1
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Abstract
Genome instability is a major cause of aging. In the budding yeast Saccharomyces cerevisiae, instability of the ribosomal RNA gene repeat (rDNA) is known to shorten replicative lifespan. In yeast, rDNA instability in an aging cell is associated with accumulation of extrachromosomal rDNA circles (ERCs) which titrate factors critical for lifespan maintenance. ERC accumulation is not detected in mammalian cells, where aging is linked to DNA damage. To distinguish effects of DNA damage from those of ERC accumulation on senescence, we re-analyzed a yeast strain with a replication initiation defect in the rDNA, which limits ERC multiplication. In aging cells of this strain (rARS-∆3) rDNA became unstable, as in wild-type cells, whereas significantly fewer ERCs accumulated. Single-cell aging analysis revealed that rARS-∆3 cells follow a linear survival curve and can have a wild-type replicative lifespan, although a fraction of the cells stopped dividing earlier than wild type. The doubling time of rARS-∆3 cells appears to increase in the final cell divisions. Our results suggest that senescence in rARS-∆3 is linked to the accumulation of DNA damage as in mammalian cells, rather than to elevated ERC level. Therefore, this strain should be a good model system to study ERC-independent aging.
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Affiliation(s)
- Mei Hattori
- Laboratory of Genome Regeneration, Institute for Quantitative Biosciences (IQB), The University of Tokyo.,Department of Biological Sciences, Graduate School of Science, The University of Tokyo
| | - Chihiro Horigome
- Laboratory of Genome Regeneration, Institute for Quantitative Biosciences (IQB), The University of Tokyo
| | - Théo Aspert
- Laboratoire de Génétique Moléculaire, Génomique et Microbiologie
| | - Gilles Charvin
- Laboratoire de Génétique Moléculaire, Génomique et Microbiologie
| | - Takehiko Kobayashi
- Laboratory of Genome Regeneration, Institute for Quantitative Biosciences (IQB), The University of Tokyo.,Department of Biological Sciences, Graduate School of Science, The University of Tokyo.,Collaborative Research Institute for Innovative Microbiology, The University of Tokyo
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2
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Quintin S, Charvin G. Left-right asymmetry in oxidative stress sensing neurons in C. elegans. MicroPubl Biol 2022; 2022:10.17912/micropub.biology.000652. [PMID: 36338152 PMCID: PMC9631000 DOI: 10.17912/micropub.biology.000652] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 09/21/2022] [Accepted: 10/18/2022] [Indexed: 11/15/2022]
Abstract
Perception of oxidative stress in nematodes involves specific neurons expressing antioxidant enzymes. Here, we carefully characterized GFP knock-in lines for C. elegans peroxiredoxin PRDX-2 and thioredoxin TRX-1, and uncovered that left and right I2, PHA and ASJ neurons reproducibly express an asymmetric level of each enzyme. We observed that high-expressing neurons are in most cases associated with a particular side, indicating a directional rather than stochastic type of asymmetry. We propose that the biological relevance of this left-right asymmetry is to fine-tune H 2 O 2 or light sensing, which remains to be investigated.
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Affiliation(s)
- Sophie Quintin
- IGBMC, Development and Stem Cells Department
,
CNRS UMR7104, INSERM U964, Université de Strasbourg, 67404 France
,
Correspondence to: Sophie Quintin (
)
| | - Gilles Charvin
- IGBMC, Development and Stem Cells Department
,
CNRS UMR7104, INSERM U964, Université de Strasbourg, 67404 France
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3
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Aspert T, Hentsch D, Charvin G. DetecDiv, a generalist deep-learning platform for automated cell division tracking and survival analysis. eLife 2022; 11:79519. [PMID: 35976090 PMCID: PMC9444243 DOI: 10.7554/elife.79519] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 08/16/2022] [Indexed: 11/13/2022] Open
Abstract
Automating the extraction of meaningful temporal information from sequences of microscopy images represents a major challenge to characterize dynamical biological processes. So far, strong limitations in the ability to quantitatively analyze single-cell trajectories have prevented large-scale investigations to assess the dynamics of entry into replicative senescence in yeast. Here, we have developed DetecDiv, a microfluidic-based image acquisition platform combined with deep learning-based software for high-throughput single-cell division tracking. We show that DetecDiv can automatically reconstruct cellular replicative lifespans with high accuracy and performs similarly with various imaging platforms and geometries of microfluidic traps. In addition, this methodology provides comprehensive temporal cellular metrics using time-series classification and image semantic segmentation. Last, we show that this method can be further applied to automatically quantify the dynamics of cellular adaptation and real-time cell survival upon exposure to environmental stress. Hence, this methodology provides an all-in-one toolbox for high-throughput phenotyping for cell cycle, stress response, and replicative lifespan assays.
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Affiliation(s)
- Théo Aspert
- Department of Developmental Biology and Stem Cells, Institute of Genetics and Molecular and Cellular Biology, Illkirch, France
| | - Didier Hentsch
- Department of Developmental Biology and Stem Cells, Institute of Genetics and Molecular and Cellular Biology, Illkirch, France
| | - Gilles Charvin
- Department of Developmental Biology and Stem Cells, Institute of Genetics and Molecular and Cellular Biology, Illkirch, France
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4
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Aspert T, Jacquel B, Charvin G. A Microfluidic Platform for Tracking Individual Cell Dynamics during an Unperturbed Nutrients Exhaustion. Bio Protoc 2022; 12:e4470. [PMID: 35978570 PMCID: PMC9350916 DOI: 10.21769/bioprotoc.4470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Revised: 06/08/2022] [Accepted: 06/08/2022] [Indexed: 12/29/2022] Open
Abstract
Microorganisms have evolved adaptive strategies to respond to the autonomous degradation of their environment. Indeed, a growing culture progressively exhausts nutrients from its media and modifies its composition. Yet, how single cells react to these modifications remains difficult to study since it requires population-scale growth experiments to allow cell proliferation to have a collective impact on the environment, while monitoring the same individuals exposed to this environment for days. For this purpose, we have previously described an integrated microfluidic pipeline, based on continuous separation of the cells from the media and subsequent perfusion of the filtered media in an observation chamber containing isolated single cells. Here, we provide a detailed protocol to implement this methodology, including the setting up of the microfluidic system and the processing of timelapse images.
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Affiliation(s)
- Théo Aspert
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
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Centre National de la Recherche Scientifique, UMR7104, Illkirch, France
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Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France
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Université de Strasbourg, Illkirch, France
,
*For correspondence:
;
| | - Basile Jacquel
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
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Centre National de la Recherche Scientifique, UMR7104, Illkirch, France
,
Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France
,
Université de Strasbourg, Illkirch, France
,
*For correspondence:
;
| | - Gilles Charvin
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
,
Centre National de la Recherche Scientifique, UMR7104, Illkirch, France
,
Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France
,
Université de Strasbourg, Illkirch, France
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5
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Gomar-Alba M, Pozharskaia V, Cichocki B, Schaal C, Kumar A, Jacquel B, Charvin G, Igual JC, Mendoza M. Nuclear pore complex acetylation regulates mRNA export and cell cycle commitment in budding yeast. EMBO J 2022; 41:e110271. [PMID: 35735140 PMCID: PMC9340480 DOI: 10.15252/embj.2021110271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Revised: 05/16/2022] [Accepted: 05/19/2022] [Indexed: 11/27/2022] Open
Abstract
Nuclear pore complexes (NPCs) mediate communication between the nucleus and the cytoplasm, and regulate gene expression by interacting with transcription and mRNA export factors. Lysine acetyltransferases (KATs) promote transcription through acetylation of chromatin‐associated proteins. We find that Esa1, the KAT subunit of the yeast NuA4 complex, also acetylates the nuclear pore basket component Nup60 to promote mRNA export. Acetylation of Nup60 recruits the mRNA export factor Sac3, the scaffolding subunit of the Transcription and Export 2 (TREX‐2) complex, to the nuclear basket. The Esa1‐mediated nuclear export of mRNAs in turn promotes entry into S phase, which is inhibited by the Hos3 deacetylase in G1 daughter cells to restrain their premature commitment to a new cell division cycle. This mechanism is not only limited to G1/S‐expressed genes but also inhibits the expression of the nutrient‐regulated GAL1 gene specifically in daughter cells. Overall, these results reveal how acetylation can contribute to the functional plasticity of NPCs in mother and daughter yeast cells. In addition, our work demonstrates dual gene expression regulation by the evolutionarily conserved NuA4 complex, at the level of transcription and at the stage of mRNA export by modifying the nucleoplasmic entrance to nuclear pores.
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Affiliation(s)
- Mercè Gomar-Alba
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Institut de Biotecnologia i Biomedicina (BIOTECMED) and Departament de Bioquímica i Biologia Molecular, Universitat de València, Burjassot, Spain
| | - Vasilisa Pozharskaia
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
| | - Bogdan Cichocki
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
| | - Celia Schaal
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
| | - Arun Kumar
- Department of Cell Biology, Universitat Pompeu Fabra (UPF), Barcelona, Spain
| | - Basile Jacquel
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
| | - Gilles Charvin
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France.,Université de Strasbourg, Strasbourg, France
| | - J Carlos Igual
- Institut de Biotecnologia i Biomedicina (BIOTECMED) and Departament de Bioquímica i Biologia Molecular, Universitat de València, Burjassot, Spain
| | - Manuel Mendoza
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France.,Université de Strasbourg, Strasbourg, France
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6
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Meinema AC, Marzelliusardottir A, Mirkovic M, Aspert T, Lee SS, Charvin G, Barral Y. DNA circles promote yeast ageing in part through stimulating the reorganization of nuclear pore complexes. eLife 2022; 11:71196. [PMID: 35373738 PMCID: PMC9020822 DOI: 10.7554/elife.71196] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 04/03/2022] [Indexed: 11/13/2022] Open
Abstract
The nuclear pore complex (NPC) mediates nearly all exchanges between nucleus and cytoplasm, and in many species it changes composition as the organism ages. However, how these changes arise and whether they contribute themselves to ageing is poorly understood. We show that SAGA-dependent attachment of DNA circles to NPCs in replicatively ageing yeast cells causes NPCs to lose their nuclear basket and cytoplasmic complexes. These NPCs were not recognized as defective by the NPC quality control machinery (SINC) and not targeted by ESCRTs. They interacted normally or more effectively with protein import and export factors but specifically lost mRNA export factors. Acetylation of Nup60 drove the displacement of basket and cytoplasmic complexes from circle-bound NPCs. Mutations preventing this remodeling extended the replicative lifespan of the cells. Thus, our data suggest that the anchorage of accumulating circles locks NPCs in a specialized state and that this process is intrinsically linked to the mechanisms by which ERCs promote ageing.
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Affiliation(s)
| | | | | | - Théo Aspert
- Department of Developmental Biology and Stem Cells, Institute of Genetics and Molecular and Cellular Biology, Illkirch, France
| | - Sung Sik Lee
- Department of Biology, ETH Zürich, Zürich, Switzerland
| | - Gilles Charvin
- Department of Developmental Biology and Stem Cells, Institute of Genetics and Molecular and Cellular Biology, Illkirch, France
| | - Yves Barral
- Department of Biology, ETH Zürich, Zürich, Switzerland
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7
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Jacquel B, Aspert T, Laporte D, Sagot I, Charvin G. Monitoring single-cell dynamics of entry into quiescence during an unperturbed life cycle. eLife 2021; 10:73186. [PMID: 34723791 PMCID: PMC8594939 DOI: 10.7554/elife.73186] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 10/15/2021] [Indexed: 12/14/2022] Open
Abstract
The life cycle of microorganisms is associated with dynamic metabolic transitions and complex cellular responses. In yeast, how metabolic signals control the progressive choreography of structural reorganizations observed in quiescent cells during a natural life cycle remains unclear. We have developed an integrated microfluidic device to address this question, enabling continuous single-cell tracking in a batch culture experiencing unperturbed nutrient exhaustion to unravel the coordination between metabolic and structural transitions within cells. Our technique reveals an abrupt fate divergence in the population, whereby a fraction of cells is unable to transition to respiratory metabolism and undergoes a reversible entry into a quiescence-like state leading to premature cell death. Further observations reveal that nonmonotonous internal pH fluctuations in respiration-competent cells orchestrate the successive waves of protein superassemblies formation that accompany the entry into a bona fide quiescent state. This ultimately leads to an abrupt cytosolic glass transition that occurs stochastically long after proliferation cessation. This new experimental framework provides a unique way to track single-cell fate dynamics over a long timescale in a population of cells that continuously modify their ecological niche.
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Affiliation(s)
- Basile Jacquel
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Théo Aspert
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Damien Laporte
- Institut de Biochimie et Génétique Cellulaires, UMR 5095 CNRS - Université de Bordeaux, Bordeaux, France, Bordeaux, France
| | - Isabelle Sagot
- Institut de Biochimie et Génétique Cellulaires, UMR 5095 CNRS - Université de Bordeaux, Bordeaux, France, Bordeaux, France
| | - Gilles Charvin
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, Illkirch, France.,Université de Strasbourg, Illkirch, France
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8
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Schlagowski AM, Knöringer K, Morlot S, Sánchez Vicente A, Flohr T, Krämer L, Boos F, Khalid N, Ahmed S, Schramm J, Murschall LM, Haberkant P, Stein F, Riemer J, Westermann B, Braun RJ, Winklhofer KF, Charvin G, Herrmann JM. Increased levels of mitochondrial import factor Mia40 prevent the aggregation of polyQ proteins in the cytosol. EMBO J 2021; 40:e107913. [PMID: 34191328 PMCID: PMC8365258 DOI: 10.15252/embj.2021107913] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 05/25/2021] [Accepted: 05/31/2021] [Indexed: 12/11/2022] Open
Abstract
The formation of protein aggregates is a hallmark of neurodegenerative diseases. Observations on patient samples and model systems demonstrated links between aggregate formation and declining mitochondrial functionality, but causalities remain unclear. We used Saccharomyces cerevisiae to analyze how mitochondrial processes regulate the behavior of aggregation‐prone polyQ protein derived from human huntingtin. Expression of Q97‐GFP rapidly led to insoluble cytosolic aggregates and cell death. Although aggregation impaired mitochondrial respiration only slightly, it considerably interfered with the import of mitochondrial precursor proteins. Mutants in the import component Mia40 were hypersensitive to Q97‐GFP, whereas Mia40 overexpression strongly suppressed the formation of toxic Q97‐GFP aggregates both in yeast and in human cells. Based on these observations, we propose that the post‐translational import of mitochondrial precursor proteins into mitochondria competes with aggregation‐prone cytosolic proteins for chaperones and proteasome capacity. Mia40 regulates this competition as it has a rate‐limiting role in mitochondrial protein import. Therefore, Mia40 is a dynamic regulator in mitochondrial biogenesis that can be exploited to stabilize cytosolic proteostasis.
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Affiliation(s)
| | | | - Sandrine Morlot
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Ana Sánchez Vicente
- Department of Molecular Cell Biology, Institute of Biochemistry and Pathobiochemistry, Ruhr University Bochum, Bochum, Germany
| | - Tamara Flohr
- Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Lena Krämer
- Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Felix Boos
- Cell Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Nabeel Khalid
- German Research Center for Artificial Intelligence DFKI, Kaiserslautern, Germany
| | - Sheraz Ahmed
- German Research Center for Artificial Intelligence DFKI, Kaiserslautern, Germany
| | - Jana Schramm
- Cell Biology, University of Bayreuth, Bayreuth, Germany
| | | | - Per Haberkant
- Proteomics Core Facility, EMBL Heidelberg, Heidelberg, Germany
| | - Frank Stein
- Proteomics Core Facility, EMBL Heidelberg, Heidelberg, Germany
| | - Jan Riemer
- Biochemistry, University of Cologne, Cologne, Germany
| | | | - Ralf J Braun
- Cell Biology, University of Bayreuth, Bayreuth, Germany.,Neurodegeneration, Danube Private University, Krems/Donau, Austria
| | - Konstanze F Winklhofer
- Department of Molecular Cell Biology, Institute of Biochemistry and Pathobiochemistry, Ruhr University Bochum, Bochum, Germany
| | - Gilles Charvin
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France.,Université de Strasbourg, Illkirch, France
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9
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Bheda P, Aguilar-Gómez D, Kukhtevich I, Becker J, Charvin G, Kirmizis A, Schneider R. Microfluidics for single-cell lineage tracking over time to characterize transmission of phenotypes in Saccharomyces cerevisiae. STAR Protoc 2020; 1:100228. [PMID: 33377118 PMCID: PMC7757727 DOI: 10.1016/j.xpro.2020.100228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The budding yeast Saccharomyces cerevisiae is an excellent model organism to dissect the maintenance and inheritance of phenotypes due to its asymmetric division. This requires following individual cells over time as they go through divisions to define pedigrees. Here, we provide a detailed protocol for collecting and analyzing time-lapse imaging data of yeast cells. The microfluidics protocol can achieve improved time resolution for single-cell tracking to enable characterization of maintenance and inheritance of phenotypes. For complete details on the use and execution of this protocol, please refer to Bheda et al. (2020a).
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Affiliation(s)
- Poonam Bheda
- Institute of Functional Epigenetics, Helmholtz Zentrum München, 85764 Neuherberg, Germany
| | | | - Igor Kukhtevich
- Institute of Functional Epigenetics, Helmholtz Zentrum München, 85764 Neuherberg, Germany
| | - Johannes Becker
- Institute of Bioengineering, School of Engineering, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
| | - Gilles Charvin
- Development and Stem Cells, IGBMC, 67400 Illkirch, France
| | - Antonis Kirmizis
- Department of Biological Sciences, University of Cyprus, 2109 Nicosia, Cyprus
| | - Robert Schneider
- Institute of Functional Epigenetics, Helmholtz Zentrum München, 85764 Neuherberg, Germany
- German Center for Diabetes Research (DZD), 85764 Neuherberg, Germany
- Faculty of Biology, Ludwig-Maximilians Universität München, 80333 Munich, Germany
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10
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Bheda P, Aguilar-Gómez D, Becker NB, Becker J, Stavrou E, Kukhtevich I, Höfer T, Maerkl S, Charvin G, Marr C, Kirmizis A, Schneider R. Single-Cell Tracing Dissects Regulation of Maintenance and Inheritance of Transcriptional Reinduction Memory. Mol Cell 2020; 78:915-925.e7. [DOI: 10.1016/j.molcel.2020.04.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 02/15/2020] [Accepted: 04/15/2020] [Indexed: 10/24/2022]
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11
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Moreno DF, Jenkins K, Morlot S, Charvin G, Csikasz-Nagy A, Aldea M. Proteostasis collapse, a hallmark of aging, hinders the chaperone-Start network and arrests cells in G1. eLife 2019; 8:48240. [PMID: 31518229 PMCID: PMC6744273 DOI: 10.7554/elife.48240] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 09/05/2019] [Indexed: 12/26/2022] Open
Abstract
Loss of proteostasis and cellular senescence are key hallmarks of aging, but direct cause-effect relationships are not well understood. We show that most yeast cells arrest in G1 before death with low nuclear levels of Cln3, a key G1 cyclin extremely sensitive to chaperone status. Chaperone availability is seriously compromised in aged cells, and the G1 arrest coincides with massive aggregation of a metastable chaperone-activity reporter. Moreover, G1-cyclin overexpression increases lifespan in a chaperone-dependent manner. As a key prediction of a model integrating autocatalytic protein aggregation and a minimal Start network, enforced protein aggregation causes a severe reduction in lifespan, an effect that is greatly alleviated by increased expression of specific chaperones or cyclin Cln3. Overall, our data show that proteostasis breakdown, by compromising chaperone activity and G1-cyclin function, causes an irreversible arrest in G1, configuring a molecular pathway postulating proteostasis decay as a key contributing effector of cell senescence.
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Affiliation(s)
- David F Moreno
- Molecular Biology Institute of Barcelona (IBMB), CSIC, Barcelona, Spain
| | - Kirsten Jenkins
- Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.,Institute of Mathematical and Molecular Biomedicine, King's College London, London, United Kingdom
| | - Sandrine Morlot
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Strasbourg, France.,Université de Strasbourg, Illkirch, France
| | - Gilles Charvin
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Strasbourg, France.,Université de Strasbourg, Illkirch, France
| | - Attila Csikasz-Nagy
- Randall Division of Cell and Molecular Biophysics, King's College London, London, United Kingdom.,Institute of Mathematical and Molecular Biomedicine, King's College London, London, United Kingdom.,Faculty of Information Technology and Bionics, Pázmány Péter Catholic University, Budapest, Hungary
| | - Martí Aldea
- Molecular Biology Institute of Barcelona (IBMB), CSIC, Barcelona, Spain.,Department of Basic Sciences, Universitat Internacional de Catalunya, Sant Cugat del Vallès, Spain
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12
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Goulev Y, Matifas A, Heyer V, Reina-San-Martin B, Charvin G. COSPLAY: An expandable toolbox for combinatorial and swift generation of expression plasmids in yeast. PLoS One 2019; 14:e0220694. [PMID: 31461461 PMCID: PMC6713393 DOI: 10.1371/journal.pone.0220694] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 07/22/2019] [Indexed: 12/05/2022] Open
Abstract
A large number of genetic studies in yeast rely on the use of expression vectors. To facilitate the experimental approach of these studies, several collections of expression vectors have been generated (YXplac, pRS series, etc.). Subsequently, these collections have been expanded by adding more diversity to many of the plasmid features, including new selection markers and new promoter sequences. However, the ever growing number of plasmid features makes it unrealistic for research labs to maintain an up-to-date collection of plasmids. Here, we developed the COSPLAY toolbox: a Golden Gate approach based on the scheme of a simple modular plasmid that recapitulates and completes all the properties of the pRS plasmids. The COSPLAY toolbox contains a basal collection of individual functional modules. Moreover, we standardized a simple and rapid, software-assisted protocol which facilitates the addition of new personalized modules. Finally, our toolbox includes the possibility to select a genomic target location and to perform a single copy integration of the expression vector.
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Affiliation(s)
- Youlian Goulev
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
- Centre National de la Recherche Scientifique, UMR7104, Illkirch, France
- Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France
- Université de Strasbourg, Illkirch, France
- * E-mail: (YG); (GC)
| | - Audrey Matifas
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
- Centre National de la Recherche Scientifique, UMR7104, Illkirch, France
- Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France
- Université de Strasbourg, Illkirch, France
| | - Vincent Heyer
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
- Centre National de la Recherche Scientifique, UMR7104, Illkirch, France
- Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France
- Université de Strasbourg, Illkirch, France
| | - Bernardo Reina-San-Martin
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
- Centre National de la Recherche Scientifique, UMR7104, Illkirch, France
- Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France
- Université de Strasbourg, Illkirch, France
| | - Gilles Charvin
- Department of Developmental Biology and Stem Cells, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France
- Centre National de la Recherche Scientifique, UMR7104, Illkirch, France
- Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France
- Université de Strasbourg, Illkirch, France
- * E-mail: (YG); (GC)
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13
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Coutelier H, Xu Z, Morisse MC, Lhuillier-Akakpo M, Pelet S, Charvin G, Dubrana K, Teixeira MT. Corrigendum: Adaptation to DNA damage checkpoint in senescent telomerase-negative cells promotes genome instability. Genes Dev 2019; 33:378. [PMID: 30824534 DOI: 10.1101/gad.324459.119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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14
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Garmendia-Torres C, Tassy O, Matifas A, Molina N, Charvin G. Multiple inputs ensure yeast cell size homeostasis during cell cycle progression. eLife 2018; 7:34025. [PMID: 29972352 PMCID: PMC6085122 DOI: 10.7554/elife.34025] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2017] [Accepted: 07/01/2018] [Indexed: 12/27/2022] Open
Abstract
Coordination of cell growth with division is essential for proper cell function. In budding yeast, although some molecular mechanisms responsible for cell size control during G1 have been elucidated, the mechanism by which cell size homeostasis is established remains to be discovered. Here, we developed a new technique based on quantification of histone levels to monitor cell cycle progression in individual cells with unprecedented accuracy. Our analysis establishes the existence of a mechanism controlling bud size in G2/M that prevents premature onset of anaphase, and controls the overall size variability. While most G1 mutants do not display impaired size homeostasis, mutants in which cyclin B-Cdk regulation is altered display large size variability. Our study thus demonstrates that size homeostasis is not controlled by a G1-specific mechanism alone but is likely to be an emergent property resulting from the integration of several mechanisms that coordinate cell and bud growth with division.
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Affiliation(s)
- Cecilia Garmendia-Torres
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U1258, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Olivier Tassy
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U1258, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Audrey Matifas
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U1258, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Nacho Molina
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U1258, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Gilles Charvin
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.,Centre National de la Recherche Scientifique, UMR7104, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, U1258, Illkirch, France.,Université de Strasbourg, Illkirch, France
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15
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Goulev Y, Morlot S, Matifas A, Huang B, Molin M, Toledano MB, Charvin G. Nonlinear feedback drives homeostatic plasticity in H 2O 2 stress response. eLife 2017; 6. [PMID: 28418333 PMCID: PMC5438251 DOI: 10.7554/elife.23971] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2016] [Accepted: 04/14/2017] [Indexed: 12/20/2022] Open
Abstract
Homeostatic systems that rely on genetic regulatory networks are intrinsically limited by the transcriptional response time, which may restrict a cell’s ability to adapt to unanticipated environmental challenges. To bypass this limitation, cells have evolved mechanisms whereby exposure to mild stress increases their resistance to subsequent threats. However, the mechanisms responsible for such adaptive homeostasis remain largely unknown. Here, we used live-cell imaging and microfluidics to investigate the adaptive response of budding yeast to temporally controlled H2O2 stress patterns. We demonstrate that acquisition of tolerance is a systems-level property resulting from nonlinearity of H2O2 scavenging by peroxiredoxins and our study reveals that this regulatory scheme induces a striking hormetic effect of extracellular H2O2 stress on replicative longevity. Our study thus provides a novel quantitative framework bridging the molecular architecture of a cellular homeostatic system to the emergence of nonintuitive adaptive properties. DOI:http://dx.doi.org/10.7554/eLife.23971.001 Harmful external conditions, such as extreme heat or radiation, can cause stress to cells that may lead to permanent damage and even death. Cell stress is responsible for some cancers and degenerative diseases, and is involved in the process of aging. Cells respond to stress by modifying their activities in order to prevent damage from occurring. Some studies have suggested that the ability of cells to survive a stressful situation might depend both on the severity of the stress and also on the way in which the stress is applied. For example, the stress might start suddenly or develop more gradually. Cells exposed to a mild level of stress develop a tolerance that enables them to survive stronger doses of the same stress in the future. However, it is not clear how cells acquire such tolerance, and whether mild levels of stress can have more general benefits to cells, such as increased lifespan. Hydrogen peroxide and other “oxidative” compounds play important roles in cells, but they are also capable of causing damage so their levels must be tightly controlled. Goulev et al. developed a “microfluidic” device to study the effects of oxidative stress on yeast cells. The device made it possible to precisely control the level of hydrogen peroxide in the cells’ environment while monitoring the cells’ stress responses. The experiments show that exposing yeast cells to gradually increasing levels of hydrogen peroxide can train the cells to be able to survive when they are exposed to high levels of this compound. This ability depends on the activity of specific enzymes called peroxidases that are known to be able to destroy hydrogen peroxide inside the cells. The experiments suggest that gradually increasing levels of hydrogen peroxide trigger increases in the production of peroxidases that protect the cells against future oxidative stress. Further experiments show that even a very low dose of hydrogen peroxide is sufficient to activate the production of the enzymes, leading to an increase in the lifespan of the cells. A future challenge will be to investigate whether the principles identified in this work also apply to other stress responses in yeast. DOI:http://dx.doi.org/10.7554/eLife.23971.002
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Affiliation(s)
- Youlian Goulev
- Developmental Biology and Stem Cells Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Strasbourg, France.,Centre National de la Recherche Scientifique, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Sandrine Morlot
- Developmental Biology and Stem Cells Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Strasbourg, France.,Centre National de la Recherche Scientifique, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Audrey Matifas
- Developmental Biology and Stem Cells Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Strasbourg, France.,Centre National de la Recherche Scientifique, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, Illkirch, France.,Université de Strasbourg, Illkirch, France
| | - Bo Huang
- Oxidative Stress and Cancer, IBITECS, SBIGEM, CEA-Saclay, Gif-sur-Yvette, France
| | - Mikael Molin
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Michel B Toledano
- Oxidative Stress and Cancer, IBITECS, SBIGEM, CEA-Saclay, Gif-sur-Yvette, France
| | - Gilles Charvin
- Developmental Biology and Stem Cells Department, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Strasbourg, France.,Centre National de la Recherche Scientifique, Illkirch, France.,Institut National de la Santé et de la Recherche Médicale, Illkirch, France.,Université de Strasbourg, Illkirch, France
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16
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Paoletti C, Quintin S, Matifas A, Charvin G. Kinetics of Formation and Asymmetrical Distribution of Hsp104-Bound Protein Aggregates in Yeast. Biophys J 2016; 110:1605-1614. [PMID: 27074685 DOI: 10.1016/j.bpj.2016.02.034] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 02/17/2016] [Accepted: 02/23/2016] [Indexed: 02/05/2023] Open
Abstract
Budding yeast cells have a finite replicative life span; that is, a mother cell produces only a limited number of daughter cells before it slows division and dies. Despite the gradual aging of the mother cell, all daughters are born rejuvenated and enjoy a full replicative lifespan. It has been proposed that entry of mother cells into senescence is driven by the progressive accumulation and retention of damaged material, including protein aggregates. This additionally allows the daughter cells to be born damage free. However, the mechanism underlying such asymmetrical segregation of protein aggregates by mother and daughter cells remains controversial, in part because of the difficulties inherent in tracking the dynamics and fate of protein aggregates in vivo. To overcome such limitations, we have developed single-cell real-time imaging methodology to track the formation of heat-induced protein aggregates in otherwise unperturbed dividing cells. By combining the imaging data with a simple computational model of protein aggregation, we show that the establishment of asymmetrical partitioning of protein aggregates upon division is driven by the large bud-specific dilution rate associated with polarized growth and the absence of significant mother/bud exchange of protein aggregates during the budded phase of the cell cycle. To our knowledge, this study sheds new light on the mechanism of establishment of a segregation bias, which can be accounted for by simple physical arguments.
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Affiliation(s)
- Camille Paoletti
- Development and Stem Cells Department, IGBMC, CNRS UMR 7104, INSERM U964, Université de Strasbourg, Illkirch, France
| | - Sophie Quintin
- Development and Stem Cells Department, IGBMC, CNRS UMR 7104, INSERM U964, Université de Strasbourg, Illkirch, France
| | - Audrey Matifas
- Development and Stem Cells Department, IGBMC, CNRS UMR 7104, INSERM U964, Université de Strasbourg, Illkirch, France
| | - Gilles Charvin
- Development and Stem Cells Department, IGBMC, CNRS UMR 7104, INSERM U964, Université de Strasbourg, Illkirch, France.
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17
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Heckel E, Boselli F, Roth S, Krudewig A, Belting HG, Charvin G, Vermot J. Oscillatory Flow Modulates Mechanosensitive klf2a Expression through trpv4 and trpp2 during Heart Valve Development. Curr Biol 2015; 25:1354-61. [DOI: 10.1016/j.cub.2015.03.038] [Citation(s) in RCA: 99] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2014] [Revised: 02/08/2015] [Accepted: 03/20/2015] [Indexed: 10/23/2022]
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18
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Abstract
By implementing an external feedback loop one can tightly control the expression of a gene over many cell generations with quantitative accuracy. Controlling precisely the level of a protein of interest will be useful to probe quantitatively the dynamical properties of cellular processes and to drive complex, synthetically-engineered networks. In this chapter we describe a platform for real-time closed-loop control of gene expression in yeast that integrates microscopy for monitoring gene expression at the cell level, microfluidics to manipulate the cells environment, and original software for automated imaging, quantification, and model predictive control. By using an endogenous osmo-stress responsive promoter and playing with the osmolarity of the cells environment, we demonstrate that long-term control can indeed be achieved for both time-constant and time-varying target profiles, at the population level, and even at the single-cell level.
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Affiliation(s)
- Jannis Uhlendorf
- INRIA Paris-Rocquencourt, Domaine de Voluceau, Rocquencourt - BP 105, 78153, Le Chesnay, France
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19
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Meitinger F, Khmelinskii A, Morlot S, Kurtulmus B, Palani S, Andres-Pons A, Hub B, Knop M, Charvin G, Pereira G. A memory system of negative polarity cues prevents replicative aging. Cell 2014; 159:1056-1069. [PMID: 25416945 DOI: 10.1016/j.cell.2014.10.014] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 08/20/2014] [Accepted: 09/25/2014] [Indexed: 10/24/2022]
Abstract
Cdc42 is a highly conserved master regulator of cell polarity. Here, we investigated the mechanism by which yeast cells never re-establish polarity at cortical sites (cytokinesis remnants [CRMs]) that have previously supported Cdc42-mediated growth as a paradigm to mechanistically understand how Cdc42-inhibitory polarity cues are established. We revealed a two-step mechanism of loading the Cdc42 antagonist Nba1 into CRMs to mark these compartments as refractory for a second round of Cdc42 activation. Our data indicate that Nba1 together with a cortically tethered adaptor protein confers memory of previous polarization events to translate this spatial legacy into a biochemical signal that ensures the local singularity of Cdc42 activation. "Memory loss" mutants that repeatedly use the same polarity site over multiple generations display nuclear segregation defects and a shorter lifespan. Our work thus established CRMs as negative polarity cues that prevent Cdc42 reactivation to sustain the fitness of replicating cells.
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Affiliation(s)
- Franz Meitinger
- Molecular Biology of Centrosomes and Cilia, German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 581, Heidelberg 69120, Germany
| | - Anton Khmelinskii
- Center for Molecular Biology of the University of Heidelberg (ZMBH), DKFZ-ZMBH Alliance, 69120 Heidelberg, Germany
| | - Sandrine Morlot
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 1 Rue Laurent Fries, 67400 Illkirch Cedex, France
| | - Bahtiyar Kurtulmus
- Molecular Biology of Centrosomes and Cilia, German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 581, Heidelberg 69120, Germany
| | - Saravanan Palani
- Molecular Biology of Centrosomes and Cilia, German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 581, Heidelberg 69120, Germany
| | - Amparo Andres-Pons
- Molecular Biology of Centrosomes and Cilia, German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 581, Heidelberg 69120, Germany
| | - Birgit Hub
- German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
| | - Michael Knop
- Center for Molecular Biology of the University of Heidelberg (ZMBH), DKFZ-ZMBH Alliance, 69120 Heidelberg, Germany
| | - Gilles Charvin
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 1 Rue Laurent Fries, 67400 Illkirch Cedex, France
| | - Gislene Pereira
- Molecular Biology of Centrosomes and Cilia, German Cancer Research Center (DKFZ), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 581, Heidelberg 69120, Germany.
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20
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Goetz JG, Steed E, Ferreira RR, Roth S, Ramspacher C, Boselli F, Charvin G, Liebling M, Wyart C, Schwab Y, Vermot J. Endothelial cilia mediate low flow sensing during zebrafish vascular development. Cell Rep 2014; 6:799-808. [PMID: 24561257 DOI: 10.1016/j.celrep.2014.01.032] [Citation(s) in RCA: 148] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Revised: 12/20/2013] [Accepted: 01/23/2014] [Indexed: 11/16/2022] Open
Abstract
VIDEO ABSTRACT The pattern of blood flow has long been thought to play a significant role in vascular morphogenesis, yet the flow-sensing mechanism that is involved at early embryonic stages, when flow forces are low, remains unclear. It has been proposed that endothelial cells use primary cilia to sense flow, but this has never been tested in vivo. Here we show, by noninvasive, high-resolution imaging of live zebrafish embryos, that endothelial cilia progressively deflect at the onset of blood flow and that the deflection angle correlates with calcium levels in endothelial cells. We demonstrate that alterations in shear stress, ciliogenesis, or expression of the calcium channel PKD2 impair the endothelial calcium level and both increase and perturb vascular morphogenesis. Altogether, these results demonstrate that endothelial cilia constitute a highly sensitive structure that permits the detection of low shear forces during vascular morphogenesis.
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Affiliation(s)
- Jacky G Goetz
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, 67404 Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, 67404 Illkirch, France; Université de Strasbourg, 67404 Illkirch, France
| | - Emily Steed
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, 67404 Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, 67404 Illkirch, France; Université de Strasbourg, 67404 Illkirch, France
| | - Rita R Ferreira
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, 67404 Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, 67404 Illkirch, France; Université de Strasbourg, 67404 Illkirch, France
| | - Stéphane Roth
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, 67404 Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, 67404 Illkirch, France; Université de Strasbourg, 67404 Illkirch, France
| | - Caroline Ramspacher
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, 67404 Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, 67404 Illkirch, France; Université de Strasbourg, 67404 Illkirch, France
| | - Francesco Boselli
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, 67404 Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, 67404 Illkirch, France; Université de Strasbourg, 67404 Illkirch, France
| | - Gilles Charvin
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, 67404 Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, 67404 Illkirch, France; Université de Strasbourg, 67404 Illkirch, France
| | - Michael Liebling
- Department of Electrical and Computer Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106, USA
| | - Claire Wyart
- Institut du Cerveau et de la Moelle Épinière (ICM), Hôpital de la Pitié-Salpêtrière, 75013 Paris, France; Inserm UMRS 1127, 75013 Paris, France; CNRS UMR 7225, 75013 Paris, France; UPMC University of Paris 06, 75005 Paris, France
| | - Yannick Schwab
- Electron Microscopy Core Facility, Cell Biology and Biophysics Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Julien Vermot
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France; Centre National de la Recherche Scientifique, UMR7104, 67404 Illkirch, France; Institut National de la Santé et de la Recherche Médicale, U964, 67404 Illkirch, France; Université de Strasbourg, 67404 Illkirch, France.
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21
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Fehrmann S, Paoletti C, Goulev Y, Ungureanu A, Aguilaniu H, Charvin G. Aging yeast cells undergo a sharp entry into senescence unrelated to the loss of mitochondrial membrane potential. Cell Rep 2013; 5:1589-99. [PMID: 24332850 DOI: 10.1016/j.celrep.2013.11.013] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Revised: 10/23/2013] [Accepted: 11/07/2013] [Indexed: 11/26/2022] Open
Abstract
In budding yeast, a mother cell can produce a finite number of daughter cells before it stops dividing and dies. Such entry into senescence is thought to result from a progressive decline in physiological function, including a loss of mitochondrial membrane potential (ΔΨ). Here, we developed a microfluidic device to monitor the dynamics of cell division and ΔΨ in real time at single-cell resolution. We show that cells do not enter senescence gradually but rather undergo an abrupt transition to a slowly dividing state. Moreover, we demonstrate that the decline in ΔΨ, which is observed only in a fraction of cells, is not responsible for entry into senescence. Rather, the loss of ΔΨ is an age-independent and heritable process that leads to clonal senescence and is therefore incompatible with daughter cell rejuvenation. These results emphasize the importance of quantitative single-cell measurements to decipher the causes of cellular aging.
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Affiliation(s)
- Steffen Fehrmann
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 1 Rue Laurent Fries, 67400 Illkirch Cedex, France
| | - Camille Paoletti
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 1 Rue Laurent Fries, 67400 Illkirch Cedex, France
| | - Youlian Goulev
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 1 Rue Laurent Fries, 67400 Illkirch Cedex, France
| | | | - Hugo Aguilaniu
- LBMC, ENS Lyon, 46 Allée d'Italie, 69364 Lyon Cedex 07, France
| | - Gilles Charvin
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, 1 Rue Laurent Fries, 67400 Illkirch Cedex, France.
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22
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Anton H, Harlepp S, Ramspacher C, Wu D, Monduc F, Bhat S, Liebling M, Paoletti C, Charvin G, Freund JB, Vermot J. Pulse propagation by a capacitive mechanism drives embryonic blood flow. Development 2013; 140:4426-34. [DOI: 10.1242/dev.096768] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Pulsatile flow is a universal feature of the blood circulatory system in vertebrates and can lead to diseases when abnormal. In the embryo, blood flow forces stimulate vessel remodeling and stem cell proliferation. At these early stages, when vessels lack muscle cells, the heart is valveless and the Reynolds number (Re) is low, few details are available regarding the mechanisms controlling pulses propagation in the developing vascular network. Making use of the recent advances in optical-tweezing flow probing approaches, fast imaging and elastic-network viscous flow modeling, we investigated the blood-flow mechanics in the zebrafish main artery and show how it modifies the heart pumping input to the network. The movement of blood cells in the embryonic artery suggests that elasticity of the network is an essential factor mediating the flow. Based on these observations, we propose a model for embryonic blood flow where arteries act like a capacitor in a way that reduces heart effort. These results demonstrate that biomechanics is key in controlling early flow propagation and argue that intravascular elasticity has a role in determining embryonic vascular function.
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Affiliation(s)
- Halina Anton
- Institut de Génétique Moleculaire et Cellulaire, CNRS/INSERM/UdS, 1 rue Laurent Fries, BP10142, 67404 Illkirch, France
| | - Sebastien Harlepp
- Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, UMR 7504, 23 rue du Loess, 67034 Strasbourg, France
| | - Caroline Ramspacher
- Institut de Génétique Moleculaire et Cellulaire, CNRS/INSERM/UdS, 1 rue Laurent Fries, BP10142, 67404 Illkirch, France
| | - Dave Wu
- Institut de Génétique Moleculaire et Cellulaire, CNRS/INSERM/UdS, 1 rue Laurent Fries, BP10142, 67404 Illkirch, France
| | - Fabien Monduc
- Institut de Génétique Moleculaire et Cellulaire, CNRS/INSERM/UdS, 1 rue Laurent Fries, BP10142, 67404 Illkirch, France
| | - Sandeep Bhat
- Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, USA
| | - Michael Liebling
- Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, USA
| | - Camille Paoletti
- Institut de Génétique Moleculaire et Cellulaire, CNRS/INSERM/UdS, 1 rue Laurent Fries, BP10142, 67404 Illkirch, France
| | - Gilles Charvin
- Institut de Génétique Moleculaire et Cellulaire, CNRS/INSERM/UdS, 1 rue Laurent Fries, BP10142, 67404 Illkirch, France
| | | | - Julien Vermot
- Institut de Génétique Moleculaire et Cellulaire, CNRS/INSERM/UdS, 1 rue Laurent Fries, BP10142, 67404 Illkirch, France
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Seol Y, Hardin AH, Strub MP, Charvin G, Neuman KC. Comparison of DNA decatenation by Escherichia coli topoisomerase IV and topoisomerase III: implications for non-equilibrium topology simplification. Nucleic Acids Res 2013; 41:4640-9. [PMID: 23460205 PMCID: PMC3632123 DOI: 10.1093/nar/gkt136] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Type II topoisomerases are essential enzymes that regulate DNA topology through a strand-passage mechanism. Some type II topoisomerases relax supercoils, unknot and decatenate DNA to below thermodynamic equilibrium. Several models of this non-equilibrium topology simplification phenomenon have been proposed. The kinetic proofreading (KPR) model postulates that strand passage requires a DNA-bound topoisomerase to collide twice in rapid succession with a second DNA segment, implying a quadratic relationship between DNA collision frequency and relaxation rate. To test this model, we used a single-molecule assay to measure the unlinking rate as a function of DNA collision frequency for Escherichia coli topoisomerase IV (topo IV) that displays efficient non-equilibrium topology simplification activity, and for E. coli topoisomerase III (topo III), a type IA topoisomerase that unlinks and unknots DNA to equilibrium levels. Contrary to the predictions of the KPR model, topo IV and topo III unlinking rates were linearly related to the DNA collision frequency. Furthermore, topo III exhibited decatenation activity comparable with that of topo IV, supporting proposed roles for topo III in DNA segregation. This study enables us to rule out the KPR model for non-equilibrium topology simplification. More generally, we establish an experimental approach to systematically control DNA collision frequency.
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Affiliation(s)
- Yeonee Seol
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
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Seol Y, Hardin AH, Charvin G, Neuman KC. Non-Equilibrium Topology Simplification by Type II Topoisomerases: A Test of Kinetic Proofreading. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.2667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022] Open
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Charvin G. Réflexions autour de l’épreuve du temps. Axe 5 du Plan cancer 2009–2013 : « Vivre pendant et après la maladie ». ONCOLOGIE 2011. [DOI: 10.1007/s10269-011-2032-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Abstract
In this issue, Trunnell et al. (2011) show that in mitotic entry the positive feedback that drives the activation of cyclin-dependent kinase (Cdk) involves a very ultrasensitive step of phosphorylation of Cdc25C by Cdk, thus strongly contributing to the switch-like behavior of this essential cell-cycle transition.
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Affiliation(s)
- Youlian Goulev
- Institut de Biologie Moléculaire et Cellulaire, 1 Rue Laurent Fries, 67400 Illkirch Cedex, France
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Bai L, Charvin G. [Nucleosome-depleted regions in promoters: consequences on robustness of transcriptional activation]. Med Sci (Paris) 2010; 26:1035-7. [PMID: 21187039 DOI: 10.1051/medsci/201026121035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Bai L, Charvin G, Siggia ED, Cross FR. Nucleosome-depleted regions in cell-cycle-regulated promoters ensure reliable gene expression in every cell cycle. Dev Cell 2010; 18:544-55. [PMID: 20412770 DOI: 10.1016/j.devcel.2010.02.007] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Revised: 12/17/2009] [Accepted: 02/24/2010] [Indexed: 12/21/2022]
Abstract
Many promoters in eukaryotes have nucleosome-depleted regions (NDRs) containing transcription factor binding sites. However, the functional significance of NDRs is not well understood. Here, we examine NDR function in two cell cycle-regulated promoters, CLN2pr and HOpr, by varying nucleosomal coverage of the binding sites of their activator, Swi4/Swi6 cell-cycle box (SCB)-binding factor (SBF), and probing the corresponding transcriptional activity in individual cells with time-lapse microscopy. Nucleosome-embedded SCBs do not significantly alter peak expression levels. Instead, they induce bimodal, "on/off" activation in individual cell cycles, which displays short-term memory, or epigenetic inheritance, from the mother cycle. In striking contrast, the same SCBs localized in NDR lead to highly reliable activation, once in every cell cycle. We further demonstrate that the high variability in Cln2p expression induced by the nucleosomal SCBs reduces cell fitness. Therefore, we propose that the NDR function in limiting stochasticity in gene expression promotes the ubiquity and conservation of promoter NDR. PAPERCLIP:
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Affiliation(s)
- Lu Bai
- Center for Studies in Physics and Biology, The Rockefeller University, New York, NY 10065, USA.
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Abstract
Budding yeast cells irreversibly commit to a new division cycle at a regulatory transition called Start. This essential decision-making step involves the activation of the SBF/MBF transcription factors. SBF/MBF promote expression of the G1 cyclins encoded by CLN1 and CLN2. Cln1,2 can activate their own expression by inactivating the Whi5 repressor of SBF/MBF. The resulting transcriptional positive feedback provides an appealing, but as yet unproven, candidate for generating irreversibility of Start. Here, we investigate the logic of the Start regulatory module by quantitative single-cell time-lapse microscopy, using strains in which expression of key regulators is efficiently controlled by changes of inducers in a microfluidic chamber. We show that Start activation is ultrasensitive to G1 cyclin. In the absence of CLN1,2-dependent positive feedback, we observe that Start transit is reversible, due to reactivation of the Whi5 transcriptional repressor. Introduction of the positive feedback loop makes Whi5 inactivation and Start activation irreversible, which therefore guarantees unidirectional entry into S phase. A simple mathematical model to describe G1 cyclin turn on at Start, entirely constrained by empirically measured parameters, shows that the experimentally measured ultrasensitivity and transcriptional positive feedback are necessary and sufficient dynamical characteristics to make the Start transition a bistable and irreversible switch. Our study thus demonstrates that Start irreversibility is a property that arises from the architecture of the system (Whi5/SBF/Cln2 loop), rather than the consequence of the regulation of a single component (e.g., irreversible protein degradation).
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Affiliation(s)
- Gilles Charvin
- Laboratoire Joliot-Curie, Ecole Normale Supérieure, Lyon, France.
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Abstract
During the past 10 years, major developments in live-cell imaging methods have accompanied growing interest in the application of microfluidic techniques to biological imaging. The broad design possibilities of microfabrication and its relative ease of implementation have led to the development of a number of powerful imaging assays. Specifically, there has been great interest in the development of devices in which single cells can be followed in real-time over the course of several generations while the growth environment is changed. With standard perfusion chambers, the duration of a typical experiment is limited to one cell generation time. Using microfluidics, however, long-term imaging setups have been developed which can measure the effects of temporally controlled gene expression or pathway activation while tracking individual cells over the course of many generations. In this paper, we describe the details of fabricating such a microfluidic device for the purpose of long-term imaging of proliferating cells, the assembly of its individual components into a complete device, and then we give an example of how to use such a device to monitor real-time changes in gene expression in budding yeast. Our goal is to make this technique accessible to cell biology researchers without prior experience with microfluidic systems.
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Affiliation(s)
- Gilles Charvin
- Laboratoire Joliot-Curie & Laboratoire de Physique, Ecole Normale Supérieure, Lyon, France
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Bai L, Charvin G, Siggia E, Cross F. Nucleosome Depleted Region In Promoter Improves Robustness In Gene Expression. Biophys J 2009. [DOI: 10.1016/j.bpj.2008.12.3715] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Charvin G, Cross FR, Siggia ED. A microfluidic device for temporally controlled gene expression and long-term fluorescent imaging in unperturbed dividing yeast cells. PLoS One 2008; 3:e1468. [PMID: 18213377 PMCID: PMC2194624 DOI: 10.1371/journal.pone.0001468] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2007] [Accepted: 12/18/2007] [Indexed: 11/28/2022] Open
Abstract
Background Imaging single cells with fluorescent markers over multiple cell cycles is a powerful tool for unraveling the mechanism and dynamics of the cell cycle. Over the past ten years, microfluidic techniques in cell biology have emerged that allow for good control of growth environment. Yet the control and quantification of transient gene expression in unperturbed dividing cells has received less attention. Methodology/Principal Findings Here, we describe a microfluidic flow cell to grow Saccharomyces Cerevisiae for more than 8 generations (≈12 hrs) starting with single cells, with controlled flow of the growth medium. This setup provides two important features: first, cells are tightly confined and grow in a remarkably planar array. The pedigree can thus be determined and single-cell fluorescence measured with 3 minutes resolution for all cells, as a founder cell grows to a micro-colony of more than 200 cells. Second, we can trigger and calibrate rapid and transient gene expression using reversible administration of inducers that control the GAL1 or MET3 promoters. We then show that periodic 10–20 minutes gene induction pulses can drive many cell division cycles with complete coherence across the cell cluster, with either a G1/S trigger (cln1 cln2 cln3 MET3-CLN2) or a mitotic trigger (cdc20 GALL-CDC20). Conclusions/Significance In addition to evident cell cycle applications, this device can be used to directly measure the amount and duration of any fluorescently scorable signal-transduction or gene-induction response over a long time period. The system allows direct correlation of cell history (e.g., hysteresis or epigenetics) or cell cycle position with the measured response.
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Affiliation(s)
- Gilles Charvin
- Center For Studies in Physics and Biology, The Rockefeller University, New York, New York, USA.
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Laurent M, Charvin G, Guespin-Michel J. Bistability and hysteresis in epigenetic regulation of the lactose operon. Since Delbrück, a long series of ignored models. Cell Mol Biol (Noisy-le-grand) 2005; 51:583-94. [PMID: 16359608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2005] [Accepted: 04/01/2005] [Indexed: 05/05/2023]
Abstract
Bistability is the capacity of a system to switch in an "all-or-none" manner between alternative steady states. This powerful concept originates from the analysis of non-linear equations driving open systems. It is one of the various patterns of regulation associated with a particular class of dynamic structures that Glansdorff and Prigogine baptised "dissipative structures". The idea of discontinuous transitions between alternative states was first formulated much earlier, by Delbrück, in 1949. Cohn and Horibata and Novick and Weiner confirmed that such transitions occur in experiments on the lactose operon carried out ten years later. Modelling with non-linear differential equations made it possible to simulate the dynamic behaviour of the lac operon, and modelling by asynchronous logical analysis elucidated the determinant role played by positive feedback circuits in the emergence of multistationarity. Nevertheless, these studies were largely ignored until the recent demonstration of the hysteretic nature of the bistable transition between alternative states of the lac operon. As originally suggested by Delbrück, the pattern of lactose consumption adopted by the bacterium is controlled epigenetically rather than genetically: the true key determinant is the direction of change of an environmental variable with respect to the structural components of the operon.
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Affiliation(s)
- M Laurent
- Dynamique Cellulaire et Modélisation, UMR 8080, Bât. 440, Université Paris-Sud, 91405 Orsay Cedex, France.
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Abstract
The recent development of new techniques to manipulate single DNA molecules has opened new opportunities for the study of the enzymes that control DNA topology: the type I and II topoisomerases. These single-molecule assays provide a unique way to study the uncoiling of single supercoiled DNA molecules and the unlinking of two intertwined DNAs. They allow for a detailed characterization of the activity of topoisomerases, including the processivity, the chiral discrimination, and the dependence of their enzymatic rate on ATP concentration, degree of supercoiling, and the tension in the molecule. These results shed new light on the mechanism of these enzymes and their function in vivo.
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Affiliation(s)
- G Charvin
- LPS, ENS, UMR 8550 CNRS, 75231 Paris Cedex 05, France.
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Abstract
Escherichia coli topoisomerase IV (Topo IV) is an essential ATP-dependent enzyme that unlinks sister chromosomes during replication and efficiently removes positive but not negative supercoils. In this article, we investigate the binding properties of Topo IV onto DNA in the absence of ATP using a single molecule micromanipulation setup. We find that the enzyme binds cooperatively (Hill coefficient alpha approximately 4) with supercoiled DNA, suggesting that the Topo IV subunits assemble upon binding onto DNA. It interacts preferentially with (+) rather than (-) supercoiled DNA (Kd+=0.15 nM, Kd-=0.23 nM) and more than two orders-of-magnitude more weakly with relaxed DNA (Kd0 approximately 36 nM). Like gyrase but unlike the eukaryotic Topo II, Topo IV bends DNA with a radius 0= 6.4 nm and locally changes its twist and/or its writhe by 0.16 turn per bound complex. We estimate its free energy of binding and study the dynamics of interaction of Topo IV with DNA at the binding threshold. We find that the protein/DNA complex alternates between two states: a weakly bound state where it stays with probability p = 0.89 and a strongly bound state (with probability p = 0.11). The methodology introduced here to characterize the Topo IV/DNA complex is very general and could be used to study other DNA/protein complexes.
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Affiliation(s)
- G Charvin
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, UMR 8550 Centre National de la Recherche Scientifique, Paris, France.
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Abstract
DNA encounters topological problems in vivo because of its extended double-helical structure. As a consequence, the semiconservative mechanism of DNA replication leads to the formation of DNA braids or catenanes, which have to be removed for the completion of cell division. To get a better understanding of these structures, we have studied the elastic behavior of two braided nicked DNA molecules using a magnetic trap apparatus. The experimental data let us identify and characterize three regimes of braiding: a slightly twisted regime before the formation of the first crossing, followed by genuine braids which, at large braiding number, buckle to form plectonemes. Two different approaches support and quantify this characterization of the data. First, Monte Carlo (MC) simulations of braided DNAs yield a full description of the molecules' behavior and their buckling transition. Second, modeling the braids as a twisted swing provides a good approximation of the elastic response of the molecules as they are intertwined. Comparisons of the experiments and the MC simulations with this analytical model allow for a measurement of the diameter of the braids and its dependence upon entropic and electrostatic repulsive interactions. The MC simulations allow for an estimate of the effective torsional constant of the braids (at a stretching force F = 2 pN): C(b) approximately 48 nm (as compared with C approximately 100 nm for a single unnicked DNA). Finally, at low salt concentrations and for sufficiently large number of braids, the diameter of the braided molecules is observed to collapse to that of double-stranded DNA. We suggest that this collapse is due to the partial melting and fraying of the two nicked molecules and the subsequent right- or left-handed intertwining of the stretched single strands.
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Affiliation(s)
- G Charvin
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, UMR 8550, Centre National de la Recherche Scientifique, Paris, France.
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Abstract
Type-II topoisomerases are responsible for untangling DNA during replication by removing supercoiled and interlinked DNA structures. Using a single-molecule micromanipulation setup, we follow the real-time decatenation of two mechanically braided DNA molecules by Drosophila melanogaster topoisomerase (Topo) II and Escherichia coli Topo IV. Although Topo II relaxes left-handed (L) and right-handed (R-) braids similarly at a rate of approximately 2.9 s-1, Topo IV has a marked preference for L-braids, which it relaxes completely and processively at a rate of approximately 2.4 s-1. However, Topo IV can unlink R-braids at about half that rate when they supercoil to form L-plectonemes. These results imply that the preferred substrate for unlinking by Topo IV has the symmetry of an L-crossing and shed new light on the decatenation of daughter strands during DNA replication, which are usually assumed to be linked in an R-braid.
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Affiliation(s)
- G Charvin
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Unité Mixte de Recherche 8550 Centre National de la Recherche Scientifique, 24 Rue Lhomond, 75231 Paris Cedex 05, France.
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