Gene Expression System
Two or more conditional, dominant, lethal gene expression systems provide high levels of penetrance in insects. Lethality is induced at an earlier stage of development and the risk of biochemical resistance is reduced, as compared to a single insect conditional, dominant, lethal gene expression system. The invention is useful for the control of insect populations.
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This application is a Continuation of U.S. application Ser. No. 16/997,416, filed Aug. 19, 2020, now issued as U.S. Pat. No. 11,737,436, which is a Continuation of U.S. application Ser. No. 15/313,922, filed Nov. 23, 2016, now abandoned, which is a U.S. National Stage Application of PCT/GB2015/051633, filed Jun. 4, 2015, which claims priority to Great Britain Application No. GB1410023.4, filed Jun. 5, 2014, the disclosures of each is herein incorporated by reference in its entirety.
REFERENCE TO AN ELECTRONIC SEQUENCE LISTINGThe contents of the electronic sequence listing (166372001302SEQLIST.xml; Size: 66,892 bytes; and Date of Creation: Jul. 11, 2023) is herein incorporated by reference in its entirety.
FIELDThe present invention relates to conditional lethal expression systems for insects, their use, and methods of population control using insects transformed therewith.
SUMMARYA significant method of control of insect populations in the wild involves irradiated Sterile Insect Technique (SIT), which serves as an environmentally friendly method of insect control, involves mass rearing the flies and rendering the males infertile by irradiation. However, SIT is not effective or economically viable in all areas when compared to other control methods, and the success of the radiation SIT programme is dependent on the irradiated fly having similar behaviour patterns to the wild populations of males. A further limitation of this method of SIT is that of separation of the males and females at the pupal stage. It is desirable to release only male insects, as the release of female insects may result in greater crop damage at the release area. In particular, the separation involves labour-intensive and time-consuming manual sorting of the insects.
An alternative method has been the introduction of the temperature-sensitive-lethal (TSL) sexing strain, whereby a chromosomal translocation of a spontaneous mutation in the Medfly has allowed a temperature sensitive separation (Caceres 2002); this transformed line is 99% effective at removing females (Mumford 2012). However, TSL strain has demonstrated a high degree of instability and, thus, requires laborious and expensive filter colony set-up in mass rearing facilities (Caceres 2002).
A further method of control is the use of a repressible, dominant, lethal genetic system introduced into the genome of an insect. A further refinement of this method has been to use a female-specific repressible, dominant, lethal genetic system. These systems provide for the female-specific expression of a lethal gene product in the absence of a repressor. Two-component systems were developed, wherein a transactivator gene product acts as a transactivator for a lethal gene, by activating a promoter for the lethal gene. The system is repressible by providing a repressor which would prevent the action of transactivator gene product on the promoter for the lethal gene. In later developments of this female-specific, repressible, dominant, lethal, genetic system, a single gene to be expressed is provided, with the gene product being both a transactivator for the gene and being the lethal product, thereby creating a positive feedback loop leading to the death of the transgenic insect.
Gong et al. disclose strains of Medfly harbouring tetracycline transactivator (tTA) that causes lethality in early developmental stages of the heterozygous progeny but has little effect on survival of the parental transgenic insects. In this system, tTA is both the transactivator and the lethal, as high levels of tTA are thought to be deleterious to cells. In fact, tTA was modified to be optimised for expression in insects, and this variant is referred to as tTAV. However, this document discloses that some insects escaped the lethal effect of tTAV, and that the possibility of biochemical resistance to the lethal effector molecule may be a drawback to this system. It is also disclosed that lethality earlier in development is preferred.
Fu et al. disclose a female-specific autocidal genetic system in C. capitata, using tTA and Cctra. Cctra inserted into tTA results in disruption of the tTA transcript in male splice variants but not in female splice variants (
However, the data obtained in Fu et al. indicates that lethality occurs in the late larval/early pupal stages of development and that most of the insect lines were not 100% penetrant. Fu et al. also discloses that a potential difficulty of this system is saturation of the response capacity. The factors regulating alternative splicing are thought to be in relatively short supply, so that the alternative splicing pathway may be saturated if too much pre-mRNA is produced. In order for the female-specific positive-feedback system to be lethal, large amounts of tTAV must be produced, so high levels of F1-type (female-type) splicing are required. Another problem is inefficiency, as a substantial proportion of the pre-mRNA in females is processed in the male forms (M1 and M2); these do not produce a functional protein, so tend to attenuate the lethality relative to non-sex-specific constructs.
It is therefore desirable to provide an improved female-specific, repressible, dominant, lethal genetic system, with earlier onset of the lethal effect in development than previously seen, preferably with improved penetrance, and preferably with a reduced risk of biochemical resistance. An additional desirable improvement is the increased stability of the system once inserted into the host genome.
Surprisingly, it has now been found that the penetrance of such a transgenic system is improved by providing a transgene having two female-specific, repressible, dominant, lethal expression systems. The provision of two such expression systems surprisingly also has the further advantage of inducing earlier onset of lethality, in addition to reducing the risk of developing biochemical resistance to the lethal product.
Thus, in a first aspect, there is provided a polynucleotide sequence comprising a first and a second gene expression system, wherein:
i) the first gene expression system comprises the components; a first dominant lethal gene operably linked to a first promoter, a gene encoding a first activating transcription factor, and a first splice control sequence,
ii) the second gene expression system comprises the components; a second dominant lethal gene operably linked to a second promoter, a gene encoding a second activating transcription factor, and a second splice control sequence, wherein
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- each of said activating transcription factors is capable of activating at least one of said promoters, provided that both of said promoters are activated when both of said transcription factors are expressed,
- each of the first and second splice control sequences mediates female-specific expression of the first and second dominant lethal genes, respectively, by alternative splicing,
- the transactivation activity of each of the first and second activating transcription factors is repressible by a first and a second exogenous control factor, respectively, wherein said first exogenous control factor is the same as or different from said second exogenous control factor, and
- each of said components of said first gene expression system are the same as or different from said components of said second gene expression system.
The expression systems of the invention are capable of being expressed in insects, preferably at least in dipterans, coleopterans and/or lepidopterans.
The expression systems of the invention preferably each comprise a promoter selected for
expression in insects, preferably at least in dipterans, coleopterans and/or lepidopterans. The promoter may be an insect promoter, or a promoter that is operational in at least one tissue of a target insect.
Two or more conditional, dominant, lethal gene expression systems have been shown to
provide high levels of penetrance in insects. Lethality is generally induced at an earlier stage of development and the risk of biochemical resistance is reduced, as compared to a single insect conditional, dominant, lethal gene expression system. The invention is useful for the control of insect populations.
Each of the two systems comprises a dominant lethal gene to be expressed and an activating transcription factor to activate expression of the lethal gene. The effect of the activating transcription factor can be repressed, and the product of the dominant lethal gene has a lethal effect on the insect when expressed in sufficient quantity. Each expression system also comprises a splice control sequence which provides for female-specificity of the lethal effect. The presence of two female-specific, repressible, dominant, lethal expression systems improves the penetrance of the system by increasing the amount of lethal product expressed, thereby increasing the probability of effective lethality. The presence of two expression systems also induces earlier onset of lethality during development due to an accumulation of lethal product, and the risk of resistance mechanisms is reduced because the probability of developing resistance to both expression systems is low.
The term “penetrance”, as used herein, refers to the proportion of individuals carrying a particular variant of a gene that also express the phenotypic trait associated with that variant. Thus, “penetrance”, in relation to the present invention, refers to the proportion of transformed organisms which express the lethal phenotype.
The term “construct”, as used herein, refers to an artificially constructed segment of DNA for insertion into a host organism, for genetically modifying the host organism. At least a portion of the construct is inserted into the host organism's genome and alters the phenotype of the host organism. The construct may form part of a vector or be the vector.
The term “transgene”, as used herein, refers to the polynucleotide sequence comprising a first and a second gene expression system to be inserted into a host organism's genome, to alter the host organism's phenotype.
The term “gene expression system”, as used herein, refers to a gene to be expressed together with any genes and DNA sequences which are required for expression of said gene to be expressed.
The term “splice control sequence”, as used herein, refers to a DNA sequence associated with a gene, wherein the DNA sequence, together with a spliceosome, mediates alternative splicing of a RNA product of said gene. Preferably, the splice control sequence, together with the spliceosome, mediates splicing of a RNA transcript of the associated gene to produce a mRNA coding for a functional protein and mediates alternative splicing of said RNA transcript to produce at least one alternative mRNA coding for a non-functional protein.
The term “transactivation activity”, as used herein, refers to the activity of an activating transcription factor, which results in an increased rate of expression of a gene. The activating transcription factor may bind a promoter operably linked to said gene, thereby activating the promoter and, consequently, enhancing the expression of said gene. Alternatively, the activating transcription factor may bind an enhancer associated with said promoter, thereby promoting the activity of said promoter via said enhancer.
The term “lethal gene”, as used herein, refers to a gene whose expression product has a lethal effect, in sufficient quantity, on the organism within which the lethal gene is expressed.
The term “lethal effect”, as used herein, refers to a deleterious or sterilising effect, such as
an effect capable of killing the organism per se or its offspring, or capable of reducing or destroying the function of certain tissues thereof, of which the reproductive tissues are particularly preferred, so that the organism or its offspring are sterile. Therefore, some lethal effects, such as poisons, will kill the organism or tissue in a short time-frame relative to their life-span, whilst others may simply reduce the organism's ability to function, for instance reproductively.
The term “tTAV gene variant”, as used herein, refers to a polynucleotides encoding the functional tTA protein but which differ in the sequence of nucleotides.
The term “promoter”, as used herein, refers to a DNA sequence, generally directly upstream to the coding sequence, required for basal and/or regulated transcription of a gene. In particular, a promoter has sufficient information to allow initiation of transcription, generally having a transcription initiation start site and a binding site for the polymerase complex.
The term “minimal promoter”, as used herein, refers to a promoter as defined above, generally having a transcription initiation start site and a binding site for the polymerase complex, and further generally having sufficient additional sequence to permit these two to be effective. Other sequence information, such as that which determines tissue specificity, for example, is usually lacking.
The term “exogenous control factor”, as used herein, refers to a substance which is not found naturally in the host organism and which is not found in a host organism's natural habitat, or an environmental condition not found in a host organism's natural habitat. Thus, the presence of the exogenous control factor is controlled by the manipulator of a transformed host organism in order to control expression of the gene expression system.
The term “tetO element”, as used herein, refers to one or more tetO operator units positioned in series.
The term, for example, “tetOx7”, as used herein, refers to a tetO element consisting of the
indicated number of tetO operator units. Thus, references to “tetOx7” indicates a tetO element consisting of seven tetO operator units. Similarly, references to “tetOx14” refers to a tetO element consisting of 14 tetO operator units, and so on.
The term “tra intron”, as used herein, refers to a splice control sequence wherein alternative splicing of the RNA transcript is regulated by the TRA protein, for instance binding thereof, alone or in combination (i.e. when complexed) with TRA2.
The term “minimal repeat”, as used herein, refers to the highly conserved repeat sequences observed to be required for the activity of a given transposase.
Where reference to a particular nucleotide or protein sequence is made, it will be understood that this includes reference to any mutant or variant thereof, having substantially equivalent biological activity thereto. Preferably, the mutant or variant has at least 85%, preferably at least 90%, preferably at least 95%, preferably at least 99%, preferably at least 99.9%, and most preferably at least 99.99% sequence identity with the reference sequences.
SEQ ID NO: 1 shows a nucleotide sequence of the insect gene expression system.
SEQ ID NO: 2 shows a nucleotide sequence of the gene expression system flanked by C. capitata genomic DNA.
SEQ ID NO: 3 shows a nucleotide sequence of the gene expression system flanked by C. capitata genomic DNA.
SEQ ID NO: 4 shows a nucleotide sequence of primer TG1-3864AttpflR.
SEQ ID NO: 5 shows a nucleotide sequence of primer TG1-AttPF2.
SEQ ID NO: 6 shows a nucleotide sequence of primer TG2-3864FRTFIF.
SEQ ID NO: 7 shows a nucleotide sequence of primer TG2-FRTNheF.
SEQ ID NO: 8 shows a nucleotide sequence of primer CcAdh2RTF.
SEQ ID NO: 9 shows a nucleotide sequence of primer CcAdh2RTR.
SEQ ID NO: 10 shows a nucleotide sequence of primer Cc3864FRTtaqF.
SEQ ID NO: 11 shows a nucleotide sequence of primer Cc3864FRTtaqR.
SEQ ID NO: 12 shows a nucleotide sequence of Cc3864FRTprobe.
SEQ ID NO: 13 shows a nucleotide sequence of primer PB5out.
SEQ ID NO: 14 shows a nucleotide sequence of primer PB3out.
SEQ ID NO: 15 shows a nucleotide sequence of primer Diag-5PBmin.
SEQ ID NO: 16 shows a nucleotide sequence of primer Diag-Pb5.
SEQ ID NO: 17 shows a nucleotide sequence of primer AmCydiagF.
SEQ ID NO: 18 shows a nucleotide sequence of primer Dlag6-pb3.
SEQ ID NO: 19 shows a nucleotide sequence of primer Dlag-K 10-1.
SEQ ID NO: 20 shows a nucleotide sequence of primer Diag7-pb3.
SEQ ID NO: 21 shows a nucleotide sequence of primer Diag2-hr5.
SEQ ID NO: 22 shows a nucleotide sequence of primer Diag3K10.
SEQ ID NO: 23 shows a nucleotide sequence of primer ttaVdiagF.
SEQ ID NO: 24 shows a nucleotide sequence of primer Med3864altF.
SEQ ID NO: 25 shows a nucleotide sequence of primer Med3864fldiagR2.
SEQ ID NO: 26 shows a nucleotide sequence of the tTAV gene.
SEQ ID NO: 27 shows a nucleotide sequence of the tTAV2 gene.
SEQ ID NO: 28 shows a nucleotide sequence of the tTAV3 gene.
SEQ ID NO: 29 shows a polypeptide sequence of the tTAV protein.
SEQ ID NO: 30 shows a nucleotide sequence of a 5′ piggyBac end including 5′ITR.
SEQ ID NO: 31 shows a nucleotide sequence of a 3′ piggyBac end including 3′ITR.
SEQ ID NO: 32 shows a nucleotide sequence of a 3′ piggyBac end including 3′ITR.
DETAILED DESCRIPTION OF THE INVENTIONThe present invention allows for selective control of the expression of the first and/or second dominant lethal genes, thereby providing selective control of the expression of a lethal phenotype. It will therefore be appreciated that each of the lethal genes encodes a functional protein. It is preferred that each gene expression system is as described in WO2005/012534.
Each of the lethal genes has a lethal effect which is conditional. An example of suitable conditions includes temperature, so that the lethal is expressed at one temperature but not, or to a lesser degree, at another temperature. Another example of a suitable condition is the presence or absence of a substance, whereby the lethal is expressed in either the presence or absence of the substance, but not both. It is preferred that the effect of the lethal gene is conditional and is not expressed under permissive conditions requiring the presence of a substance which is absent from the natural environment of the organism, such that the lethal effect of the lethal system occurs in the natural environment of the organism.
Each lethal genetic system may act on specific cells or tissues or impose its effect on the whole organism. Systems that are not strictly lethal but impose a substantial fitness cost are also envisioned, for example leading to blindness, flightlessness (for organisms that could normally fly), or sterility. Systems that interfere with sex determination are also envisioned, for example transforming or tending to transform all or part of an organism from one sexual type to another. However, it is preferred that the product of each lethal gene results in sterilisation, as this allows the organism to compete in the natural environment (“in the wild”) with wild-type organisms, but the sterile organism cannot then produce viable offspring. In this way, the present invention achieve a similar result to techniques such as the Sterile Insect Technique (SIT) in insects, without the problems associated with SIT, such as the cost, danger to the user, and reduced competitiveness of the irradiated organism.
In some embodiments, the product of at least one of the lethal genes is preferably an apoptosis-inducing factor, such as the AIF protein described for instance in Cande et al (Journal of Cell Science 115, 4727-4734 (2002)) or homologues thereof. AIF homologues are found in mammals and even in invertebrates, including insects, nematodes, fungi, and plants, meaning that the AIF gene has been conserved throughout the eukaryotic kingdom. In other embodiments, the product of at least one of the lethal genes is Hid, the protein product of the head involution defective gene of Drosophila melanogaster, or Reaper (Rpr), the product of the reaper gene of Drosophila, or mutants thereof. Use of Hid was described by Heinrich and Scott (Proc. Natl Acad. Sci USA 97, 8229-8232 (2000)). Use of a mutant derivative, HidAla5 was described by
Horn and Wimmer (Nature Biotechnology 21, 64-70 (2003)). Use of a mutant derivative of Rpr, RprKR, is described herein (see also White et al 1996, Wing et al., 2001, and Olson et al., 2003). Both Rpr and Hid are pro-apoptotic proteins, thought to bind to IAP1. IAP1 is a well-conserved anti-apoptotic protein. Hid and Rpr are therefore expected to work across a wide phylogenetic range (Huang et al., 2002, Vernooy et al., 2000) even though their own sequence is not well conserved.
In other embodiments, at least one of the lethal genes is Nipp 1Dm, the Drosophila homologue of mammalian Nippl (Parker et al Biochemical Journal 368, 789-797 (2002); Bennett et al., Genetics 164, 235-245 (2003)). NipplDm is another example of a protein with lethal effect if expressed at a suitable level, as would be understood by the skilled person. Indeed, many other examples of proteins with a lethal effect will be known to the person skilled in the art.
Preferably, at least one of the lethal genes is tTA or a tTAV gene variant. tTAV is an analogue of tTA, wherein the sequence of tTA has been modified to enhance the compatibility with the desired insect species. Variants of tTAV are possible, encoding the tTA protein, such that the tTAV variant gene products have the same functionality as the tTA gene product. Thus, the variants of the tTAV gene comprise modified nucleotide sequences as compared to the tTA nucleotide sequence and to each other, but encode proteins with the same function. Thus, tTAV gene variants can be used in the place of tTA. Indeed, it is preferred to use tTAV gene variants in the transgene of the invention.
Any combination of lethal genes may be used, and, in some embodiments, the lethal genes are the same while, in other embodiments, the lethal genes are different. The improved penetrance of the lethal effect and the earlier onset of lethality is achieved by an accumulation of lethal product.
In preferred embodiments, each of the first and second lethal genes is independently tTA or a tTAV gene variant. In some embodiments, each of the first and second lethal gene is independently one of tTAV (SEQ ID NO: 26), tTAV2 (SEQ ID NO: 27) and tTAV3 (SEQ ID NO: 28). In other embodiments, the first and second lethal genes are the same. In further embodiments, one of the first and second lethal genes is tTAV (SEQ ID NO: 26) and the other gene is tTAV3 (SEQ ID NO: 28). However, any combination of tTAV variants may be used; thus, in some embodiments, one of the first and second genes is tTAV (SEQ ID NO: 26) and the other is tTAV2 (SEQ ID NO: 27), while, in a further embodiment, one of the first and second genes is tTAV2 (SEQ ID NO: 27) and the other gene is tTAV3 (SEQ ID NO: 28). In other embodiments, the first lethal gene is tTAV (SEQ ID NO: 26) and the second lethal gene is tTAV3 (SEQ ID NO: 28).
Each lethal gene is operably linked to a promoter, wherein said promoter is capable of being activated by an activating transcription factor encoded by a gene also included in at least one of the gene expression systems.
The promoter may be a large or complex promoter, but these often suffer the disadvantage of being poorly or patchily utilised when introduced into non-host insects.
Accordingly, in some embodiments, it is preferred to employ minimal promoters. It will be appreciated that minimal promoters may be obtained directly from known sources of promoters, or derived from larger naturally occurring, or otherwise known, promoters. Suitable minimal promoters and how to obtain them will be readily apparent to those skilled in the art. For example, suitable minimal promoters include a minimal promoter derived from Hsp70, a P minimal promoter, a CMV minimal promoter, an Act5C-based minimal promoter, a BmA3 promoter fragment, and an Adh core promoter (Bieschke, E., Wheeler, J., and Tower, J. (1998). “Doxycycline-induced transgene expression during Drosophila development and aging”. Mol Gen Genet, 258, 571-579). Not all minimal promoters will necessarily work in all species of insect, but it is readily apparent to those skilled in the art as to how to ensure that the promoter is active.
It is preferred that at least one of the operably-linked promoters present in the invention is active during early development of the host organism, and particularly preferably during embryonic stages, in order to ensure that the lethal gene is expressed during early development of the organism.
In some embodiments, at least one of the promoters is the minimal promoter is a heat shock promoter, such as Hsp70. In other embodiments, at least one of the promoters is the srya embryo-specific promoter (Horn & Wimmer (2003)) from Drosophila melanogaster, or its homologues, or promoters from other embryo-specific or embryo-active genes, such as that of the Drosophila gene slow as molasses (slam), or its homologues from other species.
In some embodiments, at least one of the promoters is a minimal promoter. In some embodiments, each of the promoters is independently Hsp70, Hsp73 or sryα. In preferred embodiments, one of the first and second promoters is Hsp70 and the other is srya. In one embodiment, the first promoter is Hsp70 and the second promoter is sryα.
Each gene expression system further comprises a gene encoding an activating transcription factor, wherein each activating transcription factor activates the expression of a lethal gene of the transgene. Thus, each gene encoding an activating transcription factor is able to be expressed by the host organism, to produce a functional protein. In particular, each activating transcription factor is capable of activating at least one promoter, wherein the promoter is operably linked to a lethal gene. Consequently, when an activating transcription factor activates a promoter, the expression of the lethal gene operably linked to the promoter is up-regulated. Each activating transcription factor may act on either the first or the second promoter, or each activating transcription factor may act on both the first and the second promoter. It is preferred that, when more than one activating transcription factor is expressed, more than one promoter is activated. Thus, when both the first and the second activating transcription factors are expressed, both the first and the second promoters are activated.
The gene products serving as activating transcription factors may act in any suitable manner. For example, the activating transcription factors may bind to an enhancer located in proximity to the at least one promoter, thereby serving to enhance polymerase binding at the promoter. Other mechanisms may be employed, such as repressor countering mechanisms, such as the blocking of an inhibitor of transcription or translation. Transcription inhibitors may be blocked, for example, by the use of hairpin RNA's or ribozymes to block translation of the mRNA encoding the inhibitor, or the product may bind the inhibitor directly, thereby preventing inhibition of transcription or translation.
In preferred embodiments, the effect of the activating transcription factor on the expression of the lethal gene can be controlled by the skilled person, preferably through the use of an exogenous control factor. It is particularly preferred that the transactivation activity of the activating transcription factor can be repressed by the exogenous control factor. Thus, it is possible to control the expression of the lethal gene by controlling the transactivating activity of the activating transcription factor. The presence of the exogenous control factor, applied by the skilled person, reduces the activity of the activating transcription factor on the relevant promoter. Consequently, activation of the promoter is repressed, such that expression of the operably linked lethal gene is reduced.
Any activating transcription factor, the transactivating activity of which can be controlled, may be used in each or either gene expression system. For example, the activating transcription factor may be the tetracycline-repressible transcription activator (tTA) protein which, when expressed, binds to the tetO operator sequence and drives expression from a nearby minimal promoter. Other examples of controllable activating transcription factors include GAL4.
The genes encoding the activating transcription factors may be the same or different. In preferred embodiments, each gene encoding an activating transcription factor is, independently, tTA or a tTAV gene variant. In particularly preferred embodiments, each of the genes encoding an activating transcription factor is independently a tTAV gene variant, and may be the same or different tTAV gene variant. Any combination of tTA and tTAV gene variant may be used. In some embodiments, each of the genes encoding an activating transcription factor is independently tTAV (SEQ ID NO: 26), tTAV2 (SEQ ID NO: 27) and tTAV3 (SEQ ID NO: 28), and the genes may be the same or different. In some embodiments each gene encoding an activating transcription factor is independently one of tTAV (SEQ ID NO: 26), tTAV2 (SEQ ID NO: 27) and tTAV3 (SEQ ID NO: 28). In further embodiments, one of the first and second genes encoding an activating transcription factor is tTAV (SEQ ID NO: 26) and the other gene is tTAV3 (SEQ ID NO: 28). Any combination of tTAV variants may be used; thus, in some embodiments, one of the first and second genes encoding an activating transcription factor is tTAV (SEQ ID NO: 26) and the other is tTAV2 (SEQ ID NO: 27), while, in a further embodiment, one of the first and second genes encoding an activating transcription factor is tTAV2 (SEQ ID NO: 27) and the other gene is tTAV3 (SEQ ID NO: 28). In other embodiments, the gene encoding the first activating transcription factor is tTAV (SEQ ID NO: 26) and the gene encoding the second activating transcription factor is tTAV3 (SEQ ID NO: 28).
As mentioned above, the activating control factors are controllable, preferably repressible, by an exogenous control factor. Control of the activating transcription factors may be by any suitable means, and may be effective at any level. For example, the control may be effective either to block transcription of the gene encoding the activating transcription factor or to block translation of the RNA product thereof, or to prevent or inhibit action of the translation product of the gene.
It will be appreciated that the exogenous control factor used will depend upon the activating transcription factor encoded in the transgene. For example, in embodiments wherein at least one of the genes encoding an activating transcription factor encodes GAL4, the control factor may be temperature (as GAL4 is somewhat cold-sensitive) and/or GAL80 or mutants thereof. In embodiments wherein at least one of the genes encoding an activating transcription factor is tTA or a tTAV gene variant, the exogenous control factor is tetracycline. Tetracycline binds the tTA or tTAV gene variant product (i.e. tTA), thereby preventing tTA from having a transactivation activity. The presence or absence, or modulation of the concentration, of tetracycline is used to control the system when tTA or an analogue thereof, such as tTAV, is used.
Expression of the dominant lethal genes of the transgene may be sex-specific, or be a combination of sex-specific and stage-specific, germline-specific or tissue-specific, due to the presence of at least one splice control sequence in each gene expression system. In preferred embodiments, the sex-specific expression is female-specific. The splice control sequence in each gene expression sequence allows an additional level of control of protein expression, in addition to the promoter. For instance, tissue or sex-specific expression in embryos only would be extremely difficult by conventional methods.
The first and second lethal genes comprise a coding sequence for a protein or polypeptide, i.e. at least one exon, and preferably two or more exons, capable of encoding a polypeptide, such as a protein or fragment thereof. Preferably, the different exons are differentially spliced together to provide alternative mRNAs. Preferably, said alternative spliced mRNAs have different coding potential, i.e. encode different proteins or polypeptide sequences. Thus, the expression of the coding sequence is regulated by alternative splicing.
Each splice control sequence in the system comprises at least one splice acceptor site and at least one splice donor site. The number of donor and acceptor sites may vary, depending on the number of segments of sequence that are to be spliced together.
In some embodiments, one or both splice control sequences regulate the alternative splicing by means of both intronic and exonic nucleotides. In other embodiments, one or both splice control sequences is an intronic splice control sequence. In other words, it is preferred that said splice control sequence(s) is substantially derived from polynucleotides that form part of an intron and are thus excised from the primary transcript by splicing, such that these nucleotides are not retained in the mature mRNA sequence.
It will be understood that in alternative splicing, sequences may be intronic under some circumstances (i.e. in some alternative splicing variants), but exonic under other circumstances (i.e. in other variants). Thus, the at least one splice control sequence of the present invention is preferably substantially derived from polynucleotides that form part of an intron in at least one alternative splicing variant, i.e. in either the first spliced mRNA product or the at least one alternatively spliced mRNA product. Thus, introns or intronic sequences can be viewed as spliced out in at least one transcript or transcript type.
In “normal” (non-alternative) splicing and in alternative splicing, introns are generally removed from the pre-RNA to form a spliced mRNA, which may then be translated into a polypeptide, such as a protein or protein fragment, having an amino acid sequence. Thus, it will be readily apparent to the skilled person how to determine those sequences of the present system that are to be considered intronic, rather than exonic.
As mentioned above, exonic sequences may be involved in the mediation of the control of alternative splicing, but it is preferred that at least some intronic control sequences are involved in the mediation of the alternative splicing. In other words, each gene expression system may also include splice control sequences present in exons, as long as there is some intronic involvement of control. In some embodiments, one or both splice control sequences is derived from or contains elements of the dsx gene, where, without being bound by theory, it is thought that exonic sequences assist in the mechanism of alternative splicing.
Thus, in some embodiments, the at least one splice control sequence does comprise exonic sequences and it will be understood that this is envisaged by definitions used to describe the present invention. Thus, as will be apparent, it is possible for some nucleotides to be encompassed within the definition of the at least one splice control sequence and also within the definition of a polynucleotide sequence encoding a functional protein. In other words, the definition of these elements can overlap, such that certain nucleotides can be covered by the definition of more than one element. However, the skilled person will recognise that this is not unusual in molecular biology, as nucleotides can often perform more than one role. In other embodiments, at least one of the splice control sequences is solely intronic, i.e. with no exonic influence.
It is preferred that at least one splice control sequence is capable of being removed from the pre-RNA, by splicing. Preferably, said at least one splice control sequence does not result in a frameshift in at least one splice variant produced. Preferably this is a splice variant encoding a full-length functional protein. In other words, at least the one splice control sequence preferably does not mediate the removal of nucleotides that form part, or were intended to form part of, the polynucleotide sequence encoding a functional protein, defined between a start codon and a stop codon, to be expressed in an organism. By this it is meant that nucleotides that are excised by splicing, in at least one splice variant, are not nucleotides that encode amino acids in the wild type form of the protein or gene. One or more splice variants may have said nucleotides excised, but at least one variant must retain these nucleotides, so that a frameshift is not induced in the at least one variant. These removed nucleotides are those that are removed in addition to the sequences that are normally spliced out such as the intron.
Interaction of the at least one splice control sequence with cellular splicing machinery, e.g. the spliceosome, leads to or mediates the removal of a series of, preferably, at least 50 consecutive nucleotides from the primary transcript and ligation (splicing) together of nucleotide sequences that were not consecutive in the primary transcript (because they, or their complement if the antisense sequence is considered, were not consecutive in the original template sequence from which the primary transcript was transcribed). Said series of at least 50 consecutive nucleotides comprises an intron. This mediation acts preferably in a sex-specific, more preferably, female-specific, manner such that equivalent primary transcripts in different sexes, and optionally also in different stages, tissue types, etc, tend to remove introns of different size or sequence, or in some cases may remove an intron in one case but not another. This phenomenon, the removal of introns of different size or sequence in different circumstances, or the differential removal of introns of a given size or sequence, in different circumstances, is known as alternative splicing. Alternative splicing is a well-known phenomenon in nature, and many instances are known, see above.
Where mediation of alternative splicing is sex-specific, it is preferred that the splice variant encoding a functional protein to be expressed in an organism is the F1 splice variant, i.e. a splice variant found only or predominantly in females, and preferably is the most abundant variant found in females, although this is not essential.
As mentioned above, in some embodiments the manner or mechanism of alternative splicing is sex-specific, preferably female-specific, and any suitable splice control sequence may be used. In preferred embodiments, at least one splice control sequence is derived from a tra intron. The Ceratitis capitata tra intron from the transformer gene was initially characterised by Pane et al (2002), supra. In insects, for instance, the TRA protein is differentially expressed in different sexes. In particular, the TRA protein is known to be present largely in females and, therefore, mediates alternative splicing in such a way that a coding sequence is expressed in a sex-specific manner, i.e. that in some cases a protein is expressed only in females or at a much higher level in females than in males or, alternatively, in other cases a protein is expressed only in males, or at a much higher level in males than in females. The mechanism for achieving this sex-specific alternative splicing mediated by the TRA protein or the TRA/TRA-2 complex is known and is discussed, for instance, in Pane et al (Development 129, 3715-3725 (2002)).
It will be appreciated that homologues of the Ceratitis capitata tra intron from the transformer gene exist in other species, and these can be easily identified in said species and also in their various genera. Thus, when reference is made to tra it will be appreciated that this also relates to tra homologues in other species. Thus, in some embodiments each of the alternative splicing mechanisms is independently derived from the Ceratitis capitata tra intron (Cctra), or from another ortholog or homolog. In some embodiments, the ortholog or homologue is from an arthropod, preferably a tephritid. In other embodiments, the ortholog or homologue is from the genus Ceratitis, Bactrocera, Anastrepha or Rhagoletis. In other embodiments, the ortholog or homolog is from C. rosa, or B. zonata. In further embodiments, the ortholog or homolog is from B. zonata, and this ortholog or homolog is referred to herein as Bztra (GenBank accession number BzTra KJ397268).
The splice control sequences of the gene expression systems may be the same or different. In some embodiments, it is preferred that the splice control sequences are derived from different species in order to reduce the risk of recombination. Thus, in preferred embodiments, one of the first and second splice control sequences is Cctra and the other is derived from a different species. In particularly preferred embodiments, one of the first and second splice control sequences is Cctra and the other is Bztra (GenBank accession number BzTra KJ397268). In another embodiment, the first splice control sequence is Cctra and the second splice control sequence is Bztra (GenBank accession number BzTra KJ397268).
The exact length of the splice control sequence derived from the tra intron is not essential, provided that it is capable of mediating alternative splicing. In this regard, it is thought that around 55 to 60 nucleotides is the minimum length for a modified tra intron, although the wild type tra intron (F1 splice variant) from C. capitata is in the region of 1345 nucleotides long.
In other embodiments, at least one of the splice control sequences is derived from the alternative splicing mechanism of the Actin-4 gene derived from an arthropod, preferably a tephritid. In embodiments wherein more than one splice sequence is derived from Actin-4, they may be derived from the same or from different tephritid species. In some embodiments, each Actin-4 gene is independently derived from a species of the Ceratitis, the Bactrocera, the Anastrepha or the Rhagoletis genera. In other embodiments, the first and second Actin-4 genes are independently derived from Ceratitis capitata, Trocera oleae, Ceratitis rosa or Bactrocera zonata. In some embodiments, at least one of the first and second Actin-4 genes is derived from Ceratitis capitata. In embodiments wherein more than one splice control sequence is derived from Actin-4, the splice control sequences may be derived from the same species. However, it is preferred that the splice control sequences are derived from different species in order to reduce the risk of recombination.
In some embodiments, at least one of the splice control sequences comprises at least a fragment of the doublesex (dsx) gene derived from an arthropod, preferably a tephritid. In some embodiments, more than one splice control sequence (e.g. both the first and second splice control sequences) is derived from dsx, and the dsx genes are derived from the same or different tephritid species. In some embodiments, each dsx gene is independently derived from a species of the Ceratitis, the Bactrocera, the Anastrepha or the Rhagoletis genera. In some embodiments, the dsx genes are independently derived from Ceratitis capitata, Trocera oleae, Ceratitis rosa or Bactrocera zonata. In some embodiments, at least one of the first and second dsx genes is derived from Ceratitis capitata. In embodiments wherein more than one splice control sequence is derived from dsx, the splice control sequences may be derived from the same species. However, it is preferred that the splice control sequences are derived from different species in order to reduce the risk of recombination.
While in some embodiments it is envisaged that the splice control sequences are derived from the same gene or intron of origin, in other embodiments the splice control sequences are derived from different genes or introns of origin. For example, in some embodiments, one of the splice control sequences is derived from the tra intron and the other splice control sequence is derived from the Actin-4 gene or the dsx gene.
In some embodiments, at least one of the first and second gene expression systems further comprises an enhancer which is associated with the promoter of the said gene expression system. At least one of the activating transcription factors, encoded in the first and/or second gene expression system, binds the enhancer, such that binding of the activating transcription factor(s) serves to enhance the activity of said associated promoter, for example, by promoting polymerase binding at the promoter.
In embodiments wherein a promoter of a gene expression system is associated with an enhancer, the promoter is substantially inactive in the absence of an active enhancer. Such promoters are preferably minimal promoters, such as those described above.
It is appreciated that those skilled in the art will recognise which enhancers are suitable for use in the present invention. In particular, the enhancer must be suitable to be bound by an activating transcription factor as described above (i.e. which is controllable by an exogenous control factor).
Thus, in embodiments wherein one or more of the dominant, lethal genes is tTA or a tTAV gene variant, an enhancer is a tetO element, comprising one or more tetO operator units. Upstream of a promoter, in either orientation, teO is capable of enhancing levels of transcription from a promoter in close proximity thereto, when bound by the product of the tTA gene or a tTAV gene variant. In some embodiments, each enhancer is independently one of tetOx1, tetOx2, tetOx3, tetOx4, tetOx5, tetOx6, tetOx7, tetOx8, tetOx9, tetOx10, tetOx11, tetOx12, tetOx13, tetOx14, tetOx15, tetOx16, tetOx17, tetOx18, tetOx19, tetOx20 and tetOx21. In some embodiments, each enhancer is independently one of tetOx7, tetOx14 and tetOx21. In embodiments comprising more than one enhancer, the first enhancer is the same as or different from the second enhancer.
In preferred embodiments, both the first and the second gene expression system further comprise an enhancer, i.e. first and second enhancers, respectively. In some embodiments, one of the first and second enhancers is tetOx7 and the other enhancer is tetOx14. In other embodiments, the first enhancer is tetOx7 and the second enhancer is tetOx14.
In some embodiments, in a given gene expression system, it is preferred to link the dominant, lethal gene of said gene expression system with the gene encoding the activating transcription factor, of the same gene expression system. This may be achieved either by placing the two genes in tandem, including the possibility of providing the two as a fusion product, or, for example, by providing each gene with its own promoter in opposite orientations but in juxtaposition to the enhancer site.
In some embodiments, at least one of the gene expression systems forms a linear expression system. Thus, when the gene encoding the activating transcription factor is expressed, said activating transcription factor activates the promoter operably linked to the lethal gene, thereby up-regulating expression of the lethal gene. In some embodiments, the activating transcription factor activates only the promoter of the gene expression system that said activating transcription factor is expressed by. In other embodiments, the activating transcription factor may also activate the promoter of the other gene expression system.
In more preferred embodiments the dominant, lethal gene of a particular gene expression system is one and the same as the gene encoding the activating transcription factor also part of said gene expression system. Thus, the lethal product acts as the activating transcription factor for at least that gene expression system. Consequently, the lethal gene product activates the promoter of said gene expression system, thereby up-regulating expression of said lethal gene, resulting in a positive feedback loop. In other words, said dominant, lethal gene is also the gene encoding the activating transcription factor of said gene expression system. Thus, enhancement of the promoter serves not only to increase transcription of the activating transcription factor, but also leads to an accumulation of the lethal product of that gene expression system, resulting in a lethal effect on the host organism. In this regards, in one embodiment, it is particularly preferred that the positive feedback loop of the first and/or second gene expression systems is as disclosed in WO2005/012534.
Preferably, the first and/or second lethal gene is tTA or a tTAV gene variant as described above. In such embodiments, the relevant gene expression system further comprises a tetO element, as described above, as an enhancer. The gene encoding the activating transcription factor is one and the same as said lethal gene. The exogenous control factor is tetracycline. Thus, control is exerted on the positive feedback mechanism by the presence or absence of tetracycline, with the presence of tetracycline repressing the transactivation activity of the tTA or tTAV gene variant product on the promoter.
While, where at least one of the gene expression systems is a positive feedback loop, the activating transcription factor of said positive feedback loop activates the promoter of said gene expression system, in some embodiments the activating transcription factor also activates the promoter of the other gene expression system.
In some embodiments, one of the gene expression systems is a linear gene expression system as described above, and the other is a positive feedback loop, as described above.
In some embodiments, both the first and the second gene expression systems act as positive feedback loops. Each of the first and second gene expression systems expresses a different lethal gene product, such that the lethal gene product of the first gene expression system acts as the activating transcription factor for only the first gene expression system, and vice versa.
In preferred embodiments, both the first and the second gene expression systems act as positive feedback loops and express the same or similar lethal products. Thus, the lethal gene product expressed by the first gene expression system acts as an activating transcription factor for both the first and the second gene expression system, and vice versa. Accordingly, in some embodiments, both the first and the second gene expression systems comprise tTA or a tTAV gene variant as both the lethal gene and the gene encoding the activating transcription factor. Accordingly, both gene expression systems comprise an enhancer which is a tetO element as described above, which drives expression from the associated promoter. The first activating transcription factor (i.e. the first lethal gene product) can bind both the first and the second enhancers, and the second activating transcription factor can bind both the first and the second enhancers.
In some embodiments, one of the gene expression systems further comprises a third dominant, lethal gene operably linked to a third promoter. The activating transcription factor which is capable of activating the promoter of the relevant gene expression system is also capable of activating the third promoter, thereby enhancing expression of the third lethal gene. Thus, the expression of the third lethal gene may also be controlled, preferably repressed, by the exogenous control factor acting on said activating transcription factor.
In some embodiments, the relevant gene expression system further comprises an enhancer as described above, as well as optionally a third lethal gene and third promoter. In some such embodiments, the promoter of said gene expression system and the third promoter are both associated with said enhancer. Preferably, the promoter of said gene expression system is associated with one end of the enhancer and the third promoter is associated with the other end of the enhancer. In particular, as described above, some enhancers are capable of enhancing levels of transcription in either orientation.
The third lethal gene expresses a lethal product and, therefore, adds to the lethal effect of the transgene due to the accumulation of total lethal product. However, the improvements, described above, provided by the transgene are observed even without the presence of the third lethal gene in the transgene.
The third lethal gene may be any known to those skilled in the art. In some embodiments, the third lethal gene is any of those mentioned above in relation to the first and second lethal genes. In some embodiments, the third lethal gene is tTA, a tTAV gene variant or VP16. In preferred embodiments, the third lethal gene is VP16.
The third promoter may be any of those previously described in relation to the first and second promoters of the transgene. In some embodiments, the third promoter is a minimal promoter. In preferred embodiments, the third promoter is expressed in early development of the organism, preferably at least during embryonic stages. Preferably, the third promoter is Hsp70 or srya. In further embodiments, the third promoter is Hsp70.
In some embodiments, the transgene further comprises a genetic marker. In some embodiments, this marker is a fluorescent marker, being a gene encoding a fluorescent protein.
Suitable genetic markers will be apparent to those skilled in the art. In preferred embodiments the fluorescent marker is DsRed2, which encodes the DsRed2 fluorescent protein. In other embodiments, the genetic marker is green fluorescent protein, or variants thereon. These genetic markers are useful in the selection of successfully transformed organisms. In addition, such markers are useful for distinguishing, for example, transgenic flies from wild type flies in the field, or those caught in the field.
It will be appreciated by those skilled in the art that, in embodiments comprising such genetic markers, the components required to express the marker will also be included in said embodiment. For example, it is envisaged that the fluorescent markers will be operably linked to a promoter therefore. Any suitable promoter may be used, for example Hr5/IE1.
In a preferred embodiment, tTAV (SEQ ID NO: 26) is the first dominant lethal gene, Hsp70 is the first promoter and Cctra is the first splice control sequence. This first gene expression system is a positive feedback loop as described above, such that the first lethal gene is also the gene encoding the first activating transcription factor. The first gene expression system further comprises a first enhancer, wherein the first enhancer is tetOx7. The second gene expression system comprises tTAV3 (SEQ ID NO: 28) as the second dominant, lethal gene, srya a as the second promoter and Bztra (GenBank accession number BzTra KJ397268) as the second splice control sequence. The second gene expression system also forms a positive feedback loop, such that the second lethal gene is the gene encoding the second activating transcription factor. The second gene expression system further comprises a second enhancer, wherein the second enhancer is tetOx14. The second gene expression system also further comprises a third lethal gene operably linked to a third promoter, wherein the third lethal gene is VP16 and the third promoter is Hsp70. The third promoter is associated with the second enhancer, with the second promoter being associated with one end of the enhancer and the third promoter being associated with the other end of the second enhancer. The transgene further comprises a genetic marker and a promoter therefor, wherein the genetic marker is DsRed2 and the promoter therefore is Hr5/IE1. In another embodiment, the transgene is a polynucleotide sequence having the sequence represented by SEQ ID NO:1.
The first and second gene expression systems are arranged in tandem, forming a transgene, and the transgene may or may not comprise linker sequences of nucleotides between each gene expression system. In embodiments not comprising a linker sequence between the gene expression systems, the first and second gene expression systems are contiguous. In embodiments which do comprise a linker sequence between the first and second gene expression systems, the linker sequence is from 1 bp to 10 kbp in length.
It will also be appreciated that, in embodiments wherein the transgene further comprises a genetic marker and its associated promoter, there may or may not be a linker sequence of nucleotides between the genetic marker (or its promoter) and the adjacent gene expression system. As above, in embodiments wherein no linker sequence is present, the genetic marker or its promoter is contiguous to one of the gene expression systems of the transgene. In embodiments wherein the transgene does comprise a linker sequence between the genetic marker and the relevant gene expression system, the linker sequence is from 1 bp to 10 kbp in length.
However, it will also be appreciated by those skilled in the art that it is preferred that there are no linker sequences present in the transgene, such that the elements of the transgene are contiguous. This is in order to reduce the risk of random mutations being introduced into the transgene and to reduce the risk of recombination.
The polynucleotide sequence, i.e. transgene, comprising the gene expression systems may form part of a genetic construct. Thus, in another aspect of the invention, there is provided a genetic construct comprising a first and a second gene expression system as described above. The genetic construct may comprise further components not forming part of the transgene. Such components may or may not be present in an organism transformed therewith.
In some embodiments, the genetic construct further comprises at least four inverted repeats, forming at least two pairs of opposing inverted repeats. The transgene is positioned between two pairs of inverted repeats. This means that excision of the pairs of inverted repeats, in situ, is effective to leave the gene expression systems inserted in the host genome, without flanking transposon-derived repeats being present in the host genome. The at least four inverted repeats are as described in WO2005/003364 and provide for elimination of transposable ends as described in Dafa'alla et al (2006).
In some embodiments, the genetic construct comprises four inverted repeats forming at least two pairs of opposing inverted repeats. In some such embodiments, it is preferred that the four inverted repeats are piggyBac inverted terminal repeats (ITRs). Two of the inverted repeats are distal to the transgene, i.e. they are external inverted repeats, and the remaining inverted repeats are internal inverted repeats. In particular, this means that one internal inverted repeat is between one external inverted repeat and the transgene. The four inverted repeats therefore form four different transposable elements, with two of the transposable elements not containing the transgene. The transposable elements which do not include the gene expression systems are much shorter than the other two transposable elements. In general, transposases will be more effective at cutting out shorter sequences so that, where a transposon has one 5′ repeat and two 3′ repeats, for example, the most common transposon that will be observed transferring to another locus will be the shorter, formed by the 5′ repeat together with the more proximal of the two 3′ repeats. Thus, as the transposons which do not contain the transgene are shorter than those which do, excision of the transposons which do not include the transgene occurs with greater frequency than excision of the transposons which do contain the transgene.
In some embodiments, the two internal piggyBac ITRs are modified to include about 160 base pairs of additional subterminal piggybac sequence. This additional sequence may be added in order to ensure that the shorter transposons (i.e. those not containing the transgene) are excised during subsequent rounds of exposure to transposase.
In preferred embodiments, the construct comprises four piggyBac inverted repeats forming at least two pairs of opposing inverted repeats. The four piggyBac inverted repeats consist of the nucleotide sequences represented by SEQ ID NOs: 30-32, with the sequence represented by SEQ ID NO: 30 being used for two of the piggyBac inverted repeats. In particular, one external inverted repeat consists of the nucleotide sequence represented by SEQ ID NO: 30 and the other external inverted repeat consists of the nucleotide sequence represented by SEQ ID NO: 31. One of the internal piggyBac repeats consists of the nucleotide sequence represented by SEQ ID NO: 30 and the other internal piggyBac inverted repeat consists of the nucleotide sequence represented by SEQ ID NO: 32. More specifically, the 5′ external piggyBac repeat consists of the nucleotide sequence represented by SEQ ID NO: 30, and a 3′ internal piggyBac inverted repeat consisting of the nucleotide sequence represented by SEQ ID NO: 32 is between the 5′ external piggyBac inverted repeat and the transgene. The 3′ external piggyBac inverted repeat consists of the nucleotide sequence represented by SEQ ID NO: 31, and a 5′ internal piggyBac inverted repeat consisting of the nucleotide sequence represented by SEQ ID NO: 30 is between the 3′ external piggyBac inverted repeat and the transgene.
Accordingly, the four transposons possible in such embodiment are between:
i) the 5′ external and 3′ external piggyBac inverted repeats,
ii) the 5′ external and 3′ internal piggyBac inverted repeats,
iii) the 3′ external and 5′ internal piggyBac inverted repeats, and
iv) the 5′ internal and the 3′ internal piggyBac inverted repeats.
As described above, transposons ii) and iii) do not contain the transgene, and are shorter than transposons i) and iv).
In some embodiments having four inverted repeats, the construct further comprises at least one genetic marker associated with at least one possible transposon in order to allow the user to follow the progress of the various steps of transposition and excision and to determine in which individuals have been said steps have successful. In some embodiments, at least one genetic marker is associated with an identifiable step in the transposition/excision process, and more preferably, the marker is associated with the transgene. Such markers associated with the transgene may be as described above.
Preferably, at least one genetic marker is associated with each possible transposon. Accordingly, at least one genetic marker is positioned between each pair of inverted repeats. It will be appreciated that any suitable genetic marker may be used, and examples of such markers include DsRed2, AmCyan and ZsGreen. In some embodiments, the construct comprises three genetic markers, wherein one marker is positioned between each pair of inverted repeats. It will be appreciated that, in order to distinguish between the transposons, each of the markers must be different.
It will be understood by those skilled in the art that embodiments comprising at least one
genetic marker will also comprise a promoter to drive the expression of the genetic marker. In some embodiments, the promoter is Hr5/IE1 (Choi & Guarino, 1995), while in other embodiments the promoter is Polyubiquitin (Handler & Harrel, 2001). However, promoters for use with the genetic marker are not limited to these two examples, and others may be used. Those skilled in the art will recognise which promoters are suitable.
In preferred embodiments, the construct comprises the transgene represented by SEQ ID NO:1 and further comprises four piggyBac inverted repeats as described above. The construct further comprises a genetic marker between the 5′ external piggyBac repeat and the 3′ internal piggyBac repeat, and a genetic marker between the 3′ external piggyBac repeat and the 5′ internal piggyBac repeat, wherein one of these genetic markers is AmCyan and the other is ZsGreen. In particularly preferred embodiments, the construct is as shown in
As mentioned above, the transgene and genetic construct of the invention are useful in the control of organism populations in the wild. Specifically, arthropods transformed with the transgene show sex-specific lethality, with improved transgene penetrance and earlier onset of lethality as compared to previously disclosed transgenic insects. The transformation of arthropods with any of the transgene or constructs above also provides a safety mechanism in the event of biochemical resistance. Constructs further comprising at least four inverted repeats, as described above, provide the further advantage that post-integration elimination of all transposon sequences is possible, leading to stability in both mass-rearing and field conditions.
Thus, in another aspect of the present invention, there are provided organisms transformed with a transgene or a construct as described above. In some embodiments, the organism is an arthropod. In some embodiments, the organism is an insect. In some embodiments, the organism is of the order Lepidoptera, Siphonaptera, Diptera, Hymenoptera, Coleoptera, Thysanoptera, Hemiptera, Orthoptera or Mesostigmata. In other embodiments, the organism is of the family Tephritidae, Drosophilidae, Lonchaeidae, Pallopteridae, Platystomatidae, Pyrogotidae, Richardiidae or Ulidiidae. In preferred embodiments, the organism is of the family Tephritidae or Drosophilidae. In preferred embodiments, the organism is of the genus Ceratitis, Drosophila, Bactrocera, Anastrepha or Rhagoletis. More preferably, the organism is of the genus Ceratitis. In particularly preferred embodiments, the organism is Ceratitis capitata.
It will be appreciated that the transgene or construct may be administered by any means known to those skilled in the art, but generally tested after integrating into the genome. Administration can be by known methods in the art, such as parenterally, intra-venous intra-muscularly, orally, transdermally, delivered across a mucous membrane, and so forth. Injection into embryos is particularly preferred. In some embodiments, the transgene or construct is administered as a plasmid.
In preferred embodiments, the transformed organism is Ceratitis capitata, and the transformed insect comprises the sequence represented by SEQ ID NO: 2 or 3. In particularly preferred embodiments, the transformed Ceratitis capitata comprises the sequence represented by SEQ ID NO: 2, and Ceratitis capitata comprising this sequence is herein referred to as OX3864A. In other embodiments, the transformed Ceratitis capitata comprises the sequence represented by SEQ ID NO: 3, and transformed Ceratitis capitata comprising this sequence is herein referred to as OX3647Q.
In some embodiments, a transformed Ceratitis capitata comprising the sequence represented by SEQ ID NO: 2 (i.e. OX3864A) is particularly preferred for the following reasons:
i) The transgene penetrance is a 100% with one copy; i.e. as seen in the Examples, even at a heterozygous state all females died in the absence of tetracycline from the larval medium;
ii) The male:female ratio in the presence of tetracycline incorporated in the larval diet is 50:50 indicating good repressibility of the transgene expression in females (this is of importance for a cost-effective propagation of the strain in a rearing facility);
iii) OX3864A showed complete pre-pupal female lethality in the absence of tetracycline;
v) Expression of the red marker (DsRed2) is robust and sustainable. The marker is apparent at all developmental stages allowing for thorough Quality Control (QC) protocols in the mass-rearing facility and reliable monitoring in the field;
vi) Life history parameters are comparable to those of the wild type strain used for transformation, as shown in the Examples, indicating that 03864A has near wild-type fitness when reared on tetracycline;
vii) The inserted construct has been stabilised post-insertion by the removal of the vector piggyBac ends, such the transgene is fixed and heritable in the insect's genome.
It is also useful to identify organisms which have been successfully transformed with a transgene or construct as described above. Thus, in another aspect of the invention, there is provided methods for detecting an organism transformed with a transgene or construct as described above, and primers for use in said method. The method comprises a PCR-based assay for detecting a transformed organism, by amplifying a DNA sequence which overlaps the organism's genomic DNA flanking the inserted transgene and the transgene itself. The method comprises contacting a sample of DNA obtained from an organism with a primer pair specific for a transgene as described above inserted into the insect genome, wherein one primer in the pair is specific for a nucleotide sequence of the transgene and the other primer in the pair is specific for a genomic nucleotide sequence flanking the inserted transgene, and amplifying the sample of DNA. Thus, one primer in a primer pair anneals the flanking genomic DNA and the other primer in the primer pair anneals the transgene. The amplification product may then be visualised, and may generally be detected using standard techniques known to those skilled in the art.
Amplification of the DNA sample is carried out using PCR techniques known to those skilled in the art. As mentioned above, the primers in the primer pair are specific to the transformed organism, such that only when the transgene is integrated in the relevant genomic position will a band of appropriate size amplify.
Those skilled in the art will appreciate that a variety of primers may be used in the method of the invention, and that such primers can be prepared using techniques known to those skilled in the art. The primers used will define the size of the PCR amplification product to be visualised or more generally detected.
In some embodiments, the method is for detecting an organism transformed with the transgene or genetic construct. In some embodiments, the organism is an arthropod. In some embodiments, the organism is an insect. In some embodiments, the organism is of the order Lepidoptera, Siphonaptera, Diptera, Hymenoptera, Coleoptera, Thysanoptera, Hemiptera, Orthoptera or Mesostigmata. In further embodiments, the organism is of the family Tephritidae, Drosophilidae, Lonchaeidae, Pallopteridae, Platystomatidae, Pyrogotidae, Richardiidae or Ulidiidae. In preferred embodiments, the organism is of the family Tephritidae or Drosophilidae.
In other embodiments, the organism is of the genus Ceratitis, Drosophila, Bactrocera, Anastrepha or Rhagoletis. In preferred embodiments, the organism is of the genus Ceratitis. In particularly preferred embodiments, the organism is Ceratitis capitata.
In preferred embodiments, the method uses primers specific to a transformed Ceratitis capitata. In some embodiments, the primers specific to Ceratitis capitata comprising the nucleotide sequence represented by SEQ ID NO: 2. In this embodiment, a first primer pair (TG1), a second primer pair (TG2) or a third primer pair is provided. TG1 consists of the primers TG1-3864AttpflR (SEQ ID NO: 4) and TG1-AttPF2, (SEQ ID NO: 5). In this pair, TG1-3864AttpflR is specific for the genomic DNA flanking the transgene and TG1-AttPF2 is specific for the transgene itself. TG2 consists of the primers represented by SEQ ID NOs: 6 and 7. TG2 consists of primers TG2-3864FRTFIF (SEQ ID NO: 6) and TG2-FRTNheF (SEQ ID NOs: 7). In TG2, TG2-3864FRTFIF is specific for the genomic DNA flanking the inserted transgene, and TG2-FRTNheF is specific for the transgene itself. The third primer pair consists of Cc3864FRTtaqF (SEQ ID NO: 10) and Cc3864FRTtaqR (SEQ ID NO: 11). In the third primer pair, Cc3864FRTtaqF is specific to the transgene and Cc3864FRTtaqR is specific to the flanking genomic DNA.
In other embodiments, any one of the primers specific to the transgene disclosed above may be paired with any one of the primers specific to the flanking genomic DNA, and a person skilled in the art will appreciate that the size of the PCR amplification product will depend upon the primer pairs used.
In other embodiments, the method for detecting an organism transformed with a transgene or construct as described above further comprises the use of a dual-labelled probe during the amplification steps.
The sequence at the junction of the integrated transgene and the organism genomic DNA presents a unique fingerprint. Thus, it is possible to detect a unique junction using three specific oligonucleotides. Two of the oligonucleotides used in the method are primers to allow for the amplification of a predetermined fragment of inserted transgene and flanking genomic DNA, to which a third, dual-labelled, oligonucleotide, i.e. the probe, anneals. In some embodiments, the probe comprises a quencher molecule and a 5′ reporter molecule.
In some embodiments, the method comprises the steps of contacting a sample of DNA obtained from an organism with a primer pair specific for a transgene as described above inserted into the organism genome, wherein one primer in the pair is specific for the transgene and the other primer in the pair is specific for a genomic nucleotide sequence flanking the inserted transgene, and amplifying the sample of DNA. This step of the method is largely as described above. The probe is added to the PCR amplification mixture with the primers. The probe specifically bridges the junction of the transgene and flanking DNA in the amplified PCR product, requiring this boundary for a positive output. At each step of PCR-amplification, the 5′-3′ exonuclease activity of Taq polymerase releases a 5′ reporter molecule (FAM) from the annealed probe, resulting in an accumulative emission that is detectable in a real time PCR machine in samples bearing the integrated transgene. Thus, the method further comprises the steps of contacting the DNA sample with a probe during PCR amplification of the DNA sample.
In some embodiments, the organism is an arthropod, and preferred arthropods have been discussed above. In preferred embodiments, the organism is an insect, preferably a tephritid, more preferably of the genus Ceratitis. In particularly preferred embodiments, the insect is of the species Ceratitis capitata. Thus, in such embodiments, the primers are specific to a transformed Ceratitis capitata. Preferably, the primers are specific to Ceratitis capitata comprising the sequence represented by SEQ ID NO: 2 (i.e. OX3864A). In this embodiment, the primers allowing for the amplification of a predetermined fragment are Cc3864FRTtaqF and Cc3864FRTtaqR, represented by SEQ ID NOs: 10 and 11 respectively. Cc3864FRTtaqF is specific for the flanking genomic DNA and Cc3864FRTtaqR is specific for the transgene. In such embodiments, the probe is Cc3864FRTprobe, as represented by SEQ ID NO: 12.
In a further aspect of the present invention, there is provided a method for the population control of an organism. In preferred embodiments, the method comprises the step of transforming an organism or organisms with a transgene or construct as described above. In some embodiments, the method further comprises releasing said transformed organism(s) into the population to be controlled. In further embodiments, the method may also comprise the step of monitoring the population to be controlled. The released organisms breed with the population to be controlled, and the female-specific lethality conferred by the gene expression systems means that the female progeny produced by such cross-breeding will die during early stages of development. The male progeny inheriting the gene expression systems survive to pass on the lethal phenotype to subsequent generations.
In some embodiments, the population to be controlled is an arthropod population. In some embodiments, the population is an insect population. In some embodiments, the population is of the order Lepidoptera, Siphonaptera, Diptera, Hymenoptera, Coleoptera, Thysanoptera, Hemiptera, Orthoptera or Mesostigmata. In other embodiments, the population is of the family Tephritidae, Drosophilidae, Lonchaeidae, Pallopteridae, Platystomatidae, Pyrogotidae, Richardiidae or Ulidiidae. In preferred embodiments, the population is of the family Tephritidae or Drosophilidae. In further embodiments, the population is of the genus Ceratitis, Drosophila, Bactrocera, Anastrepha or Rhagoletis. In preferred embodiments, the population is of the genus Ceratitis. In some embodiments, the population is a population of Ceratitis capitata.
The release of organisms may be by any method known to those skilled in the art, for example, by a method such as cage release or paperbag release, such as those described in Simmons et al. (2011) or Harris et al. (2011).
The step of monitoring the population of organisms may be by any method known to those skilled in the art. In some embodiments, the transgene inserted into the transformed organism(s) includes a genetic marker, such as DsRed2. Thus, monitoring of the population to be controlled may be by trapping insects from the population, after release of the transformed organism(s) and visualisation, or, more generally, detection, for the genetic marker in the trapped individuals.
The invention will now be illustrated with reference to the following, non-limiting Examples.
EXAMPLES Example 1: Selection of the Lead Product C. capitata StrainTransformed strains were generated through piggyBac-mediated transformation using the construct shown in
The sex ratio under these two diet conditions was used to assess functionality of the construct in two crucial parameters: 1) total suppression of female lethality when fed tetracycline, and 2) full female lethality in the absence of tetracycline. Lines were selected for further testing based on their ability to meet these parameters and on the strength of fluorescence.
11 lines failed to provide complete penetrance with a single copy of the transgene and were discarded. One line demonstrated incomplete tetracycline repressibility and was also discarded. Two lines did not produce enough progeny, possibly due to fitness penalties imposed by the transgene insertion, and were therefore discontinued. Fluorescence was good in all lines generated; however, construct OX3864 provided in general a stronger and clearer fluorescence phenotype. Photographs of OX3864A and OX3647Q adult male flies can be seen in
Further analysis of the strains generated included:
a single transgene insertion originally measured as marker allele segregation in G2,
potential for homozygosis measured as marker allele segregation when males and females of the same line were crossed together,
piggyBac end removal via crossing to strain OX3133, which provides a source of transposase, following the method described by Dafa'alla et al. (2006).
Five lines exhibited multiple insertions, and for three lines the transgene insertion was found to be sex linked. All eight lines were, therefore, discarded. Strain OX3864E contained a silent insertion (confirmed by flanking sequence analysis) and was discarded. All remaining strains were positive for homozygosis potential and thus crossed to the medfly strain OX3133 for piggyBac excision (Dafa'alla et al., 2006). Only strains OX3864A and OX3647Q demonstrated complete removal of all piggyBac sequences and were thus selected as potential product strains.
Subsequently, homozygous lines of each of OX3864A and OX3647Q were derived by inbreeding to produce putative homozygotes, with confirmation by PCR. Further evidence for complete piggyBac sequence removal is provided by PCR (
The PCR reaction resulting in the gel shown in panel A of
Following insertion and excision analysis, strains OX3864A and OX3647Q were further tested for life history parameters in comparison to the TOLIMAN wild-type strain that they were both derived from and also the temperature-sensitive-lethal (tsl) Vienna 8 strain (reference). tsl is the genetic sexing strain T(Y;5)101 called also Vienna-8 (without the pericentric inversion D53) (Caceres, 2002), introgressed into the TOLIMAN wt that is currently used in many Sterile Insect Technique (SIT) programmes worldwide. Details of the tests performed are given below. Graphs are presented in
Longevity tests were performed at 21° C. and a relative humidity (R.H.) 50% in six replicate plastic cages (9 cm×9cm×9 cm), each containing 30 males and 30 females of the same genotype (1 insect/8.1 cm 2). Three of the cages were randomly assigned to a “stress” test of no food and no water. This was done to assess relative measures of nutrient reserves available at eclosion, an important indicator of potential longevity under release conditions. The remaining cages had an ad libitum supply of food and water. Cages were monitored on a daily basis; dead adults were removed and sexed, until all flies were dead, in line with FAO/IAEA/USDA guidelines.
Flies held under the stress conditions had, significantly reduced life spans compared to those provided with food and water (Log Rank Test χ21=1307, P<0.001); all stressed flies were dead within six days (
From the non-stressed cages described above, eggs were collected over 24 hour periods and counted under a dissecting microscope. The egg samples were then incubated on wet Whatman filter paper (Fisher Scientific) and sealed into a Petri dish with parafilm (200 eggs per Petri dish, 600 eggs per line in total). 72 hours after egg collection, Petri dishes were unsealed and examined under a dissection microscope in order to count the number of empty versus unhatched egg casings.
Per-cage daily egg production from the “non-stressed” cages declined significantly over time (Repeated Measures ANOVA: F1.6, 12.9=253.04, P<0.001) and there was a significant effect of genotype (F4.8, 12.9=5.19, P=0.008). Pairwise comparisons with a Bonferroni correction revealed that significantly fewer eggs were produced over the lifetime for both RIDL and tsl lines in comparison to the wt (wt mean lifetime egg production=4315±48.51; OX3864A=3470+226, P<0.014; OX3647Q=2593±147, P<0.001; tsl=2465±93.29, P<0.001). OX3647Q and tsl strains also produced significantly fewer eggs than OX3864A (0X3647Q vs. wt, P<0.001; tsl versus wt, P=0.005,
By recording daily mortality it was also possible to estimate age-specific egg-production per female. Consistent with the above, this also showed that fecundity declined significantly with time (Repeated Measures ANOVA: F1.9, 15.2=131.85, P<0.001). However, there was no significant effect of genotype on this decline (F5.7,15.2=2.19, P=0.104,
There was a significant effect of age on egg hatching rates (Repeated Measures ANOVA F5,40=207.3, P<0.001), as well as a significant effect of genotype (F15,40=4.52, P<0.001,
300 pupae from each line were kept singly and monitored for eclosion. Adults were checked for sex and visible deformity before recording. Uneclosed or partially eclosed pupae casings were counted and then discarded.
There was also a significant difference in adult eclosion rates between lines (ANOVA: F3, 10 =9.89, P<0.001). A Tukey HSD post hoc test revealed that this was mostly attributable to a significantly lower adult eclosion rate in OX3647Q in comparison to wt (wt=86.1%±0.69; OX3647Q=75.7%±2.43, P<0.01; OX3864A=84.7%±0.91, P=0.9; tsl=81.2%±1.04, P=0.25). There was a significant effect of genotype on adult sex ratio (F3,10=5.06, P=0.036), attributable to a difference in the sex ratio of males to females in OX3647Q but not in the other lines (Tukey HSD post hoc tests: wt=47%±1.8; OX3647Q=54%±1, P=0.035; OX3864A=55%±2.3, P=0.055; tsl=50%±1.5, P=0.83).
Fitness IndicesFrom the individual life history components, the net reproductive rate per female (R0) and average generation time (G) (spanning the peak of female fertility from one generation to the next) were calculated (Table 2). From these estimates, an index of fitness (r) per female was then derived. The r value for the wt was 0.195, which equates to each female contributing on average 0.195 females per day to the next generation. The other lines had lower fitness indices (OX3864A: r=0.187, OX3647Q: r=0.176, tsl: r=0.165).
Adult OX3864A, OX3647Q, TOLIMAN wt were obtained from larvae reared off-tet at low density (1 larva/0.5 g medium). Field cages (1.25 m tall with a base of 0.5 m 2) were constructed inside a greenhouse at the Zoology Department, Oxford University (Oxford, UK), with small orange trees (˜1 m in height) placed inside, experiments took place during August (sunrise 06.00) utilizing natural light and a stable temperature and humidity (25° C., 50% R.H.). 30 males from either OX3864A or OX3647Q were placed together with 30 wt males at 06:30, and 30 females introduced 30 minutes later.
The basic sequence of courtship and copulation is well characterised in the medfly, and follows a distinct sequence of male behaviour patterns (Cayol et al., 2002), consisting of “pheromone calling” and rapid wing vibrations. After courting the male will leap onto the female and if successful intromission occurs, the pair will generally remain still. Copulation generally lasts between 90 to 195 minutes. Mating pairs were removed from cages following intromission, and carefully introduced into horizontally-placed 1.5 ml eppendorfs. Copulation initiation time was recorded and copulations were scored as successful only if the pair mated for >30 minutes after transfer to the eppendorf. Short copulations (<15 minutes) were eliminated from the data as they often result in no sperm transfer. The mating experiments ended 9 hairs after initiation (16:00) or whenever all females had copulated, whichever was sooner. The identity of the mating males was determined by scoring males for the presence or absence of the DsRed2 fluorescent marker under a fluorescence microscope. Tests were performed with 10 replicates for each line. 167 and 237 couples were assessed for OX3864A and OX3647Q, respectively.
The relative sterility index (RSI) was used as a measure of male sexual competitiveness (McInnis et al., 2002; FAO/IAEA/USDA, 2003). RSI ranges between 0 and 1, a RSI of 1 would represent 100% of matings by transgenic males, a value of 0, 100% with the wt and 0.5 representing equal numbers of matings. The results showed that neither transgenic strain showed a significant reduction in competitiveness relative to wt males (t-test: OX3864A: RSI 0.46±0.05, t18=−2.09, OX3864A mated males n=77, wt mated males n=90, P=0.05; OX3647Q: RSI 0.47±0.09, t18=−1.72, OX3647Q mated males n=112, wt mated males n=125, P=0.1).
No significant differences in female remating frequency between females initially mated with either wt or fsRIDL males were seen (Fisher's Exact test: OX3864A: Ψ2 1=0.82, n=40, P=0.775; seven females first mated to OX3864A males remated, eight females first mated to wt males remated; OX3647Q: χ21=0, n=40, P=1, 12 females first mated to OX3647Q males remated and 12 females first mated to wt males remated). For those females that did re-mate when first mated to a RIDL male, the genotype of the second male had no effect on remating frequency (0X3864A: χ2 1=0.58, P=0.4 (females that first mated with OX3864A then remated with wt n=3, remated with OX3864A n=4; females that first mated with wt then remated with wt n=5, remated with OX3864A n=3); OX3647Q: χ2 1=0.17, P=0.5 (females that first mated with OX3647Q then remated with wt n=6, remated with OX3647Q n=6, females that first mated with wt then remated with wt n=7, remated with OX3647Q n=5)).
Although both medfly strains displayed good rearing and mating characteristics compared to the tsl Vienna 8 strain and the wt TOLIMAN strain, strain OX3864A outperformed strain OX3647Q and was therefore selected as the lead Medfly product strain.
Example 2: Molecular Characteristics of Strain OX3864A PCR-Based Assay for Specific Identification of Event OX3864AIn order to carry out quality control on the OX3864A strain and to monitor field use, an event-specific, PCR-based nucleotide detection assay was developed. The protocol for this assay is shown in Example 4, below, and the primers used are described in Table 3.
Each transgene-detecting primer pair comprises one primer that anneals within the
transgene and one that anneals in the flanking genomic DNA of 0X3864. Thus, only when the transgene is integrated in the genomic position described for OX3864 will a band of the appropriate size amplify. Primer pairs TG1 and TG2 target the flanking DNA at the opposite ends of the transgene. A primer pair that amplifies a fragment of the endogenous Adh gene was used as a positive control to assure the quality of genomic DNA used in this assay.
Results from the PCR-based assay are shown in
TAQMAN Assay for Specifically Detecting the Junction of the Integrated Transgene and Flanking Sequence
This assay was developed to detect the sequence at the junction of the integrated transgene and Ceratitis capitata gDNA, which present a unique fingerprint for OX3864. This assay was developed to detect one junction using three specific oligonucleotides (Table 4). Two of the primers allow for the amplification of a 98 bp (52 bp flanking gDNA+46 bp transgene) fragment to which a third, dual-labelled [5′ reporter (FAM)-3′ quencher (BHQ1)] oligonucleotide, the probe, anneals. The probe specifically bridges the junction of the integration and flanking DNA in the amplified PCR product, requiring this boundary for a positive output. At each step of PCR-amplification, the 5′-3′ exonuclease activity of Taq polymerase releases the 5′ fluorescent reporter (FAM) from the annealed probe, resulting in an accumulative emission that is detectable in a real time PCR machine in samples bearing OX3864 DNA. The primer and probes used in this assay are shown on Table 4.
The presence of plasmid backbone in the genome of this strain was verified by PCR utilising primers annealing to the piggyBac elements: PB5out (CTCTGGACGTCATCTTCACTTACGTG) (SEQ ID NO: 13) and PB3out (CTCGATATACAGACCGATAAAACACATGC) (SEQ ID NO: 14), which give a 4045 bp fragment if the plasmid backbone is present. Results are shown in
The possibility of silent insertions in this strain was investigated by PCR analysis. Wild-type males were crossed with OX3864A heterozygote females, and vice versa at a ratio of 1:3 (male:female). The next generation were reared to pupae and screened for fluorescence. 1000 non-fluorescent individuals were kept at −20 and analysed by PCR.
Results are shown in
Competitive mating tests of the strains against wt males for wt females were carried out according to FAO/IAEA/USDA guidelines (FAO/IAEA/USDA, 2003). To test the ability of males to induce refractoriness to re-mating in females, the mated females were separated into two groups of 40 based on their initial mating choice (wt or Oxitec male) then re-exposed them to equal numbers of wt and Oxitec males on the following day. This process was run for 3 days, with cages scored for matings for 9 hours daily. Mating pairs were removed during mating as described above and the males were again genotyped by screening fluorescence. For mating competitiveness tests with wild-derived flies, pupae were recovered from infested oranges gathered from insecticide-free orange orchards in Heraklion province, Crete. Wild-derived adults were separated by sex immediately after eclosion. Wild-derived flies were left at 25° C., 50% relative humidity (R.H.) for 10-13 days to reach sexual maturity. All flies were allowed to adjust to natural light and temperature conditions of the glasshouse for a minimum of 24 hours prior to the start of the experiment. Each experiment began one hour after sunrise and lasted for a minimum of 9 hours. Mating tests were performed in green-house facilities at the University of Crete. OX3864A mating competition tests were performed in 7 replicates with 89 pairs assessed.
The mean RSI value of the OX3864A flies, when mating with wild-derived medfly from Crete, was 0.45±0.13 (t-test: t12=−0.9, n=89, P=0.38), which gave no evidence of a significant difference in mating competitiveness between OX3864A and wild-derived males.
Caged Suppression of Stable Wild-Type PopulationsStable populations of wt medfly were established in four large field cages with two cages chosen at random to be “treatment” cages into which, in addition to the normal number of pupae added to the cages, approximately 1500 RIDL males per week were released. This protocol was based on that of Wise de Valdez et al. The greenhouse-based field cages were 8 m3 each and contained a 1.5 m tall lemon tree, and were housed at the University of Crete, Heraklion, utilising natural light and a stable temperature and humidity (c. 25° C., 50% R.H.,). Cages contained three food and water sources and two oviposition pots filled with deionised water (emptied daily), each with two 40 cm2 egg laying surfaces.
Wt populations were established over an 8 week period by introducing a fixed number of pupae to each cage per week (200 in week 1, 300 in week 2, 180 in week 3 and 230 thereafter weeks 4-8). Pupal additions for the first 4 weeks originated from a wt stock colony; thereafter all pupal additions were from eggs caught in the oviposition pots, and reared in the laboratory at low density (1 larva/0.5 g medium) before re-introduction to field cages as pupae. Egg numbers were counted daily from the oviposition pots, while adult numbers were calculated weekly.
At week 7, cages were randomly divided into treatment or control. From week 8 onwards, RIDL treatment cages received weekly additions of 1700 OX3864A pupae reared off-tet (resulting in the addition of approximately 1,500 adult males per week). This gave an initial ratio of .about.? OX3864A males to 1 wt male in week 8, based on estimates of cage populations (1500 males released into cages with an approximate population of 220 wt males) and a weekly recruitment ratio of roughly 15:1 (OX3864A to wt males). Once OX3864A introductions began, the pupal return to a treatment cage was made proportional to its rate of pupae production, with the control cages providing a stable weekly pupal return coefficient for this calculation. For example, in week 16 the mean number of pupae recovered from the control cages was 300. Because returns to the control cages were set at a constant 230 per week, the number of pupae to return to all cages, out of all of those which developed is set by a coefficient of (230/300=0.76). For example in the same week one of the treatment cages produced a total of 126 pupae. The number of pupae which were returned to this cage (using the coefficient), was therefore 96 (126 ×0.76). This methodology allowed for a dynamic pupal return that was dependent on egg production and pupal survival, and reflects the number of eggs laid and the action of RIDL on female larval survival. Results are shown in
Dramatic decreases in weekly egg production were observed by 7 weeks post-RIDL release (PR) in treatment cages, compared with a continued stable rate of egg production in control cages, and continued until eventual extinction of the wild-type population in both treatment cages (as assessed by two weeks of no egg production) by week 22 (
This assay was used to detect the presence or absence of the 0X3864 transgene in a variety of OX3864 insect samples (field, mass-rearing and laboratory). The same protocol can also be used to provide evidence of stability of the OX3864 transgene over time. Successful amplification of the OX3864 transgene over time provides evidence of its stability, as one primer anneals to the transgene, the other to the flanking genomic sequence, so mobilisation of the transgene results in a negative PCR.
a. Materials
-
- Purelink genomic extraction kit (supplied by Invitrogen)
- BioTaq DNA Polymerase (PCR Biosystems)
- Primers—described in section C (synthesized by Life Technologies)
- 10×Bovine serum albumin (BSA, New England Biolabs)
- Smart Ladder 200 bp-10 kb (Eurogentec)
- Milli-Q de-ionised pure water
- Agarose (Web Scientific)
- Tris-acetate-EDTA solution (10×TAE)
- Ethidium Bromide
- 6×gel loading solution (comprising 30% glycerol, 0.25% bromophenol blue)
b. Equipment
-
- Biometra Thermocyclers (T3000)
- Gilson pipettes,
- Pipette tips,
- 96-well micro-titre plates or 0.2 ml PCR tubes, adhesive plate lids or 8 well strip lids,
- 2 ml microfuge tubes,
- Gel electrophoresis tank, Power pack, cast and combs.
- Ultra-violet (UV) visualisation system.
c. Methods
i. Extraction of Genomic DNA
Genomic DNA was isolated from individual insects using the protocol below (also found in TD/SOP/00142) using the Invitrogen Purelink genomic extraction kit.
-
- 1. Add 96-100% ethanol to PureLink™ Genomic Wash Buffer 1 and PureLink™ Genomic Wash Buffer 2 according to Instructions on each label. Mix well. Mark on the labels that ethanol is added. Store both wash buffers with ethanol at room temperature.
- 2. Set a water bath or heat block at 55° C.
- 3. Add 180 μl PureLink™ Genomic Digestion Buffer and 20 μl Proteinase K to each pool of abdomens. Break the insect samples up with a sterile pestle. After use, put the pestles in a beaker of Virkon for at least 24 hours before washing and autoclaving. Ensure the tissue is completely immersed in the buffer mix.
- 4. Incubate at 55° C. with occasional vortexing until lysis is complete (1-4 hours). You may perform overnight digestion.
- 5. To remove any particulate materials, centrifuge the lysate at maximum speed for 3 minutes at room temperature. Transfer supernatant to a new mi1rocentrifuge tube.
- 6. Add 20 μl RNase A to lysate, mix well by briefly vortexing, and incubate at room temperature for 2 minutes.
- 7. Add 200 μl PureLink™ Genomic Lysis/Binding Buffer and mix well by vortexing to yield a homogenous solution.
- 8. Add 200 μl 96-100% ethanol to the lysate. Mix well by vortexing to yield a homogenous solution. The Lysis/binding buffer and 100% Ethanol can be mixed before adding.
- 9. Remove a PureLink™ Spin Column in a Collection Tube from the kit. Add the lysate (.about.640 μl) prepared with PureLink™ Genomic Lysis/Binding Buffer and ethanol to the spin column.
- 10. Centrifuge the column at 10,000×g for 1 minute at room temperature. Discard the collection tube and place the spin column into a clean PureLink™ Collection Tube supplied with the kit.
- 11. Add 500 μl Wash Buffer 1 prepared with ethanol to the column. Centrifuge column at 10,000×g for 1 minute at room temperature. Discard the collection tube and place the spin column into a clean PureLink™ collection tube supplied with the kit.
- 12. Add 500 μl Wash Buffer 2 prepared with ethanol to the column. Centrifuge the column at maximum speed for 3 minutes at room temperature. Discard flow through and re-spin for a further minute at 10,000×g.
- 13. Place the spin column in a sterile 1.5-ml microcentrifuge tube. Add 100 μl of PureLink™ Genomic Elution Buffer to the column.
- 14. Incubate at room temperature for 1 minute. Centrifuge the column at maximum speed for 1 minute at room temperature.
- 15. Remove and discard the column. Use DNA for the desired downstream application or store the purified DNA at 4° C. (short-term) or −20° C. (long-term).
- 16. Record all details in lab book.
ii. PCR Protocol
Primers are from the Oxitec catalogue; numbers refer to Oxitec internal primer catalogue and are synthesised off site by Life Technologies
Transgene specific and Actin 4 endogenous gene sequences were amplified by PCR using PCR BIO polymerase as follows:
OX3864 Transgene Primers:
1087)FRTNheF (GGTGTGGCTAGCTCGAAGAAGTTCCTATTCCGAAGTTCC; SEQ ID NO: 7) and 1272)3864FRTFIF (CAACGAGTGACAGCAATGATATTCCTTAC; SEQ ID NO: 6) produces a product of 532 bp. FRTNheF anneals to the transgene, whereas 3864FRTFIF anneals to the genomic sequence flanking the transgene. This primer set will only amplify samples containing the OX3864 transgene.
Adh Control Primers:
A primer set was included to check amplification of Ceratitis capitata genomic DNA, as an internal control. The primers are 1131)CcAdh2RTF (GAAAGCTGTTCGGGCTTCAGGC; SEQ ID NO: 8) and 1132)CcAdh2RTR (CTTGGAGGTGATGTCGAATTTGGTG; SEQ ID NO: 9) producing a 491 bp product.
PCR master mix was prepared (enough for the number of samples plus 1-5 extras, to allow for pipetting error), by adding the following ingredients to a microfuge tube, in the order they appear below:
18 μl master mix was pipetted into each PCR tube or well of the 96 well plate.
2 μl gDNA template was added.
Templates include a known positive control of OX3864 homozygous gDNA sample (from the mass-rearing stock, or previously shown to be positive) a negative control of a wild type gDNA sample and milli-Q water negative control.
PCRs were run on a Biometra T3000 thermocycler using the following program:
1. 94° C. 2 min
2. 94° C. 15 s
3. 60° C. 30 s (reduce temperature by 0.5° C. each cycle)
4. 72° C. 15 s Go to step 2×10 cycles
5. 94° C. 15 s
6. 55° C. 30 s
7. 72° C. 15 s Go to step 5×25 cycles 8. 72° C. 7 mins 9. 4.° C. hold. 8 μl of the PCR product is mixed with 1.5 μl gel loading buffer (30% glycerol with 0.25% bromophenol blue) and run on a 1% agarose gel (see below) at 120V for 25 minutes for visualisation. The Eurogentec Smart Ladder is loaded at each end of the gel. Gels are visualised and photographed using a Uvitec gel visualisation system.
iii. Agarose Gel Preparation
1 g agarose mixed with 100 ml 1×TAE buffer, dissolved by microwaving for about 2 minutes, cooled under cold running water for 30 seconds, 1.5 Ill 1% Ethidium Bromide was added, then poured into a cast and allowed to set.
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Claims
1-32. (canceled)
33. A polynucleotide comprising a first and a second gene expression system, wherein:
- i) the first gene expression system comprises the following components: a first dominant lethal gene operably linked to a first promoter, a gene encoding a first activating transcription factor, and a first splice control sequence, and
- ii) the second gene expression system comprises the following components: a second dominant lethal gene operably linked to a second promoter, a gene encoding a second activating transcription factor, and a second splice control sequence,
- wherein:
- each of said activating transcription factors is capable of activating at least one of said promoters, provided that both of said promoters are activated when both of said transcription factors are expressed,
- each of the first and second splice control sequences mediates female-specific expression of the first and second dominant lethal genes, respectively, by alternative splicing,
- the transactivation activity of each of the first and second activating transcription factors is repressible by a first and a second exogenous control factor, respectively, wherein said first exogenous control factor is the same as or different from said second exogenous control factor, and
- each of said components of said first gene expression system are the same as or different from said components of said second gene expression system.
34. The polynucleotide according to claim 33, wherein the first activating transcription factor is the gene product of the first dominant lethal gene and/or the second activating transcription factor is the gene product of the second dominant lethal gene, such that said transcription factor also provides the lethal effect conferred by said dominant lethal gene.
35. The polynucleotide according to claim 33, wherein one or both of the first and second splice control sequences mediates female-specific expression of the respective dominant lethal gene by, together with a spliceosome, mediating splicing of a RNA transcript of the respective dominant lethal gene to produce a mRNA coding for a functional protein and at least one mRNA coding for a non-functional protein, wherein the mRNA coding for a functional protein is produced in a female.
36. The polynucleotide according to claim 33, wherein each of the first and second promoters is substantially inactive in the absence of the activating transcription factor capable of activating said promoter.
37. The polynucleotide according to claim 33, wherein one or both of the first and second lethal genes is, independently, tTA or a tTAV gene variant.
38. The polynucleotide according to claim 33, wherein one or both of the first and second splice control sequences is, independently, derived from a tra intron, dsx gene, or Actin-4 gene.
39. The polynucleotide according to claim 33, wherein one or both of the first and second gene expression systems further comprises an enhancer.
40. The polynucleotide according to claim 33, wherein one or both of the first and second promoters is expressed during at least embryonic development.
41. The polynucleotide according to claim 33, wherein one of the first and second gene expression systems comprises:
- (a) a third dominant lethal gene; and
- (b) a third promoter, wherein the third promoter is operably linked to the third dominant lethal gene, wherein the activating transcription factor capable of activating the promoter of said gene expression system is also capable of activating the third promoter.
42. The polynucleotide according to claim 41, wherein one of the first and second gene expression systems further comprises an enhancer associated with the promoter of said gene expression system, wherein the third promoter is also associated with said enhancer.
43. The polynucleotide according to claim 33, wherein the polynucleotide further comprises a fluorescent marker.
44. The polynucleotide according to claim 33, wherein:
- the first dominant lethal gene is tTAV (SEQ ID NO: 26), the first activating transcription factor is the tTAV gene product, the first promoter is Hsp70, the first splice control sequence is Cctra,
- the second dominant lethal gene is tTAV3 (SEQ ID NO: 28), the second activating transcription factor is the tTAV3 gene product, the second promoter is srya and the second splice control sequence is Bztra,
- the first gene expression system further comprises a first enhancer associated with the first promoter, wherein the first enhancer is tetOx7,
- the second gene expression system further comprises a second enhancer associated with the second promoter, wherein the second enhancer is tetOx14, the polynucleotide further comprises a third dominant lethal gene operably linked to a third promoter, the third promoter being associated with the second enhancer, wherein the third dominant lethal gene is VP16 and the third promoter is Hsp70, wherein the second promoter is associated with one end of the second enhancer and the third promoter is associated with the other end of the second enhancer,
- the polynucleotide further comprises a first genetic marker, which is DsRed2.
45. A genetic construct for transforming an insect, comprising the polynucleotide as described in claim 33.
46. The genetic construct according to claim 45, wherein the construct further comprises at least four transposon inverted repeats, forming at least two pairs of opposing transposon inverted repeats, wherein said polynucleotide is located between two pairs of opposing transposon inverted repeats such that excision by a transposase or transposases of said pairs, in situ, is effective to be able to leave said polynucleotide integrated in the host genome, without flanking transposon inverted repeats in the host genome.
47. The genetic construct according to claim 46, wherein each of the transposon inverted repeats bounding said polynucleotide is a minimal terminal inverted repeat.
48. The genetic construct according to claim 46, wherein four of the at least four transposon inverted repeats form a first and a second pair of opposing inverted repeats, wherein:
- the four transposon inverted repeats are piggyBac inverted repeats,
- the first pair consists of an internal 3′ piggyBac end proximal the polynucleotide and an external 5′ piggyBac end distal the polynucleotide, and
- the second pair consists of an internal 5′ piggyBac end proximal the polynucleotide and an external 3′ piggyBac end distal the polynucleotide.
49. The genetic construct according to claim 48, wherein:
- the internal 3′ piggyBac end has a nucleic acid sequence consisting of SEQ ID NO: 32;
- the external 5′ piggyBac end has a nucleic acid sequence consisting of SEQ ID NO:30;
- the internal 5′ piggyBac end has a nucleic acid sequence consisting of SEQ ID NO: 30; and
- the external 3′ piggyBac end has a nucleic acid sequence consisting of SEQ ID NO: 31.
51. The genetic construct according to claim 46, further comprising at least one genetic marker between the transposon inverted repeats of at least one pair of opposing transposon inverted repeats.
51. An insect comprising the polynucleotide as described in claim 33, wherein the insect is a Tephritidae, Drosophilidae, Lonchaeidae, Pallopteridae, Platystomatidae, Pyrgotidae, Richardiidae, or Ulidiidae.
52. The insect according to claim 51, wherein the insect is Ceratitis capitata.
53. A method of controlling an insect population comprising release of the insect as described in claim 51.
Type: Application
Filed: Jul 14, 2023
Publication Date: Jan 18, 2024
Applicant: Oxitec Limited (Abingdon)
Inventors: Martha Koukidou (Abingdon), Luke Alphey (Abingdon), Simon Warner (Abingdon)
Application Number: 18/353,012
