CD110, also known as c-MPL, is a 635 amino acid transmembrane domain, with two extracellular cytokine receptor domains and two intracellular cytokine receptor box motifs. It is expressed at a low level in a large number of cells of hematopoietic origin. C-MPL is homologous with members of the hematopoietic receptor superfamily. Presence of anti-sense oligodeoxynucleotides of c-mpl inhibited megakaryocyte colony formation. Thrombopoietin is the ligand for c-mpl. It was shown to be the major regulator of megakaryocytopoiesis and platelet formation. Defects in c-MPL are a cause of congenital amegakaryocytic thrombocytopeniawhich is a disease characterized by isolated thrombocytopenia and megakaryocytopenia with no physical anomalies. Defects in c-MPL also cause thrombocythemia type 2 and myelofibrosis with myeloid metaplasia.