Apoptosis Susceptibility Genes on Mouse Chromosome 9 (Rapop2) and Chromosome 3 (Rapop3)

The strain distribution pattern of susceptibility to thymocyte apoptosis induced by ionizing radiation in 20 CcS/Dem recombinant congenic (RC) strains derived from the strains BALB/cHeA (susceptible) and STS/A (resistant) indicates that this trait is controlled by several genes. Recently, we mapped a novel apoptosis susceptibility gene Rapop1 (radiation-induced apoptosis 1) to chromosome 16 (N. Mori et al., 1995, Genomics 25: 604-614). In the present study, the analysis of F2 crosses between the resistant RC strain CcS-8 and the susceptible strain BALB/cHeA or the highly susceptible RC strain CcS-10 demonstrated two additional apoptosis susceptibility genes, Rapop2 and Rapop3, located in the proximal region of chromosome 9 and the telomeric region of chromosome 3, respectively. The possible candidate genes for these loci are discussed.     

Genetic and Physical Mapping of a Gene Encoding a Methyl CpG Binding Protein, Mecp2, to the Mouse X Chromosome

The methyl CpG binding proteins (MeCP1 and MeCP2) are a class of proteins that bind to templates containing symmetrically methylated CpGs. Using an interspecific backcross segregating a number of X-linked markers, we have localized the Mecp2 gene in mouse to the X chromosome close to the microsatellite marker DXMit1. Detailed physical mapping utilizing an available YAC contig encompassing the DXMit1 locus has localized the Mecp2 gene to a 40-kb region between the L1cam and the Rsvp loci, indicating the probable position of a homologue on the human X chromosome.     

Mapping of theKHSRPGene to a Region of Conserved Synteny on Human Chromosome 19p13.3 and Mouse Chromosome 17

The K homology-type splicing regulatory protein, KSRP, activates splicing through intronic splicing enhancer sequences. It is highly expressed in neural cells and is required for the neural-specific splicing of the c-src N1 exon. In this study, we mapped the gene (gene symbolsKHSRPandKhsrp) to human chromosome 19 by using radiation hybrid panels and to mouse chromosome 17 by studying an interspecific backcross panel. HumanKHSRPis a positional candidate gene for familial febrile convulsion and Cayman type cerebellar ataxia. Comparative analysis of the human and mouse genomes indicates that theKHSRPgene is located in regions of conserved synteny between the two species.     

Conserved Linkage within a 4-Cm Region of Mouse Chromosome 9 and Human Chromosome 11

A six-point cross was carried out to determine the gene order and distances among loci on mouse chromosome 9. Our results are consistent with the following arrangement: centromere – Lap-1 – (1.2 ± 0.8) – Es-17 – (3.0 ± 1.0) – Ups – (1.3 ± 0.7) – Alp-1 – (23.1 ± 3.4) – Mod-1 – (10.9 ± 2.6) – Acy-1 . This study provides the first estimate of the distances between Es-17, Ups and Alp-1. Exceptions to the preferred association of alleles of Es-17 and Ups have been found in three feral populations and one inbred strain. Evidence is presented for the homology of this chromosome region with the ESA4 – UPS – APO-AI region on the long arm of human chromosome 11.     

Molecular Cloning and in Situ Localization of the Human Contactin Gene (CNTN1) on Chromosome 12q11-q12

Chick contactin/F11 (also known as F3 in mouse) is a neuronal cell adhesion molecule of the immunoglobulin (Ig) gene family that is implicated in playing a role in the formation of axon connections in the developing nervous system. In human brain, contactin was first identified by amino terminal and peptide sequencing of the lentil-lectin-binding glycoprotein Gp135. We now report the isolation and characterization of cDNA clones encoding human contactin. Human contactin is composed of six C2 Ig-domains and four fibronectin type III (FNIII) repeats and is anchored to the membrane via a glycosyl phosphatidylinositol moiety, as shown by PI-PLC treatment of cells transfected with contactin cDNA and metabolic labeling with [3H]-ethanolamine. At the amino acid level, h-contactin is 78% identical to chick contactin/F11 and 94% to mouse F3. Independent cDNAs encoding two putative contactin isoforms were isolated and sequenced: h-contactin 1 cDNA encodes a protein with the amino-terminal sequence of purified Gp135, while the putative h-contactin 2 gene has a deletion of 33 nucleotides that predicts a protein with a shortened amino terminus. Northern analysis with a probe common for both isoforms detects one mRNA species of approximately 6.6 kb in adult human brain. Fluorescence in situ hybridization maps the gene for human contactin to human chromosome 12q11-q12. The h-contactin gene locus is thus in close proximity to homeobox 3, integrin subunit α5, several proto-oncogene genes, a chromosomal breakpoint associated with various tumors, and the gene locus for Stickler syndrome. The cloning of human contactin now permits the study of its role in disorders of the human nervous system.     

Cloning of cDNAs Encoding the Human BAG1 Protein and Localization of the HumanBAG1Gene to Chromosome 9p12

cDNAs encoding the human homolog of BAG1, a Bcl-2-binding protein with anti-apoptotic function, were cloned. DNA sequence analysis of humanBAG1cDNAs predicts a protein with an additional 55 amino acids at its NH2-terminus compared to the mouse protein. Immunoblot assays using monoclonal antibodies raised against bacterially produced h-BAG1 protein confirmed the larger size of the human protein (34 kDa) compared to mouse. PCR analysis of DNA from human × rodent somatic cell hybrids using human BAG1-specific primers localized the gene to human chromosome 9. Cosmid clones of h-BAG1 were obtained and used for fluorescencein situhybridization analysis of normal metaphase chromosomes, thus localizing h-BAG1 to 9p12, a region associated with hereditary disorders that may involve developmental dysregulation of programmed cell death.     

Assignment of the βB1 Crystallin Gene (CRYBB1) to Human Chromosome 22 and Mouse Chromosome 5

By using primers complementary to the rat βB1 crystallin gene sequence, we amplified exons 5 and 6 of the orthologous human gene (CRYBB1). The amplified human segments displayed greater than 88% sequence homology to the corresponding rat and bovine sequences.CRYBB1was assigned to the group 5 region in 22q11.2–q12.1 by hybridizing the exon 6 PCR product to somatic cell hybrids containing defined portions of human chromosome 22. The exon 5 and exon 6 PCR products ofCRYBB1were used to localize, by interspecific backcross mapping, the mouse gene (Crybb1) to the central portion of chromosome 5. Three other β crystallin genes (βB2(−1), βB3, and βA4) have previously been mapped to the same regions in human and mouse. We demonstrate that the βB1 and βA4 crystallin genes are very closely linked in the two species. These assignments complete the mapping and identification of the human and mouse homologues of the major β crystallins genes that are expressed in the bovine lens.