Altered tubulin structure in Rac1/Cdc42^-/- MKs is associated with changes in cofilin activation. (A) Analysis of actin and tubulin structure in early proplatelet-forming MKs by confocal microscopy. Representative stainings for actin, tubulin, and DAPI from at least 3 different samples per group are shown. Bar, 25 µm. (B) Increased phosphorylation of cofilin and LIMK, and reduced expression level of IQGAP1 in Rac1/Cdc42^−/− MKs. Western blot analysis of FLC-derived MKs. MKs on day 3 of culture were purified with a bovine serum albumin gradient, and protein lysates were obtained. Equal amounts of proteins were loaded, and the expression was detected with specific antibodies and quantified by densitometry with Image J software (National Institutes of Health). Shown blots are representative of at least 3 independent samples. **P < .01; *P < .05.