Fig. 5. Summary of PvuBra expression, from 3D induction to the end of gastrulation. Color shading corresponds to observed PvuBra RNA expression. (A) 32-cell stage (3 h.p.f.c.). (B) 64-cell stage (4 h.p.f.c.). (C) 88-cell stage (5 h.p.f.c.). Division of 3c¹, 3d¹ and 2d² (see text for details). (D) 6 h.p.f.c.. Division of 3c², 3d² and the midline stem cell, so that the midline is now made of two cells. 3D derivatives are now omitted. (E) 10 h.p.f.c.. The posterior edge of the blastopore migrates anteriorly, together with the two lateral stomatoblasts. Terminal cells have lost PvuBra expression. A third small cell is added to the midline by the stem cell. (F,G) Late gastrulae, showing the growing midline, and the closing blastopore. (H) 13 h.p.f.c. young trochophore expression pattern. v.p., vegetal plate; t.c. teminal cell; m.s.c. midline stem cell; sb. stomatoblast; st. stomodaeum.

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