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Nakazawa K, Chauvin B, Mangenot S, Bertin A. Reconstituted in vitro systems to reveal the roles and functions of septins. J Cell Sci 2023; 136:jcs259448. [PMID: 37815088 DOI: 10.1242/jcs.259448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/11/2023] Open
Abstract
Septins are essential cytoskeletal proteins involved in key cellular processes and have also been implicated in diseases from cancers to neurodegenerative pathologies. However, they have not been as thoroughly studied as other cytoskeletal proteins. In vivo, septins interact with other cytoskeletal proteins and with the inner plasma membrane. Hence, bottom-up in vitro cell-free assays are well suited to dissect the roles and behavior of septins in a controlled environment. Specifically, in vitro studies have been invaluable in describing the self-assembly of septins into a large diversity of ultrastructures. Given that septins interact specifically with membrane, the details of these septin-membrane interactions have been analyzed using reconstituted lipid systems. In particular, at a membrane, septins are often localized at curvatures of micrometer scale. In that context, in vitro assays have been performed with substrates of varying curvatures (spheres, cylinders or undulated substrates) to probe the sensitivity of septins to membrane curvature. This Review will first present the structural properties of septins in solution and describe the interplay of septins with cytoskeletal partners. We will then discuss how septins interact with biomimetic membranes and induce their reshaping. Finally, we will highlight the curvature sensitivity of septins and how they alter the mechanical properties of membranes.
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Affiliation(s)
- Koyomi Nakazawa
- Physico Chimie Curie , Institut Curie, CNRS UMR 168, Sorbonne Université, 11 Rue Pierre et Paris Curie, 75005 Paris, France
| | - Brieuc Chauvin
- Physico Chimie Curie , Institut Curie, CNRS UMR 168, Sorbonne Université, 11 Rue Pierre et Paris Curie, 75005 Paris, France
| | - Stéphanie Mangenot
- Laboratoire Matière et Systèmes Complexes , Université de Paris Cité, CNRS UMR 7057, 45 Rue des Saint Pères, 75006 Paris, France
| | - Aurélie Bertin
- Physico Chimie Curie , Institut Curie, CNRS UMR 168, Sorbonne Université, 11 Rue Pierre et Paris Curie, 75005 Paris, France
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Curvature sensing as an emergent property of multiscale assembly of septins. Proc Natl Acad Sci U S A 2023; 120:e2208253120. [PMID: 36716363 PMCID: PMC9963131 DOI: 10.1073/pnas.2208253120] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The ability of cells to sense and communicate their shape is central to many of their functions. Much is known about how cells generate complex shapes, yet how they sense and respond to geometric cues remains poorly understood. Septins are GTP-binding proteins that localize to sites of micrometer-scale membrane curvature. Assembly of septins is a multistep and multiscale process, but it is unknown how these discrete steps lead to curvature sensing. Here, we experimentally examine the time-dependent binding of septins at different curvatures and septin bulk concentrations. These experiments unexpectedly indicated that septins' curvature preference is not absolute but rather is sensitive to the combinations of membrane curvatures present in a reaction, suggesting that there is competition between different curvatures for septin binding. To understand the physical underpinning of this result, we developed a kinetic model that connects septins' self-assembly and curvature-sensing properties. Our experimental and modeling results are consistent with curvature-sensitive assembly being driven by cooperative associations of septin oligomers in solution with the bound septins. When combined, the work indicates that septin curvature sensing is an emergent property of the multistep, multiscale assembly of membrane-bound septins. As a result, curvature preference is not absolute and can be modulated by changing the physicochemical and geometric parameters involved in septin assembly, including bulk concentration, and the available membrane curvatures. While much geometry-sensitive assembly in biology is thought to be guided by intrinsic material properties of molecules, this is an important example of how curvature sensing can arise from multiscale assembly of polymers.
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Abstract
The cytoskeleton is a complex of detergent-insoluble components of the cytoplasm playing critical roles in cell motility, shape generation, and mechanical properties of a cell. Fibrillar polymers-actin filaments, microtubules, and intermediate filaments-are major constituents of the cytoskeleton, which constantly change their organization during cellular activities. The actin cytoskeleton is especially polymorphic, as actin filaments can form multiple higher-order assemblies performing different functions. Structural information about cytoskeleton organization is critical for understanding its functions and mechanisms underlying various forms of cellular activity. Because of the nanometer-scale thickness of cytoskeletal fibers, electron microscopy (EM) is a key tool to determine the structure of the cytoskeleton.This article describes application of rotary shadowing (or platinum replica ) EM (PREM) for visualization of the cytoskeleton . The procedure is applicable to thin cultured cells growing on glass coverslips and consists of detergent extraction (or mechanical "unroofing") of cells to expose their cytoskeleton , chemical fixation to provide stability, ethanol dehydration and critical point drying to preserve three-dimensionality, rotary shadowing with platinum to create contrast, and carbon coating to stabilize replicas. This technique provides easily interpretable three-dimensional images, in which individual cytoskeletal fibers are clearly resolved and individual proteins can be identified by immunogold labeling. More importantly, PREM is easily compatible with live cell imaging, so that one can correlate the dynamics of a cell or its components, e.g., expressed fluorescent proteins, with high-resolution structural organization of the cytoskeleton in the same cell.
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Affiliation(s)
- Tatyana Svitkina
- Department of Biology, University of Pennsylvania, Philadelphia, PA, USA.
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Johnson A, Dahhan DA, Gnyliukh N, Kaufmann WA, Zheden V, Costanzo T, Mahou P, Hrtyan M, Wang J, Aguilera-Servin J, van Damme D, Beaurepaire E, Loose M, Bednarek SY, Friml J. The TPLATE complex mediates membrane bending during plant clathrin-mediated endocytosis. Proc Natl Acad Sci U S A 2021; 118:e2113046118. [PMID: 34907016 PMCID: PMC8691179 DOI: 10.1073/pnas.2113046118] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/01/2021] [Indexed: 01/08/2023] Open
Abstract
Clathrin-mediated endocytosis is the major route of entry of cargos into cells and thus underpins many physiological processes. During endocytosis, an area of flat membrane is remodeled by proteins to create a spherical vesicle against intracellular forces. The protein machinery which mediates this membrane bending in plants is unknown. However, it is known that plant endocytosis is actin independent, thus indicating that plants utilize a unique mechanism to mediate membrane bending against high-turgor pressure compared to other model systems. Here, we investigate the TPLATE complex, a plant-specific endocytosis protein complex. It has been thought to function as a classical adaptor functioning underneath the clathrin coat. However, by using biochemical and advanced live microscopy approaches, we found that TPLATE is peripherally associated with clathrin-coated vesicles and localizes at the rim of endocytosis events. As this localization is more fitting to the protein machinery involved in membrane bending during endocytosis, we examined cells in which the TPLATE complex was disrupted and found that the clathrin structures present as flat patches. This suggests a requirement of the TPLATE complex for membrane bending during plant clathrin-mediated endocytosis. Next, we used in vitro biophysical assays to confirm that the TPLATE complex possesses protein domains with intrinsic membrane remodeling activity. These results redefine the role of the TPLATE complex and implicate it as a key component of the evolutionarily distinct plant endocytosis mechanism, which mediates endocytic membrane bending against the high-turgor pressure in plant cells.
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Affiliation(s)
| | - Dana A Dahhan
- Department of Biochemistry, Hector F. DeLuca Laboratories, University of Wisconsin-Madison, Madison, WI 53706
| | | | | | - Vanessa Zheden
- Institute of Science and Technology, 3400 Klosterneuburg, Austria
| | - Tommaso Costanzo
- Institute of Science and Technology, 3400 Klosterneuburg, Austria
| | - Pierre Mahou
- CNRS, INSERM, Laboratory for Optics and Biosciences Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau, France
| | - Mónika Hrtyan
- Institute of Science and Technology, 3400 Klosterneuburg, Austria
| | - Jie Wang
- Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium
- Vlaams Instituut voor Biotechnologie (VIB) Center for Plant Systems Biology, 9052 Ghent, Belgium
| | | | - Daniël van Damme
- Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium
- Vlaams Instituut voor Biotechnologie (VIB) Center for Plant Systems Biology, 9052 Ghent, Belgium
| | - Emmanuel Beaurepaire
- CNRS, INSERM, Laboratory for Optics and Biosciences Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau, France
| | - Martin Loose
- Institute of Science and Technology, 3400 Klosterneuburg, Austria
| | - Sebastian Y Bednarek
- Department of Biochemistry, Hector F. DeLuca Laboratories, University of Wisconsin-Madison, Madison, WI 53706
| | - Jiří Friml
- Institute of Science and Technology, 3400 Klosterneuburg, Austria;
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Yao L, Zhang L, Chen L, Gong X, Zhong J, Wang B, Fei Y, Mi L, Ma J. Dynamic Structure of Yeast Septin by Fast Fluctuation-Enhanced Structured Illumination Microscopy. Microorganisms 2021; 9:microorganisms9112255. [PMID: 34835381 PMCID: PMC8620077 DOI: 10.3390/microorganisms9112255] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 10/23/2021] [Accepted: 10/25/2021] [Indexed: 12/05/2022] Open
Abstract
When Saccharomyces cerevisiae divides, a structure composed of different septin proteins arranged according to a certain rule is formed at the cell division site. The structure undergoes multiple remodeling stages during the cell cycle, thus guiding the yeast cells to complete the entire division process. Although the higher-order structure of septins can be determined using electron microscopy, the septin’s dynamic processes are poorly understood because of limitations in living cell super-resolution imaging technology. Herein, we describe a high lateral resolution and temporal resolution technique, known as fast fluctuation-enhanced structured illumination microscopy (fFE-SIM), which more than doubles the SIM resolution at a frame rate of 38 Hz in living cells. This allows a highly dynamic and sparse septin structure to be observed in Saccharomyces cerevisiae.
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Affiliation(s)
- Longfang Yao
- Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, School of Information Science and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China; (L.Y.); (L.C.); (X.G.); (Y.F.)
| | - Li Zhang
- Shanghai Engineering Research Center of Industrial Microorganisms, The Multiscale Research Institute of Complex Systems (MRICS), School of Life Sciences, Fudan University, 220 Handan Road, Shanghai 200433, China;
| | - Liwen Chen
- Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, School of Information Science and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China; (L.Y.); (L.C.); (X.G.); (Y.F.)
| | - Xingyu Gong
- Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, School of Information Science and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China; (L.Y.); (L.C.); (X.G.); (Y.F.)
| | - Jiahui Zhong
- Institute of Biomedical Engineering and Technology, Academy for Engineer and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China;
| | - Baoju Wang
- Centre for Optical and Electromagnetic Research, Guangdong Provincial Key Laboratory of Optical Information Materials and Technology, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, China;
| | - Yiyan Fei
- Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, School of Information Science and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China; (L.Y.); (L.C.); (X.G.); (Y.F.)
| | - Lan Mi
- Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, School of Information Science and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China; (L.Y.); (L.C.); (X.G.); (Y.F.)
- Institute of Biomedical Engineering and Technology, Academy for Engineer and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China;
- Correspondence: (L.M.); (J.M.)
| | - Jiong Ma
- Shanghai Engineering Research Center of Ultra-Precision Optical Manufacturing, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, School of Information Science and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China; (L.Y.); (L.C.); (X.G.); (Y.F.)
- Shanghai Engineering Research Center of Industrial Microorganisms, The Multiscale Research Institute of Complex Systems (MRICS), School of Life Sciences, Fudan University, 220 Handan Road, Shanghai 200433, China;
- Institute of Biomedical Engineering and Technology, Academy for Engineer and Technology, Fudan University, 220 Handan Road, Shanghai 200433, China;
- Correspondence: (L.M.); (J.M.)
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Henson JH, Samasa B, Burg EC. High resolution imaging of the cortex isolated from sea urchin eggs and embryos. Methods Cell Biol 2019; 151:419-432. [PMID: 30948022 DOI: 10.1016/bs.mcb.2019.01.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The cellular cortex-consisting of the plasma membrane and the adjacent outer few microns of the cytoplasm-is a critically important, dynamic and complex region in the sea urchin egg and embryo. Some 40 years ago it was discovered that isolated cortices could be obtained from eggs adhered to glass coverslips and since that time this preparation has been used in a wide range of studies, including seminal research on fertilization, exocytosis, the cytoskeleton, and cytokinesis. In this chapter, we discuss methods for isolating cortices from eggs and embryos, including those undergoing cell division. We also provide protocols for analyzing cortical architecture and dynamics using specific localization methods combined with super-resolution Structured Illumination and Stimulated Emission Depletion light microscopy and platinum replica transmission electron microscopy.
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Affiliation(s)
- J H Henson
- Department of Biology, Dickinson College, Carlisle, PA, United States; Friday Harbor Laboratories, University of Washington, Friday Harbor, WA, United States.
| | - Bakary Samasa
- Department of Biology, Dickinson College, Carlisle, PA, United States; Friday Harbor Laboratories, University of Washington, Friday Harbor, WA, United States
| | - E C Burg
- Department of Biology, Dickinson College, Carlisle, PA, United States; Friday Harbor Laboratories, University of Washington, Friday Harbor, WA, United States
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