Thrombopoietin is a glycoprotein that primarily regulates thrombopoiesis, that is, platelet production. Produced constitutively in
the liver and inductively in the bone marrow to promote
the proliferation and differentiation of megakaryocytes and
their progenitors, and maintain hematopoietic stem cells. After the nature of platelets was described by Donne,
Addison, Osler, and Bizzozero in the 1800s, Wright reported that the origin of human platelets (thrombocytes) was the bone marrow. The tentative name thrombopoietin (TPO) was proposed for a humoral factor of
platelet production, independently by Komiya and by
Kelemen. It was not apparent whether TPO activity
was identical to in vitro activity defined as a megakaryocyte colony stimulating factor. TPO molecules were
finally identified simultaneously by independent
research groups. Concurrently,
c-Mpl (Mpl) expressing megakaryocytes was confirmed as the TPO receptor.
