Immunofluorescent appearance of a platelet-producing WAS MK. Cultures were performed and labeled as described in Fig 2. Phalloidin staining (FITC) was distributed linearly all along the pseudopod that gives rise to platelets by breaking irregularly at several constriction sites (A). vWF (TRITC) was present in this pseudopod (B), while Hoechst staining determined the localization of the nucleus (C). This immunofluorescent appearance of platelet-producing WAS MK was similar to that observed in normal control platelet-producing MKs (not shown).