Differential localization of P-selectin and von Willebrand factor during megakaryocyte maturation.

An important step in megakaryocyte maturation is the appropriate assembly of at least two distinct subsets of alpha-granules. The mechanism that sorts the alpha-granule components into distinct structures and mediates their release in response to specific stimuli is now emerging. P-selectin and von Willebrand factor are two proteins present in the alpha-granules that recognize P-selectin glycoprotein ligand on neutrophils and collagen in the subendothelial matrix. These proteins may play an important role in determining the differential release of the alpha-granule contents in response to external stimuli. If P-selectin and von Willebrand factor are localized in the same or different alpha-granules is not known. To clarify this question, we analyzed by immunoelectron microscopy the localization of von Willebrand factor and P-selectin during the maturation of wild-type and Gata1