PT - JOURNAL ARTICLE AU - Wueseke, Oliver AU - Zwicker, David AU - Schwager, Anne AU - Wong, Yao Liang AU - Oegema, Karen AU - Jülicher, Frank AU - Hyman, Anthony A. AU - Woodruff, Jeffrey B. TI - Polo-like kinase phosphorylation determines <em>Caenorhabditis</em> <em>elegans</em> centrosome size and density by biasing SPD-5 toward an assembly-competent conformation AID - 10.1242/bio.020990 DP - 2016 Oct 15 TA - Biology Open PG - 1431--1440 VI - 5 IP - 10 4099 - http://bio.biologists.org/content/5/10/1431.short 4100 - http://bio.biologists.org/content/5/10/1431.full SO - Biology Open2016 Oct 15; 5 AB - 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.