Figure 4.

The Arp2/3 complex is not required for cell spreading. (A) Phalloidin stainings of Actr3^fl/fl cells (clone Arp3.19) with or without tamoxifen treatment (96 h) and subjected to cell spreading for different time points (0, 15, 60 min, and 24 h). Except for the 0-min time point, for which poly-L-lysine was used (see Methods), cells were allowed to spread on 25 μg/ml fibronectin. (B) Box and whiskers plots displaying quantification of spreading area using images as shown in (A). Boxes include 50% (25–75%) and whiskers 80% (10–90%) of all measurements. Outliers are shown as dots. Median values are given in red. n = total number of cells analyzed from three independent experiments. Differences in average cell area of control and tamoxifen-treated cells at different time points of spreading were confirmed to be statistically significant using non-parametric Mann-Whitney rank sum test (***p < 0.001). (C) Spreading kinetics of Actr3^fl/fl (EtOH/DMSO, blue) and tamoxifen-treated cells (red) reported as fold change after normalization to cell size at time point 0. Data taken from (B). Data are arithmetic means and error bars represent SEMs. Note that Arp3 knockout cells spread with kinetics highly similar to corresponding control cells, but adopt a much larger area 24 h after seeding, due perhaps to continuous increase in cell size effected by Arp3 removal.