Identification and genetic mapping of the murine gene and 20 related sequences encoding chromosomal protein HMG-17

HMG-17 is an abundant, nonhistone chromosomal protein that binds preferentially to nucleosomal core particles of mammalian chromatin. The human gene for HMG-17 has been localized to Chromosome (Chr) 1p, but the murine gene has not been previously mapped. Here we identify the murine functional gene, Hmg17, from among more than 25 related sequences (probably processed pseudogenes) and show that it is located on mouse Chr 4, in a region known to have conserved linkage relationships with human Chr 1p. We also report the map locations of 20 additional Hmg17-related sequences on mouse Chrs 1, 2, 3, 5, 7, 8, 9, 13, 15, 16, 17, 18, and X. The multiple, dispersed members of the Hmg17 multigene family can be detected efficiently with a single cDNA probe and provide useful markers for genetic mapping studies in mice.     

Chromosomal protein HMG-14 is overexpressed in Down syndrome.

The physical phenotype of Down syndrome, one of the most prevalent genetic disorders, results from an extra copy of regions q22.1 to q22.3 of chromosome 21 in cells of affected individuals. The gene coding for chromosomal protein HMG-14 is among the limited number of genes, coding for known functions, which has been mapped to this region of chromosome 21. Here we report a gene dosage effect on the expression of HMG-14 in both cultured cells and brain tissue samples obtained from Down syndrome patients. The putative role of HMG-14 in the structure of active chromatin raises the possibility that elevated levels of this protein may be a contributing factor in the etiology of Down syndrome.     

A brain L-type calcium channel alpha 1 subunit gene (CCHL1A2) maps to mouse chromosome 14 and human chromosome 3.

A rat brain cDNA probe was used to localize a gene encoding the alpha 1 subunit of neuronal dihydropyridine-sensitive L-type calcium channels in the mouse and human genomes. Hybridization of the probe to Southern blots made with DNAs from a Chinese hamster x mouse somatic cell hybrid panel indicated that this gene maps to mouse chromosome 14 (Chr 14). Southern blot analysis of an intersubspecies cross demonstrated that the calcium channel alpha 1 subunit gene, termed Cchl1a2, can be positioned 7.5 cM proximal to Np-1. Similarly, segregation among human X rodent somatic cell hybrids indicated that CCHL1A2 maps to human chromosome 3. These assignments are consistent with a region of linkage homology between human chromosome 3p and a proximal region of mouse Chr 14.     

A multipoint genetic linkage map of mouse chromosome 18

We have mapped 13 loci on mouse Chromosome 18 by Southern blot analysis of restriction fragment length polymorphisms among progeny from an interspecific backcross: (C57BL/6J X Mus spretus) X M. spretus. Complete haplotype analysis of 136 of these progeny was used to establish gene order and estimate genetic distances between loci. The gene order (from centromere to telomere) and recombination distances (in centimorgans) were as follows: PGK-1rs5-4.3-Tpi-10-11.8-(Egr-1, Hmg17-rs9)-2.1-Fgfa-2.2-Grl-1-10.1-(Cdx-1, Csfmr, Pdgfrb, Pdea, Rps14)-2.1-Adrb-2-22.9-Mbp. Pgk-1rs5, Tpi-10, Hmg17-rs9, and Rps14 had not been previously mapped in the mouse; Egr-1 had only been syntenically assigned to mouse Chr 18. Nine of the loci, spanning 18 cM, have homologs on the distal long arm of human Chr5--a region rich in genes encoding growth factors and receptors. An additional previously unmapped gene, Drd-1, predicted to be on mouse Chr 18 based on its human chromosomal location, was mapped to the middle region of mouse Chr 13.     

Ts65Dn -- localization of the translocation breakpoint and trisomic gene content in a mouse model for Down syndrome

Fluorescent in situ hybridization (FISH) -- using mouse chromosome paints, probes for the mouse major centromeric satellite DNA, and probes for genes on chromosomes (Chr) 16 and 17 -- was employed to locate the breakpoint in a translocation used to produce a mouse model for Down syndrome. The Ts65Dn trisomy is derived from the reciprocal translocation T(16;17)65Dn. The Ts65Dn mouse carries a marker chromosome containing the distal segment of Chr 16, a region that shows linkage conservation with human Chr 21, and the proximal end of Chr 17. This chromosome confers trisomy for most of the genes in the Chr 16 segment and Ts65Dn mice show many of the phenotypic features characteristic of Down syndrome. We used FISH on metaphase chromosomes from translocation T65Dn/+ heterozygotes and Ts65Dn mice to show that the Chr 17 breakpoint is distal to the heterochromatin of Chr 17, that the Ts65Dn marker chromosome contains a small portion of Chr 17 euchromatin, that the Chr 16 breakpoint lies between the Ncam2 and Gabpa/App genes, and that the Ts65Dn chromosome contains >80% of the human Chr 21 homologs. The significance of this finding is discussed in terms of the utility of this mouse model.     

Sequence-ready physical map of the mouse Chromosome 16 region with conserved synteny to the human Velocardiofacial syndrome region on 22q11.2

Proximal mouse Chromosome (Chr) 16 shows conserved synteny with human Chrs 16, 8, 22, and 3. The mouse Chr 16/human Chr 22 conserved synteny region includes the DiGeorge/Velocardiofacial syndrome region of human Chr 22q11.2. A physical map of the entire mouse Chr 16/human Chr 22 region of conserved synteny has been constructed to provide a substrate for gene discovery, genomic sequencing, and animal model development. A YAC contig was constructed that extends ca. 5.4 Mb from a region of conserved synteny with human Chr 8 at Prkdc through the region conserved with human Chr 3 at DVL3. Sixty-one markers including 37 genes are mapped with average marker spacing of 90 kb. Physical distance was determined across the 2.6-Mb region from D16Mit74 to Hira with YAC fragmentation. The central region from D16Jhu28 to Igl-C1 was converted into BAC and PAC clones, further refining the physical map and providing sequence-ready template. The gene content and borders of three blocks of conserved linkage between human Chr 22q11.2 mouse Chr 16 are refined. Received: 4 November 1998 / Accepted: 21 December 1998     

Molecular characterization of the translocation breakpoints in the Down syndrome mouse model Ts65Dn

Ts65Dn is a mouse model of Down syndrome: a syndrome that results from chromosome (Chr) 21 trisomy and is associated with congenital defects, cognitive impairment, and ultimately Alzheimer's disease. Ts65Dn mice have segmental trisomy for distal mouse Chr 16, a region sharing conserved synteny with human Chr 21. As a result, this strain harbors three copies of over half of the human Chr 21 orthologs. The trisomic segment of Chr 16 is present as a translocation chromosome (Mmu17(16)), with breakpoints that have not been defined previously. To molecularly characterize the Chrs 16 and 17 breakpoints on the translocation chromosome in Ts65Dn mice, we used a selective enrichment and high-throughput paired-end sequencing approach. Analysis of paired-end reads flanking the Chr 16, Chr 17 junction on Mmu17(16) and de novo assembly of the reads directly spanning the junction provided the precise locations of the Chrs 16 and 17 breakpoints at 84,351,351 and 9,426,822?bp, respectively. These data provide the basis for low-cost, highly efficient genotyping of Ts65Dn mice. More importantly, these data provide, for the first time, complete characterization of gene dosage in Ts65Dn mice.     

Mapping of the Hmg1 gene and of seven related sequences in the mouse

The High Mobility Group 1 protein (HMG1) is an abundant and highly conserved chromosomal protein. Mouse HMG1 is encoded by the Hmg1 gene, containing four introns, but the murine genome contains many related sequences that are mostly retrotransposed pseudogenes. By using an interspecific cross, we have mapped the functional Hmg1 gene on mouse Chromosome (Chr) 5 and seven Hmg1-related sequences on Chrs 6, 8, 17, 18, and X.     

Comparative sequence analysis of a single-gene conserved segment in mouse and human

Comparative mapping and sequencing of the mouse and human genomes have defined large, conserved chromosomal segments in which gene content and order are highly conserved. These regions span megabase-sized intervals and together comprise the vast majority of both genomes. However, the evolutionary relationships among the small remaining portions of these genomes are not as well characterized. Here we describe the sequencing and annotation of a 341-kb region of mouse Chr 2 containing nine genes, including biliverdin reductase A (Blvra), and its comparison with the orthologous regions of the human and rat genomes. These analyses reveal that the known conserved synteny between mouse Chromosome (Chr) 2 and human Chr 7 reflects an interval containing one gene (Blvra/BLVRA) that is, at most, just 34 kb in the mouse genome. In the mouse, this segment is flanked proximally by genes orthologous to human chromosome 15q21 and distally by genes orthologous to human Chr 2q11. The observed differences between the human and mouse genomes likely resulted from one or more rearrangements in the rodent lineage. In addition to the resulting changes in gene order and location, these rearrangements also appear to have included genomic deletions that led to the loss of at least one gene in the rodent lineage. Finally, we also have identified a recent mouse-specific segmental duplication. These finding illustrate that small genomic regions outside the large mouse–human conserved segments can contain a single gene as well as sequences that are apparently unique to one genome. The nucleotide sequence data reported in this paper have been submitted to GenBank and assigned the accession numbers AC074224 and AC074041.     

Genetic and physical mapping of the natural resistance-associated macrophage protein 1 (NRAMP1) in chicken

The chicken natural resistance-associated macrophage protein 1 (NRAMP1) gene has been mapped by linkage analysis by use of a reference panel to develop the chicken molecular genetic linkage map and by fluorescence in situ hybridization. The chicken homolog of the murine Nramp1 gene was mapped to a linkage group located on Chromosome (Chr) 7q13, which includes three genes (CD28, NDUSF1, and EF1B) that have previously been mapped either to mouse Chr 1 or to human Chr 2q. Physical mapping by pulsed-field gel electrophoresis revealed that NRAMP1 is tightly linked to the villin gene and that the genomic organization (gene order and presence of CpG islands) of the chromosomal region carrying NRAMP1 is well conserved between the chicken and mammalian genomes. The regions on mouse Chr 1, human Chr 2q, and chicken Chr 7q that encompass NRAMP1 represent large conserved chromosomal segments between the mammalian and avian genomes. The chromosome mapping of the chicken NRAMP1 gene is a first step in determining its possible role in differential susceptibility to salmonellosis in this species.     

Comparative mapping of human Chromosome 14q11.2-q13 genes with mouse homologous gene regions

An examination of the synteny blocks between mouse and human chromosomes aids in understanding the evolution of chromosome divergence between these two species. We comparatively mapped the human (HSA) Chromosome (Chr) 14q11.2-q13 cytogenetic region with the intervals of orthologous genes on mouse (MMU) chromosomes. A lack of conserved gene order was identified between the human cytogenetic region and the interval of orthologs on MMU 12. The evolutionary breakpoint junction was defined within 2.5 Mb, where the conserved synteny of genes on HSA 14 changes from MMU 12 to MMU 14. At the evolutionary breakpoint junction, a human EST (GI: 1114654) with identity to the human and mouse BCL2 interacting gene, BNIP3, was mapped to mouse Chr 3. New gene homologs of LAMB1, MEOX2, NRCAM, and NZTF1 were identified on HSA 7 and on the proximal cytogenetic region of HSA 14 by mapping mouse genes recently reported to be genetically linked within the relevant MMU 12 interval. This study contributes to the identification of homology relationships between the genes of HSA 14q11.2-q13 and mouse Chr 3, 12, and 14. Received: 16 March 2000 / Accepted: 16 June 2000     

Neither HMG-14a nor HMG-17 gene function is required for growth of chicken DT40 cells or maintenance of DNaseI-hypersensitive sites.

HMG-14 and HMG-17 form a family of ubiquitous non-histone chromosomal proteins and have been reported to bind preferentially to regions of active chromatin structure. Our previous studies demonstrated that the chicken HMG-17 gene is dispensable for normal growth of the DT40 chicken lymphoid cell line. Here it is shown that the major chicken HMG-14 gene,HMG-14a, is also dispensable and, moreover, that DT40-derived cells lacking both HMG-17 and HMG-14a proteins show no obvious change in phenotype with respect to the parental DT40 cells. Furthermore, no compensatory changes in HMG-14b or histone protein levels were observed in cells lacking both HMG-14a and HMG-17, nor were any alterations detected in such hallmarks of chromatin structure as DNaseI-hypersensitive sites or micrococcal nuclease digestion patterns. It is concluded that the HMG-14a and HMG-17 proteins are not required for normal growth of avian cell linesin vitro, nor for the maintenance of DNaseI-hypersensitive sites in chromatin.     

High-resolution comparative physical mapping of mouse Chromosome 10 in the region of homology with human Chromosome 21

Comparative mapping of human and mouse chromosomes can be used to predict locations of homologous loci between the species, provides the substrate to examine the process of chromosomal evolution, and facilitates the continuing development of mouse genetic models for human disorders. A YAC contig of the region of mouse Chromosome (Chr) 10 (MMU10) that demonstrates conserved linkage with the distal portion of human Chr 21 (HSA21) has been constructed. The contig contains all known genes mapped in both species, defines the proximal region of homology between MMU10 and HSA22, and contains the evolutionary junction between HSA21 and HSA22 on MMU10. It consists of 23 YACs and 2 PACs, and covers 3.2 Mb of MMU10. The average marker density for this region is 1 marker/69 kb. Nine of 22 expressed sequences are mapped here for the first time in mouse, and two are newly characterized expressed sequences. The contig also contains 12 simple sequence repeats (SSRs) and 16 YAC and PAC endclone markers. YAC fragmentation analysis was used to create a physical map for the proximal 2.2 Mb of the contig. Cloning of the corresponding region of HSA21 has proven difficult, and the mouse contig includes segments absent from previously described sequence ready maps of HSA21. Received: 22 July 1998 / Accepted: 13 November 1998