Phenotypic changes in the megakaryocyte-platelet lineage.

Morphologic and phenotypic changes occur during the maturation of megakaryocytes (MK) from the pluripotent stem cell to platelets. As the MK acquires organelles, it also acquires membrane glycoproteins and granule contents. Platelet membrane GP IIb/IIIa and platelet peroxidase are present from early stages of maturation to the final product of the megakaryocyte, the platelet, while Ia-like antigen appears to be expressed only during early stages of maturation. The MK synthesizes increasing amounts of lysosomal enzymes, GP Ib, and alpha granule proteins as it matures from the megakaryoblast stage to the mature cell. The platelet contains only vestiges of a protein synthetic apparatus; it therefore has acquired most of its contents, except for serotonin, during the maturation of the MK.