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Bischerour J, Arnaiz O, Zangarelli C, Régnier V, Iehl F, Ropars V, Charbonnier JB, Bétermier M. Uncoupling programmed DNA cleavage and repair scrambles the Paramecium somatic genome. Cell Rep 2024; 43:114001. [PMID: 38547127 DOI: 10.1016/j.celrep.2024.114001] [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: 11/06/2023] [Revised: 01/24/2024] [Accepted: 03/11/2024] [Indexed: 04/28/2024] Open
Abstract
In the ciliate Paramecium, precise excision of numerous internal eliminated sequences (IESs) from the somatic genome is essential at each sexual cycle. DNA double-strands breaks (DSBs) introduced by the PiggyMac endonuclease are repaired in a highly concerted manner by the non-homologous end joining (NHEJ) pathway, illustrated by complete inhibition of DNA cleavage when Ku70/80 proteins are missing. We show that expression of a DNA-binding-deficient Ku70 mutant (Ku70-6E) permits DNA cleavage but leads to the accumulation of unrepaired DSBs. We uncoupled DNA cleavage and repair by co-expressing wild-type and mutant Ku70. High-throughput sequencing of the developing macronucleus genome in these conditions identifies the presence of extremities healed by de novo telomere addition and numerous translocations between IES-flanking sequences. Coupling the two steps of IES excision ensures that both extremities are held together throughout the process, suggesting that DSB repair proteins are essential for assembly of a synaptic precleavage complex.
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Affiliation(s)
- Julien Bischerour
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France.
| | - Olivier Arnaiz
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France
| | - Coralie Zangarelli
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France
| | - Vinciane Régnier
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France; Université Paris Cité, UFR Sciences du vivant, 75205 Paris Cedex 13, France
| | - Florence Iehl
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France
| | - Virginie Ropars
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France
| | - Jean-Baptiste Charbonnier
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France
| | - Mireille Bétermier
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France.
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2
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Balan T, Lerner LK, Holoch D, Duharcourt S. Small-RNA-guided histone modifications and somatic genome elimination in ciliates. WILEY INTERDISCIPLINARY REVIEWS. RNA 2024; 15:e1848. [PMID: 38605483 DOI: 10.1002/wrna.1848] [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: 01/25/2024] [Revised: 03/22/2024] [Accepted: 03/22/2024] [Indexed: 04/13/2024]
Abstract
Transposable elements and other repeats are repressed by small-RNA-guided histone modifications in fungi, plants and animals. The specificity of silencing is achieved through base-pairing of small RNAs corresponding to the these genomic loci to nascent noncoding RNAs, which allows the recruitment of histone methyltransferases that methylate histone H3 on lysine 9. Self-reinforcing feedback loops enhance small RNA production and ensure robust and heritable repression. In the unicellular ciliate Paramecium tetraurelia, small-RNA-guided histone modifications lead to the elimination of transposable elements and their remnants, a definitive form of repression. In this organism, germline and somatic functions are separated within two types of nuclei with different genomes. At each sexual cycle, development of the somatic genome is accompanied by the reproducible removal of approximately a third of the germline genome. Instead of recruiting a H3K9 methyltransferase, small RNAs corresponding to eliminated sequences tether Polycomb Repressive Complex 2, which in ciliates has the unique property of catalyzing both lysine 9 and lysine 27 trimethylation of histone H3. These histone modifications that are crucial for the elimination of transposable elements are thought to guide the endonuclease complex, which triggers double-strand breaks at these specific genomic loci. The comparison between ciliates and other eukaryotes underscores the importance of investigating small-RNAs-directed chromatin silencing in a diverse range of organisms. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > RNAi: Mechanisms of Action.
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Affiliation(s)
- Thomas Balan
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
| | | | - Daniel Holoch
- Université Paris Cité, CNRS, Institut Jacques Monod, Paris, France
- Institut Curie, INSERM U934/CNRS UMR 3215, Paris Sciences et Lettres Research University, Sorbonne University, Paris, France
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3
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Bétermier M, Klobutcher LA, Orias E. Programmed chromosome fragmentation in ciliated protozoa: multiple means to chromosome ends. Microbiol Mol Biol Rev 2023; 87:e0018422. [PMID: 38009915 PMCID: PMC10732028 DOI: 10.1128/mmbr.00184-22] [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] [Indexed: 11/29/2023] Open
Abstract
SUMMARYCiliated protozoa undergo large-scale developmental rearrangement of their somatic genomes when forming a new transcriptionally active macronucleus during conjugation. This process includes the fragmentation of chromosomes derived from the germline, coupled with the efficient healing of the broken ends by de novo telomere addition. Here, we review what is known of developmental chromosome fragmentation in ciliates that have been well-studied at the molecular level (Tetrahymena, Paramecium, Euplotes, Stylonychia, and Oxytricha). These organisms differ substantially in the fidelity and precision of their fragmentation systems, as well as in the presence or absence of well-defined sequence elements that direct excision, suggesting that chromosome fragmentation systems have evolved multiple times and/or have been significantly altered during ciliate evolution. We propose a two-stage model for the evolution of the current ciliate systems, with both stages involving repetitive or transposable elements in the genome. The ancestral form of chromosome fragmentation is proposed to have been derived from the ciliate small RNA/chromatin modification process that removes transposons and other repetitive elements from the macronuclear genome during development. The evolution of this ancestral system is suggested to have potentiated its replacement in some ciliate lineages by subsequent fragmentation systems derived from mobile genetic elements.
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Affiliation(s)
- Mireille Bétermier
- Department of Genome Biology, Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell, Gif-sur-Yvette, France
| | - Lawrence A. Klobutcher
- Department of Molecular Biology and Biophysics, UCONN Health (University of Connecticut), Farmington, Connecticut, USA
| | - Eduardo Orias
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, California, USA
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4
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Bazin-Gélis M, Eleftheriou E, Zangarelli C, Lelandais G, Sperling L, Arnaiz O, Bétermier M. Inter-generational nuclear crosstalk links the control of gene expression to programmed genome rearrangement during the Paramecium sexual cycle. Nucleic Acids Res 2023; 51:12337-12351. [PMID: 37953377 PMCID: PMC10711438 DOI: 10.1093/nar/gkad1006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 10/09/2023] [Accepted: 10/23/2023] [Indexed: 11/14/2023] Open
Abstract
Multinucleate cells are found in many eukaryotes, but how multiple nuclei coordinate their functions is still poorly understood. In the cytoplasm of the ciliate Paramecium tetraurelia, two micronuclei (MIC) serving sexual reproduction coexist with a somatic macronucleus (MAC) dedicated to gene expression. During sexual processes, the MAC is progressively destroyed while still ensuring transcription, and new MACs develop from copies of the zygotic MIC. Several gene clusters are successively induced and switched off before vegetative growth resumes. Concomitantly, programmed genome rearrangement (PGR) removes transposons and their relics from the new MACs. Development of the new MACs is controlled by the old MAC, since the latter expresses genes involved in PGR, including the PGM gene encoding the essential PiggyMac endonuclease that cleaves the ends of eliminated sequences. Using RNA deep sequencing and transcriptome analysis, we show that impairing PGR upregulates key known PGR genes, together with ∼600 other genes possibly also involved in PGR. Among these genes, 42% are no longer induced when no new MACs are formed, including 180 genes that are co-expressed with PGM under all tested conditions. We propose that bi-directional crosstalk between the two coexisting generations of MACs links gene expression to the progression of MAC development.
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Affiliation(s)
- Mélanie Bazin-Gélis
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
| | - Evangelia Eleftheriou
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
- Institut Pasteur, Université Paris Cité, Inserm U1223, Innate Immunity Unit, Paris, France
| | - Coralie Zangarelli
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
| | - Gaëlle Lelandais
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
| | - Linda Sperling
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
| | - Olivier Arnaiz
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
| | - Mireille Bétermier
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
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5
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Long H, Johri P, Gout JF, Ni J, Hao Y, Licknack T, Wang Y, Pan J, Jiménez-Marín B, Lynch M. Paramecium Genetics, Genomics, and Evolution. Annu Rev Genet 2023; 57:391-410. [PMID: 38012024 DOI: 10.1146/annurev-genet-071819-104035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
The ciliate genus Paramecium served as one of the first model systems in microbial eukaryotic genetics, contributing much to the early understanding of phenomena as diverse as genome rearrangement, cryptic speciation, cytoplasmic inheritance, and endosymbiosis, as well as more recently to the evolution of mating types, introns, and roles of small RNAs in DNA processing. Substantial progress has recently been made in the area of comparative and population genomics. Paramecium species combine some of the lowest known mutation rates with some of the largest known effective populations, along with likely very high recombination rates, thereby harboring a population-genetic environment that promotes an exceptionally efficient capacity for selection. As a consequence, the genomes are extraordinarily streamlined, with very small intergenic regions combined with small numbers of tiny introns. The subject of the bulk of Paramecium research, the ancient Paramecium aurelia species complex, is descended from two whole-genome duplication events that retain high degrees of synteny, thereby providing an exceptional platform for studying the fates of duplicate genes. Despite having a common ancestor dating to several hundred million years ago, the known descendant species are morphologically indistinguishable, raising significant questions about the common view that gene duplications lead to the origins of evolutionary novelties.
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Affiliation(s)
- Hongan Long
- Institute of Evolution and Marine Biodiversity, KLMME, Ocean University of China, Qingdao, Shandong Province, China;
- Laboratory for Marine Biology and Biotechnology, Laoshan Laboratory, Qingdao, Shandong Province, China
| | - Parul Johri
- Department of Biology, University of North Carolina, Chapel Hill, North Carolina, USA
| | - Jean-Francois Gout
- Department of Biological Sciences, Mississippi State University, Starkville, Mississippi, USA
| | - Jiahao Ni
- Institute of Evolution and Marine Biodiversity, KLMME, Ocean University of China, Qingdao, Shandong Province, China;
| | - Yue Hao
- Cancer and Cell Biology Division, Translational Genomics Research Institute, Phoenix, Arizona, USA
- Biodesign Center for Mechanisms of Evolution, Arizona State University, Tempe, Arizona, USA;
| | - Timothy Licknack
- Biodesign Center for Mechanisms of Evolution, Arizona State University, Tempe, Arizona, USA;
| | - Yaohai Wang
- Institute of Evolution and Marine Biodiversity, KLMME, Ocean University of China, Qingdao, Shandong Province, China;
| | - Jiao Pan
- Institute of Evolution and Marine Biodiversity, KLMME, Ocean University of China, Qingdao, Shandong Province, China;
| | - Berenice Jiménez-Marín
- Biodesign Center for Mechanisms of Evolution, Arizona State University, Tempe, Arizona, USA;
| | - Michael Lynch
- Biodesign Center for Mechanisms of Evolution, Arizona State University, Tempe, Arizona, USA;
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6
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Gao Y, Solberg T, Wang C, Gao F. Small RNA-mediated genome rearrangement pathways in ciliates. Trends Genet 2023; 39:94-97. [PMID: 36371355 DOI: 10.1016/j.tig.2022.10.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 08/23/2022] [Accepted: 10/19/2022] [Indexed: 11/11/2022]
Abstract
Most eukaryotes employ a combination of transcriptional and post-transcriptional silencing mechanisms to suppress transposons, yet ciliates employ a more extreme approach. They separate germline and somatic functions into distinct nuclei, enabling the elimination of transposons from the active somatic genome through diverse small RNA-mediated genome rearrangement pathways during sexual processes.
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Affiliation(s)
- Yunyi Gao
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China; Key Laboratory of Mariculture (Ocean University of China), Ministry of Education, Qingdao 266003, China
| | - Therese Solberg
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
| | - Chundi Wang
- Laboratory of Marine Protozoan Biodiversity & Evolution, Ocean College, Shandong University, Weihai 264209, China
| | - Feng Gao
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China; Key Laboratory of Mariculture (Ocean University of China), Ministry of Education, Qingdao 266003, China.
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7
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Lu MW, Beh LY, Yerlici VT, Fang W, Kulej K, Garcia BA, Landweber LF. Exploration of the Nuclear Proteomes in the Ciliate Oxytricha trifallax. Microorganisms 2023; 11:microorganisms11020343. [PMID: 36838311 PMCID: PMC9958989 DOI: 10.3390/microorganisms11020343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 01/17/2023] [Accepted: 01/21/2023] [Indexed: 01/31/2023] Open
Abstract
Nuclear dimorphism is a fundamental feature of ciliated protozoa, which have separate somatic and germline genomes in two distinct organelles within a single cell. The transcriptionally active somatic genome, contained within the physically larger macronucleus, is both structurally and functionally different from the silent germline genome housed in the smaller micronucleus. This difference in genome architecture is particularly exaggerated in Oxytricha trifallax, in which the somatic genome comprises tens of thousands of gene-sized nanochromosomes maintained at a high and variable ploidy, while the germline has a diploid set of megabase-scale chromosomes. To examine the compositional differences between the nuclear structures housing the genomes, we performed a proteomic survey of both types of nuclei and of macronuclear histones using quantitative mass spectrometry. We note distinct differences between the somatic and germline nuclei, with many functional proteins being highly enriched in one of the two nuclei. To validate our conclusions and the efficacy of nuclear separation, we used protein localization through a combination of transformations and immunofluorescence. We also note that the macronuclear histones strikingly display only activating marks, consistent with the conclusion that the macronucleus is the hub of transcription. These observations suggest that the compartmentalization of different genome features into separate structures has been accompanied by a similar specialization of nuclear components that maintain and facilitate the functions of the genomes specific to each nucleus.
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Affiliation(s)
- Michael W. Lu
- Department of Biological Sciences, Columbia University, New York, NY 10025, USA
| | - Leslie Y. Beh
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - V. Talya Yerlici
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Wenwen Fang
- RNA Therapeutics Institute, UMass Chan Medical School, Worcester, MA 01655, USA
| | - Katarzyna Kulej
- Division of Protective Immunity and Division of Cancer Pathobiology, The Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA
| | - Benjamin A. Garcia
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Laura F. Landweber
- Department of Biological Sciences, Columbia University, New York, NY 10025, USA
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
- Correspondence:
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8
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Fu J, Chi Y, Lu X, Gao F, Al-Farraj SA, Petroni G, Jiang J. Doublets of the unicellular organism Euplotes vannus (Alveolata, Ciliophora, Euplotida): the morphogenetic patterns of the ciliary and nuclear apparatuses associated with cell division. MARINE LIFE SCIENCE & TECHNOLOGY 2022; 4:527-535. [PMID: 37078083 PMCID: PMC10077243 DOI: 10.1007/s42995-022-00150-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2022] [Accepted: 10/05/2022] [Indexed: 05/03/2023]
Abstract
Ciliated protists are one of the most diverse and highly differentiated group among unicellular organisms. Doublets occur in ciliates when two cells fuse into a single individual. Doublets contain two major cellular components (either cell in a doublet) and have traditionally been considered as developmental anomalies. Nevertheless, doublets can divide or even conjugate effectively, which may represent dispersal forms of the life stages. In addition, morphogenesis, as an important process in the life cycle, will provide important insights into the complex differentiation mechanism and various physiological phenomena. However, morphogenetic studies focusing on doublets of ciliates are very limited, which has become an obstacle to understand their complete life history. Here we isolated a doublet strain from the marine species Euplotes vannus (Müller, 1786) Diesing, 1850 and investigated its morphogenetic events during asexual reproduction. Our results indicate that: (1) the opisthe's oral primordium develops de novo beneath the cortex; (2) the frontoventral and transverse cirral anlagen, cirrus I/1, and marginal anlagen in both dividers develop de novo separately; (3) the dorsal kinety anlagen, the three rightmost ones of which produce three caudal cirri for the proter, occur within the parental structures in the mid-body region; (4) the opisthe acquires two caudal cirri, one from the end of each two rightmost kineties; and (5) there are two macronuclei and one micronucleus in the doublet and they divide amitotically and mitotically, respectively. Finally, we speculate that this special differentiation may be an adaptive form to adverse environments.
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Affiliation(s)
- Jinyu Fu
- Institute of Evolution and Marine Biodiversity, Ocean University of China, Qingdao, 266003 China
| | - Yong Chi
- Institute of Evolution and Marine Biodiversity, Ocean University of China, Qingdao, 266003 China
| | - Xiaoteng Lu
- Department of Biology, Shenzhen MSU-BIT University, Shenzhen, 518172 China
| | - Feng Gao
- Institute of Evolution and Marine Biodiversity, Ocean University of China, Qingdao, 266003 China
| | - Saleh A. Al-Farraj
- Zoology Department, College of Science, King Saud University, Riyadh, 11451 Saudi Arabia
| | - Giulio Petroni
- Department of Biology, University of Pisa, 56126 Pisa, Italy
| | - Jiamei Jiang
- Engineering Research Center of Environmental DNA and Ecological Water Health Assessment, Shanghai Ocean University, Shanghai, 201306 China
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9
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Singh A, Maurer‐Alcalá XX, Solberg T, Häußermann L, Gisler S, Ignarski M, Swart EC, Nowacki M. Chromatin remodeling is required for sRNA-guided DNA elimination in Paramecium. EMBO J 2022; 41:e111839. [PMID: 36221862 PMCID: PMC9670198 DOI: 10.15252/embj.2022111839] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 09/14/2022] [Accepted: 09/19/2022] [Indexed: 01/13/2023] Open
Abstract
Small RNAs mediate the silencing of transposable elements and other genomic loci, increasing nucleosome density and preventing undesirable gene expression. The unicellular ciliate Paramecium is a model to study dynamic genome organization in eukaryotic cells, given its unique feature of nuclear dimorphism. Here, the formation of the somatic macronucleus during sexual reproduction requires eliminating thousands of transposon remnants (IESs) and transposable elements scattered throughout the germline micronuclear genome. The elimination process is guided by Piwi-associated small RNAs and leads to precise cleavage at IES boundaries. Here we show that IES recognition and precise excision are facilitated by recruiting ISWI1, a Paramecium homolog of the chromatin remodeler ISWI. ISWI1 knockdown substantially inhibits DNA elimination, quantitatively similar to development-specific sRNA gene knockdowns but with much greater aberrant IES excision at alternative boundaries. We also identify key development-specific sRNA biogenesis and transport proteins, Ptiwi01 and Ptiwi09, as ISWI1 cofactors in our co-immunoprecipitation studies. Nucleosome profiling indicates that increased nucleosome density correlates with the requirement for ISWI1 and other proteins necessary for IES excision. We propose that chromatin remodeling together with small RNAs is essential for efficient and precise DNA elimination in Paramecium.
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Affiliation(s)
- Aditi Singh
- Institute of Cell BiologyUniversity of BernBernSwitzerland,Graduate School for Cellular and Biomedical SciencesUniversity of BernBernSwitzerland,Max Planck Institute for BiologyTubingenGermany
| | | | - Therese Solberg
- Institute of Cell BiologyUniversity of BernBernSwitzerland,Graduate School for Cellular and Biomedical SciencesUniversity of BernBernSwitzerland
| | | | - Silvan Gisler
- Institute of Cell BiologyUniversity of BernBernSwitzerland
| | | | - Estienne C Swart
- Institute of Cell BiologyUniversity of BernBernSwitzerland,Max Planck Institute for BiologyTubingenGermany
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10
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Wang C, Solberg T, Maurer-Alcalá XX, Swart EC, Gao F, Nowacki M. A small RNA-guided PRC2 complex eliminates DNA as an extreme form of transposon silencing. Cell Rep 2022; 40:111263. [PMID: 36001962 PMCID: PMC10073204 DOI: 10.1016/j.celrep.2022.111263] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 06/27/2022] [Accepted: 08/04/2022] [Indexed: 01/04/2023] Open
Abstract
In animal germlines, transposons are silenced at the transcriptional or post-transcriptional level to prevent deleterious expression. Ciliates employ a more direct approach by physically eliminating transposons from their soma, utilizing piRNAs to recognize transposons and imprecisely excise them. Ancient, mutated transposons often do not require piRNAs and are precisely eliminated. Here, we characterize the Polycomb Repressive Complex 2 (PRC2) in Paramecium and demonstrate its involvement in the removal of transposons and transposon-derived DNA. Our results reveal a striking difference between the elimination of new and ancient transposons at the chromatin level and show that the complex may be guided by Piwi-bound small RNAs (sRNAs). We propose that imprecise elimination in ciliates originates from an ancient transposon silencing mechanism, much like in plants and metazoans, through sRNAs, repressive methylation marks, and heterochromatin formation. However, it is taken a step further by eliminating DNA as an extreme form of transposon silencing.
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Affiliation(s)
- Chundi Wang
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland; Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China; Laboratory of Marine Protozoan Biodiversity & Evolution, Marine College, Shandong University, Weihai 264209, China
| | - Therese Solberg
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
| | - Xyrus X Maurer-Alcalá
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland; Division of Invertebrate Zoology and Sackler Institute for Comparative Genomics, American Museum of Natural History, New York, NY 10024, USA
| | - Estienne C Swart
- Max Planck Institute for Biology, Max Planck Ring 5, 72076 Tuebingen, Germany
| | - Feng Gao
- Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China; Key Laboratory of Mariculture (OUC), Ministry of Education, Qingdao 266003, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China.
| | - Mariusz Nowacki
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland.
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11
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Drews F, Boenigk J, Simon M. Paramecium epigenetics in development and proliferation. J Eukaryot Microbiol 2022; 69:e12914. [PMID: 35363910 DOI: 10.1111/jeu.12914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The term epigenetics is used for any layer of genetic information aside from the DNA base-sequence information. Mammalian epigenetic research increased our understanding of chromatin dynamics in terms of cytosine methylation and histone modification during differentiation, aging, and disease. Instead, ciliate epigenetics focused more on small RNA-mediated effects. On the one hand, these do concern the transport of RNA from parental to daughter nuclei, representing a regulated transfer of epigenetic information across generations. On the other hand, studies of Paramecium, Tetrahymena, Oxytricha, and Stylonychia revealed an almost unique function of transgenerational RNA. Rather than solely controlling chromatin dynamics, they control sexual progeny's DNA content quantitatively and qualitatively. Thus epigenetics seems to control genetics, at least genetics of the vegetative macronucleus. This combination offers ciliates, in particular, an epigenetically controlled genetic variability. This review summarizes the epigenetic mechanisms that contribute to macronuclear heterogeneity and relates these to nuclear dimorphism. This system's adaptive and evolutionary possibilities raise the critical question of whether such a system is limited to unicellular organisms or binuclear cells. We discuss here the relevance of ciliate genetics and epigenetics to multicellular organisms.
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Affiliation(s)
- Franziska Drews
- Molecular Cell Biology and Microbiology, School of Mathematics and Natural Sciences, University of Wuppertal
| | | | - Martin Simon
- Molecular Cell Biology and Microbiology, School of Mathematics and Natural Sciences, University of Wuppertal
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12
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Zangarelli C, Arnaiz O, Bourge M, Gorrichon K, Jaszczyszyn Y, Mathy N, Escoriza L, Bétermier M, Régnier V. Developmental timing of programmed DNA elimination in Paramecium tetraurelia recapitulates germline transposon evolutionary dynamics. Genome Res 2022; 32:2028-2042. [PMID: 36418061 PMCID: PMC9808624 DOI: 10.1101/gr.277027.122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 11/11/2022] [Indexed: 11/24/2022]
Abstract
With its nuclear dualism, the ciliate Paramecium constitutes a unique model to study how host genomes cope with transposable elements (TEs). P. tetraurelia harbors two germline micronuclei (MICs) and a polyploid somatic macronucleus (MAC) that develops from one MIC at each sexual cycle. Throughout evolution, the MIC genome has been continuously colonized by TEs and related sequences that are removed from the somatic genome during MAC development. Whereas TE elimination is generally imprecise, excision of approximately 45,000 TE-derived internal eliminated sequences (IESs) is precise, allowing for functional gene assembly. Programmed DNA elimination is concomitant with genome amplification. It is guided by noncoding RNAs and repressive chromatin marks. A subset of IESs is excised independently of this epigenetic control, raising the question of how IESs are targeted for elimination. To gain insight into the determinants of IES excision, we established the developmental timing of DNA elimination genome-wide by combining fluorescence-assisted nuclear sorting with high-throughput sequencing. Essentially all IESs are excised within only one endoreplication round (32C to 64C), whereas TEs are eliminated at a later stage. We show that DNA elimination proceeds independently of replication. We defined four IES classes according to excision timing. The earliest excised IESs tend to be independent of epigenetic factors, display strong sequence signals at their ends, and originate from the most ancient integration events. We conclude that old IESs have been optimized during evolution for early and accurate excision by acquiring stronger sequence determinants and escaping epigenetic control.
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Affiliation(s)
- Coralie Zangarelli
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France
| | - Olivier Arnaiz
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France
| | - Mickaël Bourge
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France
| | - Kevin Gorrichon
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France
| | - Yan Jaszczyszyn
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France
| | - Nathalie Mathy
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France
| | - Loïc Escoriza
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France
| | - Mireille Bétermier
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France
| | - Vinciane Régnier
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette Cedex, France;,Université Paris Cité, UFR Sciences du Vivant, 75205 Paris Cedex 13, France
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13
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Sellis D, Guérin F, Arnaiz O, Pett W, Lerat E, Boggetto N, Krenek S, Berendonk T, Couloux A, Aury JM, Labadie K, Malinsky S, Bhullar S, Meyer E, Sperling L, Duret L, Duharcourt S. Massive colonization of protein-coding exons by selfish genetic elements in Paramecium germline genomes. PLoS Biol 2021; 19:e3001309. [PMID: 34324490 PMCID: PMC8354472 DOI: 10.1371/journal.pbio.3001309] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 08/10/2021] [Accepted: 06/04/2021] [Indexed: 11/18/2022] Open
Abstract
Ciliates are unicellular eukaryotes with both a germline genome and a somatic genome in the same cytoplasm. The somatic macronucleus (MAC), responsible for gene expression, is not sexually transmitted but develops from a copy of the germline micronucleus (MIC) at each sexual generation. In the MIC genome of Paramecium tetraurelia, genes are interrupted by tens of thousands of unique intervening sequences called internal eliminated sequences (IESs), which have to be precisely excised during the development of the new MAC to restore functional genes. To understand the evolutionary origin of this peculiar genomic architecture, we sequenced the MIC genomes of 9 Paramecium species (from approximately 100 Mb in Paramecium aurelia species to >1.5 Gb in Paramecium caudatum). We detected several waves of IES gains, both in ancestral and in more recent lineages. While the vast majority of IESs are single copy in present-day genomes, we identified several families of mobile IESs, including nonautonomous elements acquired via horizontal transfer, which generated tens to thousands of new copies. These observations provide the first direct evidence that transposable elements can account for the massive proliferation of IESs in Paramecium. The comparison of IESs of different evolutionary ages indicates that, over time, IESs shorten and diverge rapidly in sequence while they acquire features that allow them to be more efficiently excised. We nevertheless identified rare cases of IESs that are under strong purifying selection across the aurelia clade. The cases examined contain or overlap cellular genes that are inactivated by excision during development, suggesting conserved regulatory mechanisms. Similar to the evolution of introns in eukaryotes, the evolution of Paramecium IESs highlights the major role played by selfish genetic elements in shaping the complexity of genome architecture and gene expression. A comparative genomics study of nine Paramecium species reveals successful invasion of genes by transposable elements in their germline genomes, showing that the internal eliminated sequences (IESs) followed an evolutionary trajectory remarkably similar to that of spliceosomal introns.
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Affiliation(s)
- Diamantis Sellis
- Université de Lyon, CNRS, Laboratoire de Biométrie et Biologie Evolutive UMR 5558, Villeurbanne, France
| | - Frédéric Guérin
- Université de Paris, CNRS, Institut Jacques Monod, Paris, France
| | - Olivier Arnaiz
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Gif-sur-Yvette, France
| | - Walker Pett
- Université de Lyon, CNRS, Laboratoire de Biométrie et Biologie Evolutive UMR 5558, Villeurbanne, France
| | - Emmanuelle Lerat
- Université de Lyon, CNRS, Laboratoire de Biométrie et Biologie Evolutive UMR 5558, Villeurbanne, France
| | - Nicole Boggetto
- Université de Paris, CNRS, Institut Jacques Monod, Paris, France
| | - Sascha Krenek
- TU Dresden, Institute of Hydrobiology, Dresden, Germany
| | | | - Arnaud Couloux
- Génomique Métabolique, Genoscope, Institut de biologie François Jacob, CEA, CNRS, Université d’Évry, Université Paris-Saclay, Evry, France
| | - Jean-Marc Aury
- Génomique Métabolique, Genoscope, Institut de biologie François Jacob, CEA, CNRS, Université d’Évry, Université Paris-Saclay, Evry, France
| | - Karine Labadie
- Genoscope, Institut de biologie François-Jacob, Commissariat à l’Energie Atomique (CEA), Université Paris-Saclay, Evry, France
| | - Sophie Malinsky
- Institut de Biologie de l’Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, Université PSL, Paris, France
- Université de Paris, Paris, France
| | - Simran Bhullar
- Institut de Biologie de l’Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, Université PSL, Paris, France
| | - Eric Meyer
- Institut de Biologie de l’Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, Université PSL, Paris, France
| | - Linda Sperling
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Gif-sur-Yvette, France
| | - Laurent Duret
- Université de Lyon, CNRS, Laboratoire de Biométrie et Biologie Evolutive UMR 5558, Villeurbanne, France
- * E-mail: (LD); (SD)
| | - Sandra Duharcourt
- Université de Paris, CNRS, Institut Jacques Monod, Paris, France
- * E-mail: (LD); (SD)
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14
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Zahid S, Seif El Dahan M, Iehl F, Fernandez-Varela P, Le Du MH, Ropars V, Charbonnier JB. The Multifaceted Roles of Ku70/80. Int J Mol Sci 2021; 22:ijms22084134. [PMID: 33923616 PMCID: PMC8073936 DOI: 10.3390/ijms22084134] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Revised: 03/31/2021] [Accepted: 04/01/2021] [Indexed: 12/11/2022] Open
Abstract
DNA double-strand breaks (DSBs) are accidental lesions generated by various endogenous or exogenous stresses. DSBs are also genetically programmed events during the V(D)J recombination process, meiosis, or other genome rearrangements, and they are intentionally generated to kill cancer during chemo- and radiotherapy. Most DSBs are processed in mammalian cells by the classical nonhomologous end-joining (c-NHEJ) pathway. Understanding the molecular basis of c-NHEJ has major outcomes in several fields, including radiobiology, cancer therapy, immune disease, and genome editing. The heterodimer Ku70/80 (Ku) is a central actor of the c-NHEJ as it rapidly recognizes broken DNA ends in the cell and protects them from nuclease activity. It subsequently recruits many c-NHEJ effectors, including nucleases, polymerases, and the DNA ligase 4 complex. Beyond its DNA repair function, Ku is also involved in several other DNA metabolism processes. Here, we review the structural and functional data on the DNA and RNA recognition properties of Ku implicated in DNA repair and in telomeres maintenance.
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15
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Sawka-Gądek N, Potekhin A, Singh DP, Grevtseva I, Arnaiz O, Penel S, Sperling L, Tarcz S, Duret L, Nekrasova I, Meyer E. Evolutionary Plasticity of Mating-Type Determination Mechanisms in Paramecium aurelia Sibling Species. Genome Biol Evol 2021; 13:evaa258. [PMID: 33313646 PMCID: PMC7900874 DOI: 10.1093/gbe/evaa258] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/09/2020] [Indexed: 12/15/2022] Open
Abstract
The Paramecium aurelia complex, a group of morphologically similar but sexually incompatible sibling species, is a unique example of the evolutionary plasticity of mating-type systems. Each species has two mating types, O (Odd) and E (Even). Although O and E types are homologous in all species, three different modes of determination and inheritance have been described: genetic determination by Mendelian alleles, stochastic developmental determination, and maternally inherited developmental determination. Previous work in three species of the latter kind has revealed the key roles of the E-specific transmembrane protein mtA and its highly specific transcription factor mtB: type O clones are produced by maternally inherited genome rearrangements that inactivate either mtA or mtB during development. Here we show, through transcriptome analyses in five additional species representing the three determination systems, that mtA expression specifies type E in all cases. We further show that the Mendelian system depends on functional and nonfunctional mtA alleles, and identify novel developmental rearrangements in mtA and mtB which now explain all cases of maternally inherited mating-type determination. Epistasis between these genes likely evolved from less specific interactions between paralogs in the P. aurelia common ancestor, after a whole-genome duplication, but the mtB gene was subsequently lost in three P. aurelia species which appear to have returned to an ancestral regulation mechanism. These results suggest a model accounting for evolutionary transitions between determination systems, and highlight the diversity of molecular solutions explored among sibling species to maintain an essential mating-type polymorphism in cell populations.
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Affiliation(s)
- Natalia Sawka-Gądek
- Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Kraków, Poland
| | - Alexey Potekhin
- Department of Microbiology, Faculty of Biology, Saint Petersburg State University, Saint Petersburg, Russia
| | - Deepankar Pratap Singh
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, Université PSL, Paris, France
| | - Inessa Grevtseva
- Department of Microbiology, Faculty of Biology, Saint Petersburg State University, Saint Petersburg, Russia
| | - Olivier Arnaiz
- CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Université Paris-Saclay, Gif-sur-Yvette, France
| | - Simon Penel
- CNRS, Laboratoire de Biométrie et Biologie Evolutive UMR 5558, Université de Lyon, Villeurbanne, France
| | - Linda Sperling
- CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Université Paris-Saclay, Gif-sur-Yvette, France
| | - Sebastian Tarcz
- Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Kraków, Poland
| | - Laurent Duret
- CNRS, Laboratoire de Biométrie et Biologie Evolutive UMR 5558, Université de Lyon, Villeurbanne, France
| | - Irina Nekrasova
- Department of Microbiology, Faculty of Biology, Saint Petersburg State University, Saint Petersburg, Russia
| | - Eric Meyer
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, Université PSL, Paris, France
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16
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The Paramecium histone chaperone Spt16-1 is required for Pgm endonuclease function in programmed genome rearrangements. PLoS Genet 2020; 16:e1008949. [PMID: 32702045 PMCID: PMC7402521 DOI: 10.1371/journal.pgen.1008949] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Revised: 08/04/2020] [Accepted: 06/24/2020] [Indexed: 12/31/2022] Open
Abstract
In Paramecium tetraurelia, a large proportion of the germline genome is reproducibly removed from the somatic genome after sexual events via a process involving small (s)RNA-directed heterochromatin formation and DNA excision and repair. How germline limited DNA sequences are specifically recognized in the context of chromatin remains elusive. Here, we use a reverse genetics approach to identify factors involved in programmed genome rearrangements. We have identified a P. tetraurelia homolog of the highly conserved histone chaperone Spt16 subunit of the FACT complex, Spt16-1, and show its expression is developmentally regulated. A functional GFP-Spt16-1 fusion protein localized exclusively in the nuclei where genome rearrangements take place. Gene silencing of Spt16-1 showed it is required for the elimination of all germline-limited sequences, for the survival of sexual progeny, and for the accumulation of internal eliminated sequence (ies)RNAs, an sRNA population produced when elimination occurs. Normal accumulation of 25 nt scanRNAs and deposition of silent histone marks H3K9me3 and H3K27me3 indicated that Spt16-1 does not regulate the scanRNA-directed heterochromatin pathway involved in the early steps of DNA elimination. We further show that Spt16-1 is required for the correct nuclear localization of the PiggyMac (Pgm) endonuclease, which generates the DNA double-strand breaks required for DNA elimination. Thus, Spt16-1 is essential for Pgm function during programmed genome rearrangements. We propose a model in which Spt16-1 mediates interactions between the excision machinery and chromatin, facilitating endonuclease access to DNA cleavage sites during genome rearrangements. The genome is generally similar in all the cells of an organism. However, in the ciliate Paramecium tetraurelia, massive and reproducible programmed DNA elimination leads to a highly streamlined somatic genome. In eukaryotes, DNA is packaged into nucleosomes, which ensure genome integrity but act as a barrier to enzymes acting on DNA. How the endonuclease PiggyMac gains access to the genome to initiate DNA elimination remains elusive. Here, we identified four P. tetraurelia genes encoding homologs of the conserved histone chaperone Spt16, which can modulate access to DNA by promoting nucleosome assembly and disassembly. We demonstrated that the most divergent gene, SPT16-1, has a highly specialized expression pattern, similar to that of PiggyMac, and a specific role in programmed DNA elimination. We show that the Spt16-1 protein, like PiggyMac, is exclusively localized in the differentiating somatic nucleus, and is also required for the dramatic elimination of germline-limited sequences. We further show that Spt16-1 directs the correct nuclear localization of the PiggyMac endonuclease. Thus, Spt16-1 is essential for PiggyMac function during programmed DNA elimination. We propose that Spt16-1 mediates the interaction between PiggyMac and chromatin or DNA, facilitating endonuclease access to DNA cleavage sites.
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