Genetic map of the lymphopenia region on rat chromosome 4

The iddm4 locus segregates with diabetes susceptibility in congenic WF.iddm4 rats

Viral antibody-free BBDR and WF rats never develop spontaneous diabetes. BBDR rats, however, develop autoimmune diabetes after perturbation of the immune system, e.g., by viral infection. We previously identified a disease-susceptibility locus in the BBDR rat, iddm4, which is associated with the development of autoimmune diabetes after treatment with polyinosinic:polycytidylic acid and an antibody that depletes ART2(+) regulatory cells. We have now developed lines of congenic WF.iddm4 rats and report that in an intercross of N5 generation WF.iddm4 rats, approximately 70% of animals either homozygous or heterozygous for the BBDR origin allele of iddm4 became hyperglycemic after treatment to induce diabetes. Fewer than 20% of rats expressing the WF origin allele of iddm4 became diabetic. Testing the progeny of various recombinant N5 WF.iddm4 congenic rats for susceptibility to diabetes suggests that iddm4 is centered on a small segment of chromosome 4 bounded by the proximal marker D4Rat135 and the distal marker D4Got51, an interval of <2.8 cM. The allele at iddm4 has 79% sensitivity and 80% specificity in prediction of diabetes in rats that are segregating for this locus. These characteristics suggest that iddm4 is one of the most powerful non-major histocompatibility complex determinants of susceptibility to autoimmune diabetes described to date.

A sequence-ready PAC contig of a 550-kb region on rat chromosome 4 including the diabetes susceptibility gene Lyp

The Lyp locus controls diabetes development in rats. The diabetogenic allele in diabetes-prone BB rats is responsible for T cell lymphopenia characterized by the absence of regulatory T cells. We present refined genetic and radiation hybrid maps of the Lyp region on rat chromosome 4, a single 800-kb rat yeast artificial chromosome and a rat P1-derived artificial chromosome (PAC) contig corresponding to approximately 550 kb, both encompassing the entire candidate region. The contig, consisting of 48 PACs, gives 3- to 12-fold coverage. Genetic, radiation hybrid, and physical data were all in agreement and supported the same marker order. Nine genes and ESTs were identified in the contig in addition to a rat EST from the University of Iowa rat EST database-all possible candidate genes for Lyp. Alignment of our rat PAC contig with sequenced human PAC/BAC contigs confirms the position within the region of 3 of the 10 candidates and identifies an additional 8 genes/ESTs as candidates. These data will facilitate identification of Lyp.

Comparative mapping of the human homologue of the rat diabetes susceptibility gene lyp to a 1.3-Mb segment on HSA7

The rat diabetes susceptibility gene, Lyp or Lymphopenia, has been localized to RNO4. Proximal to Lyp are the genes caspase-2 (Casp2) and pancreatic trypsin 1 (Prss1), while neuropeptide Y (Npy) is the closest distally positioned gene. In human, the three genes are syntenic on HSA7, but they are not on a conserved segment: CASP2 and PRSS1 are localized to 7q35, while NPY is localized to 7p15.1. This raises the question whether the human homologue of Lyp is linked to CASP2/PRSS1 or to NPY. We present a comparative map of the Lyp region in rat and human, assigning the gene to a 1.3-Mb segment between RNY3 and ABP1 at 7q35.