Distribution of α-granule proteins and tubulin in shear-induced proplatelets and platelets. Confocal microscope analysis of immunofluorescence showing labeling (left panels) with anti–P-selectin, anti-tubulin antibodies, and overlay of (from top to bottom) an MK extending a thick proplatelet, a long and thin proplatelet, a dumbbell-shaped proplatelet with its central narrowing, and 2 platelets. P-selectin staining is seen in organelles in forming proplatelets and in platelets in different spots, whereas tubulin stains the entire microtubule shaft of the proplatelet and the periphery of platelets. Right panels: labeling with phalloidin, anti-tubulin antibodies, and overlay of (from top to bottom) an MK extending proplatelet, a long and thin proplatelet with its shaft as well as its tip, labeled for tubulin, a dumbbell-shaped proplatelet with its central narrowing, and a platelet exhibiting a circular labeling pattern. No colocalization between actin and tubulin is visible. The bars represent 10 μm.