ER-xSmad6 remains stable through neurulation but does not disrupt morphology unless induced prior to stage 11. (A) Western blot analysis of ER-xSmad6 stability. Embryos were injected at the 2-cell stage with 1 ng/embryo of ER-xSmad6 mRNA and cultured in the absence of E2. Protein was harvested at the stages indicated (UJ = uninjected; St. = stage). The Western blot was probed with a polyclonal antibody against the F domain of the human estrogen receptor. (B) Graphic summary of the morphologic phenotypes derived from induction of ER-xSmad6 at various stages throughout development after injection into ventral blastomeres at the 4-cell stage. n = 125 (uninjected), 63 (no hormone), 58 (stages 7-9), 59 (stage 10.5), 74 (stages 11.5-12), 35 (stage 13), and 68 (stages 14-19)