Branched actin polymerization is essential for pore expansion and stabilization. Time-lapse video of representative LSVs from CK666100 µM SGs undergoing full collapse (FC) and kiss-and-run (KAR; SRRF intensity-projection; corresponds to Fig 2 A). Top: FC appears as a content release that precedes actomyosin assembly. The fusion pore expands, and the vesicle appears to integrate into the apical surface. Middle: KAR w actomyosin, appearing as deformation and displacement of the LSV from the apical membrane upon actomyosin contraction. The same LSV fuse again at 11:28, suggesting it detached between fusion events. Bottom: KAR w/o actomyosin, appearing as consecutive fusion events without content release. Actomyosin was recruited after the second fusion event (01:52), leading to membrane crumpling. Time mm:ss; relative to fusion seen in the second frames. Video frames were taken every 16 s. LifeAct-Ruby (magenta; left column; expression driven by c135-GAL4) and Glue-GFP (green; middle column; endogenous promoter). The merged image of both imaging channels is presented in the right column. Scale bars = 1 µm.
