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Weber MS, Eibauer M, Sivagurunathan S, Magin TM, Goldman RD, Medalia O. Structural heterogeneity of cellular K5/K14 filaments as revealed by cryo-electron microscopy. eLife 2021; 10:70307. [PMID: 34323216 PMCID: PMC8360650 DOI: 10.7554/elife.70307] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Accepted: 07/23/2021] [Indexed: 12/11/2022] Open
Abstract
Keratin intermediate filaments are an essential and major component of the cytoskeleton in epithelial cells. They form a stable yet dynamic filamentous network extending from the nucleus to the cell periphery, which provides resistance to mechanical stresses. Mutations in keratin genes are related to a variety of epithelial tissue diseases. Despite their importance, the molecular structure of keratin filaments remains largely unknown. In this study, we analyzed the structure of keratin 5/keratin 14 filaments within ghost mouse keratinocytes by cryo-electron microscopy and cryo-electron tomography. By averaging a large number of keratin segments, we have gained insights into the helical architecture of the filaments. Two-dimensional classification revealed profound variations in the diameter of keratin filaments and their subunit organization. Computational reconstitution of filaments of substantial length uncovered a high degree of internal heterogeneity along single filaments, which can contain regions of helical symmetry, regions with less symmetry and regions with significant diameter fluctuations. Cross-section views of filaments revealed that keratins form hollow cylinders consisting of multiple protofilaments, with an electron dense core located in the center of the filament. These findings shed light on the complex and remarkable heterogenic architecture of keratin filaments, suggesting that they are highly flexible, dynamic cytoskeletal structures.
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Affiliation(s)
- Miriam S Weber
- Department of Biochemistry, University of Zurich, Zurich, Switzerland
| | - Matthias Eibauer
- Department of Biochemistry, University of Zurich, Zurich, Switzerland
| | - Suganya Sivagurunathan
- Department of Cell and Developmental Biology, Northwestern University Feinberg School of Medicine, Chicago, United States
| | - Thomas M Magin
- Institute of Biology, University of Leipzig, Leipzig, Germany
| | - Robert D Goldman
- Department of Cell and Developmental Biology, Northwestern University Feinberg School of Medicine, Chicago, United States
| | - Ohad Medalia
- Department of Biochemistry, University of Zurich, Zurich, Switzerland
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2
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Gontard LC, Schierholz R, Yu S, Cintas J, Dunin-Borkowski RE. Photogrammetry of the three-dimensional shape and texture of a nanoscale particle using scanning electron microscopy and free software. Ultramicroscopy 2016; 169:80-88. [DOI: 10.1016/j.ultramic.2016.07.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2016] [Revised: 06/28/2016] [Accepted: 07/03/2016] [Indexed: 11/28/2022]
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Nafeey S, Martin I, Felder T, Walther P, Felder E. Branching of keratin intermediate filaments. J Struct Biol 2016; 194:415-22. [PMID: 27039023 DOI: 10.1016/j.jsb.2016.03.023] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Revised: 03/22/2016] [Accepted: 03/30/2016] [Indexed: 11/18/2022]
Abstract
Keratin intermediate filaments (IFs) are crucial to maintain mechanical stability in epithelial cells. Since little is known about the network architecture that provides this stiffness and especially about branching properties of filaments, we addressed this question with different electron microscopic (EM) methods. Using EM tomography of high pressure frozen keratinocytes, we investigated the course of several filaments in a branching of a filament bundle. Moreover we found several putative bifurcations in individual filaments. To verify our observation we also visualized the keratin network in detergent extracted keratinocytes with scanning EM. Here bifurcations of individual filaments could unambiguously be identified additionally to bundle branchings. Interestingly, identical filament bifurcations were also found in purified keratin 8/18 filaments expressed in Escherichia coli which were reassembled in vitro. This excludes that an accessory protein contributes to the branch formation. Measurements of the filament cross sectional areas showed various ratios between the three bifurcation arms. This demonstrates that intermediate filament furcation is very different from actin furcation where an entire new filament is attached to an existing filament. Instead, the architecture of intermediate filament bifurcations is less predetermined and hence consistent with the general concept of IF formation.
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Affiliation(s)
- Soufi Nafeey
- Central Facility for Electron Microscopy, Ulm University, 89081 Ulm, Germany
| | - Ines Martin
- Institute of Experimental Physics, Ulm University, 89081 Ulm, Germany
| | - Tatiana Felder
- Institute of General Physiology, Ulm University, 89081 Ulm, Germany
| | - Paul Walther
- Central Facility for Electron Microscopy, Ulm University, 89081 Ulm, Germany.
| | - Edward Felder
- Institute of General Physiology, Ulm University, 89081 Ulm, Germany
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Moch M, Windoffer R, Schwarz N, Pohl R, Omenzetter A, Schnakenberg U, Herb F, Chaisaowong K, Merhof D, Ramms L, Fabris G, Hoffmann B, Merkel R, Leube RE. Effects of Plectin Depletion on Keratin Network Dynamics and Organization. PLoS One 2016; 11:e0149106. [PMID: 27007410 PMCID: PMC4805305 DOI: 10.1371/journal.pone.0149106] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 01/27/2016] [Indexed: 12/19/2022] Open
Abstract
The keratin intermediate filament cytoskeleton protects epithelial cells against various types of stress and is involved in fundamental cellular processes such as signaling, differentiation and organelle trafficking. These functions rely on the cell type-specific arrangement and plasticity of the keratin system. It has been suggested that these properties are regulated by a complex cycle of assembly and disassembly. The exact mechanisms responsible for the underlying molecular processes, however, have not been clarified. Accumulating evidence implicates the cytolinker plectin in various aspects of the keratin cycle, i.e., by acting as a stabilizing anchor at hemidesmosomal adhesion sites and the nucleus, by affecting keratin bundling and branching and by linkage of keratins to actin filament and microtubule dynamics. In the present study we tested these hypotheses. To this end, plectin was downregulated by shRNA in vulvar carcinoma-derived A431 cells. As expected, integrin β4- and BPAG-1-positive hemidesmosomal structures were strongly reduced and cytosolic actin stress fibers were increased. In addition, integrins α3 and β1 were reduced. The experiments furthermore showed that loss of plectin led to a reduction in keratin filament branch length but did not alter overall mechanical properties as assessed by indentation analyses using atomic force microscopy and by displacement analyses of cytoplasmic superparamagnetic beads using magnetic tweezers. An increase in keratin movement was observed in plectin-depleted cells as was the case in control cells lacking hemidesmosome-like structures. Yet, keratin turnover was not significantly affected. We conclude that plectin alone is not needed for keratin assembly and disassembly and that other mechanisms exist to guarantee proper keratin cycling under steady state conditions in cultured single cells.
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Affiliation(s)
- Marcin Moch
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, Aachen, Germany
| | - Reinhard Windoffer
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, Aachen, Germany
| | - Nicole Schwarz
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, Aachen, Germany
| | - Raphaela Pohl
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, Aachen, Germany
| | - Andreas Omenzetter
- Institute of Materials in Electrical Engineering 1, RWTH Aachen University, Aachen, Germany
| | - Uwe Schnakenberg
- Institute of Materials in Electrical Engineering 1, RWTH Aachen University, Aachen, Germany
| | - Fabian Herb
- Institute of Imaging & Computer Vision, RWTH Aachen University, Aachen, Germany
| | | | - Dorit Merhof
- Institute of Imaging & Computer Vision, RWTH Aachen University, Aachen, Germany
| | - Lena Ramms
- Institute of Complex Systems, Forschungszentrum Jülich, Jülich, Germany
| | - Gloria Fabris
- Institute of Complex Systems, Forschungszentrum Jülich, Jülich, Germany
| | - Bernd Hoffmann
- Institute of Complex Systems, Forschungszentrum Jülich, Jülich, Germany
| | - Rudolf Merkel
- Institute of Complex Systems, Forschungszentrum Jülich, Jülich, Germany
| | - Rudolf E. Leube
- Institute of Molecular and Cellular Anatomy, RWTH Aachen University, Aachen, Germany
- * E-mail:
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5
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Woodward JD, Wepf RA. Macromolecular 3D SEM reconstruction strategies: signal to noise ratio and resolution. Ultramicroscopy 2014; 144:43-9. [PMID: 24830764 DOI: 10.1016/j.ultramic.2014.04.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Revised: 04/16/2014] [Accepted: 04/21/2014] [Indexed: 10/25/2022]
Abstract
Three-dimensional scanning electron microscopy generates quantitative volumetric structural data from SEM images of macromolecules. This technique provides a quick and easy way to define the quaternary structure and handedness of protein complexes. Here, we apply a variety of preparation and imaging methods to filamentous actin in order to explore the relationship between resolution, signal-to-noise ratio, structural preservation and dataset size. This information can be used to define successful imaging strategies for different applications.
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Affiliation(s)
- J D Woodward
- Department of Molecular and Cell Biology, University of Cape Town, South Africa; Electron Microscope Unit, University of Cape Town, South Africa.
| | - R A Wepf
- Electron Microscopy (EMEZ), ETH, Zürich, Switzerland
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You YW, Chang HY, Liao HY, Kao WL, Yen GJ, Chang CJ, Tsai MH, Shyue JJ. Electron tomography of HEK293T cells using scanning electron microscope-based scanning transmission electron microscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2012; 18:1037-1042. [PMID: 23026379 DOI: 10.1017/s1431927612001158] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Based on a scanning electron microscope operated at 30 kV with a homemade specimen holder and a multiangle solid-state detector behind the sample, low-kV scanning transmission electron microscopy (STEM) is presented with subsequent electron tomography for three-dimensional (3D) volume structure. Because of the low acceleration voltage, the stronger electron-atom scattering leads to a stronger contrast in the resulting image than standard TEM, especially for light elements. Furthermore, the low-kV STEM yields less radiation damage to the specimen, hence the structure can be preserved. In this work, two-dimensional STEM images of a 1-μm-thick cell section with projection angles between ±50° were collected, and the 3D volume structure was reconstructed using the simultaneous iterative reconstructive technique algorithm with the TomoJ plugin for ImageJ, which are both public domain software. Furthermore, the cross-sectional structure was obtained with the Volume Viewer plugin in ImageJ. Although the tilting angle is constrained and limits the resulting structural resolution, slicing the reconstructed volume generated the depth profile of the thick specimen with sufficient resolution to examine cellular uptake of Au nanoparticles, and the final position of these nanoparticles inside the cell was imaged.
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Affiliation(s)
- Yun-Wen You
- Research Center for Applied Sciences, Academia Sinica, Taipei 115, Taiwan
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7
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Leitner A, Paust T, Marti O, Walther P, Herrmann H, Beil M. Properties of intermediate filament networks assembled from keratin 8 and 18 in the presence of Mg²+. Biophys J 2012; 103:195-201. [PMID: 22853896 PMCID: PMC3403007 DOI: 10.1016/j.bpj.2012.06.014] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 06/04/2012] [Accepted: 06/06/2012] [Indexed: 01/10/2023] Open
Abstract
The mechanical properties of epithelial cells are modulated by structural changes in keratin intermediate filament networks. To investigate the relationship between network architecture and viscoelasticity, we assembled keratin filaments from recombinant keratin proteins 8 (K8) and 18 (K18) in the presence of divalent ions (Mg(2+)). We probed the viscoelastic modulus of the network by tracking the movement of microspheres embedded in the network during assembly, and studied the network architecture using scanning electron microscopy. Addition of Mg(2+) at physiological concentrations (<1 mM) resulted in networks whose structure was similar to that of keratin networks in epithelial cells. Moreover, the elastic moduli of networks assembled in vitro were found to be within the same magnitude as those measured in keratin networks of detergent-extracted epithelial cells. These findings suggest that Mg(2+)-induced filament cross-linking represents a valid model for studying the cytoskeletal mechanics of keratin networks.
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Affiliation(s)
- Anke Leitner
- Institut für Experimentelle Physik, University of Ulm, Ulm, Germany
| | - Tobias Paust
- Institut für Experimentelle Physik, University of Ulm, Ulm, Germany
| | - Othmar Marti
- Institut für Experimentelle Physik, University of Ulm, Ulm, Germany
| | - Paul Walther
- Electron Microscopy Facility, University of Ulm, Ulm, Germany
| | - Harald Herrmann
- Division of Molecular Genetics, German Cancer Research Center, Heidelberg, Germany
| | - Michael Beil
- Department of Medicine I, University of Ulm, Ulm, Germany
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9
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Lück S, Fichtl A, Sailer M, Joos H, Brenner RE, Walther P, Schmidt V. Statistical analysis of the intermediate filament network in cells of mesenchymal lineage by greyvalue-oriented image segmentation. Comput Stat 2011. [DOI: 10.1007/s00180-011-0265-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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10
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Höhn K, Sailer M, Wang L, Lorenz M, Schneider M, Walther P. Preparation of cryofixed cells for improved 3D ultrastructure with scanning transmission electron tomography. Histochem Cell Biol 2010; 135:1-9. [DOI: 10.1007/s00418-010-0765-z] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/09/2010] [Indexed: 11/29/2022]
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