Acute inhibition of branched actin polymerization results in an accumulation of stalled, actomyosin coated, LSVs with narrow pores. Left: Time-lapse video of a representative SG treated with an acute dose Arp2/3 inhibitor CK666 (confocal Z-projection; corresponds to Fig. 2 D). Upon treatment with CK666500 µM (time 00:00), secretion slows down quickly while stalled, actin-coated LSVs accumulate at the cell apical membrane. Less fusion events are detected as time progresses. Right: Time-lapse video of a representative LSV (SRRF intensity-projection) stalled with a narrow pore that arrests before completing expansion under CK666500 µM treatment (corresponds to Fig. 2 E). Time mm:ss; relative to CK666 treatment (left; first frame) and to fusion (right; second frame). Video frames were taken every 16 s. On the left panel, the merged image of both imaging channels is presented, on the right, the LifeAct-Ruby (magenta; expression driven by c135-GAL4) is presented on top, the Glue-GFP (green; endogenous promoter) is presented in the middle, and the merged on the bottom. Scale bar, 20 µm (left) and 1 µm (right).
