Migration of cells during zebrafish morphogenesis: The movement of cells is mediated by actin structures stimulated by integrins, extracellular matrix, and ligands. Migration or cell polarization is then activated by, for example, interaction of Rho GTPases and focal adhesion complexes, and/or interactions of cadherins with p120ctn and the Rho GTPases. We are studying molecules that define the pathways of cell migration and tissue migration in zebrafish embryos. These molecules include focal adhesion kinase (FAK), paxillin, zyxin, cadherins, p120ctn, and the Rho GTPases, Rho, Rac and cdc42. We have shown that phosphorylated focal adhesion kinase (FAK) is seen on tissue boundaries such as that the notochord-somite boundary and intersomitic boundaries, consistent with a role for FAK in boundary formation. We have shown using the knypek;trilobite double mutant that the polarization of Fak mRNA distribution in somite border cells is independent of internal mesenchyme cells and likely dependent on the polarization of somite border cells (Henry et al. 2000, 2001). We have also shown that the focal adhesion protein paxillin is localized in a novel manner to either adherens or tight junctions the epithelial enveloping layer of the zebrafish. FAK is also localized to these epithelial adherens or tight junctions, but is phosphorylated in a non-canonical manner, and not on Tyr-397 (Crawford et al. submitted, 9/02). We are currently studying the roles of cadherins, p120ctn, Rho GTPases in cell polarization and migration and the cooperation of adherens junction and focal adhesions in the enveloping epithelial layer, the mesenchymal deep cells, intercalating notochord cells, and forming somites.
