Formation and disassembly of a contractile actomyosin network mediates content release from large secretory vesicles

Secretion of adhesive glycoproteins to the lumen of Drosophila larval salivary glands is carried out by contraction of an actomyosin network that is assembled around large secretory vesicles, following their fusion to the apical membranes. We have identified a cycle of actin coat nucleation and disassembly that is independent of myosin. Recruitment of active Rho1 to the fused vesicle triggers activation of the formin Diaphanous and nucleation of linear actin. This, in turn, leads to actin-dependent localization of a RhoGAP protein that locally shuts off Rho1, promoting disassembly of the actin coat. Recruitment of the branched actin nucleation machinery is also required for effective Rho1 inactivation. Interestingly, different blocks to actin coat disassembly arrested vesicle contraction, indicating that actin turnover is an integral part of the actomyosin contraction cycle. The capacity of F-actin to trigger a negative feedback on its own production may be utilized in a variety of scenarios, to coordinate a succession of morphogenetic events or maintain homeostasis. . CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/216044 doi: bioRxiv preprint first posted online Nov. 8, 2017;