The elegant platelet: signals controlling actin assembly.

In summary, the actin-based cytoskeleton of the human platelet has been assembled to serve two primary purposes. The first allows the platelet to circulate throughout the blood vascular system in near proximity to the endothelial cells. To accomplish this feat, a small discoid fragment has been meticulously assembled in the megakaryocyte. This released platelet is maintained in the discoid shape using a cytoplasmic scaffolding composed of rigidly crosslinked actin filament laminated to both a spectrin membrane skeleton and the cell surface by the alpha-chain of the vWFR. The small size and discoid shape of the platelet causes it to be pushed to the endothelial surface of the blood vascular system during blood flow. The second purpose of the cytoskeleton is to allow for a massive cell spreading to plug wounds. To accomplish this task, the cytoskeleton is quickly taken apart and reassembled. The temporal nature of this reaction makes the platelet one of the most useful cells in which to understand both the proteins and the signaling pathways that initiate cell shape changes mediated by the actin filament system of cells.