Effect of disabling the ERK2-DBP domain on erythropoiesis and JAK2V617F-driven PV progression. (A) Photograph of representative spleens from Erk2-WT and ERK2^Y261A/Y261A mice. (B) Flow cytometry analysis on the effect of disabling the ERK2-DBP domain on expansion of red blood cell precursors (CD44⁺/Ter119⁺) in mice of the indicated genotypes. (C) Adoptive transfer model of PV. Lin⁻ HSPCs were harvested from the BM of ERK2-WT, -KO or -Y261A (DBP) mice; transduced with JAK2V617F-expressing retrovirus; and IV injected into sublethally irradiated immunodeficient recipient mice (n = 7 per group). (D) Peripheral blood smears from ERK2-WT, -KO, and –DBP-Y261A HSPC recipient mice at 12 weeks after transfer. Scale bars, 20 µm, Wright-Giemsa stain. (E-F) Spleen size and weight of mice transferred with JAK2V617F-transduced ERK-WT–, -KO–, and -DBP–mutant HSPCs. Results are expressed as the mean ± standard deviation (SD). *P < .05. (G) BM cell counts of JAK2V617F-transduced ERK-WT–, -KO–, or -DBP–mutant mice. The data are expressed as the mean ± SD. *P < .05; n.s., not significant.