Many secretory organs utilize giant vesicles (ranging in size from 2 to 10 microns in diameter) to expel their contents. Following fusion to the apical membrane, these vesicles are typically coated by actomyosin to facilitate cargo release. Maintenance of membrane homeostasis is a major challenge in situations of prolonged secretion phases. We are addressing this issue in the Drosophila larval salivary gland that secretes glue proteins. We identified a novel mechanism of secretion termed “crumpling”: During cargo release to the lumen, the vesicle membrane folds and remains insulated from the apical membrane. Clathrin-mediated endocytosis subsequently recycles the vesicle membrane.

The talk will present two mechanisms that facilitate vesicle crumpling. Punctate recruitment of RhoGEF from the cytoplasm to the fused vesicle membrane drives anisotropic recruitment of Myosin II, which executes membrane folding. To insulate the vesicle membrane during secretion, a specialized pore “neck” structure is formed. Identification of a BAR-domain protein that is essential for the process sheds light on the dynamics of pore formation and its roles.