Fig. 7. Different regulation of Nodal target genes by bon and sur. All embryos are at 50% epiboly; animal pole view except M-P, which are lateral views. (A-D) Expression of gsc in prechordal plate progenitors is weakly reduced in bon (B), strongly reduced in MZsur (C) and absent in MZsur;bon mutant embryos (D). (E-H) Expression of bik is not affected in bon (F) but downregulated in MZsur (G) and MZsur;bon (H) mutant embryos. (I-L) Expression of mezzo is not affected in bonMO (J) but downregulated in MZsur (K) and MZsur;bonMO (L) embryos. (M-P) Expression of cas in endodermal progenitors (arrows) is strongly reduced in bon (N) and MZsur;bon (P) mutant embryos. Notice that cas expression in the yolk syncytial layer is not regulated by Nodal signaling. Expression of snail (Q-T) and flh (U-X) are not affected in any of the mutants.