FIG. 1.

Outline of platelet formation in the bone marrow environment. Immature megakaryocytes in contact with the osteoblastic niche are inhibited in their maturation. Upon migration toward the vascular niche, megakaryocytes extend proplatelets and release platelets into the blood stream. Interactions of megakaryocytes with matrices supposed to fill the vascular niche, such as fibrinogen (FBG) or von Willebrand factor (vWF), are able to sustain proplatelet formation, whereas type I collagen, in the osteoblastic niche, totally suppresses this event and prevents premature platelet release. SDF-1α is produced locally by the stromal cells and promotes the migration and contact of megakaryocytes with the permissive vascular niche. Color images available online at www.liebertonline.com/tec