Fig. 1. Regulation of bon and sur expression by Nodal signaling. Expression of sur (A,B) and bon (C-G) at 50% epiboly. Expression of bon at dome stage (H,I) and 30% epiboly (J,K). Wild-type (A,C,H,J), MZoep (B,D,I,K), bon (E), MZsur (F) and MZsur;bon (G) embryos. Expression of sur is not affected by loss of Nodal signaling (A,B). Expression of bon is abolished at 50% epiboly in MZoep embryos (C,D) but weak bon expression can be detected in dome stage (H,I) and 30% epiboly (J,K). Expression of bon is not affected in bon mutants (E) but reduced in MZsur and MZsur;bon mutant embryos at 50% epiboly (F,G).