Multifaceted modes of γ-tubulin complex recruitment and microtubule nucleation at mitotic centrosomes

Abstract

Microtubule nucleation is mediated by {gamma}-tubulin ring complexes ({gamma}-TuRCs). In most eukaryotes, a GCP4/5/4/6 "core" complex promotes {gamma}-tubulin small complex ({gamma}-TuSC) association to generate cytosolic {gamma}-TuRCs. Unlike {gamma}-TuSCs, however, this core complex is non-essential in various species and absent from budding yeasts. In Drosophila, Spindle defective-2 (Spd-2) and Centrosomin (Cnn) redundantly recruit {gamma}-tubulin complexes to mitotic centrosomes. Here we show that Spd-2 recruits {gamma}-TuRCs formed via the GCP4/5/4/6 core, but that Cnn can recruit {gamma}-TuSCs directly via its well-conserved CM1 domain, similar to its homologues in budding yeast. When centrosomes fail to recruit {gamma}-tubulin complexes, they still nucleate microtubules via the TOG domain protein Mini-spindles (Msps), but these microtubules have different dynamic properties. Our data therefore help explain the dispensability of the GCP4/5/4/6 core and highlight the robustness of centrosomes as microtubule organising centres. They also suggest that the dynamic properties of microtubules are influenced by how they were nucleated.