a, Expression of gsc, Xbra and Xnot-2 at early neurula stage 13 in control embryos and in embryos injected with Nodal recombinant protein at stage 10 or 11. Dorsal views for gsc and Xnot-2, ventral views for Xbra. b, Expression of sox2 and foxD5 (left: front view; right: dorsal view) and N-tubulin (ectopic neurons indicated by a white asterisk) in control and Nodal-injected embryos. c, Embryos were injected with GR-t-Smad2 mRNA, animal caps were explanted at early gastrula stage, induced or not with dexamethasone at stage 11 and processed for sox2 in situ hybridization. d, Expression of sox2 and k81 in control embryos and in embryos injected with zBMP4, Nodal or both recombinant proteins. Scale bar, 250 µm. e, Confocal images of pSmad1 immunostaining and nuclear DAPI staining in control embryos and in embryos injected with zBMP4, Nodal or both recombinant proteins. Scale bar, 50 µm. f, in situ hybridization of sox2 and foxD5 in animal caps treated with cycloheximide, Activin, or both. Scale bars, 200 µm. The number of embryos showing the phenotype displayed over the total number of embryos analyzed is indicated on each panel.