MT growth speed is directly correlated with branch frequency and inversely correlated with branch length. (A) Relationships between branch frequency (left; fold increase) or branch length (right; fold increase) and MT growth speed. r, Pearson correlation coefficient. (B, left) Outlines of a HUVEC expressing GFP-EB3 migrating in a 0.7 kPa 3D sandwich gel at 5 min intervals, color-coded by time as shown on the far left. (B, right) Color-coded MT growth track subpopulation overlays from 30-min time-lapse movies of GFP-EB3 (frame rate = 2 s) from the boxed region of selected time points during branching morphogenesis. Arrows, elongating cell branches; arrowheads, retracting cell branch. A color key for MT growth dynamics classifications is shown below. Bar, 10 µm. (C) Summary table depicting data trends (red triangles/squares) for cell branching frequency (fold change) compared with myosin II activity and MT assembly dynamics (mean values) on substrates of varying compliance in 2D and 3D ECMs. (*, Straight et al., 2003; **, Fischer et al., 2009).