Fig. 7. Expression of marker genes of the medial neural plate in embryos in which Nodal signalling has been inhibited. (A) Experimental conditions are shown at the top of the panels and the marker analysed is indicated on the left of the panels. Neural plate views are shown for all embryos except cytochalasin B-treated embryos (lower panels). Insert shows a control cleaving embryo for Ci-Otx expression. Open arrowheads indicate A7.8 blastomeres. In all panels, filled arrowheads indicate ectopic marker expression. Ci-Otx expression was observed in one or both A7.8 blastomeres in 0/80 control embryos, 64/67 SB431542-treated embryos, 13/15 Ci-tALK4/5/7 injected embryos and 18/20 Ci-Nodal-MO injected embryos. (B) The marker analysed is indicated at the top of each graph. Graphs show the percentage of embryos (y-axis) that express the marker genes in 0-8 neural plate cells (x-axis). Control embryos (n=more than 100) are indicated by red bars; SB431542-treated embryos (n=82 for Ci-HB9/MNX and n=59 for Ci-FGF9/16/20) by blue horizontal striped bars; Ci-tALK4/5/7 injected embryos (n=37 for Ci-HB9/MNX and n=11 for Ci-FGF9/16/20) by blue diagonal striped bars; and Ci-Nodal-MO-injected embryos (n=24 for Ci-HB9/MNX and n=31 for Ci-FGF9/16/20) by filled blue bars.