BMP4 arrest of T-cell development. E15 FTOC was cultured for 7 days in the presence or absence of BMP4 (30 μg/mL). (A) Representative fluorescence-activated cell sorter (FACS) dot plots of CD44/CD25 (upper panels) and CD4/CD8 (lower panels) expression by thymocytes in untreated (left panels) and BMP4-treated (right panels) FTOCs. 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 a total of 22 experiments. Changes are significant (^*) with greater than 99.9% confidence by P values. (C) Bars represent the relative change in total cell number per lobe in these cultures in a total of 14 experiments. The decrease with BMP4 treatment is again significant (^*) with greater than 99.9% confidence. Error bars indicate mean ± SD.