Cell migration is a fascinating feature of embryonic development, and improperly regulated cell migration contributes to birth defects and tumor metastasis. We have developed a simple model system for a forward genetic approach to the study of cell motility in vivo, the migration of a subset of follicle cells, known as border cells, in the Drosophila ovary. We have established that multiple extracellular signals regulate their movement. 1) a global steroid hormone signal, ecdysone, acting through the ecdysone receptor and a transcriptional coactivator called Taiman; 2) a highly localized cytokine signal, which activates the JAK/STAT pathway; and 3) several growth factors, which signal through the EGFR and PVR receptor tyrosine kinases to guide the cells to their destination. In addition we have studied a variety of cytoskeleton-associated proteins and cell adhesion molecules that function in border cell migration. This proposal explores the mechanisms by which cell adhesion is dynamically regulated in migrating border cells, an important aspect of cell motility that is not well understood for any cell type. We propose three specific aims. The first is to investigate the mechanisms that govern trafficking and stability of E-cadherin, a homophilic cell-cell adhesion molecule that is required in border cells and in the cells upon which they migrate. To test whether E-cadherin is turned over more rapidly in border cells than in non-migrating follicle cells, we will employ a previously characterized variant of the red fluorescent protein that changes color over time, fused to E-cadherin. We will investigate whether EGFR and PVR signaling destabilizes cell adhesion by phosphorylation of specific tyrosine residues on beta-catenin/Armadillo. We will also determine whether endocytosis is important for regulating cell surface E-cadherin in migrating border cells. We will test whether Drosophila moesin contributes to E-cadherin dynamics. And we will investigate the mechanisms by which Myosin VI contributes to E-cadherin dynamics in border cells. In the second specific aim we propose to investigate in detail the mechanisms by which RhoGAP93B contributes to border cell migration by studying its biochemical activity, its expression pattern, subcellular localization, lethal phenotype and its regulation. Finally we propose to study a putative downstream target of Rho in border cells, rhophilin by characterizing the mutant phenotype, epistasis analysis with Rho and by identifying and characterizing interacting proteins.
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