uM each primer, while still in the 96-well plate format. PCR was in a 96-well plate in the same format as the primer pairs, using a master mix containing Phire polymerase, template consisting of the BAC clone pVYS 173i and primers at 0.5 uM. At the conclusion of the PCR, additional primer, Taq polymerase and dNTP was added and the plate subjected to an additional 8 cycles to increase the product yield. The products were analyzed by 96-well eGel, and show strong clean bands for 91 of the 96 wells. The contents of the PCR wells were combined, and the DNA isolated by ethanol precipitation and PEG precipitation. The mixture was sonicated by the same means used for fragmenting BAC DNA for other probes.
p53 probe from 1-step PCR process:
To prepare p53 probes from the 1-step PCR process, the sonicated product was aminated and labeled with Spectrum Orange, then subjected to 75° C. 72h formamide treatment.
p53 probe from 2-step PCR process:
To prepare p53 probes from the 2-step PCR process, a portion of the sonicated product was fractionated using disposable silica based spin columns (PureLink PCR Purification Kit) but adjusting the binding buffer to isolate a fraction ranging from 100-300 bp. A portion of this fraction was treated with a blunting agent and ligated to adaptors. This adapted product was used as template in a second PCR reaction, this time using only a single primer, with sequence corresponding to the adaptor. The PCR product was aminated, labeled with Spectrum Orange, and subjected to 75° C. 72h formamide treatment.
p53 PCR probe via aminoallyl dUTP amination:
This probe was prepared as described above except the PCR step included aminoallyl dUTP added to the PCR mixture. The PCR product was labeled with Spectrum Orange and subjected to 75° C. 72h formamide treatment.
A portion of the sonicated blunted repeat-free p53 DNA was ligated to adaptors containing a BspQI restriction site. The product was used as template with a pair of primers corresponding to adaptors in a PCR reaction containing aminoallyl dUTP and the product exposed to BspQI restriction enzyme to remove the adaptor ends. The digestion product, containing only the sequence specific to p53, was labeled with Spectrum Orange and then subjected to the 7° C. 72h formamide treatment.
Oligo-PCR Probe for p53Sequences for p53 Oligo Probe were identified as above; however in this case, in addition to masking repeat sequence, all subsequences of 5 or more consecutive “G” and “C” were masked. Parameters were set to identify subsequences of length 140, with GC content of 45-60% . The 289 sequences identified were subjected to NCBI BLAST to find matches to other loci in the human genome. 281 unique sequences remained after this. To 280 of these was appended a common Forward and Reverse sequence, each 25 bases, and containing restriction sites, to give 280 sequences each 190 bases. These sequences were sent to IDT for synthesis as “Ultramers” in 96-well plate format. The products were combined and used as template in PCR with primer sequences corresponding to the adaptors. The adaptor ends were removed by digestion with the restriction enzyme, and the product aminated, labeled with Spectrum Orange, and subjected to 75° C. 72h formamide treatment.
Table 2 shows the 190 bp sequences.
Table 3 shows the summary of the probe designs and the downstream/cleanup methods.
Probes were first tested on male lymphocyte slides, and probe intensity, specificity, background and cross-hybridization were evaluated, with corresponding BAC probe as the control.
All probes tested passed the cross-hybridization test on lymphocyte slides. Once a probe design passed on lymphocyte slides, it was then tested on FFPE slides. All probes were tested on breast cancer tissue FFPE slides. Some probes were tested on both breast and gastric slides. Universal pretreatment method was used for all FFPE slides. HER2 and p53 BAC probes from AM inventory were used as controls for all experiments. BAC control probes passed overnight hybridization on both lymphocyte slides and FFPE tissue slides, but failed 1 hour hybridization on both slide types.
Results indicate that RF PCR probe designs surpassed the performance of synthesized oligo designed either by direct synthesis or oligo-PCR hybrid. Directly synthesized HER2 oligo probe and oligo-PCR hybrid p53 probe failed lhr FFPE, while oligo-PCR hybrid HER2 probe failed all quality evaluation. Based on these data, oligo probe designs were excluded from further evaluation, while RF PCR method was used for the selection of optimal probe designs.
All RF PCR designs passed quality evaluation for 1 hour and overnight hybridization on both lymphocytes and FFPE slides, except some sub-optimal specificity data points observed on lymphocyte slides.
2-step PCR design has several downstream or cleanup options, such as DNA fragment fractionation after sonication, 2nd PCR with aminoallyl-dUTP, and adaptor removal after 2nd PCR. Table 1 lists all the downstream or cleanup steps for each probe designs For both HER2 2-step probes, the different fractionation size, 2nd PCR with aminoallyld-UTP or not, and adaptor removal or not after 2nd PCR did not have a positive impact on the final probe quality.
Same as the three p53 2-step PCR probes, 2nd PCR with aminoallyl-dUTP vs. amination, and adaptor removal or not after 2nd PCR did not impact final probe quality.
The final procedure for Repeat-Free PCR FISH Probe design and preparation is the following.
- 1: Identify desired coordinates of locus on Genome Browser.
- 2: Download sequence with repeats masked to N.
- 3: Enter sequence in Sequence Processing program.
- 4: Process to identify kilomers of unique sequence, and format for BatchPrimer3
- 5: Use BatchPrimer3 (web) to identify F and R primers for each kilomer.
- 6: Order mixed primers in 96-well plate format.
- 7: PCR in plate using Phusion polymerase, assess by eGel-96.
- 8: Combine PCR products, fragment by sonication.
- 9: Blunt sonicated DNA.
- 10: Ligate Adaptors to make template.
- 11: PCR with: Adaptor-primers to make bulk DNA for amination, labeling.
- OR Adaptor-primers and AAdUTP to make aminated DNA for labeling.
- 13: Aminate (if needed)
- 14: Label, formamide treat.
This example describes the development of repeat-free probes targeting p16. A map of the p16 probe is shown in
PCR of 1200mers with Phusion: To 24, each pl6RF 5 uM, 184, Phusion MM was added and placed on thermocycler with program 98 deg 30 sec, 25×(98° C. 8 sec, 68° C. 30 sec, 72 deg lmin), 72° C. 10 min, 4° C. Extend PCR: To each well, 24, of the same 5 μM primer and 24, (80 uL 2×perMM+60 μL dNTP+20 μL 1M MgCl2) was added and thermocyling was performed: 10×(98° C. 8 sec, 68° C. 30 sec, 72° C. 2 min). Loaded 3 μL to wells of eGel, electrophoresed 8 min. Most wells (68/73) showed strong clean bands at expected (same) MW. However some show closely spaced doublets. Wells of p16RF Phusion PCR were combined to total 1200 μL, split to 3×400 μL in tubes and 40 μL 3M NaAc and 1 mL EtOH was added and tubes were placed at −20° C. Tubes were spun at 15000 rpm at 4 deg for 12 min, pellets were washed in 400 μL 70% EtOH, dried in speedvac, combined, and resuspended in 200 μL water, placed in 65 deg oven 5 min, and spun at 4000 rpm 5 min to sediment polymerase. The supernate was transferred to a new tube, 300 μL PEG rgt was added. After 15 min, the tube was spun at 14000 rpm for 5 min, the pellet was resuspended in 400 μL water. Electrophoresis showed bands consistent with 1200mer mix.
Sonicate p16-1200mer: (reserved 20 μL for use as template) To 380 uL p16-1200mer, 40 uL 3M NaAc was added, the tube was sonicated intensity 3, 30% duty cycle 2×10 min, and 1 mL EtOH was added. The tube was spun at 15000 rpm 4° C. for 10 min, the pellet washed in 4004, 70% EtOH, dried, and resuspended in 1004, water. The tubes was then spun at15000 rpm 4 deg 5 min to sediment residue from sonicator probe. Electrophoresis showed a size range of approximately 50-400 bp.
Fractionation: To 10 μL of the sonicated 1200mer, 40 μL water and 10 μL buffer was added, the tube was mixed and pipetted to spin column 1, spun 14000 rpm 1 min; to effluent added 10 μL buffer, mixed, pipetted to spin column 2, spun 14000 rpm 1 min; to effluent added 10 μL buffer, mixed, pipetted to spin column 3, spun 14000 rpm 1 min. Columns were washed with 2×200 μL wash buffer and eluted with 50 μL elution buffer. Electrophoresis showed size of approximately 100-300 bp.
Blunt p16son and p16s2 using Fast DNA End Repair Kit: To 3 μL of the above in 40 μL water, 5 μL of 10×buffer and 2.5 uL enzyme mix was added and the tube was vortexed and placed in 20° C. bath for 20 min. An Inverse PCR purification kit (Life Technologies) was used according to directions to isolate products in 50 μL buffer.
Ligate Adaptors to p16sonB, p16s2B: One μL each of 1000 μM PadBsPD1, CadBsPD1, PadEcoR1, CadEcoR1, 5 μL 10×Ligase Buffer, 5 μL 50% PEG4000, 5 μL 7/28(p16sonB, p16s2B) was added to each tube, the tube was vortexed and 1 μL Ligase was added. An Inverse PCR purification kit was used to isolate products.
PCR of adapted p16: To wells of strip added (8,8,2,8,2) μL water and (1 each 20 μM, 2, 8 μL 20 uM PadBsPD1; 2, 84, 20 uM PadEcoR1). To wells added 10 μL of 50 μL DreamTaq Green 2×perMM+2 μL of the above probe. Thermocycling was performed with program 25×(95° C. 30 sec, 55° C. 30 sec, 72° C. 30 sec). Analysis showed product bands from p16sonA template slightly broader than those from p16p2A. For both, single primer at 2 μM gave yield similar to 8 μM; no difference between PadBsPD1 and PadEcoR1 primers. PadEcoR1 gave best overall performance.
Prep PCR of adapted p16 with PadEcoR1 single primer 5 μM. To wells of strip added 100 μL (400 μL water+4 μL 1000 μM PadEcoR1+2 μL (p16sonA, p16s2A)+200 μL DreamTaq 2×perMM), capped, placed on thermocycler with program 25×(95° C. 30 sec, 55° C. 30 sec, 72° C. 30 sec). Next, an additional 3.0 μL (30 μL 25 mM dNTP+10 μL 1M MgCl2+8 μL 1000 μM PadEcoR1) was added to each well and thermocycling was performed with program 10×(94° C. 30 sec, 55° C. 30 sec, 72° C. 2 min). Product was precipitated and resuspended as above.
Aminate p16 preps: Transferred 50 μL of above p16son to tube and used speedvac to reduce volume to 20 μL. Placed this and remaining 20 μL 7/29 p16sp, p16sp2p in boiling water bath 1 min, then to each added 180 μL (500 μL water+300 μL TFA+174 μL ethylenediamine+95 mg Na2S2O3 and placed in 65° C. water bath for 15 minutes. Next, solutions were desalted into water and 450 μL of each nanodrop was collected. TMED/NaCl was added, the tubes were placed in 65° C. bath 5 min, 50 μL 3M NaAc and 1 mL isopropanol were added. The resulting solutions were precipitated and resuspended in water.
Label aminated p16 products with TAMRA, CR6G: One μL 1M NaOH was added to above; after 1 min 25 μL (75 μL TMED/NaCl+75 μL DMSO), were added, the tubes were vortexed, and 2 μL (100 mM TAMRA, 100 mM CR6G) was added. Resulting solutions were precipitated and resuspended in water+15 μL 20×SSC and 105 μL formamide to give 150 μL at 2×SSC. Resulting solutions were purified as above.
All publications and patents mentioned in the present application and/or listed below are herein incorporated by reference. Various modification, recombination, and variation of the described features and embodiments will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although specific embodiments have been described, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes and embodiments that are obvious to those skilled in the relevant fields are intended to be within the scope of the following claims.
Claims
1-20. (canceled)
21. A probe set generated by a method of generating a probe to a nucleic acid target of interest, comprising:
- a) identifying regions of said nucleic acid target of interest substantially free of undesired sequences that are at least 100 bp in length;
- b) generating a plurality of probe-containing nucleic acids corresponding to said regions substantially free of undesired sequence; and
- c) fragmenting said probe-containing nucleic acids to generate probes of said probe set.
22. The probe set of claim 21, wherein said probes are hybridization probes.
23. The probe set of claim 21, wherein said probes detect expression of an oncogene or chromosomal aneuploidy.
24. The probe set of claim 23, wherein said oncogene is selected from Her2, p53, and p16.
25. A method of performing a hybridization assay, comprising contacting a target nucleic acid with said probes of claim 21.
26. The method of claim 25, wherein said hybridization assay is an ISH assay.
Type: Application
Filed: Jul 24, 2018
Publication Date: Dec 27, 2018
Inventors: John Russell (Des Plaines, IL), Ekaterina Pestova (Des Plaines, IL), Neeraj Adya (Des Plaines, IL)
Application Number: 16/043,795
