title: A mitotic SKAP isoform regulates spindle positioning at astral microtubule plus ends.
abstract: The Astrin/SKAP complex plays important roles in mitotic chromosome alignment and centrosome integrity, but previous work found conflicting results for SKAP function. Here, we demonstrate that SKAP is expressed as two distinct isoforms in mammals: a longer, testis-specific isoform that was used for the previous studies in mitotic cells and a novel, shorter mitotic isoform. Unlike the long isoform, short SKAP rescues SKAP depletion in mitosis and displays robust microtubule plus-end tracking, including localization to astral microtubules. Eliminating SKAP microtubule binding results in severe chromosome segregation defects. In contrast, SKAP mutants specifically defective for plus-end tracking facilitate proper chromosome segregation but display spindle positioning defects. Cells lacking SKAP plus-end tracking have reduced Clasp1 localization at microtubule plus ends and display increased lateral microtubule contacts with the cell cortex, which we propose results in unbalanced dynein-dependent cortical pulling forces. Our work reveals an unappreciated role for the Astrin/SKAP complex as an astral microtubule mediator of mitotic spindle positioning.
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, MA 02142 Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: David M
authors.initials: DM
authors.lastname: Kern
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, MA 02142.
authors.forename: Peter K
authors.initials: PK
authors.lastname: Nicholls
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, MA 02142 Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139 Howard Hughes Medical Institute, Chevy Chase, MD 20815.
authors.forename: David C
authors.initials: DC
authors.lastname: Page
authors.affiliation: Whitehead Institute for Biomedical Research, Cambridge, MA 02142 Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139 icheese@wi.mit.edu.
authors.forename: Iain M
authors.initials: IM
authors.lastname: Cheeseman
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D008958:Models, Molecular; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D008941:Spindle Apparatus / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D018797:Cell Cycle Proteins; C555984:KNSTRN protein, human; D008869:Microtubule-Associated Proteins; D020033:Protein Isoforms