An Acentriolar Centrosome At The C. elegans Ciliary Base

SUMMARY In animal cells the functions of the cytoskeleton are coordinated by centriole-based centrosomes via microtubule-nucleating γ-tubulin complexes embedded in the pericentriolar material or PCM [1]. PCM assembly has been best studied in the context of mitosis, where centriolar SPD-2 recruits PLK-1, which in turn phosphorylates key scaffolding components such as SPD-5 and CNN to promote expansion of the PCM polymer [2–4]. To what extent these mechanisms apply to centrosomes in interphase or in differentiated cells remains unclear [5]. Here, we examine a novel type of centrosome found at the ciliary base of C. elegans sensory neurons, which we show plays important roles in neuronal morphogenesis, cellular trafficking and ciliogenesis. These centrosomes display similar dynamic behavior to canonical, mitotic centrosomes, with a stable PCM scaffold and dynamically localized client proteins. Unusually, however, they are not organized by centrioles, which degenerate early in terminal differentiation [6]. Yet, PCM not only persists but continues to grow with key scaffolding proteins including SPD-5 expressed under control of the RFX transcription factor DAF-19. This assembly occurs in the absence of the mitotic regulators SPD-2, AIR-1 and PLK-1, but requires tethering by PCMD-1, a protein which also plays a role in the initial, interphase recruitment of PCM in early embryos [7]. These results argue for distinct mechanisms for mitotic and non-mitotic PCM assembly, with only the former requiring PLK-1 phosphorylation to drive rapid expansion of the scaffold polymer. ETOC BLURBCentrioles play a critical role in mitotic centrosome assembly. Here, Garbrecht et al. show that pericentriolar material (PCM) persists at the ciliary base of C. elegans sensory neurons after centriole degeneration, where it contributes to neuronal morphogenesis and cellular trafficking. Remarkably, this PCM displays dynamic properties similar to canonical centrosomes, yet its continued assembly and maintenance is independent of known mitotic regulators, suggesting differential mechanisms for mitotic and non-mitotic centrosome assembly. HIGHLIGHTSPCM persists at the acentriolar ciliary base in C. elegansPCM assembles in a SPD-2, AIR-1 and PLK-1-independent mannerPCMD-1 tethers PCM at the ciliary base in the absence of centriolesPCM is required for neuronal morphogenesis and cilium assembly