Signaling effects of heterozygous and homozygous Jak2V617F in erythroid progenitors. Primary erythroblasts were derived from the BM and spleen of control (V617F/+), heterozygous, and homozygous Jak2V617F mice. For signaling studies, erythroblasts were starved in Iscove modified Dulbecco medium plus 0.5% BSA for 4 hours. Cell lysates were prepared in radioimmunoprecipitation assay (RIPA) buffer and subjected to immunoblotting with anti-phosphotyrosine (4G10) antibody (A) or phospho-specific antibodies against Stat5, Akt, and Erk1/2 (B).