Chibby’s function in the dock

Burke et al. describe how the coiled-coil protein Chibby promotes the formation of a membranous cap that helps centrioles dock with the plasma membrane during ciliogenesis.

Centrioles, also known as basal bodies, dock with the plasma membrane to nucleate the axonemal microtubules of both primary and motile cilia. Mice lacking the centriolar protein Chibby suffer chronic respiratory infections because their airway epithelial cells fail to form enough motile cilia to clear the respiratory tract of mucus and debris. The cells’ centrioles are unable to efficiently dock with the apical plasma membrane during ciliogenesis, but Chibby’s precise role in the process is unclear.

Burke et al. used super-resolution and electron microscopy to localize Chibby to the distal appendages of tracheal cell centrioles. Chibby was recruited to these appendages by CEP164, a protein that tethers small, Golgi-derived vesicles to centrioles during ciliogenesis. These vesicles subsequently merge into a large, membranous cap called the ciliary vesicle, which is proposed to fuse with the plasma membrane and anchor the centriole at the cell surface. Centrioles lacking Chibby either failed to recruit small vesicles or were unable to merge them into a larger ciliary membrane structure, explaining their inability to dock with the apical membrane.

Chibby bound to the guanine nucleotide exchange factor Rabin8, enhancing this protein’s association with CEP164. Rabin8 activates the small GTPase Rab8 to promote ciliary vesicle assembly. Senior author Ken-Ichi Takemaru now wants to characterize the roles of other Chibby-interacting proteins in ciliary vesicle formation and basal body docking.