TPO is a lineage-specific growth factor produced in the liver, kidney and skeletal muscle. It stimulates the proliferation and maturation of megakaryocytes, and promotes increased circulating levels of platelets in vivo. TPO signals through the c-mpl receptor, and acts as an important regulator of circulating platelets. Human and murine TPO exhibit cross-species reactivity. The human TPO gene encodes for a 353 amino acid glycoprotein, which contains a 21 amino acid signal sequence, a 15 amino acid erythropoietin-like domain, and a highly glycosylated 179 amino acid C-terminal domain. Recombinant Human TPO is a fully biologically active 174 amino acid polypeptide (18.6 kDa), which contains the erythropoietin-like domain of the full length TPO protein.