Interaction with the Notch intracellular domain converts the RBP-J corepressor complex into a coactivator complex and mediates

gene transcription.2 Human genetic disease and mutant mouse models have illustrated the importance of Notch signaling in the specification and remodeling of intrahepatic bile ducts (IHBDs). Alagille syndrome (AGS) is an autosomal dominant disorder in humans caused by mutations in the Notch ligand Jagged1 (JAG1) and less commonly selleck inhibitor in the Notch receptor N2.3-5 AGS is predominantly characterized by neonatal cholestasis due to paucity of IHBDs, although patients may also have significant cardiac, ocular, renal, pancreatic, and vascular defects.6 Mice heterozygous both for a null JAG1 allele and for a hypomorphic N2 mutation exhibit developmental defects similar to human AGS, including IHBD paucity.7 Recent studies in mice have further demonstrated the importance of JAG1 and N2 in causing IHBD remodeling defects,8-10 as well as identifying a role for Notch signaling in lineage commitment within the bipotential hepatoblast population. Mice with hepatoblast-specific

deletion of RBP-J demonstrate a visible decrease in specified ductal cells contributing to ductal plate formation as well as a decrease in formed ductal structures.11, 12 These studies illustrate that Notch signaling is important in the process of IHBD formation Selleck R788 in mice as well as humans. Along with Notch signaling, hepatocyte nuclear factor-6 (HNF-6, also known as Onecut-1) is one

of the few known genetic factors that affect lineage commitment within the bipotential hepatoblast progenitor cell (BHPC) population in mice, directing differentiation into either hepatocyte or biliary epithelial cell (BEC) lineages in vitro.13 medchemexpress Mice with global loss of HNF-6 display disordered and delayed IHBD development during embryogenesis, which is associated with early postnatal cholestatic liver disease and a high rate of mortality. However, the mice that survived into adulthood showed no signs of overt hepatic defects,14 suggesting that HNF-6 functions primarily during embryonic development of the biliary tract and that other genetic factors direct continued IHBD development in the absence of HNF-6. Experiments both in vitro and in vivo have shown that HNF-6 and Notch signaling modulate expression of various transcription factors, including HNF-1β and Sox9 (sex determining region Y–related HMG box transcription factor 9).12, 14-16 Inactivation of HNF-1β within the liver of mice results in severe cholestasis and paucity of IHBDs.17 Inactivation of Sox9 within the liver leads to a prolonged presence of asymmetrical primitive ductal structures during early ductal development.18 The ability of both HNF-6 and Notch signaling to modulate similar transcription factors suggests that similarities exist within their control of IHBD development.