Microtubule coils in FlnA-null platelets. (A) Size of microtubule coils in control and FlnA-null platelets matured in vitro or in vivo. Microtubule coils were visualized by immunofluorescence for β-tubulin. Images are representative of 4 separate MK cultures and 3 mice. FlnA-null platelets had larger and brighter microtubule coils. (B) Quantification of platelet size. The diameters of microtubule coils were analyzed using MetaMorph Version 7.7 software. (C) Electron micrographs of mouse peripheral blood platelets in transverse sections show the increased number of microtubules in the marginal coils of FlnA-null platelets compared with controls: (i-v) control platelets; (vi-x) FlnA-null platelets. Electron micrographs of negative stained platelets show the increased thickness of the microtubule coils in FlnA-null platelets (xii) compared with control platelets (xi). Representative images of 3 independent experiments are shown. (D) Quantification of the number of microtubule coils in the marginal band in transverse images of thin sections of platelets. Results are mean ± SD (n = 10). *P < .05.