Fig. 7. Epistatic analysis of the function of Wnt and Fgf in patterning the neural ectoderm. Dorsal views of whole embryos at late gastrula stage. Gain and loss of function of Wnt activity was achieved by LiCl treatment (B,G,L) and dkk1 injection (C,H,M), respectively. Epistasis with Fgf was examined by XFD injection followed by LiCl treatment (D,I,N) and by fgf3 +dkk1 co-injection (E,J,O). Embryos were fixed at late gastrula and stained with cyp26 (A-E), otx2 (F-J) and hoxb1b (K-O). Arrowheads in C and M indicate the limit of caudal expansion of cyp26 expression (C) and remaining hoxb1b expression (M). In some cases, only half the embryo is affected when one of two cells is injected (N, arrowhead).