Myeloproliferation in Mx1-Cre, Nras^G12D mice. Hematopoietic tissues from F1 Mx1-Cre, Nras^G12D mice (Nras, n = 14) that appeared well at 6 months of age were analyzed in parallel with specimens from WT littermates (n = 10). (A) Peripheral blood analysis and spleen weight from Mx1-Cre, Nras^G12D mice and WT littermates. P value for the mean white blood cell counts, hemoglobin concentrations (Hb), peripheral lymphocyte and myeloid cell (neutrophils and monocytes) counts, and spleen (SP) weights are .0356, .1825, .0084, .1093, and .0053, respectively. (B) Flow cytometric analysis of bone marrow cells (BM) and splenocytes (SP) with the myeloid markers Gr1 and Mac1. The frequency of the cells in the red gate (mac1⁺Gr1^low and Mac1⁺Gr1⁺) was used to calculate the percentage of myeloid cells. A summary of 14 Nras mutant and 10 WT animals is shown on the right. P values for bone marrow and spleen are .0015 and .0379, respectively. (C) CFU-GM colonies were enumerated from WT and Nras mutant BM and SP in methylcellulose cultures containing no cytokines or a saturating dose concentration of GM-CSF (10 ng/mL). (D) Morphology of CFU-GM colonies from WT, Mx1-Cre, Nras^G12D (Nras), and Mx1-Cre, Kras^G12D (Kras) BM (original magnification × 40).