Stat5-deficient (Stat5 KO) BMMCs exhibit delayed cell cycle progression and cyclin up-regulation. (A) Wild-type or Stat5-deficient BMMCs were cultured in IL-3 (5ng/mL), SCF (50ng/mL), or IL-3 + SCF for the indicated times, and assessed for S-phase progression by PI/BrdU staining. Data shown are means and standard error values from 6 to 9 measurements taken from 5 independent experiments. *P < .001 when comparing wild-type and Stat5-deficient cells under identical conditions. The lower panel shows a representative PI-DNA staining profile for BMMCs cultured in IL-3 alone for 48 hours. Under these conditions, subdiploid content (apoptotic cells) represented approximately 5% of wild-type or Stat5-deficient populations. (B-C) Cells were cultured as in panel A for the indicated times (B) or for 36 hours (C). Total cellular RNA or protein was assessed for cyclin expression by RPA analysis (B) or Western blot analysis (C). Western blots were stripped and reprobed for actin expression to show equal protein loading.