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Li Z, Gilbert C, Peng H, Pollet N. Discovery of numerous novel Helitron-like elements in eukaryote genomes using HELIANO. Nucleic Acids Res 2024:gkae679. [PMID: 39119924 DOI: 10.1093/nar/gkae679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2024] [Revised: 07/19/2024] [Accepted: 07/25/2024] [Indexed: 08/10/2024] Open
Abstract
Helitron-like elements (HLEs) are widespread eukaryotic DNA transposons employing a rolling-circle transposition mechanism. Despite their prevalence in fungi, animals, and plant genomes, identifying Helitrons remains a formidable challenge. We introduce HELIANO, a software for annotating and classifying autonomous and non-autonomous HLE sequences from whole genomes. HELIANO overcomes several limitations of existing tools in speed and accuracy, demonstrated through benchmarking and its application to the complex genomes of frogs (Xenopus tropicalis and Xenopus laevis) and rice (Oryza sativa), where it uncovered numerous previously unidentified HLEs. In an extensive analysis of 404 eukaryote genomes, we found HLEs widely distributed across phyla, with exceptions in specific taxa. HELIANO's application led to the discovery of numerous new HLEs in land plants and identified 20 protein domains captured by certain autonomous HLE families. A comprehensive phylogenetic analysis further classified HLEs into two primary clades, HLE1 and HLE2, and revealed nine subgroups, some of which are enriched within specific taxa. The future use of HELIANO promises to improve the global analysis of HLEs across genomes, significantly advancing our understanding of this fascinating transposon superfamily.
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Affiliation(s)
- Zhen Li
- Université Paris-Saclay, CNRS, IRD, UMR Évolution, Génomes, Comportement et Écologie, 91198 Gif-sur-Yvette, France
| | - Clément Gilbert
- Université Paris-Saclay, CNRS, IRD, UMR Évolution, Génomes, Comportement et Écologie, 91198 Gif-sur-Yvette, France
| | - Haoran Peng
- Crop Genome Dynamics Group, Agroscope, 1260 Nyon, Switzerland
| | - Nicolas Pollet
- Université Paris-Saclay, CNRS, IRD, UMR Évolution, Génomes, Comportement et Écologie, 91198 Gif-sur-Yvette, France
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2
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Barro-Trastoy D, Köhler C. Helitrons: genomic parasites that generate developmental novelties. Trends Genet 2024; 40:437-448. [PMID: 38429198 DOI: 10.1016/j.tig.2024.02.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2023] [Revised: 02/03/2024] [Accepted: 02/05/2024] [Indexed: 03/03/2024]
Abstract
Helitrons, classified as DNA transposons, employ rolling-circle intermediates for transposition. Distinguishing themselves from other DNA transposons, they leave the original template element unaltered during transposition, which has led to their characterization as 'peel-and-paste elements'. Helitrons possess the ability to capture and mobilize host genome fragments, with enormous consequences for host genomes. This review discusses the current understanding of Helitrons, exploring their origins, transposition mechanism, and the extensive repercussions of their activity on genome structure and function. We also explore the evolutionary conflicts stemming from Helitron-transposed gene fragments and elucidate their domestication for regulating responses to environmental challenges. Looking ahead, further research in this evolving field promises to bring interesting discoveries on the role of Helitrons in shaping genomic landscapes.
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Affiliation(s)
- Daniela Barro-Trastoy
- Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany
| | - Claudia Köhler
- Max Planck Institute of Molecular Plant Physiology, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany; Department of Plant Biology, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala 75007, Sweden.
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3
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Ma H, Wang M, Zhang YE, Tan S. The power of "controllers": Transposon-mediated duplicated genes evolve towards neofunctionalization. J Genet Genomics 2023; 50:462-472. [PMID: 37068629 DOI: 10.1016/j.jgg.2023.04.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 04/04/2023] [Accepted: 04/05/2023] [Indexed: 04/19/2023]
Abstract
Since the discovery of the first transposon by Dr. Barbara McClintock, the prevalence and diversity of transposable elements (TEs) have been gradually recognized. As fundamental genetic components, TEs drive organismal evolution not only by contributing functional sequences (e.g., regulatory elements or "controllers" as phrased by Dr. McClintock) but also by shuffling genomic sequences. In the latter respect, TE-mediated gene duplications have contributed to the origination of new genes and attracted extensive interest. In response to the development of this field, we herein attempt to provide an overview of TE-mediated duplication by focusing on common rules emerging across duplications generated by different TE types. Specifically, despite the huge divergence of transposition machinery across TEs, we identify three common features of various TE-mediated duplication mechanisms, including end bypass, template switching, and recurrent transposition. These three features lead to one common functional outcome, namely, TE-mediated duplicates tend to be subjected to exon shuffling and neofunctionalization. Therefore, the intrinsic properties of the mutational mechanism constrain the evolutionary trajectories of these duplicates. We finally discuss the future of this field including an in-depth characterization of both the duplication mechanisms and functions of TE-mediated duplicates.
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Affiliation(s)
- Huijing Ma
- Key Laboratory of Zoological Systematics and Evolution & State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China
| | - Mengxia Wang
- Key Laboratory of Zoological Systematics and Evolution & State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yong E Zhang
- Key Laboratory of Zoological Systematics and Evolution & State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China; CAS Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming, Yunnan 650223, China; Chinese Institute for Brain Research, Beijing 102206, China.
| | - Shengjun Tan
- Key Laboratory of Zoological Systematics and Evolution & State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
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4
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Dai Z, Ren J, Tong X, Hu H, Lu K, Dai F, Han MJ. The Landscapes of Full-Length Transcripts and Splice Isoforms as Well as Transposons Exonization in the Lepidopteran Model System, Bombyx mori. Front Genet 2021; 12:704162. [PMID: 34594358 PMCID: PMC8476886 DOI: 10.3389/fgene.2021.704162] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Accepted: 09/01/2021] [Indexed: 11/13/2022] Open
Abstract
The domesticated silkworm, Bombyx mori, is an important model system for the order Lepidoptera. Currently, based on third-generation sequencing, the chromosome-level genome of Bombyx mori has been released. However, its transcripts were mainly assembled by using short reads of second-generation sequencing and expressed sequence tags which cannot explain the transcript profile accurately. Here, we used PacBio Iso-Seq technology to investigate the transcripts from 45 developmental stages of Bombyx mori. We obtained 25,970 non-redundant high-quality consensus isoforms capturing ∼60% of previous reported RNAs, 15,431 (∼47%) novel transcripts, and identified 7,253 long non-coding RNA (lncRNA) with a large proportion of novel lncRNA (∼56%). In addition, we found that transposable elements (TEs) exonization account for 11,671 (∼45%) transcripts including 5,980 protein-coding transcripts (∼32%) and 5,691 lncRNAs (∼79%). Overall, our results expand the silkworm transcripts and have general implications to understand the interaction between TEs and their host genes. These transcripts resource will promote functional studies of genes and lncRNAs as well as TEs in the silkworm.
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Affiliation(s)
- Zongrui Dai
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture and Rural Affairs, College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing, China.,WESTA College, Southwest University, Chongqing, China
| | - Jianyu Ren
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture and Rural Affairs, College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing, China
| | - Xiaoling Tong
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture and Rural Affairs, College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing, China
| | - Hai Hu
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture and Rural Affairs, College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing, China
| | - Kunpeng Lu
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture and Rural Affairs, College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing, China
| | - Fangyin Dai
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture and Rural Affairs, College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing, China
| | - Min-Jin Han
- State Key Laboratory of Silkworm Genome Biology, Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture and Rural Affairs, College of Sericulture, Textile and Biomass Science, Southwest University, Chongqing, China
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5
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Xin Y, Ma B, Xiang Z, He N. Amplification of miniature inverted-repeat transposable elements and the associated impact on gene regulation and alternative splicing in mulberry ( Morus notabilis). Mob DNA 2019; 10:27. [PMID: 31289464 PMCID: PMC6593561 DOI: 10.1186/s13100-019-0169-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Accepted: 06/17/2019] [Indexed: 12/13/2022] Open
Abstract
Background Miniature inverted-repeat transposable elements (MITEs) are common in eukaryotic genomes, and are important for genomic evolution. Results In the present study, the identification of MITEs in the mulberry genome revealed 286,122 MITE-related sequences, including 90,789 full-length elements. The amplification of mulberry MITEs and the influence of MITEs on the evolution of the mulberry genome were analyzed. The timing of MITE amplifications varied considerably among the various MITE families. Fifty-one MITE families have undergone a single round of amplification, while the other families developed from multiple amplifications. Most mulberry MITEs were inserted near genes and some could regulate gene expression through small RNAs. An analysis of transgenic plants indicated that MITE insertions can upregulate the expression of a target gene. Moreover, MITEs are frequently associated with alternative splicing events (exonizations). Conclusion The data presented herein provide insights into the generation of MITEs as well as their impact on gene regulation and evolution in mulberry. Electronic supplementary material The online version of this article (10.1186/s13100-019-0169-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Youchao Xin
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing, 400715 China
| | - Bi Ma
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing, 400715 China
| | - Zhonghuai Xiang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing, 400715 China
| | - Ningjia He
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing, 400715 China
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6
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Han G, Zhang N, Xu J, Jiang H, Ji C, Zhang Z, Song Q, Stanley D, Fang J, Wang J. Characterization of a novel Helitron family in insect genomes: insights into classification, evolution and horizontal transfer. Mob DNA 2019; 10:25. [PMID: 31164927 PMCID: PMC6544945 DOI: 10.1186/s13100-019-0165-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 04/30/2019] [Indexed: 01/09/2023] Open
Abstract
Background Helitrons play an important role in shaping eukaryotic genomes due to their ability to transfer horizontally between distantly related species and capture gene fragments during the transposition. However, the mechanisms of horizontal transfer (HT) and the process of gene fragment capturing of Helitrons still remain to be further clarified. Results Here, we characterized a novel Helitron family discontinuously distributed in 27 out of 256 insect genomes. The most prominent characteristic of Hel1 family is its high sequence similarity among species of different insect orders. Related elements were also identified in two spiders, representing the first report of spider Helitrons. All these elements were classified into 2 families, 9 subfamilies and 35 exemplars based on our new classification criteria. Autonomous partners of Helitron were reconstructed in the genomes of three insects and one spider. Integration pattern analysis showed that majority of Hel1A elements in Papilio xuthus and Pieris rapae inserted into introns. Consistent with filler DNA model, stepwise sequence acquisition was observed in Sfru_Hel1Aa, Sfru_Hel1Ab and Sfru_Hel1Ac in Spodoptera frugiperda. Remarkably, the evidence that Prap_Hel1Aa in a Lepdidoptera insect, Pieris rapae, was derived from Cves_Hel1Aa in a parasitoid wasp, Cotesia vestalis, suggested the role of nonregular host-parasite interactions in HT of Helitrons. Conclusions We proposed a modified classification criteria of Helitrons based on the important role of the 5′-end of Helitrons in transposition, and provided evidence for stepwise sequence acquisition and recurrent HT of a novel Helitron family. Our findings of the nonregular host-parasite interactions may be more conducive to the HT of transposons. Electronic supplementary material The online version of this article (10.1186/s13100-019-0165-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Guangjie Han
- 1College of Horticulture and Plant Protection, Yangzhou University, Yangzhou, 225009 China.,Jiangsu Lixiahe Institute of Agricultural Sciences, Yangzhou, 225007 China
| | - Nan Zhang
- 1College of Horticulture and Plant Protection, Yangzhou University, Yangzhou, 225009 China
| | - Jian Xu
- Jiangsu Lixiahe Institute of Agricultural Sciences, Yangzhou, 225007 China
| | - Heng Jiang
- 1College of Horticulture and Plant Protection, Yangzhou University, Yangzhou, 225009 China
| | - Caihong Ji
- 1College of Horticulture and Plant Protection, Yangzhou University, Yangzhou, 225009 China
| | - Ze Zhang
- 3School of Life Sciences, Chongqing University, Chongqing, 400044 China
| | - Qisheng Song
- 4Division of Plant Sciences, University of Missouri, Columbia, MO USA
| | - David Stanley
- 5USDA/Agricultural Research Service, Biological Control of Insects Research Laboratory, Columbia, MO USA
| | - Jichao Fang
- 6Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, 210014 China
| | - Jianjun Wang
- 1College of Horticulture and Plant Protection, Yangzhou University, Yangzhou, 225009 China
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7
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Helraiser intermediates provide insight into the mechanism of eukaryotic replicative transposition. Nat Commun 2018; 9:1278. [PMID: 29599430 PMCID: PMC5876387 DOI: 10.1038/s41467-018-03688-w] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 03/05/2018] [Indexed: 02/06/2023] Open
Abstract
Helitrons are eukaryotic DNA transposons that have profoundly affected genome variability via capture and mobilization of host genomic sequences. Defining their mode of action is therefore important for understanding how genome landscapes evolve. Sequence similarities with certain prokaryotic mobile elements suggest a “rolling circle” mode of transposition, involving only a single transposon strand. Using the reconstituted Helraiser transposon to study Helitron transposition in cells and in vitro, we show that the donor site must be double-stranded and that single-stranded donors will not suffice. Nevertheless, replication and integration assays demonstrate the use of only one of the transposon donor strands. Furthermore, repeated reuse of Helraiser donor sites occurs following DNA synthesis. In cells, circular double-stranded intermediates that serve as transposon donors are generated and replicated by Helraiser transposase. Cell-free experiments demonstrate strand-specific cleavage and strand transfer, supporting observations made in cells. Helitrons are eukaryotic DNA transposons that have profoundly affected genome variation due to their ability to capture and mobilize host genomic fragments. Here the authors provide insight into the mechanism of action of these transposons both in cells and in vitro.
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8
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Chellapan BV, van Dam P, Rep M, Cornelissen BJC, Fokkens L. Non-canonical Helitrons in Fusarium oxysporum. Mob DNA 2016; 7:27. [PMID: 27990178 PMCID: PMC5148889 DOI: 10.1186/s13100-016-0083-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 12/03/2016] [Indexed: 01/18/2023] Open
Abstract
Background Helitrons are eukaryotic rolling circle transposable elements that can have a large impact on host genomes due to their copy-number and their ability to capture and copy genes and regulatory elements. They occur widely in plants and animals, and have thus far been relatively little investigated in fungi. Results Here, we comprehensively survey Helitrons in several completely sequenced genomes representing the F. oxysporum species complex (FOSC). We thoroughly characterize 5 different Helitron subgroups and determine their impact on genome evolution and assembly in this species complex. FOSC Helitrons resemble members of the Helitron2 variant that includes Helentrons and DINEs. The fact that some Helitrons appeared to be still active in FOSC provided the opportunity to determine whether Helitrons occur as a circular intermediate in FOSC. We present experimental evidence suggesting that at least one Helitron subgroup occurs with joined ends, suggesting a circular intermediate. We extend our analyses to other Pezizomycotina and find that most fungal Helitrons we identified group phylogenetically with Helitron2 and probably have similar characteristics. Conclusions FOSC genomes harbour non-canonical Helitrons that are characterized by asymmetric terminal inverted repeats, show hallmarks of recent activity and likely transpose via a circular intermediate. Bioinformatic analyses indicate that they are representative of a large reservoir of fungal Helitrons that thus far has not been characterized. Electronic supplementary material The online version of this article (doi:10.1186/s13100-016-0083-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Biju Vadakkemukadiyil Chellapan
- Department of Computational Biology and Bioinformatics, University of Kerala, Karyavattom Campus, Karyavattom PO, Trivandrum, Kerala India ; Molecular Plant Pathology, Swammerdam Institute for Life Sciences, Faculty of Science, University of Amsterdam, P.O. Box 94215, 1090 Amsterdam, GE The Netherlands
| | - Peter van Dam
- Molecular Plant Pathology, Swammerdam Institute for Life Sciences, Faculty of Science, University of Amsterdam, P.O. Box 94215, 1090 Amsterdam, GE The Netherlands
| | - Martijn Rep
- Molecular Plant Pathology, Swammerdam Institute for Life Sciences, Faculty of Science, University of Amsterdam, P.O. Box 94215, 1090 Amsterdam, GE The Netherlands
| | - Ben J C Cornelissen
- Molecular Plant Pathology, Swammerdam Institute for Life Sciences, Faculty of Science, University of Amsterdam, P.O. Box 94215, 1090 Amsterdam, GE The Netherlands
| | - Like Fokkens
- Molecular Plant Pathology, Swammerdam Institute for Life Sciences, Faculty of Science, University of Amsterdam, P.O. Box 94215, 1090 Amsterdam, GE The Netherlands
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9
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Zhang HH, Li GY, Xiong XM, Han MJ, Dai FY. Horizontal transfer of a novel Helentron in insects. Mol Genet Genomics 2016; 292:243-250. [DOI: 10.1007/s00438-016-1270-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 11/02/2016] [Indexed: 11/24/2022]
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10
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Warren IA, Naville M, Chalopin D, Levin P, Berger CS, Galiana D, Volff JN. Evolutionary impact of transposable elements on genomic diversity and lineage-specific innovation in vertebrates. Chromosome Res 2016; 23:505-31. [PMID: 26395902 DOI: 10.1007/s10577-015-9493-5] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Since their discovery, a growing body of evidence has emerged demonstrating that transposable elements are important drivers of species diversity. These mobile elements exhibit a great variety in structure, size and mechanisms of transposition, making them important putative actors in organism evolution. The vertebrates represent a highly diverse and successful lineage that has adapted to a wide range of different environments. These animals also possess a rich repertoire of transposable elements, with highly diverse content between lineages and even between species. Here, we review how transposable elements are driving genomic diversity and lineage-specific innovation within vertebrates. We discuss the large differences in TE content between different vertebrate groups and then go on to look at how they affect organisms at a variety of levels: from the structure of chromosomes to their involvement in the regulation of gene expression, as well as in the formation and evolution of non-coding RNAs and protein-coding genes. In the process of doing this, we highlight how transposable elements have been involved in the evolution of some of the key innovations observed within the vertebrate lineage, driving the group's diversity and success.
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Affiliation(s)
- Ian A Warren
- Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Magali Naville
- Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Domitille Chalopin
- Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France.,Department of Genetics, University of Georgia, Athens, Georgia, 30602, USA
| | - Perrine Levin
- Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Chloé Suzanne Berger
- Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Delphine Galiana
- Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Jean-Nicolas Volff
- Institut de Génomique Fonctionnelle de Lyon, CNRS UMR5242, Ecole Normale Supérieure de Lyon, Lyon, France.
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Huang K, Li CF, Wu J, Wei JH, Zou Y, Han MJ, Zhou ZY. Enhancer activity of Helitron in sericin-1 gene promoter from Bombyx mori. INSECT SCIENCE 2016; 23:396-405. [PMID: 27067405 DOI: 10.1111/1744-7917.12347] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 03/30/2016] [Indexed: 06/05/2023]
Abstract
Sericin is a kind of water-soluble protein expressed specifically in the middle silk gland of Bombyx mori. When the sericin-1 gene promoter was cloned and a transgenic vector was constructed to express a foreign protein, a specific Helitron, Bmhel-8, was identified in the sericin-1 gene promoter sequence in some genotypes of Bombyx mori and Bombyx mandarina. Given that the Bmhel-8 Helitron transposon was present only in some genotypes, it could be the source of allelic variation in the sericin-1 promoter. The length of the sericin-1 promoter sequence is approximately 1063 or 643 bp. The larger size of the sequence or allele is ascribed to the presence of Bmhel-8. Silkworm genotypes can be homozygous for either the shorter or larger promoter sequence or heterozygous, containing both alleles. Bmhel-8 in the sericin-1 promoter exhibits enhancer activity, as demonstrated by a dual-luciferase reporter system in BmE cell lines. Furthermore, Bmhel-8 displays enhancer activity in a sericin-1 promoter-driven gene expression system but does not regulate the tissue-specific expression of sericin-1.
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Affiliation(s)
- Ke Huang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
- College of Forestry & Life Science, Chongqing University of Arts & Sciences, Yongchuan, China
| | - Chun-Feng Li
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Jie Wu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Jun-Hong Wei
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Yong Zou
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
- College of Forestry & Life Science, Chongqing University of Arts & Sciences, Yongchuan, China
| | - Min-Jin Han
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
| | - Ze-Yang Zhou
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, China
- Laboratory of Animal Biology, Chongqing Normal University, Chongqing, China
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12
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Abstract
Helitrons, the eukaryotic rolling-circle transposable elements, are widespread but most prevalent among plant and animal genomes. Recent studies have identified three additional coding and structural variants of Helitrons called Helentrons, Proto-Helentron, and Helitron2. Helitrons and Helentrons make up a substantial fraction of many genomes where nonautonomous elements frequently outnumber the putative autonomous partner. This includes the previously ambiguously classified DINE-1-like repeats, which are highly abundant in Drosophila and many other animal genomes. The purpose of this review is to summarize what we have learned about Helitrons in the decade since their discovery. First, we describe the history of autonomous Helitrons, and their variants. Second, we explain the common coding features and difference in structure of canonical Helitrons versus the endonuclease-encoding Helentrons. Third, we review how Helitrons and Helentrons are classified and discuss why the system used for other transposable element families is not applicable. We also touch upon how genome-wide identification of candidate Helitrons is carried out and how to validate candidate Helitrons. We then shift our focus to a model of transposition and the report of an excision event. We discuss the different proposed models for the mechanism of gene capture. Finally, we will talk about where Helitrons are found, including discussions of vertical versus horizontal transfer, the propensity of Helitrons and Helentrons to capture and shuffle genes and how they impact the genome. We will end the review with a summary of open questions concerning the biology of this intriguing group of transposable elements.
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13
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A Helitron transposon reconstructed from bats reveals a novel mechanism of genome shuffling in eukaryotes. Nat Commun 2016; 7:10716. [PMID: 26931494 PMCID: PMC4778049 DOI: 10.1038/ncomms10716] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Accepted: 01/14/2016] [Indexed: 02/08/2023] Open
Abstract
Helitron transposons capture and mobilize gene fragments in eukaryotes, but experimental evidence for their transposition is lacking in the absence of an isolated active element. Here we reconstruct Helraiser, an ancient element from the bat genome, and use this transposon as an experimental tool to unravel the mechanism of Helitron transposition. A hairpin close to the 3′-end of the transposon functions as a transposition terminator. However, the 3′-end can be bypassed by the transposase, resulting in transduction of flanking sequences to new genomic locations. Helraiser transposition generates covalently closed circular intermediates, suggestive of a replicative transposition mechanism, which provides a powerful means to disseminate captured transcriptional regulatory signals across the genome. Indeed, we document the generation of novel transcripts by Helitron promoter capture both experimentally and by transcriptome analysis in bats. Our results provide mechanistic insight into Helitron transposition, and its impact on diversification of gene function by genome shuffling. Helitron elements are proposed rolling-circle transposons in eukaryotic genomes, but experimental evidence for their transposition has been lacking. Here, Grabundzija et al. reconstruct an active Helitron from bats which they name Helraiser, and characterize its mechanism of transposition in cell-free reactions and in human cell cultures in vitro.
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Platt RN, Blanco-Berdugo L, Ray DA. Accurate Transposable Element Annotation Is Vital When Analyzing New Genome Assemblies. Genome Biol Evol 2016; 8:403-10. [PMID: 26802115 PMCID: PMC4779615 DOI: 10.1093/gbe/evw009] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Transposable elements (TEs) are mobile genetic elements with the ability to replicate themselves throughout the host genome. In some taxa TEs reach copy numbers in hundreds of thousands and can occupy more than half of the genome. The increasing number of reference genomes from nonmodel species has begun to outpace efforts to identify and annotate TE content and methods that are used vary significantly between projects. Here, we demonstrate variation that arises in TE annotations when less than optimal methods are used. We found that across a variety of taxa, the ability to accurately identify TEs based solely on homology decreased as the phylogenetic distance between the queried genome and a reference increased. Next we annotated repeats using homology alone, as is often the case in new genome analyses, and a combination of homology and de novo methods as well as an additional manual curation step. Reannotation using these methods identified a substantial number of new TE subfamilies in previously characterized genomes, recognized a higher proportion of the genome as repetitive, and decreased the average genetic distance within TE families, implying recent TE accumulation. Finally, these finding-increased recognition of younger TEs-were confirmed via an analysis of the postman butterfly (Heliconius melpomene). These observations imply that complete TE annotation relies on a combination of homology and de novo-based repeat identification, manual curation, and classification and that relying on simple, homology-based methods is insufficient to accurately describe the TE landscape of a newly sequenced genome.
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Affiliation(s)
- Roy N Platt
- Department of Biological Sciences, Texas Tech University
| | | | - David A Ray
- Department of Biological Sciences, Texas Tech University
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Roffler S, Menardo F, Wicker T. The making of a genomic parasite - the Mothra family sheds light on the evolution of Helitrons in plants. Mob DNA 2015; 6:23. [PMID: 26688693 PMCID: PMC4683698 DOI: 10.1186/s13100-015-0054-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Accepted: 12/04/2015] [Indexed: 11/29/2022] Open
Abstract
Background Helitrons are Class II transposons which are highly abundant in almost all eukaryotes. However, most Helitrons lack protein coding sequence. These non-autonomous elements are thought to hijack recombinase/helicase (RepHel) and possibly further enzymes from related, autonomous elements. Interestingly, many plant Helitrons contain an additional gene encoding a single-strand binding protein homologous to Replication Factor A (RPA), a highly conserved, single-copy gene found in all eukaryotes. Results Here, we describe the analysis of DHH_Mothra, a high-copy non-autonomous Helitron in the genome of rice (Oryza sativa). Mothra has a low GC-content and consists of two distinct blocs of tandem repeats. Based on homology between their termini, we identified a putative mother element which encodes an RPA-like protein but has no RepHel gene. Additionally, we found a putative autonomous sister-family with strong homology to the Mothra mother element in the RPA protein and terminal sequences, which we propose provides the RepHel domain for the Mothra family. Furthermore, we phylogenetically analyzed the evolutionary history of RPA-like proteins. Interestingly, plant Helitron RPAs (PHRPAs) are only found in monocotyledonous and dicotyledonous plants and they form a monophyletic group which branched off before the eukaryotic “core” RPAs. Conclusions Our data show how erosion of autonomous Helitrons can lead to different “levels” of autonomy within Helitron families and can create highly successful subfamilies of non-autonomous elements. Most importantly, our phylogenetic analysis showed that the PHRPA gene was most likely acquired via horizontal gene transfer from an unknown eukaryotic donor at least 145–300 million years ago in the common ancestor of monocotyledonous and dicotyledonous plants. This might have led to the evolution of a separate branch of the Helitron superfamily in plants. Electronic supplementary material The online version of this article (doi:10.1186/s13100-015-0054-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Stefan Roffler
- Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, Zürich, CH-8008 Switzerland
| | - Fabrizio Menardo
- Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, Zürich, CH-8008 Switzerland
| | - Thomas Wicker
- Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, Zürich, CH-8008 Switzerland
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Subirana JA, Albà MM, Messeguer X. High evolutionary turnover of satellite families in Caenorhabditis. BMC Evol Biol 2015; 15:218. [PMID: 26438045 PMCID: PMC4595182 DOI: 10.1186/s12862-015-0495-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Accepted: 09/22/2015] [Indexed: 02/07/2023] Open
Abstract
Background The high density of tandem repeat sequences (satellites) in nematode genomes and the availability of genome sequences from several species in the group offer a unique opportunity to better understand the evolutionary dynamics and the functional role of these sequences. We take advantage of the previously developed SATFIND program to study the satellites in four Caenorhabditis species and investigate these questions. Methods The identification and comparison of satellites is carried out in three steps. First we find all the satellites present in each species with the SATFIND program. Each satellite is defined by its length, number of repeats, and repeat sequence. Only satellites with at least ten repeats are considered. In the second step we build satellite families with a newly developed alignment program. Satellite families are defined by a consensus sequence and the number of satellites in the family. Finally we compare the consensus sequence of satellite families in different species. Results We give a catalog of individual satellites in each species. We have also identified satellite families with a related sequence and compare them in different species. We analyze the turnover of satellites: they increased in size through duplications of fragments of 100-300 bases. It appears that in many cases they have undergone an explosive expansion. In C. elegans we have identified a subset of large satellites that have strong affinity for the centromere protein CENP-A. We have also compared our results with those obtained from other species, including one nematode and three mammals. Conclusions Most satellite families found in Caenorhabditis are species-specific; in particular those with long repeats. A subset of these satellites may facilitate the formation of kinetochores in mitosis. Other satellite families in C. elegans are either related to Helitron transposons or to meiotic pairing centers. Electronic supplementary material The online version of this article (doi:10.1186/s12862-015-0495-x) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Juan A Subirana
- Department of Computer Science, Universitat Politècnica de Catalunya, Jordi Girona 31, Barcelona, 08034, Spain. .,Evolutionary Genomics Group, Research Programme on Biomedical Informatics (GRIB) - Hospital del Mar Research Institute (IMIM), Universitat Pompeu Fabra (UPF), Dr. Aiguader 86, Barcelona, 08003, Spain.
| | - M Mar Albà
- Evolutionary Genomics Group, Research Programme on Biomedical Informatics (GRIB) - Hospital del Mar Research Institute (IMIM), Universitat Pompeu Fabra (UPF), Dr. Aiguader 86, Barcelona, 08003, Spain.
| | - Xavier Messeguer
- Department of Computer Science, Universitat Politècnica de Catalunya, Jordi Girona 31, Barcelona, 08034, Spain.
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Differential pre-mRNA Splicing Alters the Transcript Diversity of Helitrons Between the Maize Inbred Lines. G3-GENES GENOMES GENETICS 2015; 5:1703-11. [PMID: 26070844 PMCID: PMC4528327 DOI: 10.1534/g3.115.018630] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The propensity to capture and mobilize gene fragments by the highly abundant Helitron family of transposable elements likely impacts the evolution of genes in Zea mays. These elements provide a substrate for natural selection by giving birth to chimeric transcripts by intertwining exons of disparate genes. They also capture flanking exons by read-through transcription. Here, we describe the expression of selected Helitrons in different maize inbred lines. We recently reported that these Helitrons produce multiple isoforms of transcripts in inbred B73 via alternative splicing. Despite sharing high degrees of sequence similarity, the splicing profile of Helitrons differed among various maize inbred lines. The comparison of Helitron sequences identified unique polymorphisms in inbred B73, which potentially give rise to the alternatively spliced sites utilized by transcript isoforms. Some alterations in splicing, however, do not have obvious explanations. These observations not only add another level to the creation of transcript diversity by Helitrons among inbred lines but also provide novel insights into the cis-acting elements governing splice-site selection during pre-mRNA processing.
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18
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Coates BS. Horizontal transfer of a non-autonomous Helitron among insect and viral genomes. BMC Genomics 2015; 16:137. [PMID: 25766741 PMCID: PMC4344730 DOI: 10.1186/s12864-015-1318-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 02/03/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The movement of mobile elements among species by horizontal transposon transfer (HTT) influences the evolution of genomes through the modification of structure and function. Helitrons are a relatively new lineage of DNA-based (class II) transposable elements (TEs) that propagate by rolling-circle replication, and are capable of acquiring host DNA. The rapid spread of Helitrons among animal lineages by HTT is facilitated by shuttling in viral particles or by unknown mechanisms mediated by close organism associations (e.g. between hosts and parasites). RESULTS A non-autonomous Helitron independently annotated as BmHel-2 from Bombyx mori and the MITE01 element from Ostrinia nubilalis was predicted in the genomes of 24 species in the insect Order Lepidoptera. Integrated Helitrons retained ≥ 65% sequence identity over a 250 bp consensus, and were predicted to retain secondary structures inclusive of a 3'-hairpin and a 5'-subterminal inverted repeat. Highly similar Hel-2 copies were predicted in the genomes of insects and associated viruses, which along with a previous documented case of real-time virus-insect cell line transposition suggests that this Helitron has likely propagated by HTT. CONCLUSIONS These findings provide evidence that insect virus may mediate the HTT of Helitron-like TEs. This movement may facilitate the shuttling of DNA elements among insect genomes. Further sampling is required to determine the putative role of HTT in insect genome evolution.
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Affiliation(s)
- Brad S Coates
- United States Department of Agriculture, Agricultural Research Service, Corn Insects & Crop Genetics Research Unit, Iowa State University, Ames, IA, 50011, USA. .,Department of Entomology, Iowa State University, Ames, IA, 50011, USA.
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Castanera R, Pérez G, López L, Sancho R, Santoyo F, Alfaro M, Gabaldón T, Pisabarro AG, Oguiza JA, Ramírez L. Highly expressed captured genes and cross-kingdom domains present in Helitrons create novel diversity in Pleurotus ostreatus and other fungi. BMC Genomics 2014; 15:1071. [PMID: 25480150 PMCID: PMC4289320 DOI: 10.1186/1471-2164-15-1071] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Accepted: 11/14/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Helitrons are class-II eukaryotic transposons that transpose via a rolling circle mechanism. Due to their ability to capture and mobilize gene fragments, they play an important role in the evolution of their host genomes. We have used a bioinformatics approach for the identification of helitrons in two Pleurotus ostreatus genomes using de novo detection and homology-based searching. We have analyzed the presence of helitron-captured genes as well as the expansion of helitron-specific helicases in fungi and performed a phylogenetic analysis of their conserved domains with other representative eukaryotic species. RESULTS Our results show the presence of two helitron families in P. ostreatus that disrupt gene colinearity and cause a lack of synteny between their genomes. Both putative autonomous and non-autonomous helitrons were transcriptionally active, and some of them carried highly expressed captured genes of unknown origin and function. In addition, both families contained eukaryotic, bacterial and viral domains within the helitron's boundaries. A phylogenetic reconstruction of RepHel helicases using the Helitron-like and PIF1-like helicase conserved domains revealed a polyphyletic origin for eukaryotic helitrons. CONCLUSION P. ostreatus helitrons display features similar to other eukaryotic helitrons and do not tend to capture host genes or gene fragments. The occurrence of genes probably captured from other hosts inside the helitrons boundaries pose the hypothesis that an ancient horizontal transfer mechanism could have taken place. The viral domains found in some of these genes and the polyphyletic origin of RepHel helicases in the eukaryotic kingdom suggests that virus could have played a role in a putative lateral transfer of helitrons within the eukaryotic kingdom. The high similarity of some helitrons, along with the transcriptional activity of its RepHel helicases indicates that these elements are still active in the genome of P. ostreatus.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | - Lucía Ramírez
- Department of Agrarian Production, Genetics and Microbiology Research Group, Public University of Navarre, 31006 Pamplona, Navarre, Spain.
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Thomas J, Phillips CD, Baker RJ, Pritham EJ. Rolling-circle transposons catalyze genomic innovation in a mammalian lineage. Genome Biol Evol 2014; 6:2595-610. [PMID: 25223768 PMCID: PMC4224331 DOI: 10.1093/gbe/evu204] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Rolling-circle transposons (Helitrons) are a newly discovered group of mobile DNA widespread in plant and invertebrate genomes but limited to the bat family Vespertilionidae among mammals. Little is known about the long-term impact of Helitron activity because the genomes where Helitron activity has been extensively studied are predominated by young families. Here, we report a comprehensive catalog of vetted Helitrons from the 7× Myotis lucifugus genome assembly. To estimate the timing of transposition, we scored presence/absence across related vespertilionid genome sequences with estimated divergence times. This analysis revealed that the Helibat family has been a persistent source of genomic innovation throughout the vespertilionid diversification from approximately 30–36 Ma to as recently as approximately 1.8–6 Ma. This is the first report of persistent Helitron transposition over an extended evolutionary timeframe. These findings illustrate that the pattern of Helitron activity is akin to the vertical persistence of LINE retrotransposons in primates and other mammalian lineages. Like retrotransposition in primates, rolling-circle transposition has generated lineage-specific variation and accounts for approximately 110 Mb, approximately 6% of the genome of M. lucifugus. The Helitrons carry a heterogeneous assortment of host sequence including retroposed messenger RNAs, retrotransposons, DNA transposons, as well as introns, exons and regulatory regions (promoters, 5′-untranslated regions [UTRs], and 3′-UTRs) of which some are evolving in a pattern suggestive of purifying selection. Evidence that Helitrons have contributed putative promoters, exons, splice sites, polyadenylation sites, and microRNA-binding sites to transcripts otherwise conserved across mammals is presented, and the implication of Helitron activity to innovation in these unique mammals is discussed.
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Affiliation(s)
- Jainy Thomas
- Department of Human Genetics, University of Utah
| | - Caleb D Phillips
- Department of Biological Sciences and Museum, Texas Tech University
| | - Robert J Baker
- Department of Biological Sciences and Museum, Texas Tech University
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Helinoto, a Helitron2 transposon from the icefish Chionodraco hamatus, contains a region with three deubiquitinase-like domains that exhibit transcriptional activity. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY D-GENOMICS & PROTEOMICS 2014; 11:49-58. [PMID: 25178533 DOI: 10.1016/j.cbd.2014.07.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Revised: 07/29/2014] [Accepted: 07/30/2014] [Indexed: 11/24/2022]
Abstract
Transposable elements have accompanied the evolution of the eukaryotic genome for millions of years. The recently discovered Helitron order (class II, subclass 2 single-strand DNA transposons) is common in eukaryotes and seems to play a highly active role in genome reshuffling. This study provides novel insights into the characteristics of Helinoto, a helitron isolated in the genome of the Antarctic fish Chionodraco hamatus. In particular, investigation of the structure of its 5' and 3' ends, which are involved in the transposition process, enabled identification of the characteristic motifs of the Helitron2 group. Moreover, identification of a deubiquitinating protease domain in the region upstream two consecutive OTU domains extended and strengthened the "deubiquitinase" character of the N-terminal portion of Helinoto. Finally, Helinoto transcriptional activity was detected in several C. hamatus tissues. Taken together, these data are particularly intriguing because they document high transcription levels for genes involved in ubiquitination, which ensures protein homeostasis in the extreme Antarctic environment.
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HelitronScanner uncovers a large overlooked cache of Helitron transposons in many plant genomes. Proc Natl Acad Sci U S A 2014; 111:10263-8. [PMID: 24982153 DOI: 10.1073/pnas.1410068111] [Citation(s) in RCA: 157] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Transposons make up the bulk of eukaryotic genomes, but are difficult to annotate because they evolve rapidly. Most of the unannotated portion of sequenced genomes is probably made up of various divergent transposons that have yet to be categorized. Helitrons are unusual rolling circle eukaryotic transposons that often capture gene sequences, making them of considerable evolutionary importance. Unlike other DNA transposons, Helitrons do not end in inverted repeats or create target site duplications, so they are particularly challenging to identify. Here we present HelitronScanner, a two-layered local combinational variable (LCV) tool for generalized Helitron identification that represents a major improvement over previous identification programs based on DNA sequence or structure. HelitronScanner identified 64,654 Helitrons from a wide range of plant genomes in a highly automated way. We tested HelitronScanner's predictive ability in maize, a species with highly heterogeneous Helitron elements. LCV scores for the 5' and 3' termini of the predicted Helitrons provide a primary confidence level and element copy number provides a secondary one. Newly identified Helitrons were validated by PCR assays or by in silico comparative analysis of insertion site polymorphism among multiple accessions. Many new Helitrons were identified in model species, such as maize, rice, and Arabidopsis, and in a variety of organisms where Helitrons had not been reported previously to our knowledge, leading to a major upward reassessment of their abundance in plant genomes. HelitronScanner promises to be a valuable tool in future comparative and evolutionary studies of this major transposon superfamily.
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Thomas J, Vadnagara K, Pritham EJ. DINE-1, the highest copy number repeats in Drosophila melanogaster are non-autonomous endonuclease-encoding rolling-circle transposable elements (Helentrons). Mob DNA 2014; 5:18. [PMID: 24959209 PMCID: PMC4067079 DOI: 10.1186/1759-8753-5-18] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 05/09/2014] [Indexed: 11/11/2022] Open
Abstract
Background The Drosophila INterspersed Elements-1 (DINE-1/INE1) transposable elements (TEs) are the most abundant component of the Drosophila melanogaster genome and have been associated with functional gene duplications. DINE-1 TEs do not encode any proteins (non-autonomous) thus are moved by autonomous partners. The identity of the autonomous partners has been a mystery. They have been allied to Helitrons (rolling-circle transposons), MITEs (DNA transposons), and non-LTR retrotransposons by different authors. Results We report multiple lines of bioinformatic evidence that illustrate the relationship of DINE-1 like TEs to endonuclease-encoding rolling-circle TEs (Helentrons). The structural features of Helentrons are described, which resemble the organization of the non-autonomous partners, but differ significantly from canonical Helitrons. In addition to the presence of an endonuclease domain fused to the Rep/Helicase protein, Helentrons have distinct structural features. Evidence is presented that illustrates that Helentrons are widely distributed in invertebrate, fish, and fungal genomes. We describe an intermediate family from the Phytophthora infestans genome that phylogenetically groups with Helentrons but that displays Helitron structure. In addition, evidence is presented that Helentrons can capture gene fragments in a pattern reminiscent of canonical Helitrons. Conclusions We illustrate the relationship of DINE-1 and related TE families to autonomous partners, the Helentrons. These findings will allow their proper classification and enable a more accurate understanding of the contribution of rolling-circle transposition to the birth of new genes, gene networks, and genome composition.
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Affiliation(s)
- Jainy Thomas
- Department of Human Genetics, University of Utah, Salt Lake City, UT 84112, USA
| | - Komal Vadnagara
- Department of Cancer Biology, MD Anderson Cancer Center, Houston, TX 77054, USA
| | - Ellen J Pritham
- Department of Human Genetics, University of Utah, Salt Lake City, UT 84112, USA
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