title: A nuclear-derived proteinaceous matrix embeds the microtubule spindle apparatus during mitosis.
abstract: The concept of a spindle matrix has long been proposed. Whether such a structure exists, however, and what its molecular and structural composition are have remained controversial. In this study, using a live-imaging approach in Drosophila syncytial embryos, we demonstrate that nuclear proteins reorganize during mitosis to form a highly dynamic, viscous spindle matrix that embeds the microtubule spindle apparatus, stretching from pole to pole. We show that this "internal" matrix is a distinct structure from the microtubule spindle and from a lamin B-containing spindle envelope. By injection of 2000-kDa dextran, we show that the disassembling nuclear envelope does not present a diffusion barrier. Furthermore, when microtubules are depolymerized with colchicine just before metaphase the spindle matrix contracts and coalesces around the chromosomes, suggesting that microtubules act as "struts" stretching the spindle matrix. In addition, we demonstrate that the spindle matrix protein Megator requires its coiled-coil amino-terminal domain for spindle matrix localization, suggesting that specific interactions between spindle matrix molecules are necessary for them to form a complex confined to the spindle region. The demonstration of an embedding spindle matrix lays the groundwork for a more complete understanding of microtubule dynamics and of the viscoelastic properties of the spindle during cell division.
authors.affiliation: Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Changfu
authors.initials: C
authors.lastname: Yao
authors.forename: Uttama
authors.initials: U
authors.lastname: Rath
authors.forename: Helder
authors.initials: H
authors.lastname: Maiato
authors.forename: David
authors.initials: D
authors.lastname: Sharp
authors.forename: Jack
authors.initials: J
authors.lastname: Girton
authors.forename: Kristen M
authors.initials: KM
authors.lastname: Johansen
authors.forename: Jørgen
authors.initials: J
authors.lastname: Johansen
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D059006:Chromosomes, Insect / Q000378:metabolism; D003911:Dextrans / Q000737:chemistry / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D034921:Lamin Type B / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008868:Microtubule Proteins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis; D009685:Nuclear Envelope / Q000378:metabolism; D034521:Nuclear Matrix-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism*; D059008:Time-Lapse Imaging; D014404:Tubulin / Q000235:genetics / Q000378:metabolism; D000097573:Red Fluorescent Protein
chemical_list: D003911:Dextrans; D029721:Drosophila Proteins; D049452:Green Fluorescent Proteins; D034921:Lamin Type B; D008164:Luminescent Proteins; D008868:Microtubule Proteins; D034521:Nuclear Matrix-Associated Proteins; D014404:Tubulin; D000097573:Red Fluorescent Protein; C511412:Jupiter protein, Drosophila; C498867:Mtor protein, Drosophila