Kinetics of recruitment of the actomyosin complex onto the secretory granules. (A–C) ISMic of salivary acini in mice expressing RFP-LF (top), GFP-NMIIA (middle), and GFP-NMIIB (bottom). (A) Low magnification of individual acini shows the localization of LF, NMIIA, and NMIIB at the APM (arrows). Bars, 20 µm. (B) Time-lapse imaging of their recruitment onto the secretory granules (arrowheads). Bars, 1 µm. (C) Kinetics of RFP-LF, GFP-NMIIA, and GFP-NMIIB recruitment onto the secretory granules. The fluorescence intensity (Fluor. Int.) around the granules was measured during their integration, normalized (Norm.), and reported as a function of time, as described in Materials and methods. (Top and middle) Curves are means ± SD from one of three animals. N = number of granules. (D) Colocalization between NMII isoforms and F-actin. GFP-NMIIA (IIA) or GFP-NMIIB (not depicted) mice were injected with ISOP, and the SGs were excised after 10 min, fixed, and stained with Texas-Red Phalloidin (Ph; red). Bar, 6 µm. (Insets) A close up of the APM and the fused granules in the broken box. Arrowheads point to fused secretory granules. Bar, 2 µm. (Right) The percentage of phalloidin-labeled granules positive for either GFP-NMIIA or GFP-NMIIB (mean ± SD). n = 3 animals. NS by Student’s t test.