A recombination hotspot leads to sequence variability within a novel gene (AK005651) and contributes to type 1 diabetes susceptibility.

More than 25 loci have been linked to type 1 diabetes (T1D) in the nonobese diabetic (NOD) mouse, but identification of the underlying genes remains challenging. We describe here the positional cloning of a T1D susceptibility locus, Idd11, located on mouse chromosome 4. Sequence analysis of a series of congenic NOD mouse strains over a critical 6.9-kb interval in these mice and in 25 inbred strains identified several haplotypes, including a unique NOD haplotype, associated with varying levels of T1D susceptibility. Haplotype diversity within this interval between congenic NOD mouse strains was due to a recombination hotspot that generated four crossover breakpoints, including one with a complex conversion tract. The Idd11 haplotype and recombination hotspot are located within a predicted gene of unknown function, which exhibits decreased expression in relevant tissues of NOD mice. Notably, it was the recombination hotspot that aided our mapping of Idd11 and confirms that recombination hotspots can create genetic variation affecting a common polygenic disease. This finding has implications for human genetic association studies, which may be affected by the approximately 33,000 estimated hotspots in the genome.

An NZW-derived interval on chromosome 7 moderates sialadenitis, but not insulitis in congenic nonobese diabetic mice.

Autoimmune lymphocytic infiltration of the salivary glands, termed sialadenitis, is a pathologic feature of Sjögren's syndrome (SjS) that is also prominent in nonobese diabetic (NOD) mice. Genetic factors regulate sialadenitis, and a previous (NOD x NZW)F2 study detected linkage to murine chromosome (Chr) 7. The locus, subsequently annotated as Ssial3, maps to the distal end of Chr7 and overlaps a region associated with type 1 diabetes susceptibility in NOD mice. To examine whether Ssial3 could contribute to both diseases, or was specific for SjS, we generated a congenic mouse strain that harbored an NZW-derived Chr7 interval on the NOD genetic background. This congenic strain exhibited reduced sialadenitis compared with NOD mice and confirmed Ssial3. This reduction, however, did not ameliorate saliva abnormalities associated with SjS-like disease in NOD mice, nor were congenic mice protected against insulitis (lymphocytic infiltration of the pancreatic islets) or diabetes onset. Thus, the Ssial3 locus appears to have a tissue-specific effect for which the NZW allele is unable to prevent other autoimmune traits in the NOD mouse. Anomalous increases for antinuclear Ab production and frequency of marginal-zone B cells were also identified in congenic mice, indicating that the NZW-derived Chr7 interval has a complex effect on the NOD immune system.

Localization of Idd11 is not associated with thymus and nkt cell abnormalities in NOD mice.

Congenic mouse strains provide a unique resource for genetic dissection and biological characterization of chromosomal regions associated with diabetes progression in the nonobese diabetic (NOD) mouse. Idd11, a mouse diabetes susceptibility locus, was previously localized to a region on chromosome 4. Comparison of a panel of subcongenic NOD mouse strains with different intervals derived from the nondiabetic C57BL/6 (B6) strain now maps Idd11 to an approximately 8-Mb interval. B6-derived intervals protected congenic NOD mice from diabetes onset, even though lymphocytic infiltration of pancreatic islets was similar to that found in NOD mice. In addition, neither thymic structural irregularities nor NKT cell deficiencies were ameliorated in diabetes-resistant congenic NOD mice, indicating that Idd11 does not contribute to these abnormalities, which do not need to be corrected to prevent disease.

A susceptibility allele from a non-diabetes-prone mouse strain accelerates diabetes in NOD congenic mice.

The nonobese diabetic (NOD) mouse is genetically predisposed for the spontaneous development of type 1 diabetes. Linkage analyses have identified at least 19 susceptibility loci (Idd1-Idd19) that contribute to disease pathogenesis in which lymphocytes mediate the specific destruction of insulin-producing beta-cells. Interestingly, nondiabetic mouse strains have been shown to confer susceptibility alleles to affected progeny in NOD outcrosses for some of the Idd loci. In particular, we noted that diabetic backcross progeny, derived from NOD and C57BL/6 (B6) mouse strains, demonstrated increased heterozygousity for an interval encompassing Idd14 on chromosome 13. This result suggested that B6 mice harbor a more diabetogenic allele(s) than NOD mice for this locus. To confirm this observation, a NOD congenic mouse strain, containing a B6-derived interval covering the majority of chromosome 13, was generated. Adding to the combination of already potent susceptibility alleles elsewhere in the NOD genome, the chromosome 13 B6-derived interval was able to increase the overall risk of developing type 1 diabetes, which resulted in an earlier onset and increased incidence of type 1 diabetes in congenic mice as compared with NOD mice. Furthermore, this B6-derived interval, in combination with the NOD genetic background, was able to overcome environmental conditions that typically suppressed type 1 diabetes in the NOD mouse strain.