Wueseke, OliverZwicker, DavidSchwager, AnneWong, Yao LiangOegema, KarenJülicher, FrankHyman, Anthony A.Woodruff, Jeffrey B.2016-11-182016Wueseke, Oliver, David Zwicker, Anne Schwager, Yao Liang Wong, Karen Oegema, Frank Jülicher, Anthony A. Hyman, and Jeffrey B. Woodruff. 2016. “Polo-like kinase phosphorylation determines Caenorhabditis elegans centrosome size and density by biasing SPD-5 toward an assembly-competent conformation.” Biology Open 5 (10): 1431-1440. doi:10.1242/bio.020990. http://dx.doi.org/10.1242/bio.020990.2046-6390http://nrs.harvard.edu/urn-3:HUL.InstRepos:29408385ABSTRACT Centrosomes are major microtubule-organizing centers composed of centrioles surrounded by an extensive proteinacious layer called the pericentriolar material (PCM). In Caenorhabditis elegans embryos, the mitotic PCM expands by Polo-like kinase 1 (PLK-1) phosphorylation-accelerated assembly of SPD-5 molecules into supramolecular scaffolds. However, how PLK-1 phosphorylation regulates SPD-5 assembly is not known. We found that a mutant version of SPD-5 that is insensitive to PLK-1 phosphorylation (SPD-54A) could localize to PCM but was unable to rescue the reduction in PCM size and density when wild-type SPD-5 levels were decreased. In vitro, purified SPD-54A self-assembled into functional supramolecular scaffolds over long time scales, suggesting that phosphorylation only controls the rate of SPD-5 scaffold assembly. Furthermore, the SPD-5 scaffold, once assembled, remained intact and supported microtubule nucleation in the absence of PLK-1 activity in vivo. We conclude that PLK-1 is required for rapid assembly of the PCM scaffold but not for scaffold maintenance or function. Based on this idea, we developed a theoretical model that adequately predicted PCM growth rates in different mutant conditions in vivo. We propose that PLK-1 phosphorylation-dependent conversion of SPD-5 into an assembly-competent form underlies PCM formation in vivo and that the rate of this conversion determines final PCM size and density.en-USPCMPolo-like kinaseSPD-5CentrosomeMicrotubuleJournal Article2016-11-1810.1242/bio.020990