Megakaryocyte organelles and granules distribute individually in proplatelets to assembling platelets. Localization of organelles in the proplatelets of mouse megakaryocytes. Proplatelets were stained with anti-von Willebrand factor⁵⁶  (A) to label α-granules, antiserotonin (C) to label dense granules, and MitoTracker (E) to label mitochondria. Corresponding antitubulin immunofluorescence (B,D) and differential-interference-contrast (F) micrographs highlight the proplatelet morphology. Scale bar, 10 μm. Granules and mitochondria are dispersed along the proplatelet shaft.