151
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Turgay Y, Eibauer M, Goldman AE, Shimi T, Khayat M, Ben-Harush K, Dubrovsky-Gaupp A, Sapra KT, Goldman RD, Medalia O. The molecular architecture of lamins in somatic cells. Nature 2017; 543:261-264. [PMID: 28241138 DOI: 10.1038/nature21382] [Citation(s) in RCA: 274] [Impact Index Per Article: 39.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 01/11/2017] [Indexed: 01/13/2023]
Abstract
The nuclear lamina is a fundamental constituent of metazoan nuclei. It is composed mainly of lamins, which are intermediate filament proteins that assemble into a filamentous meshwork, bridging the nuclear envelope and chromatin. Besides providing structural stability to the nucleus, the lamina is involved in many nuclear activities, including chromatin organization, transcription and replication. However, the structural organization of the nuclear lamina is poorly understood. Here we use cryo-electron tomography to obtain a detailed view of the organization of the lamin meshwork within the lamina. Data analysis of individual lamin filaments resolves a globular-decorated fibre appearance and shows that A- and B-type lamins assemble into tetrameric filaments of 3.5 nm thickness. Thus, lamins exhibit a structure that is remarkably different from the other canonical cytoskeletal elements. Our findings define the architecture of the nuclear lamin meshworks at molecular resolution, providing insights into their role in scaffolding the nuclear lamina.
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Affiliation(s)
- Yagmur Turgay
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Matthias Eibauer
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Anne E Goldman
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Chicago, Illinois 60611, USA
| | - Takeshi Shimi
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Chicago, Illinois 60611, USA
| | - Maayan Khayat
- Department of Life Sciences and the National Institute for Biotechnology in the Negev, Ben-Gurion University, 84105 Beer-Sheva, Israel
| | - Kfir Ben-Harush
- Department of Chemical Engineering, Shamoon College of Engineering, Jabotinsky 84, 77245 Ashdod, Israel
| | - Anna Dubrovsky-Gaupp
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - K Tanuj Sapra
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Robert D Goldman
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, 303 E Chicago Avenue, Chicago, Illinois 60611, USA
| | - Ohad Medalia
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.,Department of Life Sciences and the National Institute for Biotechnology in the Negev, Ben-Gurion University, 84105 Beer-Sheva, Israel
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152
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Lusk CP, King MC. The nucleus: keeping it together by keeping it apart. Curr Opin Cell Biol 2017; 44:44-50. [PMID: 28236735 DOI: 10.1016/j.ceb.2017.02.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 01/29/2017] [Accepted: 02/01/2017] [Indexed: 12/15/2022]
Abstract
It has been postulated that the segregation of nucleus and cytoplasm supported the development of increased organismal complexity. For example, separating transcription and translation allows for mRNA splicing, while the sequestration of genomic DNA supports the innate immune system's ability to equate cytoplasmic DNA with pathogens. Consistent with the importance of nucleocytoplasmic compartmentalization in a broad array of cellular processes, defects in maintaining discrete nuclear and cytoplasmic compartments, either due to loss of nuclear pore complex integrity, disrupted nuclear transport or ruptures of the nuclear envelope, lead to cellular dysfunction, cell death and disease. Here, we discuss recent insights into how loss of compartmentalization can arise as well as the consequences for cellular and organismal homeostasis.
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Affiliation(s)
- C Patrick Lusk
- Department of Cell Biology, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8002, USA.
| | - Megan C King
- Department of Cell Biology, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8002, USA.
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153
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Abstract
SUMMARYThe nucleoskeleton is an important structural feature of the metazoan nucleus and is involved in the regulation of genome expression and maintenance. The nuclear lamins are intermediate filament proteins that form a peripheral nucleoskeleton in concert with other lamin-associated proteins. Several other proteins normally found in the cytoskeleton have also been identified in the nucleus, but, as will be discussed here, their roles in forming a nucleoskeleton have not been elucidated. Nevertheless, mutations in lamins and lamin-associated proteins cause a spectrum of diseases, making them interesting targets for future research.
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Affiliation(s)
- Stephen A Adam
- Department of Cell and Molecular Biology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois 60611
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154
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Stephens AD, Banigan EJ, Adam SA, Goldman RD, Marko JF. Chromatin and lamin A determine two different mechanical response regimes of the cell nucleus. Mol Biol Cell 2017; 28:1984-1996. [PMID: 28057760 PMCID: PMC5541848 DOI: 10.1091/mbc.e16-09-0653] [Citation(s) in RCA: 277] [Impact Index Per Article: 39.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 11/04/2016] [Accepted: 12/29/2016] [Indexed: 02/02/2023] Open
Abstract
The cell nucleus must continually resist and respond to intercellular and intracellular mechanical forces to transduce mechanical signals and maintain proper genome organization and expression. Altered nuclear mechanics is associated with many human diseases, including heart disease, progeria, and cancer. Chromatin and nuclear envelope A-type lamin proteins are known to be key nuclear mechanical components perturbed in these diseases, but their distinct mechanical contributions are not known. Here we directly establish the separate roles of chromatin and lamin A/C and show that they determine two distinct mechanical regimes via micromanipulation of single isolated nuclei. Chromatin governs response to small extensions (<3 μm), and euchromatin/heterochromatin levels modulate the stiffness. In contrast, lamin A/C levels control nuclear strain stiffening at large extensions. These results can be understood through simulations of a polymeric shell and cross-linked polymer interior. Our results provide a framework for understanding the differential effects of chromatin and lamin A/C in cell nuclear mechanics and their alterations in disease.
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Affiliation(s)
- Andrew D Stephens
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208
| | - Edward J Banigan
- Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208
| | - Stephen A Adam
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
| | - Robert D Goldman
- Department of Cell and Molecular Biology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611
| | - John F Marko
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208.,Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208
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155
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Drozdz MM, Vaux DJ. Shared mechanisms in physiological and pathological nucleoplasmic reticulum formation. Nucleus 2017; 8:34-45. [PMID: 27797635 PMCID: PMC5287099 DOI: 10.1080/19491034.2016.1252893] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 10/13/2016] [Accepted: 10/19/2016] [Indexed: 12/14/2022] Open
Abstract
The mammalian nuclear envelope (NE) can develop complex dynamic membrane-bounded invaginations in response to both physiological and pathological stimuli. Since the formation of these nucleoplasmic reticulum (NR) structures can occur during interphase, without mitotic NE breakdown and reassembly, some other mechanism must drive their development. Here we consider models for deformation of the interphase NE, together with the evidence for their potential roles in NR formation.
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Affiliation(s)
| | - David John Vaux
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
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156
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Roller RJ, Baines JD. Herpesvirus Nuclear Egress. ADVANCES IN ANATOMY, EMBRYOLOGY, AND CELL BIOLOGY 2017; 223:143-169. [PMID: 28528443 DOI: 10.1007/978-3-319-53168-7_7] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Herpesviruses assemble and package their genomes into capsids in the nucleus, but complete final assembly of the mature virion in the cell cytoplasm. This requires passage of the genome-containing capsid across the double-membrane nuclear envelope. Herpesviruses have evolved a mechanism that relies on a pair of conserved viral gene products to shuttle the capsids from the nucleus to the cytoplasm by way of envelopment and de-envelopment at the inner and outer nuclear membranes, respectively. This complex process requires orchestration of the activities of viral and cellular factors to alter the architecture of the nuclear membrane, select capsids at the appropriate stage for egress, and accomplish efficient membrane budding and fusion events. The last few years have seen major advances in our understanding of the membrane budding mechanism and helped clarify the roles of viral and cellular proteins in the other, more mysterious steps. Here, we summarize and place into context this recent research and, hopefully, clarify both the major advances and major gaps in our understanding.
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Affiliation(s)
- Richard J Roller
- Department of Microbiology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA, USA
| | - Joel D Baines
- Kenneth F. Burns Chair in Veterinary Medicine, School of Veterinary Medicine, Skip Bertman Drive, Louisiana State University, Baton Rouge, LA, USA.
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157
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Pecorari I, Puzzi L, Sbaizero O. Atomic force microscopy and lamins: A review study towards future, combined investigations. Microsc Res Tech 2016; 80:97-108. [PMID: 27859883 DOI: 10.1002/jemt.22801] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 09/21/2016] [Accepted: 10/20/2016] [Indexed: 12/13/2022]
Abstract
In the last decades, atomic force microscopy (AFM) underwent a rapid and stunning development, especially for studying mechanical properties of biological samples. The numerous discoveries relying to this approach, have increased the credit of AFM as a versatile tool, and potentially eligible as a diagnostic equipment. Meanwhile, it has become strikingly evident that lamins are involved on the onset and development of certain diseases, including cancer, Hutchinson-Gilford progeria syndrome, cardiovascular pathologies, and muscular dystrophy. A new category of pathologies has been defined, the laminopathies, which are caused by mutations in the gene encoding for A-type lamins. As the majority of medical issues, lamins, and all their related aspects can be considered as a quite complex problem. Indeed, there are many facets to explore, and this definitely requires a multidisciplinary approach. One of the most intriguing aspects concerning lamins is their remarkable contribute to cells mechanics. Over the years, this has led to the speculation of the so-called "structural hypothesis", which attempts to elucidate the etiology and some features of the laminopathies. Among the various techniques tried to figure out the role of lamins in the cells mechanics, the AFM has been already successfully applied, proving its versatility. Therefore, the present work aims both to highlight the qualities of AFM and to review the most relevant knowledge about lamins, in order to promote the study of the latter, taking advantage from the former. Microsc. Res. Tech. 80:97-108, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Ilaria Pecorari
- Department of Engineering and Architecture, University of Trieste, Via Valerio 6-34127, Trieste, Italy
| | - Luca Puzzi
- Department of Engineering and Architecture, University of Trieste, Via Valerio 6-34127, Trieste, Italy
| | - Orfeo Sbaizero
- Department of Engineering and Architecture, University of Trieste, Via Valerio 6-34127, Trieste, Italy
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158
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Extragenic Suppression of a Mutation in Herpes Simplex Virus 1 UL34 That Affects Lamina Disruption and Nuclear Egress. J Virol 2016; 90:10738-10751. [PMID: 27654296 DOI: 10.1128/jvi.01544-16] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Accepted: 09/13/2016] [Indexed: 01/06/2023] Open
Abstract
Nuclear egress of herpesviruses is accompanied by changes in the architecture of the nuclear membrane and nuclear lamina that are thought to facilitate capsid access to the inner nuclear membrane (INM) and curvature of patches of the INM around the capsid during budding. Here we report the properties of a point mutant of pUL34 (Q163A) that fails to induce gross changes in nuclear architecture or redistribution of lamin A/C. The UL34(Q163A) mutant shows a roughly 100-fold defect in single-step growth, and it forms small plaques. This mutant has a defect in nuclear egress, and furthermore, it fails to disrupt nuclear shape or cause observable displacement of lamin A/C despite retaining the ability to recruit the pUS3 and PKC protein kinases and to mediate phosphorylation of emerin. Extragenic suppressors of the UL34(Q163A) phenotype were isolated, and all of them carry a single mutation of arginine 229 to leucine in UL31. Surprisingly, although this UL31 mutation largely restores virus replication, it does not correct the lamina disruption defect, suggesting that, in Vero cells, changes in nuclear shape and gross displacements of lamin A/C may facilitate but are unnecessary for nuclear egress. IMPORTANCE Herpesvirus nuclear egress is an essential and conserved process that requires close association of the viral capsid with the inner nuclear membrane and budding of the capsid into that membrane. Access to the nuclear membrane and tight curvature of that membrane are thought to require disruption of the nuclear lamina that underlies the inner nuclear membrane, and consistent with this idea, herpesvirus infection induces biochemical and architectural changes at the nuclear membrane. The significance of the nuclear membrane architectural changes is poorly characterized. The results presented here address that deficiency in our understanding and show that a combination of mutations in two of the viral nuclear egress factors results in a failure to accomplish at least two components of lamina disruption while still allowing relatively efficient viral replication, suggesting that changes in nuclear shape and displacement of lamins are not necessary for herpes simplex virus 1 (HSV-1) nuclear egress.
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159
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Armiger TJ, Spagnol ST, Dahl KN. Nuclear mechanical resilience but not stiffness is modulated by αII-spectrin. J Biomech 2016; 49:3983-3989. [PMID: 27836504 DOI: 10.1016/j.jbiomech.2016.10.034] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 10/18/2016] [Accepted: 10/21/2016] [Indexed: 11/18/2022]
Abstract
Spectrins are multi-domain, elastic proteins that provide elasticity to the plasma membrane of erythrocytes and select nucleated cells. Spectrins have also been found in the nucleus of non-erythrocytes, but their function remains to be uncovered. It has been hypothesized that a spring-like spectrin network exists within the lamina nucleoskeleton, however, experiments testing a spectrin network׳s mechanical impact on the nucleus are lacking. Here, we knock-down levels of nuclear αII-spectrin with the goal of disrupting this nucleoskeletal spectrin network. We mechanically test live cells with intranuclear particle tracking and compression assays to probe changes in nuclear mechanics with decreases in αII-spectrin. We show no changes in chromatin mechanics or in the stiffness of nuclei under compression. However, we do observe a reduction in the ability of nuclei with decreased αII-spectrin to recover after compression. These results establish spectrin as a nucleoskeletal component that specifically contributes to elastic recovery after compression.
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Affiliation(s)
- Travis J Armiger
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Stephen T Spagnol
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Kris Noel Dahl
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA; Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA.
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160
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Abstract
Lamins are major components of the nuclear lamina, a network of proteins that supports the nuclear envelope in metazoan cells. Over the past decade, biochemical studies have provided support for the view that lamins are not passive bystanders providing mechanical stability to the nucleus but play an active role in the organization of the genome and the function of fundamental nuclear processes. It has also become apparent that lamins are critical for human health, as a large number of mutations identified in the gene that encodes for A-type lamins are associated with tissue-specific and systemic genetic diseases, including the accelerated aging disorder known as Hutchinson-Gilford progeria syndrome. Recent years have witnessed great advances in our understanding of the role of lamins in the nucleus and the functional consequences of disease-associated A-type lamin mutations. Many of these findings have been presented in comprehensive reviews. In this mini-review, we discuss recent breakthroughs in the role of lamins in health and disease and what lies ahead in lamin research.
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Affiliation(s)
- Sita Reddy
- Department of Biochemistry and Molecular Biology, Institute for Genetic Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Lucio Comai
- Department of Biochemistry and Molecular Biology, Institute for Genetic Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA; Department of Molecular Microbiology and Immunology, Institute for Genetic Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
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161
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A-type Lamins Form Distinct Filamentous Networks with Differential Nuclear Pore Complex Associations. Curr Biol 2016; 26:2651-2658. [PMID: 27641764 DOI: 10.1016/j.cub.2016.07.049] [Citation(s) in RCA: 105] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Revised: 06/30/2016] [Accepted: 07/20/2016] [Indexed: 11/22/2022]
Abstract
The nuclear lamina is a universal feature of metazoan nuclear envelopes (NEs) [1]. In mammalian cells, it appears as a 10-30 nm filamentous layer at the nuclear face of the inner nuclear membrane (INM) and is composed primarily of A- and B-type lamins, members of the intermediate filament family [2]. While providing structural integrity to the NE, the lamina also represents an important signaling and regulatory platform [3]. Two A-type lamin isoforms, lamins A and C (LaA and LaC), are expressed in most adult human cells. Encoded by a single gene, these proteins are largely identical, diverging only in their C-terminal tail domains. By contrast with that of LaC, the unique LaA tail undergoes extensive processing, including farnesylation and endo-proteolysis [4, 5]. However, functional differences between LaA and LaC are still unclear. Compounding this uncertainty, the structure of the lamina remains ill defined. In this study, we used BioID, an in vivo proximity-labeling method to identify differential interactors of A-type lamins [6]. One of these, Tpr, a nuclear pore complex (NPC) protein, is highlighted by its selective association with LaC. By employing superresolution microscopy, we demonstrate that this Tpr association is mirrored in enhanced interaction of LaC with NPCs. Further superresolution studies visualizing both endogenous A- and B-type lamins have allowed us to construct a nanometer-scale model of the mammalian nuclear lamina. Our data indicate that different A- and B-type lamin species assemble into separate filament networks that together form an extended composite structure at the nuclear periphery providing attachment sites for NPCs, thereby regulating their distribution.
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162
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McGregor AL, Hsia CR, Lammerding J. Squish and squeeze-the nucleus as a physical barrier during migration in confined environments. Curr Opin Cell Biol 2016; 40:32-40. [PMID: 26895141 PMCID: PMC4887392 DOI: 10.1016/j.ceb.2016.01.011] [Citation(s) in RCA: 139] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Accepted: 01/23/2016] [Indexed: 01/22/2023]
Abstract
From embryonic development to cancer metastasis, cell migration plays a central role in health and disease. It is increasingly becoming apparent that cells migrating in three-dimensional (3-D) environments exhibit some striking differences compared with their well-established 2-D counterparts. One key finding is the significant role the nucleus plays during 3-D migration: when cells move in confined spaces, the cell body and nucleus must deform to squeeze through available spaces, and the deformability of the large and relatively rigid nucleus can become rate-limiting. In this review, we highlight recent findings regarding the role of nuclear mechanics in 3-D migration, including factors that govern nuclear deformability, and emerging mechanisms by which cells apply cytoskeletal forces to the nucleus to facilitate nuclear translocation. Intriguingly, the 'physical barrier' imposed by the nucleus also impacts cytoplasmic dynamics that affect cell migration and signaling, and changes in nuclear structure resulting from the mechanical forces acting on the nucleus during 3-D migration could further alter cellular function. These findings have broad relevance to the migration of both normal and cancerous cells inside living tissues, and motivate further research into the molecular details by which cells move their nuclei, as well as the consequences of the mechanical stress on the nucleus.
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Affiliation(s)
- Alexandra Lynn McGregor
- Nancy C. and Peter E. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY 14853, USA; Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Chieh-Ren Hsia
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA; Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Jan Lammerding
- Nancy C. and Peter E. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY 14853, USA; Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA.
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163
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Abstract
Super resolution imaging is becoming an increasingly important tool in the arsenal of methods available to cell biologists. In recognition of its potential, the Nobel Prize for chemistry was awarded to three investigators involved in the development of super resolution imaging methods in 2014. The availability of commercial instruments for super resolution imaging has further spurred the development of new methods and reagents designed to take advantage of super resolution techniques. Super resolution offers the advantages traditionally associated with light microscopy, including the use of gentle fixation and specimen preparation methods, the ability to visualize multiple elements within a single specimen, and the potential to visualize dynamic changes in living specimens over time. However, imaging of living cells over time is difficult and super resolution imaging is computationally demanding. In this review, we discuss the advantages/disadvantages of different super resolution systems for imaging fixed live specimens, with particular regard to cytoskeleton structures.
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Affiliation(s)
- Eric A Shelden
- School of Molecular Biosciences, Washington State University, Pullman, WA, USA
| | - Zachary T Colburn
- School of Molecular Biosciences, Washington State University, Pullman, WA, USA
| | - Jonathan C R Jones
- School of Molecular Biosciences, Washington State University, Pullman, WA, USA
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164
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Czapiewski R, Robson MI, Schirmer EC. Anchoring a Leviathan: How the Nuclear Membrane Tethers the Genome. Front Genet 2016; 7:82. [PMID: 27200088 PMCID: PMC4859327 DOI: 10.3389/fgene.2016.00082] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Accepted: 04/20/2016] [Indexed: 12/21/2022] Open
Abstract
It is well established that the nuclear envelope has many distinct direct connections to chromatin that contribute to genome organization. The functional consequences of genome organization on gene regulation are less clear. Even less understood is how interactions of lamins and nuclear envelope transmembrane proteins (NETs) with chromatin can produce anchoring tethers that can withstand the physical forces of and on the genome. Chromosomes are the largest molecules in the cell, making megadalton protein structures like the nuclear pore complexes and ribosomes seem small by comparison. Thus to withstand strong forces from chromosome dynamics an anchoring tether is likely to be much more complex than a single protein-protein or protein-DNA interaction. Here we will briefly review known NE-genome interactions that likely contribute to spatial genome organization, postulate in the context of experimental data how these anchoring tethers contribute to gene regulation, and posit several hypotheses for the physical nature of these tethers that need to be investigated experimentally. Significantly, disruption of these anchoring tethers and the subsequent consequences for gene regulation could explain how mutations in nuclear envelope proteins cause diseases ranging from muscular dystrophy to lipodystrophy to premature aging progeroid syndromes. The two favored hypotheses for nuclear envelope protein involvement in disease are (1) weakening nuclear and cellular mechanical stability, and (2) disrupting genome organization and gene regulation. Considerable experimental support has been obtained for both. The integration of both mechanical and gene expression defects in the disruption of anchoring tethers could provide a unifying hypothesis consistent with both.
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Affiliation(s)
| | | | - Eric C. Schirmer
- The Wellcome Trust Centre for Cell Biology and Institute of Cell Biology, University of EdinburghEdinburgh, UK
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165
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166
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Wallrath LL, Bohnekamp J, Magin TM. Cross talk between the cytoplasm and nucleus during development and disease. Curr Opin Genet Dev 2016; 37:129-136. [PMID: 27110666 DOI: 10.1016/j.gde.2016.03.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 03/09/2016] [Accepted: 03/15/2016] [Indexed: 01/03/2023]
Abstract
Mechanotransduction is a process whereby mechanical stimuli outside the cell are sensed by components of the plasma membrane and transmitted as signals through the cytoplasm that terminate in the nucleus. The nucleus responds to these signals by altering gene expression. During mechanotransduction, complex networks of proteins are responsible for cross talk between the cytoplasm and the nucleus. These proteins include cell membrane receptors, cytoplasmic filaments, LINC complex members that bridge the nucleus and cytoplasm, and nuclear envelope proteins that connect to the chromatin. Mechanotransduction also plays a critical role in development. Furthermore, it is possible that disrupted mechanotransduction leads to changes in gene expression that underlie the pathogenic mechanisms of disease.
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Affiliation(s)
- Lori L Wallrath
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA.
| | - Jens Bohnekamp
- Institute of Biology and Translational Center for Regenerative Medicine, University of Leipzig, D-04103 Leipzig, Germany
| | - Thomas M Magin
- Institute of Biology and Translational Center for Regenerative Medicine, University of Leipzig, D-04103 Leipzig, Germany
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167
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A model for coordinating nuclear mechanics and membrane remodeling to support nuclear integrity. Curr Opin Cell Biol 2016; 41:9-17. [PMID: 27031045 DOI: 10.1016/j.ceb.2016.03.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Revised: 03/10/2016] [Accepted: 03/11/2016] [Indexed: 11/20/2022]
Abstract
A polymer network of intranuclear lamin filaments underlies the nuclear envelope and provides mechanical stability to the nucleus in metazoans. Recent work demonstrates that the expression of A-type lamins scales positively with the stiffness of the cellular environment, thereby coupling nuclear and extracellular mechanics. Using the spectrin-actin network at the erythrocyte plasma membrane as a model, we contemplate how the relative stiffness of the nuclear scaffold impinges on the growing number of interphase-specific nuclear envelope remodeling events, including recently discovered, nuclear envelope-specialized quality control mechanisms. We suggest that a stiffer lamina impedes these remodeling events, necessitating local lamina remodeling and/or concomitant scaling of the efficacy of membrane-remodeling machineries that act at the nuclear envelope.
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168
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Denais CM, Gilbert RM, Isermann P, McGregor AL, te Lindert M, Weigelin B, Davidson PM, Friedl P, Wolf K, Lammerding J. Nuclear envelope rupture and repair during cancer cell migration. Science 2016; 352:353-8. [PMID: 27013428 DOI: 10.1126/science.aad7297] [Citation(s) in RCA: 816] [Impact Index Per Article: 102.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 02/25/2016] [Indexed: 12/14/2022]
Abstract
During cancer metastasis, tumor cells penetrate tissues through tight interstitial spaces, which requires extensive deformation of the cell and its nucleus. Here, we investigated mammalian tumor cell migration in confining microenvironments in vitro and in vivo. Nuclear deformation caused localized loss of nuclear envelope (NE) integrity, which led to the uncontrolled exchange of nucleo-cytoplasmic content, herniation of chromatin across the NE, and DNA damage. The incidence of NE rupture increased with cell confinement and with depletion of nuclear lamins, NE proteins that structurally support the nucleus. Cells restored NE integrity using components of the endosomal sorting complexes required for transport III (ESCRT III) machinery. Our findings indicate that cell migration incurs substantial physical stress on the NE and its content and requires efficient NE and DNA damage repair for cell survival.
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Affiliation(s)
- Celine M Denais
- Nancy E. and Peter C. Meinig School of Biomedical Engineering and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Rachel M Gilbert
- Nancy E. and Peter C. Meinig School of Biomedical Engineering and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Philipp Isermann
- Nancy E. and Peter C. Meinig School of Biomedical Engineering and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Alexandra L McGregor
- Nancy E. and Peter C. Meinig School of Biomedical Engineering and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Mariska te Lindert
- Department of Cell Biology, Radboud University Medical Center, Nijmegen, Netherlands
| | - Bettina Weigelin
- Department of Cell Biology, Radboud University Medical Center, Nijmegen, Netherlands
| | - Patricia M Davidson
- Nancy E. and Peter C. Meinig School of Biomedical Engineering and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
| | - Peter Friedl
- Department of Cell Biology, Radboud University Medical Center, Nijmegen, Netherlands. Department of Genitourinary Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA. Cancer Genomics Center, Netherlands (CGC.nl)
| | - Katarina Wolf
- Department of Cell Biology, Radboud University Medical Center, Nijmegen, Netherlands
| | - Jan Lammerding
- Nancy E. and Peter C. Meinig School of Biomedical Engineering and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA.
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169
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Abstract
The nuclear lamina represents a multifunctional platform involved in such diverse yet interconnected processes as spatial organization of the genome, maintenance of mechanical stability of the nucleus, regulation of transcription and replication. Most of lamina activities are exerted through tethering of lamina-associated chromatin domains (LADs) to the nuclear periphery. Yet, the lamina is a dynamic structure demonstrating considerable expansion during the cell cycle to accommodate increased number of LADs formed during DNA replication. We analyzed dynamics of nuclear growth during interphase and changes in lamina structure as a function of cell cycle progression. The nuclear lamina demonstrates steady growth from G1 till G2, while quantitative analysis of lamina meshwork by super-resolution microscopy revealed that microdomain organization of the lamina is maintained, with lamin A and lamin B microdomain periodicity and interdomain gap sizes unchanged. FRAP analysis, in contrast, demonstrated differences in lamin A and B1 exchange rates; the latter showing higher recovery rate in S-phase cells. In order to further analyze the mechanism of lamina growth in interphase, we generated a lamina-free nuclear envelope in living interphase cells by reversible hypotonic shock. The nuclear envelope in nuclear buds formed after such a treatment initially lacked lamins, and analysis of lamina formation revealed striking difference in lamin A and B1 assembly: lamin A reassembled within 30 min post-treatment, whereas lamin B1 did not incorporate into the newly formed lamina at all. We suggest that in somatic cells lamin B1 meshwork growth is coordinated with replication of LADs, and lamin A meshwork assembly seems to be chromatin-independent process.
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170
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Davidson PM, Sliz J, Isermann P, Denais C, Lammerding J. Design of a microfluidic device to quantify dynamic intra-nuclear deformation during cell migration through confining environments. Integr Biol (Camb) 2015; 7:1534-46. [PMID: 26549481 DOI: 10.1039/c5ib00200a] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The ability of cells to migrate through tissues and interstitial spaces is an essential factor during development and tissue homeostasis, immune cell mobility, and in various human diseases. Deformation of the nucleus and its associated lamina during 3-D migration is gathering increasing interest in the context of cancer metastasis, with the underlying hypothesis that a softer nucleus, resulting from reduced levels of lamin A/C, may aid tumour spreading. However, current methods to study the migration of cells in confining three dimensional (3-D) environments are limited by their imprecise control over the confinement, physiological relevance, and/or compatibility with high resolution imaging techniques. We describe the design of a polydimethylsiloxane (PDMS) microfluidic device composed of channels with precisely-defined constrictions mimicking physiological environments that enable high resolution imaging of live and fixed cells. The device promotes easy cell loading and rapid, yet long-lasting (>24 hours) chemotactic gradient formation without the need for continuous perfusion. Using this device, we obtained detailed, quantitative measurements of dynamic nuclear deformation as cells migrate through tight spaces, revealing distinct phases of nuclear translocation through the constriction, buckling of the nuclear lamina, and severe intranuclear strain. Furthermore, we found that lamin A/C-deficient cells exhibited increased and more plastic nuclear deformations compared to wild-type cells but only minimal changes in nuclear volume, implying that low lamin A/C levels facilitate migration through constrictions by increasing nuclear deformability rather than compressibility. The integration of our migration devices with high resolution time-lapse imaging provides a powerful new approach to study intracellular mechanics and dynamics in a variety of physiologically-relevant applications, ranging from cancer cell invasion to immune cell recruitment.
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Affiliation(s)
- Patricia M Davidson
- Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY, USA
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171
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Bhattacharjee P, Dasgupta D, Sengupta K. Molecular Events in Lamin B1 Homopolymerization: A Biophysical Characterization. J Phys Chem B 2015; 119:14014-21. [PMID: 26465373 DOI: 10.1021/acs.jpcb.5b07320] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Lamin B1 is one of the major constituents of the nuclear lamina, a filamentous network underlying the nucleoplasmic side of the inner nuclear membrane. Homopolymerization of lamin B1, coupled to the homotypic and heterotypic association of other lamin types, is central to building the higher order network pattern inside the nucleus. This in turn maintains the mechanical and functional integrity of the lamina. We have characterized the molecular basis of the self-association of lamin B1 using spectroscopic and calorimetric methods. We report that concentration dependent lamin B1 oligomerization involves significant alterations in secondary and tertiary structures of the protein resulting in fairly observable compaction in size. Comparison of the energetics of the homotypic association of lamin B1 with that of lamin A reported earlier led to the finding that lamin A oligomers had higher thermodynamic stability. This leads us to conjecture that lamin B1 has less stress bearing ability compared to lamin A.
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Affiliation(s)
- Pritha Bhattacharjee
- Biophysics and Structural Genomics Division, Saha Institute of Nuclear Physics , 1/AF Bidhannagar, Kolkata-700064, India
| | - Dipak Dasgupta
- Biophysics and Structural Genomics Division, Saha Institute of Nuclear Physics , 1/AF Bidhannagar, Kolkata-700064, India
| | - Kaushik Sengupta
- Biophysics and Structural Genomics Division, Saha Institute of Nuclear Physics , 1/AF Bidhannagar, Kolkata-700064, India
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172
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Makarov AA, Rizzotto A, Meinke P, Schirmer EC. Purification of Lamins and Soluble Fragments of NETs. Methods Enzymol 2015; 569:79-100. [PMID: 26778554 DOI: 10.1016/bs.mie.2015.09.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Lamins and associated nuclear envelope transmembrane proteins (NETs) present unique problems for biochemical studies. Lamins form insoluble intermediate filament networks, associate with chromatin, and are also connected via specific NETs to the cytoskeleton, thus further complicating their isolation and purification from mammalian cells. Adding to this complexity, NETs at the inner nuclear membrane function in three distinct environments: (a) their nucleoplasmic domain(s) can bind lamins, chromatin, and transcriptional regulators; (b) they possess one or more integral transmembrane domains; and (c) their lumenal domain(s) function in the unique reducing environment of the nuclear envelope/ER lumen. This chapter describes strategic considerations and protocols to facilitate biochemical studies of lamins and NET proteins in vitro. Studying these proteins in vitro typically involves first expressing specific polypeptide fragments in bacteria and optimizing conditions to purify each fragment. We describe parameters for choosing specific fragments and designing purification strategies and provide detailed purification protocols. Biochemical studies can provide fundamental knowledge including binding strengths and the molecular consequences of disease-causing mutations that will be essential to understand nuclear envelope-genome interactions and nuclear envelope linked disease mechanisms.
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Affiliation(s)
- Alexandr A Makarov
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Andrea Rizzotto
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Peter Meinke
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Eric C Schirmer
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, United Kingdom.
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