ARPC3^−/− fibroblast cells are deficient in lamellipodia formation. (A and B) Representative phase-contrast images showing the morphology of ARPC3^+/+ (A) and ARPC3^−/− (B) fibroblast cells after 7 d of differentiation. Arrows indicate lamellipodia (wild type) and FLPs (mutant). Bar, 50 µm. (C and D) Time-lapse montage showing spreading morphology of ARPC3^+/+ (C) and ARPC3^−/− cells (D) on 5 mg/ml fibronectin-coated glass surface. Frame interval is 15 min. Bars, 15 µm. (E) Quantification of cell area from experiments as described in C and D. Plots show mean and standard error of the mean (SEM) from 13 (APRC3^+/+) and 11 (APRC3^−/−) spreading cell movies made in three different experiments.