Dependence of BMP4 action on stroma and thymocytes. (A) RT-PCR analysis of BMP4 and BMP4 receptor expression in stroma and thymocyte compartments. The cDNAs were prepared from DN1, total DN, and DP thymocytes and dexoyguanosine-treated E15 thymic lobes. (B-C) Representative FACS plots of CD44/CD25 and CD4/CD8 expression by thymocytes from reconstitution experiments. Flow cytometric analysis was performed 2.5 to 3 weeks after FTOC. R6, R7, and R8 denote DN1, DN2, and DN3 subpopulations, respectively. Panel B shows untreated (left panels) and BMP4 (30 μg/mL)–treated (right panels) deoxyguanosine-treated lobes (for 5 days) that were later reconstituted with untreated whole bone marrow. Panel C shows untreated thymocyte-depleted thymic lobes reconstituted with untreated (left panels) and BMP4 (30 μg/mL)–treated (right panels) whole bone marrow (for 8 hours prior to reconstitution) (D) Untreated thymocyte-depleted thymic lobes reconstituted with untreated (upper panels) and BMP4 (30 μg/mL)–treated (lower panels) DN1 thymocytes (treated for 8 hours prior to reconstitution).