The Centrosome Is a Selective Condensate that Nucleates Microtubules by Concentrating Tubulin
Centrosomes are non membrane bound compartments that nucleate microtubule arrays. They consist of nanometer scale centrioles surrounded by a micron scale, dynamic assembly of protein called the pericentriolar material (PCM) To study how PCM forms a spherical compartment that nucleates microtubules, we reconstituted PCM dependent microtubule nucleation in vitro using recombinant C. elegans proteins. We found that macromolecular crowding drives assembly of the key PCM scaffold protein SPD 5 into spherical condensates that morphologically and dynamically resemble in vivo PCM. These SPD 5 condensates recruited the microtubule polymerase ZYG 9 (XMAP215 homolog) and the microtubule stabilizing protein TPXL 1 (TPX2 homolog) Together, these three proteins concentrated tubulin ~4 fold over background, which was sufficient to reconstitute nucleation of microtubule asters in vitro. Our results suggest that in vivo PCM is a selective phase that organizes microtubule arrays through localized concentration of tubulin by microtubule effector proteins.
Cell