Survivin mediates enhanced proliferation and growth factor–independent growth of CFU-GMs induced by ITD-Flt3. Bone marrow cells from littermate control Survivin^flox/flox or Cre-ER Survivin^flox/flox mice were transduced with wild-type Flt3, ITD-Flt3 (N51) in MSCV-IRES-EGFP vector, or vector alone. GFP⁺-transduced cells were FACS sorted and 50 000 GFP⁺ cells plated in 0.3% agar McCoy medium with 30% HI-FBS without growth factors in the presence or absence of 1 μM 4OH-tamoxifen. Colonies were scored on day 14. Data are expressed as mean ± SEM for 5 independent experiments. The bottom panel shows Survivin gene deletion induced by 4OH-tamoxifen in replicate liquid cultures incubated without cytokines.