title: Microtubule nucleation in mitosis by a RanGTP-dependent protein complex.
abstract: BACKGROUND
  The γ-tubulin ring complex (γTuRC) is a multisubunit complex responsible for microtubule (MT) nucleation in eukaryotic cells. During mitosis, its spatial and temporal regulation promotes MT nucleation through different pathways. One of them is triggered around the chromosomes by RanGTP. Chromosomal MTs are essential for functional spindle assembly, but the mechanism by which RanGTP activates MT nucleation has not yet been resolved.
  
  
  RESULTS
  We used a combination of Xenopus egg extracts and in vitro experiments to dissect the mechanism by which RanGTP triggers MT nucleation. In egg extracts, NEDD1-coated beads promote MT nucleation only in the presence of RanGTP. We show that RanGTP promotes a direct interaction between one of its targets, TPX2, and XRHAMM that defines a specific γTuRC subcomplex. Through depletion/add-back experiments using mutant forms of TPX2 and NEDD1, we show that the activation of MT nucleation by RanGTP requires both NEDD1 phosphorylation on S405 by the TPX2-activated Aurora A and the recruitment of the complex through a TPX2-dependent mechanism.
  
  
  CONCLUSIONS
  The XRHAMM-γTuRC complex is the target for activation by RanGTP that promotes an interaction between TPX2 and XRHAMM. The resulting TPX2-RHAMM-γTuRC supracomplex fulfills the two essential requirements for the activation of MT nucleation by RanGTP: NEDD1 phosphorylation on S405 by the TPX2-activated Aurora A and the recruitment of the complex onto a TPX2-dependent scaffold. Our data identify TPX2 as the only direct RanGTP target and NEDD1 as the only Aurora A substrate essential for the activation of the RanGTP-dependent MT nucleation pathway.
authors.affiliation: Cell and Developmental Biology Programme, Centre for Genomic Regulation (CRG), Doctor Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu Fabra (UPF), Doctor Aiguader 88, 08003 Barcelona, Spain.
authors.forename: Jacopo
authors.initials: J
authors.lastname: Scrofani
authors.affiliation: Cell and Developmental Biology Programme, Centre for Genomic Regulation (CRG), Doctor Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu Fabra (UPF), Doctor Aiguader 88, 08003 Barcelona, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Sardon
authors.affiliation: Cell and Developmental Biology Programme, Centre for Genomic Regulation (CRG), Doctor Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu Fabra (UPF), Doctor Aiguader 88, 08003 Barcelona, Spain. Electronic address: sylvain.meunier@crg.eu.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Meunier
authors.affiliation: Cell and Developmental Biology Programme, Centre for Genomic Regulation (CRG), Doctor Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu Fabra (UPF), Doctor Aiguader 88, 08003 Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig de Lluis Companys 23, 08010 Barcelona, Spain. Electronic address: isabelle.vernos@crg.eu.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Vernos
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism; D022101:Microtubule-Organizing Center / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D010063:Ovum / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D029867:Xenopus Proteins / Q000235:genetics* / Q000378:metabolism; D014982:Xenopus laevis / Q000235:genetics* / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000235:genetics* / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D008869:Microtubule-Associated Proteins; C529826:NEDD1 protein, Xenopus; D009687:Nuclear Proteins; D010750:Phosphoproteins; C486551:TPX2 protein, Xenopus; D029867:Xenopus Proteins; D020931:ran GTP-Binding Protein