Signal transduction in bone marrow cells from Mx1-Cre, Nf1 ^flox/flox and Cre^- mice. (A) Bone marrow cells from mutant and control mice showing Ras-GTP levels in unstimulated cells and 5 minutes after GM-CSF. (B) Bone marrow cells from mutant and control mice showing basal and growth factor-induced levels of phosphorylated (p)-Akt and p-MEK in response to GM-CSF (at 5 minutes). (C) Ras-GTP, p-MEK, and p-Akt from panels A and B were quantified by densitometry. (D) Mac1-positive bone marrow cells from mutant and control mice showing basal and growth factor-induced activation of p-MEK in response to GM-CSF. The time course is shown from 5 to 60 minutes. Relative p-MEK activity is shown in the right panel. Levels in mutant and control cells were normalized for background and loading, with the unstimulated sample assigned arbitrary units of 100.