Fig. 1. The pre-placodal region is induced by converging signals from the heart mesoderm and the neural plate. In the extra-embryonic region, Hensen's node (A-C,A'-C'; brown) rapidly induces the pre-neural marker Sox3 (A,A'; blue), while the pre-placodal marker Six4 (B,B'; blue) and the epidermal marker Dlx5 (C,C'; blue) are induced only at the edge of the neural plate after 14-16 hours. Stage 5/6 neural plate grafts (D-H,D'-H'; brown) induce the expression of the pre-placodal markers Six1 (D,D'; blue) and Dach1 (E,E'; blue), as well as Dlx5 (F,F') and the crest markers Slug (G,G'; blue) and Sox9 (H,H'; blue). Head mesoderm ablation (I,J; I',J'; broken line in I,J) results in the loss of Six4 (I,I', arrow) and Eya2 (J,J', arrow). Grafts of head mesoderm (K-P,K'-P'; brown) induce the expression of Six1 (K,K'; blue), Six4 (L,L'; blue), Eya2 (M,M'; blue), Dach1 (N,N'; blue), Dlx5 (O,O'; blue) and low levels of Sox3 (P,P'; blue). Horizontal lines in A-P indicate the level of the sections shown in A'-P', respectively. Brown staining in A-H,A'-H',K-P and K'-P' represents QCPN immunoreactivity labelling quail tissue.