Nuclear envelope insertion of spindle pole bodies and nuclear 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.

Download Full-text

The NIMA Kinase Is Required To Execute Stage-Specific Mitotic Functions after Initiation of Mitosis

Eukaryotic Cell ◽

10.1128/ec.00231-13 ◽

2013 ◽

Vol 13 (1) ◽

pp. 99-109 ◽

Cited By ~ 11

Author(s):

Meera Govindaraghavan ◽

Alisha A. Lad ◽

Stephen A. Osmani

Keyword(s):

Spindle Assembly Checkpoint ◽

Spindle Pole Body ◽

Spindle Pole ◽

Cycle Phase ◽

Nuclear Pore ◽

Nuclear Pore Complexes ◽

Content Type ◽

Mitotic Entry ◽

Spindle Pole Bodies ◽

Pore Complexes

ABSTRACTThe G2-M transition inAspergillus nidulansrequires the NIMA kinase, the founding member of the Nek kinase family. Inactivation of NIMA results in a late G2arrest, while overexpression of NIMA is sufficient to promote mitotic events independently of cell cycle phase. Endogenously tagged NIMA-GFP has dynamic mitotic localizations appearing first at the spindle pole body and then at nuclear pore complexes before transitioning to within nuclei and the mitotic spindle and back at the spindle pole bodies at mitotic exit, suggesting that it functions sequentially at these locations. Since NIMA is indispensable for mitotic entry, it has been difficult to determine the requirement of NIMA for subaspects of mitosis. We show here that when NIMA is partially inactivated, although mitosis can be initiated, a proportion of cells fail to successfully generate two daughter nuclei. We further define the mitotic defects to show that normal NIMA function is required for the formation of a bipolar spindle, nuclear pore complex disassembly, completion of chromatin segregation, and the normal structural rearrangements of the nuclear envelope required to generate two nuclei from one. In the remaining population of cells that enter mitosis with inadequate NIMA, two daughter nuclei are generated in a manner dependent on the spindle assembly checkpoint, indicating highly penetrant defects in mitotic progression without sufficient NIMA activity. This study shows that NIMA is required not only for mitotic entry but also sequentially for successful completion of stage-specific mitotic events.

Download Full-text

Expression of TorsinA in a heterologous yeast system reveals interactions with conserved lumenal domains of LINC and nuclear pore complexes

10.1101/421909 ◽

2018 ◽

Author(s):

Madeleine Chalfant ◽

Karl W. Barber ◽

Sapan Borah ◽

David Thaller ◽

C. Patrick Lusk

Keyword(s):

Nuclear Envelope ◽

Genetic Interaction ◽

Spindle Pole ◽

Nuclear Pore ◽

Physical Interaction ◽

Nuclear Pore Complexes ◽

Gene Encoding ◽

Aaa Atpase ◽

Dyt1 Dystonia ◽

Pore Complexes

ABSTRACTDYT1 dystonia is caused by an in-frame deletion of a glutamic acid codon in the gene encoding the AAA+ ATPase TorsinA. TorsinA localizes within the lumen of the nuclear envelope/ER and binds to a membrane-spanning co-factor, LAP1 or LULL1, to form an ATPase; the substrate(s) of TorsinA remain ill defined. Here we use budding yeast, which lack Torsins, to interrogate TorsinA function. We show that TorsinA accumulates at nuclear envelope embedded spindle pole bodies (SPBs) in a way that requires its oligomerization and the conserved SUN-domain protein, Mps3. TorsinA is released from SPBs upon expression of LAP1 and stabilized by LAP1 mutants incapable of stimulating TorsinA ATPase activity, suggesting the recapitulation of a TorsinA-substrate cycle. While the expression of TorsinA or TorsinA-ΔE impacts the fitness of strains expressing mps3 alleles, a genetic interaction with a conserved component of the nuclear pore complex, Pom152, is specific for TorsinA. This specificity is mirrored by a physical interaction between Pom152 and TorsinA, but not TorsinA-ΔE. These data suggest that TorsinA-nucleoporin interactions would be abrogated by TorsinA-ΔE, providing new experimental avenues to interrogate the molecular basis behind nuclear envelope herniations seen in cells lacking TorsinA function.

Download Full-text

Tts1, the fission yeast homologue of the TMEM33 family, functions in NE remodeling during mitosis

Molecular Biology of the Cell ◽

10.1091/mbc.e13-12-0729 ◽

2014 ◽

Vol 25 (19) ◽

pp. 2970-2983 ◽

Cited By ~ 22

Author(s):

Dan Zhang ◽

Snezhana Oliferenko

Keyword(s):

Fission Yeast ◽

Structural Features ◽

Spindle Pole ◽

Nuclear Pore ◽

Nuclear Pore Complexes ◽

C Terminus ◽

Spindle Pole Bodies ◽

Evolutionarily Conserved ◽

Pore Complexes ◽

Insight Into

The fission yeast Schizosaccharomyces pombe undergoes “closed” mitosis in which the nuclear envelope (NE) stays intact throughout chromosome segregation. Here we show that Tts1, the fission yeast TMEM33 protein that was previously implicated in organizing the peripheral endoplasmic reticulum (ER), also functions in remodeling the NE during mitosis. Tts1 promotes insertion of spindle pole bodies (SPBs) in the NE at the onset of mitosis and modulates distribution of the nuclear pore complexes (NPCs) during mitotic NE expansion. Structural features that drive partitioning of Tts1 to the high-curvature ER domains are crucial for both aspects of its function. An amphipathic helix located at the C-terminus of Tts1 is important for ER shaping and modulating the mitotic NPC distribution. Of interest, the evolutionarily conserved residues at the luminal interface of the third transmembrane region function specifically in promoting SPB-NE insertion. Our data illuminate cellular requirements for remodeling the NE during “closed” nuclear division and provide insight into the structure and functions of the eukaryotic TMEM33 family.

Download Full-text

cut11 +: A Gene Required for Cell Cycle-dependent Spindle Pole Body Anchoring in the Nuclear Envelope and Bipolar Spindle Formation in Schizosaccharomyces pombe

Molecular Biology of the Cell ◽

10.1091/mbc.9.10.2839 ◽

1998 ◽

Vol 9 (10) ◽

pp. 2839-2855 ◽

Cited By ~ 117

Author(s):

Robert R. West ◽

Elena V. Vaisberg ◽

Rubai Ding ◽

Paul Nurse ◽

J. Richard McIntosh

Keyword(s):

Cell Cycle ◽

Nuclear Envelope ◽

Fluorescent Protein ◽

Spindle Pole ◽

Early Prophase ◽

Nuclear Pore ◽

Nuclear Pore Complexes ◽

Spindle Formation ◽

Bipolar Spindle ◽

Pore Complexes

The “cut” mutants of Schizosaccharomyces pombeare defective in spindle formation and/or chromosome segregation, but they proceed through the cell cycle, resulting in lethality. Analysis of temperature-sensitive alleles of cut11 +suggests that this gene is required for the formation of a functional bipolar spindle. Defective spindle structure was revealed with fluorescent probes for tubulin and DNA. Three-dimensional reconstruction of mutant spindles by serial sectioning and electron microscopy showed that the spindle pole bodies (SPBs) either failed to complete normal duplication or were free floating in the nucleoplasm. Localization of Cut11p tagged with the green fluorescent protein showed punctate nuclear envelope staining throughout the cell cycle and SPBs staining from early prophase to mid anaphase. This SPB localization correlates with the time in the cell cycle when SPBs are inserted into the nuclear envelope. Immunoelectron microscopy confirmed the localization of Cut11p to mitotic SPBs and nuclear pore complexes. Cloning and sequencing showed thatcut11 + encodes a novel protein with seven putative membrane-spanning domains and homology to theSaccharomyces cerevisiae gene NDC1. These data suggest that Cut11p associates with nuclear pore complexes and mitotic SPBs as an anchor in the nuclear envelope; this role is essential for mitosis.

Download Full-text

Saccharomyces cerevisiae Ndc1p Is a Shared Component of Nuclear Pore Complexes and Spindle Pole Bodies

The Journal of Cell Biology ◽

10.1083/jcb.143.7.1789 ◽

1998 ◽

Vol 143 (7) ◽

pp. 1789-1800 ◽

Cited By ~ 105

Author(s):

Heidi J. Chial ◽

Michael P. Rout ◽

Thomas H. Giddings ◽

Mark Winey

Keyword(s):

Saccharomyces Cerevisiae ◽

Immunofluorescence Microscopy ◽

Spindle Pole ◽

Nuclear Pore ◽

Nuclear Pore Complexes ◽

Indirect Immunofluorescence Microscopy ◽

Spindle Pole Bodies ◽

Shared Component ◽

Pore Complexes ◽

Mutant Cells

We report a novel connection between nuclear pore complexes (NPCs) and spindle pole bodies (SPBs) revealed by our studies of the Saccharomyces cerevisiae NDC1 gene. Although both NPCs and SPBs are embedded in the nuclear envelope (NE) in yeast, their known functions are quite distinct. Previous work demonstrated that NDC1 function is required for proper SPB duplication (Winey, M., M.A. Hoyt, C. Chan, L. Goetsch, D. Botstein, and B. Byers. 1993. J. Cell Biol. 122:743–751). Here, we show that Ndc1p is a membrane protein of the NE that localizes to both NPCs and SPBs. Indirect immunofluorescence microscopy shows that Ndc1p displays punctate, nuclear peripheral localization that colocalizes with a known NPC component, Nup49p. Additionally, distinct spots of Ndc1p localization colocalize with a known SPB component, Spc42p. Immunoelectron microscopy shows that Ndc1p localizes to the regions of NPCs and SPBs that interact with the NE. The NPCs in ndc1-1 mutant cells appear to function normally at the nonpermissive temperature. Finally, we have found that a deletion of POM152, which encodes an abundant but nonessential nucleoporin, suppresses the SPB duplication defect associated with a mutation in the NDC1 gene. We show that Ndc1p is a shared component of NPCs and SPBs and propose a shared function in the assembly of these organelles into the NE.

Download Full-text

Nuclear Fusion and Genome Encounter during Yeast Zygote Formation

Molecular Biology of the Cell ◽

10.1091/mbc.e08-12-1193 ◽

2009 ◽

Vol 20 (12) ◽

pp. 2932-2942 ◽

Cited By ~ 10

Author(s):

Alan Michael Tartakoff ◽

Purnima Jaiswal

Keyword(s):

Spindle Pole ◽

Nuclear Pore ◽

Nuclear Pore Complexes ◽

Zygote Formation ◽

Spindle Pole Bodies ◽

Higher Eukaryotes ◽

Underlying Mechanisms ◽

Pore Complexes ◽

The Impact ◽

Chromosome Tethering

When haploid cells of Saccharomyces cerevisiae are crossed, parental nuclei congress and fuse with each other. To investigate underlying mechanisms, we have developed assays that evaluate the impact of drugs and mutations. Nuclear congression is inhibited by drugs that perturb the actin and tubulin cytoskeletons. Nuclear envelope (NE) fusion consists of at least five steps in which preliminary modifications are followed by controlled flux of first outer and then inner membrane proteins, all before visible dilation of the waist of the nucleus or coalescence of the parental spindle pole bodies. Flux of nuclear pore complexes occurs after dilation. Karyogamy requires both the Sec18p/NSF ATPase and ER/NE luminal homeostasis. After fusion, chromosome tethering keeps tagged parental genomes separate from each other. The process of NE fusion and evidence of genome independence in yeast provide a prototype for understanding related events in higher eukaryotes.

Download Full-text

Nuclear Envelope Dynamics During Mitosis

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100103188 ◽

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.

Download Full-text

In Vivo Dynamics of Nuclear Pore Complexes in Yeast

The Journal of Cell Biology ◽

10.1083/jcb.136.6.1185 ◽

1997 ◽

Vol 136 (6) ◽

pp. 1185-1199 ◽

Cited By ~ 82

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.

Download Full-text

Phosphorylation-dependent mitotic SUMOylation drives nuclear envelope–chromatin interactions

The Journal of Cell Biology ◽

10.1083/jcb.202103036 ◽

2021 ◽

Vol 220 (12) ◽

Cited By ~ 1

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.

Download Full-text