Fig. 3. Activation of MAPK by β-catenin is non-cell autonomous. Stage 16-cell embryos were injected ventrally in one blastomere with myc-tagged β-catenin mRNA (500 pg) and in an adjacent blastomere with β-galactosidase mRNA (1 ng). Embryos were fixed at stage 9 and analyzed by immunofluorescence on equatorial sections. (A) Double staining for myc-β-catenin (anti-myc, red) and P-MAPK (green). (B) Double staining for β-galactosidase (red) and P-MAPK (green). (A) and (B) show consecutive sections. Nuclei were stained with DAPI (blue). P-MAPK signal was not only increased in β-catenin-overexpressing cells (arrowheads in A), but also in adjacent cells (arrows).