FOXO3(A3) induces apoptosis in wild-type but not bim^–/– mast cells. (A) SCF withdrawal–induced mast cell death is reduced by loss of Bim. BMCMCs from wt or bim^–/– mice were either deprived of SCF (–) or grown in SCF + IL-3 (+) for the indicated times. Cell viability was measured by propidium iodide staining and FACS analysis. (B) BMCMCs from wt or bim^–/– mice were infected with a retrovirus encoding a dominant-active mutant of FOXO3(A3):ER and treated with SCF in the presence or absence of 4-OHT. The experiment was repeated 3 times. The results are presented as the percentage of apoptotic cells determined by annexin V staining of 1 representative experiment in duplicate (mean ± SEM).