Fig. 1

Floor plate precursor cells express her9. A: Dorsal view of a 6 hpf (shield stage) whole-mount embryo probed for her9 expression. The animal pole is toward the top. Dorsal cells close to the blastoderm margin (arrows) express her9. B: Sagittal section at the dorsal margin of 6 hpf embryo probed for her9 (blue) and ntl (red). Dorsal is to the right. Some cells are both her9⁺ and ntl⁺ (arrow). C: Sagittal section at the dorsal margin of a 7 hpf embryo. Some her9⁺ cells (arrowhead) are anterior to the ntl expression domain, while others appear to coexpress her9 and ntl (arrow). D: Whole-mount, dorsal view, at 8 hpf (75% epiboly) showing her9⁺ cells at the midline (arrowhead). E: Sagittal section at the dorsal midline, 8 hpf, showing her9 expression in presumptive floor plate cells (arrowheads) overlying ntl⁺ notochord precursors. F: Transverse section across the midline, 8 hpf, approximately at the level of the lower arrowhead in (E). her9⁺ cells are superficial (arrowhead) and lateral to (arrow) ntl⁺ notochord precursors. These are presumptive floor plate and hypochord precursors, respectively. G: Transverse section, 11 hpf (3-somite stage), showing her9 expression in floor plate cells (arrowhead) overlying the notochord (nc) and hypochord cells (arrow) underneath the notochord. Neural plate cells also express her9 at this stage (asterisk). Scale bar = 80 µm in A,D; 40 µm in E; 20 µm in B,C,F,G.