Cdc42^−/− platelets are able to form filopodia and to spread on fibrinogen. (A) Washed platelets from the indicated mice were allowed to adhere and spread on immobilized human fibrinogen (100 μg/mL) upon activation with thrombin (0.01 U/mL). Differential interference contrast (DIC) images were taken at the indicated time points (5, 15, and 30 minutes), representative of 4 individual experiments. Scale bar equals 5 μm. (B) Statistical analysis of the percentage of spread Cdc42^−/− and wild-type platelets observed at different spreading stages at the indicated time points. 1 indicates roundish, no filopodia, no lamellipodia; 2, only filopodia; 3, filopodia and lamellipodia; and 4, full spreading, only lamellipodia. Scale bar equals 5 μm. (C) Scanning electron microscopy (SEM) of wild-type and Cdc42^−/− platelets upon spreading on 100 μg/mL fibrinogen without agonist stimulation. Scale bar equals 2.5 μm.