Fig. 5. Segregation of pre-placodal region (PPR) and neural crest markers between head-fold (A-F') and early somite (G-J') stages. At stage 5-6 (A-F'), Six1 (A,A'), Six4 (B,B') and Eya2 (C,C') are expressed in the ectoderm encircling the anterior neural plate, while Dach1 (D,D') is found in the entire ectoderm. Pax7 (E,E') is expressed in a band of cells along the neural plate and partially overlaps with Six1, Six4 and Eya2 expression. PPR markers never colocalise with the neural plate marker Sox2 (F,F'). By stage 8, Six1 (G,G'), Six4 (H,H') and Eya2 (I,I') continue to surround the neural plate, but there is no overlap with Pax7 (K,K') or Slug (L,L'), which are confined to the neural folds. Dach1 remains expressed in most of the ectoderm (J,J'). Arrowheads in A'-C',G-I' label the medial limit of PPR gene expression; lines in A-L indicate the plane of the sections shown in A'-L', respectively.