Inactivation of Icmt reduces splenomegaly and colony growth of splenocytes in mice with K-RAS–induced MPD. (A) Spleen weight of Icmt^fl/+K^LSLM (n = 3, 5, and 9 at the 3 indicated times, respectively) and Icmt^fl/flK^LSLM mice (n = 4, 6, and 9). Average spleen weight of wild-type mice (dashed line; n = 20) was 3 mg/g body weight. (B) Flow cytometry showing an increased percentage of CD11b/Gr-1 double-positive cells in spleens of Icmt^fl/+K^LSLM compared with Icmt^fl/flK^LSLM and wild-type mice. Shown are representative scatter plots from one mouse of each genotype and the mean percentage of double-positive cells (n = 4 for all genotypes). The increase in double-positive cells in the spleens of Icmt^fl/+K^LSLM mice was statistically significant (P = .043 vs Icmt^fl/flK^LSLM; P = .009 vs control). (C,D) Methylcellulose colony assays of splenocytes (n = 3-4) cultured in the absence (C) and presence (D) of exogenous growth factors (SCF, IL-3, IL-6, and EPO). CFU indicates colony-forming unit; GEMM, granulocyte-erythroid-macrophage-megakaryocyte; BFU-E, burst-forming unit erythroid; GM, granulocyte-macrophage; G, granulocyte; M, macrophage. (E) Colony growth of splenocytes (n = 3-4 for each genotype) seeded in methylcellulose at the indicated concentrations of GM-CSF. (F) May-Grünwald-Giemsa–stained cytospins of individual colonies from experiment in panel D (original magnification ×100; 1.30 NA oil objective).