Interplay between Rab5 and PtdIns(4,5)P₂ controls early endocytosis in the Drosophila germline

Julien Compagnon, Louis Gervais, Mabel San Roman, Sophy Chamot-Buf, and Antoine Guichet^*

Phosphoinositides have emerged as key regulators of membrane traffic through their control of the localization and activity of several effector proteins. Both Rab5 and phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P₂] are involved in the early steps of the clathrin-dependent endocytic pathway, but little is known about how their functions are coordinated. We have studied the role of PtdIns(4,5)P₂ and Rab5 in the Drosophila germline during oogenesis. We found that Rab5 is required for the maturation of early endocytic vesicles. We show that PtdIns(4,5)P₂ is required for endocytic-vesicle formation, for Rab5 recruitment to endosomes and, consistently, for endocytosis. Furthermore, we reveal a previously undescribed role of Rab5 in releasing PtdIns(4,5)P₂, PtdIns(4,5)P₂-binding budding factors and F-actin from early endocytic vesicles. Finally, we show that overexpressing the PtdIns(4,5)P₂-synthesizing enzyme Skittles leads to an endocytic defect that is similar to that seen in rab5 loss-of-function mutants. Hence, our results argue strongly in favor of the hypothesis that the Rab5-dependant release of PtdIns(4,5)P₂ from endosomes that we discovered in this study is crucial for endocytosis to proceed.