Mechanisms of cell cycle-dependent conversion of the mother centriole to the basal body

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Primary cilia are formed by conversion of the mother centriole to the basal body. Ciliary membranes are generated by fusion of vesicles to the pericentrosome, a process requiring Rab11-mediated recruitment of Rabin8, Rab8 activation and Rabin8 binding to Sec15, a component of the exocyst.This study showed that NDR2 phosphorylates Rabin8 at Ser-272 and defects in this phosphorylation impair preciliary membrane assembly and ciliogenesis, resulting in accumulation of Rabin8/Rab11-containing vesicles at the pericentrosome. Rabin8 binds to and colocalizes with GTP-bound Rab11 and phosphatidylserine (PS) on pericentrosomal vesicles. The phospho-mimetic S272E mutation of Rabin8 decreases affinity for PS but increases affinity for Sec15. These results suggest that NDR2-mediated Rabin8 phosphorylation is crucial for ciliogenesis by triggering the switch in binding specificity of Rabin8 from PS to Sec15, thereby promoting local activation of Rab8 and ciliary membrane formation.