Augmin promotes meiotic spindle formation and bipolarity in Xenopus egg extracts. Author Sabine Petry, Céline Pugieux, François Nédélec, Ronald Vale Publication Year 2011 Type Journal Article Abstract Female meiotic spindles in many organisms form in the absence of centrosomes, the organelle typically associated with microtubule (MT) nucleation. Previous studies have proposed that these meiotic spindles arise from RanGTP-mediated MT nucleation in the vicinity of chromatin; however, whether this process is sufficient for spindle formation is unknown. Here, we investigated whether a recently proposed spindle-based MT nucleation pathway that involves augmin, an 8-subunit protein complex, also contributes to spindle morphogenesis. We used an assay system in which hundreds of meiotic spindles can be observed forming around chromatin-coated beads after introduction of Xenopus egg extracts. Spindles forming in augmin-depleted extracts showed reduced rates of MT formation and were predominantly multipolar, revealing a function of augmin in stabilizing the bipolar shape of the acentrosomal meiotic spindle. Our studies also have uncovered an apparent augmin-independent MT nucleation process from acentrosomal poles, which becomes increasingly active over time and appears to partially rescue the spindle defects that arise from augmin depletion. Our studies reveal that spatially and temporally distinct MT generation pathways from chromatin, spindle MTs, and acentrosomal poles all contribute to robust bipolar spindle formation in meiotic extracts. Keywords Animals, Multiprotein Complexes, Female, Microtubule-Associated Proteins, Xenopus Proteins, Xenopus laevis, Ovum, Centrosome, Microtubules, Spindle Apparatus, Meiosis, Protein Subunits Journal Proc Natl Acad Sci U S A Volume 108 Issue 35 Pages 14473-8 Date Published 2011 Aug 30 ISSN Number 1091-6490 DOI 10.1073/pnas.1110412108 Alternate Journal Proc Natl Acad Sci U S A PMCID PMC3167534 PMID 21844347 PubMedPubMed CentralGoogle ScholarBibTeXEndNote X3 XML