The Repertoire of Newly Developing Regulatory T Cells in the Type I Diabetes-Prone NOD Mouse is Very Diverse

Regulatory T lymphocytes expressing the forkhead/winged helix transcription factor Foxp3 (Treg) play a vital role in the protection of the organism from autoimmune disease and other immunopathologies. The antigen-specificity of Treg plays an important role in their <i>in vivo</i> activity. We therefore assessed the diversity of the T cell receptors for antigen (TCR) expressed by Treg newly developed in the thymus of autoimmune type I diabetes-prone NOD mice and compared it to the control mouse strain C57BL/6. Our results demonstrate that usage of the TCRa and TCRb variable (V) and joining (J) segments, length of the complementarity determining region (CDR) 3, and the diversity of the TCRa and TCRb chains are comparable between NOD and C57BL/6 mice. Genetic defects affecting the diversity of the TCR expressed by newly developed Treg therefore do not appear to be involved in the etiology of type I diabetes in the NOD mouse.

The Repertoire of Newly Developing Regulatory T Cells in the Type I Diabetes-Prone NOD Mouse is Very Diverse

Regulatory T lymphocytes expressing the forkhead/winged helix transcription factor Foxp3 (Treg) play a vital role in the protection of the organism from autoimmune disease and other immunopathologies. The antigen-specificity of Treg plays an important role in their <i>in vivo</i> activity. We therefore assessed the diversity of the T cell receptors for antigen (TCR) expressed by Treg newly developed in the thymus of autoimmune type I diabetes-prone NOD mice and compared it to the control mouse strain C57BL/6. Our results demonstrate that usage of the TCRa and TCRb variable (V) and joining (J) segments, length of the complementarity determining region (CDR) 3, and the diversity of the TCRa and TCRb chains are comparable between NOD and C57BL/6 mice. Genetic defects affecting the diversity of the TCR expressed by newly developed Treg therefore do not appear to be involved in the etiology of type I diabetes in the NOD mouse.

Disruption of foxc1 genes in zebrafish results in dosage-dependent phenotypes overlapping Axenfeld-Rieger syndrome

The Forkhead Box C1 (FOXC1) gene encodes a forkhead/winged helix transcription factor involved in embryonic development. Mutations in this gene cause dysgenesis of the anterior segment of the eye, most commonly Axenfeld-Rieger syndrome (ARS), often with other systemic features. The developmental mechanisms and pathways regulated by FOXC1 remain largely unknown. There are two conserved orthologs of FOXC1 in zebrafish, foxc1a and foxc1b. To further examine the role of FOXC1 in vertebrates, we generated foxc1a and foxc1b single knockout zebrafish lines and bred them to obtain various allelic combinations. Three genotypes demonstrated visible phenotypes: foxc1a−/− single homozygous and foxc1−/− double knockout homozygous embryos presented with similar characteristics comprised of severe global vascular defects and early lethality, as well as microphthalmia, periocular edema and absence of the anterior chamber of the eye; additionally, fish with heterozygous loss of foxc1a combined with homozygosity for foxc1b (foxc1a+/−;foxc1b−/−) demonstrated craniofacial defects, heart anomalies and scoliosis. All other single and combined genotypes appeared normal. Analysis of foxc1 expression detected a significant increase in foxc1a levels in homozygous and heterozygous mutant eyes, suggesting a mechanism for foxc1a upregulation when its function is compromised; interestingly, the expression of another ARS-associated gene, pitx2, was responsive to the estimated level of wild-type Foxc1a, indicating a possible role for this protein in the regulation of pitx2 expression. Altogether, our results support a conserved role for foxc1 in the formation of many organs, consistent with the features observed in human patients, and highlight the importance of correct FOXC1/foxc1 dosage for vertebrate development.

Foxa2-dependent hepatic gene regulatory networks depend on physiological state

Bile acids are powerful detergents produced by the liver to aid in the absorption of dietary lipids. We recently reported a novel role for Foxa2 in bile acid metabolism. The winged helix transcription factor Foxa2 is required to prevent intrahepatic cholestasis and liver injury in mice fed a cholic acid-enriched diet. Here, we use functional genomics to study how Foxa2 regulates its targets in a cholic acid-dependent manner. We found that multiple signaling pathways essential for the hepatic response to acute liver injury are impaired in livers of Foxa2-deficient mice, suggesting that the deletion of Foxa2 in the hepatocyte affects the liver on a large scale. We also discovered distinct feed-forward regulatory loops controlling Foxa2-dependent targets in a cholic acid-dependent or -independent manner. We show that Foxa2 interacts with different transcription factors to achieve gene expression responses appropriate for each physiologic state.