title: Microcephaly protein Asp focuses the minus ends of spindle microtubules at the pole and within the spindle.
abstract: Depletion of Drosophila melanogaster Asp, an orthologue of microcephaly protein ASPM, causes spindle pole unfocusing during mitosis. However, it remains unclear how Asp contributes to pole focusing, a process that also requires the kinesin-14 motor Ncd. We show that Asp localizes to the minus ends of spindle microtubule (MT) bundles and focuses them to make the pole independent of Ncd. We identified a critical domain in Asp exhibiting MT cross-linking activity in vitro. Asp was also localized to, and focuses the minus ends of, intraspindle MTs that were nucleated in an augmin-dependent manner and translocated toward the poles by spindle MT flux. Ncd, in contrast, functioned as a global spindle coalescence factor not limited to MT ends. We propose a revised molecular model for spindle pole focusing in which Asp at the minus ends cross-links MTs at the pole and within the spindle. Additionally, this study provides new insight into the dynamics of intraspindle MTs by using Asp as a minus end marker.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Ami
authors.initials: A
authors.lastname: Ito
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan goshima@bio.nagoya-u.ac.jp.
authors.forename: Gohta
authors.initials: G
authors.lastname: Goshima
mesh_terms: D000818:Animals; D001921:Brain; D003432:Cross-Linking Reagents / Q000737:chemistry; D029721:Drosophila Proteins / Q000502:physiology*; D004331:Drosophila melanogaster; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015151:Immunoblotting; D008853:Microscopy; D018613:Microscopy, Confocal; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D008870:Microtubules / Q000378:metabolism*; D010641:Phenotype; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D008941:Spindle Apparatus / Q000378:metabolism*; D013552:Swine
chemical_list: D003432:Cross-Linking Reagents; D029721:Drosophila Proteins; D008869:Microtubule-Associated Proteins; C106174:asp protein, Drosophila; D049452:Green Fluorescent Proteins