Depletion of Rac1 effectors rescues the cytokinesis defect of cells expressing the CYK4 arginine finger mutant. HeLa cells expressing inducible EGFP-CYK4 or GAP activity–defective CYK4R385A were transfected with control or CYK4 3′-UTR siRNA duplexes in combination with siRNA duplexes targeting Rac1-specific effectors and Cdc42. CYK4 expression was induced for 60 h, and then, the cells were fixed and stained with antibodies to tubulin and DAPI to detect DNA. CYK4 was directly visualized by EGFP fluorescence. Binucleate cells are marked with asterisks. The number of binucleate cells was counted for each condition and plotted as in the bar graph. Error bars indicate the standard deviation from the means (n = 3). The dotted line indicates the extent of cytokinesis failure. siControl, nonsilencing control; WT, wild type. Bars, 10 µm.
