Visualization of microtubule polymerization in living platelets during activation. (Ai) Thrombin-activated human platelets fixed and stained with anti-EB1 antibodies. An average of 25.5 (± 8.6) sites of EB1 localization are seen. (Aii) Thrombin-activated human platelets fixed and double-labeled with anti-EB1 (green) and antidetyrosinated tubulin (red) antibodies. (B) A platelet released from a megakaryocyte infected with EB3-GFP. Note the microtubule growth (indicated by the fluorescent comets) that occurred during activation. (C) In vivo labeling of extended filopodia with multiple EB3-GFP comets. Note (arrowheads) the movement of a single EB3-GFP comet, which appears to move away from the cell body. (D) Kymograph of EB3-GFP comet movements; platelet cell body faces up in this figure. Arrowheads track the movements of a single EB3-GFP comet in consecutive frames.