Microtubule nucleation by gamma-tubulin complexes and beyond

In this short review, we give an overview of microtubule nucleation within cells. It is nearly 30 years since the discovery of gamma-tubulin, a member of the tubulin superfamily essential for proper microtubule nucleation in all eukaryotes. gamma-tubulin associates with other proteins to form multiprotein gamma-tubulin ring complexes (gamma-TuRCs) that template and catalyse the otherwise kinetically unfavourable assembly of microtubule filaments. These filaments can be dynamic or stable and they perform diverse functions, such as chromosome separation during mitosis and intracellular transport in neurons. The field has come a long way in understanding gamma-TuRC biology but several important and unanswered questions remain, and we are still far from understanding the regulation of microtubule nucleation in a multicellular context. Here, we review the current literature on gamma-TuRC assembly, recruitment, and activation and discuss the potential importance of gamma-TuRC heterogeneity, the role of non-gamma-TuRC proteins in microtubule nucleation, and whether gamma-TuRCs could serve as good drug targets for cancer therapy.