Fig. 4

Maternal Activin-like signals are not required during the cleavage stages. Images of live embryos at 24 hpf. Embryos were treated with DMSO (A, B) or with SB-505124 at 0.75 hpf (C, D, G–L) or at 3 hpf (E, F). In panels G–L, the drug was applied at 0.75 hpf and washed out at the indicated time. Embryos treated with SB-505124 at 0.75 hpf and 3 hpf (C, E) lack all derivatives of the mesoderm and endoderm in the head and trunk, and are severely cyclopic (D, F). (G, H) When embryos are exposed to the drug only between 0.75 hpf and 3 hpf, they are indistinguishable from wild type (A, B). (I, J) When embryos are exposed to SB-505124 between 0.75 hpf and 4.3 hpf, they lack head mesoderm and endoderm, as indicated by severe cyclopia (J), but contain trunk somites and notochord (I). Finally, embryos exposed to SB-505124 between 0.75 hpf and 6 hpf lack notochord, but contain trunk somites (K), and are severely cyclopic (L). Lateral views, anterior is to the left (A, C, E, G, I, K) or ventral views (B, D, F, H, J, L).