Interestingly, we found a robust genetic interaction between Rab11 and Rac1, which directs border cell migration (22). also affects migration. Together, our data demonstrate a fundamental role for a plasma membraneCendosome trafficking cycle in the maintenance of active RTK at the leading edge of border cells during their migration. egg chamber is a potent model system to study the directed migration of a cluster of cells through a complex tissue (1, 2). Directed migration implies that cells are able to integrate an extracellular signal that forms a gradient along the length of the cell. Migrating cells need to convert a subtle gradient into a robust intracellular polarization, which might be achieved through feedback loops (2). BMS-777607 During border cell migration, the extracellular signals are ligands of receptor tyrosine kinases (RTK). The receptors on which they act are the epidermal growth factor receptor (EGFR) and PVR, which is the sole homolog of the platelet-derived growth factor receptor and vascular endothelial growth factor receptor (3). Endocytosis is the general name given to the process by which cells uptake extracellular material and plasma membrane proteins and lipids inside the cell (4). The endocytic pathway is composed of the different compartments reached successively by endocytosed material packed into vesicles at the plasma membrane. The first compartment reached by these vesicles is called the early or sorting endosome. From that compartment, proteins are sorted to different routes. Proteins can be sent to the degradative pathway composed of late endosomes and lysosomes. They can also be targeted back to the plasma membrane, either directly or via the slow recycling route through the recycling endosome compartment (5, 6). Different lines of BMS-777607 evidence point to a fundamental role for endocytosis during cell migration (7). Indeed, key proteins involved in migration are regulated by the endocytic pathway, including cell attachment proteins, such as cadherins (8) and integrins (9), as well as guidance receptors during directed migration (10). Trafficking between the different stations of the endocytic pathway is controlled by specific small GTPases of the Rab family (11). BMS-777607 Rab5 regulates transport through the early endosome, Rab4 through the rapid recycling pathway, Rab11 through the recycling endosome, and Rab7 to late endosomes. Furthermore, another endosomal Rab protein has been recently characterized in and was named RabX4 (12). Small GTPases can be locked into an active form or an inactive form by a single-amino-acid change. In BMS-777607 the latter case, the Rab mutants have a dominant negative effect as they trap guanine nucleotide exchange factors (GEF) and thereby maintain their wild-type counterpart in an inactive form. Thus, expressing a dominant negative Rab causes a loss of function of this particular Rab protein and eventually blocks the transport step regulated by this Rab. By using such dominant negative Rab proteins, we identified Rab5 and Rab11 as necessary for border cell migration. We focused our analysis on the role of Rabbit Polyclonal to APBA3 Rab11 and of the recycling endosome in this process and found that this transport step is key for the maintenance of RTK activity at the leading edge of migrating cells. The exocyst is a complex of eight proteins involved in the delivery of material to the plasma membrane (13, 14). We found that the Sec15 subunit is polarized during cell migration. Because Sec15 is a Rab11 binding protein (15, 16), we tested further the relationship between these two proteins. We found that Sec15 polarity is controlled by activity and that and other subunits of the exocyst are necessary for the spatial restriction of RTK activity and for border cell migration. Altogether, we show the requirement of a trafficking loop between the plasma membrane and the recycling endosome for collective cell migration in vivo. This loop regulates the spatial restriction.