Our long-term research objective is to understand the cellular mechanisms involved in development and maintenance of epithelial cell polarity. Sheets of polarized epithelial cells play fundamental roles in the ontogeny and function of a variety of tissues and organs. For instance, they form barriers between biological compartments and maintain homeostasis by vectorially transporting ions and solutes between compartments. In order to do this, epithelial cells must organize the plasma membrane into apical and basal-lateral membrane domains and construct a tight gasket-like seal (tight junction) between these domains. Understanding basic mechanisms responsible for establishing and maintaining epithelial cell polarity will provide important insights into the molecular basis for major human diseases. We know that development of epithelial cell polarity is a multistage process requiring instructive extracellular spatial cues (e.g. cell-cell and cell-substratum contact) and the reorganization of proteins in the cytoplasm and on the plasma membrane. Once established, polarity is maintained by targeting and retention of proteins to the correct plasma membrane domain. Research in our lab is focused primarily on defining the cellular mechanisms responsible for faithful and efficient targeting of exocytic transport vesicles to apical and basal-lateral plasma membrane domains and understanding how these exocytic pathways are first established during epithelial polarity development. Our immediate goal is to define the role of the Sec6/8 complex (a.k.a. ""exocyst"") in epithelial polarity development. This large multi-protein complex fulfills two fundamental requirements expected of a component of a lateral membrane vesicle-targeting patch. First, upon initiation of E-cadherin-mediated cell-cell adhesion the Sec6/8 complex is recruited cell-cell contact sites, where insertion of new membrane is required. Second, it is actively involved in delivery of vesicles carrying basal-lateral proteins to these sites, but not for delivery of vesicles carrying apical proteins to non-contacting membranes. On-going research projects in the lab involve identifying the mechanisms responsible for membrane recruitment of the Sec6/8 complex, elucidating the signal transduction pathway initiated by E-cadherin-mediated cell adhesion that results in activation of Sec6/8 complex function, and designing functional assays to dissect the mechanism by which Sec6/8 complex and associated vesicle trafficking proteins operate. Our lab employs several experimental strategies to address molecular and biochemical aspects of the mechanisms involved in epithelial polarity development: (i) Analysis of membrane and cytoplasmic protein sorting, targeting and distribution in established cell lines of polarized renal epithelia in tissue culture (e.g. MDCK cells) using biochemical and immunochemical methods. (ii) In vitro studies of protein trafficking and vesicle sorting in purified and reconstituted cell systems. Identification of molecular mechanisms involved in exocytic vesicle docking and fusion in polarized epithelial cells. (iii) Structural and functional analysis of polarized exocytosis in epithelial cells; molecular genetic approaches to disrupting functions of Sec6/8 complex and associated proteins in cell culture and animal models.