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Ho S, Theurkauf W, Rice N. piRNA-Guided Transposon Silencing and Response to Stress in Drosophila Germline. Viruses 2024; 16:714. [PMID: 38793595 PMCID: PMC11125864 DOI: 10.3390/v16050714] [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: 03/28/2024] [Revised: 04/23/2024] [Accepted: 04/27/2024] [Indexed: 05/26/2024] Open
Abstract
Transposons are integral genome constituents that can be domesticated for host functions, but they also represent a significant threat to genome stability. Transposon silencing is especially critical in the germline, which is dedicated to transmitting inherited genetic material. The small Piwi-interacting RNAs (piRNAs) have a deeply conserved function in transposon silencing in the germline. piRNA biogenesis and function are particularly well understood in Drosophila melanogaster, but some fundamental mechanisms remain elusive and there is growing evidence that the pathway is regulated in response to genotoxic and environmental stress. Here, we review transposon regulation by piRNAs and the piRNA pathway regulation in response to stress, focusing on the Drosophila female germline.
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Affiliation(s)
- Samantha Ho
- Program in Molecular Medicine, University Campus, University of Massachusetts Chan Medical School, Worcester, MA 01655, USA;
| | | | - Nicholas Rice
- Program in Molecular Medicine, University Campus, University of Massachusetts Chan Medical School, Worcester, MA 01655, USA;
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2
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Ho S, Rice NP, Yu T, Weng Z, Theurkauf WE. Aub, Vasa and Armi localization to phase separated nuage is dispensable for piRNA biogenesis and transposon silencing in Drosophila. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.25.549160. [PMID: 37546958 PMCID: PMC10402007 DOI: 10.1101/2023.07.25.549160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/08/2023]
Abstract
From nematodes to placental mammals, key components of the germline transposon silencing piRNAs pathway localize to phase separated perinuclear granules. In Drosophila, the PIWI protein Aub, DEAD box protein Vasa and helicase Armi localize to nuage granules and are required for ping-pong piRNA amplification and phased piRNA processing. Drosophila piRNA mutants lead to genome instability and Chk2 kinase DNA damage signaling. By systematically analyzing piRNA pathway organization, small RNA production, and long RNA expression in single piRNA mutants and corresponding chk2/mnk double mutants, we show that Chk2 activation disrupts nuage localization of Aub and Vasa, and that the HP1 homolog Rhino, which drives piRNA precursor transcription, is required for Aub, Vasa, and Armi localization to nuage. However, these studies also show that ping-pong amplification and phased piRNA biogenesis are independent of nuage localization of Vasa, Aub and Armi. Dispersed cytoplasmic proteins thus appear to mediate these essential piRNA pathway functions.
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Affiliation(s)
- Samantha Ho
- Program in Molecular Medicine, UMass Chan Medical School, Worcester MA
| | - Nicholas P Rice
- Program in Molecular Medicine, UMass Chan Medical School, Worcester MA
| | - Tianxiong Yu
- Program in Bioinformatics and Integrative Biology, UMass Chan Medical School, Worcester MA
| | - Zhiping Weng
- Program in Bioinformatics and Integrative Biology, UMass Chan Medical School, Worcester MA
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3
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Casier K, Autaa J, Gueguen N, Delmarre V, Marie PP, Ronsseray S, Carré C, Brasset E, Teysset L, Boivin A. The histone demethylase Kdm3 prevents auto-immune piRNAs production in Drosophila. SCIENCE ADVANCES 2023; 9:eade3872. [PMID: 37027460 PMCID: PMC10081847 DOI: 10.1126/sciadv.ade3872] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Accepted: 03/08/2023] [Indexed: 06/19/2023]
Abstract
Genome integrity of the animal germline is protected from transposable element activity by PIWI-interacting RNAs (piRNAs). While piRNA biogenesis is intensively explored, little is known about the genetical determination of piRNA clusters, the genomic sources of piRNAs. Using a bimodal epigenetic state piRNA cluster (BX2), we identified the histone demethylase Kdm3 as being able to prevent a cryptic piRNA production. In the absence of Kdm3, dozens of coding gene-containing regions become genuine germline dual-strand piRNA clusters. Eggs laid by Kdm3 mutant females show developmental defects phenocopying loss of function of genes embedded into the additional piRNA clusters, suggesting an inheritance of functional ovarian "auto-immune" piRNAs. Antagonizing piRNA cluster determination through chromatin modifications appears crucial to prevent auto-immune genic piRNAs production.
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Affiliation(s)
- Karine Casier
- Transgenerational Epigenetics and Small RNA Biology, Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, F-75005 Paris, France
| | - Julie Autaa
- Transgenerational Epigenetics and Small RNA Biology, Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, F-75005 Paris, France
| | - Nathalie Gueguen
- iGReD, CNRS, INSERM, Faculté de Médecine, Université Clermont Auvergne, 63000 Clermont-Ferrand, France
| | - Valérie Delmarre
- Transgenerational Epigenetics and Small RNA Biology, Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, F-75005 Paris, France
| | - Pauline P. Marie
- Transgenerational Epigenetics and Small RNA Biology, Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, F-75005 Paris, France
| | - Stéphane Ronsseray
- Transgenerational Epigenetics and Small RNA Biology, Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, F-75005 Paris, France
| | - Clément Carré
- Transgenerational Epigenetics and Small RNA Biology, Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, F-75005 Paris, France
| | - Emilie Brasset
- iGReD, CNRS, INSERM, Faculté de Médecine, Université Clermont Auvergne, 63000 Clermont-Ferrand, France
| | - Laure Teysset
- Transgenerational Epigenetics and Small RNA Biology, Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, F-75005 Paris, France
| | - Antoine Boivin
- Transgenerational Epigenetics and Small RNA Biology, Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, F-75005 Paris, France
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4
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Wang X, Ramat A, Simonelig M, Liu MF. Emerging roles and functional mechanisms of PIWI-interacting RNAs. Nat Rev Mol Cell Biol 2023; 24:123-141. [PMID: 36104626 DOI: 10.1038/s41580-022-00528-0] [Citation(s) in RCA: 61] [Impact Index Per Article: 61.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/01/2022] [Indexed: 02/02/2023]
Abstract
PIWI-interacting RNAs (piRNAs) are a class of small non-coding RNAs that associate with proteins of the PIWI clade of the Argonaute family. First identified in animal germ line cells, piRNAs have essential roles in germ line development. The first function of PIWI-piRNA complexes to be described was the silencing of transposable elements, which is crucial for maintaining the integrity of the germ line genome. Later studies provided new insights into the functions of PIWI-piRNA complexes by demonstrating that they regulate protein-coding genes. Recent studies of piRNA biology, including in new model organisms such as golden hamsters, have deepened our understanding of both piRNA biogenesis and piRNA function. In this Review, we discuss the most recent advances in our understanding of piRNA biogenesis, the molecular mechanisms of piRNA function and the emerging roles of piRNAs in germ line development mainly in flies and mice, and in infertility, cancer and neurological diseases in humans.
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Affiliation(s)
- Xin Wang
- State Key Laboratory of Molecular Biology, Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China.,Key Laboratory of Systems Health Science of Zhejiang Province, School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China
| | - Anne Ramat
- Institute of Human Genetics, University of Montpellier, CNRS, Montpellier, France
| | - Martine Simonelig
- Institute of Human Genetics, University of Montpellier, CNRS, Montpellier, France.
| | - Mo-Fang Liu
- State Key Laboratory of Molecular Biology, Shanghai Key Laboratory of Molecular Andrology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China. .,Key Laboratory of Systems Health Science of Zhejiang Province, School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou, China. .,School of Life Science and Technology, Shanghai Tech University, Shanghai, China.
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5
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Baumgartner L, Handler D, Platzer SW, Yu C, Duchek P, Brennecke J. The Drosophila ZAD zinc finger protein Kipferl guides Rhino to piRNA clusters. eLife 2022; 11:80067. [PMID: 36193674 PMCID: PMC9531945 DOI: 10.7554/elife.80067] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Accepted: 08/11/2022] [Indexed: 12/15/2022] Open
Abstract
RNA interference systems depend on the synthesis of small RNA precursors whose sequences define the target spectrum of these silencing pathways. The Drosophila Heterochromatin Protein 1 (HP1) variant Rhino permits transcription of PIWI-interacting RNA (piRNA) precursors within transposon-rich heterochromatic loci in germline cells. Current models propose that Rhino’s specific chromatin occupancy at piRNA source loci is determined by histone marks and maternally inherited piRNAs, but also imply the existence of other, undiscovered specificity cues. Here, we identify a member of the diverse family of zinc finger associated domain (ZAD)-C2H2 zinc finger proteins, Kipferl, as critical Rhino cofactor in ovaries. By binding to guanosine-rich DNA motifs and interacting with the Rhino chromodomain, Kipferl recruits Rhino to specific loci and stabilizes it on chromatin. In kipferl mutant flies, Rhino is lost from most of its target chromatin loci and instead accumulates on pericentromeric Satellite arrays, resulting in decreased levels of transposon targeting piRNAs and impaired fertility. Our findings reveal that DNA sequence, in addition to the H3K9me3 mark, determines the identity of piRNA source loci and provide insight into how Rhino might be caught in the crossfire of genetic conflicts. The genes within our DNA encode the essentials of our body plan and how each task in the body is achieved. However, our genome also contains many repetitive regions of DNA that do not encode functional genes. Some of these regions are genetic parasites known as transposons that try to multiply and spread around the DNA of their host. To prevent transposon DNA from interfering with the way the body operates, humans and other animals have evolved elaborate defense mechanisms to identify transposons and prevent them from multiplying. In one such mechanism, known as the piRNA pathway, the host makes small molecules known as piRNAs that have sequences complementary to those of transposons, and act as guides to silence the transposons. The instructions to make these piRNAs are stored in the form of transposon fragments in dedicated regions of host DNA called piRNA clusters. These clusters thereby act as genetic memory, allowing the host to recognize and silence specific transposons in other locations within the host’s genome. In fruit flies, a protein called Rhino binds to piRNA clusters that are densely packed to allow piRNAs to be made. However, it remained unclear how Rhino is able to identify and bind to piRNA clusters, but not to other similarly densely packed regions of DNA. Baumgartner et al. used a combination of genetic, genomic, and imaging approaches to study how Rhino finds its way in the fruit fly genome. They found that another protein called Kipferl interacts with Rhino and is required for Rhino to bind to nearly all piRNA clusters. Since Kipferl can by itself bind to the sequences that Rhino needs to find, the results suggest that Kipferl acts to recruit and initiate Rhino binding within densely packed piRNA clusters. Further experiments found that, in flies lacking Kipferl, Rhino binds to regions of DNA called Satellite repeats, hinting that these selfish sequences may compete for Rhino for their own benefit. The finding that Kipferl and Rhino work together to define the memory system of the piRNA pathway strongly advances our understanding of how a sequence-specific defense system based on small RNAs can be established.
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Affiliation(s)
- Lisa Baumgartner
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna BioCenter, Vienna, Austria.,Vienna BioCenter PhD Program, Doctoral School of the University of Vienna and Medical University of Vienna, Vienna, Austria
| | - Dominik Handler
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna BioCenter, Vienna, Austria
| | - Sebastian Wolfgang Platzer
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna BioCenter, Vienna, Austria
| | - Changwei Yu
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna BioCenter, Vienna, Austria
| | - Peter Duchek
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna BioCenter, Vienna, Austria
| | - Julius Brennecke
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna BioCenter, Vienna, Austria
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6
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ElMaghraby MF, Tirian L, Senti KA, Meixner K, Brennecke J. A genetic toolkit for studying transposon control in the Drosophila melanogaster ovary. Genetics 2022; 220:iyab179. [PMID: 34718559 PMCID: PMC8733420 DOI: 10.1093/genetics/iyab179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 09/19/2021] [Indexed: 11/12/2022] Open
Abstract
Argonaute proteins of the PIWI clade complexed with PIWI-interacting RNAs (piRNAs) protect the animal germline genome by silencing transposable elements. One of the leading experimental systems for studying piRNA biology is the Drosophila melanogaster ovary. In addition to classical mutagenesis, transgenic RNA interference (RNAi), which enables tissue-specific silencing of gene expression, plays a central role in piRNA research. Here, we establish a versatile toolkit focused on piRNA biology that combines germline transgenic RNAi, GFP marker lines for key proteins of the piRNA pathway, and reporter transgenes to establish genetic hierarchies. We compare constitutive, pan-germline RNAi with an equally potent transgenic RNAi system that is activated only after germ cell cyst formation. Stage-specific RNAi allows us to investigate the role of genes essential for germline cell survival, for example, nuclear RNA export or the SUMOylation pathway, in piRNA-dependent and independent transposon silencing. Our work forms the basis for an expandable genetic toolkit provided by the Vienna Drosophila Resource Center.
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Affiliation(s)
- Mostafa F ElMaghraby
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Vienna 1030, Austria
- Vienna BioCenter PhD Program, Doctoral School at the University of Vienna and Medical University of Vienna, Vienna 1030, Austria
| | - Laszlo Tirian
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Vienna 1030, Austria
| | - Kirsten-André Senti
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Vienna 1030, Austria
| | - Katharina Meixner
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Vienna 1030, Austria
| | - Julius Brennecke
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Vienna 1030, Austria
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7
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To export, or not to export: how nuclear export factor variants resolve Piwi's dilemma. Biochem Soc Trans 2021; 49:2073-2079. [PMID: 34643228 DOI: 10.1042/bst20201171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 09/06/2021] [Accepted: 09/15/2021] [Indexed: 11/17/2022]
Abstract
Piwi-interacting RNAs (piRNAs) defend animal gonads by guiding PIWI-clade Argonaute proteins to silence transposons. The nuclear Piwi/piRNA complexes confer transcriptional repression of transposons, which is accompanied with heterochromatin formation at target loci. On the other hand, piRNA clusters, genomic loci that transcribe piRNA precursors composed of transposon fragments, are often recognized by piRNAs to define their heterochromatic identity. Therefore, Piwi/piRNA complexes must resolve this conundrum of silencing transposons while allowing the expression of piRNA precursors, at least in Drosophila germlines. This review is focused on recent advances how the piRNA pathway deals with this genetic conflict.
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8
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Zhang G, Yu T, Parhad SS, Ho S, Weng Z, Theurkauf WE. piRNA-independent transposon silencing by the Drosophila THO complex. Dev Cell 2021; 56:2623-2635.e5. [PMID: 34547226 DOI: 10.1016/j.devcel.2021.08.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Revised: 06/18/2021] [Accepted: 08/27/2021] [Indexed: 12/19/2022]
Abstract
piRNAs guide Piwi/Panoramix-dependent H3K9me3 chromatin modification and transposon silencing during Drosophila germline development. The THO RNA export complex is composed of Hpr1, Tho2, and Thoc5-7. Null thoc7 mutations, which displace Thoc5 and Thoc6 from a Tho2-Hpr1 subcomplex, reduce expression of a subset of germline piRNAs and increase transposon expression, suggesting that THO silences transposons by promoting piRNA biogenesis. Here, we show that the thoc7-null mutant combination increases transposon transcription but does not reduce anti-sense piRNAs targeting half of the transcriptionally activated transposon families. These mutations also fail to reduce piRNA-guided H3K9me3 chromatin modification or block Panoramix-dependent silencing of a reporter transgene, and unspliced transposon transcripts co-precipitate with THO through a Piwi- and Panoramix-independent mechanism. Mutations in piwi also dominantly enhance germline defects associated with thoc7-null alleles. THO thus functions in a piRNA-independent transposon-silencing pathway, which acts cooperatively with Piwi to support germline development.
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Affiliation(s)
- Gen Zhang
- Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605, USA
| | - Tianxiong Yu
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605, USA; Department of Bioinformatics, School of Life Sciences and Technology, Tongji University, Shanghai, People's Republic of China
| | - Swapnil S Parhad
- Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605, USA
| | - Samantha Ho
- Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605, USA
| | - Zhiping Weng
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605, USA.
| | - William E Theurkauf
- Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605, USA.
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9
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Parhad SS, Yu T, Zhang G, Rice NP, Weng Z, Theurkauf WE. Adaptive Evolution Targets a piRNA Precursor Transcription Network. Cell Rep 2021; 30:2672-2685.e5. [PMID: 32101744 PMCID: PMC7061269 DOI: 10.1016/j.celrep.2020.01.109] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Revised: 10/23/2019] [Accepted: 01/30/2020] [Indexed: 12/18/2022] Open
Abstract
In Drosophila, transposon-silencing piRNAs are derived from heterochromatic clusters and a subset of euchromatic transposon insertions, which are bound by the Rhino-Deadlock-Cutoff complex. The HP1 homolog Rhino binds to Deadlock, which recruits TRF2 to promote non-canonical transcription from both genomic strands. Cuff function is less well understood, but this Rai1 homolog shows hallmarks of adaptive evolution, which can remodel functional interactions within host defense systems. Supporting this hypothesis, Drosophila simulans Cutoff is a dominant-negative allele when expressed in Drosophila melanogaster, in which it traps Deadlock, TRF2, and the conserved transcriptional co-repressor CtBP in stable complexes. Cutoff functions with Rhino and Deadlock to drive non-canonical transcription. In contrast, CtBP suppresses canonical transcription of transposons and promoters flanking the major germline clusters, and canonical transcription interferes with downstream non-canonical transcription and piRNA production. Adaptive evolution thus targets interactions among Cutoff, TRF2, and CtBP that balance canonical and non-canonical piRNA precursor transcription.
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Affiliation(s)
- Swapnil S Parhad
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Tianxiong Yu
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA; School of Life Sciences and Technology, Tongji University, Shanghai 200092, China
| | - Gen Zhang
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Nicholas P Rice
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Zhiping Weng
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
| | - William E Theurkauf
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA.
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Yu T, Fan K, Özata DM, Zhang G, Fu Y, Theurkauf WE, Zamore PD, Weng Z. Long first exons and epigenetic marks distinguish conserved pachytene piRNA clusters from other mammalian genes. Nat Commun 2021; 12:73. [PMID: 33397987 PMCID: PMC7782496 DOI: 10.1038/s41467-020-20345-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Accepted: 11/17/2020] [Indexed: 02/06/2023] Open
Abstract
In the male germ cells of placental mammals, 26-30-nt-long PIWI-interacting RNAs (piRNAs) emerge when spermatocytes enter the pachytene phase of meiosis. In mice, pachytene piRNAs derive from ~100 discrete autosomal loci that produce canonical RNA polymerase II transcripts. These piRNA clusters bear 5' caps and 3' poly(A) tails, and often contain introns that are removed before nuclear export and processing into piRNAs. What marks pachytene piRNA clusters to produce piRNAs, and what confines their expression to the germline? We report that an unusually long first exon (≥ 10 kb) or a long, unspliced transcript correlates with germline-specific transcription and piRNA production. Our integrative analysis of transcriptome, piRNA, and epigenome datasets across multiple species reveals that a long first exon is an evolutionarily conserved feature of pachytene piRNA clusters. Furthermore, a highly methylated promoter, often containing a low or intermediate level of CG dinucleotides, correlates with germline expression and somatic silencing of pachytene piRNA clusters. Pachytene piRNA precursor transcripts bind THOC1 and THOC2, THO complex subunits known to promote transcriptional elongation and mRNA nuclear export. Together, these features may explain why the major sources of pachytene piRNA clusters specifically generate these unique small RNAs in the male germline of placental mammals.
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Affiliation(s)
- Tianxiong Yu
- Department of Thoracic Surgery, Clinical Translational Research Center, Shanghai Pulmonary Hospital, The School of Life Sciences and Technology, Tongji University, 200092, Shanghai, China
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA, 01605, USA
| | - Kaili Fan
- Department of Thoracic Surgery, Clinical Translational Research Center, Shanghai Pulmonary Hospital, The School of Life Sciences and Technology, Tongji University, 200092, Shanghai, China
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA, 01605, USA
| | - Deniz M Özata
- RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA, 01605, USA
| | - Gen Zhang
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA, 01605, USA
| | - Yu Fu
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA, 01605, USA
- Bioinformatics Program, Boston University, 44 Cummington Mall, Boston, MA, 02215, USA
- Oncology Drug Discovery Unit, Takeda Pharmaceuticals, Cambridge, MA, 02139, USA
| | - William E Theurkauf
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA, 01605, USA.
| | - Phillip D Zamore
- RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA, 01605, USA.
| | - Zhiping Weng
- Department of Thoracic Surgery, Clinical Translational Research Center, Shanghai Pulmonary Hospital, The School of Life Sciences and Technology, Tongji University, 200092, Shanghai, China.
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA, 01605, USA.
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11
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Luna R, Rondón AG, Pérez-Calero C, Salas-Armenteros I, Aguilera A. The THO Complex as a Paradigm for the Prevention of Cotranscriptional R-Loops. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2020; 84:105-114. [PMID: 32493765 DOI: 10.1101/sqb.2019.84.039594] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Different proteins associate with the nascent RNA and the RNA polymerase (RNAP) to catalyze the transcription cycle and RNA export. If these processes are not properly controlled, the nascent RNA can thread back and hybridize to the DNA template forming R-loops capable of stalling replication, leading to DNA breaks. Given the transcriptional promiscuity of the genome, which leads to large amounts of RNAs from mRNAs to different types of ncRNAs, these can become a major threat to genome integrity if they form R-loops. Consequently, cells have evolved nuclear factors to prevent this phenomenon that includes THO, a conserved eukaryotic complex acting in transcription elongation and RNA processing and export that upon inactivation causes genome instability linked to R-loop accumulation. We revise and discuss here the biological relevance of THO and a number of RNA helicases, including the THO partner UAP56/DDX39B, as a paradigm of the cellular mechanisms of cotranscriptional R-loop prevention.
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Affiliation(s)
- Rosa Luna
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, 41092 Seville, Spain
| | - Ana G Rondón
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, 41092 Seville, Spain
| | - Carmen Pérez-Calero
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, 41092 Seville, Spain
| | - Irene Salas-Armenteros
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, 41092 Seville, Spain
| | - Andrés Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, 41092 Seville, Spain
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Kelleher ES, Barbash DA, Blumenstiel JP. Taming the Turmoil Within: New Insights on the Containment of Transposable Elements. Trends Genet 2020; 36:474-489. [PMID: 32473745 DOI: 10.1016/j.tig.2020.04.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 04/15/2020] [Accepted: 04/17/2020] [Indexed: 12/28/2022]
Abstract
Transposable elements (TEs) are mobile genetic parasites that can exponentially increase their genomic abundance through self-propagation. Classic theoretical papers highlighted the importance of two potentially escalating forces that oppose TE spread: regulated transposition and purifying selection. Here, we review new insights into mechanisms of TE regulation and purifying selection, which reveal the remarkable foresight of these theoretical models. We further highlight emergent connections between transcriptional control enacted by small RNAs and the contribution of TE insertions to structural mutation and host-gene regulation. Finally, we call for increased comparative analysis of TE dynamics and fitness effects, as well as host control mechanisms, to reveal how interconnected forces shape the differential prevalence and distribution of TEs across the tree of life.
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13
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Abstract
Transposons are major genome constituents that can mobilize and trigger mutations, DNA breaks and chromosome rearrangements. Transposon silencing is particularly important in the germline, which is dedicated to transmission of the inherited genome. Piwi-interacting RNAs (piRNAs) guide a host defence system that transcriptionally and post-transcriptionally silences transposons during germline development. While germline control of transposons by the piRNA pathway is conserved, many piRNA pathway genes are evolving rapidly under positive selection, and the piRNA biogenesis machinery shows remarkable phylogenetic diversity. Conservation of core function combined with rapid gene evolution is characteristic of a host–pathogen arms race, suggesting that transposons and the piRNA pathway are engaged in an evolutionary tug of war that is driving divergence of the biogenesis machinery. Recent studies suggest that this process may produce biochemical incompatibilities that contribute to reproductive isolation and species divergence.
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Affiliation(s)
- Swapnil S Parhad
- Program in Molecular Medicine, University of Massachusetts Medical School , 373 Plantation Street, Worcester, MA 01605 , USA
| | - William E Theurkauf
- Program in Molecular Medicine, University of Massachusetts Medical School , 373 Plantation Street, Worcester, MA 01605 , USA
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14
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Kordyukova M, Sokolova O, Morgunova V, Ryazansky S, Akulenko N, Glukhov S, Kalmykova A. Nuclear Ccr4-Not mediates the degradation of telomeric and transposon transcripts at chromatin in the Drosophila germline. Nucleic Acids Res 2020; 48:141-156. [PMID: 31724732 PMCID: PMC7145718 DOI: 10.1093/nar/gkz1072] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Revised: 10/28/2019] [Accepted: 10/30/2019] [Indexed: 01/05/2023] Open
Abstract
Ccr4-Not is a highly conserved complex involved in cotranscriptional RNA surveillance pathways in yeast. In Drosophila, Ccr4-Not is linked to the translational repression of miRNA targets and the posttranscriptional control of maternal mRNAs during oogenesis and embryonic development. Here, we describe a new role for the Ccr4-Not complex in nuclear RNA metabolism in the Drosophila germline. Ccr4 depletion results in the accumulation of transposable and telomeric repeat transcripts in the fraction of chromatin-associated RNA; however, it does not affect small RNA levels or the heterochromatin state of the target loci. Nuclear targets of Ccr4 mainly comprise active full-length transposable elements (TEs) and telomeric and subtelomeric repeats. Moreover, Ccr4-Not foci localize at telomeres in a Piwi-dependent manner, suggesting a functional relationship between these pathways. Indeed, we detected interactions between the components of the Ccr4-Not complex and piRNA machinery, which indicates that these pathways cooperate in the nucleus to recognize and degrade TE transcripts at transcription sites. These data reveal a new layer of transposon control in the germline, which is critical for the maintenance of genome integrity.
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Affiliation(s)
- Maria Kordyukova
- Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia
| | - Olesya Sokolova
- Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia
| | - Valeriya Morgunova
- Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia
| | - Sergei Ryazansky
- Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia
| | - Natalia Akulenko
- Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia
| | - Sergey Glukhov
- Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia
| | - Alla Kalmykova
- Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia
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15
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The piRNA Response to Retroviral Invasion of the Koala Genome. Cell 2019; 179:632-643.e12. [PMID: 31607510 DOI: 10.1016/j.cell.2019.09.002] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 07/19/2019] [Accepted: 08/30/2019] [Indexed: 12/20/2022]
Abstract
Antisense Piwi-interacting RNAs (piRNAs) guide silencing of established transposons during germline development, and sense piRNAs drive ping-pong amplification of the antisense pool, but how the germline responds to genome invasion is not understood. The KoRV-A gammaretrovirus infects the soma and germline and is sweeping through wild koalas by a combination of horizontal and vertical transfer, allowing direct analysis of retroviral invasion of the germline genome. Gammaretroviruses produce spliced Env mRNAs and unspliced transcripts encoding Gag, Pol, and the viral genome, but KoRV-A piRNAs are almost exclusively derived from unspliced genomic transcripts and are strongly sense-strand biased. Significantly, selective piRNA processing of unspliced proviral transcripts is conserved from insects to placental mammals. We speculate that bypassed splicing generates a conserved molecular pattern that directs proviral genomic transcripts to the piRNA biogenesis machinery and that this "innate" piRNA response suppresses transposition until antisense piRNAs are produced, establishing sequence-specific adaptive immunity.
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16
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Abstract
RNA export is tightly coupled to splicing in metazoans. In the Drosophila germline, precursors for the majority of Piwi-interacting RNAs (piRNAs) are unspliced. In this issue of Genes & Development, Kneuss and colleagues (pp. 1208-1220) identify Nxf3 as a novel germline-specific export adapter for such unspliced transcripts. Their findings reveal the sequence of events leading from its role at the site of transcription to delivery of the cargo to cytoplasmic piRNA biogenesis sites.
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Affiliation(s)
- Mateusz Mendel
- Department of Molecular Biology, Science III, University of Geneva, CH-1211 Geneva 4, Switzerland
| | - Ramesh S Pillai
- Department of Molecular Biology, Science III, University of Geneva, CH-1211 Geneva 4, Switzerland
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17
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Kneuss E, Munafò M, Eastwood EL, Deumer US, Preall JB, Hannon GJ, Czech B. Specialization of the Drosophila nuclear export family protein Nxf3 for piRNA precursor export. Genes Dev 2019; 33:1208-1220. [PMID: 31416967 PMCID: PMC6719614 DOI: 10.1101/gad.328690.119] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2019] [Accepted: 07/15/2019] [Indexed: 12/29/2022]
Abstract
The PIWI-interacting RNA (piRNA) pathway is a conserved small RNA-based immune system that protects animal germ cell genomes from the harmful effects of transposon mobilization. In Drosophila ovaries, most piRNAs originate from dual-strand clusters, which generate piRNAs from both genomic strands. Dual-strand clusters use noncanonical transcription mechanisms. Although transcribed by RNA polymerase II, cluster transcripts lack splicing signatures and poly(A) tails. mRNA processing is important for general mRNA export mediated by nuclear export factor 1 (Nxf1). Although UAP56, a component of the transcription and export complex, has been implicated in piRNA precursor export, it remains unknown how dual-strand cluster transcripts are specifically targeted for piRNA biogenesis by export from the nucleus to cytoplasmic processing centers. Here we report that dual-strand cluster transcript export requires CG13741/Bootlegger and the Drosophila nuclear export factor family protein Nxf3. Bootlegger is specifically recruited to piRNA clusters and in turn brings Nxf3. We found that Nxf3 specifically binds to piRNA precursors and is essential for their export to piRNA biogenesis sites, a process that is critical for germline transposon silencing. Our data shed light on how dual-strand clusters compensate for a lack of canonical features of mature mRNAs to be specifically exported via Nxf3, ensuring proper piRNA production.
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Affiliation(s)
- Emma Kneuss
- Cancer Research UK Cambridge Institute, Li Ka Shing Centre, University of Cambridge, Cambridge CB2 0RE, United Kingdom
| | - Marzia Munafò
- Cancer Research UK Cambridge Institute, Li Ka Shing Centre, University of Cambridge, Cambridge CB2 0RE, United Kingdom
| | - Evelyn L Eastwood
- Cancer Research UK Cambridge Institute, Li Ka Shing Centre, University of Cambridge, Cambridge CB2 0RE, United Kingdom
| | - Undine-Sophie Deumer
- Cancer Research UK Cambridge Institute, Li Ka Shing Centre, University of Cambridge, Cambridge CB2 0RE, United Kingdom
| | - Jonathan B Preall
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
| | - Gregory J Hannon
- Cancer Research UK Cambridge Institute, Li Ka Shing Centre, University of Cambridge, Cambridge CB2 0RE, United Kingdom
| | - Benjamin Czech
- Cancer Research UK Cambridge Institute, Li Ka Shing Centre, University of Cambridge, Cambridge CB2 0RE, United Kingdom
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18
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ElMaghraby MF, Andersen PR, Pühringer F, Hohmann U, Meixner K, Lendl T, Tirian L, Brennecke J. A Heterochromatin-Specific RNA Export Pathway Facilitates piRNA Production. Cell 2019; 178:964-979.e20. [PMID: 31398345 DOI: 10.1016/j.cell.2019.07.007] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Revised: 06/18/2019] [Accepted: 06/29/2019] [Indexed: 01/22/2023]
Abstract
PIWI-interacting RNAs (piRNAs) guide transposon silencing in animals. The 22-30 nt piRNAs are processed in the cytoplasm from long non-coding RNAs that often lack RNA processing hallmarks of export-competent transcripts. By studying how these transcripts achieve nuclear export, we uncover an RNA export pathway specific for piRNA precursors in the Drosophila germline. This pathway requires Nxf3-Nxt1, a variant of the hetero-dimeric mRNA export receptor Nxf1-Nxt1. Nxf3 interacts with UAP56, a nuclear RNA helicase essential for mRNA export, and CG13741/Bootlegger, which recruits Nxf3-Nxt1 and UAP56 to heterochromatic piRNA source loci. Upon RNA cargo binding, Nxf3 achieves nuclear export via the exportin Crm1 and accumulates together with Bootlegger in peri-nuclear nuage, suggesting that after export, Nxf3-Bootlegger delivers precursor transcripts to the piRNA processing sites. These findings indicate that the piRNA pathway bypasses nuclear RNA surveillance systems to export unprocessed transcripts to the cytoplasm, a strategy also exploited by retroviruses.
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Affiliation(s)
- Mostafa F ElMaghraby
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Dr. Bohrgasse 3, 1030 Vienna, Austria
| | - Peter Refsing Andersen
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Dr. Bohrgasse 3, 1030 Vienna, Austria.
| | - Florian Pühringer
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Dr. Bohrgasse 3, 1030 Vienna, Austria
| | - Ulrich Hohmann
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Dr. Bohrgasse 3, 1030 Vienna, Austria; Institute of Molecular Pathology (IMP), Vienna BioCenter (VBC), Campus-Vienna-Biocenter 1, 1030 Vienna, Austria
| | - Katharina Meixner
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Dr. Bohrgasse 3, 1030 Vienna, Austria
| | - Thomas Lendl
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Dr. Bohrgasse 3, 1030 Vienna, Austria; Institute of Molecular Pathology (IMP), Vienna BioCenter (VBC), Campus-Vienna-Biocenter 1, 1030 Vienna, Austria
| | - Laszlo Tirian
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Dr. Bohrgasse 3, 1030 Vienna, Austria
| | - Julius Brennecke
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), Dr. Bohrgasse 3, 1030 Vienna, Austria.
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