Mx1-Cre, Nras^G12D myeloid progenitors show distinct patterns of cytokine hypersensitivity. (A). CFU-GM colony growth from WT (blue lines), Mx1-Cre, Nras^G12D (red lines), and Mx1-Cre, Kras^G12D (black lines) cells in response to GM-CSF (left panel), IL-3 (middle panel), and SCF (right panel). (B). Adding SCF (10 ng/mL) to methylcellulose cultures containing a range of IL-3 concentrations revealed synergistic effects on CFU-GM growth from WT and Mx1-Cre, Nras^G12D bone marrow (left and middle panels), but not Mx1-Cre, Kras^G12D (right panel) marrow. The data are derived from 5 independent experiments. Well-appearing 3-month-old F1 Nras and Kras mutant mice were used.