Mouse chromosome 7

Physical mapping of the albino-deletion complex in the mouse to localize alf/hsdr-1, a locus required for neonatal survival

The albino-deletion complex in the mouse defines a genetically well-characterized region of chromosome 7 in which a number of loci essential for normal development and viability reside. One locus, designated alf or hsdr-1, is necessary for neonatal survival. Its absence results in hypoglycemia associated with biochemical and ultrastructural abnormalities in hepatocytes and proximal tubule cells of the kidney. We constructed a long-range physical map of the region defined by the proximal segment of the albino-deletion complex as a step toward localizing alf/hsdr-1. Sixteen markers, including 11 whose isolation is described here and in the accompanying paper (A. Schedl et al., 1992, Genomics 14, 288-297), were ordered on a panel of albino-deletion DNAs and their distribution was examined by pulsed-field gel electrophoresis. The resulting approximately 4300-kb physical map covers the entire region absent from the prototypic alf/hsdr-1 deletion c14CoS, estimated as approximately 3600 kb. Since the deletion c11DSD complements and overlaps most of c14CoS, alf/hsdr-1 was mapped at the proximal extreme of c14CoS, approximately 3000 kb from the albino locus. The density of CpG islands was found to be very heterogeneous across the region mapped.

Close linkage of the olfactory marker protein gene to the mouse deafness mutation shaker-1

One thousand sixty-six progeny have been generated from a backcross segregating for the mouse deafness mutation, shaker-1 (sh-1). One thousand fifty-two mice were analyzed for a protein polymorphism segregating for the distal flanking marker, beta-globin (Hbb), and 13 recombinants between Hbb and sh-1 were identified. One thousand eight mice were analyzed for a restriction fragment length polymorphism segregating for the proximal flanking marker, tyrosinase (c), and 54 recombinants between c and sh-1 were identified, completing a panel of 67 recombinant mice from the backcross in the vicinity of the sh-1 mutation. This panel allows the identification of markers closely linked to the sh-1 mutation that may act as start points for a chromosomal walk to the gene. One such marker, the olfactory marker protein gene (Omp), is recombinant with sh-1 in only one mouse from the recombinant panel. Thus, the Omp gene lies 0.1 cM from sh-1, on average, a distance of 200 kb. Haplotype analysis indicates that Omp lies proximal to sh-1.

Physical analysis of murine albino deletions that disrupt liver-specific gene regulation or mesoderm development

Complementation analyses of radiation-induced deletion mutations involving the albino (c) locus in Chromosome (Chr) 7 of the mouse have identified several loci, in addition to c, that have important roles in development. The "mesoderm-deficient" (msd) and "hepatocyte-specific developmental regulation-1" (hsdr-1) loci, which are proximal and tightly linked to c, are important in the formation of mesoderm and in the regulation of liver- and kidney-specific induction of various enzymes and proteins, respectively. Cloning deletion-breakpoint-fusion fragments caused by lethal albino deletions that genetically define the extents of the msd and hsdr-1 loci is one way of generating molecular probes for studying the gene(s) involved in these phenotypes. The distal breakpoints of five such deletions were positioned on a long-range (PFGE) map of approximately 1.7 Mb of wild-type DNA surrounding the c, D7Was12, and Emv-23 loci. In addition, the distal breakpoints of two viable albino deletions, which remove part of the tyrosinase gene and extend distally, were localized in the vicinity of the lethal deletion breakpoints. Therefore, the viable deletions can be exploited to generate additional DNA probes that should facilitate the isolation of breakpoint clones from chromosomes carrying lethal deletions defining hsdr-1 and msd.