Mapping of the Pim-1 oncogene in mouse t-haplotypes and its use to define the relative map positions of the tcl loci t0(t6) and tw12 and the marker tf (tufted)

Genetic predisposition to lymphomas in mice

The spontaneous mouse lymphoma is a model of multifactorial genetic disease. It is induced by the endogenous murine leukemia virus (MuLV), whose genome is inherited as a Mendelian dominant trait. Lymphoma development takes place in multiple stages affected by many host genetic and epigenetic factors. An inbred strain SL/Kh with a high incidence of pre-B lymphomas has been established and the genetic predisposition of SL/Kh mice to lymphomas is being studied in the crosses with other inbred strains of mice. In the cross to the NFS/N lacking endogenous MuLV genome, it has been shown that lymphomas are induced by the expression of Emv-11 provirus (Chr. 7), and the types of B-lineage lymphomas are determined by combinations of the host genes, Esl-1 (Chr. 17) and Foc-1 (Chr. 4). Another gene, Tlsm-1 (Chr. 7) that determines the type of lymphomas to be T-lineage, is identified in the cross with AKR/Ms, with a high incidence of T-lymphomas. The role of the thymus in the development of T-lymphomas in the mouse, and the possible relevance of Tlsm-1 in this step, is discussed. The length of the latent period is determined by a gene Lia-1 (Chr. 17). A maternal resistance factor that is a maternal antibody to MuLV transmitted via milk and that epigenetically inhibits MuLV expression in SL/Ni-Eco-, one of subline of SL/NI mice, has been shown. Weak but definitive maternal resistance also operates in SL/Ni-Eco+, a subline lacking the maternal antibody to MuLV. In the latter, there is a recessive resistance gene Nir-1 (Chr. 4). In the cross with MSM/Ms, a wild mice-derived inbred strain, two resistance genes, Msmr-1 (Chr. 17) and Msmr-2 (Chr. 18), have been identified. In SL/Kh, all of these host genetic and epigenetic factors are favorable for lymphoma development. This model offers not only an understanding of the pathogenesis of virus-induced lymphomas but also may provide starting material for the comparative approach to homologous human diseases.

Chromosomal localization of the murine gene and two related sequences encoding high-mobility-group I and Y proteins

HMG-I and its isoform HMG-Y are members of the abundant high-mobility-group of nonhistone chromatin proteins; they bind to A + T-rich regions of chromosomal DNA and are expressed at high levels in rapidly dividing, undifferentiated mammalian cells. HMG-I and HMG-Y are alternatively spliced products of a single functional gene, designated Hmgi in the mouse. Here, we report the occurrence of at least three distinct Hmgi-related loci in the mouse. Only one of these loci was present in all of the 10 mouse strains examined; therefore, this locus most likely represents the transcriptionally active, functional gene, Hmgi. Genetic linkage analysis of interspecific and intersubspecific backcrosses showed that Hmgi is located in the t-complex region of mouse Chromosome 17. Two additional Hmgi-related sequences, Hmgi-rs1 and Hmgi-rs2, were found only in certain mouse strains and probably represent pseudogenes. Hmgi-rs1 is located on Chromosome 11; it was present in all of the standard laboratory inbred mouse strains examined but was absent in wild-derived inbred strains of Mus spretus, M. musculus castaneus, and M. m. molossinus. Hmgi-rs2 was found only in M. m. castaneus and is located on Chromosome 6. Hmgi genes have not been previously mapped in any species, but the location of the probable functional gene on murine Chromosome 17 suggests that the homologous gene in humans is located on Chromosome 6.