Transmission electron micrographs of Crx-/- photoreceptors in the photoreceptor layer at P7. (A) Photoreceptor layer of Crx+/+ retina demonstrating nascent outer segment structures (arrow) emerging from photoreceptor connecting cilia (cc). (B) Crx-/- photoreceptors exhibited connecting cilia (cc) at this early stage, however, nascent outer segment structures were not observed. Scale Bar = 1 μm.