Multiple microtubules polymerize along the marginal band in living platelets. (A) Fluorescence microscopy of platelets released from cultured mouse megakaryocytes directed to express EB3-GFP showing the movements of multiple EB3-GFP comets, an indicator of polymerizing microtubules, along the periphery of the platelet. The time course follows a platelet with EB3-GFP comets moving both clockwise () and counterclockwise () over the course of 32 seconds. The final panel (76 seconds) shows the same cell with several EB3-GFP comets and foci (). (B) Life history plots of 8 individual EB3-GFP comets within a resting platelet show distance traveled over time. (C) Western blot detection of endogenously expressed EB3 in platelet lysates.