Contractomeric myosin II activity is linked to actin accumulation. (A) Immunofluorescence showing synaptopodin (synpo) colocalization with latrunculin-resistant actin puncta at the apical junction. Scale bar is 2 μm. (B) Immunofluorescence showing myosin IIB colocalization with actin puncta. Scale bar is 1 μm. (C) Myosin II inhibition by blebbistatin prevents the formation of latrunculin-resistant actin at the apical junction. Scale bar is 2 μm. (D) Myosin II inhibition by blebbistatin (Bleb) prevents the formation of latrunculin (LatB)-resistant actin either in the presence or absence of cytochalasin D (CytoD). Graphs show intensity measurements of actin on individual contractomeres. Bars mark the means. N (untreated) = 101, n (Bleb) = 146, n (LatB) = 101, n (LatB + Bleb) = 109, n (LatB + CytoD) = 100, n (LatB + CytoD + Belb) = 114. Wilconox–Mann–Whitney test P < 0.0001 between untreated and blebbistatin treated groups for all three graphs. Scale bar is 10 μm. (E) Non-invasion wound healing assay showing the formation of latrunculin-resistant actin surrounding the wound edge (circled). Latrunculin-resistant actin puncta are formed after 1-h incubation with cytochalasin D (CytoD) and latrunculin B (Lat B), but are absent when myosin II was inhibited by blebbistatin (Bleb). In untreated cells, control wound is closed in an hour. Upper right panels show phase-contrast images of MDCK dome before wounding. Scale bars are 10 μm.