Phase separation of TPX2 enhances and spatially coordinates microtubule nucleation. Author Matthew King, Sabine Petry Publication Year 2020 Type Journal Article Abstract Phase separation of substrates and effectors is proposed to enhance biological reaction rates and efficiency. Targeting protein for Xklp2 (TPX2) is an effector of branching microtubule nucleation in spindles and functions with the substrate tubulin by an unknown mechanism. Here we show that TPX2 phase separates into a co-condensate with tubulin, which mediates microtubule nucleation in vitro and in isolated cytosol. TPX2-tubulin co-condensation preferentially occurs on pre-existing microtubules, the site of branching microtubule nucleation, at the endogenous and physiologically relevant concentration of TPX2. Truncation and chimera versions of TPX2 suggest that TPX2-tubulin co-condensation enhances the efficiency of TPX2-mediated branching microtubule nucleation. Finally, the known inhibitor of TPX2, the importin-α/β heterodimer, regulates TPX2 condensation in vitro and, consequently, branching microtubule nucleation activity in isolated cytosol. Our study demonstrates how regulated phase separation can simultaneously enhance reaction efficiency and spatially coordinate microtubule nucleation, which may facilitate rapid and accurate spindle formation. Keywords Animals, Microtubule-Associated Proteins, Cell Cycle Proteins, Xenopus Proteins, Xenopus laevis, Ovum, Microtubules, Spindle Apparatus, Meiosis, Cytosol, Tubulin, Microtubule-Organizing Center, Karyopherins Journal Nat Commun Volume 11 Issue 1 Pages 270 Date Published 2020 Jan 14 ISSN Number 2041-1723 DOI 10.1038/s41467-019-14087-0 Alternate Journal Nat Commun PMCID PMC6959270 PMID 31937751 PubMedPubMed CentralGoogle ScholarBibTeXEndNote X3 XML