Fig. 2

Notch signaling is required during gastrulation for hypochord specification and a complete floor plate. (A–F) Side views, anterior to the left, of 24 hpf embryos showing col2a1 expression in the floor plate (fp) and hypochord (hc). (A) Control embryo incubated in 1% DMSO showing normal floor plate and hypochord arrangement. (B) Embryo treated with DAPT at 6 hpf to block Notch signaling. Floor plate was reduced, whereas hypochord was absent (asterisk). (C) Embryo treated with DAPT at 8.4 hpf (80% epiboly, midgastrulation) showing fewer hypochord cells. Floor plate cells form a complete row but are fewer in number (see G). (D) Embryo treated with DAPT at 12 hpf (6-somite stage) showing complete rows of both hypochord and floor plate. (E) Tg(hsp70l:XdnSu(H)myc) embryo heat-shocked at 6 hpf had no hypochord cells (asterisk). (F) Tg(hsp70l:XdnSu(H)myc) embryo heat-shocked at 9.5 hpf developed a complete row of hypochord cells. (G) We counted the number of col2a1-expressing floor plate and hypochord cells between somite 1 and 17 in control embryos and embryos treated with DAPT at the different times indicated. Embryos treated with DAPT at 6 hpf had reduced floor plate and few hypochord cells, whereas embryos treated with DAPT at later times had less severe floor plate and hypochord defects. Floor plate and hypochord cells were counted in ten embryos per sample, and the average number of cells (number shown within each bar) is expressed as a percentage of the control value (100%). Asterisks (*) indicate significance beyond the 0.001 level using Student′s t test. Scale bar: 40 μm for panels A–F.