Centrioles generate two scaffolds with distinct biophysical properties to build mitotic centrosomes

Mitotic centrosomes form when centrioles recruit large amounts of pericentriolar material (PCM) around themselves. The PCM comprises hundreds of proteins, yet it can assemble and disassemble within minutes, leading to much debate about its physical nature. Here we show that Drosophila Spd-2 fluxes out from centrioles, recruiting Polo and Aurora A to catalyse the assembly of a solid-like Cnn-scaffold and a more liquid-like TACC-scaffold, respectively. Both scaffolds can assemble and recruit PCM proteins independently, but both are required for proper centrosome assembly, with the Cnn-scaffold providing mechanical strength, and the TACC-scaffold locally concentrating centriole and centrosome proteins. Recruiting Spd-2, but not Cnn or TACC, to the surface of synthetic beads injected into early embryos reconstitutes several aspects of mitotic centrosome assembly on the bead surface, and this depends on the ability of Spd-2 to recruit Polo and AurA. Thus, Spd-2 molecules flux out from the centriole recruiting Polo and AurA to promote the assembly of two scaffolds with distinct properties to support mitotic centrosome assembly in flies.