Markedly reduced peripheral platelet counts and abnormal platelet ultrastructure in ADF/n-cofilin–null mice. (A) Peripheral platelet counts were determined by flow cytometry. Results are mean ± SD (n = 6). ***P < .001. (B left, C) TEM analysis of resting platelets. Boxed area in panel C shows accumulation of filamentous material (see also higher magnification). (B right) Visualization of the cytoskeleton of resting platelets on poly-L-lysine. (D) SEM after denudation of the membrane of an ADF/n-cofilin–null platelet spread for 60 minutes on fibrinogen. Scale bars represent 2 μm (B left, D), 1 μm (B right), and 0.5 μm (C).