title: Branching microtubule nucleation in Xenopus egg extracts mediated by augmin and TPX2.
abstract: The microtubules that comprise mitotic spindles in animal cells are nucleated at centrosomes and by spindle assembly factors that are activated in the vicinity of chromatin. Indirect evidence has suggested that microtubules also might be nucleated from pre-existing microtubules throughout the spindle, but this process has not been observed directly. Here, we demonstrate microtubule nucleation from the sides of existing microtubules in meiotic Xenopus egg extracts. Daughter microtubules grow at a low branch angle and with the same polarity as mother filaments. Branching microtubule nucleation requires γ-tubulin and augmin and is stimulated by factors previously implicated in chromatin-stimulated nucleation, guanosine triphosphate(GTP)-bound Ran and its effector, TPX2. Because of the rapid amplification of microtubule numbers and the preservation of microtubule polarity, microtubule-dependent microtubule nucleation is well suited for spindle assembly and maintenance.
authors: Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, 600 16(th) Street, San Francisco, CA 94158, USA.
authors: Sabine
authors: S
authors: Petry
authors: Aaron C
authors: AC
authors: Groen
authors: Keisuke
authors: K
authors: Ishihara
authors: Timothy J
authors: TJ
authors: Mitchison
authors: Ronald D
authors: RD
authors: Vale
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism*; D008540:Meiosis; D008853:Microscopy / Q000379:methods; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010063:Ovum / Q000737:chemistry / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D029867:Xenopus Proteins / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; C486551:TPX2 protein, Xenopus; D029867:Xenopus Proteins