Centriolar satellites are membrane-less structures that localize and move around the centrosome and cilium complex in a microtubuledependent manner. They play important roles in centrosome-and cilium-related processes, including protein trafficking to the centrosome and cilium complex, and ciliogenesis, and they are implicated in ciliopathies. Despite the important regulatory roles of centriolar satellites in the assembly and function of the centrosome and cilium complex, the molecular mechanisms of their functions remain poorly understood. To dissect the mechanism for their regulatory roles during ciliogenesis, we performed an analysis to determine the proteins that localize in close proximity to the satellite protein CEP72, among which was the retinal degeneration gene product CCDC66. We identified CCDC66 as a microtubuleassociated protein that dynamically localizes to the centrosome, centriolar satellites and the primary cilium throughout the cell cycle. Like the BBSome component BBS4, CCDC66 distributes between satellites and the primary cilium during ciliogenesis. CCDC66 has extensive proximity interactions with centrosome and centriolar satellite proteins, and co-immunoprecipitation experiments revealed interactions between CCDC66, CEP290 and PCM1. Ciliogenesis, ciliary recruitment of BBS4 and centriolar satellite organization are impaired in cells depleted for CCDC66. Taken together, our findings identify CCDC66 as a targeting factor for centrosome and cilium proteins.

Highlights d CCDC57 localizes to pericentriolar material, microtubules, and satellites d CCDC57 co-localizes with CEP63 at the proximal end of centrioles d CCDC57 binds to CEP63 and functions during initiation of centriole duplication d CCDC57 interacts with microtubules and ensures proper mitotic progression

Highlights d CCDC57 localizes to pericentriolar material, microtubules, and satellites d CCDC57 co-localizes with CEP63 at the proximal end of centrioles d CCDC57 binds to CEP63 and functions during initiation of centriole duplication d CCDC57 interacts with microtubules and ensures proper mitotic progression