Basal bodies (BBs), which act as anchors for cilia formation at the cell membrane, share a high structural similarity with centrioles, but their composition differs during their maturation. The centrin-binding protein POC5 is involved in centriole elongation and maturation and can colocalise with centrin in ciliary structures, but its function in BBs still remains poorly understood. Now, Mark Winey and colleagues (Heydeck et al., 2020) take advantage of the BB-rich cytoskeleton of the ciliate Tetrahymena thermophila to identify a POC5 orthologue, TtPoc5, and investigate its function in BB formation and maturation. TtPoc5 localises exclusively at assembling BBs, whereas it is absent from mature BBs; this transient incorporation of TtPoc5 persists until it is removed prior to the onset of cilia formation. TtPoc5-knockout (KO) cells display an increase in BB density, although they present fewer cilia, and both phenotypes can be rescued with re-expression of TtPoc5. Moreover, the authors also identify a second POC5 orthologue, Sfr1, whose KO exhibits similar phenotypes to those of TtPoc5-KO cells, pointing to a functional redundancy between the two proteins. Depletion of both orthologues leads to an excessive increase in BB production, defective ciliogenesis and cell death. Hence, this study reveals the importance of dynamic POC5 localisation for BB formation and maturation, which might also have implications for ciliopathies associated with POC5 mutations.

• © 2020. Published by The Company of Biologists Ltd