Decreased MLCK activity causes bigger protrusions by increasing edge lifetime. (a) Representative edge velocity map (left) and cell contours sampled at the indicated times (right) for a 4-dpf multiple-front cell treated with 25 µM ML7 at the indicated time. The arrow indicates little change in the lateral propagation rate after drug addition. The arrowhead indicates prolonging of edge lifetime after drug addition, resulting in increased protrusion width. Data are representative of 33 independent experiments. (b–d) Mean protrusion width, lateral propagation speed, and edge lifetime measured in individual 4-dpf cells before and after DMSO control (n = 14) or 25 µM ML7 treatment (n = 33). (e) Mean change in the size of the largest protruding region and the largest retracting region in individual 4-dpf cells over time as normalized to their respective sizes before drug treatment. Shaded regions show standard error. (f and g) Change in F-actin density after MLCK inhibition. 4-dpf cells either treated with DMSO control (n = 155) or drug (n = 149) for 15 min (f) or derived from mock (n = 72) or morpholino-injected embryos (n = 79; g) were fixed and stained with 0.2 µM Texas Red-X phalloidin. Mean phalloidin intensity is shown quantified in either the entire cell or only at leading edges. **, P < 0.01; *, P < 0.05; n.s., P > 0.05 as measured by a two-sample Wilcoxon rank sum test.