title: TPX2 levels modulate meiotic spindle size and architecture in Xenopus egg extracts.
abstract: The spindle segregates chromosomes in dividing eukaryotic cells, and its assembly pathway and morphology vary across organisms and cell types. We investigated mechanisms underlying differences between meiotic spindles formed in egg extracts of two frog species. Small Xenopus tropicalis spindles resisted inhibition of two factors essential for assembly of the larger Xenopus laevis spindles: RanGTP, which functions in chromatin-driven spindle assembly, and the kinesin-5 motor Eg5, which drives antiparallel microtubule (MT) sliding. This suggested a role for the MT-associated protein TPX2 (targeting factor for Xenopus kinesin-like protein 2), which is regulated by Ran and binds Eg5. Indeed, TPX2 was threefold more abundant in X. tropicalis extracts, and elevated TPX2 levels in X. laevis extracts reduced spindle length and sensitivity to Ran and Eg5 inhibition. Higher TPX2 levels recruited Eg5 to the poles, where MT density increased. We propose that TPX2 levels modulate spindle architecture through Eg5, partitioning MTs between a tiled, antiparallel array that promotes spindle expansion and a cross-linked, parallel architecture that concentrates MTs at spindle poles.
authors: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720.
authors: Kara J
authors: KJ
authors: Helmke
authors: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720 bheald@berkeley.edu.
authors: Rebecca
authors: R
authors: Heald
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002457:Cell Extracts; D002474:Cell-Free System; D016547:Kinesins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism* / Q000648:ultrastructure; D010750:Phosphoproteins / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D029867:Xenopus Proteins / Q000378:metabolism*; D014982:Xenopus laevis; D020931:ran GTP-Binding Protein / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D002457:Cell Extracts; C088335:KIF11 protein, Xenopus; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; C486551:TPX2 protein, Xenopus; D029867:Xenopus Proteins; D016547:Kinesins; D020931:ran GTP-Binding Protein