Fig. 2. Separable organiser activities. (A,B) The zebrafish dorsal organiser is the embryonic shield (between the arrowheads), and is shown in (A) lateral and (B) animal-pole views. (C) Deep organiser tissue expresses gooscoid (gsc), while (D) superficial tissue expresses floating head (flh) mRNA. (E) By separating deep (grey) and superficial (red) organiser tissues and grafting the individual pieces, superficial tissue was found to induce a secondary axis that possessed only trunk and tail (F), while deep tissue induced a secondary axis that possessed only a head (G). (F,G) Embryos are stained for sonic hedgehog expression by in situ hybridisation. Arrows indicate (F) anterior limit of secondary axis and (G) posterior limit of secondary axis. Adapted, with permission, from Saúde et al. (Saúde et al., 2000).