NOD is homozygous for recessive alleles for susceptibility at all three loci, Idd1s, Idd2s, and Idd3s. The dominant alleles for non-susceptibility to IDD, Idd1r, etc., occur in the NON strain. Homozygosity for the recessive alleles at all three loci is necessary for the development of IDD.The Idd1 locus is linked to the major histocompatibility locus on Chr 17, but Idd2 is on Chr 9 (1) and Idd3 is on Chr 3 (J:8783, J:3351).
This locus is also linked to peripheral CD4 lymphocytosis.
Mapping and Phenotype information for this QTL, its variants and associated markers
Congenic animals were created to observe the effect of diabetes QTL Idd1 on mouse Chromosome 17. The congenic NOD.CTS-H2 carries CTS-derived DNA at the H2 locus, which is part of Idd1, on an NOD diabetes-susceptible genetic background. Parental strain CTS is diabetes resistant but shares the same H2 alleles as NOD. Interestingly the NOD.CTS-H2 congenic is susceptible to diabetes but with lower incidence compared to NOD. Authors state that the H2 locus is responsible for the diabetes susceptible effect ofIdd1 but does not explain it entirely. A closely linked but distinct QTL, Idd16 at 18 cM, may also contribute to the NOD susceptible phenotype. A candidate gene for Idd16 is Tnf (19.06 cM). Haplotype analysis was performed to assess the candidacy of Tnf.The non-diabetic inbred strain NON shares the same Tnf alleles as the diabetic strain NOD. The congenic NON.NOD-H2 carryies NON-derived DNA around the H2 locus (including Tnf) on a NOD genetic background and is diabetes susceptible. This data supports the candidacy of Tnf for Idd16.
To study the Idd3 candidate gene, Il2 (19.2 cM on mouse Chromosome 3), a congenic line was constructed. NOD.IIS-Il2 carries ISS-derived DNA at Il2 on an NOD diabetes susceptible background. Parental strain ISS is resistant to diabetes but shares alleles with NOD at Il2. The congenic is phenotypically indistinguishable from the NOD parental indicating that the NOD alleles at Il2 exert an effect on diabetes susceptibility. Another candidate gene for Idd3 is Il21. Il21 is closely linked to and forms a haplotype with Il2, making Il21 a strong candidate for Idd3.
Idd10 maps to 48.5 cM on mouse Chromosome 3. Fcgr1 (45.2 cM) has been identified as a possible candidate gene for Idd10. Sequence analysis revealed 17 amino acid differences between NOD and C57BL/10 in addition to deletion of 75% of the cytoplasmic tail. A congenic line carrying diabetes resistant ISS-derived DNA at Idd10 on an NOD diabetes susceptible background was constructed. However, the NOD.IIS-Idd10 congenic is not susceptible to diabetes, therefore excluding Fcgr1 from the candidate gene list. Further analysis of the Idd10 locus revealed 3 multiply linked loci: Idd10, Idd17, and Idd18.
The effect of Idd1 (19.5 cM ) was confirmed using congenic strain B6.NOD-(D17Mit164-D17Mit152). This congenic strain carries NOD-derived chromosome 17 DNA from 5.3 cM to 63.8 cM on a C57BL/6 genetic background. Parental strain NOD exhibits peripheral CD4lymphocytosis compared to C57BL/6. Congenic strain B6.NOD-(D17Mit164-D17Mit152) also exhibits peripheral CD4 lymphocytosis, therefore NOD-derived alleles between D17Mit164 and D17Mit152 may house a gene or genes responsible for the phenotype.
NOD.B10Sn-H2<b>/J, a congenic strain that carries the H2<b> allele from B10Sn/J on an NOD genetic background also exhibits CD4 lymphocytosis and is diabetes resistant but differs from B6.NOD-(D17Mit164-D17Mit152) between D17Mit100 (24.9 cM) and D17Mit176 (41 cM). This region contains C57BL/6-derived DNA instead of NOD-derived DNA and was ruled out for carrying the gene responsible for CD4 lymphocytosis. Authors conclude that the most likely location for the gene responsible for lymphocytosis is either between D17Mit164 (5.3 cM) and D17Mit100 (24.9 cM) or between D17Mit21 (33 cM) and D17Mit142 (77 cM). These 2 regions exclude the H2 locus. A potential candidate gene for Idd1 is Pdpk1.
Development of type 1 diabetes in NOD/Jsd mice can be accelerated with cyclophosphamide treatment, but not in NOR/LtJ diabetes resistant mice. This phenotype was mapped using linkage analysis of 66 (NOD/Jsd x NOR/LtJ)F1 x NOD/Jsd backcross animals. NOR/LtJ is a recombinant inbred strain derived from a NOD genetic background (88%) with C57BLKS/J donor regions over 10 different chromosomes. Some of these regions contain Idd susceptibility loci. NOD/Jsd is susceptible to spontaneous and cyclophosphamide-accelerated type 1 diabetes whereas NOR/LtJ is resistant.
Significant linkage to severe insulitis in cyclophosphamide-treated backcross animals mapped to 43 cM on mouse chromosome 11 near D11Mit219 (LOD=4.9) and to 60 cM on mouse Chromosome 4 near D4Mit338 (LOD=7.4). The chromosome 11 locus accounts for 30% of the variance and corresponds to previously identified diabetes QTL Idd4. The Idd4 1-LOD confidence interval spans a 7.8 cM interval on chromosome 11 between 37 cM - 44.8 cM. The chromosome 4 locus accounts for 43% of the variance and corresponds to previously identified diabetes QTL Idd9. The Idd9 1-LOD confidence interval spans a 12.4 cM interval on chromosome 4 between 53.6 cM -66 cM. All animals with progression to severe insulitis following cyclophosphamide treatment are homozygous for NOD/Jsd-derived alleles at both Idd4 and Idd9.
Analysis of reciprocal congenic strains derived from NOD/Jsd and NOR/LtJ confirmed the involvement of Idd4 and Idd9 in cylcophosphamide-accelerated insulitis. Furthermore, Idd4 was localized to a 6.9 cM interval between D11Mit30 (40 cM) and D11Mit33 (46.9 cM). NOR/LtJ-derived alleles at Idd4 confer protection from cyclophospamide-induced insulitis in female animals, but not in male animals. NOR/LtJ-derived alleles at Idd9 confer protection from cyclophosphamide-induced insulitis in both male and female animals. The NOR/LtJ allele at Idd4 also protects against spontaneous development of type 1 diabetes. The NOD/Jsd allele at Idd4 confers susceptibility to type 1 diabetes with a stronger effect observed in male animals.
Potential candidate genes mapping near the Idd4 interval are Nos2 (45.6 cM), Tnfaip1 (45.1 cM), Evi2a (46.1 cM), Tcf2 (44 cM), Cryba1 (44.7 cM), and the Scya cluster (47 cM). Previously identified QTLs Eae7 (48 cM) and Orch3 (44 cM) also map to this region.
Potential candidate genes for Idd9 include Csf3r (57.5 cM), Iapls1-19 (57.2 cM), sno (58.3 cM), and Lck (59 cM). Previously identified diabetes QTL Idd11 colocalizes with Idd9 at 65 cM on mouse Chromosome 4. Idd11 confers a protective effect against cyclophosphamide-accelerated type 1 diabetes, which corroborates with the findings from this study.
Animals doubly congenic for NOD/Jsd-derived alleles both Idd4 and Idd9 exhibit significantly greater susceptibility to cyclophosphamide-accelerated type 1 diabetes compared to NOR/LtJ controls, but less so than NOD/Jsd parentals. This finding suggested the presence of other protective loci in the NOR/LtJ background, possibly contributed by Idd5 (40 cM)on mouse Chromosome 1 or Idd13 (71 cM) on mouse Chromosome 2. Reciprocal congenic lines for Idd5 and Idd13 were derived from NOD/Jsd and NOR/LtJ to evaluate this hypothesis. NOD.NOR-Idd5 congenic animals exhibited protection from cyclophosphamide-accelerated type 1 diabetes whereas NOD.NOR-Idd13 congenics did not. However, the reciprocal congenic NOR.NOD-Idd5 did not exhibit increased susceptibility to type 1 diabetes after cyclophosphamide treatment, indicating that Idd5 only confers a protective effectwith the NOR/LtJ-derived allele. Ctla4 was previously identified as a potential candidate gene for Idd5 but since the resistant Idd5 congenic in this study carried NOD/Jsd-derived Ctla4 DNA its candidacy was excluded. Potential Idd5 candidate genes include Slc11a1 (formerly Nramp1, 39.2 cM), Chrng (52.3 cM), Col6a3 (53.9 cM), Hdlbp (55.3 cM), and Ramp1 (56 cM).
NOD/Jsd and NOR/LtJ share the same Idd1 alleles at 19.5 cM on mouse Chromosome 17. After cyclophosphamide treatment both strains show signs of insulitis, although it is mild in NOR/LtJ and severe in NOD/Jsd, progressing to diabetes after 18 days of continued treatment. Controls strains C57BL/6J and BALB/cJ do not exhibit any signs of insulitis after cyclophosphamide treatment. This finding suggests that NOD-derived alleles at Idd1 confer susceptibility to cyclophosphamide-induced insulitis.
H2 congenic strains B10.RIII/Lund-H2<r> and B10.Q/Lund-H2<q> are highly susceptible to collagen-induced arthritis (CIA). Congenic B10.RIII/Lund-H2<r> is derived from CIA resistant donor strain RIII/WySn-H2<r> and CIA susceptible background strain C57BL/10Sn-H2<b>. Congenic B10.Q/Lund-H2<q> is derived from donor strain DBA/1-H2<q> and background strain C57BL/10Sn-H2<b>. These 2 congenics should only differ from their background strains at the H2 locus. However, genome scan using 150 microsatellite markersrevealed RIII/WySn contamination on a segment of mouse Chromosome 10 from D10Mit196 (31 cM) to D10Mit178 (59 cM) in the B10.RIII/Lund-H2<r> congenic. This locus coincides with Cia8 and is thought to be the same QTL.
A new congenic was created by introgressing an RIII/WySn-derived Cia8 interval onto the genetic background of B10.Q/Lund-H2<q>. The reciprocal congenic was also created in which a C57BL/10Sn-derived Cia8 interval from donor strain B10.Q/Lund-H2<q> was introgressed onto the genetic backgroundof B10.RIII/Lund-H2<r>. As expected, the RIII/WySn-derived Cia8 interval significantly increased CIA incidence and severity on the B10.Q/Lund-H2<q> background while the C57BL/10-derived Cia8 interval decreased CIA incidence and severity on the B10.RIII/Lund-H2<r> background. This finding suggests that Cia8 in conjunction with the H2 interval on mouse Chromosome 17 influences CIA susceptibility. Cia8 appears to have an additive effect.
Potential candidate genes mapping near Cia8 are Bsg (42.4 cM), Lilrb4 (32 cM),Ostm1 (29 cM), Prf1 (36 cM), Mif (40.9 cM), Mmp11 (40.9 cM), Aire (41.6 cM), Timp3 (47 cM), Itgb2 (41.5 cM), Igf1 (48 cM), and Socs2 (52 cM). Previously identified arthritis QTLs mapping near Cia8 are Pgia6 (12 cM), Eae17 (36 cM), Asm1 (39 cM), Lmb4 (41 cM), Asthm1 (44 cM), and Bbaa18 (31.5 cM).
Several autoimmune QTLs have been mapped to the H2 locus on mouse Chromosome 17. These QTLs include Cia1, Pgia17, Bbaa8, Eae1, Eae5, Sles1, Asbb3, Mbis4, Orch1, Cdcs5, Ssial4, and Idd1.