Myosin-IIA localization in mouse fetal liver–derived mature MKs and blood platelets. (A) Merge of actin (phalloidin, red), myosin-IIA (antibody, green), and nuclear (DAPI [4,6-diamidino-2-phenylindole], blue) staining in a representative mouse fetal liver–derived MK, with actin and myosin-IIA staining shown separately in panels Aii and Aiii, respectively. Myosin-IIA is expressed diffusely in the cytoplasm with slight increase at the cell cortex. (B-D) Myosin-IIA (green) or merge of actin (C) (red) or α-tubulin (D) (red) and myosin-IIA (green) signals in mouse fetal liver–derived proplatelets. Myosin-IIA is expressed uniformly along the proplatelet length, even though the increased cytoplasmic mass in proplatelet swellings conveys the false impression that it concentrates in these structures. Insets in panels B and C show portions of similar proplatelets at higher magnification. An organized reticular distribution is detected at the tips of individual proplatelets (D), where MK microtubules form a characteristic coil. (E) Myosin-IIA distribution in proplatelet ends resembles that seen in blood platelets. Scale bars represent 3 μm (A), 15 μm (B-C), 3 μm (B-C, insets; D), and 0.5 μm (E).