Fig. 4. PvuBra in situ hybridisation, later stages. (A) Posterior view of a 8 h.p.f.c. embryo. The vegetal plate (v.p.) is just visible above the five stained cells marking its posterior edge. The apical pole (a.p.) is below. Staining is now barely visible in the wings, and not apparent in the midline stem cell. (B) 10 h.p.f.c. embryo, ventral view. The posterior edge of the blastopore takes a V-shape (arrowhead). Posteriorly, the ventral midline is being formed, and also expresses PvuBra. A spot of expression appears terminally, consistently on the right side. It probably corresponds to the midline stem cell (m.s.c.). The prototroch (pt.) is visible in the background. (C) Young trochophore (13 h.p.f.c.), three quarter view, from the right-ventral side. Gastrulation has proceeded to its end. Stomodaeum (st.) is to the right, ventral midline to the bottom, and terminal cells (t.c.) to the left. (D) Older trochophore (24 h.p.f.c.). ventral-posterior view. The ectodermal cells underlying the stomodaeum (st.) still show transcripts. Midline and terminal expression has fainted away. More dorsally, right at the mantle edge (m.e.), four new spots of expression can now be seen. sb., stomatoblast; pt., prototroch; m.e., mantle edge.
