Immunofluorescent and transmission electron microscopic changes in platelets and megakaryocytes. (A-B) Immunofluorescence photomicrographs of platelets stained with anti–β1-tubulin antibody at 1000 ×; bars represent 5 μM. (A) A/J +/? control platelets showing normal β1-tubulin immunoreactivity. (B) Enlarged A/J-trac/trac platelets showing increased β1-tubulin immunoreactivity. (C-F) TEM of platelets and megakaryocytes. (C) A/J +/+ platelet showing normal structure. (D) A/J-trac/trac platelet showing large size, numerous small alpha granules, and increased numbers of mitochondria in each platelet. (E) A/J +/+ megakaryocyte showing well-developed platelet demarcation membrane system (DMS). (F) A/J-trac/trac megakaryocyte showing altered DMS. (C-F) Bars represent 500 nM.