(A-D) Epistasis experiment in embryos injected with Admp MO, Chordin MO, or a mixture of both (n = 23 or more per experimental set).
(E) Injection of xAdmp mRNA (25 pg in each blastomere at the four-cell stage) abolishes CNS formation (absence of Sox2 expression).
(F) A single dorsal injection of Chordin mRNA (50 pg) rescues CNS formation in embryos ventralized by Admp mRNA injection.
(G) Secondary axes (marked by Sox2, n = 37) induced by a single ventral injection of Chordin mRNA (50 pg) lack eye and forebrain tissues (marked by Six3, inset).
(H) In ADMP-depleted embryos, Chordin mRNA induces complete secondary axes including eye and forebrain tissues (n = 21).
(I) Spemann organizer grafts at midgastrula (stage 10¾ ) induce trunks with no eyes (n = 9) or cyclopic eyes (n = 4).
(J) ADMP-depleted Spemann organizer grafts transplanted at midgastrula (stage 10¾ ) induce complete head structures with two eyes (in 7 of 13 grafts).