megakariocyty

Megakariocyty, also called megakaryocytes, are large bone marrow cells responsible for producing blood platelets. They arise from hematopoietic stem cells through the megakaryocyte-erythroid progenitor pathway and reside primarily in the bone marrow, where they can be relatively large compared with surrounding cells.

A hallmark of megakaryocytes is polyploidy. Through a process called endomitosis, they multiply their DNA without undergoing conventional cell division, yielding oversized, lobulated nuclei. The cytoplasm of megakaryocytes extends long processes known as proplatelets into the sinusoidal blood vessels of the marrow. Platelets are released from these extensions into the bloodstream as tiny cellular fragments that participate in hemostasis.

Thrombopoietin is the principal regulator of megakaryocyte development and platelet production, with support from other cytokines such as interleukins. Transcription factors including GATA-1, RUNX1, and TAL1 help control lineage commitment and maturation of these cells. The process of platelet production is termed thrombopoiesis and is intertwined with overall hematopoiesis.

Clinically, megakaryocytes are central to disorders of platelet formation. An increased or morphologically abnormal megakaryocyte population can be seen in myeloproliferative neoplasms such as essential thrombocythemia, while reduced platelet production or increased platelet destruction leads to thrombocytopenia. Bone marrow examination of megakaryocytes informs diagnosis in various hematologic conditions.