In SituHybridization with33P-Labeled RNA Probes for Determination of Cellular Expression Patterns of Liver Transcription Factors in Mouse Embryos☆

Abstract Murine hepatocyte nuclear factor-3β (HNF-3β) protein is a member of a large family of developmentally regulated transcription factors that share homology in the winged helix/ fork head DNA binding domain and that participate in embryonic pattern formation. HNF-3β also mediates cell-specific transcription of genes important for the function of hepatocytes, intestinal and bronchiolar epithelium, and pancreatic acinar cells. We have previously identified a hepatocyte and pancreatic cut-homeodomain transcription factor, HNF-6, which is required for HNF-3β promoter activity. In this study, we used in situ hybridization studies of stage-specific embryos to demonstrate that HNF-6 and its target gene, HNF-3β, are coexpressed in the foregut endoderm and in the pancreatic and hepatic diverticulum. More detailed analysis of HNF-6 and HNF-3β's developmental expression patterns provides evidence of colocalization in hepatocytes, intestinal epithelium, and pancreatic ductal epithelium and exocrine acinar cells. In support of the role of HNF-6 in regulating HNF-3β expression in developing hepatocytes, their liver expression levels are both transiently reduced between 14 and 15 days of gestation. At day 18 of gestation and in adult pancreas, HNF-6 and HNF-3β transcripts remain colocalized in the exocrine acinar cells, but their expression patterns diverge in endocrine cells. HNF-3β expression is restricted to the endocrine cells of the islets of Langerhans, whereas the ductal epithelium expresses HNF-6. We discuss these expression patterns with respect to specification of hepatocytes and differentiation of the endocrine and exocrine pancreas.