scholarly journals Factors promoting nuclear envelope assembly independent of the canonical ESCRT pathway

2020 ◽  
Vol 219 (6) ◽  
Author(s):  
I-Ju Lee ◽  
Ema Stokasimov ◽  
Nathaniel Dempsey ◽  
Joseph M. Varberg ◽  
Etai Jacob ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Membrane Protein ◽  
Nuclear Envelope ◽  
Unsaturated Fatty Acids ◽  
Genetic Screen ◽  
Prior Work ◽  
General Role ◽  
Alternate Pathway ◽  
Nuclear Envelope Assembly ◽  
Inner Nuclear Membrane Protein

The nuclear envelope (NE) undergoes dynamic remodeling to maintain NE integrity, a process involving the inner nuclear membrane protein LEM2 recruiting CHMP7/Cmp7 and then ESCRT-III. However, prior work has hinted at CHMP7/ESCRT-independent mechanisms. To identify such mechanisms, we studied NE assembly in Schizosaccharomyces japonicus, a fission yeast that undergoes partial mitotic NE breakdown and reassembly. S. japonicus cells lacking Cmp7 have compromised NE sealing after mitosis but are viable. A genetic screen identified mutations that promote NE integrity in cmp7Δ cells. Unexpectedly, loss of Lem2 or its interacting partner Nur1 suppressed cmp7Δ defects. In the absence of Cmp7, Lem2 formed aggregates that appear to interfere with ESCRT-independent NE sealing. A gain-of-function mutation implicated a membrane and ESCRT-III regulator, Alx1, in this alternate pathway. Additional results suggest a potentially general role for unsaturated fatty acids in NE integrity. These findings establish the existence of mechanisms for NE sealing independent of the canonical ESCRT pathway.

Function and assembly of nuclear pore complex proteins

1999 ◽  
Vol 77 (4) ◽  
pp. 321-329 ◽  
Author(s):  
Khaldon Bodoor ◽  
Sarah Shaikh ◽  
Paul Enarson ◽  
Sharmin Chowdhury ◽  
Davide Salina ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Pore Complex ◽  
Nuclear Membrane ◽  
Current View ◽  
Nuclear Pore ◽  
Dynamic Component ◽  
Inner Nuclear Membrane ◽  
Inner Nuclear Membrane Protein ◽  
Nuclear Membrane Protein

Nuclear pore complexes (NPCs) are extremely elaborate structures that mediate the bidirectional movement of macromolecules between the nucleus and cytoplasm. The current view of NPC organization features a massive symmetrical framework that is embedded in the double membranes of the nuclear envelope. It embraces a central channel of as yet ill-defined structure but which may accommodate particles with diameters up to 26 nm provided that they bear specific import/export signals. Attached to both faces of the central framework are peripheral structures, short cytoplasmic filaments, and a nuclear basket assembly, which interact with molecules transiting the NPC. The mechanisms of assembly and the nature of NPC structural intermediates are still poorly understood. However, mutagenesis and expression studies have revealed discrete sequences within certain NPC proteins that are necessary and sufficient for their appropriate targeting. In addition, some details are emerging from observations on cells undergoing mitosis where 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 to form nuclear envelopes in the two daughter cells. To date, it has been possible to define a time course of postmitotic assembly for a group of NPC components (CAN/Nup214, Nup153, POM121, p62 and Tpr) relative to the integral inner nuclear membrane protein LAP2 and the NPC membrane glycoprotein gp210. Nup153, a dynamic component of the nuclear basket, associates with chromatin towards the end of anaphase coincident with, although independent of, the inner nuclear membrane protein, LAP2. 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, p54, p45) 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 and which may therefore represent an essential component of the central framework of the NPC. Key words: nuclear pore complex, nucleoporin, mitosis, nuclear transport

scholarly journals Temporal control of nuclear envelope assembly by phosphorylation of lamin B receptor

2011 ◽  
Vol 22 (18) ◽  
pp. 3306-3317 ◽  
Author(s):  
Li-Chuan Tseng ◽  
Rey-Huei Chen
Keyword(s):  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Chromatin Binding ◽  
Temporal Control ◽  
Lamin B ◽  
Lamin B Receptor ◽  
Nuclear Envelope Assembly ◽  
Nuclear Membrane Protein

The nuclear envelope of metazoans disassembles during mitosis and reforms in late anaphase after sister chromatids have well separated. The coordination of these mitotic events is important for genome stability, yet the temporal control of nuclear envelope reassembly is unknown. Although the steps of nuclear formation have been extensively studied in vitro using the reconstitution system from egg extracts, the temporal control can only be studied in vivo. Here, we use time-lapse microscopy to investigate this process in living HeLa cells. We demonstrate that Cdk1 activity prevents premature nuclear envelope assembly and that phosphorylation of the inner nuclear membrane protein lamin B receptor (LBR) by Cdk1 contributes to the temporal control. We further identify a region in the nucleoplasmic domain of LBR that inhibits premature chromatin binding of the protein. We propose that this inhibitory effect is partly mediated by Cdk1 phosphorylation. Furthermore, we show that the reduced chromatin-binding ability of LBR together with Aurora B activity contributes to nuclear envelope breakdown. Our studies reveal for the first time a mechanism that controls the timing of nuclear envelope reassembly through modification of an integral nuclear membrane protein.

scholarly journals Direct membrane protein–DNA interactions required early in nuclear envelope assembly

2006 ◽  
Vol 173 (4) ◽  
pp. 469-476 ◽  
Author(s):  
Sebastian Ulbert ◽  
Melpomeni Platani ◽  
Stephanie Boue ◽  
Iain W. Mattaj
Keyword(s):  
Membrane Proteins ◽  
Membrane Protein ◽  
Nuclear Envelope ◽  
Dna Interactions ◽  
Membrane Recruitment ◽  
Free Dna ◽  
Protein Dna Interactions ◽  
Nuclear Envelope Assembly ◽  
Initial Membrane ◽  
Chromatin Proteins

Among the earliest events in postmitotic nuclear envelope (NE) assembly are the interactions between chromatin and the membranes that will fuse to form the NE. It has been proposed that interactions between integral NE proteins and chromatin proteins mediate initial membrane recruitment to chromatin. We show that several transmembrane NE proteins bind to DNA directly and that NE membrane proteins as a class are enriched in long, basic domains that potentially bind DNA. Membrane fractions that are essential for NE formation are shown to bind directly to protein-free DNA, and our data suggest that these interactions are critical for early steps in NE assembly.

scholarly journals TorsinA controls TAN line assembly and the retrograde flow of dorsal perinuclear actin cables during rearward nuclear movement

2017 ◽  
Vol 216 (3) ◽  
pp. 657-674 ◽  
Author(s):  
Cosmo A. Saunders ◽  
Nathan J. Harris ◽  
Patrick T. Willey ◽  
Brian M. Woolums ◽  
Yuexia Wang ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Retrograde Flow ◽  
Reporter Construct ◽  
Nuclear Movement ◽  
Aaa Atpase ◽  
Actin Cables ◽  
Migratory Cells ◽  
Inner Nuclear Membrane Protein

The nucleus is positioned toward the rear of most migratory cells. In fibroblasts and myoblasts polarizing for migration, retrograde actin flow moves the nucleus rearward, resulting in the orientation of the centrosome in the direction of migration. In this study, we report that the nuclear envelope–localized AAA+ (ATPase associated with various cellular activities) torsinA (TA) and its activator, the inner nuclear membrane protein lamina-associated polypeptide 1 (LAP1), are required for rearward nuclear movement during centrosome orientation in migrating fibroblasts. Both TA and LAP1 contributed to the assembly of transmembrane actin-associated nuclear (TAN) lines, which couple the nucleus to dorsal perinuclear actin cables undergoing retrograde flow. In addition, TA localized to TAN lines and was necessary for the proper mobility of EGFP-mini–nesprin-2G, a functional TAN line reporter construct, within the nuclear envelope. Furthermore, TA and LAP1 were indispensable for the retrograde flow of dorsal perinuclear actin cables, supporting the recently proposed function for the nucleus in spatially organizing actin flow and cytoplasmic polarity. Collectively, these results identify TA as a key regulator of actin-dependent rearward nuclear movement during centrosome orientation.

The inner nuclear membrane protein Lem2 is critical for normal nuclear envelope morphology

FEBS Letters ◽  
2006 ◽  
Vol 580 (27) ◽  
pp. 6435-6441 ◽  
Author(s):  
Sebastian Ulbert ◽  
Wolfram Antonin ◽  
Melpomeni Platani ◽  
Iain W. Mattaj
Keyword(s):  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Inner Nuclear Membrane ◽  
Inner Nuclear Membrane Protein ◽  
Nuclear Membrane Protein

scholarly journals Opposing roles for distinct LINC complexes in regulation of the small GTPase RhoA

2017 ◽  
Vol 28 (1) ◽  
pp. 182-191 ◽  
Author(s):  
Ketan Thakar ◽  
Christopher K. May ◽  
Anna Rogers ◽  
Christopher W. Carroll
Keyword(s):  
Membrane Protein ◽  
Actin Cytoskeleton ◽  
Nuclear Envelope ◽  
Focal Adhesion ◽  
Nuclear Membrane ◽  
Active Form ◽  
Small Gtpase ◽  
Inner Nuclear Membrane ◽  
Inner Nuclear Membrane Protein ◽  
Nuclear Membrane Protein

Linker of Nucleoskeleton and Cytoskeleton (LINC) complexes span the nuclear envelope and transduce force from dynamic cytoskeletal networks to the nuclear lamina. Here we show that LINC complexes also signal from the nuclear envelope to critical regulators of the actin cytoskeleton. Specifically, we find that LINC complexes that contain the inner nuclear membrane protein Sun2 promote focal adhesion assembly by activating the small GTPase RhoA. A key effector in this process is the transcription factor/coactivator complex composed of SRF/Mkl1. A constitutively active form of SRF/Mkl1 was not sufficient to induce focal adhesion assembly in cells lacking Sun2, however, suggesting that LINC complexes support RhoA activity through a transcription-independent mechanism. Strikingly, we also find that the inner nuclear membrane protein Sun1 antagonizes Sun2 LINC complexes and inhibits RhoA activation and focal adhesion assembly. Thus different LINC complexes have opposing roles in the transcription-independent control of the actin cytoskeleton through the small GTPase RhoA.

scholarly journals Temporal Differences in the Appearance of NEP-B78 and an LBR-like Protein during Xenopus Nuclear Envelope Reassembly Reflect the Ordered Recruitment of Functionally Discrete Vesicle Types

1999 ◽  
Vol 144 (2) ◽  
pp. 225-240 ◽  
Author(s):  
Sheona Drummond ◽  
Paul Ferrigno ◽  
Carol Lyon ◽  
Jackie Murphy ◽  
Martin Goldberg ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Protein ◽  
Nuclear Envelope ◽  
Nuclear Membrane ◽  
Free System ◽  
Present Evidence ◽  
Cell Free System ◽  
Lamin B ◽  
Lamin B Receptor ◽  
Inner Nuclear Membrane Protein

In this work, we have used novel mAbs against two proteins of the endoplasmic reticulum and outer nuclear membrane, termed NEP-B78 and p65, in addition to a polyclonal antibody against the inner nuclear membrane protein LBR (lamin B receptor), to study the order and dynamics of NE reassembly in the Xenopus cell-free system. Using these reagents, we demonstrate differences in the timing of recruitment of their cognate membrane proteins to the surface of decondensing chromatin in both the cell-free system and XLK-2 cells. We show unequivocally that, in the cell-free system, two functionally and biochemically distinct vesicle types are necessary for NE assembly. We find that the process of distinct vesicle recruitment to chromatin is an ordered one and that NEP-B78 defines a vesicle population involved in the earliest events of reassembly in this system. Finally, we present evidence that NEP-B78 may be required for the targeting of these vesicles to the surface of decondensing chromatin in this system. The results have important implications for the understanding of the mechanisms of nuclear envelope disassembly and reassembly during mitosis and for the development of systems to identify novel molecules that control these processes.

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