Fig. 6. Expansion of RPE into the presumptive neural retina in Fgf9^-/- embryos. In wild-type E13.5 eyes (A,C), the neural retina (NR) is morphologically distinguished from the RPE. The anterior boundary of the RPE (arrow) is clearly defined by the shape of the cells and the presence of pigment granules. In E13.5 Fgf9^-/- embryos, the anterior border of the ventral neural retina is consistently affected (B,D). The RPE extends around the anterior margin and occupies a small zone on the inner layer of the optic cup (arrows in B,D). High-magnification images of the boxed regions in A,B are shown in C,D, respectively. Dark-field images of the wild-type (E) and mutant (F) eyes clearly show extension of pigmentation around the anterior margin in Fgf9^-/- embryos. Scale bars: 60 µm in A,B; 20 µm in C,D; 40 µm in E,F.