Defective actin reorganization in MYH9Δ megakaryocytes following adhesion to collagen. WT (A-C) and MYH9Δ (D-F) megakaryocytes were allowed to adhere to collagen for 3 hours. (A,D) Actin filaments were visualized by phalloidin-AF488 labeling (green). (B,E) Myosin was stained with an anti–myosin IIA antibody followed by goat anti–rabbit AF555 antibodies (red). (C,F) Merged images. No stress fibers are seen in MYH9Δ cells despite the presence of actin filaments. Images are representative of 3 experiments. Bars equal 25 μm.