Thrombopoietin receptor (Tpo R), also known as myeloproliferative leukemia protein (c-Mpl), is a type I transmembrane protein that is a member of the hematopoietin/cytokine receptor superfamily. As a consequence of alternative splicing, there are four identified mRNA variants. The functional receptor is encoded by the P isoform of mRNA. The human and mouse receptors share approximately 81% amino acid sequence identity. Tpo R is expressed at low levels in various cell types, including hematopoietic progenitor cells, megakaryocytes and platelets.