Congenic Mapping of the Type 1 Diabetes Locus,Idd3, to a 780-kb Region of Mouse Chromosome 3: Identification of a Candidate Segment of Ancestral DNA by Haplotype Mapping

Abstract

Type 1 diabetes in the nonobese diabetic (NOD) mouse arises as a consequence of T cell-mediated destruction of the insulin-producing ␤ cells of the pancreas. Although little is known of the events that initiate and subsequently drive ␤-cell destruction it is clear that the entire process is under complex genetic control. At present 19 loci have been mapped that influence the development of diabetes either at the level of initiation of insulitis or at the level of progression from insulitis to overt diabetes, or both. Previously, we have mapped one of these loci, Idd3, to a 0.35-cM interval on proximal mouse chromosome 3. In the present study we have narrowed the map position of this locus to an interval of 0.15 cM by a combination of novel congenic strains and an ancestral haplotype analysis approach. We have constructed a physical contig in bacterial artificial chromosome (BAC) clones across the minimal interval. Restriction mapping of the BAC contig placed the maximum size of the Idd3 interval at 780 kb between the markers D3Nds36 and D3Nds76. To refine further the Idd3 interval we developed a series of novel single nucleotide polymorphisms (SNPs) and carried out haplotype analysis on DNA from mouse strains known to carry either Idd3 susceptibility or protective alleles. This haplotype analysis identified a 145-kb segment of ancestral DNA between the microsatellite marker D3Nds6 and the SNP 81.3. One haplotype of this ancestral segment of DNA is found in mouse strains carrying an Idd3 susceptibility allele and another is found in mouse strains carrying an Idd3 protective allelle. Within the 780-kb congenically defined interval this 145-kb segment represents the most likely location for Idd3. The Il2 gene, which encodes the cytokine interleukin 2 (IL2), maps to this interval and is a strong candidate for Idd3. To investigate whether sequence variation exists in the promoter region of the Il2 gene, which might alter its expression, we sequenced the promoter region of the Il2 gene from mouse strains carrying either an Idd3 susceptibility or resistance allele. Two sequence variants were identified, neither of which fell in known regulatory elements within the Il2 promoter. In agreement with this observation steady-state Il2 mRNA levels showed no variation between susceptible and resistant mouse strains. These data suggest that the profound protection from diabetes seen in congenic mice carrying an Idd3 protective allele is unlikely to be due to differences in the level of expression of the Il2 gene. Instead, all of the current data support our hypothesis that Idd3 corresponds to amino acid variation at the amino terminus of Il2.

Increased Entry into the IFN-γ Effector Pathway by CD4+ T Cells Selected by I-Ag7 on a Nonobese Diabetic Versus C57BL/6 Genetic Background

“…4). This is an interesting result because Idd3 may be IL-2 (64,65). Relatively decreased IL-2 effect on cellular proliferation could therefore represent a mechanism of Idd3-mediated disease susceptibility.…”

Loss of parity between IL-2 and IL-21 in the NOD Idd3 locus

“…Congenic NOD B6.Idd3 mice are NOD mice that carry the Idd3 T1D susceptibility locus encompassing 780 Kb of chromosome 3 from C57BL/6 mice. The incidence of diabetes in NOD B6.Idd3 mice is reduced to 20% compared with 80% of NOD mice (27). We extended our analyses to the kinetics of IL-21 mRNA production in purified CD4 ϩ T cells.…”

The same genomic region conditions clonal deletion and clonal deviation to the CD8αα and regulatory T cell lineages in NOD versus C57BL/6 mice

“…Thus, the QTLs for resistance to clonal deletion and for ineffective clonal deviation to the CD8␣␣ lineage are very tightly linked, if not identical. These QTLs mapped quite closely to the position of the idd3 locus, an important component of susceptibility to autoimmune diabetes in the NOD mouse, one component of which is located between 36.3 and 37.2 Mb on chromosome 3 (24,25). We tested whether the idd3 region might contain the clonal deletion/ deviation QTL by crossing the BDC2.5 transgene onto the NOD.B6idd3R450 line and analyzing FTOC cultures prepared from such mice.…”