Fig. 3. The temporal requirement of Nodal signalling for Ci-Bra expression in the secondary notochord precursors at the early gastrula stage. (A) Embryos were treated with SB431542 at different developmental time points, indicated along the x-axis of the graph. l32 corresponds to the late 32-cell stage. The percentage of embryos expressing Ci-Bra in one or two B8.6 blastomeres is indicated on the y-axis. A representative embryo for each time point is shown below the graph. (B) Schematic drawings of embryos from the late 32-cell stage to the 110-cell stage. The secondary notochord lineages are shown in blue. The name of the secondary notochord precursor at the different stages and the stage and orientation of the embryos in the drawings is indicated below each drawing. Nodal-expressing blastomeres are marked with a black dot for those with strong expression and a grey dot for those with weak expression. Black bars connecting blastomeres indicate their sister cell relationship. Below the drawings is shown a cell lineage tree of the B6.2 presumptive secondary notochord precursor from the 32-cell stage until the generation of the secondary notochord precursor at the 110-cell stage. Blastomeres containing notochord fate are outlined in blue.