Fig. 2. Fgf3 and Fgf8 might account for the involvement of Fgf signalling pathway in the Nodal positive-feedback loop. (A-U) Whole mount embryos showing expression of fgf3, fgf8, oep and tar in blue (the probe is indicated in the bottom left and the stage at the bottom right of each panel: sh, shield stage: 80%, 80% epiboly). (A-L) Views from the animal pole, dorsal to the bottom of embryos uninjected (uninj) or injected with sqt, cyc, fgf3 and fgf8 synthetic mRNA (indicated top right). (M-R) Expression pattern of fgf3 (M-O) and fgf8 (P-R) throughout epiboly in the MZoep background. Arrows in R point to the dorsal limit of the marginal staining. (S-U) Lateral views, dorsal to the right, of untreated (control) embryos or embryos treated with SU5402 (top right). 10 µM SU5402 (T) phenocopies the ace mutant phenotype and 30 µM SU5402 (U) abolishes the expression of oep at the blastoderm margin. Note that oep is still expressed on the dorsal side, consistent with the involvement of other pathways.