Fig. 5. Suppression of notochord fate by a signal from ectoderm. (A-B') Expression of Hr-Bra in 110-cell embryos (A,B; vegetal views) and of ETR-1 in cleavage-arrested 110-cell embryos (A',B'; animal views). Anterior is up. (A,A') Embryos with a-line cells removed at the early 32-cell stage. Arrowheads indicate cells in the nerve cord lineage that ectopically expressed Bra. (B,B') Embryos with a-line cells removed at the early 64-cell stage. (C-E') Expression of Hr-Bra and ETR-1 in partial embryos. (C,C') Every a-line cell (Ecto) and nerve cord/notochord precursor was co-isolated from early 32-cell embryos and cultured until the 110-cell stage. Arrowheads in C' indicate cells of notochord lineage. They did not express ETR1. (D,D',E,E') The same co-isolate as in C was recombined at the notochord side with a-line cells (D,D') or mesenchyme precursors (E,E'). In D', four rows of ETR1-expressing cells were observed, consisting of two rows of notochord and nerve cord precursors flanked by two rows of brain cells. Br, brain; Epi, epidermis; Mes, mesenchyme; NC, nerve cord; Not, notochord precursors. Scale bar: 100 µm.