Myo-II contractile pulses require MBS. (A) MBS is apically enriched in ventral furrow cells. Images of XY semisagittal and YZ cross sections for fixed sqh::GFP embryos stained for MBS. Bar, 10 µm. (B) MBS structures colocalize with Myo-II foci and the supracellular Myo-II meshwork (arrowheads). Images are from fixed sqh::GFP embryos stained for MBS. Bars, 5 µm. Segmented cell outlines are from subapical sqh::GFP signal. (C) MBS colocalizes with Rok foci (arrowheads). Images are from fixed GFP::Rok embryos stained for MBS. Bars, 5 µm. Segmented cell outlines are from subapical Rok signal. (D and E) MBS knockdown inhibits Myo-II pulses. Time-lapse images are cells from embryos expressing control-shRNA (ctl-shRNA) (D) or MBS-shRNA (E), sqh::GFP (Myo-II), and Memb::Cherry (membrane). (F) Quantification of Medioapical polarity in Myo-II organization (n = 115 ctl-shRNA cells, two embryos; n = 123 MBS-shRNA cells, two embryos). Error bars are SEM. (G) Frequency of rapid increases of Myo-II intensity (n = 82 ctl-shRNA cells, two embryos; n = 70 MBS-shRNA cells, three embryos). Error bars are SEM. (H) Mean cross-correlation between constriction rate and change in Myo-II intensity for cells as a function of time offset (n = 118 ctl-shRNA cells, two embryos; n = 84 MBS-shRNA cells, three embryos). P-values were calculated at 0 time offset. **, P < 0.01; n.s, not significant.