title: An organelle-exclusion envelope assists mitosis and underlies distinct molecular crowding in the spindle region.
abstract: The mitotic spindle is a microtubular assembly required for chromosome segregation during mitosis. Additionally, a spindle matrix has long been proposed to assist this process, but its nature has remained elusive. By combining live-cell imaging with laser microsurgery, fluorescence recovery after photobleaching, and fluorescence correlation spectroscopy in Drosophila melanogaster S2 cells, we uncovered a microtubule-independent mechanism that underlies the accumulation of molecules in the spindle region. This mechanism relies on a membranous system surrounding the mitotic spindle that defines an organelle-exclusion zone that is conserved in human cells. Supported by mathematical modeling, we demonstrate that organelle exclusion by a membrane system causes spatio-temporal differences in molecular crowding states that are sufficient to drive accumulation of mitotic regulators, such as Mad2 and Megator/Tpr, as well as soluble tubulin, in the spindle region. This membranous "spindle envelope" confined spindle assembly, and its mechanical disruption compromised faithful chromosome segregation. Thus, cytoplasmic compartmentalization persists during early mitosis to promote spindle assembly and function.
authors: Chromosome Instability & Dynamics Laboratory, Instituto de Biologia Molecular e Celular, Universidade do Porto, 4150-180 Porto, Portugal Cell Division Unit, Department of Experimental Biology, Faculdade de Medicina, Universidade do Porto, Alameda Prof. Hernâni Monteiro, 4200-319 Porto, Portugal Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto, Portugal.
authors: Nina
authors: N
authors: Schweizer
authors: Experimental Physics I, University of Bayreuth, D-95440 Bayreuth, Germany.
authors: Nisha
authors: N
authors: Pawar
authors: Experimental Physics I, University of Bayreuth, D-95440 Bayreuth, Germany.
authors: Matthias
authors: M
authors: Weiss
authors: Chromosome Instability & Dynamics Laboratory, Instituto de Biologia Molecular e Celular, Universidade do Porto, 4150-180 Porto, Portugal Cell Division Unit, Department of Experimental Biology, Faculdade de Medicina, Universidade do Porto, Alameda Prof. Hernâni Monteiro, 4200-319 Porto, Portugal Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto, Portugal maiato@ibmc.up.pt.
authors: Helder
authors: H
authors: Maiato
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D029721:Drosophila Proteins / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology; D004721:Endoplasmic Reticulum / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D064246:Mad2 Proteins / Q000378:metabolism; D008870:Microtubules / Q000502:physiology*; D008938:Mitosis / Q000502:physiology*; D009685:Nuclear Envelope / Q000502:physiology*; D034521:Nuclear Matrix-Associated Proteins / Q000378:metabolism; D061848:Optical Imaging; D015388:Organelles / Q000502:physiology; D008941:Spindle Apparatus / Q000502:physiology*; D014404:Tubulin / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D064246:Mad2 Proteins; C577685:Mad2 protein, Drosophila; C498867:Mtor protein, Drosophila; D034521:Nuclear Matrix-Associated Proteins; D014404:Tubulin; D049452:Green Fluorescent Proteins