3D traction forces during cell division. (A) For cells treated with blebbistatin, the distribution of angles (θ) between the protrusion and division axes cannot be distinguished from a uniform distribution (K-S test, P > 0.18, n = 17). The mean interaxis angles are significantly different in the presence and absence of blebbistatin (n = 17 and n = 23, respectively; *, P < 0.05, Mann-Whitney-Wilcoxon test). (B) 3D maximum intensity projections of fluorescent particles around a rounding cell (t = 0) and daughter cells (t = 210 min). (C) Quiver plots of 3D matrix displacements show that the cell applies traction to the matrix primarily at the tips of its long protrusions during division (t = 0, arrowheads). Approximately 3 h after division, the daughter cells apply displacements to other regions of the matrix as they respread. See Videos 7–9 for additional time points. (D) During rounding, cells cause larger matrix displacements near the tips of cellular protrusions than near the cell body (**, mean significantly <1; Student’s t test, P < 0.01, n = 7).