Sub-ciliary localization of CEP290 and effects of its loss in mouse photoreceptors during development

The most common genetic cause of the childhood blindness disease Leber congenital amaurosis is mutation of the ciliopathy gene CEP290. Despite extensive study, the photoreceptor-specific roles of CEP290 remain unclear. Using advanced microscopy techniques, we investigated the sub-ciliary localization of CEP290 and its role in mouse photoreceptors during development. CEP290 was found throughout the connecting cilium between the microtubules and membrane, with nine-fold symmetry. In the absence of CEP290 ciliogenesis occurs, but the connecting cilium membrane is aberrant, and sub-structures, such as the ciliary necklace and Y-links, are confined to the proximal connecting cilium. Transition zone (TZ) proteins AHI1 and NPHP1 were abnormally restricted to the proximal connecting cilium in the absence of CEP290, whereas other TZ proteins, like NPHP8 and CEP89 were unaffected. Although outer segment disc formation is inhibited in Cep290 mutant retina, we observed large numbers of extracellular vesicles. These results suggest roles for CEP290 in ciliary membrane structure, outer segment disc formation and photoreceptor-specific spatial distribution of a subset of TZ proteins, which collectively lead to failure of outer segment formation and photoreceptor degeneration.