Localization of the muscle, liver, and brain glycogen phosphorylase genes on linkage maps of mouse chromosomes 19, 12, and 2, respectively

Mammalian glycogen phosphorylases comprise a family of three isozymes, muscle, liver, and brain, which are expressed selectively and to varying extents in a wide variety of cell types. To better understand the regulation of phosphorylase gene expression, we isolated partial cDNAs for all three isozymes from the rat and used these to map the corresponding genes in the mouse. Chromosome mapping was accomplished by comparing the segregation of phosphorylase restriction fragment length polymorphisms (RFLPs) with 16 reference loci in a multipoint interspecies backcross between Mus musculus domesticus and Mus spretus. The genes encoding muscle, liver, and brain phosphorylases (Pygm, Pygl, and Pygb) are assigned to mouse chromosomes 19, 12, and 2, respectively. Their location on separate chromosomes indicates that distinct cis-acting elements govern the differential expression of phosphorylase isozymes in various tissues. Our findings significantly extend the genetic maps of mouse chromosomes 2, 12, and 19 and can be used to define the location of phosphorylase genes in man more precisely. Finally, this analysis suggests that the previously mapped "muscle-deficient" mutation in mouse, mdf, is closely linked to the muscle phosphorylase gene. However, muscle phosphorylase gene structure and expression appear to be unaltered in mdf/mdf mice, indicating that this mutation is not an animal model for the human genetic disorder McArdle's disease.     

Coding Sequence, Genomic Organization, and Conserved Chromosomal Localization of the Mouse Gene Scn11a Encoding the Sodium Channel NaN

Previous studies have shown that sodium channel alpha-subunit NaN is preferentially expressed in small-diameter sensory neurons of dorsal root ganglia and trigeminal ganglia. These neurons include high-threshold nociceptors that are involved in transduction of pain associated with tissue and nerve injury. In this study, we show that mouse NaN is a 1765-amino-acid peptide that is predicted to produce a current that is resistant to tetrodotoxin (TTX-R). Mouse and rat NaN are 80 and 89% identical at the nucleotide and amino acid levels, respectively. The Scn11a gene encoding this cDNA is organized into 24 exons. Unlike some alpha-subunits, Scn11a does not have an alternative exon 5 in domain I. Introns of the U2 and U12 spliceosome types are present at conserved positions relative to other members of this family. Scn11a is located on mouse chromosome 9, close to the two other TTX-R sodium channel genes, Scn5a and Scn10a. The human gene, SCN11A, was mapped to the conserved linkage group on chromosome 3p21-p24, close to human SCN5A and SCN10A. The colocalization of the three sodium channel genes supports a common lineage of the TTX-R sodium channels.     

Mapping of mouse carbonic anhydrase-3, Car-3: another locus in the homologous region of mouse chromosome 3 and human chromosome 8

At least six separate genes determining tissue- and organelle-specific isoforms of carbonic anhydrase are known. We have determined the chromosome location of one of these genes, carbonic anhydrase-3 (Car-3), in the mouse and carried out a linkage analysis of Car-1, Car-2, and Car-3. Car-3 has been assigned to band 3A2 by in situ hybridization. We identified a PstI restriction fragment length polymorphism between Mus spretus and Mus mus domesticus and, by using an interspecific backcross, showed that Car-3 is 2.4 +/- 1.7% SE from both Car-1 and Car-2, calculating genetic distance as percentage recombination. No recombinants were found between Car-1 and Car-2 in 100 backcross offspring, and when these data are combined with earlier results, these two loci are estimated to be 1.2 cM from each other at the 95% confidence interval. The three homologous carbonic anhydrase loci in man had earlier been assigned to 8q22, and the finding of linkage of Car-3 to Car-1 and Car-2 in the mouse adds another locus to the conserved segments on mouse chromosome 3 and human chromosome 8.     

The myosin alkali light chains of mouse ventricular and slow skeletal muscle are indistinguishable and are encoded by the same gene

We have isolated a cDNA recombinant plasmid (pA29) identified as encoding part of the ventricular muscle myosin light chain MLC1v. This cDNA contains a 300-base pair fragment which under conditions of moderate stringency shows specific hybridization to MLC1v mRNA with no detectable cross-hybridization with the mRNAs encoding the fast skeletal muscle isoforms MLC1F and MLC3F, or the atrial muscle isoform MLC1A. Under these conditions hybridization is seen with an abundant mRNA present in slow skeletal muscle (soleus) which is indistinguishable from ventricular MLC1V mRNA on the basis of size and of thermal stability of hybrids formed with plasmid pA29. The mouse MLC1V and MLC1S proteins are found to co-migrate on two-dimensional gels. We therefore conclude that these isoforms are the same and are encoded by the same mRNA. Analysis of mouse DNA has identified a single region of the genome which hybridizes to this same fragment of pA29. This region has been isolated in a recombinant phage and has been shown to contain a single gene showing homology with MLC1V mRNA by R-loop analysis. We therefore conclude that MLC1V and MLC1S are encoded by a single gene. The pattern of segregation of a restriction fragment length polymorphism identified for this gene between Mus musculus and Mus spretus has been followed in an F1 backcross between these two mouse species. The results show the MLC1V/MLC1S gene to be closely linked to a marker at the distal end of mouse chromosome 9.     

Genetic mapping of the lurcher locus on mouse chromosome 6 using an intersubspecific backcross.

The lurcher (Lc) mutant mouse strain exhibits postnatal degeneration of cerebellar Purkinje cells. We have typed progeny from an intersubspecific, phenotypic backcross at seven loci to develop a genetic linkage map which spans approximately 35 cM surrounding and including the Lc locus on mouse chromosome 6. [(Mus musculus castaneus x B6CBA-Aw-J/A-Lc)F1 x B6CBA-Aw-J/A]N2 progeny were scored visually for the lurcher phenotype and molecularly, through restriction fragment length polymorphism analysis, for six cloned markers. Two candidate genes, Npy and Pcp-1, which map to mouse chromosome 6 and which are expressed in the cerebellum, are demonstrated to be distinct from Lc. Three genes are shown to be closely linked to the Lc locus, and the map order cen-Cpa-Npy-Cbl-1-Lc-Igk, Fabpl-Pcp-1 is determined. The molecular genetic linkage map presented here represents progress toward isolating a clone of the Lc gene.     

Cardiac and skeletal muscle troponin I isoforms are encoded by a dispersed gene family on mouse Chromosomes 1 and 7

We mapped the locations of the genes encoding the slow skeletal muscle, fast skeletal muscle, and cardiac isoforms of troponin I (Tnni) in the mouse genome by interspecific hybrid backcross analysis of species-specific (C57BL/6 vs Mus spretus) restriction fragment length polymorphisms (RFLPs). The slow skeletal muscle troponin I locus (Tnni1) mapped to Chromosome (Chr) 1. The fast skeletal muscle troponin I locus (Tnni2), mapped to Chr 7, approximately 70 cM from the centromere. The cardiac troponin I locus (Tnni3) also mapped to Chr 7, approximately 5–10 cM from the centromere and unlinked to the fast skeletal muscle troponin I locus. Thus, the troponin I gene family is dispersed in the mouse genome. Received: 10 May 1995 / Accepted: 1 September 1995     

Genetic modifiers affecting severity of epilepsy caused by mutation of sodium channelScn2a

Mutations in the voltage-gated sodium channels SCN1A and SCN2A are responsible for several types of human epilepsy. Variable expressivity among family members is a common feature of these inherited epilepsies, suggesting that genetic modifiers may influence the clinical manifestation of epilepsy. The transgenic mouse model Scn2a^Q54 has an epilepsy phenotype as a result of a mutation in Scn2a that slows channel inactivation. The mice display progressive epilepsy that begins with short-duration partial seizures that appear to originate in the hippocampus. The partial seizures become more frequent and of longer duration with age and often induce secondary generalized seizures. Clinical severity of the Scn2a^Q54 phenotype is influenced by genetic background. Congenic C57BL/6J.Q54 mice exhibit decreased incidence of spontaneous seizures, delayed seizure onset, and longer survival in comparison with [C57BL/6J × SJL/J]F₁.Q54 mice. This observation indicates that strain SJL/J carries dominant modifier alleles at one or more loci that determine the severity of the epilepsy phenotype. Genome-wide interval mapping in an N₂ backcross revealed two modifier loci on Chromosomes 11 and 19 that influence the clinical severity of of this sodium channel-induced epilepsy. Modifier genes affecting clinical severity in the Scn2a^Q54 mouse model may contribute to the variable expressivity seen in epilepsy patients with sodium channel mutations.     

Close linkage of the murine locus bare patches to the X-linked visual pigment gene: implications for mapping human X-linked dominant chondrodysplasia punctata

The murine X-linked dominant mutation bare patches (Bpa) has a phenotype similar to and is likely homologous to human X-linked dominant chondrodysplasia punctata (CDPX2). Classic two-point linkage analysis in the mouse with distant markers suggested that Bpa maps near glucose-6-phosphate dehydrogenase (G6pd). We have confirmed the regional localization using interspecific matings with Mus spretus. We have also detected a restriction fragment length polymorphism (RFLP) at the murine X-linked visual pigment (Rsvp) locus in inbred Bpa females using the restriction enzyme PstI. Cumulative data from segregation of alleles using the PstI RFLP and analysis of interspecific backcross progeny at the Rsvp locus suggest that Bpa is tightly linked to Rsvp. Thus, the human CDPX2 gene probably maps within Xq27-Xq28 and not within Xp22.3-Xpter, where deletions associated with X-linked recessive chondrodysplasia punctata (CDPX) have been noted. This strategy should be applicable to the fine mapping of other dominant murine mutations.     

Mapping of alpha-spectrin on distal mouse chromosome 1

DNAs from different strains of inbred mice and feral Mus spretus were found to exhibit restriction fragment length polymorphisms (RFLP) when hybridized with a probe prepared from a c-DNA clone of the mouse alpha-spectrin (Spna-1) gene. Studies of five recombinant inbred strains and (C57BL/6 X M. spretus) F1 X C57BL/6 backcross mice demonstrated that these RFLPs were allelic and that Spna-1 is closely linked to Ly-9 and Ly-17 on the distal region of chromosome 1.     

Mapping of the glycine receptor alpha 2-subunit gene and the GABAA alpha 3-subunit gene on the mouse X chromosome.

We have mapped the gene for the alpha 2-subunit of the inhibitory glycine receptor (Glra2) to the telomeric end of the mouse X chromosome by backcross analysis of a Mus musculus/Mus spretus interspecific cross. In addition, we have extended the mapping of the GABAA alpha 3-subunit receptor gene (Gabra3). A deduced gene order of cen-Cybb-Hprt-DXPas6-Gabra3-Rsvp-Gdx/Cf-8- Dmd-Pgk-1-DXPas2-Plp-DXPas1-Glra2-tel places Gabra3 proximal to the visual pigment gene Rsvp and Glra2 in the region of loci for hypophosphatemia (Hyp), steroid sulfatase (Sts), and the E1 alpha-subunit of pyruvate dehydrogenase (Pdha1). This establishes the XF region of the mouse X chromosome as homologous with the Xp22.1-p22.3 region of the human X chromosome and indicates the presence of an evolutionary breakpoint in the region of Xp21.3.     

Genes encoding the H,K-ATPase α and Na,K-ATPase α3 subunits are linked on mouse Chromosome 7 and human Chromosome 19

We have used linkage analysis and fluorescence in situ hybridization to determine the chromosomal organization and location of the mouse (Atp4a) and human (ATP4A) genes encoding the H,K-ATPase subunit. Linkage analysis in recombinant inbred (BXD) strains of mice localized Atp4a to mouse Chromosome (Chr) 7. Segregation of restriction fragment length polymorphisms in backcross progeny of Mus musculusxMus spretus mating confirmed this assignment and indicates that Atp4a and Atp1a3 (gene encoding the murine Na,K-ATPase 3 subunit) are linked and separated by a distance of 2 cM. Analysis of the segregation of simple sequence repeats suggested the gene order centromere-D7Mit21-D7Mit57/Atpla3-D7Mit72/Atp4a. A human Chr 19-enriched cosmid library was screened with both H,K-ATPase and Na,K-ATPase 3 subunit cDNA probes to isolate the corresponding human genes (ATP4A and ATP1A3, respectively). Fluorescence in situ hybridization with gene-specific cosmid clones localized ATP4A to the q13.1 region, and proximal to ATP1A3, which maps to the q13.2 region, of Chr 19. These results indicate that ATP4A and ATP1A3 are linked in both the mouse and human genomes.     

Chromosomal mapping of glutamate dehydrogenase gene sequences to mouse chromosomes 7 and 14

Glutamate dehydrogenase (GLUD) plays an important role in mammalian neuronal transmission. In human, GLUD is encoded by a small gene family. To determine whether defects in Glud genes are associated with known neurological mutations in the mouse and to contribute to the comparative mapping of homologous genes in man and mouse, the chromosomal location of genes reactive with a mouse brain GLUD cDNA were determined. Genomic Southern analysis of a well-characterized panel of Chinese hamster x mouse somatic cell hybrids identified two GLUD-reactive loci, one residing on mouse Chromosome 14 and the other on Chromosome 7. Progeny of an intersubspecies backcross were used to map one of these genes, Glud, proximal to Np-1 on Chromosome 14, but no restriction fragment polymorphisms could be identified for the second locus, Glud-2.     

A new Pax gene,Pax-9, maps to mouse Chromosome 12

Members of the Pax gene family have recently been shown to play important roles in mouse embryogenesis. Of eight so far characterized Pax genes, three have been associated with mouse developmental mutants. Here we report the cloning of a new Pax gene, Pax-9. Most of the DNA sequence encoding the highly conserved paired domain has been determined and compared with previously known paired domains. This comparison classifies Pax-9 as a member of the same subgroup as Pax-1/undulated. By analysis of the segregation of a Pax-9 restriction fragment length polymorphism and a large number of simple sequence length polymorphisms in an interspecific C57BL/6 x Mus musculus mollosinus backcross, Pax-9 was mapped close to the D12Nds1 locus on the proximal part of Chromosome (Chr) 12.     

The α-subunit of the skeletal muscle sodium channel is encoded proximal to Tk-1 on mouse Chromosome 11

Recent evidence suggests that the human neuromuscular disorders, hyperkalemic periodic paralysis and paramyotonia congenita, are both caused by genetic defects in the -subunit of the adult skeletal muscle sodium channel, which maps near the growth hormone cluster (GH) on Chromosome (Chr) 17q. In view of the extensive homology between this human chromosome and mouse Chr 11, we typed an interspecies backcross to determine whether the murine homolog (Scn4a) of this sodium channel gene mapped within the conserved chromosomal segment. The cytosolic thymidine kinase gene, Tk-1, was also positioned on the genetic map of Chr 11. Both Scn4a and Tk-1 showed clear linkage to mouse Chr 11 loci previously typed in this backcross, yielding the map order: Tr ^J-(Re, Hox-2, Krt-1)-Scn4a-Tk-1. No mouse mutant that could be considered a model of either hyperkalemic periodic paralysis or paramyotonia congenita has been mapped to the appropriate region of mouse Chr 11. These data incorporate an additional locus into the already considerable degree of homology observed for these human and mouse chromosomes. These data are also consistent with the view that the conserved segment region may extend to the telomere on mouse Chr 11 and on human 17q.     

The Gene Encoding Protein Kinase SEK1 Maps to Mouse Chromosome 11 and Human Chromosome 17

We report the mapping of the human and mouse genes encoding SEK1 (SAPK/ERK kinase-1), a newly identified protein kinase that is a potent physiological activator of the stress-activated protein kinases. The human SERK1 gene was assigned to human chromosome 17 using genomic DNAs from human–rodent somatic cell hybrid lines. A specific human PCR product was observed solely in the somatic cell line containing human chromosome 17. The mouseSerk1gene was mapped to chromosome 11, closely linked toD11Mit4,using genomic DNAs from a (C57BL/6J ×Mus spretus)F₁×M. spretusbackcross.     

Mouse ferritin H multigene family is polymorphic and contains a single multiallelic functional gene located on chromosome 19.

Multiple ferritin H subunit sequences are present in the genome of higher vertebrates, but it is not yet known with certainty if more than one is expressed. In this paper, we provide evidence that there is only one functional ferritin H gene in the mouse. We screened a mouse genomic library using a mouse ferritin H cDNA as a probe and characterized five clones. These genomic clones proved to contain three pseudogenes and two allelic forms of a unique functional gene. These two alleles differed by only two point mutations in the promoter and three in the first intron and by a 31-bp insertion in the first intron. They were equally expressed when transiently transfected in HeLa cells. These five genomic clones account for all the bands observed on a Southern blot of mouse genomic DNA hybridized with a ferritin H cDNA, and these bands present a restriction fragment length polymorphism between various representatives of the genus Mus. Using a DNA panel prepared from the backcross progeny (C57BL/6 X Mus spretus)F1 X C57BL/6, we localized the functional ferritin H gene (Fth) in region B of mouse chromosome 19 and established cen-Ly-1-Fth-Pax-2 as the most likely gene order, thus defining a conserved syntenic fragment with human chromosome 11q.     

Localization of two alkaline phosphatase genes to the proximal region of mouse chromosome 1

Using a human cDNA clone encoding the intestinal form of alkaline phosphatase, we have identified and mapped by RFLP analysis in a Mus spretus x C57BL/6J interspecies backcross two alkaline phosphatase genes which segregate independently on the proximal part of mouse Chromosome 1. The gene order and intergene distances were determined by standard backcross analysis as: centromere- Len-2 - 19.0 cM - Akp-3 - 20.0 cM - Akp-4 - 2.0 cM - Ren-1.