Expansion of the CD41⁺ megakaryocytes in Npm1-TCTG/WT;Cre⁺ and Npm1-TCTG/TCTG;Cre⁺ mice. (A) Flow cytometric analysis of single-cell suspensions of BM from representative Npm1-TCTG/WT;Cre⁺, Npm1-TCTG/TCTG;Cre⁺, and Npm1-TCTG/WT;Cre⁻ pIpC-treated control mice demonstrates an increase in the percentage of CD41⁺ megakaryocytic cells. (B) Quantification of CD41⁺ megakaryocytic cells in the BM of age-matched mutant mice analyzed as in panel A: Npm1-TCTG/WT;Cre⁺ (n = 11) and Npm1-TCTG/TCTG;Cre⁺ (n = 6); CTRL indicates control mice including Npm1-WT/WT;Cre⁺ (n = 3), Npm1-TCTG/WT;Cre⁻ (n = 7), and Npm1-TCTG/TCTG;Cre⁻ (n = 2) pIpC-treated mice. (C) BM cellularity in Npm1-TCTG/WT;Cre⁺ (n = 11), Npm1-TCTG/TCTG;Cre⁺ (n = 6), and control mice (genotypes and numbers are the same as in panel B). (D) Percentage of CD41⁺ megakaryocytic cells in the spleen of heterozygous (n = 10) and homozygous (n = 6) mutant mice compared with pIpc-treated Cre⁻ controls (n = 6). (E) Composite data from age-matched littermates of indicated genotypes demonstrating mild hypersplenism in Npm1-TCTG/WT;Cre⁺ and Npm1-TCTG/TCTG;Cre⁺ mice. (F) Comparison of serum TPO concentration between Cre⁻ pIpC control mice, Npm1-TCTG/WT;Cre⁺, and Npm1-TCTG/TCTG;Cre⁺ (n = 12 per genotype). *P < .05, **P < .01, ***P < .001 (unequal-variance t test). n.s. = not statistically significant.