Polygenic disease

Functional genomics in early autoimmunity

The molecular mechanisms initiating the autoimmune process in type 1 diabetes mellitus (T1DM) remain unknown, and studies aiming to address this question have been compromised by the difficulty of predicting the disease at an early age both in humans and in animal models. An additional hindrance in selecting individuals at an early age has been the complex genetic inheritance of autoimmune diabetes, implicating not only several genes but also environmental factors. We have previously demonstrated the predictive value of insulin autoantibodies (IAAs) at an early age, between three to five weeks in the NOD mouse. Animals positive for early appearance of IAAs (E-IAAs) develop autoimmune diabetes earlier. We showed a correlation between the presence of IAAs in the mothers during pregnancy, E-IAAs in the litters, and the early appearance of T1DM. NOD mice, E-IAA-positive, within litters from IAA-positive mothers during pregnancy, develop diabetes earlier and at a much greater rate than animals that are IAA-negative and from IAA-negative mothers. The molecular mechanisms responsible for this early autoimmune subphenotype were addressed by a global approach to differential gene expression analysis in the pancreatic lymph nodes (PaLNs). Although the data analysis is currently in progress, gene expression signatures were observed that are characteristic for PaLNs with regard to the presence or absence of IAAs. Overall, these data are consistent with the hypothesis of an early environmental influence from the autoimmune maternal environment on the genetic predisposition of the offspring, characterized by specific gene signatures leading to autoimmune disease.

Complex traits and polygenic inheritance in the mouse

Polygenic inheritance has recently become an increasingly active field of research due to the availability of techniques allowing in-depth screening of genetic markers across the entire genome. The mouse is being used both in its own right and as a model system for certain human traits. The advantages and disadvantages of the mouse for such studies are outlined and in this context, the adequacy of the mouse as a model for polygenic traits in humans is discussed. A detailed overview of the approaches and methods used in the analysis of polygenic inheritance in the mouse is presented.

Colorectal hyperplasia and inflammation in keratin 8-deficient FVB/N mice

We report that keratin 8 (mK8) gene disruption causes colorectal hyperplasia in FVB/N mice. The intestinal lesions affect uniformly the cecum, colon, and rectum but not the small intestine. The elongation of the crypts is accompanied by an inflammation of the lamina propria and submucosa. Hepatic, renal, and pancreatic functions tested in clinical assays are within nonpathological range, suggesting that the major defect lies in colonic epithelial cells. Still, small but consistent elevation in the hepatic enzymes alanine (AST) and asparate (ALT) aminotransferase are observed, along with a 70% increase in spleen weight. No homozygous mouse line has been established, because of a markedly reduced fertility of the mK8-/- females. Previously, we reported that the mK8- targeted mutation causes embryonic lethality in (C57B1/6x129Sv) mice. This strong effect of the genetic background on the mK8- mutant phenotype emphasizes the importance of using several inbred mouse strains to reveal the polygenic contribution to mutant phenotypes. Our results demonstrate that genetic modifiers of K8/K18 filament functions, with profound effects on embryogenesis and gut functional integrity, are differentially active in the FVB/N and C57B1/6 genetic backgrounds. More importantly, the increase in mK8-/- gut epithelial cell number, rather than cell disruption, contrasts with the known function of epidermal keratins in providing mechanical strength.