Project Summary/Abstract: The vital functions of the liver—detoxification, serum protein synthesis, and bile production—critically depend on the establishment of a unique hepatic polarity and the formation of bile canaliculi (BC). Defects in these processes contribute to serious liver diseases, including cholestasis and hepatocarcinoma. Using the rat hepatocyte line Can 10, the only known cells that can proliferate and form “tubular” BCs in vitro resembling those in vivo, we discovered that hepatocyte polarization and “primordial” BC formation are linked to cytokinesis. Our collaborative work suggests that this division-linked mechanism underlies BC biogenesis in mice during liver development and regeneration. However, it remains unclear how hepatic polarity is established and maintained at the molecular level, and how a primordial BC, formed between daughter cells at the division site, is remodeled into a tubular BC nestled between aligned hepatocytes produced by oriented divisions. We hypothesize that hepatocyte polarization and BC morphogenesis require the spatiotemporal coordination of cytokinesis with adherens junction and tight junction assembly and remodeling, spindle orientation, and polarized membrane trafficking. Within this conceptual framework, we address three interrelated questions, each guided by a specific hypothesis involving key players identified from our genomic and proteomic screens. In Aim 1, we will investigate the mechanisms underlying our surprising finding that knockdown of Epithelial(E)-cadherin impairs BC elongation, whereas knockdown of Neural(N)-cadherin causes a switch from hepatic polarity to columnar polarity. While both cadherins are required for establishing hepatic polarity at the division site, E-cadherin promotes BC elongation via GEF-mediated Rho activation, whereas N- cadherin maintains hepatic polarity via GAP-mediated Rho inactivation. In Aim 2, we will determine how the actin-binding LIM domain proteins Ablim1 and Alblim3 f