Fig. 8. Epistatic analysis of the function of Wnt and RA in patterning the neural ectoderm. Dorsal views of whole embryos at late gastrula stage (A-F,I,J), and animal views of 55% epiboly stage embryos (G,H). cyp26-injected embryos were treated with LiCl at the 50% epiboly stage (B,E), and dkk1-injected embryos were treated with RA at 40% epiboly stage (C,F). Embryos were fixed at late gastrula and stained with otx2 (A-C) and hoxb1b (D-F). Regulation of the expression of raldh2 was examined in dkk1-injected embryos (H,J). At 55% epiboly stage, raldh2 expression is not suppressed at the blastoderm margin by dkk1 injection though the raldh2 negative area in the dorsal-most margin is slightly expanded (H). At late gastrula stage, raldh2 expression remains restricted to the blastoderm margin in dkk1-injected embryos (J, arrowhead).