Photoreceptor differentiation and planar organization in control and γ-secretase-inhibited (CE) embryos. (A, B) Double-cones labeled by zpr-1 at 65 hpf (N = 15 embryos). (C, D) The outer limiting membrane (apical surface) was labeled by zs-4 (N = 15 embryos). (E–J) Whole-mount preparations of control and CE-treated eyes processed for in situ hybridization using opsin-specific riboprobes. Rod (Fast Red-pseudo-colored magenta) and UV (FITC-green) opsin in control (E) and CE-treated (F) retinas at 65 hpf. Red opsin (Fast Red-red) in control (G) and CE-treated (H) retinas at 65 hpf. Higher magnification of control (I) and CE-treated (J) retinas stained for red opsin expression (NBT/BCIP-purple). Scale bar = 50 μm (A-H); 20 μm (I, J).