Comparison of hematopoiesis and survival of JAK2-V617F–transgenic mice activated by 3 different Cre transgenes. (A) Blood counts and survival after induction with pIpC or tamoxifen. (B) Ratio between human JAK2-V617F and mouse Jak2 in the BM of JAK2-V617F–transgenic mice at 10 and 34 weeks. (C) Blood counts and survival after transplantation of 2 × 10⁶ BM cells collected from JAK2-V617F mouse donors into lethally irradiated recipients. (D) Ratio between human JAK2-V617F and mouse Jak2 in the BM of hosts transplanted with JAK2-V617F BM cells. The BM samples were collected 35 weeks after transplantation. Mx indicates MxCre;FF1 mice (red symbols); Scl, SclCre;FF1 mice (green symbols); Vav, VavCre;FF1 mice (blue symbols); and WT, wild-type controls (black symbols). Note that all SclCre;FF1 mice died within 30 weeks after tamoxifen induction and therefore no blood counts were available beyond this time point. Survival is shown as Kaplan-Meier curves. (E-F) Numbers of hematopoietic progenitors assessed by colony assays in methylcellulose or collagen-based medium. BFU-E indicates burst forming unit erythroid; and Tpo, thrombopoietin. BM from 3 mice per group were analyzed on duplicate plates. (G-H) Percentages of LSK cells within the lineage⁻ BM cell population of nontransplanted mice induced by pIpC or tamoxifen (G) and in the lethally irradiated hosts transplanted with the BM cells from JAK2-V617F mice (H). (I) Blood counts and survival of SclCre;FF1 mice with Jak2^fl/+ or Jak2^fl/fl genotypes after induction with tamoxifen. (J) Ratio between human JAK2-V617F and mouse Jak2 in the BM of SclCre;FF1 mice with the Jak2^+/+, Jak2^fl/+, or Jak2^fl/fl genotypes. Error bars represent SEM. One-way ANOVA is shown for comparisons between wild-type and transgenic mice. ns indicates not significant. *P ≤ .05; **P ≤ .01; ***P ≤ .001.