Effects of Stat3 deficiency on the phenotype of JAK2-V617F transgenic and control mice. (A) Time course of blood counts in recipients of bone marrow transplantation. Bone marrow cells (2 × 10⁶) from noninduced donors were transplanted into lethally irradiated hosts, and 6 weeks after transplantation, the Cre^ER fusion protein was activated with tamoxifen supplied in the food (1 mg/g). The group sizes were n = 6 for WT, SclCre;Stat3^fl/+, and SclCre;V617F;Stat3^fl/+ mice and n = 10 mice for all other genotypes. Results are presented as means ± SEM. Two-way ANOVA with subsequent Bonferroni post-test was used, and *P < .05 between SclCre;V617F;Stat3^+/+ and SclCre;V617F;Stat3^fl/fl is indicated. (B) Spleen weights 25 weeks after starting tamoxifen (n = 5 mice per group). (C) Survival of mice is shown as Kaplan-Meier curves from 2 independent pooled experiments, including the mice mentioned above. Together the group sizes were n = 12 for WT, n = 6 for SclCre;Stat3^fl/+ and SclCre;V617F;Stat3^fl/+ mice, n = 20 for SclCre;V617F;Stat3^+/+, and n = 22 for SclCre;Stat3^fl/fl and SclCre;V617F;Stat3^fl/fl. *P < .05 vs WT is indicated. (D) Relative Stat3 mRNA expression in bone marrow 25 weeks after starting tamoxifen was determined by reverse transcription and quantitative PCR and normalized against GusB mRNA (n = 3 mice per genotype).