Sustained expression of miR-cluster 99b/let-7e/125a induces MPNs with occasional progression to leukemia. (A) PB WBC counts for empty vector, miR-cluster 99b/let-7e/125a, and miR-155 mice at time of sacrifice. Closed/black squares represent nonmorbid miR-cluster mice, whereas open/red squares represent moribund miR-cluster mice. L indicates leukemic mouse. (B) Photographs of femur and tibia bones, BM cellularity (representing 2 femurs, 2 tibias and pelvic bones) and spleen weight for empty vector, miR-cluster 99b/let-7e/125a and miR-155 mice at time of sacrifice. Closed/black squares represent nonmorbid miR-cluster mice, whereas open/red squares represent moribund miR-cluster mice. P values (*.01 < P < .05; **.001 < P < .01) are displayed (Mann-Whitney test). L indicates leukemic mouse. (C) Percentage EGFP⁺ cells in PB, BM, and spleen (n = 5 for EV, n = 6 for CLUS, n = 3 for 155). Nonmorbid and moribund miR-cluster 99b/let-7e/125a mice showed similar percentages and were therefore combined. Shown is the mean ± SEM. (D) Cell-type distribution in PB, BM, and spleen of empty vector, miR-cluster 99b/let-7e/125a, and miR-155 mice as assessed by FACS. Shown is the mean ± SEM. Data for nonmorbid and moribund mice are shown separately for PB (n = 5 for EV, n = 3 for nonmorbid [N] CLUS, n = 3 for moribund [M] CLUS, n = 3 for 155) and combined for BM and spleen (n = 5 for EV, n = 6 CLUS, n = 3 for 155), because the cell-type distributions between these mice differed in PB, but not in BM and spleen. (E) Representative MGG-stained cytospin preparations from BM and spleen cells. For the miR-cluster 99b/let-7e/125a, 2 pictures are shown: 1 representative of a nonmorbid mouse (N) and 1 of the leukemic mouse (L).