Fibrinogen γ-chain mRNA is not detected in human megakaryocytes

Abstract

Human megakaryocytes and platelets contain counterparts of several plasma proteins. The origin of most of these α-granule proteins is unclear. Fibrinogen represents one of those molecules, being essential in hemostasis, thrombosis, and platelet aggregation. To study whether fibrinogen is endocytosed by megakaryocytes and packaged into α-granules or newly synthesized by these cells, we established a highly sensitive nested primer polymerase chain reaction for the detection of human fibrinogen γ-chain mRNA. In enriched megakaryocyte fractions, as well as fluorescence-activated cell sorter-purified megakaryocytes from bone marrow samples of healthy volunteers, no fibrinogen γ-chain mRNA could be detected, despite the presence of the corresponding fibrinogen γ-chain DNA. We conclude that fibrinogen γ-chain mRNA, as detectable by our amplification system, is missing in megakaryocytes. This finding suggests that fibrinogen might be acquired from plasma by endocytosis and sequestered in α-granules before reentering the circulation after platelet activation. © 1991 by The American Society of Hematology.