PML-RARα and MYC cooperate to alter myeloid maturation. (A) Control (Cntr) or PML-RARA (PR) transgenic bone marrow was transduced with MIG (Cntr) or MYC retroviruses, and lethally irradiated mice were reconstituted with this bone marrow. 5 wk after transplantation, mice were euthanized and GFP⁺ cells were sorted from bone marrow and stained with Wright’s Giemsa stain. Results are representative of three to four animals per group. Bars, 8 µm. Each panel is comprised of two images of equal size, showing two different microscopic fields. L, Lymphocyte. (B) GFP⁺ bone marrow cells were stained as in A. 200 cell differential counts were performed. Percentages of cell types within the myeloid compartment are shown. Immat, Immature forms (blasts and promyelocytes); Intermed, myeloid intermediate forms; Neut, neutrophils; Mono, monocytes; Eos, eosinophils; n: Cntr+Cntr = 4; Cntr+MYC = 3; PR+Cntr = 4; PR+MYC = 3. Mice in each group were generated in single experiments. Means ± SD are shown. Differences in the percentages of intermediate forms and/or neutrophils were statistically significant for all comparisons except Cntr+Cntr versus Cntr+MYC. PR+MYC data for mature neutrophils differs from other three groups: PR+MYC versus Cntr+Cntr, P < 0.0001; PR+MYC versus Cntr+MYC, P < 0.01; PR+MYC versus PR+Cntr, P < 0.02. (C) Bone marrow cells from mice described in A were stained as described in Materials and methods. 34,000 GFP⁺ cells negative for lymphoid and erythroid antigens were analyzed for Gr-1 and CD34. Gr-1 and CD34 fluorescence histograms representative of three mice per group are shown. (D) Gr-1 and CD34 levels were analyzed in C. All values were normalized to Cntr+Cntr. Means ± SD are shown. n = 3 in each group. Mice in each group were generated in single experiments. *, P < .05; **, P < .01 for comparison to Cntr+Cntr; #, P < 0.05 PR+MYC versus PR+Cntr and P < 0.01 PR+MYC versus Cntr+MYC; ##, P < 0.01 PR+MYC versus Cntr+MYC.