Molecular basis of centriole duplication

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The centrosome, a unique membrane-less multiprotein organelle that serves as the main microtubule-organizing center in animal cells, plays a pivotal role in the orderly progression of the cell cycle. Since faulty assembly and duplication of the centrosome results in abnormal cell division, which then leads to various human disorders, elucidating the molecular mechanisms underlying centrosome assembly and function is likely a key step to understanding the etiology of centrosome-associated human diseases. By combining cell biology with biophysical methods and X-ray crystallography, we demonstrated that two pericentriolar scaffolds, Cep152 and Cep63, possess intrinsic activity of co-phase-separating into condensates and form a heterotetrameric complex that serves as a building block for generating a nanoscale cylindrical self-assembly around a centriole. Remarkably, two short uncharacterized regions named Self-Assembly Motifs (one each from Cep63 and Cep152) cooperatively conferred physicochemical properties that allowed them to undergo density transition and self-assemble into a cylindrical architecture. Interestingly, the Cep152-Cep63 condensates exhibited a rapid turnover, underwent fusion with other assemblies, and carried out a significant degree of internal rearrangement within a condensate. A Cep152-Cep63 cylindrical architecture that self-assembled on a flat substrate displayed a decreased but still detectable level of dynamic turnover. Interestingly, Polo-like kinase 4 (Plk4), a key regulator of centriole biogenesis, also dynamically phase-separated from a Cep152-bound state around a centriole (i.e., ring state) into a dot-like, low-nanoscale spherical condensate (i.e., dot state) upon autophosphorylating its C-terminal cryptic polo-box domain. Additional in vitro and in vivo data suggest that the Plk4 condensate serves as an assembling body at the future procentriole assembly site by amassing downstream procentriole assembly components such as STIL and Sas6 and facilitating Plk4-mediated centriole biogenesis. Thus, the formation of biomolecular condensates appears to be a fundamental step that not only promotes the self-assembly of a pericentriolar architecture but also triggers the process of centriole duplication. Along with this progress, we are currently examining the mechanism underlying pericentriolar material (PCM) organization, self-assembling activity of pericentriolar scaffold proteins, molecular basis of building higher-order PCM architectures.