Thrombopoietin (TPO) is a glycoprotein hormone which belongs to the EPO/TPO family. It produced by the liver and kidney which regulates the production of platelets.Mature mouse Tpo shares 71% and 81% aa sequence homology with human and rat Tpo, respectively. It is an 80-85 kDa protein that consists of an N-terminal domain with homology to Erythropoietin (Epo) and a C-terminal domain that contains multiple N-linked and O-linked glycosylation sites. TPO stimulates the production and differentiation of megakaryocytes, the bone marrow cells that bud off large numbers of platelets. Lineage-specific cytokine affects the proliferation and maturation of megakaryocytes from their committed progenitor cells. It acts at a late stage of megakaryocyte development. It may be the major physiological regulator of circulating platelets.