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Kawase M, Ichiyanagi K. Mouse retrotransposons: sequence structure, evolutionary age, genomic distribution and function. Genes Genet Syst 2024; 98:337-351. [PMID: 37989301 DOI: 10.1266/ggs.23-00221] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2023] Open
Abstract
Retrotransposons are transposable elements that are transposed via transcription and reverse transcription. Their copies have accumulated in the genome of mammals, occupying approximately 40% of mammalian genomic mass. These copies are often involved in numerous phenomena, such as chromatin spatial organization, gene expression, development and disease, and have been recognized as a driving force in evolution. Different organisms have gained specific retrotransposon subfamilies and retrotransposed copies, such as hundreds of Mus-specific subfamilies with diverse sequences and genomic locations. Despite this complexity, basic information is still necessary for present-day genomic and epigenomic studies. Herein, we describe the characteristics of each subfamily of Mus-specific retrotransposons in terms of sequence structure, phylogenetic relationships, evolutionary age, and preference for A or B compartments of chromatin.
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Affiliation(s)
- Masaki Kawase
- Laboratory of Genome and Epigenome Dynamics, Department of Animal Sciences, Graduate School of Bioagricultural Sciences, Nagoya University
| | - Kenji Ichiyanagi
- Laboratory of Genome and Epigenome Dynamics, Department of Animal Sciences, Graduate School of Bioagricultural Sciences, Nagoya University
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2
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Zong W, Wang J, Zhao R, Niu N, Su Y, Hu Z, Liu X, Hou X, Wang L, Wang L, Zhang L. Associations of genome-wide structural variations with phenotypic differences in cross-bred Eurasian pigs. J Anim Sci Biotechnol 2023; 14:136. [PMID: 37805653 PMCID: PMC10559557 DOI: 10.1186/s40104-023-00929-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Accepted: 08/03/2023] [Indexed: 10/09/2023] Open
Abstract
BACKGROUND During approximately 10,000 years of domestication and selection, a large number of structural variations (SVs) have emerged in the genome of pig breeds, profoundly influencing their phenotypes and the ability to adapt to the local environment. SVs (≥ 50 bp) are widely distributed in the genome, mainly in the form of insertion (INS), mobile element insertion (MEI), deletion (DEL), duplication (DUP), inversion (INV), and translocation (TRA). While studies have investigated the SVs in pig genomes, genome-wide association studies (GWAS)-based on SVs have been rarely conducted. RESULTS Here, we obtained a high-quality SV map containing 123,151 SVs from 15 Large White and 15 Min pigs through integrating the power of several SV tools, with 53.95% of the SVs being reported for the first time. These high-quality SVs were used to recover the population genetic structure, confirming the accuracy of genotyping. Potential functional SV loci were then identified based on positional effects and breed stratification. Finally, GWAS were performed for 36 traits by genotyping the screened potential causal loci in the F2 population according to their corresponding genomic positions. We identified a large number of loci involved in 8 carcass traits and 6 skeletal traits on chromosome 7, with FKBP5 containing the most significant SV locus for almost all traits. In addition, we found several significant loci in intramuscular fat, abdominal circumference, heart weight, and liver weight, etc. CONCLUSIONS: We constructed a high-quality SV map using high-coverage sequencing data and then analyzed them by performing GWAS for 25 carcass traits, 7 skeletal traits, and 4 meat quality traits to determine that SVs may affect body size between European and Chinese pig breeds.
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Affiliation(s)
- Wencheng Zong
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Jinbu Wang
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Runze Zhao
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
- College of Animal Science, Shanxi Agricultural University, Jinzhong, 030801, China
| | - Naiqi Niu
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Yanfang Su
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Ziping Hu
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
- College of Animal Science and Technology, Qingdao Agricultural University, Qingdao, 266109, China
| | - Xin Liu
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Xinhua Hou
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Ligang Wang
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Lixian Wang
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
| | - Longchao Zhang
- State Key Laboratory of Animal Biotech Breeding, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
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Garcia-Cañadas M, Sanchez-Luque FJ, Sanchez L, Rojas J, Garcia Perez JL. LINE-1 Retrotransposition Assays in Embryonic Stem Cells. Methods Mol Biol 2023; 2607:257-309. [PMID: 36449167 DOI: 10.1007/978-1-0716-2883-6_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
The ongoing mobilization of active non-long terminal repeat (LTR) retrotransposons continues to impact the genomes of most mammals, including humans and rodents. Non-LTR retrotransposons mobilize using an intermediary RNA and a copy-and-paste mechanism termed retrotransposition. Non-LTR retrotransposons are subdivided into long and short interspersed elements (LINEs and SINEs, respectively), depending on their size and autonomy; while active class 1 LINEs (LINE-1s or L1s) encode the enzymatic machinery required to mobilize in cis, active SINEs use the enzymatic machinery of active LINE-1s to mobilize in trans. The mobilization mechanism used by LINE-1s/SINEs was exploited to develop ingenious plasmid-based retrotransposition assays in cultured cells, which typically exploit a reporter gene that can only be activated after a round of retrotransposition. Retrotransposition assays, in cis or in trans, are instrumental tools to study the biology of mammalian LINE-1s and SINEs. In fact, these and other biochemical/genetic assays were used to uncover that endogenous mammalian LINE-1s/SINEs naturally retrotranspose during early embryonic development. However, embryonic stem cells (ESCs) are typically used as a cellular model in these and other studies interrogating LINE-1/SINE expression/regulation during early embryogenesis. Thus, human and mouse ESCs represent an excellent model to understand how active retrotransposons are regulated and how their activity impacts the germline. Here, we describe robust and quantitative protocols to study human/mouse LINE-1 (in cis) and SINE (in trans) retrotransposition using (human and mice) ESCs. These protocols are designed to study the mobilization of active non-LTR retrotransposons in a cellular physiologically relevant context.
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Affiliation(s)
- Marta Garcia-Cañadas
- Pfizer-University of Granada-Andalusian Government Centre for Genomics and Oncological Research (GENYO), PTS Granada, Granada, Spain.
| | - Francisco J Sanchez-Luque
- Institute of Parasitology and Biomedicine "Lopez-Neyra" (IPBLN), Spanish National Research Council (CSIC), PTS Granada, Granada, Spain
| | - Laura Sanchez
- Pfizer-University of Granada-Andalusian Government Centre for Genomics and Oncological Research (GENYO), PTS Granada, Granada, Spain
| | - Johana Rojas
- Pfizer-University of Granada-Andalusian Government Centre for Genomics and Oncological Research (GENYO), PTS Granada, Granada, Spain
| | - Jose L Garcia Perez
- Pfizer-University of Granada-Andalusian Government Centre for Genomics and Oncological Research (GENYO), PTS Granada, Granada, Spain.
- MRC Human Genetics Unit, Institute of Genetics and Cancer (IGC)/University of Edinburgh, Western General Hospital Campus, Edinburgh, UK.
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Zhang Q, Pan J, Cong Y, Mao J. Transcriptional Regulation of Endogenous Retroviruses and Their Misregulation in Human Diseases. Int J Mol Sci 2022; 23:ijms231710112. [PMID: 36077510 PMCID: PMC9456331 DOI: 10.3390/ijms231710112] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 08/28/2022] [Accepted: 09/01/2022] [Indexed: 11/22/2022] Open
Abstract
Endogenous retroviruses (ERVs), deriving from exogenous retroviral infections of germ line cells occurred millions of years ago, represent ~8% of human genome. Most ERVs are highly inactivated because of the accumulation of mutations, insertions, deletions, and/or truncations. However, it is becoming increasingly apparent that ERVs influence host biology through genetic and epigenetic mechanisms under particular physiological and pathological conditions, which provide both beneficial and deleterious effects for the host. For instance, certain ERVs expression is essential for human embryonic development. Whereas abnormal activation of ERVs was found to be involved in numbers of human diseases, such as cancer and neurodegenerative diseases. Therefore, understanding the mechanisms of regulation of ERVs would provide insights into the role of ERVs in health and diseases. Here, we provide an overview of mechanisms of transcriptional regulation of ERVs and their dysregulation in human diseases.
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Kong L, Saha K, Hu Y, Tschetter JN, Habben CE, Whitmore LS, Yao C, Ge X, Ye P, Newkirk SJ, An W. Subfamily-specific differential contribution of individual monomers and the tether sequence to mouse L1 promoter activity. Mob DNA 2022; 13:13. [PMID: 35443687 PMCID: PMC9022269 DOI: 10.1186/s13100-022-00269-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Accepted: 03/28/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The internal promoter in L1 5'UTR is critical for autonomous L1 transcription and initiating retrotransposition. Unlike the human genome, which features one contemporarily active subfamily, four subfamilies (A_I, Gf_I and Tf_I/II) have been amplifying in the mouse genome in the last one million years. Moreover, mouse L1 5'UTRs are organized into tandem repeats called monomers, which are separated from ORF1 by a tether domain. In this study, we aim to compare promoter activities across young mouse L1 subfamilies and investigate the contribution of individual monomers and the tether sequence. RESULTS We observed an inverse relationship between subfamily age and the average number of monomers among evolutionarily young mouse L1 subfamilies. The youngest subgroup (A_I and Tf_I/II) on average carry 3-4 monomers in the 5'UTR. Using a single-vector dual-luciferase reporter assay, we compared promoter activities across six L1 subfamilies (A_I/II, Gf_I and Tf_I/II/III) and established their antisense promoter activities in a mouse embryonic fibroblast cell line and a mouse embryonal carcinoma cell line. Using consensus promoter sequences for three subfamilies (A_I, Gf_I and Tf_I), we dissected the differential roles of individual monomers and the tether domain in L1 promoter activity. We validated that, across multiple subfamilies, the second monomer consistently enhances the overall promoter activity. For individual promoter components, monomer 2 is consistently more active than the corresponding monomer 1 and/or the tether for each subfamily. Importantly, we revealed intricate interactions between monomer 2, monomer 1 and tether domains in a subfamily-specific manner. Furthermore, using three-monomer 5'UTRs, we established a complex nonlinear relationship between the length of the outmost monomer and the overall promoter activity. CONCLUSIONS The laboratory mouse is an important mammalian model system for human diseases as well as L1 biology. Our study extends previous findings and represents an important step toward a better understanding of the molecular mechanism controlling mouse L1 transcription as well as L1's impact on development and disease.
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Affiliation(s)
- Lingqi Kong
- Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD, 57007, USA
| | - Karabi Saha
- Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD, 57007, USA
| | - Yuchi Hu
- Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD, 57007, USA
| | - Jada N Tschetter
- Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD, 57007, USA
| | - Chase E Habben
- Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD, 57007, USA
| | - Leanne S Whitmore
- Department of Immunology, University of Washington, Seattle, WA, 98109, USA
| | - Changfeng Yao
- Anhui University of Traditional Chinese Medicine, Hefei, 230012, Anhui, China
| | - Xijin Ge
- Department of Mathematics & Statistics, South Dakota State University, Brookings, SD, 57007, USA
| | - Ping Ye
- Department of Pharmacy Practice, South Dakota State University, Brookings, SD, 57007, USA
| | - Simon J Newkirk
- Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD, 57007, USA
| | - Wenfeng An
- Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD, 57007, USA.
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Gazquez-Gutierrez A, Witteveldt J, R Heras S, Macias S. Sensing of transposable elements by the antiviral innate immune system. RNA (NEW YORK, N.Y.) 2021; 27:rna.078721.121. [PMID: 33888553 PMCID: PMC8208052 DOI: 10.1261/rna.078721.121] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Accepted: 04/17/2021] [Indexed: 05/15/2023]
Abstract
Around half of the genome in mammals is composed of transposable elements (TEs) such as DNA transposons and retrotransposons. Several mechanisms have evolved to prevent their activity and the detrimental impact of their insertional mutagenesis. Despite these potentially negative effects, TEs are essential drivers of evolution, and in certain settings, beneficial to their hosts. For instance, TEs have rewired the antiviral gene regulatory network and are required for early embryonic development. However, due to structural similarities between TE-derived and viral nucleic acids, cells can misidentify TEs as invading viruses and trigger the major antiviral innate immune pathway, the type I interferon (IFN) response. This review will focus on the different settings in which the role of TE-mediated IFN activation has been documented, including cancer and senescence. Importantly, TEs may also play a causative role in the development of complex autoimmune diseases characterised by constitutive type I IFN activation. All these observations suggest the presence of strong but opposing forces driving the coevolution of TEs and antiviral defence. A better biological understanding of the TE replicative cycle as well as of the antiviral nucleic acid sensing mechanisms will provide insights into how these two biological processes interact and will help to design better strategies to treat human diseases characterised by aberrant TE expression and/or type I IFN activation.
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Affiliation(s)
| | - Jeroen Witteveldt
- University of Edinburgh - Institute of Immunology and Infection Research
| | - Sara R Heras
- GENYO. Centre for Genomics and Oncological Research, Pfizer University of Granada
| | - Sara Macias
- Institute of Immunology and Infection Research
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Vasilyev SA, Tolmacheva EN, Vasilyeva OY, Markov AV, Zhigalina DI, Zatula LA, Lee VA, Serdyukova ES, Sazhenova EA, Nikitina TV, Kashevarova AA, Lebedev IN. LINE-1 retrotransposon methylation in chorionic villi of first trimester miscarriages with aneuploidy. J Assist Reprod Genet 2021; 38:139-149. [PMID: 33170392 PMCID: PMC7823001 DOI: 10.1007/s10815-020-02003-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2020] [Accepted: 11/02/2020] [Indexed: 01/15/2023] Open
Abstract
PURPOSE High frequency of aneuploidy in meiosis and cleavage stage coincides with waves of epigenetic genome reprogramming that may indicate a possible association between epigenetic mechanisms and aneuploidy occurrence. This study aimed to assess the methylation level of the long interspersed repeat element 1 (LINE-1) retrotransposon in chorionic villi of first trimester miscarriages with a normal karyotype and aneuploidy. METHODS The methylation level was assessed at 19 LINE-1 promoter CpG sites in chorionic villi of 141 miscarriages with trisomy of chromosomes 2, 6, 8-10, 13-15, 16, 18, 20-22, and monosomy X using massive parallel sequencing. RESULTS The LINE-1 methylation level was elevated statistically significant in chorionic villi of miscarriages with both trisomy (45.2 ± 4.3%) and monosomy X (46.9 ± 4.2%) compared with that in induced abortions (40.0 ± 2.4%) (p < 0.00001). The LINE-1 methylation levels were specific for miscarriages with different aneuploidies and significantly increased in miscarriages with trisomies 8, 14, and 18 and monosomy X (p < 0.05). The LINE-1 methylation level increased with gestational age both for group of miscarriages regardless of karyotype (R = 0.21, p = 0.012) and specifically for miscarriages with trisomy 16 (R = 0.48, p = 0.007). LINE-1 methylation decreased with maternal age in miscarriages with a normal karyotype (R = - 0.31, p = 0.029) and with trisomy 21 (R = - 0.64, p = 0.024) and increased with paternal age for miscarriages with trisomy 16 (R = 0.38, p = 0.048) and monosomy X (R = 0.73, p = 0.003). CONCLUSION Our results indicate that the pathogenic effects of aneuploidy in human embryogenesis can be supplemented with significant epigenetic changes in the repetitive sequences.
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Affiliation(s)
- Stanislav A Vasilyev
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia.
- Biological Institute, National Research Tomsk State University, Lenina, 36, Tomsk, Russia.
| | - Ekaterina N Tolmacheva
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia
| | - Oksana Yu Vasilyeva
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia
| | - Anton V Markov
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia
| | - Daria I Zhigalina
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia
| | - Lada A Zatula
- Department of Medical Genetics, Siberian State Medical University, Moskovskiy Trakt, 2, Tomsk, Russia
| | - Vasilissa A Lee
- Department of Medical Genetics, Siberian State Medical University, Moskovskiy Trakt, 2, Tomsk, Russia
| | - Ekaterina S Serdyukova
- Biological Institute, National Research Tomsk State University, Lenina, 36, Tomsk, Russia
| | - Elena A Sazhenova
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia
| | - Tatyana V Nikitina
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia
| | - Anna A Kashevarova
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia
| | - Igor N Lebedev
- Research Institute of Medical Genetics, Tomsk National Research Medical Center, Nab. R. Ushaiki, 10, Tomsk, Russia
- Department of Medical Genetics, Siberian State Medical University, Moskovskiy Trakt, 2, Tomsk, Russia
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Geis FK, Goff SP. Silencing and Transcriptional Regulation of Endogenous Retroviruses: An Overview. Viruses 2020; 12:v12080884. [PMID: 32823517 PMCID: PMC7472088 DOI: 10.3390/v12080884] [Citation(s) in RCA: 87] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Revised: 08/03/2020] [Accepted: 08/11/2020] [Indexed: 12/16/2022] Open
Abstract
Almost half of the human genome is made up of transposable elements (TEs), and about 8% consists of endogenous retroviruses (ERVs). ERVs are remnants of ancient exogenous retrovirus infections of the germ line. Most TEs are inactive and not detrimental to the host. They are tightly regulated to ensure genomic stability of the host and avoid deregulation of nearby gene loci. Histone-based posttranslational modifications such as H3K9 trimethylation are one of the main silencing mechanisms. Trim28 is one of the identified master regulators of silencing, which recruits most prominently the H3K9 methyltransferase Setdb1, among other factors. Sumoylation and ATP-dependent chromatin remodeling factors seem to contribute to proper localization of Trim28 to ERV sequences and promote Trim28 interaction with Setdb1. Additionally, DNA methylation as well as RNA-mediated targeting of TEs such as piRNA-based silencing play important roles in ERV regulation. Despite the involvement of ERV overexpression in several cancer types, autoimmune diseases, and viral pathologies, ERVs are now also appreciated for their potential positive role in evolution. ERVs can provide new regulatory gene elements or novel binding sites for transcription factors, and ERV gene products can even be repurposed for the benefit of the host.
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Affiliation(s)
- Franziska K. Geis
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, New York, NY 10032, USA;
- Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY 10032, USA
- Howard Hughes Medical Institute, Columbia University Medical Center, New York, NY 10032, USA
| | - Stephen P. Goff
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, New York, NY 10032, USA;
- Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY 10032, USA
- Howard Hughes Medical Institute, Columbia University Medical Center, New York, NY 10032, USA
- Correspondence: ; Tel.: +1-212-305-3794
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Lanciano S, Cristofari G. Measuring and interpreting transposable element expression. Nat Rev Genet 2020; 21:721-736. [PMID: 32576954 DOI: 10.1038/s41576-020-0251-y] [Citation(s) in RCA: 164] [Impact Index Per Article: 41.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/19/2020] [Indexed: 12/21/2022]
Abstract
Transposable elements (TEs) are insertional mutagens that contribute greatly to the plasticity of eukaryotic genomes, influencing the evolution and adaptation of species as well as physiology or disease in individuals. Measuring TE expression helps to understand not only when and where TE mobilization can occur but also how this process alters gene expression, chromatin accessibility or cellular signalling pathways. Although genome-wide gene expression assays such as RNA sequencing include transposon-derived transcripts, most computational analytical tools discard or misinterpret TE-derived reads. Emerging approaches are improving the identification of expressed TE loci and helping to discriminate TE transcripts that permit TE mobilization from chimeric gene-TE transcripts or pervasive transcription. Here we review the main challenges associated with the detection of TE expression, including mappability, insertional and internal sequence polymorphisms, and the diversity of the TE transcriptional landscape, as well as the different experimental and computational strategies to solve them.
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Del Re B, Giorgi G. Long INterspersed element-1 mobility as a sensor of environmental stresses. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:465-493. [PMID: 32144842 DOI: 10.1002/em.22366] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Revised: 03/03/2020] [Accepted: 03/04/2020] [Indexed: 06/10/2023]
Abstract
Long INterspersed element (LINE-1, L1) retrotransposons are the most abundant transposable elements in the human genome, constituting approximately 17%. They move by a "copy-paste" mechanism, involving reverse transcription of an RNA intermediate and insertion of its cDNA copy at a new site in the genome. L1 retrotransposition (L1-RTP) can cause insertional mutations, alter gene expression, transduce exons, and induce epigenetic dysregulation. L1-RTP is generally repressed; however, a number of observations collected over about 15 years revealed that it can occur in response to environmental stresses. Moreover, emerging evidence indicates that L1-RTP can play a role in the onset of several neurological and oncological diseases in humans. In recent years, great attention has been paid to the exposome paradigm, which proposes that health effects of an environmental factor should be evaluated considering both cumulative environmental exposures and the endogenous processes resulting from the biological response. L1-RTP could be an endogenous process considered for this application. Here, we summarize the current understanding of environmental factors that can affect the retrotransposition of human L1 elements. Evidence indicates that L1-RTP alteration is triggered by numerous and various environmental stressors, such as chemical agents (heavy metals, carcinogens, oxidants, and drugs), physical agents (ionizing and non-ionizing radiations), and experiential factors (voluntary exercise, social isolation, maternal care, and environmental light/dark cycles). These data come from in vitro studies on cell lines and in vivo studies on transgenic animals: future investigations should be focused on physiologically relevant models to gain a better understanding of this topic.
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Affiliation(s)
- Brunella Del Re
- Department of Pharmacy and Biotechnology, Alma Mater Studiorum University of Bologna, Bologna, Italy
| | - Gianfranco Giorgi
- Department of Biological, Geological and Environmental Sciences, Alma Mater Studiorum University of Bologna, Bologna, Italy
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Nishihara H. Transposable elements as genetic accelerators of evolution: contribution to genome size, gene regulatory network rewiring and morphological innovation. Genes Genet Syst 2020; 94:269-281. [PMID: 31932541 DOI: 10.1266/ggs.19-00029] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
In the current era, as a growing number of genome sequence assemblies have been reported in animals, an in-depth analysis of transposable elements (TEs) is one of the most fundamental and essential studies for evolutionary genomics. Although TEs have, in general, been regarded as non-functional junk/selfish DNA, parasitic elements or harmful mutagens, studies have revealed that TEs have had a substantial and sometimes beneficial impact on host genomes in several ways. First, TEs are themselves diverse and thus provide lineage-specific characteristics to the genomes. Second, because TEs constitute a substantial fraction of animal genomes, they are a major contributing factor to evolutionary changes in genome size and composition. Third, host organisms have co-opted many repetitive sequences as genes, cis-regulatory elements and chromatin domain boundaries, which alter gene regulatory networks and in addition are partly involved in morphological evolution, as has been well documented in mammals. Here, I review the impact of TEs on various aspects of the genome, such as genome size and diversity in animals, as well as the evolution of gene networks and genome architecture in mammals. Given that a number of TE families probably remain to be discovered in many non-model organisms, unknown TEs may have contributed to gene networks in a much wider variety of animals than considered previously.
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Chen C, Wang W, Wang X, Shen D, Wang S, Wang Y, Gao B, Wimmers K, Mao J, Li K, Song C. Retrotransposons evolution and impact on lncRNA and protein coding genes in pigs. Mob DNA 2019; 10:19. [PMID: 31080521 PMCID: PMC6501411 DOI: 10.1186/s13100-019-0161-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 04/11/2019] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Retrotransposons are the major determinants of genome sizes and they have shaped both genes and genomes in mammalian organisms, but their overall activity, diversity, and evolution dynamics, particularly their impact on protein coding and lncRNA genes in pigs remain largely unknown. RESULTS In the present study, we performed de novo detection of retrotransposons in pigs by using multiple pipelines, four distinct families of pig-specific L1 s classified into 51 distinct subfamilies and representing four evolution models and three expansion waves of pig-specific SINEs represented by three distinct families were identified. ERVs were classified into 18 families and found two most "modern" subfamilies in the pig genome. The transposition activity of pig L1 was verified by experiment, the sense and antisense promoter activities of young L1 5'UTRs and ERV LTRs and expression profiles of young retrotransposons in multiple tissues and cell lines were also validated. Furthermore, retrotransposons had an extensive impact on lncRNA and protein coding genes at both the genomic and transcriptomic levels. Most protein coding and lncRNA (> 80%) genes contained retrotransposon insertions, and about half of protein coding genes (44.30%) and one-fourth (24.13%) of lncRNA genes contained the youngest retrotransposon insertions. Nearly half of protein coding genes (43.78%) could generate chimeric transcripts with retrotransposons. Significant distribution bias of retrotransposon composition, location, and orientation in lncRNA and protein coding genes, and their transcripts, were observed. CONCLUSIONS In the current study, we characterized the classification and evolution profile of retrotransposons in pigs, experimentally proved the transposition activity of the young pig L1 subfamily, characterized the sense and antisense expression profiles and promoter activities of young retrotransposons, and investigated their impact on lncRNA and protein coding genes by defining the mobilome landscapes at the genomic and transcriptomic levels. These findings help provide a better understanding of retrotransposon evolution in mammal and their impact on the genome and transcriptome.
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Affiliation(s)
- Cai Chen
- Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou University, Yangzhou, 225009 Jiangsu China
| | - Wei Wang
- Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou University, Yangzhou, 225009 Jiangsu China
| | - Xiaoyan Wang
- Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou University, Yangzhou, 225009 Jiangsu China
| | - Dan Shen
- Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou University, Yangzhou, 225009 Jiangsu China
| | - Saisai Wang
- Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou University, Yangzhou, 225009 Jiangsu China
| | - Yali Wang
- Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou University, Yangzhou, 225009 Jiangsu China
| | - Bo Gao
- Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou University, Yangzhou, 225009 Jiangsu China
| | - Klaus Wimmers
- Leibniz Institute for Farm Animal Biology (FBN), 18196 Dummerstorf, Germany
| | - Jiude Mao
- Life Science Center, University of Missouri, Columbia, MO 65211 USA
| | - Kui Li
- Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Chengyi Song
- Institute of Animal Mobilome and Genome, College of Animal Science & Technology, Yangzhou University, Yangzhou, 225009 Jiangsu China
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13
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Wang Z, McSwiggin H, Newkirk SJ, Wang Y, Oliver D, Tang C, Lee S, Wang S, Yuan S, Zheng H, Ye P, An W, Yan W. Insertion of a chimeric retrotransposon sequence in mouse Axin1 locus causes metastable kinky tail phenotype. Mob DNA 2019; 10:17. [PMID: 31073336 PMCID: PMC6500023 DOI: 10.1186/s13100-019-0162-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2019] [Accepted: 04/21/2019] [Indexed: 12/12/2022] Open
Abstract
Background Transposable elements (TEs) make up > 50% of the human genome, and the majority of retrotransposon insertions are truncated and many are located in introns. However, the effects of retrotransposition on the host genes remain incompletely known. Results We report here that insertion of a chimeric L1 (cL1), but not IAP solo LTR, into intron 6 of Axin1 using CRIPSR/Cas9 induced the kinky tail phenotype with ~ 80% penetrance in heterozygous Axin cL1 mice. Both penetrant (with kinky tails) and silent (without kinky tails) Axin cL1 mice, regardless of sex, could transmit the phenotype to subsequent generations with similar penetrance (~ 80%). Further analyses revealed that a longer Axin1 transcript isoform containing partial cL1-targeted intron was present in penetrant, but absent in silent and wild type mice, and the production of this unique Axin1 transcript appeared to correlate with altered levels of an activating histone modification, H3K9ac. Conclusions The mechanism for Axin cL1 mice is different from those previously identified in mice with spontaneous retrotransposition of IAP, e.g., Axin Fu and A vy , both of which have been associated with DNA methylation changes. Our data suggest that Axin1 locus is sensitive to genetic and epigenetic alteration by retrotransposons and thus, ideally suited for studying the effects of new retrotransposition events on target gene function in mice.
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Affiliation(s)
- Zhuqing Wang
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Hayden McSwiggin
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Simon J Newkirk
- 3Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD 57007 USA
| | - Yue Wang
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Daniel Oliver
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Chong Tang
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Sandy Lee
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Shawn Wang
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Shuiqiao Yuan
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Huili Zheng
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA
| | - Ping Ye
- 2Avera McKennan Hospital and University Health Center, Sioux Falls, SD 57108 USA.,3Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD 57007 USA
| | - Wenfeng An
- 3Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD 57007 USA
| | - Wei Yan
- 1Department of Physiology and Cell Biology, University of Nevada School of Medicine Center for Molecular Medicine, Room 207B 1664 North Virginia Street MS/0575, Reno, NV 89557 USA.,4Department of Obstetrics and Gynecology, University of Nevada, Reno School of Medicine, Reno, NV 89557 USA.,5Department of Biology, University of Nevada, Reno, Reno, NV 89557 USA
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14
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Morozov SY, Lezzhov AA, Lazareva EA, Erokhina TN, Solovyev AG. Potential Role of Accessory Domains in Polyproteins Encoded by Retrotransposons in Anti-viral Defense of Host Cells. Front Microbiol 2019; 9:3193. [PMID: 30687243 PMCID: PMC6338049 DOI: 10.3389/fmicb.2018.03193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Accepted: 12/10/2018] [Indexed: 11/30/2022] Open
Affiliation(s)
- Sergey Y Morozov
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.,Department of Virology, Biological Faculty, Moscow State University, Moscow, Russia
| | - Alexander A Lezzhov
- Faculty of Bioengineering and Bioinformatics, Moscow State University, Moscow, Russia
| | - Ekaterina A Lazareva
- Department of Virology, Biological Faculty, Moscow State University, Moscow, Russia
| | - Tatiana N Erokhina
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - Andrey G Solovyev
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.,Department of Virology, Biological Faculty, Moscow State University, Moscow, Russia.,Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Moscow, Russia
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15
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Giudice A, Crispo A, Grimaldi M, Polo A, Bimonte S, Capunzo M, Amore A, D'Arena G, Cerino P, Budillon A, Botti G, Costantini S, Montella M. The Effect of Light Exposure at Night (LAN) on Carcinogenesis via Decreased Nocturnal Melatonin Synthesis. Molecules 2018; 23:E1308. [PMID: 29844288 PMCID: PMC6100442 DOI: 10.3390/molecules23061308] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 05/24/2018] [Accepted: 05/29/2018] [Indexed: 12/13/2022] Open
Abstract
In mammals, a master clock is located within the suprachiasmatic nucleus (SCN) of the hypothalamus, a region that receives input from the retina that is transmitted by the retinohypothalamic tract. The SCN controls the nocturnal synthesis of melatonin by the pineal gland that can influence the activity of the clock's genes and be involved in the inhibition of cancer development. On the other hand, in the literature, some papers highlight that artificial light exposure at night (LAN)-induced circadian disruptions promote cancer. In the present review, we summarize the potential mechanisms by which LAN-evoked disruption of the nocturnal increase in melatonin synthesis counteracts its preventive action on human cancer development and progression. In detail, we discuss: (i) the Warburg effect related to tumor metabolism modification; (ii) genomic instability associated with L1 activity; and (iii) regulation of immunity, including regulatory T cell (Treg) regulation and activity. A better understanding of these processes could significantly contribute to new treatment and prevention strategies against hormone-related cancer types.
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Affiliation(s)
- Aldo Giudice
- Epidemiology Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Anna Crispo
- Epidemiology Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Maria Grimaldi
- Epidemiology Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Andrea Polo
- Experimental Pharmacology Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Sabrina Bimonte
- Division of Anesthesia and Pain Medicine, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Mario Capunzo
- Department of Medicine Surgery and Dentistry, University of Salerno, Baronissi, 84081 Salerno, Italy.
| | - Alfonso Amore
- Abdominal Surgical Oncology and Hepatobiliary Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Giovanni D'Arena
- Department of Hematology and Stem Cell Transplantation Unit, IRCCS, Cancer Referral Center of Basilicata, 85028 Rionero in Vulture, Italy.
| | - Pellegrino Cerino
- Istituto Zooprofilattico Sperimentale del Mezzogiorno (IZSM), 80055 Portici, Napoli, Italy.
| | - Alfredo Budillon
- Experimental Pharmacology Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Gerardo Botti
- Pathology Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Susan Costantini
- Experimental Pharmacology Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
| | - Maurizio Montella
- Epidemiology Unit, IRCCS Istituto Nazionale Tumori "Fondazione G. Pascale", 80131 Napoli, Italy.
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16
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Ishiguro K, Higashino S, Hirakawa H, Sato S, Aizawa Y. Establishment of a genome-wide and quantitative protocol for assessment of transcriptional activity at human retrotransposon L1 antisense promoters. Genes Genet Syst 2018; 92:243-249. [PMID: 28381655 DOI: 10.1266/ggs.16-00053] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Long interspersed element 1 (L1) retrotransposon sequences are widespread in the human genome, occupying ~500,000 locations. The majority of L1s have lost their retrotransposition capability, although a significant population of human L1s maintains bidirectional transcriptional activity from the internal promoter. While the sense promoter drives transcription of the entire L1 mRNA and leads to L1 retrotransposition, the antisense promoter (ASP) transcribes L1-gene chimeric RNAs that include neighboring exon sequences. Activation mechanisms and functional impacts of L1ASP transcription are thought to vary at every L1ASP location. To explore the locus-specific regulation and function of L1ASP transcription, quantitative methodology is necessary for identifying the genomic positions of highly active L1ASPs on a genome-wide scale. Here, we employed deep-sequencing techniques and built a 3' RACE-based experimental and bioinformatics protocol, named the L1 antisense transcriptome protocol (LATRAP). In LATRAP, the PCR primer and the read mapping scheme were designed to reduce false positives and negatives, which may have been included as hits in previous cloning studies. LATRAP was here applied to the A549 human lung cancer cell line, and 313 L1ASP loci were detected to have transcriptional activity but differed in the number of mapped reads by four orders of magnitude. This indicates that transcriptional activities of the individual L1ASPs can vary greatly and that only a small population of L1ASP loci is active within individual nuclei. LATRAP is the first experimental method for ranking L1ASPs according to their transcriptional activity and will thus open a new avenue to unveiling the locus-specific biology of L1ASPs.
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Affiliation(s)
- Koichi Ishiguro
- Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology
| | - Saneyuki Higashino
- Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology
| | | | | | - Yasunori Aizawa
- Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology.,Center for Biological Resources and Informatics, Tokyo Institute of Technology
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17
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Morozov SY, Lazareva EA, Solovyev AG. RNA helicase domains of viral origin in proteins of insect retrotransposons: possible source for evolutionary advantages. PeerJ 2017; 5:e3673. [PMID: 28828268 PMCID: PMC5563155 DOI: 10.7717/peerj.3673] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Accepted: 07/21/2017] [Indexed: 12/15/2022] Open
Abstract
Recently, a novel phenomenon of horizontal gene transfer of helicase-encoding sequence from positive-stranded RNA viruses to LINE transposons in insect genomes was described. TRAS family transposons encoding an ORF2 protein, which comprised all typical functional domains and an additional helicase domain, were found to be preserved in many families during the evolution of the order Lepidoptera. In the present paper, in species of orders Hemiptera and Orthoptera, we found helicase domain-encoding sequences integrated into ORF1 of retrotransposons of the Jockey family. RNA helicases encoded by transposons of TRAS and Jockey families represented separate brunches in a phylogenetic tree of helicase domains and thus could be considered as independently originated in the evolution of insect transposons. Transcriptome database analyses revealed that both TRAS and Jockey transposons encoding the helicase domain represented transcribed genome sequences. Moreover, the transposon-encoded helicases were found to contain the full set of conserved motifs essential for their enzymatic activities. Taking into account the previously reported ability of RNA helicase encoded by TRAS ORF2 to suppress post-transcriptional RNA silencing, we propose possible scenarios of evolutionary fixation of actively expressed functional helicases of viral origin in insect retrotransposons as genetic elements advantageous for both transposons and their insect hosts.
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Affiliation(s)
- Sergey Y Morozov
- Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia
| | - Ekaterina A Lazareva
- Department of Virology, Biological Faculty, Moscow State University, Moscow, Russia
| | - Andrey G Solovyev
- Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.,Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Moscow, Russia
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18
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Switching of dominant retrotransposon silencing strategies from posttranscriptional to transcriptional mechanisms during male germ-cell development in mice. PLoS Genet 2017; 13:e1006926. [PMID: 28749988 PMCID: PMC5549759 DOI: 10.1371/journal.pgen.1006926] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2016] [Revised: 08/08/2017] [Accepted: 07/15/2017] [Indexed: 12/13/2022] Open
Abstract
Mammalian genomes harbor millions of retrotransposon copies, some of which are transpositionally active. In mouse prospermatogonia, PIWI-interacting small RNAs (piRNAs) combat retrotransposon activity to maintain the genomic integrity. The piRNA system destroys retrotransposon-derived RNAs and guides de novo DNA methylation at some retrotransposon promoters. However, it remains unclear whether DNA methylation contributes to retrotransposon silencing in prospermatogonia. We have performed comprehensive studies of DNA methylation and polyA(+) RNAs (transcriptome) in developing male germ cells from Pld6/Mitopld and Dnmt3l knockout mice, which are defective in piRNA biogenesis and de novo DNA methylation, respectively. The Dnmt3l mutation greatly reduced DNA methylation levels at most retrotransposons, but its impact on their RNA abundance was limited in prospermatogonia. In Pld6 mutant germ cells, although only a few retrotransposons exhibited reduced DNA methylation, many showed increased expression at the RNA level. More detailed analysis of RNA sequencing, nascent RNA quantification, profiling of cleaved RNA ends, and the results obtained from double knockout mice suggest that PLD6 works mainly at the posttranscriptional level. The increase in retrotransposon expression was larger in Pld6 mutants than it was in Dnmt3l mutants, suggesting that RNA degradation by the piRNA system plays a more important role than does DNA methylation in prospermatogonia. However, DNA methylation had a long-term effect: hypomethylation caused by the Pld6 or Dnmt3l mutation resulted in increased retrotransposon expression in meiotic spermatocytes. Thus, posttranscriptional silencing plays an important role in the early stage of germ cell development, then transcriptional silencing becomes important in later stages. In addition, intergenic and intronic retrotransposon sequences, in particular those containing the antisense L1 promoters, drove ectopic expression of nearby genes in both mutant spermatocytes, suggesting that retrotransposon silencing is important for the maintenance of not only genomic integrity but also transcriptomic integrity. Retrotransposons are a class of transposable elements, of which mobility has mutagenic potential. Therefore, it is important to regulate the expression of retrotransposons for maintaining the genomic integrity. In male germ cells, DNA methylation and the piRNA system are thought to play roles in retrotransposon silencing. However, genome-wide DNA methylation is once erased (in primordial germ cells) and reestablished (in prospermatogonia) during development. In prospermatogonia, piRNAs guide de novo DNA methylation at some retrotransposons. To clarify the contribution of DNA methylation and the piRNA system to retrotransposon silencing in the course of male germ cell development, we analyzed DNA methylation and RNA expression in Dnmt3l and Pld6 knockout mice, which are defective in de novo DNA methylation and piRNA biogenesis, respectively. Our results reveal that, in prospermatogonia, the piRNA system works mainly at the posttranscriptional level, and plays a more important role than does DNA methylation in retrotransposon silencing. However, DNA methylation becomes much more important in later stages when germ cells enter meiosis (in spermatocytes). We also found that hypomethylated retrotransposons can drive ectopic expression of nearby genes; therefore, their transcriptional silencing by DNA methylation is important for maintaining the transcriptomic integrity as well.
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19
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Groh S, Schotta G. Silencing of endogenous retroviruses by heterochromatin. Cell Mol Life Sci 2017; 74:2055-2065. [PMID: 28160052 PMCID: PMC11107624 DOI: 10.1007/s00018-017-2454-8] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 12/14/2016] [Accepted: 01/03/2017] [Indexed: 02/05/2023]
Abstract
Endogenous retroviruses (ERV) are an abundant class of repetitive elements in mammalian genomes. To ensure genomic stability, ERVs are largely transcriptionally silent. However, these elements also feature physiological roles in distinct developmental contexts, under which silencing needs to be partially relieved. ERV silencing is mediated through a heterochromatic structure, which is established by histone modification and DNA methylation machineries. This heterochromatic structure is largely refractory to transcriptional stimulation, however, challenges to the heterochromatic state, such as DNA replication, require re-establishment of the heterochromatic state in competition with transcriptional activators. In this review, we discuss the major pathways leading to efficient establishment of robust and inaccessible heterochromatin across ERVs.
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Affiliation(s)
- Sophia Groh
- Biomedical Center and Center for Integrated Protein Science Munich, Ludwig-Maximilians-University, 82152, Planegg-Martinsried, Germany
| | - Gunnar Schotta
- Biomedical Center and Center for Integrated Protein Science Munich, Ludwig-Maximilians-University, 82152, Planegg-Martinsried, Germany.
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20
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Kannan M, Li J, Fritz SE, Husarek KE, Sanford JC, Sullivan TL, Tiwary PK, An W, Boeke JD, Symer DE. Dynamic silencing of somatic L1 retrotransposon insertions reflects the developmental and cellular contexts of their genomic integration. Mob DNA 2017; 8:8. [PMID: 28491150 PMCID: PMC5424313 DOI: 10.1186/s13100-017-0091-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 05/03/2017] [Indexed: 02/15/2023] Open
Abstract
Background The ongoing mobilization of mammalian transposable elements (TEs) contributes to natural genetic variation. To survey the epigenetic control and expression of reporter genes inserted by L1 retrotransposition in diverse cellular and genomic contexts, we engineered highly sensitive, real-time L1 retrotransposon reporter constructs. Results Here we describe different patterns of expression and epigenetic controls of newly inserted sequences retrotransposed by L1 in various somatic cells and tissues including cultured human cancer cells, mouse embryonic stem cells, and tissues of pseudofounder transgenic mice and their progeny. In cancer cell lines, the newly inserted sequences typically underwent rapid transcriptional gene silencing, but they lacked cytosine methylation even after many cell divisions. L1 reporter expression was reversible and oscillated frequently. Silenced or variegated reporter expression was strongly and uniformly reactivated by treatment with inhibitors of histone deacetylation, revealing the mechanism for their silencing. By contrast, de novo integrants retrotransposed by L1 in pluripotent mouse embryonic stem (ES) cells underwent rapid silencing by dense cytosine methylation. Similarly, de novo cytosine methylation also was identified at new integrants when studied in several distinct somatic tissues of adult founder mice. Pre-existing L1 elements in cultured human cancer cells were stably silenced by dense cytosine methylation, whereas their transcription modestly increased when cytosine methylation was experimentally reduced in cells lacking DNA methyltransferases DNMT1 and DNMT3b. As a control, reporter genes mobilized by piggyBac (PB), a DNA transposon, revealed relatively stable and robust expression without apparent silencing in both cultured cancer cells and ES cells. Conclusions We hypothesize that the de novo methylation marks at newly inserted sequences retrotransposed by L1 in early pre-implantation development are maintained or re-established in adult somatic tissues. By contrast, histone deacetylation reversibly silences L1 reporter insertions that had mobilized at later timepoints in somatic development and differentiation, e.g., in cancer cell lines. We conclude that the cellular contexts of L1 retrotransposition can determine expression or silencing of newly integrated sequences. We propose a model whereby reporter expression from somatic TE insertions reflects the timing, molecular mechanism, epigenetic controls and the genomic, cellular and developmental contexts of their integration. Electronic supplementary material The online version of this article (doi:10.1186/s13100-017-0091-2) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Manoj Kannan
- Department of Biological Sciences, Birla Institute of Technology and Science Pilani, Pilani, 333031 Rajasthan India.,Laboratory of Immunobiology, Mouse Cancer Genetics Program and Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702 USA.,Present Address: Birla Institute of Technology and Science, Pilani, Dubai campus, Dubai, United Arab Emirates
| | - Jingfeng Li
- Laboratory of Immunobiology, Mouse Cancer Genetics Program and Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702 USA.,Department of Cancer Biology and Genetics, The Ohio State University, Columbus, OH USA.,Department of Internal Medicine, The Ohio State University, Columbus, OH USA
| | - Sarah E Fritz
- Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH USA.,Present Address: National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD USA
| | - Kathryn E Husarek
- Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH USA.,Present Address: Aventiv Research, Inc., Columbus, OH USA
| | - Jonathan C Sanford
- Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH USA.,Present Address: Drug Safety Research and Development, Pfizer, Inc., Groton, CT USA
| | - Teresa L Sullivan
- Laboratory of Immunobiology, Mouse Cancer Genetics Program and Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702 USA
| | - Pawan Kumar Tiwary
- Laboratory of Immunobiology, Mouse Cancer Genetics Program and Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702 USA.,Present Address: Biocon, Bangalore, India
| | - Wenfeng An
- Department of Molecular Biology and Genetics, The Johns Hopkins University School of Medicine, Baltimore, MD USA.,Present Address: Department of Pharmaceutical Sciences, South Dakota State University, Brookings, SD USA
| | - Jef D Boeke
- Department of Molecular Biology and Genetics, The Johns Hopkins University School of Medicine, Baltimore, MD USA.,Present Address: Institute for Systems Genetics, New York University Langone Medical Center, New York, NY USA
| | - David E Symer
- Laboratory of Immunobiology, Mouse Cancer Genetics Program and Basic Research Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD 21702 USA.,Department of Cancer Biology and Genetics, The Ohio State University, Columbus, OH USA.,Human Cancer Genetics Program, and Department of Biomedical Informatics, The Ohio State University, Columbus, OH USA.,Human Cancer Genetics Program, Department of Cancer Biology and Genetics, and Department of Biomedical Informatics, The Ohio State University, Tzagournis Research Facility, Room 440, 420 West 12th Ave, Columbus, OH 43210 USA
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21
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Ge SX. Exploratory bioinformatics investigation reveals importance of "junk" DNA in early embryo development. BMC Genomics 2017; 18:200. [PMID: 28231763 PMCID: PMC5324221 DOI: 10.1186/s12864-017-3566-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 02/07/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Instead of testing predefined hypotheses, the goal of exploratory data analysis (EDA) is to find what data can tell us. Following this strategy, we re-analyzed a large body of genomic data to study the complex gene regulation in mouse pre-implantation development (PD). RESULTS Starting with a single-cell RNA-seq dataset consisting of 259 mouse embryonic cells derived from zygote to blastocyst stages, we reconstructed the temporal and spatial gene expression pattern during PD. The dynamics of gene expression can be partially explained by the enrichment of transposable elements in gene promoters and the similarity of expression profiles with those of corresponding transposons. Long Terminal Repeats (LTRs) are associated with transient, strong induction of many nearby genes at the 2-4 cell stages, probably by providing binding sites for Obox and other homeobox factors. B1 and B2 SINEs (Short Interspersed Nuclear Elements) are correlated with the upregulation of thousands of nearby genes during zygotic genome activation. Such enhancer-like effects are also found for human Alu and bovine tRNA SINEs. SINEs also seem to be predictive of gene expression in embryonic stem cells (ESCs), raising the possibility that they may also be involved in regulating pluripotency. We also identified many potential transcription factors underlying PD and discussed the evolutionary necessity of transposons in enhancing genetic diversity, especially for species with longer generation time. CONCLUSIONS Together with other recent studies, our results provide further evidence that many transposable elements may play a role in establishing the expression landscape in early embryos. It also demonstrates that exploratory bioinformatics investigation can pinpoint developmental pathways for further study, and serve as a strategy to generate novel insights from big genomic data.
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Affiliation(s)
- Steven Xijin Ge
- Department of Mathematics and Statistics, South Dakota State University, Box 2225, Brookings, SD, 57110, USA.
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22
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Bodak M, Cirera-Salinas D, Yu J, Ngondo RP, Ciaudo C. Dicer, a new regulator of pluripotency exit and LINE-1 elements in mouse embryonic stem cells. FEBS Open Bio 2017; 7:204-220. [PMID: 28174687 PMCID: PMC5292673 DOI: 10.1002/2211-5463.12174] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Revised: 11/18/2016] [Accepted: 12/05/2016] [Indexed: 12/18/2022] Open
Abstract
A gene regulation network orchestrates processes ensuring the maintenance of cellular identity and genome integrity. Small RNAs generated by the RNAse III DICER have emerged as central players in this network. Moreover, deletion of Dicer in mice leads to early embryonic lethality. To better understand the underlying mechanisms leading to this phenotype, we generated Dicer‐deficient mouse embryonic stem cells (mESCs). Their detailed characterization revealed an impaired differentiation potential, and incapacity to exit from the pluripotency state. We also observed a strong accumulation of LINE‐1 (L1s) transcripts, which was translated at protein level and led to an increased L1s retrotransposition. Our findings reveal Dicer as a new essential player that sustains mESCs self‐renewal and genome integrity by controlling L1s regulation.
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Affiliation(s)
- Maxime Bodak
- Department of Biology RNAi and Genome Integrity IMHS Swiss Federal Institute of Technology Zurich Zurich Switzerland; Life Science Zurich Graduate School Molecular Life Science Program University of Zurich Switzerland
| | - Daniel Cirera-Salinas
- Department of Biology RNAi and Genome Integrity IMHS Swiss Federal Institute of Technology Zurich Zurich Switzerland
| | - Jian Yu
- Department of Biology RNAi and Genome Integrity IMHS Swiss Federal Institute of Technology Zurich Zurich Switzerland; Life Science Zurich Graduate School Molecular and Translational Biomedicine Program University of Zurich Switzerland
| | - Richard P Ngondo
- Department of Biology RNAi and Genome Integrity IMHS Swiss Federal Institute of Technology Zurich Zurich Switzerland
| | - Constance Ciaudo
- Department of Biology RNAi and Genome Integrity IMHS Swiss Federal Institute of Technology Zurich Zurich Switzerland
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23
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Vasilyev SA, Tolmacheva EN, Lebedev IN. Epigenetic regulation and role of LINE-1 retrotransposon in embryogenesis. RUSS J GENET+ 2016. [DOI: 10.1134/s1022795416120152] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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24
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Muñoz-Lopez M, Vilar-Astasio R, Tristan-Ramos P, Lopez-Ruiz C, Garcia-Pérez JL. Study of Transposable Elements and Their Genomic Impact. Methods Mol Biol 2016; 1400:1-19. [PMID: 26895043 DOI: 10.1007/978-1-4939-3372-3_1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Transposable elements (TEs) have been considered traditionally as junk DNA, i.e., DNA sequences that despite representing a high proportion of genomes had no evident cellular functions. However, over the last decades, it has become undeniable that not only TE-derived DNA sequences have (and had) a fundamental role during genome evolution, but also TEs have important implications in the origin and evolution of many genomic disorders. This concise review provides a brief overview of the different types of TEs that can be found in genomes, as well as a list of techniques and methods used to study their impact and mobilization. Some of these techniques will be covered in detail in this Method Book.
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Affiliation(s)
- Martin Muñoz-Lopez
- Department of Human DNA Variability, Pfizer/University of Granada and Andalusian Regional Government Center for Genomics and Oncology (GENYO), Avda Ilustracion 114, PTS Granada, 18016, Granada, Spain.
| | - Raquel Vilar-Astasio
- Department of Human DNA Variability, Pfizer/University of Granada and Andalusian Regional Government Center for Genomics and Oncology (GENYO), Avda Ilustracion 114, PTS Granada, 18016, Granada, Spain
| | - Pablo Tristan-Ramos
- Department of Human DNA Variability, Pfizer/University of Granada and Andalusian Regional Government Center for Genomics and Oncology (GENYO), Avda Ilustracion 114, PTS Granada, 18016, Granada, Spain
| | - Cesar Lopez-Ruiz
- Department of Human DNA Variability, Pfizer/University of Granada and Andalusian Regional Government Center for Genomics and Oncology (GENYO), Avda Ilustracion 114, PTS Granada, 18016, Granada, Spain
| | - Jose L Garcia-Pérez
- -Genyo (Center for Genomics and Oncological Research), Pfizer/Universidad de Granada/Junta de Andalucia. PTS Granada, Spain-Institute of Genetics and Molecular Medicine (IGMM), University of Edinburgh,, Edinburgh, UK
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25
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Criscione SW, Theodosakis N, Micevic G, Cornish TC, Burns KH, Neretti N, Rodić N. Genome-wide characterization of human L1 antisense promoter-driven transcripts. BMC Genomics 2016; 17:463. [PMID: 27301971 PMCID: PMC4908685 DOI: 10.1186/s12864-016-2800-5] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 05/26/2016] [Indexed: 11/23/2022] Open
Abstract
Background Long INterspersed Element-1 (LINE-1 or L1) is the only autonomously active, transposable element in the human genome. L1 sequences comprise approximately 17 % of the human genome, but only the evolutionarily recent, human-specific subfamily is retrotransposition competent. The L1 promoter has a bidirectional orientation containing a sense promoter that drives the transcription of two proteins required for retrotransposition and an antisense promoter. The L1 antisense promoter can drive transcription of chimeric transcripts: 5’ L1 antisense sequences spliced to the exons of neighboring genes. Results The impact of L1 antisense promoter activity on cellular transcriptomes is poorly understood. To investigate this, we analyzed GenBank ESTs for messenger RNAs that initiate in the L1 antisense promoter. We identified 988 putative L1 antisense chimeric transcripts, 911 of which have not been previously reported. These appear to be alternative genic transcripts, sense-oriented with respect to gene and initiating near, but typically downstream of, the gene transcriptional start site. In multiple cell lines, L1 antisense promoters display enrichment for YY1 transcription factor and histone modifications associated with active promoters. Global run-on sequencing data support the activity of the L1 antisense promoter. We independently detected 124 L1 antisense chimeric transcripts using long read Pacific Biosciences RNA-seq data. Furthermore, we validated four chimeric transcripts by quantitative RT-PCR and Sanger sequencing and demonstrated that they are readily detectable in many normal human tissues. Conclusions We present a comprehensive characterization of human L1 antisense promoter-driven transcripts and provide substantial evidence that they are transcribed in a variety of human cell-types. Our findings reveal a new wide-reaching aspect of L1 biology by identifying antisense transcripts affecting as many as 4 % of all human genes. Electronic supplementary material The online version of this article (doi:10.1186/s12864-016-2800-5) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Steven W Criscione
- Department of Molecular Biology, Cell Biology, and Biochemistry, Center for Computational Molecular Biology, Brown University, Providence, RI, 02912, USA
| | - Nicholas Theodosakis
- Department of Pathology, Yale University, New Haven, CT, 06510, USA.,Department of Dermatology, Division of Dermatopathology, Yale University, New Haven, CT, 06510, USA
| | - Goran Micevic
- Department of Pathology, Yale University, New Haven, CT, 06510, USA.,Department of Dermatology, Division of Dermatopathology, Yale University, New Haven, CT, 06510, USA
| | - Toby C Cornish
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Kathleen H Burns
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,High Throughput (HiT) Biology Center, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Nicola Neretti
- Department of Molecular Biology, Cell Biology, and Biochemistry, Center for Computational Molecular Biology, Brown University, Providence, RI, 02912, USA.
| | - Nemanja Rodić
- Department of Pathology, Yale University, New Haven, CT, 06510, USA. .,Department of Dermatology, Division of Dermatopathology, Yale University, New Haven, CT, 06510, USA.
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26
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Harrington AW, Steiniger M. Bioinformatic analyses of sense and antisense expression from terminal inverted repeat transposons in Drosophila somatic cells. Fly (Austin) 2016; 10:1-10. [PMID: 26986720 DOI: 10.1080/19336934.2016.1165372] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
Understanding regulation of transposon movement in somatic cells is important as mobile elements can cause detrimental genomic rearrangements. Generally, transposons move via one of 2 mechanisms; retrotransposons utilize an RNA intermediate, therefore copying themselves and amplifying throughout the genome, while terminal inverted repeat transposons (TIR Tns) excise DNA sequences from the genome and integrate into a new location. Our recently published work indicates that retrotransposons in Drosophila tissue culture cells are actively transcribed in the antisense direction. Our data support a model in which convergent transcription of retrotransposons from intra element transcription start sites results in complementary RNAs that hybridize to form substrates for Dicer-2, the endogenous small interfering (esi)RNA generating enzyme. Here, we extend our previous analysis to TIR Tns. In contrast to retrotransposons, our data show that antisense TIR Tn RNAs result from transcription of intronic TIR Tns oriented antisense to their host genes. Also, disproportionately less esiRNAs are generated from TIR transcripts than from retrotransposons and transcription of very few individual TIR Tns could be confirmed. Collectively, these data support a model in which TIR Tns are regulated at the level of Transposase production while retrotransposons are regulated with esiRNA post-transcriptional mechanisms in Drosophila somatic cells.
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Affiliation(s)
| | - Mindy Steiniger
- a Department of Biology , University of Missouri , St. Louis , MO , USA
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27
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Abstract
Transposable elements have had a profound impact on the structure and function of mammalian genomes. The retrotransposon Long INterspersed Element-1 (LINE-1 or L1), by virtue of its replicative mobilization mechanism, comprises ∼17% of the human genome. Although the vast majority of human LINE-1 sequences are inactive molecular fossils, an estimated 80-100 copies per individual retain the ability to mobilize by a process termed retrotransposition. Indeed, LINE-1 is the only active, autonomous retrotransposon in humans and its retrotransposition continues to generate both intra-individual and inter-individual genetic diversity. Here, we briefly review the types of transposable elements that reside in mammalian genomes. We will focus our discussion on LINE-1 retrotransposons and the non-autonomous Short INterspersed Elements (SINEs) that rely on the proteins encoded by LINE-1 for their mobilization. We review cases where LINE-1-mediated retrotransposition events have resulted in genetic disease and discuss how the characterization of these mutagenic insertions led to the identification of retrotransposition-competent LINE-1s in the human and mouse genomes. We then discuss how the integration of molecular genetic, biochemical, and modern genomic technologies have yielded insight into the mechanism of LINE-1 retrotransposition, the impact of LINE-1-mediated retrotransposition events on mammalian genomes, and the host cellular mechanisms that protect the genome from unabated LINE-1-mediated retrotransposition events. Throughout this review, we highlight unanswered questions in LINE-1 biology that provide exciting opportunities for future research. Clearly, much has been learned about LINE-1 and SINE biology since the publication of Mobile DNA II thirteen years ago. Future studies should continue to yield exciting discoveries about how these retrotransposons contribute to genetic diversity in mammalian genomes.
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28
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Flórez-Vargas O, Brass A, Karystianis G, Bramhall M, Stevens R, Cruickshank S, Nenadic G. Bias in the reporting of sex and age in biomedical research on mouse models. eLife 2016; 5. [PMID: 26939790 PMCID: PMC4821800 DOI: 10.7554/elife.13615] [Citation(s) in RCA: 73] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 02/23/2016] [Indexed: 12/21/2022] Open
Abstract
In animal-based biomedical research, both the sex and the age of the animals studied affect disease phenotypes by modifying their susceptibility, presentation and response to treatment. The accurate reporting of experimental methods and materials, including the sex and age of animals, is essential so that other researchers can build on the results of such studies. Here we use text mining to study 15,311 research papers in which mice were the focus of the study. We find that the percentage of papers reporting the sex and age of mice has increased over the past two decades: however, only about 50% of the papers published in 2014 reported these two variables. We also compared the quality of reporting in six preclinical research areas and found evidence for different levels of sex-bias in these areas: the strongest male-bias was observed in cardiovascular disease models and the strongest female-bias was found in infectious disease models. These results demonstrate the ability of text mining to contribute to the ongoing debate about the reproducibility of research, and confirm the need to continue efforts to improve the reporting of experimental methods and materials. DOI:http://dx.doi.org/10.7554/eLife.13615.001
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Affiliation(s)
- Oscar Flórez-Vargas
- Bio-health Informatics Group, School of Computer Science, The University of Manchester, Manchester, United Kingdom
| | - Andy Brass
- Bio-health Informatics Group, School of Computer Science, The University of Manchester, Manchester, United Kingdom
| | - George Karystianis
- Text Mining Group, School of Computer Science, The University of Manchester, Manchester, United Kingdom
| | - Michael Bramhall
- Bio-health Informatics Group, School of Computer Science, The University of Manchester, Manchester, United Kingdom
| | - Robert Stevens
- Bio-health Informatics Group, School of Computer Science, The University of Manchester, Manchester, United Kingdom
| | - Sheena Cruickshank
- Manchester Immunology Group, Faculty of Life Science, The University of Manchester, Manchester, United Kingdom
| | - Goran Nenadic
- Text Mining Group, School of Computer Science, The University of Manchester, Manchester, United Kingdom.,Manchester Institute of Biotechnology, University of Manchester, Manchester, United Kingdom
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29
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Lin S, Zhang L, Luo W, Zhang X. Characteristics of Antisense Transcript Promoters and the Regulation of Their Activity. Int J Mol Sci 2015; 17:E9. [PMID: 26703594 PMCID: PMC4730256 DOI: 10.3390/ijms17010009] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2015] [Revised: 11/23/2015] [Accepted: 12/16/2015] [Indexed: 02/07/2023] Open
Abstract
Recently, an increasing number of studies on natural antisense transcripts have been reported, especially regarding their classification, temporal and spatial expression patterns, regulatory functions and mechanisms. It is well established that natural antisense transcripts are produced from the strand opposite to the strand encoding a protein. Despite the pivotal roles of natural antisense transcripts in regulating the expression of target genes, the transcriptional mechanisms initiated by antisense promoters (ASPs) remain unknown. To date, nearly all of the studies conducted on this topic have focused on the ASP of a single gene of interest, whereas no study has systematically analyzed the locations of ASPs in the genome, ASP activity, or factors influencing this activity. This review focuses on elaborating on and summarizing the characteristics of ASPs to extend our knowledge about the mechanisms of antisense transcript initiation.
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Affiliation(s)
- Shudai Lin
- Department of Animal Genetics, Breeding and Reproduction, College of Animal Science, South China Agricultural University, Guangzhou 510642, China.
- Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou 510642, China.
- Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou 510642, China.
| | - Li Zhang
- Department of Animal Genetics, Breeding and Reproduction, College of Animal Science, South China Agricultural University, Guangzhou 510642, China.
- Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou 510642, China.
- Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou 510642, China.
- Agricultural College, Guangdong Ocean University, Zhanjiang 524088, China.
| | - Wen Luo
- Department of Animal Genetics, Breeding and Reproduction, College of Animal Science, South China Agricultural University, Guangzhou 510642, China.
- Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou 510642, China.
- Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou 510642, China.
| | - Xiquan Zhang
- Department of Animal Genetics, Breeding and Reproduction, College of Animal Science, South China Agricultural University, Guangzhou 510642, China.
- Guangdong Provincial Key Lab of Agro-Animal Genomics and Molecular Breeding, Guangzhou 510642, China.
- Key Lab of Chicken Genetics, Breeding and Reproduction, Ministry of Agriculture, Guangzhou 510642, China.
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Antisense Transcription of Retrotransposons in Drosophila: An Origin of Endogenous Small Interfering RNA Precursors. Genetics 2015; 202:107-21. [PMID: 26534950 DOI: 10.1534/genetics.115.177196] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Accepted: 10/23/2015] [Indexed: 11/18/2022] Open
Abstract
Movement of transposons causes insertions, deletions, and chromosomal rearrangements potentially leading to premature lethality in Drosophila melanogaster. To repress these elements and combat genomic instability, eukaryotes have evolved several small RNA-mediated defense mechanisms. Specifically, in Drosophila somatic cells, endogenous small interfering (esi)RNAs suppress retrotransposon mobility. EsiRNAs are produced by Dicer-2 processing of double-stranded RNA precursors, yet the origins of these precursors are unknown. We show that most transposon families are transcribed in both the sense (S) and antisense (AS) direction in Dmel-2 cells. LTR retrotransposons Dm297, mdg1, and blood, and non-LTR retrotransposons juan and jockey transcripts, are generated from intraelement transcription start sites with canonical RNA polymerase II promoters. We also determined that retrotransposon antisense transcripts are less polyadenylated than sense. RNA-seq and small RNA-seq revealed that Dicer-2 RNA interference (RNAi) depletion causes a decrease in the number of esiRNAs mapping to retrotransposons and an increase in expression of both S and AS retrotransposon transcripts. These data support a model in which double-stranded RNA precursors are derived from convergent transcription and processed by Dicer-2 into esiRNAs that silence both sense and antisense retrotransposon transcripts. Reduction of sense retrotransposon transcripts potentially lowers element-specific protein levels to prevent transposition. This mechanism preserves genomic integrity and is especially important for Drosophila fitness because mobile genetic elements are highly active.
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31
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The Fine LINE: Methylation Drawing the Cancer Landscape. BIOMED RESEARCH INTERNATIONAL 2015; 2015:131547. [PMID: 26448926 PMCID: PMC4584040 DOI: 10.1155/2015/131547] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 11/17/2014] [Accepted: 11/25/2014] [Indexed: 01/08/2023]
Abstract
LINE-1 (L1) is the most abundant mammalian transposable element that comprises nearly 20% of the genome, and nearly half of the mammalian genome has stemmed from L1-mediated mobilization. Expression and retrotransposition of L1 are suppressed by complex mechanisms, where the key role belongs to DNA methylation. Alterations in L1 methylation may lead to aberrant expression of L1 and have been described in numerous diseases. Accumulating evidence clearly indicates that loss of global DNA methylation observed in cancer development and progression is tightly associated with hypomethylation of L1 elements. Significant progress achieved in the last several years suggests that such parameters as L1 methylation status can be potentially utilized as clinical biomarkers for determination of the disease stage and in predicting the disease-free survival in cancer patients. In this paper, we summarize the current knowledge on L1 methylation, with specific emphasis given to success and challenges on the way of introduction of L1 into clinical practice.
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32
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Miousse IR, Chalbot MCG, Lumen A, Ferguson A, Kavouras IG, Koturbash I. Response of transposable elements to environmental stressors. MUTATION RESEARCH. REVIEWS IN MUTATION RESEARCH 2015; 765:19-39. [PMID: 26281766 PMCID: PMC4544780 DOI: 10.1016/j.mrrev.2015.05.003] [Citation(s) in RCA: 93] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Revised: 05/27/2015] [Accepted: 05/28/2015] [Indexed: 12/21/2022]
Abstract
Transposable elements (TEs) comprise a group of repetitive sequences that bring positive, negative, as well as neutral effects to the host organism. Earlier considered as "junk DNA," TEs are now well-accepted driving forces of evolution and critical regulators of the expression of genetic information. Their activity is regulated by epigenetic mechanisms, including methylation of DNA and histone modifications. The loss of epigenetic control over TEs, exhibited as loss of DNA methylation and decondensation of the chromatin structure, may result in TEs reactivation, initiation of their insertional mutagenesis (retrotransposition) and has been reported in numerous human diseases, including cancer. Accumulating evidence suggests that these alterations are not the simple consequences of the disease, but often may drive the pathogenesis, as they can be detected early during disease development. Knowledge derived from the in vitro, in vivo, and epidemiological studies, clearly demonstrates that exposure to ubiquitous environmental stressors, many of which are carcinogens or suspected carcinogens, are capable of causing alterations in methylation and expression of TEs and initiate retrotransposition events. Evidence summarized in this review suggests that TEs are the sensitive endpoints for detection of effects caused by such environmental stressors, as ionizing radiation (terrestrial, space, and UV-radiation), air pollution (including particulate matter [PM]-derived and gaseous), persistent organic pollutants, and metals. Furthermore, the significance of these effects is characterized by their early appearance, persistence and presence in both, target organs and peripheral blood. Altogether, these findings suggest that TEs may potentially be introduced into safety and risk assessment and serve as biomarkers of exposure to environmental stressors. Furthermore, TEs also show significant potential to become invaluable surrogate biomarkers in clinic and possible targets for therapeutic modalities for disease treatment and prevention.
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Affiliation(s)
- Isabelle R Miousse
- Department of Environmental and Occupational Health, Fay W. Boozman College of Public Health, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
| | - Marie-Cecile G Chalbot
- Department of Environmental and Occupational Health, Fay W. Boozman College of Public Health, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
| | - Annie Lumen
- Division of Biochemical Toxicology, National Center for Toxicological Research, US Food and Drug Administration, Jefferson, AR 72079, USA.
| | - Alesia Ferguson
- Department of Environmental and Occupational Health, Fay W. Boozman College of Public Health, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
| | - Ilias G Kavouras
- Department of Environmental and Occupational Health, Fay W. Boozman College of Public Health, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
| | - Igor Koturbash
- Department of Environmental and Occupational Health, Fay W. Boozman College of Public Health, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
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33
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Jachowicz JW, Torres-Padilla ME. LINEs in mice: features, families, and potential roles in early development. Chromosoma 2015; 125:29-39. [PMID: 25975894 DOI: 10.1007/s00412-015-0520-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 04/27/2015] [Accepted: 05/05/2015] [Indexed: 01/08/2023]
Abstract
Approximately half of the mammalian genome is composed of repetitive elements, including LINE-1 (L1) elements. Because of their potential ability to transpose and integrate into other regions of the genome, their activation represents a threat to genome stability. Molecular pathways have emerged to tightly regulate and repress their transcriptional activity, including DNA methylation, histone modifications, and RNA pathways. It has become evident that Line-L1 elements are evolutionary diverse and dedicated repression pathways have been recently uncovered that discriminate between evolutionary old and young elements, with RNA-directed silencing mechanisms playing a prominent role. During periods of epigenetic reprogramming in development, specific classes of repetitive elements are upregulated, presumably due to the loss of most heterochromatic marks in this process. While we have learnt a lot on the molecular mechanisms that regulate Line-L1 expression over the last years, it is still unclear whether reactivation of Line-L1 after fertilization serves a functional purpose or it is a simple side effect of reprogramming.
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Affiliation(s)
- Joanna W Jachowicz
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM U964, Université de Strasbourg, 67404, Illkirch, France
| | - Maria-Elena Torres-Padilla
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM U964, Université de Strasbourg, 67404, Illkirch, France.
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Retrotransposons in pluripotent cells: Impact and new roles in cellular plasticity. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1849:417-26. [PMID: 25042909 DOI: 10.1016/j.bbagrm.2014.07.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Revised: 07/08/2014] [Accepted: 07/10/2014] [Indexed: 12/27/2022]
Abstract
Transposable Elements are pieces of DNA able to mobilize from one location to another within genomes. Although they constitute more than 50% of the human genome, they have been classified as selfish DNA, with the only mission to spread within genomes and generate more copies of themselves that will ensure their presence over generations. Despite their remarkable prevalence, only a minor group of transposable elements remain active in the human genome and can sporadically be associated with the generation of a genetic disorder due to their ongoing mobility. Most of the transposable elements identified in the human genome corresponded to fixed insertions that no longer move in genomes. As selfish DNA, transposable element insertions accumulate in cell types where genetic information can be passed to the next generation. Indeed, work from different laboratories has demonstrated that the main heritable load of TE accumulation in humans occurs during early embryogenesis. Thus, active transposable elements have a clear impact on our pluripotent genome. However, recent findings suggest that the main proportion of fixed non-mobile transposable elements might also have emerging roles in cellular plasticity. In this concise review, we provide an overview of the impact of currently active transposable elements in our pluripotent genome and further discuss new roles of transposable elements (active or not) in regulating pluripotency. This article is part of a Special Issue entitled: Stress as a fundamental theme in cell plasticity.
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35
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Mourier T, Nielsen LP, Hansen AJ, Willerslev E. Transposable elements in cancer as a by-product of stress-induced evolvability. Front Genet 2014; 5:156. [PMID: 24910642 PMCID: PMC4038923 DOI: 10.3389/fgene.2014.00156] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Accepted: 05/11/2014] [Indexed: 01/18/2023] Open
Abstract
Transposable elements (TEs) are ubiquitous in eukaryotic genomes. Barbara McClintock's famous notion of TEs acting as controlling elements modifying the genetic response of an organism upon exposure to stressful environments has since been solidly supported in a series of model organisms. This requires the TE activity response to possess an element of specificity and be targeted toward certain parts of the genome. We propose that a similar TE response is present in human cells, and that this stress response may drive the onset of human cancers. As such, TE-driven cancers may be viewed as an evolutionary by-product of organisms' abilities to genetically adapt to environmental stress.
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Affiliation(s)
- Tobias Mourier
- Natural History Museum of Denmark, Centre for GeoGenetics, University of Copenhagen Copenhagen, Denmark
| | - Lars P Nielsen
- Department of Virology and the Danish National Biobank, Statens Serum Institut Copenhagen, Denmark
| | - Anders J Hansen
- Natural History Museum of Denmark, Centre for GeoGenetics, University of Copenhagen Copenhagen, Denmark
| | - Eske Willerslev
- Natural History Museum of Denmark, Centre for GeoGenetics, University of Copenhagen Copenhagen, Denmark
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