Figure 9.

The head and trunk sub-cluster genes show distinct responses to organizer signaling. Three genes were selected from each sub-cluster, and tested by in situ hybridization at stage 10.5 (top row) and 11.5 (bottom row), in embryos ventrally injected with noggin or noggin+dkk-1. Black arrowheads mark ectopic staining. Xlim-1 (A-F) and otx2 (M-R) expression are similarly induced at stage 10.5 by Noggin and Noggin+Dkk-1, but by stage 11.5 Noggin+Dkk-1 induction is clearly much stronger and more widespread. For Xlim-1, ectopic expression induced by Noggin+Dkk-1 is observed migrating away from the blastopore lip region, but never for Noggin alone. (M-R) Frzb-1 expression is ectopically induced only by the combination of Noggin+Dkk-1, not Noggin alone, and neither can sustain expression into late gastrulation. For the three trunk genes, FoxD5b (XFD-12') (S-X), FoxA4a (pintallavis) (Y-D'), and Xsox-2 (E'-J') ectopic induction is similar in both intensity and spread in Noggin and Noggin+Dkk-1 overexpressing embryos at stage 10.5 and 11.5. A-L and S-J' vegetal view; M-R animal view. Dorsal faces up in all pictures. (K') Otx2 expression was assayed by real-time RT-PCR, in stage 11.5 ventral tissues injected with the same mixtures used to create the microarray samples. Weak, but significant (p = 0.043 by one-sided t-test), induction in Dkk-1 overexpressing tissues are seen compared to ventral, supporting the weak Dkk-1 inductions seen on the microarray. Error bars show the standard error calculated from two biological replicates.