Discoid shape promotes durable thrombi. (A) Platelets that lack α4A-and β1-tubulin demonstrate a spherical morphology and lack the microtubule-derived marginal band, a cross-section of which is shown in the left panel. (B) Under flow conditions, the discoid shape of wild-type platelets provides an increased surface area for attachment to the vessel wall (black line) and to each other. By comparison, spherical platelets form looser attachments that are prone to give way to flow. (C) As a result, thrombi formed by discoid platelets are more compact. (D) The friability of thrombi formed by spherical platelets results in increased bleeding. (Electron micrographs were extracted from their original Figures 1 and 3 in Kimmerlin et al that begins on page 2290. Professional illustration by Patrick Lane, ScEYEnce Studios.)