1
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Sequeira AN, O’Keefe IP, Katju V, Bergthorsson U. Friend turned foe: selfish behavior of a spontaneously arising mitochondrial deletion in an experimentally evolved Caenorhabditis elegans population. G3 (BETHESDA, MD.) 2024; 14:jkae018. [PMID: 38261394 PMCID: PMC11090458 DOI: 10.1093/g3journal/jkae018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 01/11/2024] [Accepted: 01/16/2024] [Indexed: 01/24/2024]
Abstract
Selfish mitochondrial DNA (mtDNA) mutations are variants that can proliferate within cells and enjoy a replication or transmission bias without fitness benefits for the host. mtDNA deletions in Caenorhabditis elegans can reach high heteroplasmic frequencies despite significantly reducing fitness, illustrating how new mtDNA variants can give rise to genetic conflict between different levels of selection and between the nuclear and mitochondrial genomes. During a mutation accumulation experiment in C. elegans, a 1,034-bp deletion originated spontaneously and reached an 81.7% frequency within an experimental evolution line. This heteroplasmic mtDNA deletion, designated as meuDf1, eliminated portions of 2 protein-coding genes (coxIII and nd4) and tRNA-thr in entirety. mtDNA copy number in meuDf1 heteroplasmic individuals was 35% higher than in individuals with wild-type mitochondria. After backcrossing into a common genetic background, the meuDf1 mitotype was associated with reduction in several fitness traits and independent competition experiments found a 40% reduction in composite fitness. Experiments that relaxed individual selection by single individual bottlenecks demonstrated that the deletion-bearing mtDNA possessed a strong transmission bias, thereby qualifying it as a novel selfish mitotype.
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Affiliation(s)
- Abigail N Sequeira
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
- Department of Biology, Pennsylvania State University, 208 Mueller Laboratory, University Park, PA 16802, USA
| | - Ian P O’Keefe
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
- Department of Biochemistry and Molecular Biology, University of Maryland, 655 W. Baltimore Street, Baltimore, MD 21201, USA
| | - Vaishali Katju
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
- Program in Evolutionary Biology, Department of Ecology and Genetics (IEG), Evolutionsbiologiskt centrum, Norbyvägen 18D, Uppsala University, 752 36 Uppsala, Sweden
| | - Ulfar Bergthorsson
- Department of Veterinary Integrative Biosciences, Texas A&M University, 402 Raymond Stotzer Parkway, College Station, TX 77845, USA
- Program in Evolutionary Biology, Department of Ecology and Genetics (IEG), Evolutionsbiologiskt centrum, Norbyvägen 18D, Uppsala University, 752 36 Uppsala, Sweden
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2
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Spinazzola A, Perez-Rodriguez D, Ježek J, Holt IJ. Mitochondrial DNA competition: starving out the mutant genome. Trends Pharmacol Sci 2024; 45:225-242. [PMID: 38402076 DOI: 10.1016/j.tips.2024.01.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2023] [Revised: 01/11/2024] [Accepted: 01/22/2024] [Indexed: 02/26/2024]
Abstract
High levels of pathogenic mitochondrial DNA (mtDNA) variants lead to severe genetic diseases, and the accumulation of such mutants may also contribute to common disorders. Thus, selecting against these mutants is a major goal in mitochondrial medicine. Although mutant mtDNA can drift randomly, mounting evidence indicates that active forces play a role in the selection for and against mtDNA variants. The underlying mechanisms are beginning to be clarified, and recent studies suggest that metabolic cues, including fuel availability, contribute to shaping mtDNA heteroplasmy. In the context of pathological mtDNAs, remodeling of nutrient metabolism supports mitochondria with deleterious mtDNAs and enables them to outcompete functional variants owing to a replicative advantage. The elevated nutrient requirement represents a mutant Achilles' heel because small molecules that restrict nutrient consumption or interfere with nutrient sensing can purge cells of deleterious mtDNAs and restore mitochondrial respiration. These advances herald the dawn of a new era of small-molecule therapies to counteract pathological mtDNAs.
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Affiliation(s)
- Antonella Spinazzola
- Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, Royal Free Campus, London NW3 2PF, UK.
| | - Diego Perez-Rodriguez
- Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, Royal Free Campus, London NW3 2PF, UK
| | - Jan Ježek
- Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, Royal Free Campus, London NW3 2PF, UK
| | - Ian J Holt
- Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, Royal Free Campus, London NW3 2PF, UK; Biodonostia Health Research Institute, 20014 San Sebastián, Spain; IKERBASQUE (Basque Foundation for Science), 48013 Bilbao, Spain; CIBERNED (Center for Networked Biomedical Research on Neurodegenerative Diseases, Ministry of Economy and Competitiveness, Institute Carlos III), 28031 Madrid, Spain; Universidad de País Vasco, Barrio Sarriena s/n, 48940 Leioa, Bilbao, Spain.
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3
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Onraet T, Zuryn S. C. elegans as a model to study mitochondrial biology and disease. Semin Cell Dev Biol 2024; 154:48-58. [PMID: 37149409 DOI: 10.1016/j.semcdb.2023.04.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 04/18/2023] [Accepted: 04/26/2023] [Indexed: 05/08/2023]
Abstract
Mitochondria perform a myriad of essential functions that ensure organismal homeostasis, including maintaining bioenergetic capacity, sensing and signalling the presence of pathogenic threats, and determining cell fate. Their function is highly dependent on mitochondrial quality control and the appropriate regulation of mitochondrial size, shape, and distribution during an entire lifetime, as well as their inheritance across generations. The roundworm Caenorhabditis elegans has emerged as an ideal model organism through which to study mitochondria. The remarkable conservation of mitochondrial biology has allowed C. elegans researchers to investigate complex processes that are challenging to study in higher organisms. In this review, we explore the key recent contributions of C. elegans to mitochondrial biology through the lens of mitochondrial dynamics, organellar removal, and mitochondrial inheritance, as well as their involvement in immune responses, various types of stress, and transgenerational signalling.
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Affiliation(s)
- Tessa Onraet
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane 4072, Australia
| | - Steven Zuryn
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane 4072, Australia.
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4
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Agarwala S, Dhabal S, Mitra K. Significance of quantitative analyses of the impact of heterogeneity in mitochondrial content and shape on cell differentiation. Open Biol 2024; 14:230279. [PMID: 38228170 PMCID: PMC10791538 DOI: 10.1098/rsob.230279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2023] [Accepted: 12/15/2023] [Indexed: 01/18/2024] Open
Abstract
Mitochondria, classically known as the powerhouse of cells, are unique double membrane-bound multifaceted organelles carrying a genome. Mitochondrial content varies between cell types and precisely doubles within cells during each proliferating cycle. Mitochondrial content also increases to a variable degree during cell differentiation triggered after exit from the proliferating cycle. The mitochondrial content is primarily maintained by the regulation of mitochondrial biogenesis, while damaged mitochondria are eliminated from the cells by mitophagy. In any cell with a given mitochondrial content, the steady-state mitochondrial number and shape are determined by a balance between mitochondrial fission and fusion processes. The increase in mitochondrial content and alteration in mitochondrial fission and fusion are causatively linked with the process of differentiation. Here, we critically review the quantitative aspects in the detection methods of mitochondrial content and shape. Thereafter, we quantitatively link these mitochondrial properties in differentiating cells and highlight the implications of such quantitative link on stem cell functionality. Finally, we discuss an example of cell size regulation predicted from quantitative analysis of mitochondrial shape and content. To highlight the significance of quantitative analyses of these mitochondrial properties, we propose three independent rationale based hypotheses and the relevant experimental designs to test them.
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Affiliation(s)
- Swati Agarwala
- Department of Biology, Ashoka University, Delhi (NCR), India
| | - Sukhamoy Dhabal
- Department of Biology, Ashoka University, Delhi (NCR), India
| | - Kasturi Mitra
- Department of Biology, Ashoka University, Delhi (NCR), India
- Department of Genetics, University of Alabama at Birmingham, Birmingham, AL, USA
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5
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Knorre DA. Mitochondrial heteroplasmy as a cause of cell-to-cell phenotypic heterogeneity in clonal populations. Front Cell Dev Biol 2023; 11:1276629. [PMID: 37886395 PMCID: PMC10598549 DOI: 10.3389/fcell.2023.1276629] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 09/26/2023] [Indexed: 10/28/2023] Open
Affiliation(s)
- Dmitry A. Knorre
- Department of Molecular Energetics of Microorganisms, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
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6
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Patten MM, Schenkel MA, Ågren JA. Adaptation in the face of internal conflict: the paradox of the organism revisited. Biol Rev Camb Philos Soc 2023; 98:1796-1811. [PMID: 37203364 DOI: 10.1111/brv.12983] [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] [Received: 12/08/2022] [Revised: 05/04/2023] [Accepted: 05/05/2023] [Indexed: 05/20/2023]
Abstract
The paradox of the organism refers to the observation that organisms appear to function as coherent purposeful entities, despite the potential for within-organismal components like selfish genetic elements and cancer cells to erode them from within. While it is commonly accepted that organisms may pursue fitness maximisation and can be thought to hold particular agendas, there is a growing recognition that genes and cells do so as well. This can lead to evolutionary conflicts between an organism and the parts that reside within it. Here, we revisit the paradox of the organism. We first outline its conception and relationship to debates about adaptation in evolutionary biology. Second, we review the ways selfish elements may exploit organisms, and the extent to which this threatens organismal integrity. To this end, we introduce a novel classification scheme that distinguishes between selfish elements that seek to distort transmission versus those that seek to distort phenotypic traits. Our classification scheme also highlights how some selfish elements elude a multi-level selection decomposition using the Price equation. Third, we discuss how the organism can retain its status as the primary fitness-maximising agent in the face of selfish elements. The success of selfish elements is often constrained by their strategy and further limited by a combination of fitness alignment and enforcement mechanisms controlled by the organism. Finally, we argue for the need for quantitative measures of both internal conflicts and organismality.
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Affiliation(s)
- Manus M Patten
- Department of Biology, Georgetown University, 37th and O St. NW, Washington, DC, 20057, USA
| | - Martijn A Schenkel
- Department of Biology, Georgetown University, 37th and O St. NW, Washington, DC, 20057, USA
- Groningen Institute of Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands
| | - J Arvid Ågren
- Department of Evolutionary Biology, Uppsala University, Norbyvägen 18D, Uppsala, 752 36, Sweden
- Lerner Research Institute, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH, 44195, USA
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7
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Estes S, Dietz ZP, Katju V, Bergthorsson U. Evolutionary codependency: insights into the mitonuclear interaction landscape from experimental and wild Caenorhabditis nematodes. Curr Opin Genet Dev 2023; 81:102081. [PMID: 37421904 DOI: 10.1016/j.gde.2023.102081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 06/07/2023] [Accepted: 06/08/2023] [Indexed: 07/10/2023]
Abstract
Aided by new technologies, the upsurgence of research into mitochondrial genome biology during the past 15 years suggests that we have misunderstood, and perhaps dramatically underestimated, the ongoing biological and evolutionary significance of our long-time symbiotic partner. While we have begun to scratch the surface of several topics, many questions regarding the nature of mutation and selection in the mitochondrial genome, and the nature of its relationship to the nuclear genome, remain unanswered. Although best known for their contributions to studies of developmental and aging biology, Caenorhabditis nematodes are increasingly recognized as excellent model systems to advance understanding in these areas. We review recent discoveries with relevance to mitonuclear coevolution and conflict and offer several fertile areas for future work.
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Affiliation(s)
- Suzanne Estes
- Portland State University, Department of Biology, Portland, OR, USA.
| | - Zachary P Dietz
- Portland State University, Department of Biology, Portland, OR, USA
| | - Vaishali Katju
- Uppsala University, Department of Ecology and Genetics, 752 36 Uppsala, Sweden
| | - Ulfar Bergthorsson
- Uppsala University, Department of Ecology and Genetics, 752 36 Uppsala, Sweden
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8
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Stefano GB, Büttiker P, Weissenberger S, Esch T, Anders M, Raboch J, Kream RM, Ptacek R. Independent and sensory human mitochondrial functions reflecting symbiotic evolution. Front Cell Infect Microbiol 2023; 13:1130197. [PMID: 37389212 PMCID: PMC10302212 DOI: 10.3389/fcimb.2023.1130197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 05/31/2023] [Indexed: 07/01/2023] Open
Abstract
The bacterial origin of mitochondria has been a widely accepted as an event that occurred about 1.45 billion years ago and endowed cells with internal energy producing organelle. Thus, mitochondria have traditionally been viewed as subcellular organelle as any other - fully functionally dependent on the cell it is a part of. However, recent studies have given us evidence that mitochondria are more functionally independent than other organelles, as they can function outside the cells, engage in complex "social" interactions, and communicate with each other as well as other cellular components, bacteria and viruses. Furthermore, mitochondria move, assemble and organize upon sensing different environmental cues, using a process akin to bacterial quorum sensing. Therefore, taking all these lines of evidence into account we hypothesize that mitochondria need to be viewed and studied from a perspective of a more functionally independent entity. This view of mitochondria may lead to new insights into their biological function, and inform new strategies for treatment of disease associated with mitochondrial dysfunction.
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Affiliation(s)
- George B. Stefano
- Department of Psychiatry, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czechia
| | - Pascal Büttiker
- Department of Psychiatry, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czechia
| | | | - Tobias Esch
- Institute for Integrative Health Care and Health Promotion, School of Medicine, Witten/Herdecke University, Witten, Germany
| | - Martin Anders
- Department of Psychiatry, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czechia
| | - Jiri Raboch
- Department of Psychiatry, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czechia
| | - Richard M. Kream
- Department of Psychiatry, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czechia
| | - Radek Ptacek
- Department of Psychiatry, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czechia
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9
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Cooney DB, Levin SA, Mori Y, Plotkin JB. Evolutionary dynamics within and among competing groups. Proc Natl Acad Sci U S A 2023; 120:e2216186120. [PMID: 37155901 PMCID: PMC10193939 DOI: 10.1073/pnas.2216186120] [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] [Received: 09/22/2022] [Accepted: 03/22/2023] [Indexed: 05/10/2023] Open
Abstract
Biological and social systems are structured at multiple scales, and the incentives of individuals who interact in a group may diverge from the collective incentive of the group as a whole. Mechanisms to resolve this tension are responsible for profound transitions in evolutionary history, including the origin of cellular life, multicellular life, and even societies. Here, we synthesize a growing literature that extends evolutionary game theory to describe multilevel evolutionary dynamics, using nested birth-death processes and partial differential equations to model natural selection acting on competition within and among groups of individuals. We analyze how mechanisms known to promote cooperation within a single group-including assortment, reciprocity, and population structure-alter evolutionary outcomes in the presence of competition among groups. We find that population structures most conducive to cooperation in multiscale systems can differ from those most conducive within a single group. Likewise, for competitive interactions with a continuous range of strategies we find that among-group selection may fail to produce socially optimal outcomes, but it can nonetheless produce second-best solutions that balance individual incentives to defect with the collective incentives for cooperation. We conclude by describing the broad applicability of multiscale evolutionary models to problems ranging from the production of diffusible metabolites in microbes to the management of common-pool resources in human societies.
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Affiliation(s)
- Daniel B Cooney
- Department of Mathematics, University of Pennsylvania, Philadelphia, PA 19104
- Center for Mathematical Biology, University of Pennsylvania, Philadelphia, PA 19104
| | - Simon A Levin
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544
| | - Yoichiro Mori
- Department of Mathematics, University of Pennsylvania, Philadelphia, PA 19104
- Center for Mathematical Biology, University of Pennsylvania, Philadelphia, PA 19104
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104
| | - Joshua B Plotkin
- Department of Mathematics, University of Pennsylvania, Philadelphia, PA 19104
- Center for Mathematical Biology, University of Pennsylvania, Philadelphia, PA 19104
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104
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10
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Tsyba N, Feng G, Grub LK, Held JP, Strozak AM, Burkewitz K, Patel MR. Tissue-specific heteroplasmy segregation is accompanied by a sharp mtDNA decline in Caenorhabditis elegans soma. iScience 2023; 26:106349. [PMID: 36968071 PMCID: PMC10031119 DOI: 10.1016/j.isci.2023.106349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Revised: 09/08/2022] [Accepted: 03/02/2023] [Indexed: 03/08/2023] Open
Abstract
Mutations in the mitochondrial genome (mtDNA) can be pathogenic. Owing to the multi-copy nature of mtDNA, wild-type copies can compensate for the effects of mutant mtDNA. Wild-type copies available for compensation vary depending on the mutant load and the total copy number. Here, we examine both mutant load and copy number in the tissues of Caenorhabditis elegans. We found that neurons, but not muscles, have modestly higher mutant load than rest of the soma. We also uncovered different effect of aak-2 knockout on the mutant load in the two tissues. The most surprising result was a sharp decline in somatic mtDNA content over time. The scale of the copy number decline surpasses the modest shifts in mutant load, suggesting that it may exert a substantial effect on mitochondrial function. In summary, measuring both the copy number and the mutant load provides a more comprehensive view of the mutant mtDNA dynamics.
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Affiliation(s)
- Nikita Tsyba
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - Gaomin Feng
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN37232, USA
| | - Lantana K. Grub
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - James P. Held
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - Adrianna M. Strozak
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - Kristopher Burkewitz
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN37232, USA
| | - Maulik R. Patel
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN37232, USA
- Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, TN37232, USA
- Evolutionary Studies, Vanderbilt University, Nashville, TN37235, USA
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11
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Schwartz AZA, Nance J. Germline TFAM levels regulate mitochondrial DNA copy number and mutant heteroplasmy in C. elegans. MICROPUBLICATION BIOLOGY 2023; 2023:10.17912/micropub.biology.000727. [PMID: 36873298 PMCID: PMC9975812 DOI: 10.17912/micropub.biology.000727] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 02/09/2023] [Accepted: 02/13/2023] [Indexed: 03/07/2023]
Abstract
The mitochondrial genome (mtDNA) is packaged into discrete protein-DNA complexes called nucleoids. mtDNA packaging factor TFAM (mitochondrial transcription factor-A) promotes nucleoid compaction and is required for mtDNA replication. Here, we investigate how changing TFAM levels affects mtDNA in the Caenorhabditis elegans germ line. We show that increasing germline TFAM activity boosts mtDNA number and significantly increases the relative proportion of a selfish mtDNA mutant, uaDf5 . We conclude that TFAM levels must be tightly controlled to ensure appropriate mtDNA composition in the germ line.
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Affiliation(s)
- Aaron Z A Schwartz
- Department of Cell Biology, NYU Grossman School of Medicine, New York NY 10016.,Skirball Institute of Biomolecular Medicine, NYU Grossman School of Medicine, New York NY 10016
| | - Jeremy Nance
- Department of Cell Biology, NYU Grossman School of Medicine, New York NY 10016.,Skirball Institute of Biomolecular Medicine, NYU Grossman School of Medicine, New York NY 10016
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12
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Haynes CM, Hekimi S. Mitochondrial dysfunction, aging, and the mitochondrial unfolded protein response in Caenorhabditis elegans. Genetics 2022; 222:iyac160. [PMID: 36342845 PMCID: PMC9713405 DOI: 10.1093/genetics/iyac160] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Accepted: 10/12/2022] [Indexed: 11/09/2022] Open
Abstract
We review the findings that establish that perturbations of various aspects of mitochondrial function, including oxidative phosphorylation, can promote lifespan extension, with different types of perturbations acting sometimes independently and additively on extending lifespan. We also review the great variety of processes and mechanisms that together form the mitochondrial unfolded protein response. We then explore the relationships between different types of mitochondrial dysfunction-dependent lifespan extension and the mitochondrial unfolded protein response. We conclude that, although several ways that induce extended lifespan through mitochondrial dysfunction require a functional mitochondrial unfolded protein response, there is no clear indication that activation of the mitochondrial unfolded protein response is sufficient to extend lifespan, despite the fact that the mitochondrial unfolded protein response impacts almost every aspect of mitochondrial function. In fact, in some contexts, mitochondrial unfolded protein response activation is deleterious. To explain this pattern, we hypothesize that, although triggered by mitochondrial dysfunction, the lifespan extension observed might not be the result of a change in mitochondrial function.
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Affiliation(s)
- Cole M Haynes
- Molecular, Cell and Cancer Biology, UMass-Chan Medical School, Worcester, MA 01655, USA
| | - Siegfried Hekimi
- Department of Biology, McGill University, Montreal, QC H3A 0G4, Canada
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13
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Schwartz AZA, Tsyba N, Abdu Y, Patel MR, Nance J. Independent regulation of mitochondrial DNA quantity and quality in Caenorhabditis elegans primordial germ cells. eLife 2022; 11:e80396. [PMID: 36200990 PMCID: PMC9536838 DOI: 10.7554/elife.80396] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 09/15/2022] [Indexed: 11/13/2022] Open
Abstract
Mitochondria harbor an independent genome, called mitochondrial DNA (mtDNA), which contains essential metabolic genes. Although mtDNA mutations occur at high frequency, they are inherited infrequently, indicating that germline mechanisms limit their accumulation. To determine how germline mtDNA is regulated, we examined the control of mtDNA quantity and quality in C. elegans primordial germ cells (PGCs). We show that PGCs combine strategies to generate a low point in mtDNA number by segregating mitochondria into lobe-like protrusions that are cannibalized by adjacent cells, and by concurrently eliminating mitochondria through autophagy, reducing overall mtDNA content twofold. As PGCs exit quiescence and divide, mtDNAs replicate to maintain a set point of ~200 mtDNAs per germline stem cell. Whereas cannibalism and autophagy eliminate mtDNAs stochastically, we show that the kinase PTEN-induced kinase 1 (PINK1), operating independently of Parkin and autophagy, preferentially reduces the fraction of mutant mtDNAs. Thus, PGCs employ parallel mechanisms to control both the quantity and quality of the founding population of germline mtDNAs.
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Affiliation(s)
- Aaron ZA Schwartz
- Department of Cell Biology, NYU Grossman School of MedicineNew YorkUnited States
- Skirball Institute of Biomolecular Medicine, NYU Grossman School of MedicineNew YorkUnited States
| | - Nikita Tsyba
- Department of Biological Sciences, Vanderbilt UniversityNashvilleUnited States
| | - Yusuff Abdu
- Department of Cell Biology, NYU Grossman School of MedicineNew YorkUnited States
- Skirball Institute of Biomolecular Medicine, NYU Grossman School of MedicineNew YorkUnited States
| | - Maulik R Patel
- Department of Biological Sciences, Vanderbilt UniversityNashvilleUnited States
- Department of Cell and Developmental Biology, Vanderbilt University School of MedicineNashvilleUnited States
- Diabetes Research and Training Center, Vanderbilt University School of MedicineNashvilleUnited States
| | - Jeremy Nance
- Department of Cell Biology, NYU Grossman School of MedicineNew YorkUnited States
- Skirball Institute of Biomolecular Medicine, NYU Grossman School of MedicineNew YorkUnited States
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14
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Garoña A, Hülter NF, Romero Picazo D, Dagan T. Segregational drift constrains the evolutionary rate of prokaryotic plasmids. Mol Biol Evol 2021; 38:5610-5624. [PMID: 34550379 PMCID: PMC8662611 DOI: 10.1093/molbev/msab283] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Plasmids are extrachromosomal genetic elements in prokaryotes that have been recognized as important drivers of microbial ecology and evolution. Plasmids are found in multiple copies inside their host cell where independent emergence of mutations may lead to intracellular genetic heterogeneity. The intracellular plasmid diversity is thus subject to changes upon cell division. However, the effect of plasmid segregation on plasmid evolution remains understudied. Here, we show that genetic drift during cell division—segregational drift—leads to the rapid extinction of novel plasmid alleles. We established a novel experimental approach to control plasmid allele frequency at the levels of a single cell and the whole population. Following the dynamics of plasmid alleles in an evolution experiment, we find that the mode of plasmid inheritance—random or clustered—is an important determinant of plasmid allele dynamics. Phylogenetic reconstruction of our model plasmid in clinical isolates furthermore reveals a slow evolutionary rate of plasmid-encoded genes in comparison to chromosomal genes. Our study provides empirical evidence that genetic drift in plasmid evolution occurs at multiple levels: the host cell and the population of hosts. Segregational drift has implications for the evolutionary rate heterogeneity of extrachromosomal genetic elements.
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Affiliation(s)
- Ana Garoña
- Institute of General Microbiology, Kiel University, Kiel, 24118, Germany
| | - Nils F Hülter
- Institute of General Microbiology, Kiel University, Kiel, 24118, Germany
| | | | - Tal Dagan
- Institute of General Microbiology, Kiel University, Kiel, 24118, Germany
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15
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Pereira CV, Gitschlag BL, Patel MR. Cellular mechanisms of mtDNA heteroplasmy dynamics. Crit Rev Biochem Mol Biol 2021; 56:510-525. [PMID: 34120542 DOI: 10.1080/10409238.2021.1934812] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Heteroplasmy refers to the coexistence of more than one variant of the mitochondrial genome (mtDNA). Mutated or partially deleted mtDNAs can induce chronic metabolic impairment and cause mitochondrial diseases when their heteroplasmy levels exceed a critical threshold. These mutant mtDNAs can be maternally inherited or can arise de novo. Compelling evidence has emerged showing that mutant mtDNA levels can vary and change in a nonrandom fashion across generations and amongst tissues of an individual. However, our lack of understanding of the basic cellular and molecular mechanisms of mtDNA heteroplasmy dynamics has made it difficult to predict who will inherit or develop mtDNA-associated diseases. More recently, with the advances in technology and the establishment of tractable model systems, insights into the mechanisms underlying the selection forces that modulate heteroplasmy dynamics are beginning to emerge. In this review, we summarize evidence from different organisms, showing that mutant mtDNA can experience both positive and negative selection. We also review the recently identified mechanisms that modulate heteroplasmy dynamics. Taken together, this is an opportune time to survey the literature and to identify key cellular pathways that can be targeted to develop therapies for diseases caused by heteroplasmic mtDNA mutations.
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Affiliation(s)
- Claudia V Pereira
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA
| | - Bryan L Gitschlag
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA
| | - Maulik R Patel
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA.,Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN, USA.,Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, TN, USA
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16
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Jeedigunta SP, Minenkova AV, Palozzi JM, Hurd TR. Avoiding Extinction: Recent Advances in Understanding Mechanisms of Mitochondrial DNA Purifying Selection in the Germline. Annu Rev Genomics Hum Genet 2021; 22:55-80. [PMID: 34038145 DOI: 10.1146/annurev-genom-121420-081805] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Mitochondria are unusual organelles in that they contain their own genomes, which are kept apart from the rest of the DNA in the cell. While mitochondrial DNA (mtDNA) is essential for respiration and most multicellular life, maintaining a genome outside the nucleus brings with it a number of challenges. Chief among these is preserving mtDNA genomic integrity from one generation to the next. In this review, we discuss what is known about negative (purifying) selection mechanisms that prevent deleterious mutations from accumulating in mtDNA in the germline. Throughout, we focus on the female germline, as it is the tissue through which mtDNA is inherited in most organisms and, therefore, the tissue that most profoundly shapes the genome. We discuss recent progress in uncovering the mechanisms of germline mtDNA selection, from humans to invertebrates.
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Affiliation(s)
- Swathi P Jeedigunta
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 1M1, Canada;
| | - Anastasia V Minenkova
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 1M1, Canada;
| | - Jonathan M Palozzi
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 1M1, Canada;
| | - Thomas R Hurd
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 1M1, Canada;
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17
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Herbst A, Prior SJ, Lee CC, Aiken JM, McKenzie D, Hoang A, Liu N, Chen X, Xun P, Allison DB, Wanagat J. Skeletal muscle mitochondrial DNA copy number and mitochondrial DNA deletion mutation frequency as predictors of physical performance in older men and women. GeroScience 2021; 43:1253-1264. [PMID: 33740224 DOI: 10.1007/s11357-021-00351-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Accepted: 03/04/2021] [Indexed: 12/31/2022] Open
Abstract
Mitochondrial DNA (mtDNA) quality and quantity relate to two hallmarks of aging-genomic instability and mitochondrial dysfunction. Physical performance relies on mitochondrial integrity and declines with age, yet the interactions between mtDNA quantity, quality, and physical performance are unclear. Using a validated digital PCR assay specific for mtDNA deletions, we tested the hypothesis that skeletal muscle mtDNA deletion mutation frequency (i.e., a measure of mtDNA quality) or mtDNA copy number predicts physical performance in older adults. Total DNA was isolated from vastus lateralis muscle biopsies and used to quantitate mtDNA copy number and mtDNA deletion frequency by digital PCR. The biopsies were obtained from a cross-sectional cohort of 53 adults aged 50 to 86 years. Before the biopsy procedure, physical performance measurements were collected, including VO2max, modified physical performance test score, 6-min walk distance, gait speed, grip strength, and total lean and leg mass. Linear regression models were used to evaluate the relationships between age, sex, and the outcomes. We found that mtDNA deletion mutation frequency increased exponentially with advancing age. On average from ages 50 to 86, deletion frequency increased from 0.008 to 0.15%, an 18-fold increase. Females may have lower deletion frequencies than males at older ages. We also measured declines in VO2max and mtDNA copy number with age in both sexes. The mtDNA deletion frequency measured from single skeletal muscle biopsies predicted 13.3% of the variation in VO2max. Copy number explained 22.6% of the variation in mtDNA deletion frequency and 10.4% of the lean mass variation. We found predictive relationships between age, mtDNA deletion mutation frequency, mtDNA copy number, and physical performance. These data are consistent with a role for mitochondrial function and genome integrity in maintaining physical performance with age. Analyses of mtDNA quality and quantity in larger cohorts and longitudinal studies could extend our understanding of the importance of mitochondrial DNA in human aging and longevity.
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Affiliation(s)
- Allen Herbst
- Department of Agricultural, Food and Nutritional Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Steven J Prior
- Department of Kinesiology, University of Maryland School of Public Health, College Park, MD, USA.,Baltimore Veterans Affairs Medical Center Geriatric Research, Education and Clinical Center, Baltimore, MD, USA
| | - Cathy C Lee
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, CA, USA.,Division of Geriatrics, Department of Medicine, University of California, Los Angeles, 650 Charles E. Young Drive South, Rm 34-115, Los Angeles, CA, 90095, USA
| | - Judd M Aiken
- Department of Agricultural, Food and Nutritional Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Debbie McKenzie
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Austin Hoang
- Division of Geriatrics, Department of Medicine, University of California, Los Angeles, 650 Charles E. Young Drive South, Rm 34-115, Los Angeles, CA, 90095, USA
| | - Nianjun Liu
- Department of Epidemiology and Biostatistics, Indiana University Bloomington, Bloomington, IN, USA
| | - Xiwei Chen
- Department of Epidemiology and Biostatistics, Indiana University Bloomington, Bloomington, IN, USA
| | - Pengcheng Xun
- Department of Epidemiology and Biostatistics, Indiana University Bloomington, Bloomington, IN, USA
| | - David B Allison
- Department of Epidemiology and Biostatistics, Indiana University Bloomington, Bloomington, IN, USA
| | - Jonathan Wanagat
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, CA, USA. .,Division of Geriatrics, Department of Medicine, University of California, Los Angeles, 650 Charles E. Young Drive South, Rm 34-115, Los Angeles, CA, 90095, USA.
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18
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Abstract
Experiments on mitochondrial DNA in worms highlight that cheating does not always pay off.
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Affiliation(s)
- M Florencia Camus
- Department of Genetics, Evolution and Environment, University College LondonLondonUnited Kingdom
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