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Jurriens D, van Batenburg V, Katrukha EA, Kapitein LC. Mapping the neuronal cytoskeleton using expansion microscopy. Methods Cell Biol 2020; 161:105-124. [PMID: 33478685 DOI: 10.1016/bs.mcb.2020.04.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Expansion microscopy (ExM) is a recently introduced technique that enables high-resolution imaging with conventional microscopes by using physical expansion of samples. While this technique does not require a complicated microscope setup (like in STED or STORM microscopy), sample preparation and handling require additional attention. Here we describe a workflow for imaging of the neuronal microtubule network with minimal artifacts and sample perturbations. We demonstrate that the use of custom-printed mounting chambers simplifies sample handling and facilitates stable imaging of the sample. In addition, refractive index matching between the sample and the objective greatly improves signal retention deeper in thick samples. To accurately determine the precise expansion factor and determine sample distortion, we describe how samples can be compared using STED and ExM. Together, these procedures enabled us to better resolve different microtubule subsets in neuronal soma and dendrites.
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Affiliation(s)
- Daphne Jurriens
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Vincent van Batenburg
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Eugene A Katrukha
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands
| | - Lukas C Kapitein
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, Utrecht, The Netherlands.
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2
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Koseki K, Taniguchi D, Yamashiro S, Mizuno H, Vavylonis D, Watanabe N. Lamellipodium tip actin barbed ends serve as a force sensor. Genes Cells 2019; 24:705-718. [PMID: 31514256 DOI: 10.1111/gtc.12720] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Revised: 09/04/2019] [Accepted: 09/04/2019] [Indexed: 01/31/2023]
Abstract
Cells change direction of migration by sensing rigidity of environment and traction force, yet its underlying mechanism is unclear. Here, we show that tip actin barbed ends serve as an active "force sensor" at the leading edge. We established a method to visualize intracellular single-molecule fluorescent actin through an elastic culture substrate. We found that immediately after cell edge stretch, actin assembly increased specifically at the lamellipodium tip. The rate of actin assembly increased with increasing stretch speed. Furthermore, tip actin polymerization remained elevated at the subsequent hold step, which was accompanied by a decrease in the load on the tip barbed ends. Stretch-induced tip actin polymerization was still observed without either the WAVE complex or Ena/VASP proteins. The observed relationships between forces and tip actin polymerization are consistent with a force-velocity relationship as predicted by the Brownian ratchet mechanism. Stretch caused extra membrane protrusion with respect to the stretched substrate and increased local tip polymerization by >5% of total cellular actin in 30 s. Our data reveal that augmentation of lamellipodium tip actin assembly is directly coupled to the load decrease, which may serve as a force sensor for directed cell protrusion.
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Affiliation(s)
- Kazuma Koseki
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Daisuke Taniguchi
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Sawako Yamashiro
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto, Japan.,Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Kyoto, Japan
| | - Hiroaki Mizuno
- Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Kyoto, Japan
| | | | - Naoki Watanabe
- Department of Pharmacology, Kyoto University Graduate School of Medicine, Kyoto, Japan.,Laboratory of Single-Molecule Cell Biology, Kyoto University Graduate School of Biostudies, Kyoto, Japan
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3
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Alarcon-Martinez L, Yilmaz-Ozcan S, Yemisci M, Schallek J, Kılıç K, Can A, Di Polo A, Dalkara T. Capillary pericytes express α-smooth muscle actin, which requires prevention of filamentous-actin depolymerization for detection. eLife 2018; 7:e34861. [PMID: 29561727 PMCID: PMC5862523 DOI: 10.7554/elife.34861] [Citation(s) in RCA: 169] [Impact Index Per Article: 28.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Accepted: 02/12/2018] [Indexed: 01/12/2023] Open
Abstract
Recent evidence suggests that capillary pericytes are contractile and play a crucial role in the regulation of microcirculation. However, failure to detect components of the contractile apparatus in capillary pericytes, most notably α-smooth muscle actin (α-SMA), has questioned these findings. Using strategies that allow rapid filamentous-actin (F-actin) fixation (i.e. snap freeze fixation with methanol at -20°C) or prevent F-actin depolymerization (i.e. with F-actin stabilizing agents), we demonstrate that pericytes on mouse retinal capillaries, including those in intermediate and deeper plexus, express α-SMA. Junctional pericytes were more frequently α-SMA-positive relative to pericytes on linear capillary segments. Intravitreal administration of short interfering RNA (α-SMA-siRNA) suppressed α-SMA expression preferentially in high order branch capillary pericytes, confirming the existence of a smaller pool of α-SMA in distal capillary pericytes that is quickly lost by depolymerization. We conclude that capillary pericytes do express α-SMA, which rapidly depolymerizes during tissue fixation thus evading detection by immunolabeling.
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Affiliation(s)
- Luis Alarcon-Martinez
- Institute of Neurological Sciences and PsychiatryHacettepe UniversityAnkaraTurkey
- Centre de Recherche du Centre Hospitalier de l’Université de MontréalUniversité de Montréal, MontréalQuébecCanada
- Department of NeuroscienceUniversité de Montréal, MontréalQuébecCanada
| | - Sinem Yilmaz-Ozcan
- Institute of Neurological Sciences and PsychiatryHacettepe UniversityAnkaraTurkey
| | - Muge Yemisci
- Institute of Neurological Sciences and PsychiatryHacettepe UniversityAnkaraTurkey
- Department of NeurologyFaculty of Medicine, Hacettepe UniversityAnkaraTurkey
| | - Jesse Schallek
- Center for Visual ScienceUniversity of RochesterNew YorkUnited States
- Flaum Eye InstituteUniversity of RochesterNew YorkUnited States
| | - Kıvılcım Kılıç
- Institute of Neurological Sciences and PsychiatryHacettepe UniversityAnkaraTurkey
| | - Alp Can
- Department of Histology and EmbryologySchool of Medicine, Ankara UniversityAnkaraTurkey
| | - Adriana Di Polo
- Centre de Recherche du Centre Hospitalier de l’Université de MontréalUniversité de Montréal, MontréalQuébecCanada
- Department of NeuroscienceUniversité de Montréal, MontréalQuébecCanada
| | - Turgay Dalkara
- Institute of Neurological Sciences and PsychiatryHacettepe UniversityAnkaraTurkey
- Department of NeurologyFaculty of Medicine, Hacettepe UniversityAnkaraTurkey
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4
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Cosette J, Moussy A, Paldi A, Stockholm D. Combination of imaging flow cytometry and time-lapse microscopy for the study of label-free morphology dynamics of hematopoietic cells. Cytometry A 2017; 91:254-260. [DOI: 10.1002/cyto.a.23064] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 12/06/2016] [Accepted: 01/15/2017] [Indexed: 12/27/2022]
Affiliation(s)
| | - Alice Moussy
- Ecole Pratique des Hautes Etudes, PSL Research University, UMRS_951, Genethon; Evry 91002 France
| | - Andras Paldi
- Ecole Pratique des Hautes Etudes, PSL Research University, UMRS_951, Genethon; Evry 91002 France
| | - Daniel Stockholm
- Ecole Pratique des Hautes Etudes, PSL Research University, UMRS_951, Genethon; Evry 91002 France
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5
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Moradi M, Sivadasan R, Saal L, Lüningschrör P, Dombert B, Rathod RJ, Dieterich DC, Blum R, Sendtner M. Differential roles of α-, β-, and γ-actin in axon growth and collateral branch formation in motoneurons. J Cell Biol 2017; 216:793-814. [PMID: 28246119 PMCID: PMC5346967 DOI: 10.1083/jcb.201604117] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Revised: 11/11/2016] [Accepted: 01/17/2017] [Indexed: 12/17/2022] Open
Abstract
α-, β-, and γ-actin differentially regulate cytoskeletal dynamics and stability in axons of motoneurons. Locally translated α-actin contributes to stable actin filaments in axonal branches, whereas β- and γ-actin give rise to highly dynamic filaments that modulate growth cone dynamics. Axonal branching and terminal arborization are fundamental events during the establishment of synaptic connectivity. They are triggered by assembly of actin filaments along axon shafts giving rise to filopodia. The specific contribution of the three actin isoforms, Actα, Actβ, and Actγ, to filopodia stability and dynamics during this process is not well understood. Here, we report that Actα, Actβ, and Actγ isoforms are expressed in primary mouse motoneurons and their transcripts are translocated into axons. shRNA-mediated depletion of Actα reduces axonal filopodia dynamics and disturbs collateral branch formation. Knockdown of Actβ reduces dynamic movements of growth cone filopodia and impairs presynaptic differentiation. Ablation of Actβ or Actγ leads to compensatory up-regulation of the two other isoforms, which allows maintenance of total actin levels and preserves F-actin polymerization. Collectively, our data provide evidence for specific roles of different actin isoforms in spatial regulation of actin dynamics and stability in axons of developing motoneurons.
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Affiliation(s)
- Mehri Moradi
- Institute of Clinical Neurobiology, University Hospital Wuerzburg, University of Wuerzburg, 97078 Wuerzburg, Germany
| | - Rajeeve Sivadasan
- Institute of Clinical Neurobiology, University Hospital Wuerzburg, University of Wuerzburg, 97078 Wuerzburg, Germany
| | - Lena Saal
- Institute of Clinical Neurobiology, University Hospital Wuerzburg, University of Wuerzburg, 97078 Wuerzburg, Germany
| | - Patrick Lüningschrör
- Institute of Clinical Neurobiology, University Hospital Wuerzburg, University of Wuerzburg, 97078 Wuerzburg, Germany
| | - Benjamin Dombert
- Institute of Clinical Neurobiology, University Hospital Wuerzburg, University of Wuerzburg, 97078 Wuerzburg, Germany
| | - Reena Jagdish Rathod
- Institute of Clinical Neurobiology, University Hospital Wuerzburg, University of Wuerzburg, 97078 Wuerzburg, Germany
| | - Daniela C Dieterich
- Institute for Pharmacology and Toxicology, Medical Faculty, University of Magdeburg, 39120 Magdeburg, Germany.,Center for Behavioral Brain Sciences, Medical Faculty, University of Magdeburg, 39120 Magdeburg, Germany
| | - Robert Blum
- Institute of Clinical Neurobiology, University Hospital Wuerzburg, University of Wuerzburg, 97078 Wuerzburg, Germany
| | - Michael Sendtner
- Institute of Clinical Neurobiology, University Hospital Wuerzburg, University of Wuerzburg, 97078 Wuerzburg, Germany
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6
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Hauser M, Wojcik M, Kim D, Mahmoudi M, Li W, Xu K. Correlative Super-Resolution Microscopy: New Dimensions and New Opportunities. Chem Rev 2017; 117:7428-7456. [PMID: 28045508 DOI: 10.1021/acs.chemrev.6b00604] [Citation(s) in RCA: 101] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Correlative microscopy, the integration of two or more microscopy techniques performed on the same sample, produces results that emphasize the strengths of each technique while offsetting their individual weaknesses. Light microscopy has historically been a central method in correlative microscopy due to its widespread availability, compatibility with hydrated and live biological samples, and excellent molecular specificity through fluorescence labeling. However, conventional light microscopy can only achieve a resolution of ∼300 nm, undercutting its advantages in correlations with higher-resolution methods. The rise of super-resolution microscopy (SRM) over the past decade has drastically improved the resolution of light microscopy to ∼10 nm, thus creating exciting new opportunities and challenges for correlative microscopy. Here we review how these challenges are addressed to effectively correlate SRM with other microscopy techniques, including light microscopy, electron microscopy, cryomicroscopy, atomic force microscopy, and various forms of spectroscopy. Though we emphasize biological studies, we also discuss the application of correlative SRM to materials characterization and single-molecule reactions. Finally, we point out current limitations and discuss possible future improvements and advances. We thus demonstrate how a correlative approach adds new dimensions of information and provides new opportunities in the fast-growing field of SRM.
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Affiliation(s)
- Meghan Hauser
- Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Michal Wojcik
- Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Doory Kim
- Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Morteza Mahmoudi
- Center for Nanomedicine and Department of Anesthesiology, Brigham and Women's Hospital, Harvard Medical School , Boston, Massachusetts 02115, United States
| | - Wan Li
- Department of Chemistry, University of California , Berkeley, California 94720, United States
| | - Ke Xu
- Department of Chemistry, University of California , Berkeley, California 94720, United States.,Division of Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
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7
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Studying neuronal microtubule organization and microtubule-associated proteins using single molecule localization microscopy. Methods Cell Biol 2015; 131:127-49. [PMID: 26794511 DOI: 10.1016/bs.mcb.2015.06.017] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The formation and maintenance of highly polarized neurons critically depends on the proper organization of the microtubule (MT) cytoskeleton. In axons, MTs are uniformly oriented with their plus-end pointing outward whereas in mature dendrites MTs have mixed orientations. MT organization and dynamics can be regulated by MT-associated proteins (MAPs). Plus-end tracking proteins are specialized MAPs that decorate plus-ends of growing MTs and regulate neuronal polarity, neurite extension, and dendritic spine morphology. Conventional fluorescence microscopy enables observation of specific cellular components through molecule-specific labeling but provides limited resolution (∼250 nm). Therefore, electron microscopy has until now provided most of our knowledge about the precise MT organization in neurons. In the past decade, super-resolution fluorescence microscopy techniques have emerged that circumvent the diffraction limit of light and enable high-resolution reconstruction of the MT network combined with selective protein labeling. However, preserving MT ultrastructure, MAP binding, high labeling density, and antibody specificity after fixation protocols is still quite challenging. In this chapter, we provide an optimized protocol for two-color direct stochastic optical reconstruction microscopy imaging of neuronal MTs together with their growing plus-ends to probe MT architecture and polarity.
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8
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Ketema M, Secades P, Kreft M, Nahidiazar L, Janssen H, Jalink K, de Pereda JM, Sonnenberg A. The rod domain is not essential for the function of plectin in maintaining tissue integrity. Mol Biol Cell 2015; 26:2402-17. [PMID: 25971800 PMCID: PMC4571296 DOI: 10.1091/mbc.e15-01-0043] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 05/06/2015] [Indexed: 11/22/2022] Open
Abstract
Plectin is a cytoskeletal linker protein that consists of a central rod domain connecting two globular domains. Rodless plectin is able to functionally compensate for the loss of full-length plectin in mice and, like full-length plectin, is able to form dimers. Epidermolysis bullosa simplex associated with late-onset muscular dystrophy (EBS-MD) is an autosomal recessive disorder resulting from mutations in the plectin gene. The majority of these mutations occur within the large exon 31 encoding the central rod domain and leave the production of a low-level rodless plectin splice variant unaffected. To investigate the function of the rod domain, we generated rodless plectin mice through conditional deletion of exon 31. Rodless plectin mice develop normally without signs of skin blistering or muscular dystrophy. Plectin localization and hemidesmosome organization are unaffected in rodless plectin mice. However, superresolution microscopy revealed a closer juxtaposition of the C-terminus of plectin to the integrin β4 subunit in rodless plectin keratinocytes. Wound healing occurred slightly faster in rodless plectin mice than in wild-type mice, and keratinocytes migration was increased in the absence of the rod domain. The faster migration of rodless plectin keratinocytes is not due to altered biochemical properties because, like full-length plectin, rodless plectin is a dimeric protein. Our data demonstrate that rodless plectin can functionally compensate for the loss of full-length plectin in mice. Thus the low expression level of plectin rather than the absence of the rod domain dictates the development of EBS-MD.
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Affiliation(s)
- Mirjam Ketema
- Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands
| | - Pablo Secades
- Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands
| | - Maaike Kreft
- Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands
| | - Leila Nahidiazar
- Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands
| | - Hans Janssen
- Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands
| | - Kees Jalink
- Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands
| | - Jose M de Pereda
- Instituto de Biología Molecular y Celular del Cancer, University of Salamanca-CSIC, E-37007 Salamanca, Spain
| | - Arnoud Sonnenberg
- Division of Cell Biology, Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands
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9
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Bushong EA, Johnson DD, Kim KY, Terada M, Hatori M, Peltier ST, Panda S, Merkle A, Ellisman MH. X-ray microscopy as an approach to increasing accuracy and efficiency of serial block-face imaging for correlated light and electron microscopy of biological specimens. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2015; 21:231-8. [PMID: 25392009 PMCID: PMC4415271 DOI: 10.1017/s1431927614013579] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The recently developed three-dimensional electron microscopic (EM) method of serial block-face scanning electron microscopy (SBEM) has rapidly established itself as a powerful imaging approach. Volume EM imaging with this scanning electron microscopy (SEM) method requires intense staining of biological specimens with heavy metals to allow sufficient back-scatter electron signal and also to render specimens sufficiently conductive to control charging artifacts. These more extreme heavy metal staining protocols render specimens light opaque and make it much more difficult to track and identify regions of interest (ROIs) for the SBEM imaging process than for a typical thin section transmission electron microscopy correlative light and electron microscopy study. We present a strategy employing X-ray microscopy (XRM) both for tracking ROIs and for increasing the efficiency of the workflow used for typical projects undertaken with SBEM. XRM was found to reveal an impressive level of detail in tissue heavily stained for SBEM imaging, allowing for the identification of tissue landmarks that can be subsequently used to guide data collection in the SEM. Furthermore, specific labeling of individual cells using diaminobenzidine is detectable in XRM volumes. We demonstrate that tungsten carbide particles or upconverting nanophosphor particles can be used as fiducial markers to further increase the precision and efficiency of SBEM imaging.
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Affiliation(s)
- Eric A Bushong
- 1Center for Research in Biological Systems,National Center for Microscopy and Imaging Research,University of California at San Diego,9500 Gilman Drive,La Jolla,CA 92093,USA
| | - Donald D Johnson
- 1Center for Research in Biological Systems,National Center for Microscopy and Imaging Research,University of California at San Diego,9500 Gilman Drive,La Jolla,CA 92093,USA
| | - Keun-Young Kim
- 1Center for Research in Biological Systems,National Center for Microscopy and Imaging Research,University of California at San Diego,9500 Gilman Drive,La Jolla,CA 92093,USA
| | - Masako Terada
- 2Carl Zeiss X-ray Microscopy Inc.,4385 Hopyard Rd #100,Pleasanton,CA 94588,USA
| | - Megumi Hatori
- 3Salk Institute for Biological Sciences,10010 N Torrey Pines Rd,La Jolla,CA 92037,USA
| | - Steven T Peltier
- 1Center for Research in Biological Systems,National Center for Microscopy and Imaging Research,University of California at San Diego,9500 Gilman Drive,La Jolla,CA 92093,USA
| | - Satchidananda Panda
- 3Salk Institute for Biological Sciences,10010 N Torrey Pines Rd,La Jolla,CA 92037,USA
| | - Arno Merkle
- 2Carl Zeiss X-ray Microscopy Inc.,4385 Hopyard Rd #100,Pleasanton,CA 94588,USA
| | - Mark H Ellisman
- 1Center for Research in Biological Systems,National Center for Microscopy and Imaging Research,University of California at San Diego,9500 Gilman Drive,La Jolla,CA 92093,USA
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10
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Abstract
Actin polymerization is harnessed by cells to generate lamellipodia for movement and by a subclass of pathogens to facilitate invasion of their infected hosts. Using electron tomography (ET), we have shown that lamellipodia are formed via the generation of subsets of actin filaments joined by branch junctions. Image averaging produced a 2.9 nm resolution model of branch junctions in situ and revealed a close fit to the electron density map of the actin-related protein 2/3 (Arp2/3)–actin complex in vitro. Correlated live-cell imaging and ET was also used to determine how actin networks are created and remodelled during the initiation and inhibition of protrusion in lamellipodia. Listeria, Rickettsia and viruses, such as vaccinia virus and baculovirus, exploit the actin machinery of host cells to generate propulsive actin comet tails to disseminate their infection. By applying ET, we have shown that baculovirus generates at its rear a fishbone-like array of subsets of branched actin filaments, with an average of only four filaments engaged in pushing at any one time. In both of these studies, the application of ET of negatively stained cytoskeletons for higher filament resolution and cryo-ET for preserving overall 3D morphology was crucial for obtaining a complete structure–function analysis of actin-driven propulsion.
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11
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Timmermans FJ, Otto C. Contributed review: Review of integrated correlative light and electron microscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:011501. [PMID: 25638065 DOI: 10.1063/1.4905434] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
New developments in the field of microscopy enable to acquire increasing amounts of information from large sample areas and at an increased resolution. Depending on the nature of the technique, the information may reveal morphological, structural, chemical, and still other sample characteristics. In research fields, such as cell biology and materials science, there is an increasing demand to correlate these individual levels of information and in this way to obtain a better understanding of sample preparation and specific sample properties. To address this need, integrated systems were developed that combine nanometer resolution electron microscopes with optical microscopes, which produce chemically or label specific information through spectroscopy. The complementary information from electron microscopy and light microscopy presents an opportunity to investigate a broad range of sample properties in a correlated fashion. An important part of correlating the differences in information lies in bridging the different resolution and image contrast features. The trend to analyse samples using multiple correlated microscopes has resulted in a new research field. Current research is focused, for instance, on (a) the investigation of samples with nanometer scale distribution of inorganic and organic materials, (b) live cell analysis combined with electron microscopy, and (c) in situ spectroscopic and electron microscopy analysis of catalytic materials, but more areas will benefit from integrated correlative microscopy.
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Affiliation(s)
- F J Timmermans
- Medical Cell Biophysics Group, MIRA Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - C Otto
- Medical Cell Biophysics Group, MIRA Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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12
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MTSS1 is a metastasis driver in a subset of human melanomas. Nat Commun 2014; 5:3465. [PMID: 24632752 DOI: 10.1038/ncomms4465] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Accepted: 02/18/2014] [Indexed: 12/21/2022] Open
Abstract
In cancers with a highly altered genome, distinct genetic alterations drive subsets rather than the majority of individual tumours. Here we use a sequential search across human tumour samples for transcript outlier data points with associated gene copy number variations that correlate with patient's survival to identify genes with pro-invasive functionality. Employing loss and gain of function approaches in vitro and in vivo, we show that one such gene, MTSS1, promotes the ability of melanocytic cells to metastasize and engages actin dynamics via Rho-GTPases and cofilin in this process. Indeed, high MTSS1 expression defines a subgroup of primary melanomas with unfavourable prognosis. These data underscore the biological, clinical and potential therapeutic implications of molecular subsets within genetically complex cancers.
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13
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Correlative light and electron microscopy: from live cell dynamic to 3D ultrastructure. Methods Mol Biol 2014; 1117:485-501. [PMID: 24357376 DOI: 10.1007/978-1-62703-776-1_21] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Correlative light and electron microscopy (CLEM) aims at combining data acquired from the same sample through both imaging modalities. Many combinations can be found in the literature where almost any kind of light microscopy (LM) has been associated to different processing in electron microscopy (EM) and applied to a wide variety of specimen, from cultured cells to multicellular organisms. In this chapter, we focus on a technique that intends to combine LM acquisition on living cells with transmission EM (TEM) analysis. A specific attention is given to the description of a method to bring precise coordinates to the object of interest, to allow a straightforward correlation between LM and EM. Moreover, we describe how, by using high-pressure freezing as a fixation technique, dynamic events observed at the LM are captured and studied at the ultrastructural level.
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14
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Koestler SA, Steffen A, Nemethova M, Winterhoff M, Luo N, Holleboom JM, Krupp J, Jacob S, Vinzenz M, Schur F, Schlüter K, Gunning PW, Winkler C, Schmeiser C, Faix J, Stradal TEB, Small JV, Rottner K. Arp2/3 complex is essential for actin network treadmilling as well as for targeting of capping protein and cofilin. Mol Biol Cell 2013; 24:2861-75. [PMID: 23885122 PMCID: PMC3771948 DOI: 10.1091/mbc.e12-12-0857] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Acute suppression of Arp2/3 complex activity in lamellipodia demonstrates its essential role in actin network treadmilling and filament organization and geometry. Arp2/3 complex activity also defines the recruitment of crucial independent factors, including capping protein and cofilin, and is essential for lamellipodia-based keratocyte migration. Lamellipodia are sheet-like protrusions formed during migration or phagocytosis and comprise a network of actin filaments. Filament formation in this network is initiated by nucleation/branching through the actin-related protein 2/3 (Arp2/3) complex downstream of its activator, suppressor of cAMP receptor/WASP-family verprolin homologous (Scar/WAVE), but the relative relevance of Arp2/3-mediated branching versus actin filament elongation is unknown. Here we use instantaneous interference with Arp2/3 complex function in live fibroblasts with established lamellipodia. This allows direct examination of both the fate of elongating filaments upon instantaneous suppression of Arp2/3 complex activity and the consequences of this treatment on the dynamics of other lamellipodial regulators. We show that Arp2/3 complex is an essential organizer of treadmilling actin filament arrays but has little effect on the net rate of actin filament turnover at the cell periphery. In addition, Arp2/3 complex serves as key upstream factor for the recruitment of modulators of lamellipodia formation such as capping protein or cofilin. Arp2/3 complex is thus decisive for filament organization and geometry within the network not only by generating branches and novel filament ends, but also by directing capping or severing activities to the lamellipodium. Arp2/3 complex is also crucial to lamellipodia-based migration of keratocytes.
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Affiliation(s)
- Stefan A Koestler
- Institute of Genetics, University of Bonn, D-53115 Bonn, Germany Institute of Molecular Biotechnology, Austrian Academy of Sciences, A-1030 Vienna, Austria Johann Radon Institute for Computational and Applied Mathematics, Austrian Academy of Sciences, A-1030 Vienna, Austria Institute for Biophysical Chemistry, Hannover Medical School, D-30625 Hannover, Germany Helmholtz Centre for Infection Research, D-38124 Braunschweig, Germany Institute for Molecular Cell Biology, University of Münster, D-48149 Münster, Germany Oncology Research Unit, School of Medical Sciences, University of New South Wales, Sydney 2052, Australia Faculty of Mathematics, University of Vienna, A-1090 Vienna, Austria
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15
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Flynn KC, Hellal F, Neukirchen D, Jacob S, Tahirovic S, Dupraz S, Stern S, Garvalov BK, Gurniak C, Shaw AE, Meyn L, Wedlich-Söldner R, Bamburg JR, Small JV, Witke W, Bradke F. ADF/cofilin-mediated actin retrograde flow directs neurite formation in the developing brain. Neuron 2013; 76:1091-107. [PMID: 23259946 DOI: 10.1016/j.neuron.2012.09.038] [Citation(s) in RCA: 143] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/25/2012] [Indexed: 01/17/2023]
Abstract
Neurites are the characteristic structural element of neurons that will initiate brain connectivity and elaborate information. Early in development, neurons are spherical cells but this symmetry is broken through the initial formation of neurites. This fundamental step is thought to rely on actin and microtubule dynamics. However, it is unclear which aspects of the complex actin behavior control neuritogenesis and which molecular mechanisms are involved. Here, we demonstrate that augmented actin retrograde flow and protrusion dynamics facilitate neurite formation. Our data indicate that a single family of actin regulatory proteins, ADF/Cofilin, provides the required control of actin retrograde flow and dynamics to form neurites. In particular, the F-actin severing activity of ADF/Cofilin organizes space for the protrusion and bundling of microtubules, the backbone of neurites. Our data reveal how ADF/Cofilin organizes the cytoskeleton to drive actin retrograde flow and thus break the spherical shape of neurons.
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Affiliation(s)
- Kevin C Flynn
- Max Planck Institute of Neurobiology, Axonal Growth and Regeneration Group, Am Klopferspitz 18, 82152 Martinsried, Germany
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16
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Xu K, Zhong G, Zhuang X. Actin, spectrin, and associated proteins form a periodic cytoskeletal structure in axons. Science 2012; 339:452-6. [PMID: 23239625 DOI: 10.1126/science.1232251] [Citation(s) in RCA: 824] [Impact Index Per Article: 68.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Actin and spectrin play important roles in neurons, but their organization in axons and dendrites remains unclear. We used stochastic optical reconstruction microscopy to study the organization of actin, spectrin, and associated proteins in neurons. Actin formed ringlike structures that wrapped around the circumference of axons and were evenly spaced along axonal shafts with a periodicity of ~180 to 190 nanometers. This periodic structure was not observed in dendrites, which instead contained long actin filaments running along dendritic shafts. Adducin, an actin-capping protein, colocalized with the actin rings. Spectrin exhibited periodic structures alternating with those of actin and adducin, and the distance between adjacent actin-adducin rings was comparable to the length of a spectrin tetramer. Sodium channels in axons were distributed in a periodic pattern coordinated with the underlying actin-spectrin-based cytoskeleton.
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Affiliation(s)
- Ke Xu
- Howard Hughes Medical Institute, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA
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17
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Göransson U, Burman R, Gunasekera S, Strömstedt AA, Rosengren KJ. Circular proteins from plants and fungi. J Biol Chem 2012; 287:27001-6. [PMID: 22700984 DOI: 10.1074/jbc.r111.300129] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Circular proteins, defined as head-to-tail cyclized polypeptides originating from ribosomal synthesis, represent a novel class of natural products attracting increasing interest. From a scientific point of view, these compounds raise questions of where and why they occur in nature and how they are formed. From a rational point of view, these proteins and their structural concept may be exploited for crop protection and novel pharmaceuticals. Here, we review the current knowledge of three protein families: cyclotides and circular sunflower trypsin inhibitors from the kingdom of plants and the Amanita toxins from fungi. A particular emphasis is placed on their biological origin, structure, and activity. In addition, the opportunity for discovery of novel circular proteins and recent insights into their mechanism of action are discussed.
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Affiliation(s)
- Ulf Göransson
- Division of Pharmacognosy, Department of Medicinal Chemistry, Biomedical Centre, Uppsala University, SE-75123 Uppsala, Sweden.
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18
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Weichsel J, Urban E, Small JV, Schwarz US. Reconstructing the orientation distribution of actin filaments in the lamellipodium of migrating keratocytes from electron microscopy tomography data. Cytometry A 2012; 81:496-507. [DOI: 10.1002/cyto.a.22050] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 02/16/2012] [Accepted: 03/12/2012] [Indexed: 12/12/2022]
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19
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Breitsprecher D, Koestler SA, Chizhov I, Nemethova M, Mueller J, Goode BL, Small JV, Rottner K, Faix J. Cofilin cooperates with fascin to disassemble filopodial actin filaments. J Cell Sci 2012; 124:3305-18. [PMID: 21940796 DOI: 10.1242/jcs.086934] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Cells use a large repertoire of proteins to remodel the actin cytoskeleton. Depending on the proteins involved, F-actin is organized in specialized protrusions such as lamellipodia or filopodia, which serve diverse functions in cell migration and sensing. Although factors responsible for directed filament assembly in filopodia have been extensively characterized, the mechanisms of filament disassembly in these structures are mostly unknown. We investigated how the actin-depolymerizing factor cofilin-1 affects the dynamics of fascincrosslinked actin filaments in vitro and in live cells. By multicolor total internal reflection fluorescence microscopy and fluorimetric assays, we found that cofilin-mediated severing is enhanced in fascin-crosslinked bundles compared with isolated filaments, and that fascin and cofilin act synergistically in filament severing. Immunolabeling experiments demonstrated for the first time that besides its known localization in lamellipodia and membrane ruffles, endogenous cofilin can also accumulate in the tips and shafts of filopodia. Live-cell imaging of fluorescently tagged proteins revealed that cofilin is specifically targeted to filopodia upon stalling of protrusion and during their retraction. Subsequent electron tomography established filopodial actin filament and/or bundle fragmentation to precisely correlate with cofilin accumulation. These results identify a new mechanism of filopodium disassembly involving both fascin and cofilin.
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Affiliation(s)
- Dennis Breitsprecher
- Institute for Biophysical Chemistry, Hannover Medical School, Carl-Neuberg-Str. 1, D-30625 Hannover, Germany
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20
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Dual-objective STORM reveals three-dimensional filament organization in the actin cytoskeleton. Nat Methods 2012; 9:185-8. [PMID: 22231642 PMCID: PMC3304438 DOI: 10.1038/nmeth.1841] [Citation(s) in RCA: 331] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 12/04/2011] [Indexed: 12/19/2022]
Abstract
By combining astigmatism imaging with a dual-objective scheme, we improved the image resolution of stochastic optical reconstruction microscopy (STORM) and obtained <10 nm lateral resolution and <20 nm axial resolution when imaging biological specimens. Using this approach, we resolved individual actin filaments in cells and revealed three-dimensional ultrastructure of the actin cytoskeleton. We observed two vertically separated layers of actin networks with distinct structural organizations in sheet-like cell protrusions.
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21
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Brown E, Van Weering J, Sharp T, Mantell J, Verkade P. Capturing endocytic segregation events with HPF-CLEM. Methods Cell Biol 2012; 111:175-201. [PMID: 22857929 DOI: 10.1016/b978-0-12-416026-2.00010-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We have advocated the use of high-pressure freezing (HPF) in specific types of Correlative Light Electron Microscopy (CLEM) experiments because the intracellular components such as the cytoskeleton and membrane tubules can only be adequately preserved via cryofixation. To allow fast transfer from the light microscope into a cryofixation device, we have developed the Rapid Transfer System (RTS) for the EMPACT2 high-pressure freezer. In this chapter, we will describe how to prepare and perform a CLEM experiment using this device and will highlight the latest changes made to the original system to optimize the workflow.
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Affiliation(s)
- Edward Brown
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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22
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Sjollema KA, Schnell U, Kuipers J, Kalicharan R, Giepmans BNG. Correlated light microscopy and electron microscopy. Methods Cell Biol 2012; 111:157-73. [PMID: 22857928 DOI: 10.1016/b978-0-12-416026-2.00009-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Understanding where, when, and how biomolecules (inter)act is crucial to uncover fundamental mechanisms in cell biology. Recent developments in fluorescence light microscopy (FLM) allow protein imaging in living cells and at the near molecular level. However, fluorescence microscopy only reveals selected biomolecules or organelles but not the (ultra)structural context, as can be examined by electron microscopy (EM). LM and EM of the same cells, so-called correlative (or correlated) light and electron microscopy (CLEM), allow examining rare or dynamic events first by LM, and subsequently by EM. Here, we review progress in CLEM, with focus on matching the areas between different microscopic modalities. Moreover, we introduce a method that includes a virtual overlay and automated large-scale imaging, allowing to switch between most microscopes. Ongoing developments will revolutionize and standardize CLEM in the near future, which thus holds great promise to become a routine technique in cell biology.
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Affiliation(s)
- Klaas A Sjollema
- Department of Cell Biology, University Medical Center Groningen (UMCG), University of Groningen, A. Deusinglaan 1, Bldg 3215, room 749, 9713 AV Groningen, The Netherlands
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23
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Vinzenz M, Nemethova M, Schur F, Mueller J, Narita A, Urban E, Winkler C, Schmeiser C, Koestler SA, Rottner K, Resch GP, Maeda Y, Small JV. Actin branching in the initiation and maintenance of lamellipodia. J Cell Sci 2012; 125:2775-85. [DOI: 10.1242/jcs.107623] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Using correlated live cell imaging and electron tomography we found that actin branch junctions in protruding and treadmilling lamellipodia are not concentrated at the front as previously supposed, but link actin filament subsets in which there is a continuum of distances from a junction to the filament plus ends, up to at least 1 µm. When branch sites were observed closely spaced on the same filament their separation was commonly a multiple of the actin helical repeat of 36 nm. Image averaging of branch junctions in the tomograms yielded a model for the in vivo branch at 2.9 nm resolution, which compared closely to that derived for the in vitro actin - Arp2/3 complex. Lamellipodia initiation was monitored in an intracellular wound-healing model and involved branching from the sides of actin filaments oriented parallel to the plasmalemma. Many filament plus ends, presumably capped, terminated behind the lamellipodium tip and localized on the dorsal and ventral surfaces of the actin network. These findings reveal how branching events initiate and maintain a network of actin filaments of variable length and provide the first structural model of the branch junction in vivo. A possible role of filament capping in generating the lamellipodium leaflet is discussed and a mathematical model of protrusion is also presented.
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24
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Jahn KA, Barton DA, Kobayashi K, Ratinac KR, Overall RL, Braet F. Correlative microscopy: providing new understanding in the biomedical and plant sciences. Micron 2011; 43:565-82. [PMID: 22244153 DOI: 10.1016/j.micron.2011.12.004] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Revised: 12/14/2011] [Accepted: 12/14/2011] [Indexed: 12/16/2022]
Abstract
Correlative microscopy is the application of two or more distinct microscopy techniques to the same region of a sample, generating complementary morphological, structural and chemical information that exceeds what is possible with any single technique. As a variety of complementary microscopy approaches rather than a specific type of instrument, correlative microscopy has blossomed in recent years as researchers have recognised that it is particularly suited to address the intricate questions of the modern biological sciences. Specialised technical developments in sample preparation, imaging methods, visualisation and data analysis have also accelerated the uptake of correlative approaches. In light of these advances, this critical review takes the reader on a journey through recent developments in, and applications of, correlative microscopy, examining its impact in biomedical research and in the field of plant science. This twin emphasis gives a unique perspective into use of correlative microscopy in fields that often advance independently, and highlights the lessons that can be learned from both fields for the future of this important area of research.
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Affiliation(s)
- K A Jahn
- Australian Centre for Microscopy & Microanalysis and The School of Biological Sciences, The University of Sydney, Sydney, NSW 2006, Australia.
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25
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Oelkers JM, Vinzenz M, Nemethova M, Jacob S, Lai FPL, Block J, Szczodrak M, Kerkhoff E, Backert S, Schlüter K, Stradal TEB, Small JV, Koestler SA, Rottner K. Microtubules as platforms for assaying actin polymerization in vivo. PLoS One 2011; 6:e19931. [PMID: 21603613 PMCID: PMC3095617 DOI: 10.1371/journal.pone.0019931] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2010] [Accepted: 04/21/2011] [Indexed: 11/19/2022] Open
Abstract
The actin cytoskeleton is continuously remodeled through cycles of actin filament assembly and disassembly. Filaments are born through nucleation and shaped into supramolecular structures with various essential functions. These range from contractile and protrusive assemblies in muscle and non-muscle cells to actin filament comets propelling vesicles or pathogens through the cytosol. Although nucleation has been extensively studied using purified proteins in vitro, dissection of the process in cells is complicated by the abundance and molecular complexity of actin filament arrays. We here describe the ectopic nucleation of actin filaments on the surface of microtubules, free of endogenous actin and interfering membrane or lipid. All major mechanisms of actin filament nucleation were recapitulated, including filament assembly induced by Arp2/3 complex, formin and Spir. This novel approach allows systematic dissection of actin nucleation in the cytosol of live cells, its genetic re-engineering as well as screening for new modifiers of the process.
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Affiliation(s)
- J. Margit Oelkers
- Helmholtz Centre for Infection Research, Braunschweig, Germany
- Institute of Genetics, University of Bonn, Bonn, Germany
| | - Marlene Vinzenz
- Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria
| | - Maria Nemethova
- Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria
| | - Sonja Jacob
- Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria
| | - Frank P. L. Lai
- Helmholtz Centre for Infection Research, Braunschweig, Germany
- Department of Developmental and Regenerative Biology, Institute of Medical Biology, Immunos, Singapore, Singapore
| | - Jennifer Block
- Helmholtz Centre for Infection Research, Braunschweig, Germany
- Institute of Genetics, University of Bonn, Bonn, Germany
| | | | - Eugen Kerkhoff
- Molecular Cell Biology Laboratory, Department of Neurology, Bavarian Genome Research Network, University Hospital Regensburg, Regensburg, Germany
| | - Steffen Backert
- School of Biomolecular and Biomedical Sciences, University College Dublin, Dublin, Ireland
| | - Kai Schlüter
- Helmholtz Centre for Infection Research, Braunschweig, Germany
- Institute for Molecular Cell Biology, University of Münster, Münster, Germany
| | - Theresia E. B. Stradal
- Helmholtz Centre for Infection Research, Braunschweig, Germany
- Institute for Molecular Cell Biology, University of Münster, Münster, Germany
| | - J. Victor Small
- Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria
| | - Stefan A. Koestler
- Helmholtz Centre for Infection Research, Braunschweig, Germany
- Institute of Genetics, University of Bonn, Bonn, Germany
| | - Klemens Rottner
- Helmholtz Centre for Infection Research, Braunschweig, Germany
- Institute of Genetics, University of Bonn, Bonn, Germany
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26
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Electron tomography reveals unbranched networks of actin filaments in lamellipodia. Nat Cell Biol 2010; 12:429-35. [PMID: 20418872 DOI: 10.1038/ncb2044] [Citation(s) in RCA: 173] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Accepted: 03/15/2010] [Indexed: 02/08/2023]
Abstract
Eukaryotic cells can initiate movement using the forces exerted by polymerizing actin filaments to extend lamellipodial and filopodial protrusions. In the current model, actin filaments in lamellipodia are organized in a branched, dendritic network. We applied electron tomography to vitreously frozen 'live' cells, fixed cells and cytoskeletons, embedded in vitreous ice or in deep-negative stain. In lamellipodia from four cell types, including rapidly migrating fish keratocytes, we found that actin filaments are almost exclusively unbranched. The vast majority of apparent filament junctions proved to be overlapping filaments, rather than branched end-to-side junctions. Analysis of the tomograms revealed that actin filaments terminate at the membrane interface within a zone several hundred nanometres wide at the lamellipodium front, and yielded the first direct measurements of filament densities. Actin filament pairs were also identified as lamellipodium components and bundle precursors. These data provide a new structural basis for understanding actin-driven protrusion during cell migration.
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27
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From dynamic live cell imaging to 3D ultrastructure: novel integrated methods for high pressure freezing and correlative light-electron microscopy. PLoS One 2010; 5:e9014. [PMID: 20140253 PMCID: PMC2815783 DOI: 10.1371/journal.pone.0009014] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Accepted: 01/11/2010] [Indexed: 11/19/2022] Open
Abstract
Background In cell biology, the study of proteins and organelles requires the combination of different imaging approaches, from live recordings with light microscopy (LM) to electron microscopy (EM). Methodology To correlate dynamic events in adherent cells with both ultrastructural and 3D information, we developed a method for cultured cells that combines confocal time-lapse images of GFP-tagged proteins with electron microscopy. With laser micro-patterned culture substrate, we created coordinates that were conserved at every step of the sample preparation and visualization processes. Specifically designed for cryo-fixation, this method allowed a fast freezing of dynamic events within seconds and their ultrastructural characterization. We provide examples of the dynamic oligomerization of GFP-tagged myotubularin (MTM1) phosphoinositides phosphatase induced by osmotic stress, and of the ultrastructure of membrane tubules dependent on amphiphysin 2 (BIN1) expression. Conclusion Accessible and versatile, we show that this approach is efficient to routinely correlate functional and dynamic LM with high resolution morphology by EM, with immuno-EM labeling, with 3D reconstruction using serial immuno-EM or tomography, and with scanning-EM.
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28
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Resch GP, Urban E, Jacob S. The actin cytoskeleton in whole mount preparations and sections. Methods Cell Biol 2010; 96:529-64. [PMID: 20869537 DOI: 10.1016/s0091-679x(10)96022-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In non-muscle cells, the actin cytoskeleton plays a key role by providing a scaffold contributing to the definition of cell shape, force for driving cell motility, cytokinesis, endocytosis, and propulsion of pathogens, as well as tracks for intracellular transport. A thorough understanding of these processes requires insight into the spatial and temporal organisation of actin filaments into diverse higher-order structures, such as networks, parallel bundles, and contractile arrays. Transmission and scanning electron microscopy can be used to visualise the actin cytoskeleton, but due to the delicate nature of actin filaments, they are easily affected by standard preparation protocols, yielding variable degrees of ultrastructural preservation. In this chapter, we describe different conventional and cryo-approaches to visualise the actin cytoskeleton using transmission electron microscopy and discuss their specific advantages and drawbacks. In the first part, we present three different whole mount techniques, which allow visualisation of actin in the peripheral, thinly spread parts of cells grown in monolayers. In the second part, we describe specific issues concerning the visualisation of actin in thin sections. Techniques for three-dimensional visualisation of actin, protein localisation, and correlative light and electron microscopy are also included.
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Affiliation(s)
- Guenter P Resch
- IMP-IMBA-GMI Electron Microscopy Facility, Institute of Molecular Biotechnology of the Austrian Academy of Sciences, 1030 Vienna, Austria
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29
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Lai FPL, Szczodrak M, Oelkers JM, Ladwein M, Acconcia F, Benesch S, Auinger S, Faix J, Small JV, Polo S, Stradal TEB, Rottner K. Cortactin promotes migration and platelet-derived growth factor-induced actin reorganization by signaling to Rho-GTPases. Mol Biol Cell 2009; 20:3209-23. [PMID: 19458196 DOI: 10.1091/mbc.e08-12-1180] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Dynamic actin rearrangements are initiated and maintained by actin filament nucleators, including the Arp2/3-complex. This protein assembly is activated in vitro by distinct nucleation-promoting factors such as Wiskott-Aldrich syndrome protein/Scar family proteins or cortactin, but the relative in vivo functions of each of them remain controversial. Here, we report the conditional genetic disruption of murine cortactin, implicated previously in dynamic actin reorganizations driving lamellipodium protrusion and endocytosis. Unexpectedly, cortactin-deficient cells showed little changes in overall cell morphology and growth. Ultrastructural analyses and live-cell imaging studies revealed unimpaired lamellipodial architecture, Rac-induced protrusion, and actin network turnover, although actin assembly rates in the lamellipodium were modestly increased. In contrast, platelet-derived growth factor-induced actin reorganization and Rac activation were impaired in cortactin null cells. In addition, cortactin deficiency caused reduction of Cdc42 activity and defects in random and directed cell migration. Reduced migration of cortactin null cells could be restored, at least in part, by active Rac and Cdc42 variants. Finally, cortactin removal did not affect the efficiency of receptor-mediated endocytosis. Together, we conclude that cortactin is fully dispensable for Arp2/3-complex activation during lamellipodia protrusion or clathrin pit endocytosis. Furthermore, we propose that cortactin promotes cell migration indirectly, through contributing to activation of selected Rho-GTPases.
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Affiliation(s)
- Frank P L Lai
- Cytoskeleton Dynamics Group, Helmholtz Centre for Infection Research, D-38124 Braunschweig, Germany
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30
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Nemethova M, Auinger S, Small JV. Building the actin cytoskeleton: filopodia contribute to the construction of contractile bundles in the lamella. J Cell Biol 2008; 180:1233-44. [PMID: 18362182 PMCID: PMC2290848 DOI: 10.1083/jcb.200709134] [Citation(s) in RCA: 139] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2007] [Accepted: 02/27/2008] [Indexed: 01/09/2023] Open
Abstract
Filopodia are rodlike extensions generally attributed with a guidance role in cell migration. We now show in fish fibroblasts that filopodia play a major role in generating contractile bundles in the lamella region behind the migrating front. Filopodia that developed adhesion to the substrate via paxillin containing focal complexes contributed their proximal part to stress fiber assembly, and filopodia that folded laterally contributed to the construction of contractile bundles parallel to the cell edge. Correlated light and electron microscopy of cells labeled for actin and fascin confirmed integration of filopodia bundles into the lamella network. Inhibition of myosin II did not subdue the waving and folding motions of filopodia or their entry into the lamella, but filopodia were not then integrated into contractile arrays. Comparable results were obtained with B16 melanoma cells. These and other findings support the idea that filaments generated in filopodia and lamellipodia for protrusion are recycled for seeding actomyosin arrays for use in retraction.
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Affiliation(s)
- Maria Nemethova
- Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna 1030, Austria
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