Although Src kinases are activated by JAK2 in erythroid cells upon Epo stimulation [28] and a Src inhibitor impaired Epo-independent maturation of PV erythroid progenitors [13], we demonstrated that polycythemia induced by JAK2 V617F was independent of Lyn, Hck, and Fgr, the three principal Src family kinases expressed in myeloerythroid cells. This evidence concerns the gene EPO and polycythemia.