Regulated cell movements are dramatic features of normal animal development and are essential to the wound healing process, while deregulated motility results in deadly metastasis of tumor cells. To investigate the molecular mechanisms regulating the timing and direction of cell migration during development, we have been studying a small group of migratory follicle cells in the Drosophila ovary, referred to as border cells. One locus required for border cell migration is slow border cells (slbo), which encodes Drosophila C/EBP, a transcriptional regulator. Several putative downstream targets of c/EBP have been identified in the border cells, including a fibroblast growth factor receptor (FGFR) homolog, which is a receptor tyrosine kinase (RTK). RTK- mediated cell motility is a phenomenon of general interest and importance. To test the hypothesis that regulated FGFR activity guides cell migration, we propose to analyze the effects of expressing a constitutively active FGFR protein. To determine the importance of Ras signaling in the migration process, we propose to monitor changes in Ras activity during cell migration, using a fluorescent fusion protein that binds specifically to activated Ras. In order to elucidate the signaling pathway mediating the migration response, we propose to identify effectors of the FGFR. Proteins known to affect cell morphology in response to growth factor treatment of tissue culture cells are those of the Rho family of 21 kd GTPases. We have shown that the Rho family member Rac is essential to border cell migration whereas Cdc42 is not. We propose to determine which of the two Drosophila Rac proteins is required and to test whether Rho activity is also essential for the migration. A second putative target of slbo in the border cells is defined by enhancer trap insertion dts3. Reporter gene expression in this line is at highest levels in the border cells and in the oocyte, the cell towards which the border cells migrate. In a slbo mutant background, the border cell expression of this line is greatly reduced. Furthermore mutant alleles of this locus display border cell migration defects. We have cloned and sequenced cDNAs from the locus. We propose to test whether graded expression of this novel 1107 amino acid protein, along the migration path, is essential to the migration process. We also propose to test the hypotheses that Dts3 associates with the cytoskeleton and is regulated by tyrosine phosphorylation.
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