Effects of Jak2V617F on hematopoietic progenitors. (A) Flow cytometric analysis of the LSK compartment (Lin⁻Sca1⁺c-kit⁺) and subsets of myeloid progenitors including CMP (Lin⁻Sca1⁻c-kit⁺CD34⁺FcγRII/III^lo), GMP (Lin⁻Sca1⁻c-kit⁺CD34⁺FcγRII/III^high), and MEP (Lin⁻Sca1⁻c-kit⁺CD34⁻FcγRII/III⁻) in the BM and spleen from control (n = 8), heterozygous (n = 8), and homozygous Jak2V617F (n = 5) mice. (B) Representative contour plots are shown. The percentage of LSK, CMP, GMP, and MEP is shown in histograms as mean ± SEM. Data are presented as percentage of total cells. *Significance between control and heterozygous or between control and homozygous; **significance between control and homozygous as well as between heterozygous and homozygous Jak2V617F mice; significant difference of P < .05. (C) Hematopoietic progenitor colonies. BM (2 × 10⁴) and spleen (1 × 10⁵) cells from control (n = 6), heterozygous (n = 6), and homozygous Jak2V617F (n = 5) mice were plated in complete methylcellulose (Methocult M3434) medium. BFU-E, CFU-GM, and CFU-GEMM colonies were counted on day 7. (D) Epo-independent CFU-E colonies. Spleen cells (1 × 10⁵) from control, heterozygous, and homozygous Jak2V617F mice were plated in methylcellulose medium without any cytokine. CFU-E colonies were counted after 2 days.