Ebm1^A/J
QTL Variant Detail

Summary

• QTL variant: Ebm1^A/J
• Name: Epidermolysis Bullosa modifier 1; A/J
• MGI ID: MGI:5817917
• QTL: Ebm1 Location: Chr19:41988439-41988439 bp Genetic Position: Chr19, Syntenic

Variant origin

• Strain of Specimen: A/J

Variant description

• Allele Type: QTL
• Inheritance: Not Specified

Notes

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

J:211010

Epidermolysis Bullosa (EB) encompasses a spectrum of mechanobullous disorders caused by rare mutations that result in structural weakening of the skin and mucous membranes. 129X1/SvJ mice homozygous for the hypomorphic Lamc2^jeb mutation develop a progressive form of junctional EB (JEB) characterized most obviously by blistering and scarring of the ears and tails as the result of separations within the dermal-epidermal basement membrane (BM).

To address whether modifier genes influence this syndrome, the authors conducted a survey of mouse strain background effects. They first generated 129X1/SvJ mice homozygous for the hypomorphic Lamc2^jeb mutation, referred to as 129X1/SvJ-Lamc2^jeb mice. These 129X1/SvJ-Lamc2^jeb mice were backcrossed 10 generations onto four other strain backgrounds: C57BL/6J, DBA/1J, FVB/NJ, and MRL/MpJ, giving rise to the following congenic strains: B6J.129X1-Lamc2^jeb, D1.129X1-Lamc2^jeb, FVB.129X1-Lamc2^jeb, and MRL.129X1-Lamc2^jeb.

Cohorts of Lamc2^jeb/jeb males from each strain were aged, visually inspected weekly, and quantitatively scored for the severity of ear and tail lesions. Striking differences in the age of onset and the intensity of these lesions among the strains were observed, with the MRL/MpJ background showing the earliest onset, followed by C57BL/6J and DBA/1J, 129X1/SvJ, and with FVB/NJ being most resistant. Similar strain patterns were observed for females, though with delayed onset and less susceptibility to tail lesions.

To determine the inheritance patterns of susceptibility and resistance, the authors analyzed Lamc2^jeb/jeb progeny from an F1 cross of the most susceptible (MRL/MpJ) and most resistant (FVB/NJ) strain backgrounds. These results were consistent with co-dominant inheritance. Immunofluorescence imaging of tail skin confirmed separation at the plane of the lamina lucida in 78 wk old male MRL-Lamc2^jeb/jeb mice, which was not apparent at this age in FVB-Lamc2^jeb/jeb mice.

Crosses were made between phenotypically disparate strains to map the modifiers. Two groups of F2 Lamc2^jeb/jeb homozygotes were produced:

(D1.129X1-Lamc2^jeb x 129X1/SvJ-Lamc2^jeb)F2-Lamc2^jeb/Lamc2^jeb

and

(B6J.129X1-Lamc2^jeb x FVB.129X1-Lamc2^jeb)F2-Lamc2^jeb/Lamc2^jeb,

with >200 mice per group. For analysis, the F2 datasets were combined to increase the statistical power. Given that males develop disease before females, there was a strong sexual dimorphism (Prob > chi<2> 3.9 x 10<-11>.

The most robust QTL (prob > chi<2> = 7.96 x 10<-7>), replicated in both mouse crosses independent of sex and explaining 5.6% of the genetic variance, was located on Chromosome 19 with a 95% confidence interval of 34.50 cM peaking at 42 cM (GRCm38). This QTL, named Ebm1 (Epidermolysis Bullosa modifier 1), has a peak LOD score of approximately 8.2.

To more directly address the contributions of the Ebm1 QTL, the Lamc2 allele was transferred onto existing Chromosome 19 consomic stocks B6.Chr19 and B6.Chr19 and a B6.Chr19<129S1/SvImJ> congenic strain. Ear and tail scores and tail tension test comparisons indicated that the Ebm1 and Ebm1<129S1/SvImJ> alleles moderately attenuated disease and the Ebm1 allele strongly attenuated disease as compared to the Ebm1 allele. Lamc2 mice which were B6.Chr19 heterozygous were phenotypically midway between B6.Chr19 and B6.Chr19 Lamc2 mice, demonstrating that the Ebm1 alleles interact in a co-dominant manner. Overall, the results demonstrated that allelic variation limited to Chromosome 19 was sufficient to discriminate three functional Ebm1 haplotypes with C57BL/6J being most susceptible, 129S1/SvImJ and A/J being intermediate, and PWD/PhJ being most resistant.

To finely map the Ebm1 QTL, the authors used consomic and congenic reduction approaches. In all genetic contexts tested, the results were consistent with the protein-coding gene Col17a1 being the candidate gene underlying Ebm1 QTL, with the C57BL/6J and 129X1/SvJ alleles being most susceptible, A/J, DBA/1J, and 129S1/SvImJ being intermediate, and PWD/PhJ being most resistant.

References

• Original: J:211010 Sproule TJ, et al., Molecular identification of collagen 17a1 as a major genetic modifier of laminin gamma 2 mutation-induced junctional epidermolysis bullosa in mice. PLoS Genet. 2014 Feb;10(2):e1004068
• All: 1 reference(s)