1
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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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2
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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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3
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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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4
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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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5
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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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6
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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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7
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Owsian D, Gruchota J, Arnaiz O, Nowak JK. The transient Spt4-Spt5 complex as an upstream regulator of non-coding RNAs during development. Nucleic Acids Res 2022; 50:2603-2620. [PMID: 35188560 PMCID: PMC8934623 DOI: 10.1093/nar/gkac106] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 01/28/2022] [Accepted: 02/04/2022] [Indexed: 12/21/2022] Open
Abstract
The Spt4-Spt5 complex is conserved and essential RNA polymerase elongation factor. To investigate the role of the Spt4-Spt5 complex in non-coding transcription during development, we used the unicellular model Paramecium tetraurelia. In this organism harboring both germline and somatic nuclei, massive transcription of the entire germline genome takes place during meiosis. This phenomenon starts a series of events mediated by different classes of non-coding RNAs that control developmentally programmed DNA elimination. We focused our study on Spt4, a small zinc-finger protein encoded in P. tetraurelia by two genes expressed constitutively and two genes expressed during meiosis. SPT4 genes are not essential in vegetative growth, but they are indispensable for sexual reproduction, even though genes from both expression families show functional redundancy. Silencing of the SPT4 genes resulted in the absence of double-stranded ncRNAs and reduced levels of scnRNAs – 25 nt-long sRNAs produced from these double-stranded precursors in the germline nucleus. Moreover, we observed that the presence of a germline-specific Spt4-Spt5m complex is necessary for transfer of the scnRNA-binding PIWI protein between the germline and somatic nucleus. Our study establishes that Spt4, together with Spt5m, is essential for expression of the germline genome and necessary for developmental genome rearrangements.
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Affiliation(s)
- Dawid Owsian
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
| | - Julita Gruchota
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
| | - Olivier Arnaiz
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
| | - Jacek K Nowak
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
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8
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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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9
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Catania F, Rothering R, Vitali V. One Cell, Two Gears: Extensive Somatic Genome Plasticity Accompanies High Germline Genome Stability in Paramecium. Genome Biol Evol 2021; 13:6443145. [PMID: 34849843 PMCID: PMC8670300 DOI: 10.1093/gbe/evab263] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/22/2021] [Indexed: 12/15/2022] Open
Abstract
Mutation accumulation (MA) experiments are conventionally employed to study spontaneous germline mutations. However, MA experiments can also shed light on somatic genome plasticity in a habitual and genetic drift-maximizing environment. Here, we revisit an MA experiment that uncovered extraordinary germline genome stability in Paramecium tetraurelia, a single-celled eukaryote with nuclear dimorphism. Our re-examination of isogenic P. tetraurelia MA lines propagated in nutrient-rich medium for >40 sexual cycles reveals that their polyploid somatic genome accrued hundreds of intervening DNA segments (IESs), which are normally eliminated during germline-soma differentiation. These IESs frequently occupy a fraction of the somatic DNA copies of a given locus, producing IES excision/retention polymorphisms, and preferentially fall into a class of epigenetically controlled sequences. Relative to control lines, retained IESs are flanked by stronger cis-acting signals and interrupt an excess of highly expressed coding exons. These findings suggest that P. tetraurelia’s elevated germline DNA replication fidelity is associated with pervasive somatic genome plasticity. They show that MA regimes are powerful tools for investigating the role that developmental plasticity, somatic mutations, and epimutations have in ecology and evolution.
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Affiliation(s)
- Francesco Catania
- Institute for Evolution and Biodiversity, University of Münster, Germany.,Institute of Environmental Radioactivity, Fukushima University, Japan
| | - Rebecca Rothering
- Institute for Evolution and Biodiversity, University of Münster, Germany
| | - Valerio Vitali
- Institute for Evolution and Biodiversity, University of Münster, Germany
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10
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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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11
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Maliszewska-Olejniczak K, Kaniowski D, Araszkiewicz M, Tymińska K, Korgul A. Molecular Mechanisms of Specific Cellular DNA Damage Response and Repair Induced by the Mixed Radiation Field During Boron Neutron Capture Therapy. Front Oncol 2021; 11:676575. [PMID: 34094980 PMCID: PMC8170402 DOI: 10.3389/fonc.2021.676575] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Accepted: 04/28/2021] [Indexed: 01/04/2023] Open
Abstract
The impact of a mixed neutron-gamma beam on the activation of DNA damage response (DDR) proteins and non-coding RNAs (ncRNAs) is poorly understood. Ionizing radiation is characterized by its biological effectiveness and is related to linear energy transfer (LET). Neutron-gamma mixed beam used in boron neutron capture therapy (BNCT) can induce another type of DNA damage such as clustered DNA or multiple damaged sites, as indicated for high LET particles, such as alpha particles, carbon ions, and protons. We speculate that after exposure to a mixed radiation field, the repair capacity might reduce, leading to unrepaired complex DNA damage for a long period and may promote genome instability and cell death. This review will focus on the poorly studied impact of neutron-gamma mixed beams with an emphasis on DNA damage and molecular mechanisms of repair. In case of BNCT, it is not clear which repair pathway is involved, and recent experimental work will be presented. Further understanding of BNCT-induced DDR mechanisms may lead to improved therapeutic efficiency against different tumors.
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Affiliation(s)
| | - Damian Kaniowski
- Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Lodz, Poland
| | - Martyna Araszkiewicz
- Faculty of Physics, University of Warsaw, Warsaw, Poland.,Nuclear Facilities Operations Department, National Centre for Nuclear Research, Otwock, Poland
| | - Katarzyna Tymińska
- Nuclear Facilities Operations Department, National Centre for Nuclear Research, Otwock, Poland
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12
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Guérineau M, Bessa L, Moriau S, Lescop E, Bontems F, Mathy N, Guittet E, Bischerour J, Bétermier M, Morellet N. The unusual structure of the PiggyMac cysteine-rich domain reveals zinc finger diversity in PiggyBac-related transposases. Mob DNA 2021; 12:12. [PMID: 33926516 PMCID: PMC8086355 DOI: 10.1186/s13100-021-00240-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Accepted: 03/09/2021] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND Transposons are mobile genetic elements that colonize genomes and drive their plasticity in all organisms. DNA transposon-encoded transposases bind to the ends of their cognate transposons and catalyze their movement. In some cases, exaptation of transposon genes has allowed novel cellular functions to emerge. The PiggyMac (Pgm) endonuclease of the ciliate Paramecium tetraurelia is a domesticated transposase from the PiggyBac family. It carries a core catalytic domain typical of PiggyBac-related transposases and a short cysteine-rich domain (CRD), flanked by N- and C-terminal extensions. During sexual processes Pgm catalyzes programmed genome rearrangements (PGR) that eliminate ~ 30% of germline DNA from the somatic genome at each generation. How Pgm recognizes its DNA cleavage sites in chromatin is unclear and the structure-function relationships of its different domains have remained elusive. RESULTS We provide insight into Pgm structure by determining the fold adopted by its CRD, an essential domain required for PGR. Using Nuclear Magnetic Resonance, we show that the Pgm CRD binds two Zn2+ ions and forms an unusual binuclear cross-brace zinc finger, with a circularly permutated treble-clef fold flanked by two flexible arms. The Pgm CRD structure clearly differs from that of several other PiggyBac-related transposases, among which is the well-studied PB transposase from Trichoplusia ni. Instead, the arrangement of cysteines and histidines in the primary sequence of the Pgm CRD resembles that of active transposases from piggyBac-like elements found in other species and of human PiggyBac-derived domesticated transposases. We show that, unlike the PB CRD, the Pgm CRD does not bind DNA. Instead, it interacts weakly with the N-terminus of histone H3, whatever its lysine methylation state. CONCLUSIONS The present study points to the structural diversity of the CRD among transposases from the PiggyBac family and their domesticated derivatives, and highlights the diverse interactions this domain may establish with chromatin, from sequence-specific DNA binding to contacts with histone tails. Our data suggest that the Pgm CRD fold, whose unusual arrangement of cysteines and histidines is found in all PiggyBac-related domesticated transposases from Paramecium and Tetrahymena, was already present in the ancestral active transposase that gave rise to ciliate domesticated proteins.
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Affiliation(s)
- Marc Guérineau
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France
| | - Luiza Bessa
- Université Paris-Saclay, CNRS, Institut de Chimie des Substances Naturelles, UPR 2301, 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France
- Present addresses: Université Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), 71 Avenue des Martyrs, 38000, Grenoble, France
| | - Séverine Moriau
- Université Paris-Saclay, CNRS, Institut de Chimie des Substances Naturelles, UPR 2301, 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France
| | - Ewen Lescop
- Université Paris-Saclay, CNRS, Institut de Chimie des Substances Naturelles, UPR 2301, 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France
| | - François Bontems
- Université Paris-Saclay, CNRS, Institut de Chimie des Substances Naturelles, UPR 2301, 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France
| | - Nathalie Mathy
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France
- Reproduction et Développement des Plantes UMR 5667, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364, Lyon Cedex 07, France
| | - Eric Guittet
- Université Paris-Saclay, CNRS, Institut de Chimie des Substances Naturelles, UPR 2301, 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France
| | - Julien Bischerour
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France
| | - Mireille Bétermier
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France.
| | - Nelly Morellet
- Université Paris-Saclay, CNRS, Institut de Chimie des Substances Naturelles, UPR 2301, 1 Avenue de la Terrasse, 91198, Gif sur Yvette Cedex, France.
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Rzeszutek I, Maurer-Alcalá XX, Nowacki M. Programmed genome rearrangements in ciliates. Cell Mol Life Sci 2020; 77:4615-4629. [PMID: 32462406 PMCID: PMC7599177 DOI: 10.1007/s00018-020-03555-2] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Revised: 05/11/2020] [Accepted: 05/15/2020] [Indexed: 12/14/2022]
Abstract
Ciliates are a highly divergent group of unicellular eukaryotes with separate somatic and germline genomes found in distinct dimorphic nuclei. This characteristic feature is tightly linked to extremely laborious developmentally regulated genome rearrangements in the development of a new somatic genome/nuclei following sex. The transformation from germline to soma genome involves massive DNA elimination mediated by non-coding RNAs, chromosome fragmentation, as well as DNA amplification. In this review, we discuss the similarities and differences in the genome reorganization processes of the model ciliates Paramecium and Tetrahymena (class Oligohymenophorea), and the distantly related Euplotes, Stylonychia, and Oxytricha (class Spirotrichea).
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Affiliation(s)
- Iwona Rzeszutek
- Institute of Biology and Biotechnology, Department of Biotechnology, University of Rzeszow, Pigonia 1, 35-310, Rzeszow, Poland.
| | - Xyrus X Maurer-Alcalá
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland
| | - Mariusz Nowacki
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012, Bern, Switzerland.
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14
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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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Vitali V, Hagen R, Catania F. Environmentally induced plasticity of programmed DNA elimination boosts somatic variability in Paramecium tetraurelia. Genome Res 2019; 29:1693-1704. [PMID: 31548355 PMCID: PMC6771405 DOI: 10.1101/gr.245332.118] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Accepted: 08/23/2019] [Indexed: 12/17/2022]
Abstract
Can ecological changes impact somatic genome development? Efforts to resolve this question could reveal a direct link between environmental changes and somatic variability, potentially illuminating our understanding of how variation can surface from a single genotype under stress. Here, we tackle this question by leveraging the biological properties of ciliates. When Paramecium tetraurelia reproduces sexually, its polyploid somatic genome regenerates from the germline genome through a developmental process that involves the removal of thousands of ORF-interrupting sequences known as internal eliminated sequences (IESs). We show that exposure to nonstandard culture temperatures impacts the efficiency of this process of programmed DNA elimination, prompting the emergence of hundreds of incompletely excised IESs in the newly developed somatic genome. These alternative DNA isoforms display a patterned genomic topography, impact gene expression, and might be inherited transgenerationally. On this basis, we conclude that environmentally induced developmental thermoplasticity contributes to genotypic diversification in Paramecium.
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Affiliation(s)
- Valerio Vitali
- Institute for Evolution and Biodiversity, University of Münster, 48149 Münster, Germany
| | - Rebecca Hagen
- Institute for Evolution and Biodiversity, University of Münster, 48149 Münster, Germany
| | - Francesco Catania
- Institute for Evolution and Biodiversity, University of Münster, 48149 Münster, Germany
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16
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Garg J, Saettone A, Nabeel-Shah S, Cadorin M, Ponce M, Marquez S, Pu S, Greenblatt J, Lambert JP, Pearlman RE, Fillingham J. The Med31 Conserved Component of the Divergent Mediator Complex in Tetrahymena thermophila Participates in Developmental Regulation. Curr Biol 2019; 29:2371-2379.e6. [PMID: 31280994 DOI: 10.1016/j.cub.2019.06.052] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 05/18/2019] [Accepted: 06/18/2019] [Indexed: 11/24/2022]
Abstract
Mediator is a large protein complex required for basal and regulated expression of most RNA polymerase II (RNAP II)-transcribed genes, in part due to its interaction with and phosphorylation of the conserved C-terminal domain (CTD) of Rpb1 [1, 2]. Mediator has been implicated in many aspects of gene expression including chromatin looping [3], higher-order chromatin folding [4], mRNA processing [5] and export [6], and transcriptional memory [7]. Mediator is thought to have played a major role during eukaryotic diversification [8, 9], although its function remains unknown in evolutionarily deep branching eukaryotes lacking canonical CTD heptad repeats. We used the ciliate protozoan Tetrahymena thermophila as a model organism whose genome encodes a highly divergent Rpb1 lacking canonical CTD heptad repeats. We endogenously tagged the Med31 subunit of the Mediator complex and performed affinity purification coupled with mass spectrometry (AP-MS) to identify Mediator subunits. We found that Med31 physically interacts with a large number of proteins (>20), several of which share similarities to canonical Mediator subunits in yeast and humans as well as Tetrahymena-specific proteins. Furthermore, Med31 ChIP-seq analysis suggested a global role for Mediator in transcription regulation. We demonstrated that MED31 knockdown in growing Tetrahymena results in the ectopic expression of developmental genes important for programmed DNA rearrangements. In addition, indirect immunofluorescence revealed Med31 localization in meiotic micronuclei, implicating Mediator in RNAPII-dependent ncRNA transcription. Our results reveal structural and functional insights and implicate Mediator as an ancient cellular machinery for transcription regulation with a possible involvement in global transcription of ncRNAs.
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Affiliation(s)
- Jyoti Garg
- Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada
| | - Alejandro Saettone
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada
| | - Syed Nabeel-Shah
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Matthew Cadorin
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada
| | - Marcelo Ponce
- SciNet HPC Consortium, University of Toronto, 661 University Avenue, Suite 1140, Toronto, ON M5G 1M1, Canada
| | - Susanna Marquez
- Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada
| | - Shuye Pu
- Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Jack Greenblatt
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Donnelly Centre, University of Toronto, Toronto, ON M5S 3E1, Canada
| | - Jean-Philippe Lambert
- Department of Molecular Medicine and Cancer Research Centre, Université Laval, Quebec, QC, Canada; CHU de Québec Research Center, CHUL, 2705 Laurier Boulevard, Quebec, QC G1V 4G2, Canada
| | - Ronald E Pearlman
- Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada
| | - Jeffrey Fillingham
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada.
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17
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Bhullar S, Denby Wilkes C, Arnaiz O, Nowacki M, Sperling L, Meyer E. A mating-type mutagenesis screen identifies a zinc-finger protein required for specific DNA excision events in Paramecium. Nucleic Acids Res 2019; 46:9550-9562. [PMID: 30165457 PMCID: PMC6182129 DOI: 10.1093/nar/gky772] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Accepted: 08/24/2018] [Indexed: 12/16/2022] Open
Abstract
In the ciliate Paramecium tetraurelia, functional genes are reconstituted during development of the somatic macronucleus through the precise excision of ∼45 000 single-copy Internal Eliminated Sequences (IESs), thought to be the degenerate remnants of ancient transposon insertions. Like introns, IESs are marked only by a weak consensus at their ends. How such a diverse set of sequences is faithfully recognized and precisely excised remains unclear: specialized small RNAs have been implicated, but in their absence up to ∼60% of IESs are still correctly excised. To get further insight, we designed a mutagenesis screen based on the hypersensitivity of a specific excision event in the mtA gene, which determines mating types. Unlike most IES-containing genes, the active form of mtA is the unexcised one, allowing the recovery of hypomorphic alleles of essential IES recognition/excision factors. Such is the case of one mutation recovered in the Piwi gene PTIWI09, a key player in small RNA-mediated IES recognition. Another mutation identified a novel protein with a C2H2 zinc finger, mtGa, which is required for excision of a small subset of IESs characterized by enrichment in a 5-bp motif. The unexpected implication of a sequence-specific factor establishes a new paradigm for IES recognition and/or excision.
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Affiliation(s)
- Simran Bhullar
- IBENS, Ecole Normale Supérieure, CNRS, Inserm, PSL University, F-75005 Paris, France.,Institute of Cell Biology, University of Bern, 3012 Bern, Switzerland
| | - Cyril Denby Wilkes
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Olivier Arnaiz
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Mariusz Nowacki
- Institute of Cell Biology, University of Bern, 3012 Bern, Switzerland
| | - Linda Sperling
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Eric Meyer
- IBENS, Ecole Normale Supérieure, CNRS, Inserm, PSL University, F-75005 Paris, France
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18
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Duharcourt S, Sperling L. The Challenges of Genome-Wide Studies in a Unicellular Eukaryote With Two Nuclear Genomes. Methods Enzymol 2018; 612:101-126. [PMID: 30502938 DOI: 10.1016/bs.mie.2018.08.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
We present here methods to study a eukaryotic microorganism with two nuclear genomes, both originating from the same zygotic genome. Paramecium, like other ciliates, is characterized by nuclear dimorphism, which is the presence of two types of nuclei with distinct organization and functions in the same cytoplasm. The two diploid germline micronuclei (MIC) undergo meiosis and fertilization to transmit the genetic information across sexual generations. The highly polyploid somatic macronucleus (MAC) contains a reduced version of the genome optimized for gene expression. Reproducible programmed DNA elimination of about 30% of the complexity of the 100Mb MIC genome occurs during development of the MAC along with endoreplication to 800 copies. Large regions that contain transposable elements and other repeats are eliminated, and short single copy remnants of transposable elements, which often interrupt coding sequences, are precisely excised to restore functional open reading frames. Genome-wide studies of this process require access to MIC DNA which has long been impossible. The breakthrough with respect to this technical obstacle came with development of a MIC purification protocol involving a critical step of flow cytometry to sort nuclei representing only 0.5% of total genomic DNA. Here, we provide a step-by-step protocol and important tips for purifying nuclei, and present the methods developed for downstream analysis of NGS data.
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Affiliation(s)
- Sandra Duharcourt
- Institut Jacques Monod, CNRS, UMR7592, Sorbonne Paris Cité, Paris, France.
| | - Linda Sperling
- Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, Univ. Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette CEDEX, France
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19
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Pang Y, Mao C, Liu S. Encoding activities of non-coding RNAs. Am J Cancer Res 2018; 8:2496-2507. [PMID: 29721095 PMCID: PMC5928905 DOI: 10.7150/thno.24677] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2018] [Accepted: 02/25/2018] [Indexed: 12/14/2022] Open
Abstract
The universal expression of various non-coding RNAs (ncRNAs) is now considered the main feature of organisms' genomes. Many regions in the genome are transcribed but not annotated to encode proteins, yet contain small open reading frames (smORFs). A widely accepted opinion is that a vast majority of ncRNAs are not further translated. However, increasing evidence underlines a series of intriguing translational events from the ncRNAs, which were previously considered to lack coding potential. Recent studies also suggest that products derived from such novel translational events display important regulatory functions in many fundamental biological and pathological processes. Here we give a critical review on the potential coding capacity of ncRNAs, in particular, about what is known and unknown in this emerging area. We also discuss the possible underlying coding mechanisms of these extraordinary ncRNAs and possible roles of peptides or proteins derived from the ncRNAs in disease development and theranostics. Our review offers an extensive resource for studying the biology of ncRNAs and sheds light into the use of ncRNAs and their corresponding peptides or proteins for disease diagnosis and therapy.
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Gruchota J, Denby Wilkes C, Arnaiz O, Sperling L, Nowak JK. A meiosis-specific Spt5 homolog involved in non-coding transcription. Nucleic Acids Res 2017; 45:4722-4732. [PMID: 28053118 PMCID: PMC5416832 DOI: 10.1093/nar/gkw1318] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 12/20/2016] [Indexed: 12/18/2022] Open
Abstract
Spt5 is a conserved and essential transcriptional regulator that binds directly to RNA polymerase and is involved in transcription elongation, polymerase pausing and various co-transcriptional processes. To investigate the role of Spt5 in non-coding transcription, we used the unicellular model Paramecium tetraurelia. In this ciliate, development is controlled by epigenetic mechanisms that use different classes of non-coding RNAs to target DNA elimination. We identified two SPT5 genes. One (STP5v) is involved in vegetative growth, while the other (SPT5m) is essential for sexual reproduction. We focused our study on SPT5m, expressed at meiosis and associated with germline nuclei during sexual processes. Upon Spt5m depletion, we observed absence of scnRNAs, piRNA-like 25 nt small RNAs produced at meiosis. The scnRNAs are a temporal copy of the germline genome and play a key role in programming DNA elimination. Moreover, Spt5m depletion abolishes elimination of all germline-limited sequences, including sequences whose excision was previously shown to be scnRNA-independent. This suggests that in addition to scnRNA production, Spt5 is involved in setting some as yet uncharacterized epigenetic information at meiosis. Our study establishes that Spt5m is crucial for developmental genome rearrangements and necessary for scnRNA production.
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Affiliation(s)
- Julita Gruchota
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
| | - Cyril Denby Wilkes
- Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, University of Paris Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Olivier Arnaiz
- Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, University of Paris Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Linda Sperling
- Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, University of Paris Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette cedex, France
| | - Jacek K Nowak
- Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
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21
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Arnaiz O, Van Dijk E, Bétermier M, Lhuillier-Akakpo M, de Vanssay A, Duharcourt S, Sallet E, Gouzy J, Sperling L. Improved methods and resources for paramecium genomics: transcription units, gene annotation and gene expression. BMC Genomics 2017; 18:483. [PMID: 28651633 PMCID: PMC5485702 DOI: 10.1186/s12864-017-3887-z] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 06/21/2017] [Indexed: 12/22/2022] Open
Abstract
Background The 15 sibling species of the Paramecium aurelia cryptic species complex emerged after a whole genome duplication that occurred tens of millions of years ago. Given extensive knowledge of the genetics and epigenetics of Paramecium acquired over the last century, this species complex offers a uniquely powerful system to investigate the consequences of whole genome duplication in a unicellular eukaryote as well as the genetic and epigenetic mechanisms that drive speciation. High quality Paramecium gene models are important for research using this system. The major aim of the work reported here was to build an improved gene annotation pipeline for the Paramecium lineage. Results We generated oriented RNA-Seq transcriptome data across the sexual process of autogamy for the model species Paramecium tetraurelia. We determined, for the first time in a ciliate, candidate P. tetraurelia transcription start sites using an adapted Cap-Seq protocol. We developed TrUC, multi-threaded Perl software that in conjunction with TopHat mapping of RNA-Seq data to a reference genome, predicts transcription units for the annotation pipeline. We used EuGene software to combine annotation evidence. The high quality gene structural annotations obtained for P. tetraurelia were used as evidence to improve published annotations for 3 other Paramecium species. The RNA-Seq data were also used for differential gene expression analysis, providing a gene expression atlas that is more sensitive than the previously established microarray resource. Conclusions We have developed a gene annotation pipeline tailored for the compact genomes and tiny introns of Paramecium species. A novel component of this pipeline, TrUC, predicts transcription units using Cap-Seq and oriented RNA-Seq data. TrUC could prove useful beyond Paramecium, especially in the case of high gene density. Accurate predictions of 3′ and 5′ UTR will be particularly valuable for studies of gene expression (e.g. nucleosome positioning, identification of cis regulatory motifs). The P. tetraurelia improved transcriptome resource, gene annotations for P. tetraurelia, P. biaurelia, P. sexaurelia and P. caudatum, and Paramecium-trained EuGene configuration are available through ParameciumDB (http://paramecium.i2bc.paris-saclay.fr). TrUC software is freely distributed under a GNU GPL v3 licence (https://github.com/oarnaiz/TrUC). Electronic supplementary material The online version of this article (doi:10.1186/s12864-017-3887-z) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Olivier Arnaiz
- Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, Univ. Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette CEDEX, France
| | - Erwin Van Dijk
- Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, Univ. Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette CEDEX, France
| | - Mireille Bétermier
- Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, Univ. Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette CEDEX, France
| | - Maoussi Lhuillier-Akakpo
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, F-75205, Paris, France.,Current address: IRCM, CEA, INSERM UMR 967, Université Paris Diderot, Université Paris-Saclay, 92265, Fontenay-aux-Roses CEDEX, France
| | - Augustin de Vanssay
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, F-75205, Paris, France
| | - Sandra Duharcourt
- Institut Jacques Monod, CNRS, UMR 7592, Université Paris Diderot, Sorbonne Paris Cité, F-75205, Paris, France
| | - Erika Sallet
- LIPM, Université de Toulouse, INRA, CNRS, Castanet-Tolosan, France
| | - Jérôme Gouzy
- LIPM, Université de Toulouse, INRA, CNRS, Castanet-Tolosan, France
| | - Linda Sperling
- Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, Univ. Paris-Sud, Université Paris-Saclay, 91198, Gif-sur-Yvette CEDEX, France.
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Allen SE, Hug I, Pabian S, Rzeszutek I, Hoehener C, Nowacki M. Circular Concatemers of Ultra-Short DNA Segments Produce Regulatory RNAs. Cell 2017; 168:990-999.e7. [PMID: 28283070 PMCID: PMC5346157 DOI: 10.1016/j.cell.2017.02.020] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Revised: 01/10/2017] [Accepted: 02/09/2017] [Indexed: 12/13/2022]
Abstract
In the ciliated protozoan Paramecium tetraurelia, Piwi-associated small RNAs are generated upon the elimination of tens of thousands of short transposon-derived DNA segments as part of development. These RNAs then target complementary DNA for elimination in a positive feedback process, contributing to germline defense and genome stability. In this work, we investigate the formation of these RNAs, which we show to be transcribed directly from the short (length mode 27 bp) excised DNA segments. Our data support a mechanism whereby the concatenation and circularization of excised DNA segments provides a template for RNA production. This process allows the generation of a double-stranded RNA for Dicer-like protein cleavage to give rise to a population of small regulatory RNAs that precisely match the excised DNA sequences. Video Abstract
In Paramecium, pieces of deleted DNA are transcribed to form regulatory RNAs Ultra-short DNA segments are concatenated and circularized, allowing transcription This concatenation is carried out by Ligase IV, which also repairs DNA ends Concatenation is random, which leads to diversity in the resulting sRNA population
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Affiliation(s)
- Sarah E Allen
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
| | - Iris Hug
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
| | - Sylwia Pabian
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
| | - Iwona Rzeszutek
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
| | - Cristina Hoehener
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
| | - Mariusz Nowacki
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland.
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Allen SE, Nowacki M. Necessity Is the Mother of Invention: Ciliates, Transposons, and Transgenerational Inheritance. Trends Genet 2017; 33:197-207. [PMID: 28174020 DOI: 10.1016/j.tig.2017.01.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Revised: 01/09/2017] [Accepted: 01/11/2017] [Indexed: 01/01/2023]
Abstract
Ciliates are a fascinating model system for the study of the interaction between eukaryotic germlines and somatic lines, especially with regard to the invasion and defence against transposable elements. They separate their germline and somatic line into two nuclei within the same cell, and they silence transposons and repetitive elements by way of deleting them from their somatic genome. This large-scale deletion event uses a series of intricate sequence targeting pathways involving small RNAs and transposases, part of which consists of a transnuclear comparison between maternal soma and daughter germline. We present recent progress in this dynamic field, and argue that these DNA targeting pathways provide an optimal system for the transgenerational inheritance of acquired traits. Ciliates thus also demonstrate the evolutionary value of transposable elements, both as sources of sequence diversity and also as drivers of adaptive evolution by necessitating defensive systems.
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Affiliation(s)
- Sarah E Allen
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland
| | - Mariusz Nowacki
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland.
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