Criq1^C57BL/6J
QTL Variant Detail

Summary

• QTL variant: Criq1^C57BL/6J
• Name: Citrobacter rodentium infection QTL 1; C57BL/6J
• MGI ID: MGI:5881901
• QTL: Criq1 Location: Chr15:33033954-33033954 bp Genetic Position: Chr15, Syntenic

Variant origin

• Strain of Specimen: C57BL/6J

Variant description

• Allele Type: QTL

Notes

Mapping and Phenotype information for this QTL, its variants and associated markers

J:239658

Inbred mouse strains C3H/HeJ, C3H/HeOuJ and C57BL/6J all differ in their susceptibility to Citrobacter rodentium infection. C3H/HeJ and C3H/HeOuJ strains succumb to the infection within 12 days following orgastric infection, where C57BL/6J not only survive but also fully recover and clear the infection.

A total of 168 progeny from a (C3H/HeJ x C57BL/6J)F2 and a total of 199 progeny from a (C3H/HeOuJ x C57BL/6J)F2 cross were orally inoculated with a strain of C. rodentium at four weeks of age. The parental strains were included as controls with every F1 and F2 infection. For survival analysis the mice were monitored one or two times daily and moribund animals were killed with CO2. At 7 days post infection a gross/clinical examination of animals was performed. Body weights were measured and signs of dehydration and diarrhea were measured. Ultimately, the entire intestinal tract was dissected and analyzed by a pathologist. DNA was extracted from tail biopsies.

Mapping for the survival phenotype for progeny from both crosses was performed using parametric survival regression at the markers under Cox proportional hazards model for the survival time distribution using the statistical R program. Significance, assessed via 100,000 bootstrapped resamples controlling for genome-wide type 1 error, was determined at 3.57 for the (C3H/HeJ x C57BL/6J)F2 cross and 3.28 for the (C3H/HeOuJ x C57BL/6J)F2 cross.

A single locus, Criq1 (Citrobacter rodentium infection QTL 1), associated with survival was identified in the (C3H/HeJ x C57BL/6J)F2 cross. Criq1 mapped to Chromosome 15 with a peak LOD score of 13.42 at rs3720676 (13.58 cM, Build 37), p<0.00001 and a 1.5 LOD support interval spanning 28.1 Mb between markers rs3714893 and rs3719583. Ninety-four percent of the mice homozygous for the C57BL/6J allele at Criq1 survived the infection. Mice heterozygous at this locus displayed a survival rate of 28% that was not significantly different from mice homozygous for the C3H/HeJ allele.

The survival of all 168 mice in the (C3H/HeJ x C57BL/6J) F2 cross was analyzed according to their genotype at the Tlr4 gene to assess whether the Tlr4 gene had any effect on mouse survival to the infection. No significant effect of the Tlr4 genotype on survival was observed.

Two loci significantly associated with survival were mapped in the (C3H/HeOuJ x C57BL/6J)F2 cross:

Criq2 (Citrobacter rodentium infection QTL 2) mapped to Chromosome 5 with a peak LOD score of 3.49 at rs3661429 (50.69 cM, Build 37), p<0.031. No such peak was identified in the (C3H/HeJ x C57BL/6J)F2 cross. Animals that inherited both copies of the C57BL/6J allele at this locus had a 35% survival rate at day 30 post infection. Littermates that were heterozygous or homozygous for the C3H/HeOuJ allele at Criq2 displayed 68 and 61% survival, respectively. The C3H/HeOuJ allele confers a modest level of resistance at Criq2 that is dominant over the C57BL/6J allele.

Criq3 (Citrobacter rodentium infection QTL 3) mapped to Chromosome 15 with a peak LOD score of 12.55 at rs3683812 (12.63 cM, Build 37), p<0.00001 and a 1.5 LOD support interval spanning 15.9 Mb between markers rs3720676 and rs3719583.

(MGI Curator Note: Because the C3H strains used in the respective mapping populations differ we have assigned unique nomenclature to the Chromosome 15 locus identified in each cross).

In the (C3H/HeOuJ x C57BL/6J)F2 cross 96% of mice homozygous for the C57BL/6J allele survived, where only 30% of homozygotes with the C3H/HeOuJ allele survived. In contrast to the heterozygous mice in the (C3H/HeJ x C57BL/6J)F2 cross, heterozygous mice in the (C3H/HeOuJ x C57BL/6J)F2 cross were significantly more resistant than homozygous C3H/HeOuJ littermates. C3H alleles confer susceptibility to C. rodentium infection in terms of survival; the C3H/HeJ allele is dominant in context of the (C3H/HeJ x C57BL/6J)F2 cross but appears co-dominant or additive in the (C3H/HeOuJ x C57BL/6J)F2 cross. [Graph Fig 4]. It appears that C3H/HeOuJ produce progeny that are consistently more resistant to infection than those from the C3H/HeJ strain.

To study the effect of Criq3 in the absence of other genetic differences between parental strains congenic mice were generated. C3HOu.B6-(rs3698904-rs3702158) carries a 60 Mb segment of C57BL/6J on a C3H/HeOuJ genetic background including the Criq3 QTL. C. rodentium infection was followed by survival analysis. There was a 96% cumulative survival rate. Heterozygotic littermates showed a complete dominance (0% cumulative survival rate 30 days post infection) of the C3H/HeOuJ susceptibility allele of Criq3.

There are a number of different phenotypes that can be studied during infection that distinguish the C3H inbred strains from the C57BL/6J. Using the congenic mice it was determined that increased, early bacterial proliferation seen in C3H strains of mice was not controlled by the Criq3 locus and was unrelated to mortality post infection. There was strong evidence that surviving congenic mice clear the infection completely by day 29 post infection. Colon weights (a measure of colonic hyperplasia) at day 9 post infection were indistinguishable between the congenic mice and C3H/HeOuJ mice and significantly different from B6 mice indicating that Criq3 des not control colonic hyperplasia post infection.

References

• Original: J:239658 Diez E, et al., Identification and characterization of Cri1, a locus controlling mortality during Citrobacter rodentium infection in mice. Genes Immun. 2011 Jun;12(4):280-90
• All: 1 reference(s)