Suppression of BMP4 activity by FGF inhibitor. E15 FTOC was cultured for 7 days in the presence of BMP4 alone or BMP4 plus FGFR2IIIb/Fc inhibitor. (A) Representative FACS dot plots of CD44/CD25 (upper panels) and CD4/CD8 (lower panels) expression by thymocytes from untreated (left panels), BMP4-treated (middle panels), and BMP4 plus FGFR2IIIb/Fc inhibitor–treated (right panels) FTOC. R6, R7, and R8 denote DN1, DN2, and DN3 subpopulations, respectively. (B) Bars represent the relative change in total DN, DN1, and DN3 subpopulations in these cultures. Restoration of DN population with FGFR2IIIb/Fc addition is significant in a total of 3 experiments; ^*P < .0115. (C) Bars represent the relative change in total cell number per lobe in these cultures. Restoration of cell numbers with FGFR2IIIb/Fc addition is significant (^*), with greater than 99.9% confidence, from a total of 3 experiments. Error bars indicate mean ± SD.