Smad4 overexpression in CB cells results in increased sensitivity to TGF-β. (A) CD34⁺ CB cells were sorted for GFP 2-3 days after transduction and plated in methylcellulose supplemented as indicated with inhibitor SB431542. Data represent number of colonies per 1000 cells plated ± SEM (n = 6). (B) Percentage of colonies formed after 0.1 ng/mL TGF-β treatment compared with untreated cultures (n = 6). (C) Dose-response curve to TGF-β plus (dotted lines) or minus (solid lines) inhibitor SB431542 (n = 3). (C) GFP⁺ cells were plated in methylcellulose supplemented with BMP-4/7 heterodimer alone or together with inhibitor SB431542 (n = 3). *P ≤ .05 (paired Student t test).