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Wierzbicki F, Kofler R. The composition of piRNA clusters in Drosophila melanogaster deviates from expectations under the trap model. BMC Biol 2023; 21:224. [PMID: 37858221 PMCID: PMC10588112 DOI: 10.1186/s12915-023-01727-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Accepted: 10/06/2023] [Indexed: 10/21/2023] Open
Abstract
BACKGROUND It is widely assumed that the invasion of a transposable element (TE) in mammals and invertebrates is stopped when a copy of the TE jumps into a piRNA cluster (i.e., the trap model). However, recent works, which for example showed that deletion of three major piRNA clusters has no effect on TE activity, cast doubt on the trap model. RESULTS Here, we test the trap model from a population genetics perspective. Our simulations show that the composition of regions that act as transposon traps (i.e., potentially piRNA clusters) ought to deviate from regions that have no effect on TE activity. We investigated TEs in five Drosophila melanogaster strains using three complementary approaches to test whether the composition of piRNA clusters matches these expectations. We found that the abundance of TE families inside and outside of piRNA clusters is highly correlated, although this is not expected under the trap model. Furthermore, the distribution of the number of TE insertions in piRNA clusters is also much broader than expected. CONCLUSIONS We found that the observed composition of piRNA clusters is not in agreement with expectations under the simple trap model. Dispersed piRNA producing TE insertions and temporal as well as spatial heterogeneity of piRNA clusters may account for these deviations.
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Affiliation(s)
- Filip Wierzbicki
- Institut für Populationsgenetik, Vetmeduni Vienna, Vienna, Austria
- Vienna Graduate School of Population Genetics, Vienna, Austria
| | - Robert Kofler
- Institut für Populationsgenetik, Vetmeduni Vienna, Vienna, Austria.
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2
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Asif-Laidin A, Casier K, Ziriat Z, Boivin A, Viodé E, Delmarre V, Ronsseray S, Carré C, Teysset L. Modeling early germline immunization after horizontal transfer of transposable elements reveals internal piRNA cluster heterogeneity. BMC Biol 2023; 21:117. [PMID: 37226160 DOI: 10.1186/s12915-023-01616-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 05/05/2023] [Indexed: 05/26/2023] Open
Abstract
BACKGROUND A fraction of all genomes is composed of transposable elements (TEs) whose mobility needs to be carefully controlled. In gonads, TE activity is repressed by PIWI-interacting RNAs (piRNAs), a class of small RNAs synthesized by heterochromatic loci enriched in TE fragments, called piRNA clusters. Maintenance of active piRNA clusters across generations is secured by maternal piRNA inheritance providing the memory for TE repression. On rare occasions, genomes encounter horizontal transfer (HT) of new TEs with no piRNA targeting them, threatening the host genome integrity. Naïve genomes can eventually start to produce new piRNAs against these genomic invaders, but the timing of their emergence remains elusive. RESULTS Using a set of TE-derived transgenes inserted in different germline piRNA clusters and functional assays, we have modeled a TE HT in Drosophila melanogaster. We have found that the complete co-option of these transgenes by a germline piRNA cluster can occur within four generations associated with the production of new piRNAs all along the transgenes and the germline silencing of piRNA sensors. Synthesis of new transgenic TE piRNAs is linked to piRNA cluster transcription dependent on Moonshiner and heterochromatin mark deposition that propagates more efficiently on short sequences. Moreover, we found that sequences located within piRNA clusters can have different piRNA profiles and can influence transcript accumulation of nearby sequences. CONCLUSIONS Our study reveals that genetic and epigenetic properties, such as transcription, piRNA profiles, heterochromatin, and conversion efficiency along piRNA clusters, could be heterogeneous depending on the sequences that compose them. These findings suggest that the capacity of transcriptional signal erasure induced by the chromatin complex specific of the piRNA cluster can be incomplete through the piRNA cluster loci. Finally, these results have revealed an unexpected level of complexity that highlights a new magnitude of piRNA cluster plasticity fundamental for the maintenance of genome integrity.
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Affiliation(s)
- Amna Asif-Laidin
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France
| | - Karine Casier
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France
- Present Address: CNRS, Institut de Biologie Physico-Chimique, Laboratoire de Biologie Moléculaire et Cellulaire des Eucaryotes, UMR8226, Telomere Biology, Paris, F-75005, France
| | - Zoheir Ziriat
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France
| | - Antoine Boivin
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France
| | - Elise Viodé
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France
| | - Valérie Delmarre
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France
| | - Stéphane Ronsseray
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France
| | - Clément Carré
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France
| | - Laure Teysset
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Biologie du Développement, UMR7622, "Transgenerational Epigenetics & Small RNA Biology", Paris, F-75005, France.
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Tomar SS, Hua-Van A, Le Rouzic A. A population genetics theory for piRNA-regulated transposable elements. Theor Popul Biol 2023; 150:1-13. [PMID: 36863578 DOI: 10.1016/j.tpb.2023.02.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Revised: 02/16/2023] [Accepted: 02/21/2023] [Indexed: 03/04/2023]
Abstract
Transposable elements (TEs) are self-reproducing selfish DNA sequences that can invade the genome of virtually all living species. Population genetics models have shown that TE copy numbers generally reach a limit, either because the transposition rate decreases with the number of copies (transposition regulation) or because TE copies are deleterious, and thus purged by natural selection. Yet, recent empirical discoveries suggest that TE regulation may mostly rely on piRNAs, which require a specific mutational event (the insertion of a TE copy in a piRNA cluster) to be activated - the so-called TE regulation "trap model". We derived new population genetics models accounting for this trap mechanism, and showed that the resulting equilibria differ substantially from previous expectations based on a transposition-selection equilibrium. We proposed three sub-models, depending on whether or not genomic TE copies and piRNA cluster TE copies are selectively neutral or deleterious, and we provide analytical expressions for maximum and equilibrium copy numbers, as well as cluster frequencies for all of them. In the full neutral model, the equilibrium is achieved when transposition is completely silenced, and this equilibrium does not depend on the transposition rate. When genomic TE copies are deleterious but not cluster TE copies, no long-term equilibrium is possible, and active TEs are eventually eliminated after an active incomplete invasion stage. When all TE copies are deleterious, a transposition-selection equilibrium exists, but the invasion dynamics is not monotonic, and the copy number peaks before decreasing. Mathematical predictions were in good agreement with numerical simulations, except when genetic drift and/or linkage disequilibrium dominates. Overall, the trap-model dynamics appeared to be substantially more stochastic and less repeatable than traditional regulation models.
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Affiliation(s)
- Siddharth S Tomar
- Université Paris-Saclay, CNRS, IRD, UMR EGCE, 12 Route 128, Gif-sur-Yvette, 91190, France.
| | - Aurélie Hua-Van
- Université Paris-Saclay, CNRS, IRD, UMR EGCE, 12 Route 128, Gif-sur-Yvette, 91190, France.
| | - Arnaud Le Rouzic
- Université Paris-Saclay, CNRS, IRD, UMR EGCE, 12 Route 128, Gif-sur-Yvette, 91190, France.
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4
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Wierzbicki F, Kofler R, Signor S. Evolutionary dynamics of piRNA clusters in Drosophila. Mol Ecol 2023; 32:1306-1322. [PMID: 34878692 DOI: 10.1111/mec.16311] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 11/24/2021] [Accepted: 12/01/2021] [Indexed: 12/21/2022]
Abstract
Small RNAs produced from transposable element (TE)-rich sections of the genome, termed piRNA clusters, are a crucial component in the genomic defence against selfish DNA. In animals, it is thought the invasion of a TE is stopped when a copy of the TE inserts into a piRNA cluster, triggering the production of cognate small RNAs that silence the TE. Despite this importance for TE control, little is known about the evolutionary dynamics of piRNA clusters, mostly because these repeat-rich regions are difficult to assemble and compare. Here, we establish a framework for studying the evolution of piRNA clusters quantitatively. Previously introduced quality metrics and a newly developed software for multiple alignments of repeat annotations (Manna) allow us to estimate the level of polymorphism segregating in piRNA clusters and the divergence among homologous piRNA clusters. By studying 20 conserved piRNA clusters in multiple assemblies of four Drosophila species, we show that piRNA clusters are evolving rapidly. While 70%-80% of the clusters are conserved within species, the clusters share almost no similarity between species as closely related as D. melanogaster and D. simulans. Furthermore, abundant insertions and deletions are segregating within the Drosophila species. We show that the evolution of clusters is mainly driven by large insertions of recently active TEs and smaller deletions mostly in older TEs. The effect of these forces is so rapid that homologous clusters often do not contain insertions from the same TE families.
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Affiliation(s)
- Filip Wierzbicki
- Institut für Populationsgenetik, Vetmeduni Vienna, Vienna, Austria
- Vienna Graduate School of Population Genetics, Vienna, Austria
| | - Robert Kofler
- Institut für Populationsgenetik, Vetmeduni Vienna, Vienna, Austria
| | - Sarah Signor
- Biological Sciences, North Dakota State University, Fargo, North Dakota, USA
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5
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Abstract
Aim: To understand the effect of HIV infection and cocaine exposure on piRNA expression in human primary astrocytes. Materials & methods: We used small RNA sequencing analysis to investigate the impacts of HIV-1 Tat and cocaine coexposure on the expression of piRNAs in human primary astrocytes. Results: We identified 27,700 piRNAs and analyzed them by small RNA next-generation sequencing. A total of 239 piRNAs were significantly altered by HIV-1 Tat and cocaine coexposure. We also identified PIWIL1, PIWIL2, PIWIL3 and PIWIL4 as interacting partners of piRNAs that were affected by cocaine and HIV-1 Tat coexposure. Epigenetic changes in the expression levels of these piRNA targets were associated with Kyoto Encyclopedia of Genes and Genomes pathways of energy metabolism and neurodegeneration. Conclusion: These findings provide evidence that cocaine exposure and HIV infection affect the expression levels of piRNA, PIWIL1, PIWIL2, PIWIL3 and PIWIL4.
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Affiliation(s)
- Mayur Doke
- Department of Pharmaceutical Sciences, Irma Lerma Rangel College of Pharmacy, Texas A&M University Health Science Center, Kingsville, TX 78363, USA
| | - Fatah Kashanchi
- National Center for Biodefense & Infectious Disease, Laboratory of Molecular Virology, George Mason University, Manassas, VA 20110, USA
| | - Mansoor A Khan
- Department of Pharmaceutical Sciences, Irma Lerma Rangel College of Pharmacy, Texas A&M University Health Science Center, Kingsville, TX 78363, USA
| | - Thangavel Samikkannu
- Department of Pharmaceutical Sciences, Irma Lerma Rangel College of Pharmacy, Texas A&M University Health Science Center, Kingsville, TX 78363, USA,Author for correspondence: Tel.: +1 361 221 0750;
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6
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Wierzbicki F, Schwarz F, Cannalonga O, Kofler R. Novel quality metrics allow identifying and generating high-quality assemblies of piRNA clusters. Mol Ecol Resour 2022; 22:102-121. [PMID: 34181811 DOI: 10.1111/1755-0998.13455] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 04/30/2021] [Accepted: 06/14/2021] [Indexed: 12/30/2022]
Abstract
In most animals, it is thought that the proliferation of a transposable element (TE) is stopped when the TE jumps into a piRNA cluster. Despite this central importance, little is known about the composition and the evolutionary dynamics of piRNA clusters. This is largely because piRNA clusters are notoriously difficult to assemble as they are frequently composed of highly repetitive DNA. With long reads, we may finally be able to obtain reliable assemblies of piRNA clusters. Unfortunately, it is unclear how to generate and identify the best assemblies, as many assembly strategies exist and standard quality metrics are ignorant of TEs. To address these problems, we introduce several novel quality metrics that assess: (a) the fraction of completely assembled piRNA clusters, (b) the quality of the assembled clusters and (c) whether an assembly captures the overall TE landscape of an organisms (i.e. the abundance, the number of SNPs and internal deletions of all TE families). The requirements for computing these metrics vary, ranging from annotations of piRNA clusters to consensus sequences of TEs and genomic sequencing data. Using these novel metrics, we evaluate the effect of assembly algorithm, polishing, read length, coverage, residual polymorphisms and finally identify strategies that yield reliable assemblies of piRNA clusters. Based on an optimized approach, we provide assemblies for the two Drosophila melanogaster strains Canton-S and Pi2. About 80% of known piRNA clusters were assembled in both strains. Finally, we demonstrate the generality of our approach by extending our metrics to humans and Arabidopsis thaliana.
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Affiliation(s)
- Filip Wierzbicki
- Institut für Populationsgenetik, Vetmeduni Vienna, Wien, Austria.,Vienna Graduate School of Population Genetics, Vetmeduni Vienna, Vienna, Austria
| | - Florian Schwarz
- Institut für Populationsgenetik, Vetmeduni Vienna, Wien, Austria.,Vienna Graduate School of Population Genetics, Vetmeduni Vienna, Vienna, Austria
| | | | - Robert Kofler
- Institut für Populationsgenetik, Vetmeduni Vienna, Wien, Austria
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7
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Palatini U, Masri RA, Cosme LV, Koren S, Thibaud-Nissen F, Biedler JK, Krsticevic F, Johnston JS, Halbach R, Crawford JE, Antoshechkin I, Failloux AB, Pischedda E, Marconcini M, Ghurye J, Rhie A, Sharma A, Karagodin DA, Jenrette J, Gamez S, Miesen P, Masterson P, Caccone A, Sharakhova MV, Tu Z, Papathanos PA, Van Rij RP, Akbari OS, Powell J, Phillippy AM, Bonizzoni M. Improved reference genome of the arboviral vector Aedes albopictus. Genome Biol 2020; 21:215. [PMID: 32847630 PMCID: PMC7448346 DOI: 10.1186/s13059-020-02141-w] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Accepted: 08/07/2020] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND The Asian tiger mosquito Aedes albopictus is globally expanding and has become the main vector for human arboviruses in Europe. With limited antiviral drugs and vaccines available, vector control is the primary approach to prevent mosquito-borne diseases. A reliable and accurate DNA sequence of the Ae. albopictus genome is essential to develop new approaches that involve genetic manipulation of mosquitoes. RESULTS We use long-read sequencing methods and modern scaffolding techniques (PacBio, 10X, and Hi-C) to produce AalbF2, a dramatically improved assembly of the Ae. albopictus genome. AalbF2 reveals widespread viral insertions, novel microRNAs and piRNA clusters, the sex-determining locus, and new immunity genes, and enables genome-wide studies of geographically diverse Ae. albopictus populations and analyses of the developmental and stage-dependent network of expression data. Additionally, we build the first physical map for this species with 75% of the assembled genome anchored to the chromosomes. CONCLUSION The AalbF2 genome assembly represents the most up-to-date collective knowledge of the Ae. albopictus genome. These resources represent a foundation to improve understanding of the adaptation potential and the epidemiological relevance of this species and foster the development of innovative control measures.
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Affiliation(s)
- Umberto Palatini
- Department of Biology and Biotechnology, University of Pavia, Pavia, 27100, Italy
| | - Reem A Masri
- Department of Entomology and the Fralin Life Science Institute, Virginia Polytechnic and State University, Blacksburg, VA, 24061, USA
| | - Luciano V Cosme
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, 06511-8934, USA
| | - Sergey Koren
- Genome Informatics Section, Computational and Statistical Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, 20892-2152, MD, USA
| | - Françoise Thibaud-Nissen
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, 20894, MD, USA
| | - James K Biedler
- Department of Entomology and the Fralin Life Science Institute, Virginia Polytechnic and State University, Blacksburg, VA, 24061, USA
| | - Flavia Krsticevic
- Department of Entomology, Robert H Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, 7610001, Rehovot, Israel
| | - J Spencer Johnston
- Department of Entomology, Texas A&M University, College Station, TX, 77843, USA
| | - Rebecca Halbach
- Department of Medical Microbiology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | | | - Igor Antoshechkin
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Anna-Bella Failloux
- Department of Virology, Arbovirus and Insect Vectors Units, Institut Pasteur, Paris, 75015, France
| | - Elisa Pischedda
- Department of Biology and Biotechnology, University of Pavia, Pavia, 27100, Italy
| | - Michele Marconcini
- Department of Biology and Biotechnology, University of Pavia, Pavia, 27100, Italy
| | - Jay Ghurye
- Genome Informatics Section, Computational and Statistical Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, 20892-2152, MD, USA
| | - Arang Rhie
- Genome Informatics Section, Computational and Statistical Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, 20892-2152, MD, USA
| | - Atashi Sharma
- Department of Entomology and the Fralin Life Science Institute, Virginia Polytechnic and State University, Blacksburg, VA, 24061, USA
| | - Dmitry A Karagodin
- Laboratory of Evolutionary Genomics of Insects, The Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia
| | - Jeremy Jenrette
- Department of Entomology and the Fralin Life Science Institute, Virginia Polytechnic and State University, Blacksburg, VA, 24061, USA
| | - Stephanie Gamez
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA, 92093-0349, USA
| | - Pascal Miesen
- Department of Medical Microbiology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Patrick Masterson
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, 20894, MD, USA
| | - Adalgisa Caccone
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, 06511-8934, USA
| | - Maria V Sharakhova
- Department of Entomology and the Fralin Life Science Institute, Virginia Polytechnic and State University, Blacksburg, VA, 24061, USA
- Laboratory of Evolutionary Genomics of Insects, The Federal Research Center Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia
- Laboratory of Ecology, Genetics and Environment Protection, Tomsk State University, Tomsk, 634041, Russia
| | - Zhijian Tu
- Department of Entomology and the Fralin Life Science Institute, Virginia Polytechnic and State University, Blacksburg, VA, 24061, USA
| | - Philippos A Papathanos
- Department of Entomology, Robert H Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, 7610001, Rehovot, Israel
| | - Ronald P Van Rij
- Department of Medical Microbiology, Radboud University Medical Center, Radboud Institute for Molecular Life Sciences, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands
| | - Omar S Akbari
- Division of Biological Sciences, University of California, San Diego, La Jolla, CA, 92093-0349, USA
| | - Jeffrey Powell
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, 06511-8934, USA
| | - Adam M Phillippy
- Genome Informatics Section, Computational and Statistical Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, 20892-2152, MD, USA
| | - Mariangela Bonizzoni
- Department of Biology and Biotechnology, University of Pavia, Pavia, 27100, Italy.
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8
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Abstract
piRNA clusters are thought to repress transposable element (TE) activity in mammals and invertebrates. Here, we show that a simple population genetics model reveals a constraint on the size of piRNA clusters: The total size of the piRNA clusters of an organism must exceed 0.2% of a genome to repress TE invasions. Moreover, larger piRNA clusters accounting for up to 3% of the genome may be necessary when populations are small, transposition rates are high, and TE insertions are recessive. If piRNA clusters are too small, the load of deleterious TE insertions that accumulate during a TE invasion may drive populations extinct before an effective piRNA-based defense against the TE can be established. Our findings are solely based on three well-supported assumptions: 1) TEs multiply within genomes, 2) TEs are mostly deleterious, and 3) piRNA clusters act as transposon traps, where a single insertion in a cluster silences all TE copies in trans. Interestingly, the piRNA clusters of some species meet our observed minimum size requirements, whereas the clusters of other species do not. Species with small piRNA clusters, such as humans and mice, may experience severe fitness reductions during invasions of novel TEs, which is possibly even threatening the persistence of some populations. This work also raises the important question of how piRNA clusters evolve. We propose that the size of piRNA clusters may be at an equilibrium between evolutionary forces that act to expand and contract piRNA clusters.
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Affiliation(s)
- Robert Kofler
- Institut für Populationsgenetik, Vetmeduni Vienna, Wien, Austria
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9
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Kotnova AP, Ilyin YV. [Comparative Analysis of the Structure of Three piRNA Clusters in the Drosophila melanogaster Genome]. Mol Biol (Mosk) 2020; 54:426-434. [PMID: 32492005 DOI: 10.31857/s0026898420030088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 01/27/2020] [Indexed: 11/24/2022]
Abstract
Here we attempt to reconstruct the sequence of events that led to the formation of three regulatory piRNA clusters, namely, 20A, 38C and flamenco in the Drosophila melanogaster genome. Both the 38C and flamenco clusters include inverted sequences, which potentially form double-stranded RNA hairpins. We present evidence in favor of the well-known hypothesis of piRNA clusters as "transposon traps". According to this model, the presence of the only copy of the transposon in the genome indicates that its expression is suppressed by an RNA-interference mechanism immediately after the mobile element enters the piRNA cluster. We also discuss high the structural variability of piRNAs in Drosophila clusters and cases of horizontal transmobile elements between related species.
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Affiliation(s)
- A P Kotnova
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119991 Russia.,
| | - Yu V Ilyin
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119991 Russia
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10
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Abstract
In mammals and invertebrates, the proliferation of an invading transposable element (TE) is thought to be stopped by an insertion into a piRNA cluster. Here, we explore the dynamics of TE invasions under this trap model using computer simulations. We found that piRNA clusters confer a substantial benefit, effectively preventing extinction of host populations from a proliferation of deleterious TEs. TE invasions consist of three distinct phases: first, the TE amplifies within the population, next TE proliferation is stopped by segregating cluster insertions, and finally the TE is inactivated by fixation of a cluster insertion. Suppression by segregating cluster insertions is unstable and bursts of TE activity may yet occur. The transposition rate and the population size mostly influence the length of the phases but not the amount of TEs accumulating during an invasion. Solely, the size of piRNA clusters was identified as a major factor influencing TE abundance. We found that a single nonrecombining cluster is more efficient in stopping invasions than clusters distributed over several chromosomes. Recombination among cluster sites makes it necessary that each diploid carries, on the average, four cluster insertions to stop an invasion. Surprisingly, negative selection in a model with piRNA clusters can lead to a novel equilibrium state, where TE copy numbers remain stable despite only some individuals in a population carrying a cluster insertion. In Drosophila melanogaster, the trap model accounts for the abundance of TEs produced in the germline but fails to predict the abundance of TEs produced in the soma.
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Affiliation(s)
- Robert Kofler
- Institut für Populationsgenetik, Vetmeduni Vienna, Wien, Austria
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11
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Yu T, Koppetsch BS, Pagliarani S, Johnston S, Silverstein NJ, Luban J, Chappell K, Weng Z, Theurkauf WE. 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] [What about the content of this article? (0)] [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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12
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Maksimov DA, Koryakov DE. Binding of SU(VAR)3-9 Partially Depends on SETDB1 in the Chromosomes of Drosophila melanogaster. Cells 2019; 8:cells8091030. [PMID: 31491894 PMCID: PMC6769583 DOI: 10.3390/cells8091030] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Revised: 09/03/2019] [Accepted: 09/03/2019] [Indexed: 02/06/2023] Open
Abstract
H3K9 methylation is known to play a critical role in gene silencing. This modification is established and maintained by several enzymes, but relationships between them are not fully understood. In the present study, we decipher the interplay between two Drosophila H3K9-specific histone methyltransferases, SU(VAR)3-9 and SETDB1. We asked whether SETDB1 is required for targeting of SU(VAR)3-9. Using DamID-seq, we obtained SU(VAR)3-9 binding profiles for the chromosomes from larval salivary glands and germline cells from adult females, and compared profiles between the wild type and SETDB1-mutant backgrounds. Our analyses indicate that the vast majority of single copy genes in euchromatin are targeted by SU(VAR)3-9 only in the presence of SETDB1, whereas SU(VAR)3-9 binding at repeated sequences in heterochromatin is largely SETDB1-independent. Interestingly, piRNA clusters 42AB and 38C in salivary gland chromosomes bind SU(VAR)3-9 regardless of SETDB1, whereas binding to the same regions in the germline cells is SETDB1-dependent. In addition, we compared SU(VAR)3-9 profiles in female germline cells at different developmental stages (germarium cells in juvenile ovaries and mature nurse cells). It turned out that SU(VAR)3-9 binding is influenced both by the presence of SETDB1, as well as by the differentiation stage.
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Affiliation(s)
- Daniil A Maksimov
- Institute of Molecular and Cellular Biology SB RAS, 630090 Novosibirsk, Russia.
- Epigenetics Laboratory, Department of Natural Sciences, Novosibirsk State University, 630090 Novosibirsk, Russia.
| | - Dmitry E Koryakov
- Institute of Molecular and Cellular Biology SB RAS, 630090 Novosibirsk, Russia.
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13
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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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14
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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: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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15
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Abstract
PIWI-interacting RNAs (piRNAs) and their associated PIWI clade Argonaute proteins constitute the core of the piRNA pathway. In gonadal cells, this conserved pathway is crucial for genome defense, and its main function is to silence transposable elements. This is achieved through posttranscriptional and transcriptional gene silencing. Precursors that give rise to piRNAs require specialized transcription and transport machineries because piRNA biogenesis is a cytoplasmic process. The ping-pong cycle, a posttranscriptional silencing mechanism, combines the cleavage-dependent silencing of transposon RNAs with piRNA production. PIWI proteins also function in the nucleus, where they scan for nascent target transcripts with sequence complementarity, instructing transcriptional silencing and deposition of repressive chromatin marks at transposon loci. Although studies have revealed numerous factors that participate in each branch of the piRNA pathway, the precise molecular roles of these factors often remain unclear. In this review, we summarize our current understanding of the mechanisms involved in piRNA biogenesis and function.
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Affiliation(s)
- Benjamin Czech
- Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge CB2 0RE, United Kingdom; ,
| | - Marzia Munafò
- Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge CB2 0RE, United Kingdom; ,
| | - Filippo Ciabrelli
- Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge CB2 0RE, United Kingdom; ,
| | - Evelyn L Eastwood
- Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge CB2 0RE, United Kingdom; ,
| | - Martin H Fabry
- Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge CB2 0RE, United Kingdom; ,
| | - Emma Kneuss
- Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge CB2 0RE, United Kingdom; ,
| | - Gregory J Hannon
- Cancer Research UK Cambridge Institute, University of Cambridge, Cambridge CB2 0RE, United Kingdom; ,
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16
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Whitfield ZJ, Dolan PT, Kunitomi M, Tassetto M, Seetin MG, Oh S, Heiner C, Paxinos E, Andino R. The Diversity, Structure, and Function of Heritable Adaptive Immunity Sequences in the Aedes aegypti Genome. Curr Biol 2017; 27:3511-3519.e7. [PMID: 29129531 DOI: 10.1016/j.cub.2017.09.067] [Citation(s) in RCA: 115] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 08/29/2017] [Accepted: 09/29/2017] [Indexed: 12/22/2022]
Abstract
The Aedes aegypti mosquito transmits arboviruses, including dengue, chikungunya, and Zika virus. Understanding the mechanisms underlying mosquito immunity could provide new tools to control arbovirus spread. Insects exploit two different RNAi pathways to combat viral and transposon infection: short interfering RNAs (siRNAs) and PIWI-interacting RNAs (piRNAs) [1, 2]. Endogenous viral elements (EVEs) are sequences from non-retroviral viruses that are inserted into the mosquito genome and can act as templates for the production of piRNAs [3, 4]. EVEs therefore represent a record of past infections and a reservoir of potential immune memory [5]. The large-scale organization of EVEs has been difficult to resolve with short-read sequencing because they tend to integrate into repetitive regions of the genome. To define the diversity, organization, and function of EVEs, we took advantage of the contiguity associated with long-read sequencing to generate a high-quality assembly of the Ae. aegypti-derived Aag2 cell line genome, an important and widely used model system. We show EVEs are acquired through recombination with specific classes of long terminal repeat (LTR) retrotransposons and organize into large loci (>50 kbp) characterized by high LTR density. These EVE-containing loci have increased density of piRNAs compared to similar regions without EVEs. Furthermore, we detected EVE-derived piRNAs consistent with a targeted processing of persistently infecting virus genomes. We propose that comparisons of EVEs across mosquito populations may explain differences in vector competence, and further study of the structure and function of these elements in the genome of mosquitoes may lead to epidemiological interventions.
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Affiliation(s)
- Zachary J Whitfield
- Department of Microbiology and Immunology, University of California, San Francisco, 600 16(th) Street, GH-S572, UCSF Box 2280, San Francisco, CA 94143-2280, USA
| | - Patrick T Dolan
- Department of Microbiology and Immunology, University of California, San Francisco, 600 16(th) Street, GH-S572, UCSF Box 2280, San Francisco, CA 94143-2280, USA; Department of Biology, Stanford University, E200 Clark Center, 318 Campus Drive, Stanford, CA 94305, USA
| | - Mark Kunitomi
- Department of Microbiology and Immunology, University of California, San Francisco, 600 16(th) Street, GH-S572, UCSF Box 2280, San Francisco, CA 94143-2280, USA
| | - Michel Tassetto
- Department of Microbiology and Immunology, University of California, San Francisco, 600 16(th) Street, GH-S572, UCSF Box 2280, San Francisco, CA 94143-2280, USA
| | - Matthew G Seetin
- Pacific Biosciences, 1305 O'Brien Drive, Menlo Park, CA 94025, USA
| | - Steve Oh
- Pacific Biosciences, 1305 O'Brien Drive, Menlo Park, CA 94025, USA
| | - Cheryl Heiner
- Pacific Biosciences, 1305 O'Brien Drive, Menlo Park, CA 94025, USA
| | - Ellen Paxinos
- Pacific Biosciences, 1305 O'Brien Drive, Menlo Park, CA 94025, USA
| | - Raul Andino
- Department of Microbiology and Immunology, University of California, San Francisco, 600 16(th) Street, GH-S572, UCSF Box 2280, San Francisco, CA 94143-2280, USA.
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17
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George P, Jensen S, Pogorelcnik R, Lee J, Xing Y, Brasset E, Vaury C, Sharakhov IV. Increased production of piRNAs from euchromatic clusters and genes in Anopheles gambiae compared with Drosophila melanogaster. Epigenetics Chromatin 2015; 8:50. [PMID: 26617674 PMCID: PMC4662822 DOI: 10.1186/s13072-015-0041-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 11/04/2015] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Specific genomic loci, termed Piwi-interacting RNA (piRNA) clusters, manufacture piRNAs that serve as guides for the inactivation of complementary transposable elements (TEs). The piRNA pathway has been accurately detailed in Drosophila melanogaster, while it remains poorly examined in other insects. This pathway is increasingly recognized as critical for germline development and reproduction. Understanding of the piRNA functions in mosquitoes could offer an opportunity for disease vector control by the reduction of their reproductive potential. RESULTS To analyze the similarities and differences in this pathway between Drosophila and mosquito, we performed an in-depth analysis of the genomic loci producing piRNAs and their targets in the African malaria vector Anopheles gambiae. We identified 187 piRNA clusters in the An. gambiae genome and 155 piRNA clusters in the D. melanogaster genome. We demonstrate that many more piRNA clusters in the mosquito compared with the fruit fly are uni-directionally transcribed and are located outside pericentromeric heterochromatin. About 11 % of the An. gambiae piRNA population map to gene transcripts. This is a noticeable increase compared with the ~6 % of the piRNA population mapped to genes in D. melanogaster. A subset of the piRNA-enriched genes in An. gambiae has functions related to reproduction and development. At least 24 and 65 % of the mapped piRNAs correspond to genomic TE sequences in An. gambiae and D. melanogaster, respectively. DNA transposons and non-LTR retrotransposons are more abundant in An. gambiae, while LTR retrotransposons are more abundant in D. melanogaster. Yet, piRNAs predominantly target LTR retrotransposons in both species, which may point to a distinct feature of these elements compared to the other classes of TEs concerning their silencing by the piRNA pathway. CONCLUSIONS Here, we demonstrate that piRNA-producing loci have more ubiquitous distribution in the An. gambiae genome than in the genome of D. melanogaster. Also, protein-coding genes have an increased role in production of piRNAs in the germline of this mosquito. Genes involved in germline and embryonic development of An. gambiae generate a substantial portion of piRNAs, suggesting a role of the piRNA pathway in the epigenetic regulation of the reproductive processes in the African malaria vector.
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Affiliation(s)
- Phillip George
- />Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA
| | - Silke Jensen
- />Laboratoire Génétique, Reproduction, et Développement, Clermont Université, Université d’Auvergne, BP 38, 63001 Clermont-Ferrand, France
- />Institut National de la Santé et de la Recherche Médicale, U 1103, BP 38, 63001 Clermont-Ferrand, France
- />Centre National de Recherche Scientifique, UMR 6293, BP 38, 63001 Clermont-Ferrand, France
| | - Romain Pogorelcnik
- />Laboratoire Génétique, Reproduction, et Développement, Clermont Université, Université d’Auvergne, BP 38, 63001 Clermont-Ferrand, France
- />Institut National de la Santé et de la Recherche Médicale, U 1103, BP 38, 63001 Clermont-Ferrand, France
- />Centre National de Recherche Scientifique, UMR 6293, BP 38, 63001 Clermont-Ferrand, France
| | - Jiyoung Lee
- />The PhD Program in Genomics Bioinformatics and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA
| | - Yi Xing
- />The PhD Program in Genomics Bioinformatics and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA
| | - Emilie Brasset
- />Laboratoire Génétique, Reproduction, et Développement, Clermont Université, Université d’Auvergne, BP 38, 63001 Clermont-Ferrand, France
- />Institut National de la Santé et de la Recherche Médicale, U 1103, BP 38, 63001 Clermont-Ferrand, France
- />Centre National de Recherche Scientifique, UMR 6293, BP 38, 63001 Clermont-Ferrand, France
| | - Chantal Vaury
- />Laboratoire Génétique, Reproduction, et Développement, Clermont Université, Université d’Auvergne, BP 38, 63001 Clermont-Ferrand, France
- />Institut National de la Santé et de la Recherche Médicale, U 1103, BP 38, 63001 Clermont-Ferrand, France
- />Centre National de Recherche Scientifique, UMR 6293, BP 38, 63001 Clermont-Ferrand, France
| | - Igor V. Sharakhov
- />Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA
- />The PhD Program in Genomics Bioinformatics and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA
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