Fig. 1. Expression pattern of Otx1 as compared to that of Otx2 and Pax2 in the developing mouse eye. Dark-field images of frontal adjacent paraffin sections of wild-type embryos at different stages of development hybridised with radioactive probes for Otx1, Pax2 and Otx2, as indicated in the figure. Note how at early stages, Otx1 (A,D) and Otx2 (C,F) signals overlap and are complementary to that of Pax2 (B,E). Note how Otx1 (M,P) but not Otx2 (O,R) expression extends only to the dorsal portion of the optic nerve at later stages, partially overlapping with Pax2 (N,Q). The signal observed in the RPE in (T) is due to pigment granules and not to hybridised probe. l, lens; nr, neural retina; on, optic nerve; os, optic stalk, ov, optic vesicle; pnr, presumptive neural retina; ppe, presumptive pigment epithelium; pe, retinal pigment epithelium. Bar: 200 µm (A-F), 300 µm (G-I), 400 µm (J-O), 500 µm (P-R), and 700 µm (S-U).