MMTV-Cre;Mib1^f/f mice exhibit the increased numbers of granulocyte progenitors, GM-CSF responsive cells, GMPs, and MPPs. (A,B) Flow cytometric analysis of BM cells from WT and MT mice. Absolute cell numbers of LSK and its subpopulations, LSKCD150⁺ and LSKCD150⁻ (A), and relative ratios of them (B). Statistical differences (t test) were P = .0015 (*), P = .0006 (**). (C,D) Flow cytometric analysis of BM cells (C) and splenocytes (D) from moribund group I/II MMTV-Cre;Mib1^f/f (MT) and littermate control (WT) mice. A distribution of GMP (Lin⁻IL-7Rα⁻Sca-1⁻c-Kit⁺CD34⁺FcγRII/III^hi) in the BM (C) and spleen (D) is shown. Numbers indicate the percentage of described populations in total BM (C) and spleen cells (D). Numbers around rectangles indicate the mean plus or minus SD (n = 3). (E) [³H]Thymidine incorporation by 14- to 15-week-old WT and MT BM cells in response to M-CSF, G-CSF, and GM-CSF. BM cells were cultured with the indicated amounts of cytokines for 48 hours. Pulse labeling was performed for the last 12 hours with [³H]thymidine. Bars indicate mean plus or minus SD. Statistical differences (t test) were P less than .0001 (*). (F,G) Colony numbers in splenocytes (F) and blood cells (G) from 15- to 19-week-old WT and MT mice, which were cultured in semisolid media in the presence of single GM-CSF (2 ng/mL). Bars indicate mean plus or minus SD. Colony numbers were barely (0.5, *) or not detected (**). (H) Flow cytometric analysis of splenocytes stained with propidium iodide and CD11b. (Bottom panels) DNA content of the SSC^hiCD11b⁺ granulocytes. (I) Cytospin of sorted CD11b⁺Gr-1^lo and CD11b⁺Gr-1^hi cells from moribund mutant spleens (Wright Giemsa, ×400). Scale bars: 50 μm.