Fig. 2

col mutants display a reduction in the expression of shield-specific markers (A–D). Animal pole views of 6 hpf (shield stage) wild-type (A, C) and col mutant (B,D) embryos. gsc is normally expressed in the shield of wild-type embryos (A) and gsc expression is down-regulated in col mutant embryos (B). A mild reduction is also seen in chd expression in the shield at 6 hpf in col mutants (D) as compared to wild-type embryos (C). A decrease in expression of prechordal plate markers is also seen in col mutant embryos (E–H). At 80% epiboly (8.5 hpf), gsc is expressed in the developing prechordal plate of wild-type embryos (E). Prechordal plate gsc expression is reduced in col mutants (F). A similar decrease in expression is seen in dorsal views of col mutant embryos at 90% epiboly (H), when dkk1 expression is observed in the prechordal plate in wild-type embryos (G). col embryos display an expansion in the expression of ventralizing signals. (I–L) Animal pole views of col mutant embryos at 80% epiboly show an expansion of bmp2 (J) and bmp4 expression (L) as compared to wild-type embryos (I,K). Arrowheads indicate approximate limits of expression domains. (M,N) In dorsal views, wnt8 expression is apparent in the ventrolateral mesoderm and is excluded from the dorsal midline in wild-type embryos (M) at 60% epiboly (7 hpf). In col mutant embryos (N) at the same stage of development, wnt8 expression expands into the dorsal midline.