The Centrosome-Specific Phosphorylation of Cnn by Polo/Plk1 Drives Cnn Scaffold Assembly and Centrosome Maturation

Centrosomes are important cell organizers. They consist of a pair of centrioles surrounded by pericentriolar material (PCM) that expands dramatically during mitosis—a process termed centrosome maturation. How centrosomes mature remains mysterious. Here, we identify a domain in Drosophila Cnn that appears to be phosphorylated by Polo/Plk1 specifically at centrosomes during mitosis. The phosphorylation promotes the assembly of a Cnn scaffold around the centrioles that is in constant flux, with Cnn molecules recruited continuously around the centrioles as the scaffold spreads slowly outward. Mutations that block Cnn phosphorylation strongly inhibit scaffold assembly and centrosome maturation, whereas phosphomimicking mutations allow Cnn to multimerize in vitro and to spontaneously form cytoplasmic scaffolds in vivo that organize microtubules independently of centrosomes. We conclude that Polo/Plk1 initiates the phosphorylation-dependent assembly of a Cnn scaffold around centrioles that is essential for efficient centrosome maturation in flies. [Display omitted] •Plk1/Polo phosphorylates Cnn in vitro•Phosphorylation appears to occur specifically at centrosomes during mitosis•Phosphorylation allows Cnn to assemble into a dynamic scaffold around centrioles•Cnn scaffold assembly is required for proper centrosome maturation Centrosomes, important cellular organizers, form when centrioles recruit pericentriolar material (PCM) around themselves. Conduit et al. shed light on PCM spreading/centrosome maturation during mitosis, showing that Polo kinase initiates phosphorylation-dependent assembly of PCM protein Cnn as a scaffold around centrioles. This scaffold then spreads outward to support an expanded PCM.