4-dpf cells have multiple protrusions because the protrusions are intrinsically small. (a) Example force–time curve showing a membrane tether force quantification. A concanavalin A–coated AFM cantilever is brought into contact with the cell for 10 s and then withdrawn. At this time, a membrane tether connecting the cell to the cantilever produces a negative force reading. After tether breakage, the force experienced by the cantilever returns to zero. The difference between the prebreakage and postbreakage force is quantified as the tether force. (b) Tether force was measured in 2-dpf (n = 25) and 4-dpf single-front (n = 8), and 4-dpf multiple-front (n = 15) cells. n.s., P > 0.05 as measured by a two-sample t test. (c) Mean protrusion width measured in individual 2-dpf (n = 61) and 4-dpf (n = 157) multiple-front cells. **, P < 0.01 as measured by a two-sample Wilcoxon rank sum test. (d) A representative 2-dpf single-front cell (top) or 4-dpf multiple-front cell (bottom) treated with 10% DMSO to depolymerize F-actin. Time shown in minutes before/after DMSO addition/washout. Images are representative of 2-dpf (n = 12) and 4-dpf (n = 35) cells. Blue lines indicate protrusions. Bars, 10 µm. (e) Mean protrusion width before and after DMSO washout as measured in individual 4-dpf multiple-front cells (n = 35). The gray shaded region indicates the duration of DMSO treatment. The blue shaded region represents standard error. (f) The mean width of protrusions before DMSO addition, and width of the first protrusion after DMSO washout were measured in individual cells (n = 35). n.s., P > 0.05, paired-sample t test. (g) Mean edge width plotted against the product of mean edge lifetime and mean lateral propagation rate for individual 4-dpf multiple-front cells (n = 154). The broken line is y = x.