Effect of spα2N1 on proplatelets. (A-B) Time-lapse DIC micrographs of permeabilized (0.4% OG) proplatelets treated with GST control polypeptide (left panels) and the spectrin-disrupting polypeptide spα2N1 (right panels) show that proplatelets treated with control GST maintain their “beads-on-a-string” structure and branches. In contrast, platelet-sized beads on proplatelets treated with spα2N1 blebbed and then underwent extensive swelling. After treatment with spα2N1, barbell-shaped proplatelets first blebbed and then fused their 2-platelet-sized swellings, forming a preplatelet-sized spheroid. (C-D) Electron micrographs of representative cytoskeletons from permeabilized proplatelets treated with either GST-control (C) or spα2N1 peptide (D). Scale bars indicate 5 μm. The cytoskeletons of GST-treated cells remain intact, whereas the cytoskeletons of spα2N1-treated cells are disrupted and aggregated.