Targeting of γ-tubulin complexes to microtubule organizing centers: conservation and divergence

Organisms with closed or open mitosis have differentially evolved various gamma-tubulin complex (gamma-TuC) recruiting factors to organize diverse cellular microtubule (MT) arrays, including the mitotic spindle. gamma-TuC recruiting factors not only target the gamma-TuC to MT nucleation sites, but also regulate MT nucleation activity by generating the template for MT nucleation or promoting the MT nucleation activity of pre-existing gamma-tubulin ring complexes (gamma-TuRCs). Here we outline the current understanding of MT nucleator assembly and its regulation by gamma-tubulin small complex (gamma-TuSC) receptors. Moreover, we discuss the emergence of gamma-TuC recruiting factors through evolution with augmented complexity and diversity and propose a hypothesis to account for the evolution of these factors in cooperative spindle assembly.