The mechanism by which cells migrate is well understood in vitro but far less is known about how invasive migration occurs within a three dimensional tissue. Migration of border cells in the Drosophila ovary provides excellent model system for this. Border cells delaminate from an epithelium surrounding the germ line tissue and migrate, as an 8-cell cluster, directionally towards the oocyte. To migrate, border cells must actively invade the germ line tissue. Studying their migration may therefore provide better understanding of how cancer cells metastasise.
Genetic studies have defined signalling molecules involved in guiding the migration: Two Receptor Tyrosine Kinases, PVR (PDGF/VEGF Receptor) and EGFR, act as guidance receptors. A small GTPase, Rac, and sp ecific Rac exchange factors, act downstream of the receptors. Studies of fixed tissues have also given some insight into the mechanism of migration: One border cell within the cluster initiates migration by extending a very long cellular extension (LCE) in the direction of migration. LCEs may provide the mechanical force for migration, pulling the border cell cluster towards the oocyte. What is missing for understanding the mechanism of spatially controlled guidance signalling and mechanism of movement i s to visualize these events dynamically.
I propose to develop a method of culturing and imaging Drosophila ovaries in order to observe border cell migration in real time. I will observe the behaviour of border cells and their LCEs in live ovaries to determine how the cell cluster translocates. I will also construct Fluorescence Resonance Energy Transfer (FRET) constructs to monitor the activities of the PVR and EGFR receptors, as well as Rac activity. This will allow me to study the spatial activation of RTK signalling and Rac activity in real time. Finally, I intend to apply the tools I generate to other models of motility, such as migration of hemocytes in the Drosophila embryo.
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