Interference with myosin-IIA function during MK maturation. (A) Bone marrow transplant evaluation of the role of myosin-IIA in platelet production by functional dominant interference. Control (GFP) and GFP-fused rod domain (GRD) groups represent results from 4 or 5 independently transplanted animals, and the differences in thrombopoietic efficiency are significant (P > .02) by the 2-tail Student t test. (B) PPF efficiency of cultured primary wild-type MKs expressing myosin-IIA constructs. Values are expressed as the fraction of all MKs (scored by cell size and morphology under phase-contrast microscopy) that extend proplatelets. Cultures were evaluated at 84 hours (black) and 96 hours (gray) after initiation of culture, and following enrichment for MKs over a BSA step-gradient.