Cilia assembly starts with centriole to basal body maturation, migration to the cell surface and docking to the plasma membrane. The basal body docking process involves the interaction of both the distal end of the basal body and the transition fibers (or mature distal appendages), with the plasma membrane. During this process, the transition zone assembles and forms the structural junction between the basal body and the nascent cilium. Mutations in numerous genes involved in basal body docking and transition zone assembly are associated with the most severe ciliopathies, highlighting the importance of these events in cilium biogenesis. The conservation of this sequence of events across phyla is paralleled by a high conservation of the proteins involved. We identified CEP90 by BioID using FOPNL as a bait. Ultrastructure expansion microscopy showed that CEP90, FOPNL and OFD1 localized at the distal end of both centrioles/basal bodies in Paramecium and mammalian cells. These proteins are recruited early after duplication on the procentriole. Finally, functional analysis performed both in Paramecium and mammalian cells demonstrate the requirement of this complex for distal appendage assembly and basal body docking. Altogether, we propose that this ternary complex is required to determine the future position of distal appendages

In metazoa, cilia assembly is a cellular process that starts with centriole to basal body maturation, migration to the cell surface, and docking to the plasma membrane. Basal body docking involves the interaction of both the distal end of the basal body and the transition fibers/distal appendages, with the plasma membrane. Mutations in numerous genes involved in basal body docking and transition zone assembly are associated with the most severe ciliopathies, highlighting the importance of these events in cilium biogenesis. In this context, the ciliate Paramecium has been widely used as a model system to study basal body and cilia assembly. However, despite the evolutionary conservation of cilia assembly events across phyla, whether the same molecular players are functionally conserved, is not fully known. Here, we demonstrated that CEP90, FOPNL, and OFD1 are evolutionary conserved proteins crucial for ciliogenesis. Using ultrastructure expansion microscopy, we unveiled that these proteins localize at the distal end of both centrioles/basal bodies in Paramecium and mammalian cells. Moreover, we found that these proteins are recruited early during centriole duplication on the external surface of the procentriole. Functional analysis performed both in Paramecium and mammalian cells demonstrate the requirement of these proteins for distal appendage assembly and basal body docking. Finally, we show that mammalian centrioles require another component, Moonraker (MNR), to recruit OFD1, FOPNL, and CEP90, which will then recruit the distal appendage proteins CEP83, CEP89, and CEP164. Altogether, we propose that this OFD1, FOPNL, and CEP90 functional module is required to determine in mammalian cells the future position of distal appendage proteins.