The ternary complex CEP90, FOPNL and OFD1 specifies the future location of centriolar distal appendages, and promotes their assembly

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 apparent 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 form an evolutionary conserved complex that is 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 after centriole duplication on the external surface of the procentriole and define the future location of the distal appendages. Functional analysis performed both in Paramecium and mammalian cells demonstrate the requirement of this complex for distal appendage assembly and basal body docking. Finally, we show that mammals require another component, Moonraker (MNR), to recruit OFD1, FOPNL, and CEP90, which will then recruits the distal appendage protein CEP83. Altogether, we propose that this ternary complex is required to determine the future position of distal appendages.