Fig. 2. Nodal signalling is required for secondary notochord fate. (A-C) Embryo treatment is indicated above the panels. The marker analysed is shown on the left of the panels. For the graphs, embryo treatment is indicated on the x-axis and percentage of embryos on the y-axis. n=total number of embryos analysed. (A) Expression of Ci-Bra at the early gastrula stage and Ci-Noto1 at the early tailbud stage following inhibition of Nodal signalling. The schematic embryo, in a vegetal pole view, shows the positions of the primary and secondary notochord precursors (in blue) at the 110-cell stage. Arrowheads indicate the secondary notochord lineage. The insert in the control Ci-Noto1 panel is a cleaving embryo to indicate the stage at which the analysis was carried out. The graphs show the percentage of embryos showing expression of the gene indicated on the left, in one or two secondary notochord precursors. (B) Ablation of b5.3 on the right hand side (rb5.3) leads to an inhibition of Ci-Bra expression in the secondary notochord precursor on the ablated side. The schematic drawing of a 16-cell stage embryo, in animal pole view, shows the position of the b5.3 blastomere. The graph shows the percentage of secondary notochord precursors expressing strong or weak Ci-Bra on the left-(L) or right-(R) hand side of the embryo at the early gastrula stage. (C) Expression of Ci-Twist-like 1 at the early gastrula stage following inhibition of Nodal signalling. The graph shows the percentage of embryos expressing Ci-Twist-like 1 in one or both blastomeres for the lineages indicated in the colour scheme (see key). The schematic embryo on the left shows the positions of these blastomeres at the 110-cell stage, using the same colour scheme. The arrows indicate the secondary notochord precursors.