title: A role for NuSAP in linking microtubules to mitotic chromosomes.
abstract: The spindle apparatus is a microtubule (MT)-based machinery that attaches to and segregates the chromosomes during mitosis and meiosis. Self-organization of the spindle around chromatin involves the assembly of MTs, their attachment to the chromosomes, and their organization into a bipolar array. One regulator of spindle self-organization is RanGTP. RanGTP is generated at chromatin and activates a set of soluble, Ran-regulated spindle factors such as TPX2, NuMA, and NuSAP . How the spindle factors direct and attach MTs to the chromosomes are key open questions. Nucleolar and Spindle-Associated Protein (NuSAP) was recently identified as an essential MT-stabilizing and bundling protein that is enriched at the central part of the spindle . Here, we show by biochemical reconstitution that NuSAP efficiently adsorbs to isolated chromatin and DNA and that it can directly produce and retain high concentrations of MTs in the immediate vicinity of chromatin or DNA. Moreover, our data reveal that NuSAP-chromatin interaction is subject to Ran regulation and can be suppressed by Importin alpha (Impalpha) and Imp7. We propose that the presence of MT binding agents such as NuSAP, which can be directly immobilized on chromatin, are critical for targeting MT production to vertebrate chromosomes during spindle self-organization.
authors.affiliation: European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany. katharina_ribbeck@hms.harvard.edu
authors.forename: Katharina
authors.initials: K
authors.lastname: Ribbeck
authors.forename: Tim
authors.initials: T
authors.lastname: Raemaekers
authors.forename: Geert
authors.initials: G
authors.lastname: Carmeliet
authors.forename: Iain W
authors.initials: IW
authors.lastname: Mattaj
mesh_terms: D000818:Animals; D002460:Cell Line; D002875:Chromosomes / Q000378:metabolism*; D033481:Chromosomes, Mammalian / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism*; D029867:Xenopus Proteins / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000378:metabolism
chemical_list: D028884:Karyopherins; D008869:Microtubule-Associated Proteins; D011994:Recombinant Proteins; D029867:Xenopus Proteins; D004247:DNA; D020931:ran GTP-Binding Protein