The R-SNARE Ykt6 is required for multiple events during oogenesis in Drosophila

Ykt6 has emerged as a key protein involved in a wide array of trafficking events, and has also been implicated in a number of human pathologies, including the progression of several cancers. It is a complex protein that simultaneously exhibits a high degree of structural and functional homology, and yet adopts differing roles in different cellular contexts. Because Ykt6 has been implicated in a variety of vesicle fusion events, we characterized the role of Ykt6 in oogenesis by observing the phenotype of Ykt6 germline clones. Immunofluorescence was used to visualize the expression of membrane proteins, organelles, and vesicular trafficking markers in mutant egg chambers. We find that Ykt6 germline clones have morphological and actin defects affecting both the nurse cells and oocyte, consistent with a role in regulating membrane growth during mid-oogenesis. Additionally, these egg chambers exhibit defects in bicoid and oskar RNA localization, and in the trafficking of Gurken during mid-to-late oogenesis. Finally, we show that Ykt6 mutations result in defects in late endosomal pathways, including endo- and exocytosis. These findings suggest a role for Ykt6 in endosome maturation and in the movement of membranes to and from the cell surface.