Distinct roles of centriole distal appendage proteins in ciliary assembly and disassembly.

The primary cilium is a cellular organelle whose assembly and disassembly are closely linked to the cell cycle. The centriole distal appendage (DA) is essential for the early stages of ciliogenesis by anchoring the mother centriole to the cell surface. Despite the identification of over twelve proteins constituting the DA, including CEP83, CEP89, CEP164, FBF1, and SCLT1, their specific functions in ciliary dynamics are not fully understood. Here, we elucidate the precise role of DA proteins in ciliary assembly and disassembly. While Cep89 mutant cells exhibit normal ciliogenesis, the kinetics of ciliary disassembly is significantly delayed. Through siRNA-mediated knockdown of DA proteins, we identified two functional subgroups within DA proteins: CEP83, SCLT1, and CEP164, which are primarily essential for ciliary assembly and centriole docking, and CEP89 and FBF1, which specifically regulate ciliary disassembly. Notably, the depletion of CEP89 and FBF1 not only impedes ciliary disassembly but also disrupts the Aurora A kinase signaling pathway, leading to its downregulation and mislocalization at the basal body during serum-induced cell cycle re-entry. These findings suggest that DA components can be functionally categorized into two modules responsible for distinct aspects of ciliary dynamics, with broad implications for cellular signaling, homeostasis, and development.