The aims in this proposal are to continue fundamental studies that have provided an initial understanding of endodermal choices in development through the study of transcription factors, particularly hepatocyte nuclear factors, HNF-3alpha, beta and gamma and HNF-4 which has been the focus of our laboratory. Adult liver contains transcription factors that are also prominent in the GI tract and its accessory tissues but scarce or not present in most other adults tissues. After cloning the genes for HNF-3alpha, Beta and gamma and HNF-4, we have shown that N+HNF-3alpha and beta are expressed very early in embryogenesis, e.g. in Henson's node, even before germ layer separation. In addition HNF-4, shown earlier to be an activator of HNF-1 in cultured hepatoma cells, was found to be expressed in the very earliest liver bud. An additional critical finding that instills confidence that the HNF-3 and HNF-4 genes are important in development is the occurrence of very similar genes in Drosophila, mutations in which prevent normal gut development in the fly. The proposal for the next period of study includes molecular genetics experiments to examine differential promoter site and/or splice site utilization in the HNF-3 family and cell biology experiments to examine the signalling required to trigger HNF-4 and HNF-3 synthesis in embryonic cells and mouse genetic experiments including transgenic experiments with HNF-3 promoters. Gene inactivation by homologous recombination has already been achieved for HNF-4 and has produced embryonic lethal which are under further study. Gene knockouts for HNF-3Beta and alpha are also underway as a first test of a required role in early embryogenesis. The correct differentiation during embryogenesis of the specialized epithelial cell types is crucial to avoid developmental during embryogenesis of the specialized epithelial cell types is crucial to avoid developmental defects of the gastrointestinal tract. Furthermore, the maintenance of specialized epithelial cells through regeneration is crucial in adult life to avoid or combat many different gastrointestinal diseases including hepatitis, toxic liver damage, pancreatitis and various intestinal abnormalities such as inflammatory large and small bowel disease and many other conditions.
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