Condensing nuclear pore assembly in oocytes

ABSTRACT In a subgroup of patients with amyotrophic lateral sclerosis (ALS)/Frontotemporal dementia (FTD), the (G4C2)-RNA repeat expansion from C9orf72 chromosome binds to the Ran-activating protein (RanGAP) at the nuclear pore, resulting in nucleocytoplasmic transport deficit and accumulation of Ran in the cytosol. Here, we found that the sigma-1 receptor (Sig-1R), a molecular chaperone, reverses the pathological effects of (G4C2)-RNA repeats in cell lines and in Drosophila. The Sig-1R colocalizes with RanGAP and nuclear pore proteins (Nups) and stabilizes the latter. Interestingly, Sig-1Rs directly bind (G4C2)-RNA repeats. Overexpression of Sig-1Rs rescues, whereas the Sig-1R knockout exacerbates, the (G4C2)-RNA repeats-induced aberrant cytoplasmic accumulation of Ran. In Drosophila, Sig-1R (but not the Sig-1R-E102Q mutant) overexpression reverses eye necrosis, climbing deficit, and firing discharge caused by (G4C2)-RNA repeats. These results on a molecular chaperone at the nuclear pore suggest that Sig-1Rs may benefit patients with C9orf72 ALS/FTD by chaperoning the nuclear pore assembly and sponging away deleterious (G4C2)-RNA repeats.

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Analysis of the initiation of nuclear pore assembly by ectopically targeting nucleoporins to chromatin

Nucleus ◽

10.1080/19491034.2015.1004260 ◽

2015 ◽

Vol 6 (1) ◽

pp. 40-54 ◽

Cited By ~ 22

Author(s):

Michal Schwartz ◽

Anna Travesa ◽

Steven W Martell ◽

Douglass J Forbes

Keyword(s):

Nuclear Pore ◽

Nuclear Pore Assembly

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Nup93, a Vertebrate Homologue of Yeast Nic96p, Forms a Complex with a Novel 205-kDa Protein and Is Required for Correct Nuclear Pore Assembly

Molecular Biology of the Cell ◽

10.1091/mbc.8.10.2017 ◽

1997 ◽

Vol 8 (10) ◽

pp. 2017-2038 ◽

Cited By ~ 111

Author(s):

Paola Grandi ◽

Tam Dang ◽

Nelly Pané ◽

Andrej Shevchenko ◽

Matthias Mann ◽

...

Keyword(s):

Nearest Neighbor ◽

Sequence Similarity ◽

Large Fraction ◽

Polyclonal Antiserum ◽

Nuclear Pore ◽

Related Sequence ◽

Reading Frame ◽

Protein Mass ◽

Cell Extracts ◽

Nuclear Pore Assembly

Yeast and vertebrate nuclear pores display significant morphological similarity by electron microscopy, but sequence similarity between the respective proteins has been more difficult to observe. Herein we have identified a vertebrate nucleoporin, Nup93, in both human and Xenopus that has proved to be an evolutionarily related homologue of the yeast nucleoporin Nic96p. Polyclonal antiserum to human Nup93 detects corresponding proteins in human, rat, and Xenopus cells. Immunofluorescence and immunoelectron microscopy localize vertebrate Nup93 at the nuclear basket and at or near the nuclear entry to the gated channel of the pore. Immunoprecipitation from both mammalian andXenopus cell extracts indicates that a small fraction of Nup93 physically interacts with the nucleoporin p62, just as yeast Nic96p interacts with the yeast p62 homologue. However, a large fraction of vertebrate Nup93 is extracted from pores and is also present in Xenopus egg extracts in complex with a newly discovered 205-kDa protein. Mass spectrometric sequencing of the human 205-kDa protein reveals that this protein is encoded by an open reading frame, KIAAO225, present in the human database. The putative human nucleoporin of 205 kDa has related sequence homologues inCaenorhabditis elegans and Saccharomyces cerevisiae. To analyze the role of the Nup93 complex in the pore, nuclei were assembled that lack the Nup93 complex after immunodepletion of a Xenopus nuclear reconstitution extract. The Nup93-complex–depleted nuclei are clearly defective for correct nuclear pore assembly. From these experiments, we conclude that the vertebrate and yeast pore have significant homology in their functionally important cores and that, with the identification of Nup93 and the 205-kDa protein, we have extended the knowledge of the nearest-neighbor interactions of this core in both yeast and vertebrates.

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Reconstitution of nuclear pore assembly and function

Seminars in Cell and Developmental Biology ◽

10.1006/scdb.1996.0060 ◽

1996 ◽

Vol 7 (4) ◽

pp. 475-486 ◽

Cited By ~ 6

Author(s):

C MACAULAY ◽

D FORBES

Keyword(s):

Nuclear Pore ◽

And Function ◽

Nuclear Pore Assembly

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A quantitative map of nuclear pore assembly reveals two distinct mechanisms

10.1101/2021.05.17.444137 ◽

2021 ◽

Author(s):

Shotaro Otsuka ◽

Jeremy O.B. Tempkin ◽

Antonio Z. Politi ◽

Arina Rybina ◽

M. Julius Hossain ◽

...

Keyword(s):

Molecular Mechanisms ◽

Computational Simulation ◽

Correlation Spectroscopy ◽

Nuclear Pore ◽

Fluorescence Correlation ◽

Molecular Events ◽

Ring Complex ◽

Dividing Cells ◽

Nuclear Pore Assembly ◽

Assembly Pathways

Understanding how the nuclear pore complex (NPC) assembles is of fundamental importance to grasp the mechanisms behind its essential function and understand its role during evolution of eukaryotes. While we know that at least two NPC assembly pathways exist, one during exit from mitosis and one during nuclear growth in interphase, we currently lack a quantitative map of their molecular events. Here, we use fluorescence correlation spectroscopy (FCS) calibrated live imaging of endogenously fluorescently-tagged nucleoporins to map the changes in composition and stoichiometry of seven major modules of the human NPC during its assembly in single dividing cells. This systematic quantitative map reveals that the two assembly pathways employ strikingly different molecular mechanisms, inverting the order of addition of two large structural components, the central ring complex and nuclear filaments. Our dynamic stoichiometry data allows us to perform the first computational simulation that predicts the structure of postmitotic NPC assembly intermediates.

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Decision letter: Age-dependent deterioration of nuclear pore assembly in mitotic cells decreases transport dynamics

10.7554/elife.48186.028 ◽

2019 ◽

Keyword(s):

Nuclear Pore ◽

Transport Dynamics ◽

Age Dependent ◽

Nuclear Pore Assembly ◽

Mitotic Cells

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Inner/Outer Nuclear Membrane Fusion in Nuclear Pore Assembly

Molecular Biology of the Cell ◽

10.1091/mbc.e10-04-0309 ◽

2010 ◽

Vol 21 (23) ◽

pp. 4197-4211 ◽

Cited By ~ 31

Author(s):

Boris Fichtman ◽

Corinne Ramos ◽

Beth Rasala ◽

Amnon Harel ◽

Douglass J. Forbes

Keyword(s):

Membrane Fusion ◽

Nuclear Membrane ◽

Nuclear Pore ◽

Channel Formation ◽

Fusion Event ◽

Diffusion Channel ◽

Unique Challenge ◽

Outer Nuclear Membrane ◽

Nuclear Membranes ◽

Nuclear Pore Assembly

Nuclear pore complexes (NPCs) are large proteinaceous channels embedded in double nuclear membranes, which carry out nucleocytoplasmic exchange. The mechanism of nuclear pore assembly involves a unique challenge, as it requires creation of a long-lived membrane-lined channel connecting the inner and outer nuclear membranes. This stabilized membrane channel has little evolutionary precedent. Here we mapped inner/outer nuclear membrane fusion in NPC assembly biochemically by using novel assembly intermediates and membrane fusion inhibitors. Incubation of a Xenopus in vitro nuclear assembly system at 14°C revealed an early pore intermediate where nucleoporin subunits POM121 and the Nup107-160 complex were organized in a punctate pattern on the inner nuclear membrane. With time, this intermediate progressed to diffusion channel formation and finally to complete nuclear pore assembly. Correct channel formation was blocked by the hemifusion inhibitor lysophosphatidylcholine (LPC), but not if a complementary-shaped lipid, oleic acid (OA), was simultaneously added, as determined with a novel fluorescent dextran-quenching assay. Importantly, recruitment of the bulk of FG nucleoporins, characteristic of mature nuclear pores, was not observed before diffusion channel formation and was prevented by LPC or OA, but not by LPC+OA. These results map the crucial inner/outer nuclear membrane fusion event of NPC assembly downstream of POM121/Nup107-160 complex interaction and upstream or at the time of FG nucleoporin recruitment.

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Assembly of the nuclear pore: biochemically distinct steps revealed with NEM, GTP gamma S, and BAPTA.

The Journal of Cell Biology ◽

10.1083/jcb.132.1.5 ◽

1996 ◽

Vol 132 (1) ◽

pp. 5-20 ◽

Cited By ~ 120

Author(s):

C Macaulay ◽

D J Forbes

Keyword(s):

Nuclear Membrane ◽

Vesicle Fusion ◽

Nuclear Pore ◽

Nuclear Pores ◽

Nuclear Assembly ◽

Nuclear Membranes ◽

Nuclear Pore Assembly ◽

Gamma S ◽

Nuclear Reconstitution

A key event in nuclear formation is the assembly of functional nuclear pores. We have used a nuclear reconstitution system derived from Xenopus eggs to examine the process of nuclear pore assembly in vitro. With this system, we have identified three reagents which interfere with nuclear pore assembly, NEM, GTP gamma S, and the Ca++ chelator, BAPTA. These reagents have allowed us to determine that the assembly of a nuclear pore requires the prior assembly of a double nuclear membrane. Inhibition of nuclear vesicle fusion by pretreatment of the membrane vesicle fraction with NEM blocks pore complex assembly. In contrast, NEM treatment of already fused double nuclear membranes does not block pore assembly. This indicates that NEM inhibits a single step in pore assembly--the initial fusion of vesicles required to form a double nuclear membrane. The presence of GTP gamma S blocks pore assembly at two distinct steps, first by preventing fusion between nuclear vesicles, and second by blocking a step in pore assembly that occurs on already fused double nuclear membranes. Interestingly, when the Ca2+ chelator BAPTA is added to a nuclear assembly reaction, it only transiently blocks nuclear vesicle fusion, but completely blocks nuclear pore assembly. This results in the formation of a nucleus surrounded by a double nuclear membrane, but devoid of nuclear pores. To order the positions at which GTP gamma S and BAPTA interfere with pore assembly, a novel anchored nuclear assembly assay was developed. This assay revealed that the BAPTA-sensitive step in pore assembly occurs after the second GTP gamma S-sensitive step. Thus, through use of an in vitro nuclear reconstitution system, it has been possible to biochemically define and order multiple steps in nuclear pore assembly.

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