scholarly journals An ESCRT-LEM protein surveillance system is poised to directly monitor the nuclear envelope and nuclear transport system

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
David J Thaller ◽  
Matteo Allegretti ◽  
Sapan Borah ◽  
Paolo Ronchi ◽  
Martin Beck ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Surveillance System ◽  
Nuclear Transport ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Nuclear Membranes ◽  
Disease Mechanisms ◽  
Pore Complexes ◽  
Membrane Sealing

The integrity of the nuclear membranes coupled to the selective barrier of nuclear pore complexes (NPCs) are essential for the segregation of nucleoplasm and cytoplasm. Mechanical membrane disruption or perturbation to NPC assembly triggers an ESCRT-dependent surveillance system that seals nuclear pores: how these pores are sensed and sealed is ill defined. Using a budding yeast model, we show that the ESCRT Chm7 and the integral inner nuclear membrane (INM) protein Heh1 are spatially segregated by nuclear transport, with Chm7 being actively exported by Xpo1/Crm1. Thus, the exposure of the INM triggers surveillance with Heh1 locally activating Chm7. Sites of Chm7 hyperactivation show fenestrated sheets at the INM and potential membrane delivery at sites of nuclear envelope herniation. Our data suggest that perturbation to the nuclear envelope barrier would lead to local nuclear membrane remodeling to promote membrane sealing. Our findings have implications for disease mechanisms linked to NPC assembly and nuclear envelope integrity.

scholarly journals An ESCRT-LEM domain inner nuclear membrane protein surveillance system is poised to directly monitor the integrity of the nuclear envelope barrier and nuclear transport system

2019 ◽  
Author(s):  
David J. Thaller ◽  
Matteo Allegretti ◽  
Sapan Borah ◽  
Paolo Ronchi ◽  
Martin Beck ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Transport System ◽  
Nuclear Membrane ◽  
Surveillance System ◽  
Electron Tomography ◽  
Nuclear Transport ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Inner Nuclear Membrane ◽  
Pore Complexes

AbstractThe integrity of the nuclear envelope membranes coupled to the diffusion barrier and selective transport properties of nuclear pore complexes (NPCs) are a prerequisite for the robust segregation of nucleoplasm and cytoplasm. Recent work supports that mechanical membrane disruption or perturbation to NPC assembly can trigger an ESCRT-dependent surveillance system that seals nuclear envelope pores: how these pores are sensed and sealed remains to be fully defined. Here, we show that the principal components of the nuclear envelope surveillance system in yeast, which includes the ESCRT Chm7 and the integral inner nuclear membrane (INM) protein Heh1, are spatially segregated by the nuclear transport system. Specifically, at steady state Chm7 is actively restricted from the nucleus by Crm1/Xpo1. Consistent with the idea that it is the exposure of the INM that triggers surveillance, the expression of a transmembrane anchor and the winged helix domain of Heh1 is sufficient to recruit and activate Chm7 at a membrane interface. Correlative light electron tomography under conditions of Chm7 hyper-activation further show the formation of an elaborate network of fenestrated sheets at the INM and suggest ER-membrane delivery at sites of nuclear envelope herniation. Our data point to a model in which exposure of Chm7 to Heh1, driven by any perturbation in the nuclear envelope barrier would lead to local nuclear envelope remodeling to promote membrane sealing. Our findings have implications for disease mechanisms associated with defects in NPC assembly and nuclear envelope integrity.

scholarly journals POM121 and Sun1 play a role in early steps of interphase NPC assembly

2011 ◽  
Vol 194 (1) ◽  
pp. 27-37 ◽  
Author(s):  
Jessica A. Talamas ◽  
Martin W. Hetzer
Keyword(s):  
Cell Cycle ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Molecular Mechanisms ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Outer Nuclear Membrane ◽  
Nuclear Membranes ◽  
Distinct Cell ◽  
Pore Complexes

Nuclear pore complexes (NPCs) assemble at the end of mitosis during nuclear envelope (NE) reformation and into an intact NE as cells progress through interphase. Although recent studies have shown that NPC formation occurs by two different molecular mechanisms at two distinct cell cycle stages, little is known about the molecular players that mediate the fusion of the outer and inner nuclear membranes to form pores. In this paper, we provide evidence that the transmembrane nucleoporin (Nup), POM121, but not the Nup107–160 complex, is present at new pore assembly sites at a time that coincides with inner nuclear membrane (INM) and outer nuclear membrane (ONM) fusion. Overexpression of POM121 resulted in juxtaposition of the INM and ONM. Additionally, Sun1, an INM protein that is known to interact with the cytoskeleton, was specifically required for interphase assembly and localized with POM121 at forming pores. We propose a model in which POM121 and Sun1 interact transiently to promote early steps of interphase NPC assembly.

scholarly journals In Vivo Dynamics of Nuclear Pore Complexes in Yeast

1997 ◽  
Vol 136 (6) ◽  
pp. 1185-1199 ◽  
Author(s):  
Mirella Bucci ◽  
Susan R. Wente
Keyword(s):  
Nuclear Envelope ◽  
Recipient Cell ◽  
Nucleocytoplasmic Transport ◽  
Yeast Cells ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Central Location ◽  
Nuclear Membranes ◽  
Mutant Strains ◽  
Pore Complexes

While much is known about the role of nuclear pore complexes (NPCs) in nucleocytoplasmic transport, the mechanism of NPC assembly into pores formed through the double lipid bilayer of the nuclear envelope is not well defined. To investigate the dynamics of NPCs, we developed a live-cell assay in the yeast Saccharomyces cerevisiae. The nucleoporin Nup49p was fused to the green fluorescent protein (GFP) of Aequorea victoria and expressed in nup49 null haploid yeast cells. When the GFP–Nup49p donor cell was mated with a recipient cell harboring only unlabeled Nup49p, the nuclei fused as a consequence of the normal mating process. By monitoring the distribution of the GFP–Nup49p, we could assess whether NPCs were able to move from the donor section of the nuclear envelope to that of the recipient nucleus. We observed that fluorescent NPCs moved and encircled the entire nucleus within 25 min after fusion. When assays were done in mutant kar1-1 strains, where nuclear fusion does not occur, GFP–Nup49p appearance in the recipient nucleus occurred at a very slow rate, presumably due to new NPC biogenesis or to exchange of GFP– Nup49p into existing recipient NPCs. Interestingly, in a number of existing mutant strains, NPCs are clustered together at permissive growth temperatures. This has been explained with two different hypotheses: by movement of NPCs through the double nuclear membranes with subsequent clustering at a central location; or, alternatively, by assembly of all NPCs at a central location (such as the spindle pole body) with NPCs in mutant cells unable to move away from this point. Using the GFP–Nup49p system with a mutant in the NPCassociated factor Gle2p that exhibits formation of NPC clusters only at 37°C, it was possible to distinguish between these two models for NPC dynamics. GFP– Nup49p-labeled NPCs, assembled at 23°C, moved into clusters when the cells were shifted to growth at 37°C. These results indicate that NPCs can move through the double nuclear membranes and, moreover, can do so to form NPC clusters in mutant strains. Such clusters may result by releasing NPCs from a nuclear tether, or by disappearance of a protein that normally prevents pore aggregation. This system represents a novel approach for identifying regulators of NPC assembly and movement in the future.

scholarly journals Nuclear envelope organization in Dictyostelium discoideum

2019 ◽  
Vol 63 (8-9-10) ◽  
pp. 509-519 ◽  
Author(s):  
Petros Batsios ◽  
Ralph Gräf ◽  
Michael P. Koonce ◽  
Denis A. Larochelle ◽  
Irene Meyer
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Nuclear Lamina ◽  
Major Constituent ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Linc Complex ◽  
Family Protein ◽  
Import And Export ◽  
Pore Complexes

The nuclear envelope consists of the outer and the inner nuclear membrane, the nuclear lamina and the nuclear pore complexes, which regulate nuclear import and export. The major constituent of the nuclear lamina of Dictyostelium is the lamin NE81. It can form filaments like B-type lamins and it interacts with Sun1, as well as with the LEM/HeH-family protein Src1. Sun1 and Src1 are nuclear envelope transmembrane proteins involved in the centrosome-nucleus connection and nuclear envelope stability at the nucleolar regions, respectively. In conjunction with a KASH-domain protein, Sun1 usually forms a so-called LINC complex. Two proteins with functions reminiscent of KASH-domain proteins at the outer nuclear membrane of Dictyostelium are known; interaptin which serves as an actin connector and the kinesin Kif9 which plays a role in the microtubule-centrosome connector. However, both of these lack the conserved KASH-domain. The link of the centrosome to the nuclear envelope is essential for the insertion of the centrosome into the nuclear envelope and the appropriate spindle formation. Moreover, centrosome insertion is involved in permeabilization of the mitotic nucleus, which ensures access of tubulin dimers and spindle assembly factors. Our recent progress in identifying key molecular players at the nuclear envelope of Dictyostelium promises further insights into the mechanisms of nuclear envelope dynamics.

scholarly journals Nuclear Envelope and Nuclear Pore Complexes in Neurodegenerative Diseases—New Perspectives for Therapeutic Interventions

2020 ◽  
Author(s):  
Naomi Hachiya ◽  
Marta Sochocka ◽  
Anna Brzecka ◽  
Takuto Shimizu ◽  
Kazimierz Gąsiorowski ◽  
...  
Keyword(s):  
Gene Expression ◽  
Neurodegenerative Diseases ◽  
Nuclear Envelope ◽  
Neurodegenerative Disorders ◽  
Nuclear Transport ◽  
Therapeutic Interventions ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Pore Complexes ◽  
Bidirectional Exchange

Abstract Transport of proteins, transcription factors, and other signaling molecules between the nucleus and cytoplasm is necessary for signal transduction. The study of these transport phenomena is particularly challenging in neurons because of their highly polarized structure. The bidirectional exchange of molecular cargoes across the nuclear envelope (NE) occurs through nuclear pore complexes (NPCs), which are aqueous channels embedded in the nuclear envelope. The NE and NPCs regulate nuclear transport but are also emerging as relevant regulators of chromatin organization and gene expression. The alterations in nuclear transport are regularly identified in affected neurons associated with human neurodegenerative diseases. This review presents insights into the roles played by nuclear transport defects in neurodegenerative disease, focusing primarily on NE proteins and NPCs. The subcellular mislocalization of proteins might be a very desirable means of therapeutic intervention in neurodegenerative disorders.

Sequential recruitment of NPC proteins to the nuclear periphery at the end of mitosis

1999 ◽  
Vol 112 (13) ◽  
pp. 2253-2264 ◽  
Author(s):  
K. Bodoor ◽  
S. Shaikh ◽  
D. Salina ◽  
W.H. Raharjo ◽  
R. Bastos ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Time Course ◽  
Nuclear Periphery ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Confocal Immunofluorescence Microscopy ◽  
Pore Complexes ◽  
Nuclear Membrane Protein

Nuclear pore complexes (NPCs) are extremely elaborate structures that mediate the bidirectional movement of macromolecules between the nucleus and cytoplasm. With a mass of about 125 MDa, NPCs are thought to be composed of 50 or more distinct protein subunits, each present in multiple copies. During mitosis in higher cells the nuclear envelope is disassembled and its components, including NPC subunits, are dispersed throughout the mitotic cytoplasm. At the end of mitosis, all of these components are reutilized. Using both conventional and digital confocal immunofluorescence microscopy we have been able to define a time course of post-mitotic assembly for a group of NPC components (CAN/Nup214, Nup153, POM121, p62 and Tpr) relative to the integral nuclear membrane protein LAP2 and the NPC membrane glycoprotein gp210. Nup153, a component of the nuclear basket, associates with chromatin towards the end of anaphase, in parallel with the inner nuclear membrane protein, LAP2. However, immunogold labeling suggests that the initial Nup153 chromatin association is membrane-independent. Assembly of the remaining proteins follows that of the nuclear membranes and occurs in the sequence POM121, p62, CAN/Nup214 and gp210/Tpr. Since p62 remains as a complex with three other NPC proteins (p58, 54, 45) during mitosis and CAN/Nup214 maintains a similar interaction with its partner, Nup84, the relative timing of assembly of these additional four proteins may also be inferred. These observations suggest that there is a sequential association of NPC proteins with chromosomes during nuclear envelope reformation and the recruitment of at least eight of these precedes that of gp210. These findings support a model in which it is POM121 rather than gp210 that defines initial membrane-associated NPC assembly intermediates.

Reticulon-like REEP4 at the inner nuclear membrane promotes nuclear pore complex formation

2021 ◽  
Vol 221 (2) ◽  
Author(s):  
Banafsheh Golchoubian ◽  
Andreas Brunner ◽  
Helena Bragulat-Teixidor ◽  
Annett Neuner ◽  
Busra A. Akarlar ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Pore Complex ◽  
Nuclear Membrane ◽  
Nucleocytoplasmic Transport ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Inner Nuclear Membrane ◽  
Pore Complexes ◽  
Late Stages ◽  
Protein Complex Assembly

Nuclear pore complexes (NPCs) are channels within the nuclear envelope that mediate nucleocytoplasmic transport. NPCs form within the closed nuclear envelope during interphase or assemble concomitantly with nuclear envelope reformation in late stages of mitosis. Both interphase and mitotic NPC biogenesis require coordination of protein complex assembly and membrane deformation. During early stages of mitotic NPC assembly, a seed for new NPCs is established on chromatin, yet the factors connecting the NPC seed to the membrane of the forming nuclear envelope are unknown. Here, we report that the reticulon homology domain protein REEP4 not only localizes to high-curvature membrane of the cytoplasmic endoplasmic reticulum but is also recruited to the inner nuclear membrane by the NPC biogenesis factor ELYS. This ELYS-recruited pool of REEP4 promotes NPC assembly and appears to be particularly important for NPC formation during mitosis. These findings suggest a role for REEP4 in coordinating nuclear envelope reformation with mitotic NPC biogenesis.

scholarly journals Actin assembly ruptures the nuclear envelope by prying the lamina away from nuclear pores and nuclear membranes in starfish oocytes

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Natalia Wesolowska ◽  
Ivan Avilov ◽  
Pedro Machado ◽  
Celina Geiss ◽  
Hiroshi Kondo ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Super Resolution ◽  
Germinal Vesicle ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Actin Assembly ◽  
Nuclear Membranes ◽  
Pore Complexes ◽  
Distinct Membrane ◽  
Nuclear Rupture

The nucleus of oocytes (germinal vesicle) is unusually large and its nuclear envelope (NE) is densely packed with nuclear pore complexes (NPCs) that are stockpiled for embryonic development. We showed that breakdown of this specialized NE is mediated by an Arp2/3-nucleated F-actin ‘shell’ in starfish oocytes, in contrast to microtubule-driven tearing in mammalian fibroblasts. Here, we address the mechanism of F-actin-driven NE rupture by correlated live-cell, super-resolution and electron microscopy. We show that actin is nucleated within the lamina, sprouting filopodia-like spikes towards the nuclear membranes. These F-actin spikes protrude pore-free nuclear membranes, whereas the adjoining stretches of membrane accumulate NPCs that are associated with the still-intact lamina. Packed NPCs sort into a distinct membrane network, while breaks appear in ER-like, pore-free regions. We reveal a new function for actin-mediated membrane shaping in nuclear rupture that is likely to have implications in other contexts, such as nuclear rupture observed in cancer cells.

Nucleocytoplasmic transport of macromolecules

1997 ◽  
Vol 61 (2) ◽  
pp. 193-211
Author(s):  
A H Corbett ◽  
P A Silver
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Transport ◽  
Bound State ◽  
Nucleocytoplasmic Transport ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Yeast Saccharomyces Cerevisiae ◽  
Soluble Factors ◽  
Pore Complexes ◽  
Transport Of Macromolecules

Nucleocytoplasmic transport is a complex process that consists of the movement of numerous macromolecules back and forth across the nuclear envelope. All macromolecules that move in and out of the nucleus do so via nuclear pore complexes that form large proteinaceous channels in the nuclear envelope. In addition to nuclear pores, nuclear transport of macromolecules requires a number of soluble factors that are found both in the cytoplasm and in the nucleus. A combination of biochemical, genetic, and cell biological approaches have been used to identify and characterize the various components of the nuclear transport machinery. Recent studies have shown that both import to and export from the nucleus are mediated by signals found within the transport substrates. Several studies have demonstrated that these signals are recognized by soluble factors that target these substrates to the nuclear pore. Once substrates have been directed to the pore, most transport events depend on a cycle of GTP hydrolysis mediated by the small Ras-like GTPase, Ran, as well as other proteins that regulate the guanine nucleotide-bound state of Ran. Many of the essential factors have been identified, and the challenge that remains is to determine the exact mechanism by which transport occurs. This review attempts to present an integrated view of our current understanding of nuclear transport while highlighting the contributions that have been made through studies with genetic organisms such as the budding yeast, Saccharomyces cerevisiae.

scholarly journals REEP4 is recruited to the inner nuclear membrane by ELYS and promotes nuclear pore complex formation

2020 ◽  
Author(s):  
Banafsheh Golchoubian ◽  
Andreas Brunner ◽  
Helena Bragulat-Teixidor ◽  
Busra A. Akarlar ◽  
Nurhan Ozlu ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Nuclear Pore Complex ◽  
Nuclear Membrane ◽  
Nucleocytoplasmic Transport ◽  
Local Deformation ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Membrane Remodeling ◽  
Inner Nuclear Membrane ◽  
Pore Complexes

AbstractNuclear pore complexes (NPCs) are channels within the nuclear envelope that mediate nucleocytoplasmic transport. NPCs assemble either into the closed nuclear envelope during interphase or concomitantly with nuclear envelope reformation during anaphase. Both, interphase and post-mitotic NPC biogenesis require local deformation of membrane. Yet, the factors that control proper membrane remodeling for post-mitotic NPC assembly are unknown. Here, we report that the reticulon homology domain-protein REEP4 localizes not only to high-curvature membrane of the cytoplasmic endoplasmic reticulum (ER) but also to the inner nuclear membrane (INM). We show that REEP4 is recruited to the INM by the NPC biogenesis factor ELYS and promotes NPC assembly. REEP4 contributes mainly to anaphase NPC assembly, suggesting that REEP4 has an unexpected role in coordinating nuclear envelope reformation with post-mitotic NPC biogenesis.

Sign in / Sign up

Export Citation Format

Share Document