Defective actin organization in Myh9^−/−MKs. (A) In vitro–differentiated WT and Myh9^−/− MKs were allowed to adhere to fibronectin-coated coverslips for 1 hour and F-actin was visualized by AF-488 phalloidin labeling. Confocal images were taken at the base of a cell in contact with the coverslip (top panels) and in the plane of the white-labeled nucleus of the same cell (bottom panels). Images are representative of 3 independent experiments. (B) F-actin labeling of bone marrow using AF-488 phalloidin. (Top panels) Wide fields from WT and Myh9^−/− marrow samples. (Bottom panels) Detail showing the F-actin distribution within a WT (left) and a Myh9^−/− (right) MK. Dotted lines delineate the MKs. Images are representative of at least 3 different bone marrow samples for each genotype.