Actin filament dynamics regulated by IQGAP1 influence the morphology and migration of NIH-3T3 cells. (A) Representative images of phalloidin-stained actin filaments from NIH-3T3 (expressing endogenous MmIQGAP1) compared with IQGAP1 knockout cells lacking (mock) or expressing HsIQGAP1 (untagged and SNAP-tagged) and SNAP-HsIQGAP1(BAD). Zoomed insets (bottom panels) highlight single cells. Scale: top, 100 µm; bottom, 25 µm. (B) Cell circularity measurements from cells in A (n = 151–261 cells, pooled from 3 different coverslips). Error bars, SE. Statistics, ANOVA: (a) P ≤ 0.05 compared with endogenous; (b) P ≤ 0.05 compared with mock (IQGAP1 knockout cells); (c) P ≤ 0.05 compared with IQGAP1 knockout cells expressing a SNAP-IQGAP1 plasmid; ns, P ≥ 0.05 compared with IQGAP1 knockout cells expressing an untagged IQGAP1 plasmid. (C) Cells as in A, plated on micropatterns. Scale, 10 µm. (D) Quantification of total actin signal from cells in C (n = 29–35 cells per condition). Error bars, SD. Statistics, ANOVA: comparisons as in B. (E) Mock and IQGAP1(BAD) cells do not migrate as effectively as cells expressing IQGAP1 in wound healing assays. Representative images from the same trial are shown 12 h after wounding event. Scale, 250 μm. (F) Quantification of wound healing assays in E. Dots represent normalized closure values for FOVs along the wound (n = 7–11 FOVs) from each condition, with shading grouped by n = 3 independent replicates. Statistics, ANOVA with comparisons as in B. (G) Model of IQGAP1 plus-end activities in cells. Disruption of IQGAP1 (green) results in less turnover of actin filament end binding proteins including formin (pink) and capping protein (yellow). Fewer IQGAP1-mediated transitions promote aberrant cell morphology and actin structures as filaments suffer prolonged capping or growth events.