scholarly journals Importin β Regulates the Seeding of Chromatin with Initiation Sites for Nuclear Pore Assembly

2009 ◽  
Vol 20 (18) ◽  
pp. 4031-4042 ◽  
Author(s):  
Asaf Rotem ◽  
Rita Gruber ◽  
Hagai Shorer ◽  
Lihi Shaulov ◽  
Eugenia Klein ◽  
...  
Keyword(s):  
Initial Step ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
High Molecular Weight Complex ◽  
Assembly Pathway ◽  
Attachment Sites ◽  
Pore Complexes ◽  
Membrane Components ◽  
Nuclear Pore Assembly ◽  
Initial Seeding

The nuclear envelope of higher eukaryotic cells reforms at the exit from mitosis, in concert with the assembly of nuclear pore complexes (NPCs). The first step in postmitotic NPC assembly involves the “seeding” of chromatin with ELYS and the Nup107-160 complex. Subsequent steps in the assembly process are poorly understood and different mechanistic models have been proposed to explain the formation of the full supramolecular structure. Here, we show that the initial step of chromatin seeding is negatively regulated by importin β. Direct imaging of the chromatin attachment sites reveals single sites situated predominantly on the highest substructures of chromatin surface and lacking any sign of annular structures or oligomerized pre-NPCs. Surprisingly, the inhibition by importin β is only partially reversed by RanGTP. Importin β forms a high-molecular-weight complex with both ELYS and the Nup107-160 complex in cytosol. We suggest that initiation sites for NPC assembly contain single copies of chromatin-bound ELYS/Nup107-160 and that the lateral oligomerization of these subunits depends on the recruitment of membrane components. We predict that additional regulators, besides importin β and Ran, may be involved in coordinating the initial seeding of chromatin with subsequent steps in the NPC assembly pathway.

scholarly journals Nup358 integrates nuclear envelope breakdown with kinetochore assembly

2003 ◽  
Vol 162 (6) ◽  
pp. 991-1001 ◽  
Author(s):  
Davide Salina ◽  
Paul Enarson ◽  
J.B. Rattner ◽  
Brian Burke
Keyword(s):  
Nuclear Envelope ◽  
Mitotic Checkpoint ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Nuclear Envelope Breakdown ◽  
Chromosome Congression ◽  
Chromatid Segregation ◽  
Pore Complexes ◽  
Membrane Components ◽  
And Function

Nuclear envelope breakdown (NEBD) and release of condensed chromosomes into the cytoplasm are key events in the early stages of mitosis in metazoans. NEBD involves the disassembly of all major structural elements of the nuclear envelope, including nuclear pore complexes (NPCs), and the dispersal of nuclear membrane components. The breakdown process is facilitated by microtubules of the mitotic spindle. After NEBD, engagement of spindle microtubules with chromosome-associated kinetochores leads to chromatid segregation. Several NPC subunits relocate to kinetochores after NEBD. siRNA-mediated depletion of one of these proteins, Nup358, reveals that it is essential for kinetochore function. In the absence of Nup358, chromosome congression and segregation are severely perturbed. At the same time, the assembly of other kinetochore components is strongly inhibited, leading to aberrant kinetochore structure. The implication is that Nup358 plays an essential role in integrating NEBD with kinetochore maturation and function. Mitotic arrest associated with Nup358 depletion further suggests that mitotic checkpoint complexes may remain active at nonkinetochore sites.

scholarly journals Postmitotic nuclear pore assembly proceeds by radial dilation of small ER membrane openings

2017 ◽  
Author(s):  
Shotaro Otsuka ◽  
Anna M. Steyer ◽  
Martin Schorb ◽  
Jean-Karim Hériché ◽  
M. Julius Hossain ◽  
...  
Keyword(s):  
Time Course ◽  
Three Dimensional ◽  
Membrane Topology ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Ring Complex ◽  
Pore Complexes ◽  
Transport Channels ◽  
Membrane Sealing ◽  
Nuclear Pore Assembly

AbstractThe nuclear envelope has to be reformed after mitosis to create viable daughter cells with closed nuclei. How membrane sealing of DNA and assembly of nuclear pore complexes (NPCs) are achieved and coordinated is poorly understood. Here, we reconstructed nuclear membrane topology and structure of assembling NPCs in a correlative three dimensional electron microscopy time-course of dividing human cells. Our quantitative ultrastructural analysis shows that nuclear membranes form from highly fenestrated ER sheets, whose shrinking holes are stabilized and then dilated into NPCs during inner ring complex assembly, forming thousands of transport channels within minutes. This mechanism is fundamentally different from interphase NPC assembly and explains how mitotic cells can rapidly establish a closed nuclear compartment while making it transport-competent at the same time.

scholarly journals Transportin Regulates Major Mitotic Assembly Events: From Spindle to Nuclear Pore Assembly

2009 ◽  
Vol 20 (18) ◽  
pp. 4043-4058 ◽  
Author(s):  
Corine K. Lau ◽  
Valerie A. Delmar ◽  
Rene C. Chan ◽  
Quang Phung ◽  
Cyril Bernis ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Mitotic Chromosomes ◽  
Nuclear Assembly ◽  
Importin Beta ◽  
Egg Extracts ◽  
Multiple Cell ◽  
Pore Complexes ◽  
Nuclear Pore Assembly

Mitosis in higher eukaryotes is marked by the sequential assembly of two massive structures: the mitotic spindle and the nucleus. Nuclear assembly itself requires the precise formation of both nuclear membranes and nuclear pore complexes. Previously, importin alpha/beta and RanGTP were shown to act as dueling regulators to ensure that these assembly processes occur only in the vicinity of the mitotic chromosomes. We now find that the distantly related karyopherin, transportin, negatively regulates nuclear envelope fusion and nuclear pore assembly in Xenopus egg extracts. We show that transportin—and importin beta—initiate their regulation as early as the first known step of nuclear pore assembly: recruitment of the critical pore-targeting nucleoporin ELYS/MEL-28 to chromatin. Indeed, each karyopherin can interact directly with ELYS. We further define the nucleoporin subunit targets for transportin and importin beta and find them to be largely the same: ELYS, the Nup107/160 complex, Nup53, and the FG nucleoporins. Equally importantly, we find that transportin negatively regulates mitotic spindle assembly. These negative regulatory events are counteracted by RanGTP. We conclude that the interplay of the two negative regulators, transportin and importin beta, along with the positive regulator RanGTP, allows precise choreography of multiple cell cycle assembly events.

scholarly journals Formation of the postmitotic nuclear envelope from extended ER cisternae precedes nuclear pore assembly

2011 ◽  
Vol 194 (3) ◽  
pp. 425-440 ◽  
Author(s):  
Lei Lu ◽  
Mark S. Ladinsky ◽  
Tomas Kirchhausen
Keyword(s):  
Nuclear Envelope ◽  
Live Cell Imaging ◽  
Cell Imaging ◽  
Current Model ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Nuclear Envelope Formation ◽  
Pore Complexes ◽  
Nuclear Pore Assembly ◽  
A Current

During mitosis, the nuclear envelope merges with the endoplasmic reticulum (ER), and nuclear pore complexes are disassembled. In a current model for reassembly after mitosis, the nuclear envelope forms by a reshaping of ER tubules. For the assembly of pores, two major models have been proposed. In the insertion model, nuclear pore complexes are embedded in the nuclear envelope after their formation. In the prepore model, nucleoporins assemble on the chromatin as an intermediate nuclear pore complex before nuclear envelope formation. Using live-cell imaging and electron microscope tomography, we find that the mitotic assembly of the nuclear envelope primarily originates from ER cisternae. Moreover, the nuclear pore complexes assemble only on the already formed nuclear envelope. Indeed, all the chromatin-associated Nup107–160 complexes are in single units instead of assembled prepores. We therefore propose that the postmitotic nuclear envelope assembles directly from ER cisternae followed by membrane-dependent insertion of nuclear pore complexes.

scholarly journals Defects in nuclear pore assembly lead to activation of an Aurora B–mediated abscission checkpoint

2010 ◽  
Vol 191 (5) ◽  
pp. 923-931 ◽  
Author(s):  
Douglas R. Mackay ◽  
Masaki Makise ◽  
Katharine S. Ullman
Keyword(s):  
Small Interfering Rna ◽  
Nuclear Pore ◽  
Aurora B ◽  
Nuclear Pore Complexes ◽  
Daughter Cells ◽  
Nuclear Environment ◽  
Genomic Regulation ◽  
Pore Complexes ◽  
Interfering Rna ◽  
Nuclear Pore Assembly

Correct assembly of nuclear pore complexes (NPCs), which directly and indirectly control nuclear environment and architecture, is vital to genomic regulation. We previously found that nucleoporin 153 (Nup153) is required for timely progression through late mitosis. In this study, we report that disruption of Nup153 function by either small interfering RNA–mediated depletion or expression of a dominant-interfering Nup153 fragment results in dramatic mistargeting of the pore basket components Tpr and Nup50 in midbody-stage cells. We find a concomitant appearance of aberrantly localized active Aurora B and an Aurora B–dependent delay in abscission. Depletion of Nup50 is also sufficient to increase the number of midbody-stage cells and, likewise, triggers distinctive mislocalization of Aurora B. Together, our results suggest that defects in nuclear pore assembly, and specifically the basket structure, at this time of the cell cycle activate an Aurora B–mediated abscission checkpoint, thereby ensuring that daughter cells are generated only when fully formed NPCs are present.

Nuclear Envelope Dynamics During Mitosis

1988 ◽  
Vol 46 ◽  
pp. 224-225
Author(s):  
Brian Burke
Keyword(s):  
Nuclear Envelope ◽  
Membrane Vesicles ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Animal Cells ◽  
Interphase Chromosome ◽  
Lamin B ◽  
Chromosome Architecture ◽  
Complex Membrane ◽  
Pore Complexes

The nuclear envelope is a complex membrane structure that forms the boundary of the nuclear compartment in eukaryotes. It regulates the passage of macromolecules between the two compartments and may be important for organizing interphase chromosome architecture. In interphase animal cells it forms a remarkably stable structure consisting of a double membrane ouerlying a protein meshwork or lamina and penetrated by nuclear pore complexes. The latter form the channels for nucleocytoplasmic exchange of macromolecules, At the onset of mitosis, however, it rapidly disassembles, the membranes fragment to yield small vesicles and the lamina, which is composed of predominantly three polypeptides, lamins R, B and C (MW approx. 74, 68 and 65 kDa respectiuely), breaks down. Lamins B and C are dispersed as monomers throughout the mitotic cytoplasm, while lamin B remains associated with the nuclear membrane vesicles.

Pore relations: nuclear pore complexes and nucleocytoplasmic exchange

2000 ◽  
Vol 36 ◽  
pp. 75-88 ◽  
Author(s):  
Michael P. Rout ◽  
John D. Aitchison
Keyword(s):  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Pore Complexes
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