Ultrastructure of β1-tubulin^—/—platelets. (A) Wild-type resting platelet, shown to highlight the intact marginal MT band. (B-C) Resting β1-tubulin^—/— platelets, showing their normal size and contents. DTS indicates dense tubular system; Gr, granules. (D) Electron micrograph showing the surface-connected canalicular system (SCCS) of β1-tubulin^—/— platelets. Scale bars: A-D, 0.5 μm. (E-F) Light (E) and electron (F) micrographs of representative β1-tubulin^—/— MKs, showing the common finding of dense cortical staining (arrows) in hematoxylin-and-eosin preparations and nearly normal cytoplasmic maturation, except for a slightly wider organelle-free peripheral zone (delineated by the H-shaped bar) in most MKs. Nuc indicates nucleus; panel E: original magnification, × 400; panel F: scale bar, 5 μm.