Sex-specific genetic dissection of diabetes in a rodent model identifies Ica1 and Ndufa4 as major candidate genes

Abstract

The aim of the study was to initiate a sex-specific investigation of the molecular basis of diabetes, using a genomic approach in the Cohen Diabetic rat model of diet-induced Type 2 diabetes. We used an F2 population resulting from a cross between Cohen Diabetic susceptible (CDs) and resistant (CDr) and consisting of 132 males and 159 females to detect relevant QTLs by linkage and cosegregation analyses. To confirm the functional relevance of the QTL, we applied the “chromosome substitution” strategy. We identified candidate genes within the quantitative trait locus (QTL) and studied their differential expression. We sequenced the differentially expressed candidate genes to account for differences in their expression. We confirmed in this new cross in males a previously detected major QTL on rat chromosome 4 (RNO4); we identified in females this major QTL as well. We found three additional diabetes-related QTLs on RNO11, 13, and 20 in females only. We pursued the investigation of the QTL on RNO4 and generated a CDs.4CDr consomic strain, which provided us with functional confirmation for the contribution of the QTL to the diabetic phenotype in both sexes. We successfully narrowed the QTL span to 2.6 cM and identified within it six candidate genes, but only two of which, Ica1 (islet cell autoantigen 1) and Ndufa4 (NADH dehydrogenase ubiquinone) were differentially expressed between CDs and CDr. We sequenced the exons and promoter regions of Ica1 and Ndufa4 but did not identify sequence variations between the strains. The detection of the QTL on RNO4 in both sexes suggests involvement of Ica1, Ndufa4, the Golgi apparatus, the mitochondria and genetic susceptibility to dietary-environmental factors in the pathophysiology of diabetes in our model. The additional sex-specific QTLs are likely to account for differences in the diabetic phenotype between the sexes.

Three Interacting Genomic Loci Incorporating Two Novel Mutations Underlie the Evolution of Diet-induced Diabetes

“…In our previous studies, focusing primarily on the initiation phase of diabetes, we detected after 1 month of DD one major genomic locus on RNO4, which failed, however, to explain the full genetic variation of the diabetic phenotype at that time point (3,2). In the current study, we confirmed the same genomic locus on RNO4 but established, based on a high LOD score at 1 month that gradually diminished after 2.5 and Figure 5.…”

“…We performed cosegregation analysis at each quantitative trait locus (genomic locus) detected by linkage analysis, as previously described (3,2). In brief, we compared by ANOVA the phenotype in F2 between those with the various phases of the development of diabetes.…”

“…We incorporated in this mode of analysis data from the current F2 cross between CDs/y and SBN/y (166 animals), as well as relevant data from two previous F2 crosses between CDs/y and CDr/y (233 animals) (3,2).…”

“…Thereafter, diabetes in this model evolves into its chronic phase over the subsequent months, as long as the animals continue to be fed with DD (3,2).…”

“…We have previously focused our studies on the pathophysiology of diabetes during the induction phase of diabetes after the first 4 weeks of exposure to DD (3,2). In the current study, we adopted an integrative genomic approach to investigate the evolution of diabetes during its different phases, from its initiation into its chronic phase.…”