Myosin accumulates more slowly in protrusions after MLCK inhibition. (a and c) Images of mApple-myosin light chain dynamics in a representative 4-dpf cell before (a) and 2 min after 25 µM ML7 addition (c). The cell edge is represented by a series of colored dots, where color indicates the velocity of each region of the edge. Red is protruding, blue is retracting (see scale at the bottom). Bars, 10 µm. (b and d) Myosin accumulation behind the leading edge over time quantified in the representative cell shown in a and c, using an image texture score (see Materials and methods) before (b) and 2–5 min after (d) addition of ML7. Measurements were made at 200 regions around the cell perimeter and aligned to the onset of retraction for each protrusion–retraction cycle. Mean protrusion velocity and texture are shown. Shaded regions indicate standard error. (e) Time lag between retraction onset and onset of myosin texture increase as measured in 4-dpf cells before and after addition of 25 µM ML7 (n = 6). *, P < 0.05 as measured by a paired-sample t test. (f) Kymographs taken from the cell shown above. Yellow arrows show that myosin takes a longer time to accumulate in protrusions after ML7 treatment. Blue arrows show that myosin often is localized further away from the protrusion tip after ML7 treatment. Red and green lines indicate duration of protrusion (red) and retraction (green).