The oncogenic property of JAK2V617F resides in its ability to initiate ligand-independent signaling downstream of the erythropoietin receptor (EPOR), thrombopoietin receptor (TPOR), and granulocyte-stimulating factor receptor (G-CSFR), resulting in erythrocytosis, thrombocytosis, and neutrophilia, respectively3. Here, MPL is linked to polycythemia.