Disrupted development of the retina in the Ccdc85c knockout rat

The coiled-coil domain-containing 85c (Ccdc85c) knockout (KO) rat generated by genome editing exhibits hydrocephalus and subcortical heterotopia. In this study, we aimed to further investigate the function of CCDC85C protein in the development of the retina. Expression of CCDC85C, acetylated tubulin, ciliary rootlet coiled-coil protein (CROCC), zonula occludens-1 (ZO-1), glutamine synthetase, and PAX6 were examined immunohistochemically in wild-type F344 rats at embryonic day (ED) 19 and at postnatal days (PNDs) 0, 4, 6, 13, and 20. Immunoelectron microscopy was performed for CCDC85C in the normal rat retina. Retinal lesions in Ccdc85c KO rats were examined using fundus photography, optical coherence tomography (OCT), and histology. In the normal rat retina, CCDC85C was co-localized with ZO-1 in the outer limiting membrane and persistently expressed after ED19. Ultrastructurally, CCDC85C was located between the outer nuclear layer and the inner segments, and showed the same location as the tight junction. In Ccdc85c KO rats, multifocal retinal dysplasia; disarrangement of the inner and outer segments, cilia, and rootlets; and impaired development of Müller cells were observed. In OCT images, Ccdc85c KO rats showed parallel hyperintense striations in the inner nuclear layer, and low reflectivity of the outer limiting membrane and layer of rods and cones. These results suggest that CCDC85C protein is located in the tight junction complex and is involved in retinal layer formation. The Ccdc85c KO rat model provides a novel tool to study retinal development as well as genetic hydrocephalus.