Fig. 4. Regulation of AP neural patterning by Wnt signalling in neurulae. (A) Albino embryos were uninjected or injected at the eight-cell stage into the four animal blastomeres with 0.05 ng/blastomere pCSKA-Xwnt8, 0.05 ng/blastomere or 0.2 ng/blastomere Xdkk1 mRNA, 0.1 ng/blastomere or 0.4 ng/blastomere NXfz8 mRNA, 0.8 ng/blastomere or 1.6 ng/blastomere Xfrzb1 mRNA. Embryos were cultured until neural plate stage (stage 15) and analysed by triple in situ hybridization for the expression of Krox20, Bf1 (black) and Otx2 (red). Frontal views are shown, dorsal points towards the top. In a, the expression domains of Bf1, Otx2 and Krox20 (rhombomeres 3 and 5) are indicated. Note residual Krox20 expression for highest doses of XFrzb1 (arrowheads in e') but not XDkk1 (c') or NXFz8 (d'). 25-35 embryos were analysed per sample in three independent experiments. (B) Summary of the results shown in A. Colour code of gene expression is on the left. WT, wild-type embryo with normal Wnt levels.