Fig. 4. Dorsal genes are ectopically expressed in XTcf3^– embryos. (A) siamois and Xnr3 are activated in animal caps from XTcf3^– embryos. Animal caps were isolated from stage-8 uninjected or XTcf3^– embryos (5 caps each) and cultured to stage 11 prior to processing for real-time RT-PCR as above. Expression levels are relative to 100% stage-11 uninjected controls. Direct Wnt target genes siamois and Xnr3 are ectopically expressed while dorsal mesoderm genes (chordin and goosecoid) are not. (B) Dorsal genes are up-regulated both dorsally and ventrally in XTcf3^– embryos. Uninjected or XTcf3^– embryos were bisected during gastrulation at the indicated stages and processed immediately for real-time RT-PCR. Expression levels were normalized to ODC and are relative to 100% uninjected stage 10.5 embryos (not shown). Dorsal genes (siamois, chordin, Xnr3 and goosecoid) are up-regulated in both dorsal and ventral explants of XTcf3^– embryos compared to controls. (C) Comparison of dorsal and ventral gene expression in XTcf3^– embryos and axin^– embryos. XTcf3^– and axin^– embryos obtained from sibling donor oocytes were bisected as above and analyzed by real-time RT-PCR. Note the more severe inhibition of Xwnt8 expression and enhanced goosecoid expression in axin^– embryos.

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