BMP signaling in ventral mesoderm is required for erythroid development. Animal cap and ventral mesoderm explants were isolated at stage 10 from uninjected embryos, or embryos injected at the 2-cell stage with 2 ng/embryo of ER-xSmad6 mRNA, and cocultured in the combinations as indicated (WE = whole embryo, NH = no hormone, and + or – indicates presence or absence, respectively, of ER-xSmad6). E2 was added to all explant cocultures at the equivalent of stage 13. Total RNA was harvested from explants and control whole embryos at stage 35 and samples were analyzed by Northern blotting (2 μg per lane). The filter was first probed with αT1-globin, then stripped and reprobed with EF-1α as a loading control. Numbers above lanes indicate percent of signal relative to uninjected control.
