Induction of ER-xSmad6 at blastula stages recapitulates overexpression of xSmad6. (A-B) Uninjected embryos develop normally when cultured in the absence (A) or presence (B) of 1 μM 17β-estradiol (E2) from blastula stages. (C) Embryos develop normally when injected at the 2-cell stage with 2 ng/embryo of ER-xSmad6 mRNA and cultured in the absence of E2. (D) Embryos similarly injected with ER-xSmad6 and cultured in the presence of E2 from stage 6 are dorsalized. (E) Embryos are dorsalized when injected at the 2-cell stage with 0.8 ng xSmad6 mRNA. Original magnification, × 20.