Structural analysis of the role of TPX2 in branching microtubule nucleation. Author Raymundo Alfaro-Aco, Akanksha Thawani, Sabine Petry Publication Year 2017 Type Journal Article Abstract The mitotic spindle consists of microtubules (MTs), which are nucleated by the γ-tubulin ring complex (γ-TuRC). How the γ-TuRC gets activated at the right time and location remains elusive. Recently, it was uncovered that MTs nucleate from preexisting MTs within the mitotic spindle, which requires the protein TPX2, but the mechanism basis for TPX2 action is unknown. Here, we investigate the role of TPX2 in branching MT nucleation. We establish the domain organization of TPX2 and define the minimal TPX2 version that stimulates branching MT nucleation, which we find is unrelated to TPX2's ability to nucleate MTs in vitro. Several domains of TPX2 contribute to its MT-binding and bundling activities. However, the property necessary for TPX2 to induce branching MT nucleation is contained within newly identified γ-TuRC nucleation activator motifs. Separation-of-function mutations leave the binding of TPX2 to γ-TuRC intact, whereas branching MT nucleation is abolished, suggesting that TPX2 may activate γ-TuRC to promote branching MT nucleation. Keywords Animals, Nuclear Proteins, Protein Binding, Microtubule-Associated Proteins, Cell Cycle Proteins, Xenopus laevis, Microtubules, Spindle Apparatus, Tubulin, Microtubule-Organizing Center Journal J Cell Biol Volume 216 Issue 4 Pages 983-997 Date Published 2017 Apr 03 ISSN Number 1540-8140 DOI 10.1083/jcb.201607060 Alternate Journal J Cell Biol PMCID PMC5379942 PMID 28264915 PubMedPubMed CentralGoogle ScholarBibTeXEndNote X3 XML