scholarly journals Subcellular analyses of planarian meiosis implicates a novel, double-membraned vesiculation process in nuclear envelope breakdown

2019 ◽  
Author(s):  
Longhua Guo ◽  
Fengli Guo ◽  
Shasha Zhang ◽  
Kexi Yi ◽  
Melainia McClain ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
De Novo ◽  
Germinal Vesicle ◽  
Protein Composition ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Cell Nuclei ◽  
Germinal Vesicle Breakdown ◽  
Evolutionary Origins ◽  
Pore Complexes

AbstractThe cell nuclei of Ophisthokonts, the eukaryotic supergroup defined by fungi and metazoans, is remarkable in the constancy of both their double-membraned structure and protein composition. Such remarkable structural conservation underscores common and ancient evolutionary origins. Yet, the dynamics of disassembly and reassembly displayed by Ophisthokont nuclei vary extensively. Besides closed mitosis in fungi and open mitosis in some animals, little is known about the evolution of nuclear envelope break down (NEBD) during cell division. Here, we uncovered a novel form of NEBD in primary oocytes of the flatworm Schmidtea mediterranea. From zygotene to metaphase II, both nuclear envelope (NE) and peripheral endoplasmic reticulum (ER) expand notably in size, likely involving de novo membrane synthesis. 3-D electron microscopy reconstructions demonstrated that the NE transforms itself into numerous double-membraned vesicles similar in membrane architecture to NE doublets in mammalian oocytes after germinal vesicle breakdown. The vesicles are devoid of nuclear pore complexes and DNA, yet are loaded with nuclear proteins, including a planarian homologue of PIWI, a protein essential for the maintenance of stem cells in this and other organisms. Our data contribute a new model to the canonical view of NE dynamics and support that NEBD is an evolutionarily adaptable trait in multicellular organisms.

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.

Evolutionary conservation of ‘Basket’ structure in nuclear pore complexes, and their possible role in mRNA export

1994 ◽  
Vol 52 ◽  
pp. 12-13 ◽  
Author(s):  
T. D. Allen ◽  
M. W. Goldberg ◽  
C. Pelling ◽  
I. Solovei
Keyword(s):  
Nuclear Envelope ◽  
Germinal Vesicle ◽  
Evolutionary Conservation ◽  
Nuclear Pore ◽  
Macromolecular Complex ◽  
Nuclear Pore Complexes ◽  
Animal Kingdom ◽  
Nuclear Interior ◽  
Cytoplasmic Filaments ◽  
Pore Complexes

The nuclear pore complex (NPC) is a macromolecular complex which provides transport through the nuclear envelope. Each NPC has a diameter of around 120 nms, and extends outwards into the cytoplasm by some 20 nms via eight cytoplasmic filaments of granular substructure. On the nucleoplasmic face, NPC ‘cages’ or ‘baskets’ project some 60 nms into the nuclear interior where they terminate in an inner basket ring that supports a further structure, the nuclear envelope lattice (NEL), a network of filaments. Both the NEL and NPC baskets have been visualised to date only in amphibian germinal vesicle nuclear envelopes. All current models of NPC structure are based on data from amphibian oocytes, mainly due to the convenience of isolating clean and well preserved nuclear envelopes. It is important therefore to determine how widely these structures are conserved in other groups throughout the animal kingdom, as a basis for the overall evolutionary conservation of NPC structure.

scholarly journals Rupture of nuclear envelope in starfish oocytes proceeds by F-actin-driven segregation of pore-dense and pore-free membranes

2018 ◽  
Author(s):  
Natalia Wesolowska ◽  
Pedro Machado ◽  
Ivan Avilov ◽  
Celina Geiss ◽  
Hiroshi Kondo ◽  
...  
Keyword(s):  
Nuclear Envelope ◽  
Light And Electron Microscopy ◽  
Super Resolution ◽  
Germinal Vesicle ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Detailed Mechanism ◽  
Nuclear Membranes ◽  
Vesicular Membrane ◽  
Pore Complexes

AbstractThe nucleus of oocytes, traditionally referred to as the germinal vesicle, is unusually large and its nuclear envelope (NE) is densely packed with nuclear pore complexes (NPCs) stockpiled for embryonic development. We have shown that breakdown of this specialized NE during meiosis of starfish oocytes is mediated by an Arp2/3-nucleated F-actin ‘shell’, in contrast to microtubule-driven tearing in somatic cells. The detailed mechanism of how the cytoskeletal forces disrupt the NE remains poorly understood in any system. Here, we address the mechanism of F-actin-driven NE rupture by using live-cell and correlated super-resolution light and electron microscopy. We show that actin is nucleated within the lamina and sprouts filopodia-like spikes towards the nuclear membranes forcing lamina and nuclear membranes apart. These F-actin spikes protrude pore-free nuclear membranes, whereas the adjoining membrane stretches accumulate packed NPCs associated with the still-intact lamin network. NPC conglomerates sort into a distinct tubular-vesicular membrane network, while breaks appear in pore-free, ER-like regions. Together, our work reveals a novel function for Arp2/3-mediated membrane shaping in NE rupture that is likely to have broad relevance in regulating NE dynamics in diverse other contexts such as nuclear rupture frequently observed in cancer cells.

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.

scholarly journals The Three Fungal Transmembrane Nuclear Pore Complex Proteins of Aspergillus nidulans Are Dispensable in the Presence of an Intact An-Nup84-120 Complex

2009 ◽  
Vol 20 (2) ◽  
pp. 616-630 ◽  
Author(s):  
Hui-Lin Liu ◽  
Colin P.C. De Souza ◽  
Aysha H. Osmani ◽  
Stephen A. Osmani
Keyword(s):  
High Temperature ◽  
Nuclear Envelope ◽  
Aspergillus Nidulans ◽  
Nuclear Pore Complex ◽  
Mitotic Spindle ◽  
Spindle Pole ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Spindle Pole Bodies ◽  
Pore Complexes

In Aspergillus nidulans nuclear pore complexes (NPCs) undergo partial mitotic disassembly such that 12 NPC proteins (Nups) form a core structure anchored across the nuclear envelope (NE). To investigate how the NPC core is maintained, we affinity purified the major core An-Nup84-120 complex and identified two new fungal Nups, An-Nup37 and An-ELYS, previously thought to be vertebrate specific. During mitosis the An-Nup84-120 complex locates to the NE and spindle pole bodies but, unlike vertebrate cells, does not concentrate at kinetochores. We find that mutants lacking individual An-Nup84-120 components are sensitive to the membrane destabilizer benzyl alcohol (BA) and high temperature. Although such mutants display no defects in mitotic spindle formation, they undergo mitotic specific disassembly of the NPC core and transient aggregation of the mitotic NE, suggesting the An-Nup84-120 complex might function with membrane. Supporting this, we show cells devoid of all known fungal transmembrane Nups (An-Ndc1, An-Pom152, and An-Pom34) are viable but that An-ndc1 deletion combined with deletion of individual An-Nup84-120 components is either lethal or causes sensitivity to treatments expected to destabilize membrane. Therefore, the An-Nup84-120 complex performs roles, perhaps at the NPC membrane as proposed previously, that become essential without the An-Ndc1 transmembrane Nup.

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 Phosphorylation-dependent mitotic SUMOylation drives nuclear envelope–chromatin interactions

2021 ◽  
Vol 220 (12) ◽  
Author(s):  
Christopher Ptak ◽  
Natasha O. Saik ◽  
Ashwini Premashankar ◽  
Diego L. Lapetina ◽  
John D. Aitchison ◽  
...  
Keyword(s):  
Gene Expression ◽  
Nuclear Envelope ◽  
Spatial Organization ◽  
G1 Phase ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Chromatin Binding ◽  
Chromatin Interactions ◽  
Sumo Ligase ◽  
Pore Complexes

In eukaryotes, chromatin binding to the inner nuclear membrane (INM) and nuclear pore complexes (NPCs) contributes to spatial organization of the genome and epigenetic programs important for gene expression. In mitosis, chromatin–nuclear envelope (NE) interactions are lost and then formed again as sister chromosomes segregate to postmitotic nuclei. Investigating these processes in S. cerevisiae, we identified temporally and spatially controlled phosphorylation-dependent SUMOylation events that positively regulate postmetaphase chromatin association with the NE. Our work establishes a phosphorylation-mediated targeting mechanism of the SUMO ligase Siz2 to the INM during mitosis, where Siz2 binds to and SUMOylates the VAP protein Scs2. The recruitment of Siz2 through Scs2 is further responsible for a wave of SUMOylation along the INM that supports the assembly and anchorage of subtelomeric chromatin at the INM and localization of an active gene (INO1) to NPCs during the later stages of mitosis and into G1-phase.

The preparation and ultrastructure of avian erythrocyte nuclear envelope enclosed by the plasma membrane

1978 ◽  
Vol 34 (1) ◽  
pp. 81-90
Author(s):  
J.R. Harris
Keyword(s):  
Plasma Membrane ◽  
Nuclear Envelope ◽  
Ammonium Molybdate ◽  
Negative Staining ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Thin Sectioning ◽  
Avian Erythrocyte ◽  
Pore Complexes ◽  
Low Ionic Strength

A procedure is described for the preparation of avian erythrocyte nuclear envelope ghosts which remain enclosed by the ellipsoid plasma membrane. Haemoglobin-free nucleated chicken erythrocyte ghosts are treated in a low ionic strength buffer plus heparin which brings about decondensation of the chromatin. This is followed by solubilization of the chromatin by digestion with pancreatic deoxyribonuclease-1. When studied by light microscopy using either phase-contrast or Nomarski interference optics, the ellipsoid plasma membrane is clearly seen to remain with the collapsed nuclear envelope trapped inside. This interpretation is supported by negative-staining electron microscopy using ammonium molybdate, which in addition reveals the presence of the nuclear pore complexes. The suggestion is advanced that structural protection is provided for the fragile nuclear envelope system by the surrounding plasma membrane, which might account for the final nuclear envelope being in the form of relatively intact ghosts with well defined nuclear pore complexes. The nuclear envelope is highly fragmented when the plasma membrane is absent, the nuclear pore complexes showing appreciable breakdown. Thin sectioning supports the results of negative staining and in addition shows the nuclear envelope retained within the plasma membrane to be composed of both inner and outer nuclear membranes, but the nuclear pore complexes are not clearly defined.

Differential accumulation of oocyte nuclear proteins by embryonic nuclei of Xenopus

Development ◽  
1987 ◽  
Vol 101 (4) ◽  
pp. 829-846 ◽  
Author(s):  
C. Dreyer
Keyword(s):  
De Novo ◽  
Germinal Vesicle ◽  
Intrinsic Property ◽  
Nuclear Proteins ◽  
Cell Nuclei ◽  
Germinal Vesicle Breakdown ◽  
Early Stages ◽  
Nuclear Antigens ◽  
Gradual Process ◽  
Oocyte Nuclear Proteins

Oocyte nuclear proteins of Xenopus are distributed into the cytoplasm of the maturing egg after germinal vesicle breakdown. Later they are found in all cell nuclei of the embryo. At early stages of development, different nuclear proteins behave differently. A class of ‘early shifting’ antigens is accumulated by pronuclei and cleavage nuclei, whereas others appear to be excluded from the nuclei at early stages but are shifted into the nuclei at blastula or during and after gastrulation. Accumulation of ‘late-shifting’ nuclear antigens is a gradual process and occurs during a period characteristic of each protein. Multiple artificial pronuclei can be formed after injection of sperm nuclei, erythrocyte nuclei or pure lambda-DNA into unfertilized eggs. The artificial pronuclei accumulate early- but not late-shifting proteins. Early-migrating proteins rapidly accumulate into the germinal vesicle after de novo synthesis in the oocyte, indicating that the efficiency of translocation into nuclei is an intrinsic property of each protein. Artificial extension of the length of the cell cycle before midblastula transition does not lead to accumulation of the late-shifting nuclear antigens investigated.

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.

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