Wangsun Choi       2009-present Postdoctoral Fellow Ph. D. University of Kentucky

Exploring the roles of Canoe/Afadin and Pyd/ZO-1 in adhesion and cytoskeletal regulation

Cells undergo coordinated changes in shape and position during animal development. This process of morphogenesis requires cells to be able to interact with other cells and the extracellular matrix, and to be able to modulate both adhesion and the connections of cell-cell and cell-matrix junctions with the actin cytoskeleton. Adherens junctions (AJs) are the major sites of cell-cell contact in epithelial cells and this multi-protein complex also links the cytoskeleton of adjacent cells. While the key components of AJs are known, there are other proteins that are recruited AJs whose functions are less well understood. These presumed non-core AJ proteins may act redundantly to modulate junctions by regulating connections to the actin cytoskeleton or to signal transduction machinery.

Two presumed non-core AJ proteins are Canoe (Cno/AF-6) and Polycheatoid (Pyd/ZO-1). Studies of the mammalian homolog of Cno, AF-6, suggest that it plays a key role in AJs. The primary function of mammalian ZO-1 is in the tight junctions, but there is some evidence that it plays a transient role in the AJs. Both Cno and Pyd localize to the AJs in flies and have been found to genetically and physically interact. However, the role(s) of Cno and Pyd in AJs remains unclear. We generated null alleles of the single Drosophila ZO protein Polychaetoid (Pyd). Most embryos lacking Pyd die with striking defects in morphogenesis of embryonic epithelia including the epidermis, segmental grooves and tracheal system. Pyd loss does not dramatically affect AJ protein localization, or initial localization of actin and myosin during dorsal closure. However, Pyd loss does affect several cell behaviors that drive dorsal closure. The defects, which include segmental grooves that fail to retract, a disrupted leading-edge actin cable, and reduced zippering as leading edges meet, closely resemble defects in canoe zygotic null mutants, and in embryos lacking the actin regulator Enabled, suggesting these proteins act together. Canoe and Pyd are required for proper Enabled localization during dorsal closure, and strong genetic interactions suggest that Canoe, Pyd and Ena act together in regulating or anchoring the actin cytoskeleton during dorsal closure.

Publications

Choi, W. , Jung, K.-C., Nelson, K.S., Bhat, M.A., Beitel, G.J., Peifer, M., and Fanning, A.S. (2011). The single Drosophila ZO-1 protein Polychaetoid regulates embryonic morphogenesis in coordination with Canoe/Afadin and Enabled. Molecular Biology of the Cell, in press.

Sawyer, J.K., Choi, W. , Jung, K.-C., Hi, L., Harris, N.J., and Peifer, M., (2011). A contractile actomyosin network linked to adherens junctions by Canoe/afadin helps drive convergent extension. Molecular Biology of the Cell, in press.

Choi W., Karim Z. A., Whiteheart S. W. (2010) Protein Expression in Platelets from Six Species that Differ in their Open Canalicular System. Platelets 2:167-75

Karim Z.A., Choi W., Whiteheart S.W. Primary platelet signaling cascades and integrin-mediated signaling control ADP-ribosylation factor (Arf) 6-GTP levels during platelet activation and aggregation. J. Biol. Chem. 2008 28:11995-2003.

Ren Q., Barber H.K., Crawford G.L., Karim Z.A., Zhao C., Choi W., Wang C.C., Hong W., Whiteheart S.W. Endobrevin/VAMP-8 is the primary v-SNARE for the platelet release reaction. Mol. Biol. Cell. 2007 18:24-33.

Choi W., Karim Z.A., Whiteheart S.W. Arf6 plays an early role in platelet activation by collagen and convulxin. Blood. 2006 107:3145-3152

Schraw T.D., Crawford G.L., Ren Q., Choi W., Thurmond D.C., Pessin J., Whiteheart S.W. Platelets from Munc18c heterozygous mice exhibit normal stimulus-induced release. Thromb. Haemost. 2004 92:829-37.

Choi W., Eum S.Y., Lee Y.W., Hennig B., Robertson L.W., Toborek M. PCB 104-induced proinflammatory reactions in human vascular endothelial cells: relationship to cancer metastasis and atherogenesis. Toxicol. Sci. 2003 75:47-56.