High resolution analysis of mammalian nuclear structure throughout the cell cycle: implications for nuclear pore complex assembly during interphase and mitosisThis paper is one of a selection of papers published in this Special Issue, entitled The Nucleus: A Cell Within A Cell.

2006 ◽  
Vol 84 (3-4) ◽  
pp. 423-430 ◽  
Author(s):  
Sheona P. Drummond ◽  
Sandra A. Rutherford ◽  
Helen S. Sanderson ◽  
Terry D. Allen
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Molecular Transport ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
High Resolution Analysis ◽  
Multiple Copies ◽  
A Cell ◽  
Specific Proteins ◽  
Pore Complexes

Nuclear pore complexes (NPCs) are the gateways for both active and passive bidirectional molecular transport between the nucleoplasm and cytoplasm. These mega-dalton assemblies are composed of multiple copies of approximately 30 distinct proteins termed nucleoporins. Higher eukaryotes display an “open” mitosis in which the NPCs, nuclear envelope, and lamina disassemble. During mitosis several nucleoporins are redistributed to kinetochores until they are recruited back to the periphery of chromatin as the NPCs are reassembled. Within this study we have developed and optimized the visualization of mammalian cells and their chromosome profiles throughout the cell-cycle. Close attention has been paid to the preservation of chromatin, membranes, and NPC structure to investigate the ultrastructural locations of specific proteins in both interphase and mitosis.

scholarly journals The nuclear pore complex: mediator of translocation between nucleus and cytoplasm

2000 ◽  
Vol 113 (10) ◽  
pp. 1651-1659 ◽  
Author(s):  
T.D. Allen ◽  
J.M. Cronshaw ◽  
S. Bagley ◽  
E. Kiseleva ◽  
M.W. Goldberg
Keyword(s):  
Nuclear Export ◽  
Mammalian Cells ◽  
Complex Structure ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Complete Breakdown ◽  
Import And Export ◽  
Complex Structural ◽  
Pore Complexes ◽  
Giant Nuclei

The enclosure of nuclear contents in eukaryotes means that cells require sites in the boundary that mediate exchange of material between nucleus and cytoplasm. These sites, termed nuclear pore complexes (NPCs), number 100–200 in yeast, a few thousand in mammalian cells and approximately 50 million in the giant nuclei of amphibian oocytes. NPCs are large (125 MDa) macromolecular complexes that comprise 50–100 different proteins in vertebrates. In spite of their size and complex structure, NPCs undergo complete breakdown and reformation at cell division. Transport through NPCs can be rapid (estimated at several hundred molecules/pore/second) and accommodates both passive diffusion of relatively small molecules, and active transport of complexes up to several megadaltons in molecular mass. Each pore can facilitate both import and export. The two processes apparently involve multiple pathways for different cargoes, and their transport signals, transport receptors and adapters, and the molecules (and their regulators) that underpin the transport mechanisms. Over the past few years there has been an increasing interest in the pore complex: structural studies have been followed by elucidation of the biochemical aspects of nuclear import, and subsequent investigations into nuclear export. The current challenge is to understand the interactions between the structural elements of the pore complex and the mechanisms that drive the physical processes of translocation through it.

scholarly journals Nuclear pore complexes form immobile networks and have a very low turnover in live mammalian cells

2001 ◽  
Vol 154 (1) ◽  
pp. 71-84 ◽  
Author(s):  
Nathalie Daigle ◽  
Joël Beaudouin ◽  
Lisa Hartnell ◽  
Gabriela Imreh ◽  
Einar Hallberg ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Fluorescent Protein ◽  
Nuclear Lamina ◽  
Nuclear Pore ◽  
Global Changes ◽  
Nuclear Pore Complexes ◽  
Annulate Lamellae ◽  
Lamin B1 ◽  
Green Fluorescent ◽  
Pore Complexes

The nuclear pore complex (NPC) and its relationship to the nuclear envelope (NE) was characterized in living cells using POM121–green fluorescent protein (GFP) and GFP-Nup153, and GFP–lamin B1. No independent movement of single pore complexes was found within the plane of the NE in interphase. Only large arrays of NPCs moved slowly and synchronously during global changes in nuclear shape, strongly suggesting mechanical connections which form an NPC network. The nuclear lamina exhibited identical movements. NPC turnover measured by fluorescence recovery after photobleaching of POM121 was less than once per cell cycle. Nup153 association with NPCs was dynamic and turnover of this nucleoporin was three orders of magnitude faster. Overexpression of both nucleoporins induced the formation of annulate lamellae (AL) in the endoplasmic reticulum (ER). Turnover of AL pore complexes was much higher than in the NE (once every 2.5 min). During mitosis, POM121 and Nup153 were completely dispersed and mobile in the ER (POM121) or cytosol (Nup153) in metaphase, and rapidly redistributed to an immobilized pool around chromatin in late anaphase. Assembly and immobilization of both nucleoporins occurred before detectable recruitment of lamin B1, which is thus unlikely to mediate initiation of NPC assembly at the end of mitosis.

scholarly journals In vivo analysis of the stability and transport of nuclear poly(A)+ RNA.

1994 ◽  
Vol 126 (4) ◽  
pp. 877-899 ◽  
Author(s):  
S Huang ◽  
T J Deerinck ◽  
M H Ellisman ◽  
D L Spector
Keyword(s):  
Rna Polymerase Ii ◽  
Mammalian Cells ◽  
Stable Population ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Nuclear Pores ◽  
Electron Microscopic ◽  
Interchromatin Granule Clusters ◽  
Interchromatin Granule ◽  
Pore Complexes

We have studied the distribution of poly(A)+ RNA in the mammalian cell nucleus and its transport through nuclear pores by fluorescence and electron microscopic in situ hybridization. Poly(A)+ RNA was detected in the nucleus as a speckled pattern which includes interchromatin granule clusters and perichromatin fibrils. When cells are fractionated by detergent and salt extraction as well as DNase I digestion, the majority of the nuclear poly(A)+ RNA was found to remain associated with the nonchromatin RNP-enriched fraction of the nucleus. After inhibition of RNA polymerase II transcription for 5-10 h, a stable population of poly(A)+ RNA remained in the nucleus and was reorganized into fewer and larger interchromatin granule clusters along with pre-mRNA splicing factors. This stable population of nuclear RNA may play an important role in nuclear function. Furthermore, we have observed that, in actively transcribing cells, the regions of poly(A)+ RNA which reached the nuclear pore complexes appeared as narrow concentrations of RNA suggesting a limited or directed pathway of movement. All of the observed nuclear pores contained poly(A)+ RNA staining suggesting that they are all capable of exporting RNA. In addition, we have directly visualized, for the first time in mammalian cells, the transport of poly(A)+ RNA through the nuclear pore complexes.

scholarly journals Spatial control of nucleoporin assembly by Fragile X-related proteins

2019 ◽  
Author(s):  
Arantxa Agote-Arán ◽  
Stephane Schmucker ◽  
Katerina Jerabkova ◽  
Inès Jmel Boyer ◽  
Alessandro Berto ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Nuclear Envelope ◽  
Fragile X Syndrome ◽  
Cell Cycle Progression ◽  
Fragile X ◽  
Nuclear Pore ◽  
Nuclear Morphology ◽  
Nuclear Pore Complexes ◽  
Cycle Progression ◽  
Pore Complexes

SummaryNucleoporins (Nups) build highly organized Nuclear Pore Complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve-like hydrogel within the central channel of the NPCs to regulate nucleocytoplasmic exchange. In the cytoplasm, a large excess of soluble Nups has been reported, but how their assembly is restricted to the NE is currently unknown. Here we show that Fragile X-related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule and dynein-dependent mechanism. Downregulation of FXR1 or closely related orthologs FXR2 and Fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup protein condensates. Likewise, several models of Fragile X syndrome (FXS), characterized by a loss of FMRP, also accumulate cytoplasmic Nup aggregates. These aggregate-containing cells display aberrant nuclear morphology and a delay in G1 cell cycle progression. Our results reveal an unexpected role for the FXR protein family and dynein in the spatial regulation of nucleoporin assembly.HighlightsCytoplasmic nucleoporins are assembled by Fragile X-related (FXR) proteins and dyneinFXR-Dynein pathway downregulation induces aberrant cytoplasmic aggregation of nucleoporinsCellular models of Fragile X syndrome accumulate aberrant cytoplasmic nucleoporin aggregates.FXR-Dynein pathway regulates nuclear morphology and G1 cell cycle progressioneTOC BlurbNucleoporins (Nups) form Nuclear Pore Complexes (NPCs) at the nuclear envelope. Agote-Arán at al. show how cells inhibit aberrant assembly of Nups in the cytoplasm and identify Fragile X-related (FXR) proteins and dynein that facilitate localization of Nups to the nuclear envelope and control G1 cell cycle progression.Graphical abstract

scholarly journals A nuclear pore sub-complex restricts the propagation of Ty retrotransposons by limiting their transcription

PLoS Genetics ◽  
2021 ◽  
Vol 17 (11) ◽  
pp. e1009889
Author(s):  
Amandine Bonnet ◽  
Carole Chaput ◽  
Noé Palmic ◽  
Benoit Palancade ◽  
Pascale Lesage
Keyword(s):  
Transcriptional Control ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Ltr Retrotransposons ◽  
Loss Of Function ◽  
Protein Coding ◽  
Multiple Copies ◽  
Ty1 Retrotransposition ◽  
Pore Complexes ◽  
The Impact

Beyond their canonical function in nucleocytoplasmic exchanges, nuclear pore complexes (NPCs) regulate the expression of protein-coding genes. Here, we have implemented transcriptomic and molecular methods to specifically address the impact of the NPC on retroelements, which are present in multiple copies in genomes. We report a novel function for the Nup84 complex, a core NPC building block, in specifically restricting the transcription of LTR-retrotransposons in yeast. Nup84 complex-dependent repression impacts both Copia and Gypsy Ty LTR-retrotransposons, all over the S. cerevisiae genome. Mechanistically, the Nup84 complex restricts the transcription of Ty1, the most active yeast retrotransposon, through the tethering of the SUMO-deconjugating enzyme Ulp1 to NPCs. Strikingly, the modest accumulation of Ty1 RNAs caused by Nup84 complex loss-of-function is sufficient to trigger an important increase of Ty1 cDNA levels, resulting in massive Ty1 retrotransposition. Altogether, our study expands our understanding of the complex interactions between retrotransposons and the NPC, and highlights the importance for the cells to keep retrotransposon under tight transcriptional control.

scholarly journals Synchronization of Interphase Events Depends neither on Mitosis nor on cdk1

2003 ◽  
Vol 14 (9) ◽  
pp. 3730-3740 ◽  
Author(s):  
Ayelet Laronne ◽  
Shay Rotkopf ◽  
Asaf Hellman ◽  
Yosef Gruenbaum ◽  
Andrew C.G. Porter ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Ubiquitin Ligase ◽  
Nuclear Membrane ◽  
Nuclear Lamina ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Polyploid Cells ◽  
Dividing Cells ◽  
Pore Complexes

Human HT2-19 cells with a conditional cdk1 mutation stop dividing upon cdk1 inactivation and undergo multiple rounds of endoreplication. We show herein that major cell cycle events remain synchronized in these endoreplicating cells. DNA replication alternates with gap phases and cell cycle-specific cyclin E expression is maintained. Centrosomes duplicate in synchrony with chromosome replication, giving rise to polyploid cells with multiple centrosomes. Centrosome migration, a typical prophase event, also takes place in endoreplicating cells. The timing of these events is unaffected by cdk1 inactivation compared with normally dividing cells. Nuclear lamina breakdown, in contrast, previously shown to be dependent on cdk1, does not take place in endoreplicating HT2-19 cells. Moreover, breakdown of all other major components of the nuclear lamina, like the inner nuclear membrane proteins and nuclear pore complexes, seems also to depend on cdk1. Interestingly, the APC/C ubiquitin ligase is activated in these endoreplicating cells by fzr but not by fzy. The oscillations of interphase events are thus independent of cdk1 and of mitosis but may depend on APC/Cfzr activity.

scholarly journals Fragile X–Related Protein 1 Regulates Nucleoporin Localization in a Cell Cycle–Dependent Manner

2021 ◽  
Vol 9 ◽  
Author(s):  
Arantxa Agote-Arán ◽  
Junyan Lin ◽  
Izabela Sumara
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Cell Cycle Progression ◽  
Fragile X ◽  
Protein Translation ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Dependent Manner ◽  
Independent Manner ◽  
Cycle Dependent

Nuclear pore complexes (NPCs) are embedded in the nuclear envelope (NE) where they ensure the transport of macromolecules between the nucleus and the cytoplasm. NPCs are built from nucleoporins (Nups) through a sequential assembly order taking place at two different stages during the cell cycle of mammalian cells: at the end of mitosis and during interphase. In addition, fragile X–related proteins (FXRPs) can interact with several cytoplasmic Nups and facilitate their localization to the NE during interphase likely through a microtubule-dependent mechanism. In the absence of FXRPs or microtubule-based transport, Nups aberrantly localize to the cytoplasm forming the so-called cytoplasmic nucleoporin granules (CNGs), compromising NPCs’ function on protein export. However, it remains unknown if Nup synthesis or degradation mechanisms are linked to the FXRP–Nup pathway and if and how the action of FXRPs on Nups is coordinated with the cell cycle progression. Here, we show that Nup localization defects observed in the absence of FXR1 are independent of active protein translation. CNGs are cleared in an autophagy- and proteasome-independent manner, and their presence is restricted to the early G1 phase of the cell cycle. Our results thus suggest that a pool of cytoplasmic Nups exists that contributes to the NPC assembly specifically during early G1 to ensure NPC homeostasis at a short transition from mitosis to the onset of interphase.

scholarly journals Mitotic checkpoint proteins HsMAD1 and HsMAD2 are associated with nuclear pore complexes in interphase

2001 ◽  
Vol 114 (5) ◽  
pp. 953-963 ◽  
Author(s):  
M.S. Campbell ◽  
G.K. Chan ◽  
T.J. Yen
Keyword(s):  
Mammalian Cells ◽  
Metaphase Plate ◽  
Mitotic Checkpoint ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Checkpoint Proteins ◽  
Anaphase Onset ◽  
Human Proteins ◽  
Tax Interaction ◽  
Pore Complexes

Mad1 was first identified in budding yeast as an essential component of the checkpoint system that monitors spindle assembly in mitosis and prevents premature anaphase onset. Using antibodies to the human homologue of Mad1 (HsMAD1), we have begun to characterize this protein in mammalian cells. HsMad1 is found localized at kinetochores in mitosis. The labeling is brightest in prometaphase and is absent from kinetochores at metaphase and anaphase. In cells where most chromosomes have reached the metaphase plate, those aligned at the plate show no labeling while remaining, unaligned chromosomes are still brightly labeled. We find HsMad1 associated with HsMad2. Association with p55CDC, a protein previously shown to bind HsMad2, was not detected. Surprisingly, unlike any other known mitotic checkpoint proteins, HsMad1 and HsMAD2 were found localized at nuclear pores throughout interphase. This was confirmed by co-labeling with an antibody to known nuclear pore complex proteins and by their co-purification with enriched nuclear envelope fractions. HsMad1 was identified serendipitously by its binding to a viral protein, HTLV-1 Tax, which affects transcription of viral and human proteins. The localization of HsMad1 to nuclear pore complexes suggests an alternate, non-mitotic role for the Mad1/Tax interaction in the viral transformation of cells.

scholarly journals Daughter-cell-specific modulation of nuclear pore complexes controls cell cycle entry during asymmetric division

2018 ◽  
Vol 20 (4) ◽  
pp. 432-442 ◽  
Author(s):  
Arun Kumar ◽  
Priyanka Sharma ◽  
Mercè Gomar-Alba ◽  
Zhanna Shcheprova ◽  
Anne Daulny ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Daughter Cell ◽  
Asymmetric Division ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Cell Cycle Entry ◽  
Pore Complexes

scholarly journals Autophagy of the Nucleus in Health and Disease

2022 ◽  
Vol 9 ◽  
Author(s):  
Georgios Konstantinidis ◽  
Nektarios Tavernarakis
Keyword(s):  
Cell Cycle ◽  
Dna Damage ◽  
Cellular Differentiation ◽  
Nuclear Material ◽  
Nuclear Pore ◽  
Common Denominator ◽  
Nuclear Pore Complexes ◽  
The Core ◽  
Health And Disease ◽  
Pore Complexes

Nucleophagy is an organelle-selective subtype of autophagy that targets nuclear material for degradation. The macroautophagic delivery of micronuclei to the vacuole, together with the nucleus-vacuole junction-dependent microautophagic degradation of nuclear material, were first observed in yeast. Nuclear pore complexes and ribosomal DNA are typically excluded during conventional macronucleophagy and micronucleophagy, indicating that degradation of nuclear cargo is tightly regulated. In mammals, similarly to other autophagy subtypes, nucleophagy is crucial for cellular differentiation and development, in addition to enabling cells to respond to various nuclear insults and cell cycle perturbations. A common denominator of all nucleophagic processes characterized in diverse organisms is the dependence on the core autophagic machinery. Here, we survey recent studies investigating the autophagic processing of nuclear components. We discuss nucleophagic events in the context of pathology, such as neurodegeneration, cancer, DNA damage, and ageing.

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