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FIG. 6. Dorsal Beta-catenin, TGF-Beta, and BMP-antagonist signalling pathways are required for endogenous XHex and cerberus expression. We tested whether the following signalling pathways are required for XHex and cerberus expression: (1) the maternal Wnt/beta-catenin pathway, (2) the dorsalising TGF-Beta signals, and (3) the dorsalising BMP antagonists noggin and chordin. Each of the pathways was blocked by the overexpression of dominant-inhibitory components of the respective pathways. Synthetic mRNA encoding deltaN-XTcf-3, 0.5 ng; XTcf-3, 0.5 ng; dnActRIIB, 1 ng; ActRBII, 1 ng; or BMP4, 1 ng was microinjected subequatorially into the two dorsal blastomeres at the 4-cell stage. At stage 10 0.5 embryos were subjected to whole-mount in situ hybridisation with XHex, cerberus, Xbra, and chordin probes. Representative embryos are shown in each case. The mRNA injected is indicated along the left and the in situ probe is indicated on the top. Inhibition of Beta-catenin or TGF-Beta signalling as well as over-expression of BMP4 blocked endogenous XHex and cerberus expression. Control injections of ActRIIB and XTcf-3 had no effect.
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