Mx1-Cre, Kras^G12D c-kit⁺ lin^−/low bone marrow cells form abnormal CFU-GM colonies and are hypersensitive to GM-CSF. (A) The c-kit⁺ lin^−/low population analyzed in these studies was isolated by first gating live, nonneutrophil cells based on scatter properties and then gating cells that expressed c-kit and had no or low expression of the mature lineage markers. (B) CFU-GM colonies grown from single c-kit⁺ lin^−/low cells were photographed (left; original magnification × 40) and cytospin preparations were stained with Wright-Giemsa (right; original magnification × 500). (C) c-kit⁺ lin^−/low cells (100-1000 per mL) from WT (▪) or Mx1-Cre, Kras^G12D (○) mice were plated in methylcellulose medium with a range of GM-CSF concentrations.