Role of SFKs and Syk kinase in MK spreading and cytoskeletal reorganization. Purified BM-derived mature MKs were incubated in the presence or absence of PP1 (10μM) or R406 (2μM) for 15 minutes at 37°C. MKs were plated on fibronectin-coated surface for 3 hours at 37°C. Adherent MKs were fixed, permeabilized, and actin fibers stained with rhodamine-phalloidin. Representative images (A) and surface area quantification (B) from 4 independent experiments are shown (scale bar = 20μm). **P < .01.