Fig. 1. Cell lineages of posterior nerve cord and notochord, and expression pattern of HrETR-1. (A-E) Schematic diagrams illustrating ascidian embryos. (A) Tailbud embryo showing nerve cord and notochord. (B) Eight-cell embryo (lateral view; anterior is upwards and vegetal pole is towards the left). (C-E) 32-, 64- and 110-cell embryos, respectively (vegetal views; anterior is upwards). Presumptive nerve cord blastomeres are colored purple. Presumptive notochord blastomeres are colored pink. Short red bars between blastomeres indicate daughter cells generated by the previous cleavages. (F) Lineage tree showing nerve cord and notochord lineages. Only lineage of bilateral half is shown. (G-I) Spatial expression of HrETR-1, as revealed by whole-mount in situ hybridization. (G) Neural plate stage embryo (dorsal view; anterior is towards the left). Expression is seen in most cells of the neural plate, including both the presumptive nerve cord region derived from A4.1 blastomeres and the presumptive brain/palp regions derived from a4.2 blastomeres. White dots indicate the boundary between a4.2 derivatives and A4.1 derivatives. (H,I) Early tailbud embryo: (H) lateral view; (I) dorsal view. Expression is evident in cells of the larval nervous system, including brain, posterior nerve cord and palps.