P-selectin mRNA is expressed at a later phase of megakaryocyte maturation than mRNAs for von Willebrand factor and glycoprotein Ib-alpha.

The assembly of alpha-granules occurs exclusively in megakaryocytes because platelets have limited capacity for the synthesis of macromolecules. Thus far, alpha-granule development in megakaryocytes has been primarily evaluated by ultrastructural studies. The aim of the study was to obtain molecular and biochemical evidence for the expression of selected alpha-granule proteins in megakaryocytes. Guinea pig megakaryocytes were purified and separated into subgroups at different phases of maturation by the Celsep procedure (Schick et al. Blood 1989;73:1801-8). Guinea pig-specific probes for P-selectin, von Willebrand factor (vWF), glycoprotein Ib-alpha (GpIb-alpha), and phosphoglycerate kinase were prepared by using the polymerase chain reaction. By Northern blot analysis, P-selectin messenger ribonucleic acid (mRNA) was primarily expressed in the mature megakaryocyte Celsep subgroup, whereas vWF and GpIb-alpha mRNA were expressed at all phases of megakaryocyte maturation. In situ hybridization confirmed that P-selectin mRNA was primarily expressed at later stages of cytoplasmic maturation: 14% +/- 6.2% of stage I, 35.5% +/- 6.1% of stage II, 72% +/- 5.2% of stage III, and 47.0% +/- 3.3% of stage IV megakaryocytes expressed P-selectin mRNA. Thus, the expression of mRNA for P-selectin appeared to peak in stage III cells. In contrast vWF mRNA was expressed in immature megakaryocytes and persisted throughout megakaryocyte maturation. In situ hybridization did not demonstrate a relationship between the expression of mRNA for P-selectin or vWF with megakaryocyte ploidy.(ABSTRACT TRUNCATED AT 250 WORDS)