title: Kif15 cooperates with eg5 to promote bipolar spindle assembly.
abstract: BACKGROUND
  The formation of a bipolar spindle is an essential step during cell division. Bipolar spindle assembly is driven by the highly conserved microtubule motor Eg5 (kinesin-5), which can slide antiparallel microtubules apart to drive centrosome separation. However, it is currently unclear whether and how additional motors can contribute to centrosome separation and bipolar spindle formation.
  
  
  RESULTS
  We have developed a novel assay to identify motors involved in spindle bipolarity; via this assay, we identify Kif15/Hklp2 (kinesin-12, hereafter referred to as Kif15). Kif15 is not required for spindle bipolarity in cells with full Eg5 activity but becomes essential when Eg5 is partially inhibited. We show that the primary function of Kif15 is to promote spindle elongation and to ensure maintenance of spindle bipolarity. Nonetheless, ectopic expression of Kif15 can fully reconstitute bipolar spindle assembly in the absence of Eg5 activity, demonstrating that Kif15 can replace all essential functions of Eg5 in bipolar spindle assembly. Importantly, this activity of Kif15 depends on its interaction with the microtubule-associated protein TPX2, indicating that a Kif15-TPX2 complex promotes centrosome separation.
  
  
  CONCLUSIONS
  These findings show that, similar to Eg5, Kif15 can drive centrosome separation during bipolar spindle assembly. For this activity, Kif15 requires both its motor domain and its interaction with TPX2. Based on these data, we propose that a complex of Kif15 and TPX2 can crosslink and slide two antiparallel microtubules apart, thereby driving centrosome separation.
authors.affiliation: Department of Medical Oncology and Cancer Genomics Centre, University Medical Center Utrecht, The Netherlands.
authors.forename: Marvin E
authors.initials: ME
authors.lastname: Tanenbaum
authors.forename: Libor
authors.initials: L
authors.lastname: Macůrek
authors.forename: Aniek
authors.initials: A
authors.lastname: Janssen
authors.forename: Erica F
authors.initials: EF
authors.lastname: Geers
authors.forename: Mónica
authors.initials: M
authors.lastname: Alvarez-Fernández
authors.forename: René H
authors.initials: RH
authors.lastname: Medema
mesh_terms: D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D016764:Cell Polarity; D018385:Centrosome / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D016547:Kinesins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D008869:Microtubule-Associated Proteins / Q000378:metabolism / Q000502:physiology; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology; D021381:Protein Transport; D034622:RNA Interference; D008941:Spindle Apparatus / Q000378:metabolism* / Q000502:physiology
chemical_list: D018797:Cell Cycle Proteins; C470243:KIF11 protein, human; C486567:KIF15 protein, human; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; C122167:TPX2 protein, human; D016547:Kinesins