Mass 1 gene, a target for anticonvulsant drug development

Abstract

The present invention relates to a novel gene which is associated with audiogenic seizures in mice. The gene is known as the Monogenic Audiogenic Seizure-susceptible gene or mass1. The product of the mass1 gene is designated MASS1. Nucleic acid molecules that encode for MASS1 have been identified and purified. The sequence of murine mass1 can be found at SEQ ID NO: 1, and the sequence of human mass1 can be found at SEQ ID NO: 3. Mammalian genes encoding a MASS1 protein are also provided. The invention also provides recombinant vectors comprising nucleic acid molecules that code for a MASS1 protein. These vectors can be plasmids. In certain embodiments, the vectors are prokaryotic or eukaryotic expression vectors. The nucleic acid coding for MASS1 can be linked to a heterologous promoter. The invention also relates to transgenic animals in which one or both alleles of the endogenous mass1 gene is mutated.

Description

CROSS-REFERENCED RELATED APPLICATIONS

This application is a divisional of prior application Ser. No. 10/220,587, filed Sep. 3, 2002, which was the National Stage Application of International Application No. PCT/US01/06962, filed Mar. 2, 2001, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/187,209 and U.S. Provisional Patent Application No. 60/222,898. Each of these applications is incorporated herein in its entirety by this reference.

BACKGROUND OF THE INVENTION

Epilepsy is a common neurological disorder that affects nearly 2.5 million people in the United States. Epilepsy is characterized by recurrent seizures resulting from a sudden burst of electrical energy in the brain. The electrical discharge of brain cells causes a change in a person's consciousness, movement, and/or sensations. The intensity and frequency of the epileptic seizures varies from person to person.

Epilepsies in humans can be separated into two forms, symptomatic and non-symptomatic. Symptomatic epilepsy is a seizure disorder related to a known cause such as metabolic disease, brain malformations, or brain tumors. In these cases, seizures presumably occur because of a very abnormal focus (or foci) in the brain. Genetic models of symptomatic epilepsy include the weaver mouse (wv), in which a mutation of the G protein-gated inwardly rectifying potassium channel GIRK2 results in neuro-developmental abnormalities and seizures. Signorini, S. et al. (1997), Proc Natl Acad Sci U S A 94: 923-7. Fragile X-associated protein knock-out mice have a neurodevelopmental syndrome with lowered thresholds to audiogenic seizures. Musumeci, S. A. et al. (2000), Epilepsia 41: 19-23. Audiogenic seizures can also be induced in seizure-resistant mice such as C57BL/6 by repetitive sound stimulation, suggesting that seizure-susceptibility can be influenced by multiple genetic and environmental factors. Henry, K. R. (1967), Science 158: 938-40.

Non-symptomatic epilepsies are defined when no structural or metabolic lesions are recognized and the patients have no other neurological findings between seizures. This latter group of patients is more likely to have primary neuronal hyperexcitability that is not caused by metabolic, developmental or structural lesions. Molecular characterization of electrical hyperexcitability in human muscle diseases led to the hypothesis that such disorders might be the result of mutations in neuronal ion channels, the primary determinants of neuronal membrane excitability. Ptacek, L. J. et al. (1991), Cell 67: 1021-7.

All non-symptomatic human epilepsy syndromes and genetic mouse seizure models that have been characterized at a molecular level are caused by mutations in ion channels. Ptacek, L. J. (1999), Semin Neurol 19: 363-9; Jen, J. & L. J. Ptacek (2000), Channelopathies: Episodic Disorders of the Nervous System. Metabolic and Molecular Bases of Inherited Disease. C. R. Schriver, A. L. Beaudet, W. S. Sly and D. Valle. New York, McGraw-Hill. pp. 5223-5238; Noebels, J. L. (2000), The Inherited Epilepsies. Metabolic and Molecular Bases of Inherited Disease. C. R. Schriver, A. L. Beaudet, W. S. Sly and D. Valle. New York, McGraw-Hill. pp 5807-5832. Some patients with febrile seizures have been recognized to have mutations in sodium channel α and β1-subunits while some patients with epilepsy and episodic ataxia were shown to have calcium channel β-subunit mutations. Wallace, R. H. et al. (1998), Nat Genet 19: 366-70; Escayg, A. et al. (2000), Am J Hum Genet 66: 1531-9; Escayg, A. et al. (2000), Nat Genet 24: 343-5. The voltage-gated potassium channel genes KCNQ2 and KCNQ3, when mutated, result in benign familial neonatal convulsions. Biervert, C. et al. (1998), Science 279: 403-6; Charlier, C. et al. (1998), Nat Genet 18: 53-5; Singh, N. A. et al. (1998), Nat Genet 18: 25-9. Ligand-gated channels can also result in epilepsy as demonstrated by mutations in the α4 subunit of the neuronal nicotinic acetylcholine receptor that result in autosomal dominant nocturnal frontal lobe epilepsy. Steinlein, O. K. et al. (1995), Nat Genet 11: 201-3. In mice, the α, β and γ subunits of the voltage-sensitive calcium channel have been associated with the tottering (tg), lethargic (lh) and stargazer (stg) models of absence seizures. Fletcher, C. F. et al (1996), Cell 87: 607-17; Burgess, D. L. et al. (1997), Cell 88: 385-92; Letts, V. A. et al. (1998), Nat Genet 19: 340-7. Finally, audiogenic seizure-susceptibility has been characterized in a mouse knockout model of the 5-HT_2C receptor; homozygous mice have audiogenic seizures and altered feeding behavior. Tecott, L. H. et al. (1995), Nature 374: 542-6; Brennan, T. J. et al. (1997), Nat Genet 16: 387-90.

The Frings mouse represents one of many strains of mice and rats that are sensitive to audiogenic seizures (AGS). These AGS-susceptible rodents represent models of generalized reflex epilepsy and include the well-studied DBA/2 mouse and GEPR-9 rat. The Frings mouse seizure phenotype is similar to other described audiogenic seizures and is characterized by wild running, loss of righting reflex, tonic flexion and tonic extension in response to high intensity sound stimulation. Schreiber, R. A. et al. (1980), Genet 10: 537-43. This strain was characterized 50 years ago when it arose as a spontaneous mutation on the Swiss Albino background. Frings, H. et al. (1951), J Mammal 32: 60-76. Selective inbreeding for seizure-susceptibility produced the current homozygous Frings strain with >99% penetrance of audiogenic seizures. The Frings mouse seizure phenotype was due to the autosomal recessive transmission of a single gene.

Audiogenic seizures have been observed in polygenic rodent models, such as the DBA/2 mouse and GEPR-9 rat. Collins, R. L. (1970), Behav Genet 1: 99-109; Seyfried, T. N. et al. (1980), Genetics 94: 701-718; Seyfried, T. N. & G. H. Glaser (1981), Genetics 99: 117-126; Neumann, P. E. & T. N. Seyfried (1990), Behav Genet 20: 307-23; Neumann, P. E. & R. L. Collins (1991), Proc Natl Acad Sci U S A 88: 5408-12; Ribak, C. E. et al. (1988), Epilepsy Pes 2: 345-55. While no genes associated with audiogenic seizures in spontaneous mutant models have been cloned, three putative loci associated with seizure-susceptibility in the DBA/2 mouse (asp1, asp2, and asp3) have been mapped to chromosomes 12, 4, and 7, respectively. Neumann & Seyfried, supra; Neumann, P. E. & R. L. Collins, supra. As a monogenic audiogenic seizures model, the Frings mice provided a unique opportunity for cloning and characterization of an audiogenic seizures gene. The Frings mice are an important naturally occurring monogenic model of a discrete non-symptomatic epilepsy and provide significant information on a novel mechanism of seizure-susceptibility as well as central nervous system excitability in general.

In light of the foregoing, it will be appreciated that it would be an advancement in the art to identify and characterize nucleic acid sequences that are associated with the monogenic AGS susceptibility in Frings mice. It would be a further advancement to identify and characterize the human orthologue of this gene. It would be a further advancement if the nucleic acid sequences could provide additional understanding of how epileptic seizures are triggered in disease. It would be a further advancement to provide a transgenic animal model wherein the endogenous gene associated with the Frings phenotype is mutated.

Such nucleic acid sequences and animals are disclosed and claimed herein.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to an isolated novel gene which has been imputed in audiogenic seizure-susceptibility in mice known as the mass1 gene. Provided herein are nucleic acid molecules that encode the MASS1 protein. The nucleic acid molecules of the present invention may also comprise the nucleotide sequence for human mass1 (SEQ ID NO: 3) and murine mass1 (SEQ ID NO: 1). In certain other embodiments, the present invention provides nucleic acid molecules that code for the amino acid sequence of human MASS1 (SEQ ID NO: 4) and murine MASS1 (SEQ ID NO: 2). The invention also provides nucleic acid molecules complementary to the nucleic acid molecules of SEQ ID NO: 3 and SEQ ID NO: 1. The invention also relates to other mammalian mass1 genes and MASS1 proteins.

The present invention also relates to an isolated nucleic acid having at least 15 consecutive nucleotides as represented by a nucleotide sequence selected from the nucleotides of the murine mass1 gene (SEQ ID NO: 1) and the nucleotides of the human mass1 gene (SEQ ID NO: 3). A nucleotide having in the range from about 15 to about 30 consecutive nucleotides as represented by a nucleotide sequence selected from the nucleotides of the murine mass1 gene (SEQ ID NO: 1) and the nucleotides of the human mass1 gene (SEQ ID NO: 3) is also within the scope of the present invention.

The present invention also provides recombinant vectors comprising nucleic acid molecules that code for MASS1. These recombinant vectors may be plasmids. In other embodiments, these recombinant vectors are prokaryotic or eukaryotic expression vectors. The nucleic acid coding for MASS1 may also be operably linked to a heterologous promoter. The present invention further provides host cells comprising a nucleic acid that codes for MASS1.

The present invention also relates to a transgenic mammal with a mutation in one or both alleles of the endogenous mass1 gene. The mutation in one or both of the endogenous mass1 genes may result in a mammal with a seizure-susceptible phenotype. The transgenic mammal of the present invention may be a mouse. The mutation may result from the insertion of a selectable marker gene sequence or other heterologous sequence into the mammal's genome by homologous recombination. The invention also provides cells derived from the transgenic mammal.

These and other advantages of the present invention will become apparent upon reading the following detailed description and appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In order that the manner in which the above-recited and other features and advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

A more particular description of the invention briefly described above will be rendered by reference to the appended drawings and graphs. These drawings and graphs only provide information concerning typical embodiments of the invention and are not therefore to be considered limiting of its scope.

FIG. 1 shows a linkage map of the mass1 locus initially defined by markers D13Mit126 and D13Mit200. Markers D13Mit69, 97, and 312 (enclosed in rectangles) were used to genotype the F2 progeny. The estimated genetic distances are shown. The location of candidate genes Nhe3, Dat1, and Adcy2 are indicated. The map inset represents the large-scale physical map of the mass1 interval spanned by yeast artificial chromosomes (YACs). SLC10 and SLC11 are novel SSLP markers, and the others are STS markers.

FIG. 2 is a fine-scale physical map of the mass1 interval defined by bacterial artificial chromosomes (BACs) and cosmids. SLC-numbers between 10 and 100 are novel SSLP markers, and SLC-numbers 100 to 200 are novel STS markers. The bars above the map represent the genotypes of the nearest recombinant mice. The gray bars represent regions where the mice are recombinant, black filled bars are regions where the mice are nonrecombinant, and white filled bars are regions where the markers were not informative. The final mass1 interval was spanned by cosmids C13A and C1B, and the complete genomic sequence was generated between the markers SLC20 and SLC14. The alignment of the mass1 exons that were identified from the sequence are shown at the bottom.

FIG. 3 is a diagram of the mass1 genomic structure showing three putative transcripts and exons that are included in each transcript. The short transcript, mass1.3, has putative 5′ untranslated sequence leading into exon 22. Exon 7a and 7b represent two alternate exons that have been identified in mouse brain cDNA. The medium transcript, mass1.2, has putative 5′ untranslated sequence leading into exon 7b, and the longest transcript, mass1.1, has only been shown to contain exon 7a. A long and short splice variant was identified in exon 27 (27L and 27S). The 27S variant removes 83 base pairs and changes the reading frame.

FIG. 4A illustrates expression analysis of the mass1 gene by RT-PCR in different tissue and cell RNA samples using primers from exons 23 and 24. Analysis of mass1 in multiple tissue RNA samples of a CF1 mouse shows expression is primarily in the brain, kidney, and lung, and not in the other tissues listed.

FIG. 4B illustrates further expression analysis of the mass1 gene by RT-PCR using brain RNA. Mass1 expression was detected in all regions of the brain tested.

FIG. 4C illustrates expression analysis by RT-PCR of the mass1 gene with pooled cultured cortical neuron RNA and cultured astrocyte RNA compared to whole brain. The mass1 specific primers span intron 23 and the expected product size was 487 base pairs. The β-actin primers also spanned two exons and the expected product size is 327 base pairs. The ladder is in 100 base pair increments.

FIG. 5A is a sequence chromatogram of the exon 27 segment from C57BL/6J and Frings DNA. The sequence chromatogram illustrates the identification of a single base pair deletion found in exon 27 of mass1 sequence of Frings mice. The Frings mouse DNA contains a single G deletion at nucleotide 7009.

FIG. 5B illustrates high resolution gel electrophoresis of PCR products from a 150 base pair segment of exon 27 encompassing 7009ΔG, showing that none of the seizure-resistant and seizure-susceptible control mouse DNA samples harbor the deletion present in the Frings mouse.

FIG. 6 illustrates the conceptual amino acid translation of the mass1.1 transcript (SEQ ID NO: 5). The 18 MASS1 repetitive motifs are boxed with a solid line and the 2 less conserved possible repeats are boxed with a dashed line. The putative multicopper oxidase I domain is underlined. The valine → stop mutation in the Frings MASS1 protein is located at amino acid number 1072 marked with the “*”.

FIG. 7 illustrates the amino acid sequence alignment of the MASS1 repeats. (SEQ ID NOS: 6-23). The first 18 lines represent the well conserved amino acid repeat motif found in MASS1. Positions of highly conserved amino acids are shaded gray. The next line shows the consensus sequence for the MASS1 repeat (SEQ ID NO: 24), and below it are the sequences of the Na⁺/Ca²⁺ exchanger (β1 and β2) segments that share homology with the MASS1 repeat (SEQ ID NOS: 25 & 26). Also shown is a homologous region of the very large G-protein coupled receptor-1 (Accession 55586) (SEQ ID NO: 27). The boxed segment outline the DDD motif that has been shown to be a Ca²⁺ binding site in the Na⁺/Ca²⁺ exchanger β1 segment.

DETAILED DESCRIPTION OF THE INVENTION

The presently preferred embodiments of the present invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the present invention, as represented in FIGS. 1 through 7, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention.

The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

The present invention relates to DNA for a novel Monogenic Audiogenic Seizure-susceptible gene (mass1). More particularly, the present invention relates to the isolation and characterization of the mouse mass1 gene (SEQ ID NO: 1) and the human mass1 gene (SEQ ID NO: 3). The discovery that the murine mass1 gene is mutated in Frings mice suggests that mass1 has a role in seizure susceptibility.

Nucleotide sequences complementary to the nucleotide sequences of SEQ ID NO: 1 and SEQ ID NO: 3 are also provided. Isolated and purified nucleotide sequences that code for the amino acid sequence of the mouse MASS1 (SEQ ID NO: 2) protein are also within the scope of the invention. Nucleotide sequences that code for the amino acid sequence of the human MASS1 (SEQ ID NO: 4) protein are within the scope of the invention. A nucleic acid sequence that codes for MASS1 of any mammal is also within the scope of the invention.

The nucleic acid molecules that code for mammalian MASS1 proteins, such as a human or murine MASS1, can be contained within recombinant vectors such as plasmids, recombinant phages or viruses, transposons, cosmids, or artificial chromosomes. Such vectors can also include elements that control the replication and expression of the mass1 nucleic acid sequences. The vectors can also have sequences that allow for the screening or selection of cells containing the vector. Such screening or selection sequences can include antibiotic resistance genes. The recombinant vectors can be prokaryotic expression vectors or eukaryotic expression vectors. The nucleic acid coding for MASS1 can be linked to a heterologous promoter.

Host cells comprising a nucleic acid that codes for mammalian MASS1 are also provided. The host cells can be prepared by transfecting an appropriate nucleic acid into a cell using transfection techniques that are known in the art. These techniques include calcium phosphate co-precipitation, microinjection, electroporation, liposome-mediated gene transfer, and high velocity microprojectiles.

The Frings mouse is unique among rodent epilepsy models. It is a naturally-occurring single gene model of audiogenic generalized seizures without any other associated neurological or behavioral phenotypes. Sequencing of cosmids from the nonrecombinant mass1 interval identified a single gene. Until recently, computer-based BLAST nucleotide sequence similarity searches did not identify significant similarity between the mass1 sequence and any other sequences in the databases. The deficiency of mass1 cDNA sequence in the databases further supports the hypothesis that mass1 is expressed in low abundance in the brain or that it is degraded very rapidly. This hypothesis is based on the fact that screening two independent brain cDNA libraries for the mass1 cDNA did not produce any positive clones, and low message levels were further supported by Northern blots, RT-PCR, and in situ hybridization. The low abundance could be due to low expression of the mass1 mRNA, or to the message being unstable and quickly degraded.

The mass1 gene was identified by positional cloning and sequencing, exon prediction, RT-PCR and PCR-based 5′ and 3′ RACE. Screening several cDNA libraries by hybridization had not identified a mass1 cDNA clone. Despite not finding a cDNA clone in the cDNA libraries, convincing data implicates mass1 as the gene causing AGS in the Frings mice. Mass1 is the only gene found in the small non-recombinant mass1 interval. The cDNA from both mouse and human Marathon cDNA libraries (Clontech, Palo Alto, Calif.) can be amplified. The intron-exon boundaries are conserved for the genomic structure of hMass1. The alternate transcript of mouse mass1 exon 27 is also found in hMass1. The mass1 transcripts contain long open reading frames which are disrupted by a single base-pair deletion in the Frings mouse.

PCR approaches have been required to clone all or parts of other genes such as the melatonin receptor. Reppert, S. M. et al. (1994), Neuron 13: 1177-85. In such cases, results must be viewed with caution because of artifacts inherent with PCR-based assays. Problems include producing inaccurate sequence due to Taq DNA polymerase errors and errors due to amplifying parts of homologous genes. To avoid these problems, the mass1 final sequence was compiled from segments amplified with a high fidelity Pfx DNA polymerase (Gibco) to produce accurate sequence from multiple templates. The mass1 cDNA sequence matched exactly with predicted exons from genomic sequencing of cosmids C1B, C13A, and C20B (FIG. 2).

The homology of the MASS1 protein sequence repetitive motifs to the sodium+-calcium²⁺ exchanger (Na⁺/Ca²⁺ exchanger) β1 and β2 repeat domains may provide an important clue toward identifying the function of this novel protein. Although the identity between these proteins is limited to a short segment of the cytosolic loop of the exchanger, it is likely to be functionally significant in MASS1 because this motif is repeated 18 times within the protein sequence (FIGS. 6 and 7). The Na⁺/Ca²⁺ exchanger is a plasma membrane associated protein that co-transports three sodium ions into a cell and one calcium ion out of the cell using the sodium electrochemical gradient. Nicoll et al., supra. The Na⁺/Ca²⁺ exchanger can be regulated by intracellular calcium at a Ca²⁺ binding site on the third cytosolic loop that is distinct from the Ca²⁺ transport site. This binding site is composed of three aspartate residues (DDD) (FIG. 7). When Ca²⁺ is bound at this site, the transporter is activated. Matsuoka, S. et al. (1993), Proc Natl Acad Sci U S A 90: 3870-4; Levitsky, D. O. et al. (1994), J Biol Chem 269: 22847-52; Matsuoka, S. et al. (1995), J Gen Physiol 105: 403-20. One of the MASS1 repeats contains the DDD motif, and three others have conservative D to E substitutions suggesting that these domains may be involved in Ca²⁺ binding.

The multicopper oxidase I consensus sequence identified within the MASS1 amino acid sequence is also an interesting putative finctional domain. The multicopper oxidases represent a family of proteins that oxidize substrates while reducing molecular O₂ to H₂O. The oxidation of multiple substrate molecules occurs serially while storing electrons in the copper atom (presumably to prevent the formation of reactive species) until a molecule of O₂ is reduced. Two known multicopper oxidases, Fet₃p in yeast and ceruloplasmin in humans, have been shown to oxidize and transport iron. Askwith, C. et al. (1994), Cell 76: 403-10; Harris, Z. L. et al. (1995), Proc Natl Acad Sci U S A 92: 2539-43. A third multicopper oxidase, hephaestin has been suggested to be a feroxidase. Vulpe, C. D. et al. (1999), Nat Genet 21: 195-9. Other known multicopper oxidase substrates include Mn²⁺, serotonin, epinephrine, dopamine, and (+)-lysergic acid diethylamide (LSD). Zaitsev, V. N. et al. (1999), J Biol Inorg Chem 4: 579-87; Brouwers, G. J. et al. (1999), Appl Environ Microbiol 65: 1762-8. Therefore, loss of this putative functional domain could possibly result in problems with the metabolism of iron or other metals, copper sequestration, neurotransmitter processing, and/or oxidative stress. Furthermore, the tyrosine kinase and cAMP/cGMP dependent phosphorylation sites may be functionally significant. However, with a large protein such as MASS1, similarities and identities to functional domains commonly occur by chance, and detailed biochemical analysis of the protein will be required to determine which of these motifs are functional domains.

The human orthologue of the mass1 gene resides on chromosome 5q. Interestingly, a gene causing a human epilepsy has also been mapped to this region of chromosome 5. This locus, FEB4, was mapped in families with a phenotype of febrile convulsions. Nakayama, J. et al. (2000), Hum Mol Genet 9: 87-91. While this temperature-sensitive phenotype is different than audiogenic seizures, hMass1 will be an important candidate to test in the FEB4-linked families.

To date, all genes that have been shown to cause non-symptomatic epilepsies have encoded ion channels (voltage- or ligand-gated and exchangers). Jen & Ptacek, supra; Noebels, supra. The mass1 gene therefore represents the first novel gene shown to cause a non-symptomatic epilepsy. The seizures in the Frings mice are different from those recognized to be caused by ion channels. The phenotype is a reflex epilepsy with seizures in response to loud auditory stimuli. This suggests that the genesis of episodes may be in brainstem rather than being due to hyperexcitability of cortical neurons. There is a growing appreciation of the role that deep brain structures and brainstem play in the integration and modulation of cortical discharges. For example, normal synchronized discharges are seen in EEGs of sleeping individuals. Perhaps some of the reflex epilepsies in humans are not the result of primary cortical hyperexcitability, but rather, of abnormal function of circuits critical for integration and modulation of cortical activity. Much work will be required to test this hypothesis, but some fascinating episodic CNS disorders have clinical and electrical manifestation that may be consistent with this idea. Fouad, G. T. et al. (1996), Am. J Hum. Genet. 59: 135-139; Ptacek, L. J. (1998), Genetics of Focal Epilepsies. P. Genton. London, John Libbey. pp 203-13; Plaster, N. M. et al. (1999), Neurology 53: 1180-3; Swoboda, K. J. et al. (2000), Neurology 55: 224-30.

Identification and characterization of the mass1 gene reveals it to be novel and rare transcript. Further research to determine the function of MASS1 will lead to understanding of how a defect in this protein results in seizures in these audiogenic seizure-susceptible mice. From the mouse mass1 cDNA, a partial human mass1 homolog has been identified. Through mapping and characterization of the human homolog, it may be possible to find an association of mass1 with a human epilepsy disorder. Together, the studies of the mouse and human MASS1 will provide insight into the function of this novel protein and is likely to lead to new insights into normal neuronal excitability and dysfunction of membrane excitability that can lead to seizures and epilepsy.

The present invention also provides transgenic mice in which one or both alleles of the endogenous mass1 gene are mutated. Such animals are useful for example to further study the physiological effects of this gene or to test potential drug candidates.

Methods for making such transgenic animals are known in the art. See, e.g., Hogan et al., Manipulating the Mouse Embryo: A Laboratory Manual (2d ed. 1994); Hasty et al. (1991), Nature 350:243-246; Mansour et al. (1988), Nature 336:348-352. Briefly, a vector containing the desired mutation is introduced into mouse embryonic stem (ES) cells. In some of these stem cells, the desired mutation may be introduced into the cell=s genome by homologous recombination. Stem cells carrying the desired mutation may be identified using selection and/or screening procedures. Such cells are then injected into a blastocyst, which may develop into a chimeric mouse with some of the mouse=s cells carrying the desired mutation. A chimeric animal carrying germ cells with the desired mutation may be bred to produce mutant offspring.

Vectors containing a desired mutation may be produced using methods known in the art. See, e.g., 1-3 Sambrook et al., Molecular Cloning: A Laboratory Manual (2d ed. 1989). Such vectors would typically include a portion of the mouse mass1 gene to facilitate homologous recombination between the vector and endogenous gene sequences. A selectable marker may be used to disrupt the coding sequence or an expression control element of the mass1 gene. Suitable selectable markers are known in the art. For example, the Neomycin resistance gene (neo), which encodes Aminoglycoside phosphotranferase (APH), allows selection in mammalian cells by conferring resistance to G418 (available from Sigma, St. Louis, Mo.). Other suitable markers may also be used to disrupt the mass1 gene. Techniques have also been developed to introduce more subtle mutations into genes. See, e.g., Hasty et al., supra.

Vectors may also include sequences to facilitate selection or screening of ES cells in which the desired mutation has been introduced by homologous recombination. For example, a vector may include one or more copies of a gene such as the herpes simplex virus thymidine kinase gene (HSV-tk) upstream and/or downstream of the mass1 gene sequences. As illustrated in Mansour et al., supra, random integration events would lead to incorporation of the HSV-tk gene into the ES cell genome, while homologous recombination events do not. ES cells carrying randomly integrated vectors (and, therefore, HSV-tk), may be selected against by growing the cells in a medium supplemented with gancyclovir.

A vector containing the desired mutation may be introduced into ES cells in any of a number of ways. For example, electroporation may be used. See Mansour et al., supra. Other techniques for introducing vectors into cells are known in the art, including viral infection, calcium phosphate co-precipitation, direct micro-injection into cultured cells, liposome mediated gene transfer, lipid-mediated transfection, and nucleic acid delivery using high-velocity microprojectiles. Graham et al. (1973), Virol. 52:456-467; M. R. Capecchi (1980), Cell 22:479-488; Mannino et al. (1988), BioTechniques 6:682-690; Felgner et al. (1987), Proc. Natl. Acad. Sci. USA 84:7413-7417; Klein et al. (1987), Nature 327:70-73.

Techniques for preparing, manipulating, and culturing ES cells have been described. See, e.g., Hogan et al., supra; Mansour et al., supra. ES cells carrying the desired mutation may be identified by screening or selection methods that are known in the art, including growth in selective media and screening using PCR-based or DNA hybridization (Southern blotting) techniques.

In order to better describe the details of the present invention, the following discussion is divided into six sections: (1) fine mapping and physical mapping of mass1; (2) candidate gene identification; (3) cloning and analysis of mass1 cDNA; (4) mapping of the hMass1 gene; (5) identification of a mass1 mutation in DNA from Frings mice; and (6) analysis of the mass1 translated protein sequence.

6.1 Fine Mapping & Physical Mapping

Referring to FIG. 1, the mass1 interval between D13Mit200 to D13Mit126 was estimated to be 3.6 cM with the initial set of 257 N2 mice tested. Skradski, S. L. et al. (1998), Genomics 49: 188-92. Approximately 1200 additional (Frings X C57BL/6J) F1 intercross mice were genotyped with microsatellite markers D13Mit312, D13Mit97, and D13Mit69 that span the interval. Analysis of the recombinations determined that the mass1 region was distal to the D13Mit97 marker and proximal of D13Mit69. Two additional microsatellite markers, D13Mit9 and D13Mit190, were identified within this interval from the Chromosome 13 Committee map. Genotyping of the border-defining recombinant mice with these markers narrowed the interval to between D13Mit9 and D13Mit190. Of the 1200 F2 mice, three were recombinant at D13Mit9 and ten mice were recombinant at D13Mit190. No other known simple sequence length polymorphisms (SSLPs) markers were mapped within this interval.

This distance between the markers D13Mit9 and D13Mit190 was covered by three overlapping YACs 151C12, 87F11, and 187D1 found on the contig WC13.27. These YACs contained four known sequence tagged sites (STSs), SLC106, SLC117, SLC111 and SLC105 shown in FIG. 2. The four STSs were used to identify BACs from the BAC library. A new single nucleotide polymorphisms was screened by sequencing small-insert pUC19 subclone libraries of the BACs. Two newly identified polymorphic markers, SLC10 and SLC11, were identified and further narrowed the distal border and defined the mass1 interval to the distance spanned by a single YAC, 151C12, between markers SLC11 and D13Mit9 as shown in FIG. 1.

Since no known SSLPs or STSs were contained within the mass1 interval, a physical map of the region was constructed by using end sequences of BAC clones to develop new STSs to re-screen the library for overlapping BACs. Simultaneous with the physical mapping, identification of SSLPs from the new BACs continued to narrow the interval. Seven overlapping BACs were required to cover the distance between SLC11 and D13Mit9. SSLPs from each end of the insert of BAC 290J21, SLC14 and SLC15, were recombinant and localized the mass1 gene to this small region as shown in FIG. 2. Based on the insert size of the BAC, this narrowed the mass1 region to less than 150 Kb.

This BAC insert was subcloned into both a cosmid vector and pUC19. Sequences from randomly selected pUC19 clones were used to develop new STSs across the BAC, and these new markers were then used to align cosmids into a complete contiguous map of BAC 290J21 as shown in FIG. 2. SSLP screening of the pUC19 library detected five new repeat markers within BAC 290J21 (SLC16-20). Two of these, SLC19 and SLC20, were mapped within the mass1 interval. Analysis of recombinants at these markers showed a recombination with SLC20 that refined the interval to two overlapping cosmids, C1B and C13A, between the markers SLC14 and SLC20 each with a single recombinant mouse (5a9 and 2d11).

6.2 Candidate Gene Identification

Intragenic STS markers were developed for known candidate genes (Dat1, Adcy2, and Nhe3) that mapped to the general region containing mass1. PCR analysis of the STSs showed that none of the YACs, BACs or cosmids comprising the physical map contained these genes. To directly identify candidate genes from the two cosmids, C1B and C13A, mouse brain cDNA libraries were screened by hybridization using cosmid DNA as probe. The library screening experiments were unsuccessful at identifying any candidate cDNAs from the region, therefore, an alternate strategy of shot-gun subcloning and sequencing of cosmids C1B and C20B was employed.

The cosmid sequences were edited and compiled to produce the complete genomic sequence from marker SLC14 to SLC20. The complete nonrecombinant mass1 interval was approximately 36 Kb. Analysis of the sequence by the exon-finding program, Genefinder, predicted one multiple-exon gene spanning the mass1 interval oriented from the distal to proximal end. Reverse transcription-PCR (RT-PCR) with primers spanning putative introns amplified products of the appropriate sizes from Frings and C57BL/6J total brain RNA. Sequence analysis of these bands confirmed that they matched the genomic sequence within the exons and identified the first intron-exon boundaries.

6.3 Cloning and Analysis of mass1 cDNA

RT-PCR experiments produced 1 Kb of open reading frame that could be amplified from mouse brain RNA. Subsequently, rapid amplification of cDNA ends (RACE) defined the 3′ end of the gene which contained 330 base pairs of untranslated sequence from the first stop codon to the polyA tail. Multiple 5′ RACE reactions produced the complete cDNA sequence of mass1 and identified three putative alternate transcripts each containing a unique 5′ untranslated sequence. When the cDNA sequence was aligned with 36 Kb of complete genomic sequence from cosmid C1B, 15 exons were noted to correspond the 3′ end of the cDNA sequence; primers were designed from the remaining 5′ cDNA sequence and used to sequence cosmid C20B. Analysis of this genomic sequence revealed 20 exons as shown in FIG. 2. Thus the longest transcript is composed of 35 exons.

The mass1 gene encodes three putative alternate transcripts. The longest transcript is approximately 9.4 Kb, the second 7.1 Kb, and the shortest 3.7 Kb. Northern blot analyses of mouse RNA failed to produce conclusive data to confirm these transcript sizes and suggested that the transcript levels were very low. However, several autoradiograms with very long exposure times (3-4 weeks) suggested that the 9.4 and 7.1 Kb transcripts are expressed in mouse brain (data not shown). In situ hybridizations using a 3 Kb product from the 3′ end of the cDNA to probe mouse brain did not reveal any signal above background further suggesting the mRNA levels to be very low.

Each putative transcript contains a unique 5′ untranslated region leading into the rest of the gene sequence. All three transcripts contain a possible splice variant in exon 27 where 83 base pairs of sequence are either included (27L) or removed (27S) from the transcript as illustrated in FIG. 3.

Referring to FIG. 4A, analysis of the expression of mass1 in mouse tissues by RT-PCR of brain, heart, kidney, liver, lung, muscle, intestine, and spleen RNA shows that the gene is predominantly found in the brain, lung, and kidney. Further analysis of the adult mouse brain showed ubiquitous mass1 expression throughout the mouse brain region including hippocampus, brain stem, cerebellum, midbrain and cortex as shown in FIG. 4B. Reverse transcription and PCR revealed mass1 transcripts to be present in RNA isolated from cultured astrocytes and in RNA aspirated and isolated from single mouse cultured cortical neurons as shown in FIG. 4C.

6.4 Mapping of the hMass1 Gene

A human genomic clone containing the human homolog of the mass1 gene was identified by screening a BAC library by PCR with primers from the mouse mass1 gene under lower stringency. This clone was used in fluorescent in situ hybridization experiments and mapped to human chromosome 5q14.

6.5 Identification of a mass1 Mutation in DNA from Frings Mice

Seventeen single nucleotide polymorphisms (SNPs) were identified between Frings and C57BL/6J mice within the nonrecombinant coding region, exons 21 to 35. One of these SNPs was a single base pair deletion detected in the Frings mouse mass1 gene by sequence analysis of PCR products. FIG. 5A shows the sequence chromatogram of this single G deletion at position 7009 in the Frings mouse DNA sample compared to the seizure-resistant control C57BL/6J. This deletion results in a frame shift of the open reading frame changing the valine to a stop codon; this change is expected to produce a truncated MASS1 protein in Frings mice. Further analysis of the deletion in other mouse strains by gel electrophoresis showed that the deletion is only detected in Frings mouse DNA and not in any of the other seizure-resistant or seizure-susceptible mouse strains tested as shown in FIG. 5b. The deletion is located in exon 27 before the long and short splice variants. Of the other SNPs identified, six altered the amino acid sequence of the protein and could, theoretically, be the genetic basis of Frings audiogenic seizure-susceptibility. Otherwise, these changes represent polymorphisms that may produce subtle alterations in the function of the protein.

6.6 Analysis of the mass1 Translated Protein Sequence

The mass1 gene produces three putative transcripts: mass1.1 (9.4 Kb), mass1.2 (7.1 Kb), and mass1.3 (3.7 Kb). The long transcript contains 9327 nucleotides and is expected to produce an approximately 337 kilodalton (kD) protein. The medium transcript contains 6714 nucleotides and the predicted protein size is 244 kD. The short transcript open reading frame is 2865 nucleotides and the predicted protein size is approximately 103 kD. These transcripts and isoforms are based on incorporation of the longer splice form of exon 27 (27L). Further putative variants are possible as a result of the 27S alternate splicing event. Using the 27S exon theoretically shortens all the transcripts by 83 nucleotides and each of the isoforms by 645 amino acids (approximately 69.4 kD). The conceptual translation of the amino acid sequence for the mass1.1 (27L) transcript is shown in FIG. 6. The MASS1 protein is strongly acidic and has a −192 charge at pH 7.0. The hydropathy plot indicated numerous hydrophobic domains that are candidates for transmembrane segments.

Database searches using the mass1.1 sequence identified no expressed sequence tags (ESTs) that were identical and no homologous genes. However, a small repetitive motif from MASS1 shared homology with numerous Na⁺/Ca²⁺ exchangers. This homology was to the β1 and β2 repeats in the third cytosolic loop of the exchanger that contains the Ca²⁺ regulatory binding domain. Nicoll, D. A. et al. (1996), Ann N Y Acad Sci 779: 86-92. Further analysis of MASS1 determined that this motif occurs 18 times within the sequence. Alignment of these sequences shows several highly conserved amino acids within this motif (FIG. 7) including a Proline-Glutamate-X-X-Glutamate (PEXXE) amino acid sequence (SEQ ID NO: 28) that is preceded by one to three acidic residues (D or E). The proline and first glutamate are completely conserved in all 18 related motifs, and the second glutamate is conserved in 16 of the motifs. In repeats 10 and 11, a lysine is substituted for the second glutamate. The PEXXE motif occurs twice more within the MASS1 sequence, however, these repeats (repeats 19 and 20) have a lower degree of identity and similarity (FIG. 6).

Three aspartic acid residues (DDD) are found in the Na⁺/Ca²⁺ exchanger β1 segment and in the segment of the very large G-protein coupled receptor-1 directly preceding the PEXXE motif. In the MASS1 repeat, however, this DDD motif is not well conserved with only repeat number 3 containing the exact DDD motif, and repeats 1, 9, and 18 containing conservative substitutions of glutamate residues. The 18 repeats are distributed across the MASS1 protein and repeats 14 to 18 would be missing from the truncated MASS1 protein (FIG. 6).

Analysis of the MASS1 sequence by Pattern Match identified a multicopper oxidase I consensus sequence site in the carboxyl-terminal region of MASS1. The multicopper oxidase I site is located in exon 29 (FIG. 6), within the region of the MASS1 protein that would be truncated by the Frings 7009ΔG mutation. Frings mice would therefore be lacking this potentially important domain. Biochemical analysis of this putative domain will determine if this is a functional multicopper oxidase I domain. Other less common motifs found within MASS1 include three tyrosine kinase phosphorylation motifs, two cAMP/cGMP-dependent phosphorylation motifs, and one glycosaminoglycan attachment motif. Finally, numerous common putative protein modification sites were identified including casein kinase II phosphorylation, protein kinase C phosphorylation, N-myristylation, and N-glycosylation sites. Further analysis of the MASS1 protein will be required to determine if any of these consensus sites are functional.

All patents, publications, and commercial materials cited herein are hereby incorporated by reference.

EXAMPLES

The following examples are given to illustrate various embodiments which have been made with the present invention. It is to be understood that the following examples are not comprehensive or exhaustive of the many types of embodiments which can be prepared in accordance with the present invention.

Example 1

Mouse Breeding, Seizure Testing and DNA Collection

Frings mice were crossed to the seizure-resistant strain C57BL/6J to produce F1 animals which, in turn, were intercrossed to generate 1200 F2 offspring. The Frings mice used in this study were bred in our colony and the C57BL/6J mice were supplied by the Jackson Laboratory (Bar Harbor, Me.). All mice were phenotyped at postnatal day 21 as seizure-susceptible or seizure-resistant as described previously. Skradski, S. L. et al., supra. Directly following seizure phenotyping, tail sections were cut for DNA preparation. Potential recombinant mice within the region were tested again to confirm the seizure phenotype, a second tail section was cut, and the mice were euthanized by CO₂ and bilateral thoracotomy. Spleens were harvested for DNA preparation by phenol/chloroform extraction and ethanol precipitation.

Example 2

Fine Mapping

All known MIT microsatellite markers between cD13Mit200 and D13Mit126 were identified from the Chromosome 13 Committee map located at [http://www.informaticsjax.org/ccr/searches/contents.cgi?&year=1999&chr=13]. All F2 mice were initially tested with polymorphic markers D13Mit312, D13Mit97, and D13Mit69 to identify recombinant mice in the mass1 region, and the new recombinant mice were genotyped with additional markers, D13Mit9 and D13Mit190. Primer sequences and information for the markers was obtained from the Whitehead Institute Database site Genetic and Physical Maps of the Mouse Genome [http://www.genome.wi.mit.edu/cgi-bin/mouse/index]. Primer synthesis and SSLP analysis was performed as previously described. Skradski, S. L. et al., supra.

Example 3

Yeast Artificial Chromosomes

YAC maps spanning the region were obtained from the Physical Maps of the Mouse Genome [http://www.genome.wi.mit.edu/cgi-bin/mouse/index]. YACs which appeared to contain SSLP markers known to be within the region were obtained from Research Genetics and YAC DNA was prepared by standard techniques. Haldi, M. L. et al. (1996), Mamm Genome 7: 767-9; Silverman, G. A. (1996), Methods in Molecular Biology, Vol. 54. D. Markie. Totowa, N.J., eds. Humana Press Inc. pp 65-68. All STSs shown to be associated with each YAC clone from the map were synthesized and tested to confirm that the clones were correct and aligned with overlapping YAC clones. Standard PCR conditions for physical mapping analyses were 10 mM Tris-HCl, 50 mM NaCl, 1.5 mM MgCl, 30 μM dNTPs, 0.5 μM of forward and reverse primers, and 50 ng of DNA in a 25 μL reaction volume. PCR thermocycles were 94° C. for 2 minutes, followed by 35-40 cycles of 94° C. for 10 seconds, 54° C. for 30 seconds, and 72° C. for 30 seconds with a 5 minute final extension at 72° C.

Example 4

Bacterial Artificial Chromosomes

BACs were identified and isolated from the PCR-based mouse BAC library available from Research Genetics using all known STSs and SSLPs found in the region on linkage and YAC maps. BAC DNA was prepared using purification columns by the recommended procedure (Magnum columns, Genome Systems, Inc). BAC end sequence was obtained using T7 and SP6 primers. Individual BAC insert sizes were determined by complete digestion of the BAC DNA with NotI and separating the fragments on a 1.0% agarose gel in 0.5× TBE circulating buffer. The field inversion gel electrophoresis (FIGE) program was 180 volts forward, 120 volts reverse, 0.1 seconds initial switching time linearly ramped to 3.5 seconds switching time for 16 hours.

Example 5

Simple Sequence Length Polymorphism (SSLP) Identification

BAC DNA was partially digested with Sau3A1 into fragments ranging from 1 to 3 Kb and subcloned into the Baml site of pUC18 with the Ready-To-Go cloning kit (Amersham Pharmacia Biotech). New repeats were identified by plating the subclone library, lifting duplicate Hybond-N membranes (Amersham Pharmacia Biotech), and hybridizing with (CA)₂₀ and (AT)₂₀ oligonucleotides end-labeled with γ32P-ATP. Hybridized membranes were exposed to autoradiographic film. Clones producing a positive signal were sequenced and primer pairs were designed to amplify new repeat sequences. New SSLP markers were tested with control and recombinant mice to finely map the interval.

Example 6

Cosmid Subcloning

BAC 290J21 was partially digested with Sau3A1 into 30-40 Kb fragments which were subcloned into cosmids as per the instructions for the SuperCos 1 cosmid vector kit (Stratagene) and packaged with Gigapack III Gold Packaging Extract (Stratagene) using XL1-Blue mrf competent cells. Cosmids were then aligned by amplification with all STSs across the region. Cosmid sequencing was performed by standard techniques using 1200 ng of cosmid DNA and 3.2 pmole of gene-specific mass1 oligos ranging from 18 to 24 nucleotides in length.

Example 7

Identifying and Cloning the mass1 Gene

The mass1 cDNA was identified by reverse transcription-PCR (RT-PCR) using primers developed from sequence of exons predicted by Genfinder [http://dot.imgen.bcm.tmc.edu:9331/gene-finder/gf.html]. Total RNA was prepared from whole mouse brain of C57BL/6J, Frings and F1 mice with Trizol reagent as per instructions (Molecular Research Center, Inc.). The standard reverse transcription reaction conditions were 1.0 μg RNA, 15 ng random hexamers, 1× First Strand Buffer, 10 mM DTT, 1 mM dNTPs, 40 U RNAse Inhibitor, and 200 U Superscript II reverse transcriptase (Gibco BRL). First strand cDNAs were amplified using pfx DNA polymerase (Gibco BRL) and multiple reactions were sequenced for each. Since the entire gene was not contained within the genomic sequence that was generated, 5′- and 3′-RACE was used to identify the remaining cDNA sequences.

Example 8

Reverse Transcription-PCR

The RT reactions to determine tissue specificity of mass1 expression were performed as described in the previous section on samples from CF1 (Charles Rivers, Wilmington, Mass.), C57BL/6J (The Jackson Laboratory, Bar Harbor, Me.), or Frings mouse tissues and cells. The tissue panel samples were isolated from a single C57BL/6J mouse. The neuronal cDNA was produced from the pooled cellular extracts of 4-6 CF1 mouse cultured cortical neurons, and the astrocyte cDNA from CF1 astrocyte culture RNA extracted with Trizol reagent (Molecular Research Center, Inc). PCR conditions to amplify the cDNAs were 10 mM Tris-HCl, 50 mM KCl, 1.5 mM MgCl, 30 μM dNTPs, 0.5 μM of forward and reverse primers, and 1 μL of the cDNA in a 25 μL reaction volume. PCR thermocycles were 94° C. for 2 minutes, followed by 25 (β-actin primers) or 40 (mass1 primers) cycles of 94° C. for 10 seconds, 54° C. for 30 seconds, and 72° C. for 30 seconds with a 5 minute final extension at 72° C. The mass1 primers spanned from exon 22 to exon 23, the forward was 5° CAG AGG ATG GAT ACA GTA C 3′ (SEQ ID NO: 29) and the reverse was 5′ GTA ATC TCC TCC TTG AGT TG 3′ (SEQ ID NO: 30) and the expected product size was 487 base pairs. The β-actin primers also spanned an intron and were forward 5′ GCA GTG TGT TGG CAT AGA G 3′ (SEQ ID NO: 31) and reverse 5′ AGA TCC TGA CCG AGC GTG 3′ (SEQ ID NO: 32) and the expected product size was 327 base pairs. PCR products for each tissue were mixed and separated by gel electrophoresis on 2% agarose gels in 1× TAE buffer at 120V, and the bands visualized by staining with ethidium bromide using an ultraviolet (UV) light source.

Example 9

Polymorphism and Mutation Identification

For SSCP, the mouse DNA samples A/J, AKR/J, BALB/cJ, C57BL/6J, C3H/HeJ, CAST/EiJ, LP/J, NON/LtJ, NOD/LtJ, SPRET/EiJ, and DBA2/J were supplied by the Jackson Laboratory (Bar Harbor, Me.). The CF1 mice were supplied by Charles Rivers (Wilmington, Mass.), and the seizure-susceptible EL, EP, and SAS mice were supplied by Dr. T. Seyfried (Boston College, Boston, Mass.). PCR reactions were identical to those conditions listed above except 0.3 μL of α³²P-dCTP was included in a 10 μL total reaction volume. A 30 μL aliquot of dilution buffer (0.1% SDS/10 mM EDTA in ddH2O) was added to the PCR reactions. A 10 μL aliquot of the dilute PCR reaction was mixed with 10 μL of loading dye (bromophenol blue/xylene cyanol) and 2 μL samples were separated by non-denaturing electrophoresis on an 9% bis-acrylamide, 10% glycerol, nondenaturing gel at 20 W for 14 hours at room temperature with a fan. The PCR forward primer sequence was 5′ TTT ATT GTA GAG GAA CCT GAG 3′ (SEQ ID NO: 33) and the reverse primer sequence was 5′ GCC AGT AGC AAA CTG TCC 3′ (SEQ ID NO: 34) and the expected product size was 126 base pairs. Exon 27 PCR products were sequenced to determine that the aberrant band was due to a single G deletion in the Frings mouse mass1 gene as shown for C57BL/6 and Frings mouse DNA.

Example 10

MASS1 Amino Acid Sequence Analysis

The amino acid sequence of MASS1 was deduced from the nucleotide sequence of the cloned mass1 cDNA by DNA Star. The amino acid sequence was compared to known proteins by BLAST sequence similarity searching [http://www.ncbi.nlm.nih.gov/blast/blast.cgi]. Identification of finctional domains utilized PSORT II Prediction [http://psort.nibb.ac jp/form2.html], Sequence Motif Search [http://www.motif.genome.adjp/], Global and Domain Similarity Search [http://www-nbrf.georgetown.edu/pirwww/search/dmsim.html], and Pattern Match [http://www-nbrf.georgetown.edu/pirwww/search/patmatch.html].

Example 11

Identification and Mapping of a BAC Containing the hMass1 Gene

Human mass1 was detected by a relaxed RT-PCR. Several primer sets corresponding to different exons of mouse mass1 were used to amplify human fetal brain cDNA. PCR conditions were the same as in mouse amplifications with an exception of the annealing temperature of 47° C. These primers were used to identify a human genomic clone containing a part of the hMass1 gene (CITB human BAC library).

Human lymphoblast cultures were treated with 0.025 mg/ml cholcimid at 37° C. for 1.5 hr. Colcimid treated cultures were pelleted at 500×g at room temperature for 8 min. Pellets were then re-suspended with 0.075M KCl, 3 ml per pellet 15 minutes at room temperature. Cells were then fixed in 3:1 MeOH:acetic acid and stored at 4° C. Human BACs were labeled with spectrum orange using a nick translation kit per the manufacturers protocol (Vysis, Downers Grove, Ill.). Slides were prepared by dropping fixed cells onto glass slides and washing with excess fixative. The slides were then washed in acetic acid for 35 min at room temperature and dehydrated in 70%, 85%, and finally 100% EtOH (2 min each). Chromosomes were denatured in 70% formamide in 2×SSC at 74° C. for 5 minutes and slides were dehydrated again as above except in ice cold EtOH. Two μg of labeled probe was blocked with 2 μg of human Cot-1 DNA in Hybrisol VI (ONCOR, Gaithersburg, Md.). The probe mixture was denatured at 74° C. for 5 minutes and then pre-annealed at 37° C. for 15 min. Twelve μL of pre-annealed probe was applied per slide, a cover slip was added and edges were sealed with rubber cement. Slides were hybridized in a darkened, humidified chamber for 16 hr at 37° C. Hybridized slides were then washed in 0.4×SSC containing 0.1% Tween-20 at 74° C. for 2 min, followed by 1 min at room temperature in 2×SSC. Slides were allowed to dry in the dark at room temperature and were stained with DAPI (Vector labs, Burlingame, Calif.) for chromosome visualization.

SUMMARY

In summary, a novel gene which is associated with the Frings phenotype in mice has been isolated and characterized. The gene is known as the Monogenic Audiogenic Seizure-susceptible gene or mass1. The product of the mass1 gene is designated MASS1. Nucleic acid molecules that encode for MASS1 have been identified and purified. The sequence of murine mass1 can be found at SEQ ID NO: 1, and the sequence of human mass1 can be found at SEQ ID NO: 3. Mammalian genes encoding a MASS1 protein are also provided. The invention also provides recombinant vectors comprising nucleic acid molecules that code for a MASS1 protein. These vectors can be plasmids. In certain embodiments, the vectors are prokaryotic or eukaryotic expression vectors. The nucleic acid coding for MASS1 can be linked to a heterologous promoter. The invention also relates to transgenic animals in which one or both alleles of the endogenous mass1 gene is mutated.

The invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. A transgenic mammal wherein one or both alleles of the endogenous mass 1 gene is mutated.

2. The transgenic mammal of claim 1, wherein the mammal is a mouse.

3. The transgenic mammal of claim 2, wherein the mutation results in a seizures susceptible phenotype.

4. The transgenic mammal of claim 1, wherein the mutation results from the insertion of a selectable marker gene sequence or other heterologous sequence into the genome by homologous recombination.

5. A cell derived from the mammal of claim 1.

6. A cell derived from the mammal of claim 2.

7. A cell derived from a transgenic mammal wherein one or both alleles of the endogenous mass 1 gene is mutated, the mutation resulting from insertion of a selectable marker gene sequence or other heterologous sequence into the genome by homologous recombination, wherein the mutation results in a seizure-susceptible phenotype.

8. A transgenic mouse whose somatic and germ cells comprise a mutated mass 1 gene, said mutated gene being introduced into the mouse or an ancestor of the mouse at an embryonic stage, the mutation being sufficient to result in a seizure-susceptible phenotype.

9. A cell derived from the mouse of claim 8.

10. A transgenic mouse whose genome is heterozygous for an engineered mutation in the mass 1 gene, wherein the engineered mutation in a homozygous state results in a seizure-susceptible phenotype.

11. A cell derived from the mouse of claim 10.