Deletion of CEP164 in mouse photoreceptors post-ciliogenesis interrupts ciliary intraflagellar transport (IFT)

Centrosomal protein 164 (CEP164) is located at the edge of distal appendages in primary cilia and is necessary for basal body (BB) docking to the apical membrane. To investigate the function of CEP164 before and after BB docking in photoreceptors, we deleted CEP164 during retina embryonic development (Six3Cre), in postnatal rod photoreceptors (iCre75) and in mature retina using tamoxifen induction. BBs dock to the cell cortex during postnatal day 6 (P6) and extend a connecting cilium (CC) and an axoneme. P6 retina-specific knockouts (ret Cep164 -/-) are unable to dock BBs, thereby preventing formation of a CC or outer segments (OS). In rodspecific knockouts (rod Cep164 -/-), Cre expression starts after P9 and CC/OS form. P16 rod Cep164 -/- rods have nearly normal OS lengths, and maintain OS attachment through P21 despite loss of CEP164. Intraflagellar transport components (IFT88, IFT57 and IFT140) were reduced at P16 rod Cep164 -/- BBs and CC tips and nearly absent at P21, indicating impaired intraflagellar transport. Nascent OS discs, labeled with a fluorescent dye on P14 and P18 and harvested on P19, showed continued rod Cep164 -/- disc morphogenesis but absence of P14 discs mid-distally, indicating OS instability. Tamoxifen induction with PROM1 ETCre; Cep164 F/F (tam Cep164 -/-) adult mice affected maintenance of both rod and cone OS. The results suggest that CEP164 is key towards recruitment and stabilization of IFT-B particles at BB/CC. Impairment of IFT may be the main driver of ciliary malfunction observed with hypomorphic CEP164 mutations.