Fig. 1

Transmission electron micrographs of transverse sections along the dorsal–ventral axis of wild type, ift57, ift88, and ift172 mutant zebrafish at 60 hpf. (A) In wild type retinas, few outer segments were observed at low magnification. The interphotoreceptor space was seen between the inner segments and the pigment epithelium (short arrows). Photoreceptor nuclei (n) were easily identified. (B and C) At higher magnification, short outer segments with loosely organized disk membranes were seen. Connecting cilia and primitive cilia (arrows) projected from the inner segment above the mitochondria (m) and nuclei (n). (D) ift57 mutants appeared similar to wild type retinas at low magnification. (E and F) High magnification of ift57 mutants revealed outer segments with stacked disk membranes and connecting cilia (arrow) that were located distal to the mitochondria (m) and nuclei (n). (G) An electron micrograph of an ift88 mutant looked similar to wild type and the interphotoreceptor space remained present (short arrows). (H and I) Outer segments were never observed in ift88 mutants and disorganized membrane structures (arrowheads) were seen at the apical surface of the inner segment, above the mitochondria and nuclei. (J) A low magnification image of ift172 mutants showed few differences from wild type. (K and L) High magnification electron micrographs revealed disorganized membrane structures (arrowheads) located deep within the inner segment below the mitochondria (m), as well as at the apical surface. Scale bars = 4 μm (A, D, G, and J), and 400 nm (B, C, E, F, H, I, K, and L).