Megakaryocytter

Megakaryocytter, or megakaryocytes in English, are large, highly polyploid cells located primarily in the bone marrow. They are responsible for the production of platelets (thrombocytes), which are essential for normal hemostasis. Megakaryocytes originate from hematopoietic stem cells via a lineage called megakaryopoiesis.

Development: Hematopoietic stem cells differentiate into megakaryocyte-erythroid progenitors (MEP), then to megakaryoblasts, promegakaryocytes, and finally mature megakaryocytes. During maturation the nucleus undergoes endomitosis, increasing DNA content without cell division and yielding polyploid cells with extensive cytoplasm. The cytoplasm extends into bone marrow sinusoids as proplatelets.

Function: Platelets are released from the cytoplasmic processes into the bloodstream, where they support hemostasis by adhering to damaged endothelium, aggregating to form clots, and releasing granule contents that promote clot stabilization and wound repair.

Regulation: Thrombopoietin (TPO) is the principal regulator of megakaryopoiesis, signaling through the c-MPL receptor. Transcription factors such as GATA-1, FOG-1, NF-E2, and RUNX1 guide maturation, while the bone marrow microenvironment provides additional signals and cytokines.

Clinical relevance: Abnormal megakaryocyte number or function can cause bleeding or thrombotic disorders. Increased megakaryocytes are seen in essential thrombocythemia and other myeloproliferative neoplasms, whereas reduced production can lead to thrombocytopenia. Understanding megakaryocytes informs studies of platelet biology and related diseases.