CD151^–/– platelets have a defect in integrin-dependent cytoskeletal reorganization. (A) Washed platelets were placed on coverslips coated with fibrinogen in the presence of PGE₁ for different time points at 37° C. Platelets were fixed, permeabilized, and stained for F-actin using rhodamine-conjugated phalloidin. Representative pictures of rhodamine-conjugated phalloidin-stained platelets spread on a fibrinogen surface for wild-type and CD151-deficient mice. The slides (panel A) were viewed under fluorescence microscopy using a Leitz DMRBE microscope (Leica, Hawthorn East, Victoria, Australia). Images were captured using a Leica DC200 digital camera. Magnification × 100. (B) Quantitation of platelet spreading per high-powered field was analyzed on confocal images from 8 random fields and expressed as a percentage of the total adherent platelets from CD151^+/+ and CD151^–/– platelets. **P < .005. (C) Washed CD151^+/+ and CD151^–/– platelets were allowed to adhere for 60 minutes at 37° C to a fibrinogen matrix. Adherent platelets were fixed and examined by scanning electron microscopy. Representative CD151^+/+ and CD151^–/– platelet scanning EM images are shown. (D) The number of filopodia per platelet were analyzed on scanning EM images from 8 random fields and expressed as a percentage of the total adherent platelets from CD151^+/+ and CD151^–/– platelets. *P < .005.