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Mizgier NA, Jones CE, Furano AV. Co-expression of distinct L1 retrotransposon coiled coils can lead to their entanglement. Mob DNA 2023; 14:16. [PMID: 37864180 PMCID: PMC10588031 DOI: 10.1186/s13100-023-00303-8] [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: 08/31/2023] [Accepted: 09/21/2023] [Indexed: 10/22/2023] Open
Abstract
L1 (LINE1) non-LTR retrotransposons are ubiquitous genomic parasites and the dominant transposable element in humans having generated about 40% of their genomic DNA during their ~ 100 million years (Myr) of activity in primates. L1 replicates in germ line cells and early embryos, causing genetic diversity and defects, but can be active in some somatic stem cells, tumors and during aging. L1 encodes two proteins essential for retrotransposition: ORF2p, a reverse transcriptase that contains an endonuclease domain, and ORF1p, a coiled coil mediated homo trimer, which functions as a nucleic acid chaperone. Both proteins contain highly conserved domains and preferentially bind their encoding transcript to form an L1 ribonucleoprotein (RNP), which mediates retrotransposition. However, the coiled coil has periodically undergone episodes of substantial amino acid replacement to the extent that a given L1 family can concurrently express multiple ORF1s that differ in the sequence of their coiled coils. Here we show that such distinct ORF1p sequences can become entangled forming heterotrimers when co-expressed from separate vectors and speculate on how coiled coil entanglement could affect coiled coil evolution.
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Affiliation(s)
- Nikola A. Mizgier
- Laboratory of Cellular and Molecular Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892 USA
| | - Charlie E. Jones
- Laboratory of Cellular and Molecular Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892 USA
| | - Anthony V. Furano
- Laboratory of Cellular and Molecular Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892 USA
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2
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Luca CD, Gupta A, Bortvin A. Ribonucleoprotein condensation driven by retrotransposon LINE-1 sustains RNA integrity and translation in mouse spermatocytes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.09.523313. [PMID: 36712121 PMCID: PMC9882024 DOI: 10.1101/2023.01.09.523313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Transposable elements (TE) are mobile DNA sequences whose excessive proliferation endangers the host. Although animals have evolved robust TE-targeting defenses, including Piwi-interacting (pi)RNAs, retrotransposon LINE-1 (L1) still thrives in humans and mice. To gain insights into L1 endurance, we characterized L1 Bodies (LBs) and ORF1p complexes in germ cells of piRNA-deficient Maelstrom null mice. We report that ORF1p interacts with TE RNAs, genic mRNAs, and stress granule proteins, consistent with earlier studies. We also show that ORF1p associates with the CCR4-NOT deadenylation complex and PRKRA, a Protein Kinase R factor. Despite ORF1p interactions with these negative regulators of RNA expression, the stability and translation of LB-localized mRNAs remain unchanged. To scrutinize these findings, we studied the effects of PRKRA on L1 in cultured cells and showed that it elevates ORF1p levels and L1 retrotransposition. These results suggest that ORF1p-driven condensates promote L1 propagation, without affecting the metabolism of endogenous RNAs.
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3
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Zhou S, Sakashita A, Yuan S, Namekawa SH. Retrotransposons in the Mammalian Male Germline. Sex Dev 2022:1-19. [PMID: 35231923 DOI: 10.1159/000520683] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 10/25/2021] [Indexed: 11/19/2022] Open
Abstract
Retrotransposons are a subset of DNA sequences that constitute a large part of the mammalian genome. They can translocate autonomously or non-autonomously, potentially jeopardizing the heritable germline genome. Retrotransposons coevolved with the host genome, and the germline is the prominent battlefield between retrotransposons and the host genome to maximize their mutual fitness. Host genomes have developed various mechanisms to suppress and control retrotransposons, including DNA methylation, histone modifications, and Piwi-interacting RNA (piRNA), for their own benefit. Thus, rapidly evolved retrotransposons often acquire positive functions, including gene regulation within the germline, conferring reproductive fitness in a species over the course of evolution. The male germline serves as an ideal model to examine the regulation and evolution of retrotransposons, resulting in genomic co-evolution with the host genome. In this review, we summarize and discuss the regulatory mechanisms of retrotransposons, stage-by-stage, during male germ cell development, with a particular focus on mice as an extensively studied mammalian model, highlighting suppression mechanisms and emerging functions of retrotransposons in the male germline.
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Affiliation(s)
- Shumin Zhou
- Institute of Reproductive Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Akihiko Sakashita
- Department of Molecular Biology, Keio University School of Medicine, Tokyo, Japan
| | - Shuiqiao Yuan
- Institute of Reproductive Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.,Shenzhen Huazhong University of Science and Technology Research Institute, Shenzhen, China
| | - Satoshi H Namekawa
- Department of Microbiology and Molecular Genetics, University of California, Davis, California, USA
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4
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Freeman BT, Sokolowski M, Roy-Engel AM, Smither ME, Belancio VP. Identification of charged amino acids required for nuclear localization of human L1 ORF1 protein. Mob DNA 2019; 10:20. [PMID: 31080522 PMCID: PMC6501352 DOI: 10.1186/s13100-019-0159-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2018] [Accepted: 04/10/2019] [Indexed: 01/10/2023] Open
Abstract
Background Long Interspersed Element 1 (LINE-1) is a retrotransposon that is present in 500,000 copies in the human genome. Along with Alu and SVA elements, these three retrotransposons account for more than a third of the human genome sequence. These mobile elements are able to copy themselves within the genome via an RNA intermediate, a process that can promote genome instability. LINE-1 encodes two proteins, ORF1p and ORF2p. Association of ORF1p, ORF2p and a full-length L1 mRNA in a ribonucleoprotein (RNP) particle, L1 RNP, is required for L1 retrotransposition. Previous studies have suggested that fusion of a tag to L1 proteins can interfere with L1 retrotransposition. Results Using antibodies detecting untagged human ORF1p, western blot analysis and manipulation of ORF1 sequence and length, we have identified a set of charged amino acids in the C-terminal region of ORF1p that are important in determining its subcellular localization. Mutation of 7 non-identical lysine residues is sufficient to make the resulting ORF1p to be predominantly cytoplasmic, demonstrating intrinsic redundancy of this requirement. These residues are also necessary for ORF1p to retain its association with KPNA2 nuclear pore protein. We demonstrate that this interaction is significantly reduced by RNase treatment. Using co-IP, we have also determined that human ORF1p associates with all members of the KPNA subfamily. Conclusions The prediction of NLS sequences suggested that specific sequences within ORF1p could be responsible for its subcellular localization by interacting with nuclear binding proteins. We have found that multiple charged amino acids in the C-terminus of ORF1p are involved in ORF1 subcellular localization and interaction with KPNA2 nuclear pore protein. Our data demonstrate that different amino acids can be mutated to have the same phenotypic effect on ORF1p subcellular localization, demonstrating that the net number of charged residues or protein structure, rather than their specific location, is important for the ORF1p nuclear localization. We also identified that human ORF1p interacts with all members of the KPNA family of proteins and that multiple KPNA family genes are expressed in human cell lines. Electronic supplementary material The online version of this article (10.1186/s13100-019-0159-2) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- B T Freeman
- 1Department of Structural and Cellular Biology, Tulane University School of Medicine, Tulane Cancer Center, Tulane Center for Aging, New Orleans, LA 70112 USA
| | - M Sokolowski
- 1Department of Structural and Cellular Biology, Tulane University School of Medicine, Tulane Cancer Center, Tulane Center for Aging, New Orleans, LA 70112 USA
| | - A M Roy-Engel
- 2Department of Epidemiology, School of Public Health and Tropical Medicine, Tulane Cancer Center, Tulane University, New Orleans, Louisiana 70112 USA
| | - M E Smither
- 1Department of Structural and Cellular Biology, Tulane University School of Medicine, Tulane Cancer Center, Tulane Center for Aging, New Orleans, LA 70112 USA
| | - V P Belancio
- 1Department of Structural and Cellular Biology, Tulane University School of Medicine, Tulane Cancer Center, Tulane Center for Aging, New Orleans, LA 70112 USA
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5
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Pereira GC, Sanchez L, Schaughency PM, Rubio-Roldán A, Choi JA, Planet E, Batra R, Turelli P, Trono D, Ostrow LW, Ravits J, Kazazian HH, Wheelan SJ, Heras SR, Mayer J, García-Pérez JL, Goodier JL. Properties of LINE-1 proteins and repeat element expression in the context of amyotrophic lateral sclerosis. Mob DNA 2018; 9:35. [PMID: 30564290 PMCID: PMC6295051 DOI: 10.1186/s13100-018-0138-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 11/15/2018] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving loss of motor neurons and having no known cure and uncertain etiology. Several studies have drawn connections between altered retrotransposon expression and ALS. Certain features of the LINE-1 (L1) retrotransposon-encoded ORF1 protein (ORF1p) are analogous to those of neurodegeneration-associated RNA-binding proteins, including formation of cytoplasmic aggregates. In this study we explore these features and consider possible links between L1 expression and ALS. RESULTS We first considered factors that modulate aggregation and subcellular distribution of LINE-1 ORF1p, including nuclear localization. Changes to some ORF1p amino acid residues alter both retrotransposition efficiency and protein aggregation dynamics, and we found that one such polymorphism is present in endogenous L1s abundant in the human genome. We failed, however, to identify CRM1-mediated nuclear export signals in ORF1p nor strict involvement of cell cycle in endogenous ORF1p nuclear localization in human 2102Ep germline teratocarcinoma cells. Some proteins linked with ALS bind and colocalize with L1 ORF1p ribonucleoprotein particles in cytoplasmic RNA granules. Increased expression of several ALS-associated proteins, including TAR DNA Binding Protein (TDP-43), strongly limits cell culture retrotransposition, while some disease-related mutations modify these effects. Using quantitative reverse transcription PCR (RT-qPCR) of ALS tissues and reanalysis of publicly available RNA-Seq datasets, we asked if changes in expression of retrotransposons are associated with ALS. We found minimal altered expression in sporadic ALS tissues but confirmed a previous report of differential expression of many repeat subfamilies in C9orf72 gene-mutated ALS patients. CONCLUSIONS Here we extended understanding of the subcellular localization dynamics of the aggregation-prone LINE-1 ORF1p RNA-binding protein. However, we failed to find compelling evidence for misregulation of LINE-1 retrotransposons in sporadic ALS nor a clear effect of ALS-associated TDP-43 protein on L1 expression. In sum, our study reveals that the interplay of active retrotransposons and the molecular features of ALS are more complex than anticipated. Thus, the potential consequences of altered retrotransposon activity for ALS and other neurodegenerative disorders are worthy of continued investigation.
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Affiliation(s)
- Gavin C. Pereira
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Laura Sanchez
- GENYO. Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain
| | - Paul M. Schaughency
- Oncology Center-Cancer Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Alejandro Rubio-Roldán
- GENYO. Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain
| | - Jungbin A. Choi
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Evarist Planet
- School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Ranjan Batra
- Department of Neurosciences, School of Medicine, University of California at San Diego, San Diego, California USA
| | - Priscilla Turelli
- School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Didier Trono
- School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Lyle W. Ostrow
- Neuromuscular Division, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - John Ravits
- Department of Neurosciences, School of Medicine, University of California at San Diego, San Diego, California USA
| | - Haig H. Kazazian
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Sarah J. Wheelan
- Oncology Center-Cancer Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Sara R. Heras
- GENYO. Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain
- Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, University of Granada, Granada, Spain
| | - Jens Mayer
- Department of Human Genetics, Medical Faculty, University of Saarland, Homburg/Saar, Germany
| | - Jose Luis García-Pérez
- GENYO. Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine (IGMM), University of Edinburgh, Western General Hospital, Edinburgh, UK
| | - John L. Goodier
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
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6
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Richardson SR, Faulkner GJ. Heritable L1 Retrotransposition Events During Development: Understanding Their Origins: Examination of heritable, endogenous L1 retrotransposition in mice opens up exciting new questions and research directions. Bioessays 2018; 40:e1700189. [PMID: 29709066 PMCID: PMC6681178 DOI: 10.1002/bies.201700189] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Revised: 03/04/2018] [Indexed: 01/08/2023]
Abstract
The retrotransposon Long Interspersed Element 1 (LINE-1 or L1) has played a major role in shaping the sequence composition of the mammalian genome. In our recent publication, "Heritable L1 retrotransposition in the mouse primordial germline and early embryo," we systematically assessed the rate and developmental timing of de novo, heritable endogenous L1 insertions in mice. Such heritable retrotransposition events allow L1 to exert an ongoing influence upon genome evolution. Here, we place our findings in the context of earlier studies, and highlight how our results corroborate, and depart from, previous research based on human patient samples and transgenic mouse models harboring engineered L1 reporter genes. In parallel, we outline outstanding questions regarding the stage-specificity, regulation, and functional impact of embryonic and germline L1 retrotransposition, and propose avenues for future research in this field.
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Affiliation(s)
- Sandra R. Richardson
- Mater Research Institute–University of QueenslandWoolloongabbaQueensland 4102Australia
| | - Geoffrey J. Faulkner
- Mater Research Institute–University of QueenslandWoolloongabbaQueensland 4102Australia
- Queensland Brain InstituteUniversity of QueenslandBrisbaneQueensland 4072Australia
- School of Biomedical SciencesUniversity of QueenslandBrisbaneQueensland 4072Australia
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7
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Barbieri D, Elvira-Matelot E, Pelinski Y, Genève L, de Laval B, Yogarajah G, Pecquet C, Constantinescu SN, Porteu F. Thrombopoietin protects hematopoietic stem cells from retrotransposon-mediated damage by promoting an antiviral response. J Exp Med 2018; 215:1463-1480. [PMID: 29615469 PMCID: PMC5940259 DOI: 10.1084/jem.20170997] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 12/28/2017] [Accepted: 03/02/2018] [Indexed: 12/13/2022] Open
Abstract
Propagation of retrotransposons induces genomic instability. Their roles in HSCs remain poorly studied. Barbieri et al. show that retrotransposon expression and mobilization are involved in long-lasting HSC impairment upon irradiation. These effects are counteracted by the self-renewal cytokine THPO through induction of interferon-like response. Maintenance of genomic integrity is crucial for the preservation of hematopoietic stem cell (HSC) potential. Retrotransposons, spreading in the genome through an RNA intermediate, have been associated with loss of self-renewal, aging, and DNA damage. However, their role in HSCs has not been addressed. Here, we show that mouse HSCs express various retroelements (REs), including long interspersed element-1 (L1) recent family members that further increase upon irradiation. Using mice expressing an engineered human L1 retrotransposition reporter cassette and reverse transcription inhibitors, we demonstrate that L1 retransposition occurs in vivo and is involved in irradiation-induced persistent γH2AX foci and HSC loss of function. Thus, RE represents an important intrinsic HSC threat. Furthermore, we show that RE activity is restrained by thrombopoietin, a critical HSC maintenance factor, through its ability to promote a potent interferon-like, antiviral gene response in HSCs. This uncovers a novel mechanism allowing HSCs to minimize irradiation-induced injury and reinforces the links between DNA damage, REs, and antiviral immunity.
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Affiliation(s)
- Daniela Barbieri
- INSERM UMR1170, Villejuif, France.,Université Paris-Saclay, Paris, France.,Gustave Roussy Cancer Campus, Paris, France
| | - Emilie Elvira-Matelot
- INSERM UMR1170, Villejuif, France.,Université Paris-Saclay, Paris, France.,Gustave Roussy Cancer Campus, Paris, France
| | - Yanis Pelinski
- INSERM UMR1170, Villejuif, France.,Université Paris-Saclay, Paris, France.,Gustave Roussy Cancer Campus, Paris, France
| | - Laetitia Genève
- INSERM UMR1170, Villejuif, France.,Université Paris-Saclay, Paris, France.,Gustave Roussy Cancer Campus, Paris, France
| | - Bérengère de Laval
- Centre d'Immunologie Marseille-Luminy, Université Aix-Marseille, Institut National de la Santé et de la Recherche Médicale, U1104, Centre National de la Recherche Scientifique, UMR 7280
| | - Gayathri Yogarajah
- INSERM UMR1170, Villejuif, France.,Université Paris-Saclay, Paris, France.,Gustave Roussy Cancer Campus, Paris, France
| | - Christian Pecquet
- Ludwig Institute for Cancer Research, Brussels, Belgium.,SIGN Pole, de Duve Institute, Université Catholique de Louvain, Brussels, Belgium
| | - Stefan N Constantinescu
- Ludwig Institute for Cancer Research, Brussels, Belgium.,SIGN Pole, de Duve Institute, Université Catholique de Louvain, Brussels, Belgium
| | - Françoise Porteu
- INSERM UMR1170, Villejuif, France .,Université Paris-Saclay, Paris, France.,Gustave Roussy Cancer Campus, Paris, France
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8
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Khazina E, Weichenrieder O. Human LINE-1 retrotransposition requires a metastable coiled coil and a positively charged N-terminus in L1ORF1p. eLife 2018; 7:34960. [PMID: 29565245 PMCID: PMC5940361 DOI: 10.7554/elife.34960] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Accepted: 03/21/2018] [Indexed: 12/22/2022] Open
Abstract
LINE-1 (L1) is an autonomous retrotransposon, which acted throughout mammalian evolution and keeps contributing to human genotypic diversity, genetic disease and cancer. L1 encodes two essential proteins: L1ORF1p, a unique RNA-binding protein, and L1ORF2p, an endonuclease and reverse transcriptase. L1ORF1p contains an essential, but rapidly evolving N-terminal portion, homo-trimerizes via a coiled coil and packages L1RNA into large assemblies. Here, we determined crystal structures of the entire coiled coil domain of human L1ORF1p. We show that retrotransposition requires a non-ideal and metastable coiled coil structure, and a strongly basic L1ORF1p amino terminus. Human L1ORF1p therefore emerges as a highly calibrated molecular machine, sensitive to mutation but functional in different hosts. Our analysis rationalizes the locally rapid L1ORF1p sequence evolution and reveals striking mechanistic parallels to coiled coil-containing membrane fusion proteins. It also suggests how trimeric L1ORF1p could form larger meshworks and indicates critical novel steps in L1 retrotransposition. Almost half of the human genome consists of DNA strings that have been copied and pasted from one part of the genome to another many thousands of times. These strings of DNA are called mobile genetic elements. Mobile elements can disrupt important genes, causing disease and cancer, but they can also drive evolution. Presently, only one type of mobile element, called LINE-1, is active in the human genome and able to multiply without help from other mobile elements. LINE-1 DNA is ‘transcribed’ to form molecules of LINE-1 RNA, which can then be ‘translated’ into two distinct proteins. These bind to LINE-1 RNA, which then gets back-transcribed into DNA and inserted as a new LINE-1 element in a new region of the genome. One of the two proteins, called L1ORF1p, forms complexes where three copies of the protein come together. These ‘trimers’ cover and protect LINE-1 RNA and are required for LINE-1 mobility. Different versions of L1ORF1p are found in different animals. Part of the protein is the same across all mammals, and this ‘conserved’ part controls the ability of L1ORF1p to bind to RNA. The non-conserved part of L1ORF1p differs even between humans and their closest animal relatives and little was known about its structure or role. However, this rapidly evolving part of L1ORF1p is essential for LINE-1 mobility. Using X-ray crystallography, Khazina and Weichenrieder obtained a molecular snapshot of the part of L1ORF1p that interacts with other copies of the protein to form trimers. Combined with earlier snapshots of L1ORF1p’s conserved part, this generated a complete structural model of the L1ORF1p trimer. Additional biophysical characterizations suggest that L1ORF1p trimers form a semi-stable structure that can partially open up, indicating how trimers could form larger assemblies of L1ORF1p on LINE-1 RNA. Indeed, the need to maintain a semi-stable structure could explain why L1ORF1p is evolving so rapidly. A second important finding is that the beginning of L1ORF1p needs to be positively charged – a requirement that warrants further exploration. The structural and mechanistic insight into L1ORF1p points to critical new steps in LINE-1 mobilization. It will help to design inhibitor molecules with the goal to halt the mobilization process at various points and to dissect such steps in great detail. Understanding how to control LINE-1 mobility could help to improve stem cell therapies and reproduction assistance techniques, due to the fact that LINE-1 mobility is a potential source of mutation in stem cells, egg and sperm cells, and newly formed embryos.
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Affiliation(s)
- Elena Khazina
- Department of Biochemistry, Max Planck Institute for Developmental Biology, Tübingen, Germany
| | - Oliver Weichenrieder
- Department of Biochemistry, Max Planck Institute for Developmental Biology, Tübingen, Germany
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9
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Spliced integrated retrotransposed element (SpIRE) formation in the human genome. PLoS Biol 2018; 16:e2003067. [PMID: 29505568 PMCID: PMC5860796 DOI: 10.1371/journal.pbio.2003067] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Revised: 03/20/2018] [Accepted: 02/14/2018] [Indexed: 12/20/2022] Open
Abstract
Human Long interspersed element-1 (L1) retrotransposons contain an internal RNA polymerase II promoter within their 5′ untranslated region (UTR) and encode two proteins, (ORF1p and ORF2p) required for their mobilization (i.e., retrotransposition). The evolutionary success of L1 relies on the continuous retrotransposition of full-length L1 mRNAs. Previous studies identified functional splice donor (SD), splice acceptor (SA), and polyadenylation sequences in L1 mRNA and provided evidence that a small number of spliced L1 mRNAs retrotransposed in the human genome. Here, we demonstrate that the retrotransposition of intra-5′UTR or 5′UTR/ORF1 spliced L1 mRNAs leads to the generation of spliced integrated retrotransposed elements (SpIREs). We identified a new intra-5′UTR SpIRE that is ten times more abundant than previously identified SpIREs. Functional analyses demonstrated that both intra-5′UTR and 5′UTR/ORF1 SpIREs lack Cis-acting transcription factor binding sites and exhibit reduced promoter activity. The 5′UTR/ORF1 SpIREs also produce nonfunctional ORF1p variants. Finally, we demonstrate that sequence changes within the L1 5′UTR over evolutionary time, which permitted L1 to evade the repressive effects of a host protein, can lead to the generation of new L1 splicing events, which, upon retrotransposition, generates a new SpIRE subfamily. We conclude that splicing inhibits L1 retrotransposition, SpIREs generally represent evolutionary “dead-ends” in the L1 retrotransposition process, mutations within the L1 5′UTR alter L1 splicing dynamics, and that retrotransposition of the resultant spliced transcripts can generate interindividual genomic variation. Long interspersed element-1 (L1) sequences comprise about 17% of the human genome reference sequence. The average human genome contains about 100 active L1s that mobilize throughout the genome by a “copy and paste” process termed retrotransposition. Active L1s encode two proteins (ORF1p and ORF2p). ORF1p and ORF2p preferentially bind to their encoding RNA, forming a ribonucleoprotein particle (RNP). During retrotransposition, the L1 RNP translocates to the nucleus, where the ORF2p endonuclease makes a single-strand nick in target site DNA that exposes a 3′ hydroxyl group in genomic DNA. The 3′ hydroxyl group then is used as a primer by the ORF2p reverse transcriptase to copy the L1 RNA into cDNA, leading to the integration of an L1 copy at a new genomic location. The evolutionary success of L1 requires the faithful retrotransposition of full-length L1 mRNAs; thus, it was surprising to find that a small number of L1 retrotransposition events are derived from spliced L1 mRNAs. By using genetic, biochemical, and computational approaches, we demonstrate that spliced L1 mRNAs can undergo an initial round of retrotransposition, leading to the generation of spliced integrated retrotransposed elements (SpIREs). SpIREs represent about 2% of previously annotated full-length primate-specific L1s in the human genome reference sequence. However, because splicing leads to intra-L1 deletions that remove critical sequences required for L1 expression, SpIREs generally cannot undergo subsequent rounds of retrotransposition and can be considered “dead on arrival” insertions. Our data further highlight how genetic conflict between L1 and its host has influenced L1 expression, L1 retrotransposition, and L1 splicing dynamics over evolutionary time.
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10
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Mita P, Wudzinska A, Sun X, Andrade J, Nayak S, Kahler DJ, Badri S, LaCava J, Ueberheide B, Yun CY, Fenyö D, Boeke JD. LINE-1 protein localization and functional dynamics during the cell cycle. eLife 2018; 7:30058. [PMID: 29309036 PMCID: PMC5821460 DOI: 10.7554/elife.30058] [Citation(s) in RCA: 82] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2017] [Accepted: 01/04/2018] [Indexed: 01/12/2023] Open
Abstract
LINE-1/L1 retrotransposon sequences comprise 17% of the human genome. Among the many classes of mobile genetic elements, L1 is the only autonomous retrotransposon that still drives human genomic plasticity today. Through its co-evolution with the human genome, L1 has intertwined itself with host cell biology. However, a clear understanding of L1’s lifecycle and the processes involved in restricting its insertion and intragenomic spread remains elusive. Here we identify modes of L1 proteins’ entrance into the nucleus, a necessary step for L1 proliferation. Using functional, biochemical, and imaging approaches, we also show a clear cell cycle bias for L1 retrotransposition that peaks during the S phase. Our observations provide a basis for novel interpretations about the nature of nuclear and cytoplasmic L1 ribonucleoproteins (RNPs) and the potential role of DNA replication in L1 retrotransposition. Only two percent of our genetic material or genome are occupied by genes, while between 60-70 percent are made up of hundreds of thousands of copies of very similar DNA sequences. These repetitive sequences evolved from genetic elements called transposons. Transposons are often referred to as ‘jumping genes’, as they can randomly move within the genome and thereby create dangerous mutations that may lead to cancer or other genetic diseases. LINE-1 is the only remaining active transposon in humans, and it expands by copying and pasting itself to new locations via a process called 'retrotransposition'. To do so, it is first transcribed into RNA – the molecules that help to make proteins – and then converted back into identical DNA sequences. Previous research has shown that LINE-1 can form complexes with a series of proteins, including the two encoded by LINE-1 RNA itself: ORF1p and ORF2p. The LINE-1 complexes can enter the nucleus of the cell and insert a new copy of LINE-1 into the genome. However, until now it was not known how they do this. To investigate this further, Mita et al. used human cancer cells grown in the lab and tracked LINE-1 during the different stages of the cell cycle. The results showed that LINE-1 enters the nucleus as the cell starts to divide and the membrane of the nucleus breaks down. The LINE-1 complexes are then retained in the nucleus while the membrane of the nucleus reforms. Later, as the cell duplicates its genetic material, LINE-1 starts to copy and paste itself. Mita et al., together with another group of researchers, also found that during this process, only LINE-1 RNA and ORF2p were found in the nucleus. This shows that the cell cycle dictates both where the LINE-1 complexes gather and when LINE-1 is active. A next step will be to further investigate how the ‘copy and paste’ mechanisms of LINE-1 and the two LINE-1 proteins are regulated during the cell cycle. In future, this may help to identify LINE-1’s role in processes like aging or in diseases such as cancer.
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Affiliation(s)
- Paolo Mita
- Institute of Systems Genetics (ISG), Department of Biochemistry and Molecular Pharmacology, NYU Langone Health, New York, United States
| | - Aleksandra Wudzinska
- Institute of Systems Genetics (ISG), Department of Biochemistry and Molecular Pharmacology, NYU Langone Health, New York, United States
| | - Xiaoji Sun
- Institute of Systems Genetics (ISG), Department of Biochemistry and Molecular Pharmacology, NYU Langone Health, New York, United States
| | - Joshua Andrade
- Proteomics laboratory, NYU Langone Health, New York, United States
| | - Shruti Nayak
- Proteomics laboratory, NYU Langone Health, New York, United States
| | - David J Kahler
- High Throughput Biology (HTB) Laboratory, NYU Langone Health, New York, United States
| | - Sana Badri
- Department of Pathology, NYU Langone Health, New York, United States
| | - John LaCava
- Institute of Systems Genetics (ISG), Department of Biochemistry and Molecular Pharmacology, NYU Langone Health, New York, United States.,Laboratory of Cellular and Structural Biology, The Rockefeller University, New York, United States
| | - Beatrix Ueberheide
- Institute of Systems Genetics (ISG), Department of Biochemistry and Molecular Pharmacology, NYU Langone Health, New York, United States.,Proteomics laboratory, NYU Langone Health, New York, United States
| | - Chi Y Yun
- High Throughput Biology (HTB) Laboratory, NYU Langone Health, New York, United States
| | - David Fenyö
- Institute of Systems Genetics (ISG), Department of Biochemistry and Molecular Pharmacology, NYU Langone Health, New York, United States
| | - Jef D Boeke
- Institute of Systems Genetics (ISG), Department of Biochemistry and Molecular Pharmacology, NYU Langone Health, New York, United States
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11
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Kalogirou EM, Piperi EP, Tosios KI, Tsiambas E, Fanourakis G, Sklavounou A. Ductal cells of minor salivary glands in Sjögren's syndrome express LINE-1 ORF2p and APOBEC3B. J Oral Pathol Med 2017; 47:179-185. [PMID: 29057505 DOI: 10.1111/jop.12656] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/17/2017] [Indexed: 01/29/2023]
Abstract
BACKGROUND Type I interferon activation is a hallmark event in Sjögren's syndrome. L1 retroelements stimulate plasmacytoid dendritic cells, activating the type I interferons, and are regulated by various mechanisms, including the APOBEC3 deaminases. As L1s are potential trigger factors in autoimmunity, we aimed to investigate the immunohistochemical localization of L1 ORF2p and its inhibitor APOBEC3B protein in minor salivary glands of Sjögren's syndrome patients. METHODS Twenty minor salivary gland-tissue samples from 20 Sjögren's syndrome patients, classified according to Tarpley's histological criteria, and 10 controls were evaluated for L1 ORF2p and APOBEC3B expression via immunohistochemistry. RESULTS L1 ORF2p was expressed in 17/20 SS patients and all controls. APOBEC3B expression was observed in 15/20 Sjögren's syndrome patients, 5/5 chronic sialadenitis, and 3/5 normal minor salivary glands. Both antibodies stained the cytoplasm of the ductal epithelial cells. Negative staining was observed in the acinar cells. L1 ORF2p-positive immunostaining was significantly lower in Tarpley IV Sjögren's syndrome patients than controls (P = .039), and APOBEC3B-positive staining was significantly lower in Tarpley I compared to Tarpley II Sjögren's syndrome patients (P = .008) and controls (P = .035). CONCLUSIONS L1 ORF2p and APOBEC3B are expressed in the ductal epithelial cells of minor salivary glands that are among the key targets in Sjögren's syndrome. L1 ORF2p expression may promote the L1 ability to act as an intrinsic antigen in Sjögren's syndrome. The potential future use of L1 ORF2-reverse transcriptase inhibitors in autoimmunity supports further investigation of L1 epigenetic regulation by APOBEC3 enzymes.
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Affiliation(s)
- Eleni-Marina Kalogirou
- Department of Oral Medicine and Pathology, Faculty of Dentistry, National and Kapodistrian University of Athens, Athens, Greece
| | - Evangelia P Piperi
- Department of Oral Medicine and Pathology, Faculty of Dentistry, National and Kapodistrian University of Athens, Athens, Greece
| | - Konstantinos I Tosios
- Department of Oral Medicine and Pathology, Faculty of Dentistry, National and Kapodistrian University of Athens, Athens, Greece
| | - Evangelos Tsiambas
- Department of Immunohistochemistry & Molecular Biology, 401 Military Hospital of Athens, Athens, Greece
| | - Galinos Fanourakis
- Department of Oral Biology, Faculty of Dentistry, National and Kapodistrian University of Athens, Athens, Greece
| | - Alexandra Sklavounou
- Department of Oral Medicine and Pathology, Faculty of Dentistry, National and Kapodistrian University of Athens, Athens, Greece
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12
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MacLennan M, García-Cañadas M, Reichmann J, Khazina E, Wagner G, Playfoot CJ, Salvador-Palomeque C, Mann AR, Peressini P, Sanchez L, Dobie K, Read D, Hung CC, Eskeland R, Meehan RR, Weichenrieder O, García-Pérez JL, Adams IR. Mobilization of LINE-1 retrotransposons is restricted by Tex19.1 in mouse embryonic stem cells. eLife 2017; 6:e26152. [PMID: 28806172 PMCID: PMC5570191 DOI: 10.7554/elife.26152] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2017] [Accepted: 07/11/2017] [Indexed: 12/21/2022] Open
Abstract
Mobilization of retrotransposons to new genomic locations is a significant driver of mammalian genome evolution, but these mutagenic events can also cause genetic disorders. In humans, retrotransposon mobilization is mediated primarily by proteins encoded by LINE-1 (L1) retrotransposons, which mobilize in pluripotent cells early in development. Here we show that TEX19.1, which is induced by developmentally programmed DNA hypomethylation, can directly interact with the L1-encoded protein L1-ORF1p, stimulate its polyubiquitylation and degradation, and restrict L1 mobilization. We also show that TEX19.1 likely acts, at least in part, through promoting the activity of the E3 ubiquitin ligase UBR2 towards L1-ORF1p. Moreover, loss of Tex19.1 increases L1-ORF1p levels and L1 mobilization in pluripotent mouse embryonic stem cells, implying that Tex19.1 prevents de novo retrotransposition in the pluripotent phase of the germline cycle. These data show that post-translational regulation of L1 retrotransposons plays a key role in maintaining trans-generational genome stability in mammals.
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Affiliation(s)
- Marie MacLennan
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
| | - Marta García-Cañadas
- Centro de Genómica e
Investigación Oncológica (GENYO), Pfizer-Universidad de
Granada-Junta de Andalucía, PTS Granada, Granada,
Spain
| | - Judith Reichmann
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
| | - Elena Khazina
- Department of
Biochemistry, Max Planck Institute for Developmental
Biology, Tübingen, Germany
| | - Gabriele Wagner
- Department of
Biochemistry, Max Planck Institute for Developmental
Biology, Tübingen, Germany
| | - Christopher J Playfoot
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
| | - Carmen Salvador-Palomeque
- Centro de Genómica e
Investigación Oncológica (GENYO), Pfizer-Universidad de
Granada-Junta de Andalucía, PTS Granada, Granada,
Spain
| | - Abigail R Mann
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
| | - Paula Peressini
- Centro de Genómica e
Investigación Oncológica (GENYO), Pfizer-Universidad de
Granada-Junta de Andalucía, PTS Granada, Granada,
Spain
| | - Laura Sanchez
- Centro de Genómica e
Investigación Oncológica (GENYO), Pfizer-Universidad de
Granada-Junta de Andalucía, PTS Granada, Granada,
Spain
| | - Karen Dobie
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
| | - David Read
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
| | - Chao-Chun Hung
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
| | - Ragnhild Eskeland
- Department of
Biosciences, University of Oslo,
Oslo,
Norway
- Norwegian Center for
Stem Cell Research, Department of Immunology, Oslo
University Hospital, Oslo, Norway
| | - Richard R Meehan
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
| | - Oliver Weichenrieder
- Department of
Biochemistry, Max Planck Institute for Developmental
Biology, Tübingen, Germany
| | - Jose Luis García-Pérez
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
- Centro de Genómica e
Investigación Oncológica (GENYO), Pfizer-Universidad de
Granada-Junta de Andalucía, PTS Granada, Granada,
Spain
| | - Ian R Adams
- MRC Human Genetics Unit,
MRC Institute of Genetics and Molecular Medicine,
University of Edinburgh, Edinburgh, United
Kingdom
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13
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Zhou L, Canagarajah B, Zhao Y, Baibakov B, Tokuhiro K, Maric D, Dean J. BTBD18 Regulates a Subset of piRNA-Generating Loci through Transcription Elongation in Mice. Dev Cell 2017; 40:453-466.e5. [PMID: 28292424 DOI: 10.1016/j.devcel.2017.02.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Revised: 11/18/2016] [Accepted: 02/09/2017] [Indexed: 11/27/2022]
Abstract
PIWI-interacting RNAs (piRNAs) are small non-coding RNAs essential for animal germ cell development. Despite intense investigation of post-transcriptional processing, chromatin regulators for piRNA biogenesis in mammals remain largely unexplored. Here we document that BTBD18 is a pachytene nuclear protein in mouse testes that occupies a subset of pachytene piRNA-producing loci. Ablation of Btbd18 in mice disrupts piRNA biogenesis, prevents spermiogenesis, and results in male sterility. Transcriptome profiling, chromatin accessibility, and RNA polymerase II occupancy demonstrate that BTBD18 facilitates expression of pachytene piRNA precursors by promoting transcription elongation. Thus, our study identifies BTBD18 as a specific controller for transcription activation through RNA polymerase II elongation at a subset of genomic piRNA loci.
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Affiliation(s)
- Liquan Zhou
- Laboratory of Cellular and Developmental Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Bertram Canagarajah
- Laboratory of Cellular and Developmental Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
| | - Yangu Zhao
- Laboratory of Cellular and Developmental Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
| | - Boris Baibakov
- Laboratory of Cellular and Developmental Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
| | - Keizo Tokuhiro
- Laboratory of Cellular and Developmental Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
| | - Dragan Maric
- NINDS Flow Cytometry Core Facility, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jurrien Dean
- Laboratory of Cellular and Developmental Biology, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA.
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14
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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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15
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Richardson SR, Gerdes P, Gerhardt DJ, Sanchez-Luque FJ, Bodea GO, Muñoz-Lopez M, Jesuadian JS, Kempen MJHC, Carreira PE, Jeddeloh JA, Garcia-Perez JL, Kazazian HH, Ewing AD, Faulkner GJ. Heritable L1 retrotransposition in the mouse primordial germline and early embryo. Genome Res 2017; 27:1395-1405. [PMID: 28483779 PMCID: PMC5538555 DOI: 10.1101/gr.219022.116] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2016] [Accepted: 05/02/2017] [Indexed: 12/31/2022]
Abstract
LINE-1 (L1) retrotransposons are a noted source of genetic diversity and disease in mammals. To expand its genomic footprint, L1 must mobilize in cells that will contribute their genetic material to subsequent generations. Heritable L1 insertions may therefore arise in germ cells and in pluripotent embryonic cells, prior to germline specification, yet the frequency and predominant developmental timing of such events remain unclear. Here, we applied mouse retrotransposon capture sequencing (mRC-seq) and whole-genome sequencing (WGS) to pedigrees of C57BL/6J animals, and uncovered an L1 insertion rate of ≥1 event per eight births. We traced heritable L1 insertions to pluripotent embryonic cells and, strikingly, to early primordial germ cells (PGCs). New L1 insertions bore structural hallmarks of target-site primed reverse transcription (TPRT) and mobilized efficiently in a cultured cell retrotransposition assay. Together, our results highlight the rate and evolutionary impact of heritable L1 retrotransposition and reveal retrotransposition-mediated genomic diversification as a fundamental property of pluripotent embryonic cells in vivo.
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Affiliation(s)
- Sandra R Richardson
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia
| | - Patricia Gerdes
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia
| | - Daniel J Gerhardt
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia.,Invenra, Incorporated, Madison, Wisconsin 53719, USA
| | - Francisco J Sanchez-Luque
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia.,Department of Genomic Medicine, GENYO, Centre for Genomics and Oncological Research, Pfizer-University of Granada-Andalusian Regional Government, PTS Granada, 18016 Granada, Spain
| | - Gabriela-Oana Bodea
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia
| | - Martin Muñoz-Lopez
- Department of Genomic Medicine, GENYO, Centre for Genomics and Oncological Research, Pfizer-University of Granada-Andalusian Regional Government, PTS Granada, 18016 Granada, Spain
| | - J Samuel Jesuadian
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia
| | | | - Patricia E Carreira
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia
| | | | - Jose L Garcia-Perez
- Department of Genomic Medicine, GENYO, Centre for Genomics and Oncological Research, Pfizer-University of Granada-Andalusian Regional Government, PTS Granada, 18016 Granada, Spain.,Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Edinburgh EH4 2XU, United Kingdom
| | - Haig H Kazazian
- Institute of Genetic Medicine and Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Adam D Ewing
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia
| | - Geoffrey J Faulkner
- Mater Research Institute-University of Queensland, Woolloongabba QLD 4102, Australia.,School of Biomedical Sciences.,Queensland Brain Institute, University of Queensland, Brisbane QLD 4072, Australia
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16
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Abstract
Retrotransposons have generated about 40 % of the human genome. This review examines the strategies the cell has evolved to coexist with these genomic "parasites", focussing on the non-long terminal repeat retrotransposons of humans and mice. Some of the restriction factors for retrotransposition, including the APOBECs, MOV10, RNASEL, SAMHD1, TREX1, and ZAP, also limit replication of retroviruses, including HIV, and are part of the intrinsic immune system of the cell. Many of these proteins act in the cytoplasm to degrade retroelement RNA or inhibit its translation. Some factors act in the nucleus and involve DNA repair enzymes or epigenetic processes of DNA methylation and histone modification. RISC and piRNA pathway proteins protect the germline. Retrotransposon control is relaxed in some cell types, such as neurons in the brain, stem cells, and in certain types of disease and cancer, with implications for human health and disease. This review also considers potential pitfalls in interpreting retrotransposon-related data, as well as issues to consider for future research.
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Affiliation(s)
- John L. Goodier
- McKusick-Nathans Institute for Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD USA 212051
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17
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SAMHD1 Inhibits LINE-1 Retrotransposition by Promoting Stress Granule Formation. PLoS Genet 2015; 11:e1005367. [PMID: 26134849 PMCID: PMC4489885 DOI: 10.1371/journal.pgen.1005367] [Citation(s) in RCA: 96] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Accepted: 06/17/2015] [Indexed: 01/17/2023] Open
Abstract
The SAM domain and HD domain containing protein 1 (SAMHD1) inhibits retroviruses, DNA viruses and long interspersed element 1 (LINE-1). Given that in dividing cells, SAMHD1 loses its antiviral function yet still potently restricts LINE-1, we propose that, instead of blocking viral DNA synthesis by virtue of its dNTP triphosphohydrolase activity, SAMHD1 may exploit a different mechanism to control LINE-1. Here, we report a new activity of SAMHD1 in promoting cellular stress granule assembly, which correlates with increased phosphorylation of eIF2α and diminished eIF4A/eIF4G interaction. This function of SAMHD1 enhances sequestration of LINE-1 RNP in stress granules and consequent blockade to LINE-1 retrotransposition. In support of this new mechanism of action, depletion of stress granule marker proteins G3BP1 or TIA1 abrogates stress granule formation and overcomes SAMHD1 inhibition of LINE-1. Together, these data reveal a new mechanism for SAMHD1 to control LINE-1 by activating cellular stress granule pathway. Long interspersed element 1 (LINE-1 or L1) comprises 17% of human genome, and has played a major role in shaping the evolution of human genome. Approximately 100 copies of LINE-1 are still active in an average individual genome. Movement of these LINE-1 sequences to new loci in the genome has the potential of causing sporadic cases of disease. Among the multi-layered mechanisms by which the host controls LINE-1 activity is a group of host restriction factors including APOBEC3 proteins. SAMHD1 was known for the association of its mutations with the Aicardi-Goutieres syndrome (AGS), a congenital autoimmune disease. SAMHD1 was recently reported as a host restriction factor that inhibits a number of retroviruses and DNA viruses including human immunodeficiency virus type 1 (HIV-1) and herpes simplex virus 1 (HSV-1). Here, we demonstrate that SAMHD1 inhibits LINE-1 retrotransposition through promoting the sequestration of LINE-1 RNP within the cytoplasmic stress granules. SAMHD1 promotes the formation of large stress granules by inducing phosphorylation of eIF2α and disrupting eIF4A/eIF4G interaction. This is the first report describing the role of SAMHD1 in modulating the formation of stress granules. We envision that this function of SAMHD1 not only contributes to the inhibition of LINE-1, but also the restriction of various viruses.
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18
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Ichiyanagi T, Ichiyanagi K, Ogawa A, Kuramochi-Miyagawa S, Nakano T, Chuma S, Sasaki H, Udono H. HSP90α plays an important role in piRNA biogenesis and retrotransposon repression in mouse. Nucleic Acids Res 2014; 42:11903-11. [PMID: 25262350 PMCID: PMC4231750 DOI: 10.1093/nar/gku881] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
HSP90, found in all kingdoms of life, is a major chaperone protein regulating many client proteins. We demonstrated that HSP90α, one of two paralogs duplicated in vertebrates, plays an important role in the biogenesis of fetal PIWI-interacting RNAs (piRNA), which act against the transposon activities, in mouse male germ cells. The knockout mutation of Hsp90α resulted in a large reduction in the expression of primary and secondary piRNAs and mislocalization of MIWI2, a PIWI homolog. Whereas the mutation in Fkbp6 encoding a co-chaperone reduced piRNAs of 28–32 nucleotides in length, the Hsp90α mutation reduced piRNAs of 24–32 nucleotides, suggesting the presence of both FKBP6-dependent and -independent actions of HSP90α. Although DNA methylation and mRNA levels of L1 retrotransposon were largely unchanged in the Hsp90α mutant testes, the L1-encoded protein was increased, suggesting the presence of post-transcriptional regulation. This study revealed the specialized function of the HSP90α isofom in the piRNA biogenesis and repression of retrotransposons during the development of male germ cells in mammals.
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Affiliation(s)
- Tomoko Ichiyanagi
- Department of Immunology, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Kita-ku, Okayama 700-8558, Japan Division of Epigenomics and Development, Medical Institute of Bioregulation, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan
| | - Kenji Ichiyanagi
- Division of Epigenomics and Development, Medical Institute of Bioregulation, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan
| | - Ayako Ogawa
- Division of Epigenomics and Development, Medical Institute of Bioregulation, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan
| | - Satomi Kuramochi-Miyagawa
- Department of Pathology, Medical School and Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan CREST, Japan Science and Technology Agency (JST), Saitama 332-0012, Japan
| | - Toru Nakano
- Department of Pathology, Medical School and Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan CREST, Japan Science and Technology Agency (JST), Saitama 332-0012, Japan
| | - Shinichiro Chuma
- Department of Development and Differentiation, Institute for Frontier Medical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
| | - Hiroyuki Sasaki
- Division of Epigenomics and Development, Medical Institute of Bioregulation, Kyushu University, Higashi-ku, Fukuoka 812-8582, Japan
| | - Heiichiro Udono
- Department of Immunology, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Kita-ku, Okayama 700-8558, Japan
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19
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Knittel G, Metzner M, Beck-Engeser G, Kan A, Ahrends T, Eilat D, Huppi K, Wabl M. Insertional hypermutation in mineral oil-induced plasmacytomas. Eur J Immunol 2014; 44:2785-801. [PMID: 24975032 PMCID: PMC4165787 DOI: 10.1002/eji.201344322] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Revised: 05/22/2014] [Accepted: 06/24/2014] [Indexed: 01/07/2023]
Abstract
Unless stimulated by a chronic inflammatory agent, such as mineral oil, plasma cell tumors are rare in young BALB/c mice. This raises the questions: What do inflammatory tissues provide to promote mutagenesis? And what is the nature of mutagenesis? We determined that mineral oil-induced plasmacytomas produce large amounts of endogenous retroelements--ecotropic and polytropic murine leukemia virus and intracisternal A particles. Therefore, plasmacytoma formation might occur, in part, by de novo insertion of these retroelements, induced or helped by the inflammation. We recovered up to ten de novo insertions in a single plasmacytoma, mostly in genes with common retroviral integration sites. Additional integrations accompany tumor evolution from a solid tumor through several generations in cell culture. The high frequency of de novo integrations into cancer genes suggests that endogenous retroelements are coresponsible for plasmacytoma formation and progression in BALB/c mice.
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Affiliation(s)
- Gero Knittel
- Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0414
| | - Mirjam Metzner
- Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0414
| | - Gabriele Beck-Engeser
- Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0414
| | - Ada Kan
- Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0414
| | - Tomasz Ahrends
- Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0414
| | - Dan Eilat
- Department of Medicine, Hadassah University Hospital and The Hebrew University Faculty of Medicine, Jerusalem 91120, Israel
| | - Konrad Huppi
- National Cancer Institute, Genetics Branch, Gene Silencing Section, Bethesda, MD 20892
| | - Matthias Wabl
- Department of Microbiology and Immunology, University of California, San Francisco, CA 94143-0414
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20
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Castañeda J, Genzor P, van der Heijden GW, Sarkeshik A, Yates JR, Ingolia NT, Bortvin A. Reduced pachytene piRNAs and translation underlie spermiogenic arrest in Maelstrom mutant mice. EMBO J 2014; 33:1999-2019. [PMID: 25063675 DOI: 10.15252/embj.201386855] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Pachytene piRNAs are a class of Piwi-interacting small RNAs abundant in spermatids of the adult mouse testis. They are processed from piRNA primary transcripts by a poorly understood mechanism and, unlike fetal transposon-derived piRNAs, lack complementary targets in the spermatid transcriptome. We report that immunopurified complexes of a conserved piRNA pathway protein Maelstrom (MAEL) are enriched in MIWI (Piwi partner of pachytene piRNAs), Tudor-domain proteins and processing intermediates of pachytene piRNA primary transcripts. We provide evidence of functional significance of these complexes in Mael129 knockout mice that exhibit spermiogenic arrest with acrosome and flagellum malformation. Mael129-null mutant testes possess low levels of piRNAs derived from MAEL-associated piRNA precursors and exhibit reduced translation of numerous spermiogenic mRNAs including those encoding acrosome and flagellum proteins. These translation defects in haploid round spermatids are likely indirect, as neither MAEL nor piRNA precursors associate with polyribosomes, and they may arise from an imbalance between pachytene piRNAs and MIWI.
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Affiliation(s)
- Julio Castañeda
- Department of Biology, Johns Hopkins University, Baltimore, MD, USA Department of Embryology, Carnegie Institution for Science, Baltimore, MD, USA
| | - Pavol Genzor
- Department of Biology, Johns Hopkins University, Baltimore, MD, USA Department of Embryology, Carnegie Institution for Science, Baltimore, MD, USA
| | | | - Ali Sarkeshik
- Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA, USA
| | - John R Yates
- Department of Chemical Physiology, The Scripps Research Institute, La Jolla, CA, USA
| | - Nicholas T Ingolia
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD, USA
| | - Alex Bortvin
- Department of Embryology, Carnegie Institution for Science, Baltimore, MD, USA
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21
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Yang L, Brunsfeld J, Scott L, Wichman H. Reviving the dead: history and reactivation of an extinct l1. PLoS Genet 2014; 10:e1004395. [PMID: 24968166 PMCID: PMC4072516 DOI: 10.1371/journal.pgen.1004395] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 04/07/2014] [Indexed: 11/18/2022] Open
Abstract
Although L1 sequences are present in the genomes of all placental mammals and marsupials examined to date, their activity was lost in the megabat family, Pteropodidae, ∼24 million years ago. To examine the characteristics of L1s prior to their extinction, we analyzed the evolutionary history of L1s in the genome of a megabat, Pteropus vampyrus, and found a pattern of periodic L1 expansion and quiescence. In contrast to the well-characterized L1s in human and mouse, megabat genomes have accommodated two or more simultaneously active L1 families throughout their evolutionary history, and major peaks of L1 deposition into the genome always involved multiple families. We compared the consensus sequences of the two major megabat L1 families at the time of their extinction to consensus L1s of a variety of mammalian species. Megabat L1s are comparable to the other mammalian L1s in terms of adenosine content and conserved amino acids in the open reading frames (ORFs). However, the intergenic region (IGR) of the reconstructed element from the more active family is dramatically longer than the IGR of well-characterized human and mouse L1s. We synthesized the reconstructed element from this L1 family and tested the ability of its components to support retrotransposition in a tissue culture assay. Both ORFs are capable of supporting retrotransposition, while the IGR is inhibitory to retrotransposition, especially when combined with either of the reconstructed ORFs. We dissected the inhibitory effect of the IGR by testing truncated and shuffled versions and found that length is a key factor, but not the only one affecting inhibition of retrotransposition. Although the IGR is inhibitory to retrotransposition, this inhibition does not account for the extinction of L1s in megabats. Overall, the evolution of the L1 sequence or the quiescence of L1 is unlikely the reason of L1 extinction.
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Affiliation(s)
- Lei Yang
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
- Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, Idaho, United States of America
| | - John Brunsfeld
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
| | - LuAnn Scott
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
| | - Holly Wichman
- Department of Biological Sciences, University of Idaho, Moscow, Idaho, United States of America
- Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, Idaho, United States of America
- * E-mail:
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22
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Dai L, LaCava J, Taylor MS, Boeke JD. Expression and detection of LINE-1 ORF-encoded proteins. Mob Genet Elements 2014; 4:e29319. [PMID: 25054082 PMCID: PMC4091050 DOI: 10.4161/mge.29319] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Revised: 05/19/2014] [Accepted: 05/22/2014] [Indexed: 11/30/2022] Open
Abstract
LINE-1 (L1) elements are endogenous retrotransposons active in mammalian genomes. The L1 RNA is bicistronic, encoding two non-overlapping open reading frames, ORF1 and ORF2, whose protein products (ORF1p and ORF2p) bind the L1 RNA to form a ribonucleoprotein (RNP) complex that is presumed to be a critical retrotransposition intermediate. However, ORF2p is expressed at a significantly lower level than ORF1p; these differences are thought to be controlled at the level of translation, due to a low frequency ribosome reinitiation mechanism controlling ORF2 expression. As a result, while ORF1p is readily detectable, ORF2p has previously been very challenging to detect in vitro and in vivo. To address this, we recently tested several epitope tags fused to the N- or C-termini of the ORF proteins in an effort to enable robust detection and affinity purification from native (L1RP) and synthetic (ORFeus-Hs) L1 constructs. An analysis of tagged RNPs from both L1RP and ORFeus-Hs showed similar host-cell-derived protein interactors. Our observations also revealed that the tag sequences affected the retrotransposition competency of native and synthetic L1s differently although they encode identical ORF proteins. Unexpectedly, we observed apparently stochastic expression of ORF2p within seemingly homogenous L1-expressing cell populations.
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Affiliation(s)
- Lixin Dai
- High Throughput Biology Center and Department of Molecular Biology and Genetics; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - John LaCava
- Laboratory of Cellular and Structural Biology; The Rockefeller University; New York, NY USA
| | - Martin S Taylor
- High Throughput Biology Center and Department of Pharmacology and Molecular Sciences; Johns Hopkins University School of Medicine; Baltimore, MD USA
| | - Jef D Boeke
- Institute for Systems Genetics; New York University School of Medicine; New York, NY USA
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23
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Crichton JH, Dunican DS, MacLennan M, Meehan RR, Adams IR. Defending the genome from the enemy within: mechanisms of retrotransposon suppression in the mouse germline. Cell Mol Life Sci 2014; 71:1581-605. [PMID: 24045705 PMCID: PMC3983883 DOI: 10.1007/s00018-013-1468-0] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Revised: 08/27/2013] [Accepted: 08/29/2013] [Indexed: 12/15/2022]
Abstract
The viability of any species requires that the genome is kept stable as it is transmitted from generation to generation by the germ cells. One of the challenges to transgenerational genome stability is the potential mutagenic activity of transposable genetic elements, particularly retrotransposons. There are many different types of retrotransposon in mammalian genomes, and these target different points in germline development to amplify and integrate into new genomic locations. Germ cells, and their pluripotent developmental precursors, have evolved a variety of genome defence mechanisms that suppress retrotransposon activity and maintain genome stability across the generations. Here, we review recent advances in understanding how retrotransposon activity is suppressed in the mammalian germline, how genes involved in germline genome defence mechanisms are regulated, and the consequences of mutating these genome defence genes for the developing germline.
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Affiliation(s)
- James H. Crichton
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU UK
| | - Donncha S. Dunican
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU UK
| | - Marie MacLennan
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU UK
| | - Richard R. Meehan
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU UK
| | - Ian R. Adams
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU UK
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24
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Belan E. LINEs of evidence: noncanonical DNA replication as an epigenetic determinant. Biol Direct 2013; 8:22. [PMID: 24034780 PMCID: PMC3868326 DOI: 10.1186/1745-6150-8-22] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Accepted: 09/06/2013] [Indexed: 12/17/2022] Open
Abstract
LINE-1 (L1) retrotransposons are repetitive elements in mammalian genomes. They are
capable of synthesizing DNA on their own RNA templates by harnessing reverse
transcriptase (RT) that they encode. Abundantly expressed full-length L1s and their
RT are found to globally influence gene expression profiles, differentiation state,
and proliferation capacity of early embryos and many types of cancer, albeit by yet
unknown mechanisms. They are essential for the progression of early development and
the establishment of a cancer-related undifferentiated state. This raises important
questions regarding the functional significance of L1 RT in these cell systems.
Massive nuclear L1-linked reverse transcription has been shown to occur in mouse
zygotes and two-cell embryos, and this phenomenon is purported to be DNA replication
independent. This review argues against this claim with the goal of understanding the
nature of this phenomenon and the role of L1 RT in early embryos and cancers.
Available L1 data are revisited and integrated with relevant findings accumulated in
the fields of replication timing, chromatin organization, and epigenetics, bringing
together evidence that strongly supports two new concepts. First, noncanonical
replication of a portion of genomic full-length L1s by means of L1 RNP-driven reverse
transcription is proposed to co-exist with DNA polymerase-dependent replication of
the rest of the genome during the same round of DNA replication in embryonic and
cancer cell systems. Second, the role of this mechanism is thought to be epigenetic;
it might promote transcriptional competence of neighboring genes linked to
undifferentiated states through the prevention of tethering of involved L1s to the
nuclear periphery. From the standpoint of these concepts, several hitherto
inexplicable phenomena can be explained. Testing methods for the model are
proposed.
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Affiliation(s)
- Ekaterina Belan
- Genetics Laboratory, Royal University Hospital, Saskatoon, SK S7N 0W8, Canada.
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25
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Reichmann J, Reddington JP, Best D, Read D, Öllinger R, Meehan RR, Adams IR. The genome-defence gene Tex19.1 suppresses LINE-1 retrotransposons in the placenta and prevents intra-uterine growth retardation in mice. Hum Mol Genet 2013; 22:1791-806. [PMID: 23364048 PMCID: PMC3613164 DOI: 10.1093/hmg/ddt029] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Revised: 12/19/2012] [Accepted: 01/24/2013] [Indexed: 12/11/2022] Open
Abstract
DNA methylation plays an important role in suppressing retrotransposon activity in mammalian genomes, yet there are stages of mammalian development where global hypomethylation puts the genome at risk of retrotransposition-mediated genetic instability. Hypomethylated primordial germ cells appear to limit this risk by expressing a cohort of retrotransposon-suppressing genome-defence genes whose silencing depends on promoter DNA methylation. Here, we investigate whether similar mechanisms operate in hypomethylated trophectoderm-derived components of the mammalian placenta to couple expression of genome-defence genes to the potential for retrotransposon activity. We show that the hypomethylated state of the mouse placenta results in activation of only one of the hypomethylation-sensitive germline genome-defence genes: Tex19.1. Tex19.1 appears to play an important role in placenta function as Tex19.1(-/-) mouse embryos exhibit intra-uterine growth retardation and have small placentas due to a reduction in the number of spongiotrophoblast, glycogen trophoblast and sinusoidal trophoblast giant cells. Furthermore, we show that retrotransposon mRNAs are derepressed in Tex19.1(-/-) placentas and that protein encoded by the LINE-1 retrotransposon is upregulated in hypomethylated trophectoderm-derived cells that normally express Tex19.1. This study suggests that post-transcriptional genome-defence mechanisms are operating in the placenta to protect the hypomethylated cells in this tissue from retrotransposons and suggests that imbalances between retrotransposon activity and genome-defence mechanisms could contribute to placenta dysfunction and disease.
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Affiliation(s)
| | | | | | | | | | - Richard R. Meehan
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, Western General Hospital, University of Edinburgh, Crewe Road, Edinburgh EH4 2XU, UK
| | - Ian R. Adams
- MRC Human Genetics Unit, MRC Institute of Genetics and Molecular Medicine, Western General Hospital, University of Edinburgh, Crewe Road, Edinburgh EH4 2XU, UK
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26
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Peddigari S, Li PWL, Rabe JL, Martin SL. hnRNPL and nucleolin bind LINE-1 RNA and function as host factors to modulate retrotransposition. Nucleic Acids Res 2013; 41:575-85. [PMID: 23161687 PMCID: PMC3592465 DOI: 10.1093/nar/gks1075] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Revised: 10/09/2012] [Accepted: 10/13/2012] [Indexed: 12/18/2022] Open
Abstract
Long INterspersed Element one (LINE-1, or L1), is a widely distributed, autonomous retrotransposon in mammalian genomes. During retrotransposition, L1 RNA functions first as a dicistronic mRNA and then as a template for cDNA synthesis. Previously, we defined internal ribosome entry sequences (IRESs) upstream of both ORFs (ORF1 and ORF2) in the dicistronic mRNA encoded by mouse L1. Here, RNA affinity chromatography was used to isolate cellular proteins that bind these regions of L1 RNA. Four proteins, the heterogeneous nuclear ribonucleoproteins (hnRNPs) R, Q and L, and nucleolin (NCL), appeared to interact specifically with the ORF2 IRES. These were depleted from HeLa cells to examine their effects on L1 IRES-mediated translation and L1 retrotransposition. NCL knockdown specifically reduced the ORF2 IRES activity, L1 and L1-assisted Alu retrotransposition without altering L1 RNA or protein abundance. These findings are consistent with NCL acting as an IRES trans-acting factor (ITAF) for ORF2 translation and hence a positive host factor for L1 retrotransposition. In contrast, hnRNPL knockdown dramatically increased L1 retrotransposition as well as L1 RNA and ORF1 protein, indicating that this cellular protein normally interferes with retrotransposition. Thus, hnRNPL joins a small, but growing list of cellular proteins that are potent negative regulators of L1 retrotransposition.
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Affiliation(s)
- Suresh Peddigari
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, PO Box 6511, MS 8108, Aurora, CO 80045, USA.
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27
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Metzner M, Jäck HM, Wabl M. LINE-1 retroelements complexed and inhibited by activation induced cytidine deaminase. PLoS One 2012; 7:e49358. [PMID: 23133680 PMCID: PMC3487726 DOI: 10.1371/journal.pone.0049358] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Accepted: 10/08/2012] [Indexed: 12/31/2022] Open
Abstract
LINE-1 (abbreviated L1) is a major class of retroelements in humans and mice. If unrestricted, retroelements accumulate in the cytoplasm and insert their DNA into the host genome, with the potential to cause autoimmune disease and cancer. Retroviruses and other retroelements are inhibited by proteins of the APOBEC family, of which activation-induced cytidine deaminase (AID) is a member. Although AID is mainly known for being a DNA mutator shaping the antibody repertoire in B lymphocytes, we found that AID also restricts de novo L1 integrations in B- and non-B-cell lines. It does so by decreasing the protein level of open reading frame 1 (ORF1) of both exogenous and endogenous L1. In activated B lymphocytes, AID deficiency increased L1 mRNA 1.6-fold and murine leukemia virus (MLV) mRNA 2.7-fold. In cell lines and activated B lymphocytes, AID forms cytoplasmic high-molecular-mass complexes with L1 mRNA, which may contribute to L1 restriction. Because AID-deficient activated B lymphocytes do not express ORF1 protein, we suggest that ORF1 protein expression is inhibited by additional restriction factors in these cells. The greater increase in MLV compared to L1 mRNA in AID-deficient activated B lymphocytes may indicate less strict surveillance of retrovirus.
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Affiliation(s)
- Mirjam Metzner
- Department of Microbiology and Immunology, University of California San Francisco, San Francisco, California, United States of America.
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28
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Muñoz-Lopez M, Garcia-Cañadas M, Macia A, Morell S, Garcia-Perez JL. Analysis of LINE-1 expression in human pluripotent cells. Methods Mol Biol 2012; 873:113-25. [PMID: 22528351 DOI: 10.1007/978-1-61779-794-1_7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Half of the human genome is composed of repeated DNA, and some types are mobile within our genome (transposons and retrotransposons). Despite their abundance, only a small fraction of them are currently active in our genome (Long Interspersed Element-1 (LINE-1), Alu, and SVA elements). LINE-1 or L1 elements are a family of active non-LTR retrotransposons, the ongoing mobilization of which still impacts our genome. As selfish DNA elements, L1 activity is more prominent in early human development, where new insertions would be transmitted to the progeny. Here, we describe the conventional methods aimed to determine the expression level of LINE-1 elements in pluripotent human cells.
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Affiliation(s)
- Martin Muñoz-Lopez
- Andalusian Stem Cell Bank, Consejeria de Salud Junta de Andalucia, Seville, Spain
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29
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Jeon BG, Kang EJ, Kumar BM, Maeng GH, Ock SA, Kwack DO, Park BW, Rho GJ. Comparative Analysis of Telomere Length, Telomerase and Reverse Transcriptase Activity in Human Dental Stem Cells. Cell Transplant 2011; 20:1693-705. [DOI: 10.3727/096368911x565001] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Stem cells from dental tissues have been isolated and established for tooth regenerative applications. However, basic characterization on their biological properties still needs to be investigated before employing them for effective clinical trials. In this study, we compared the telomere length, relative telomerase activity (RTA), and relative reverse transcriptase activity (RRA) as well as the surface antigen profile and mesenchymal differentiation ability in human dental papilla stem cells (DPaSCs), dental pulp stem cells (DPuSCs), and dental follicle stem cells (DFSCs) with mesenchymal stem cells (MSCs) derived from bone marrow. Dental stem cells (DSCs) were strongly positive for cell surface markers, such as CD44 and CD90. However, slightly lower expression of CD105 was observed in DPaSCs and DPuSCs compared to DFSCs and MSCs. Following specific induction, DPaSCs, DFSCs, and MSCs were successfully differentiated into adipocytes and osteocytes. However, DPuSCS, in particular, were able to differentiate into adipocytes but failed to induce into osteogenic differentiation. Further, all DSCs, MSCs, and MRC-5 fibroblasts as control were investigated for telomere length by nonradioactive chemiluminescent assay, RTA by relative-quantitative telomerase repeat amplification protocol (RQ-TRAP), and RRA by PCR-based assay. Mean telomere lengths in DPaSCs, DPuSCs, DFSCs, and MSCs was ~11 kb, and the values did not differ significantly ( p < 0.05) among the cells analyzed. RTA levels in DPaSCs were significantly ( p < 0.05) higher than in MSCs, DPuSCs, DFSCs, and MRC-5 fibroblasts and among DSCs, DFSCs showed a significantly ( p < 0.05) lower RTA. Moreover, RRA levels were significantly ( p < 0.05) higher in DPaSCs, DPuSCs, and MSCs than in DFSCs. Based on these observations, we conclude that among DSCs, DPaSCs possessed ideal characteristics on telomere length, telomerase activity and reverse transcriptase (RTase) activity, and may serve as suitable alternative candidates for regenerative medicine.
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Affiliation(s)
- Byeong-Gyun Jeon
- OBS/Theriogenology and Biotechnology, College of Veterinary Medicine, Gyeongsang National University, Jinju, Republic of Korea
| | - Eun-Ju Kang
- OBS/Theriogenology and Biotechnology, College of Veterinary Medicine, Gyeongsang National University, Jinju, Republic of Korea
| | - B. Mohana Kumar
- OBS/Theriogenology and Biotechnology, College of Veterinary Medicine, Gyeongsang National University, Jinju, Republic of Korea
| | - Geun-Ho Maeng
- OBS/Theriogenology and Biotechnology, College of Veterinary Medicine, Gyeongsang National University, Jinju, Republic of Korea
| | - Sun-A Ock
- OBS/Theriogenology and Biotechnology, College of Veterinary Medicine, Gyeongsang National University, Jinju, Republic of Korea
| | - Dae-Oh Kwack
- Department of Biology Education, College of Education, Gyeongsang National University, Jinju, Republic of Korea
| | - Bong-Wook Park
- Department of Oral & Maxillofacial Surgery, School of Medicine and Institute of Health Sciences, Gyeongsang National University, Jinju, Republic of Korea
| | - Gyu-Jin Rho
- OBS/Theriogenology and Biotechnology, College of Veterinary Medicine, Gyeongsang National University, Jinju, Republic of Korea
- Research Institute of Life Science, Gyeongsang National University, Jinju, Republic of Korea
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30
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Nelson HH, Marsit CJ, Kelsey KT. Global methylation in exposure biology and translational medical science. ENVIRONMENTAL HEALTH PERSPECTIVES 2011; 119:1528-33. [PMID: 21669556 PMCID: PMC3226501 DOI: 10.1289/ehp.1103423] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Accepted: 06/13/2011] [Indexed: 05/16/2023]
Abstract
BACKGROUND Many groups are actively investigating how the epigenetic state relates to environmental exposures and development of disease, including cancer. There are myriad choices for capturing and measuring the epigenetic state of a tissue, ranging from assessing the total methyl-CpG content to array-based platforms that simultaneously probe hundreds of thousands of CpG loci. There is an emerging literature that uses CpG methylation at repetitive sequences, including LINE-1 (long interspersed nuclear element-1) elements, to capture the epigenomic state. OBJECTIVES We explored the complexity of using CpG methylation at repetitive sequences in epidemiology and translational medical research and suggest needed avenues of research to clarify its meaning and utility. CONCLUSIONS Among the most urgent avenues of research is the need for prospective studies to eliminate the possibilities of reverse causality, and development of new LINE-1 assays that capture both class of LINE-1 element and copy number.
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Affiliation(s)
- Heather H Nelson
- Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA.
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31
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Wissing S, Muñoz-Lopez M, Macia A, Yang Z, Montano M, Collins W, Garcia-Perez JL, Moran JV, Greene WC. Reprogramming somatic cells into iPS cells activates LINE-1 retroelement mobility. Hum Mol Genet 2011; 21:208-18. [PMID: 21989055 DOI: 10.1093/hmg/ddr455] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Long interspersed element-1 (LINE-1 or L1) retrotransposons account for nearly 17% of human genomic DNA and represent a major evolutionary force that has reshaped the structure and function of the human genome. However, questions remain concerning both the frequency and the developmental timing of L1 retrotransposition in vivo and whether the mobility of these retroelements commonly results in insertional and post-insertional mechanisms of genomic injury. Cells exhibiting high rates of L1 retrotransposition might be especially at risk for such injury. We assessed L1 mRNA expression and L1 retrotransposition in two biologically relevant cell types, human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs), as well as in control parental human dermal fibroblasts (HDFs). Full-length L1 mRNA and the L1 open reading frame 1-encoded protein (ORF1p) were readily detected in hESCs and iPSCs, but not in HDFs. Sequencing analysis proved the expression of human-specific L1 element mRNAs in iPSCs. Bisulfite sequencing revealed that the increased L1 expression observed in iPSCs correlates with an overall decrease in CpG methylation in the L1 promoter region. Finally, retrotransposition of an engineered human L1 element was ~10-fold more efficient in iPSCs than in parental HDFs. These findings indicate that somatic cell reprogramming is associated with marked increases in L1 expression and perhaps increases in endogenous L1 retrotransposition, which could potentially impact the genomic integrity of the resultant iPSCs.
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Affiliation(s)
- Silke Wissing
- Gladstone Institute of Virology and Immunology, University of California, San Francisco, CA, USA
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Yabuta Y, Ohta H, Abe T, Kurimoto K, Chuma S, Saitou M. TDRD5 is required for retrotransposon silencing, chromatoid body assembly, and spermiogenesis in mice. ACTA ACUST UNITED AC 2011; 192:781-95. [PMID: 21383078 PMCID: PMC3051809 DOI: 10.1083/jcb.201009043] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Tdrd5-deficient mice develop a functional haploid genome despite spermiogenesis arrest at the round spermatid stage. The Tudor domain–containing proteins (TDRDs) are an evolutionarily conserved family of proteins involved in germ cell development. We show here that in mice, TDRD5 is a novel component of the intermitochondrial cements (IMCs) and the chromatoid bodies (CBs), which are cytoplasmic ribonucleoprotein granules involved in RNA processing for spermatogenesis. Tdrd5-deficient males are sterile because of spermiogenic arrest at the round spermatid stage, with occasional failure in meiotic prophase. Without TDRD5, IMCs and CBs are disorganized, with mislocalization of their key components, including TDRD1/6/7/9 and MIWI/MILI/MIWI2. In addition, Tdrd5-deficient germ cells fail to repress LINE-1 retrotransposons with DNA-demethylated promoters. Cyclic adenosine monophosphate response element modulator (CREM) and TRF2, key transcription factors for spermiogenesis, are expressed in Tdrd5-deficient round spermatids, but their targets, including Prm1/Prm2/Tnp1, are severely down-regulated, which indicates the importance of IMC/CB-mediated regulation for postmeiotic gene expression. Strikingly, Tdrd5-deficient round spermatids injected into oocytes contribute to fertile offspring, demonstrating that acquisition of a functional haploid genome may be uncoupled from TDRD5 function.
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Affiliation(s)
- Yukihiro Yabuta
- Department of Anatomy and Cell Biology, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
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Hedges DJ, Belancio VP. Restless genomes humans as a model organism for understanding host-retrotransposable element dynamics. ADVANCES IN GENETICS 2011; 73:219-62. [PMID: 21310298 DOI: 10.1016/b978-0-12-380860-8.00006-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Since their initial discovery in maize, there have been various attempts to categorize the relationship between transposable elements (TEs) and their host organisms. These have ranged from TEs being selfish parasites to their role as essential, functional components of organismal biology. Research over the past several decades has, in many respects, only served to complicate the issue even further. On the one hand, investigators have amassed substantial evidence concerning the negative effects that TE-mutagenic activity can have on host genomes and organismal fitness. On the other hand, we find an increasing number of examples, across several taxa, of TEs being incorporated into functional biological roles for their host organism. Some 45% of our own genomes are comprised of TE copies. While many of these copies are dormant, having lost their ability to mobilize, several lineages continue to actively proliferate in modern human populations. With its complement of ancestral and active TEs, the human genome exhibits key aspects of the host-TE dynamic that has played out since early on in organismal evolution. In this review, we examine what insights the particularly well-characterized human system can provide regarding the nature of the host-TE interaction.
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Affiliation(s)
- Dale J Hedges
- Hussman Institute for Human Genomics, Dr. John T. Macdonald Foundation Department of Human Genetics, Miller School of Medicine, University of Miami, Miami, Florida, USA
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Wang XF, Jin X, Wang X, Liu J, Feng J, Yang Q, Mu W, Shi X, Lu Z. Effects of L1-ORF2 fragments on green fluorescent protein gene expression. Genet Mol Biol 2009; 32:688-96. [PMID: 21637438 PMCID: PMC3036906 DOI: 10.1590/s1415-47572009005000068] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2009] [Accepted: 05/15/2009] [Indexed: 11/22/2022] Open
Abstract
The retrotransposon known as long interspersed nuclear element-1 (L1) is 6 kb long, although most L1s in mammalian and other eukaryotic cells are truncated. L1 contains two open reading frames, ORF1 and ORF2, that code for an RNA-binding protein and a protein with endonuclease and reverse transcriptase activities, respectively. In this work, we examined the effects of full length L1-ORF2 and ORF2 fragments on green fluorescent protein gene (GFP) expression when inserted into the pEGFP-C1 vector downstream of GFP. All of the ORF2 fragments in sense orientation inhibited GFP expression more than when in antisense orientation, which suggests that small ORF2 fragments contribute to the distinct inhibitory effects of this ORF on gene expression. These results provide the first evidence that different 280-bp fragments have distinct effects on the termination of gene transcription, and that when inserted in the antisense direction, fragment 280-9 (the 3' end fragment of ORF2) induces premature termination of transcription that is consistent with the effect of ORF2.
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Affiliation(s)
- Xiu-Fang Wang
- Hebei Key Lab of Laboratory Animal, Department of Genetics, Hebei Medical University, Shijiazhuang, Hebei Province China
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Reuter M, Chuma S, Tanaka T, Franz T, Stark A, Pillai RS. Loss of the Mili-interacting Tudor domain-containing protein-1 activates transposons and alters the Mili-associated small RNA profile. Nat Struct Mol Biol 2009; 16:639-46. [PMID: 19465913 DOI: 10.1038/nsmb.1615] [Citation(s) in RCA: 210] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2008] [Accepted: 05/06/2009] [Indexed: 12/18/2022]
Abstract
Piwi proteins and their associated Piwi-interacting RNAs (piRNAs) are implicated in transposon silencing in the mouse germ line. There is currently little information on additional proteins in the murine Piwi complex and how they might regulate the entry of transcripts that accumulate as piRNAs in the Piwi ribonucleoprotein (piRNP). We isolated Mili-containing complexes from adult mouse testes and identified Tudor domain-containing protein-1 (Tdrd1) as a factor specifically associated with the Mili piRNP throughout spermatogenesis. Complex formation is promoted by the recognition of symmetrically dimethylated arginines at the N terminus of Mili by the tudor domains of Tdrd1. Similar to a Mili mutant, mice lacking Tdrd1 show derepression of L1 transposons accompanied by a loss of DNA methylation at their regulatory elements and delocalization of Miwi2 from the nucleus to the cytoplasm. Finally, we show that Mili piRNPs devoid of Tdrd1 accept the entry of abundant cellular transcripts into the piRNA pathway and accumulate piRNAs with a profile that is drastically different from that of the wild type. Our data suggest that Tdrd1 ensures the entry of correct transcripts into the normal piRNA pool.
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Affiliation(s)
- Michael Reuter
- European Molecular Biology Laboratory, Grenoble Outstation, France
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Landriscina M, Bagalà C, Piscazzi A, Schinzari G, Quirino M, Fabiano A, Bianchetti S, Cassano A, Sica G, Barone C. Nevirapine restores androgen signaling in hormone-refractory human prostate carcinoma cells both in vitro and in vivo. Prostate 2009; 69:744-54. [PMID: 19152342 DOI: 10.1002/pros.20923] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
BACKGROUND Prostate carcinomas are androgen-dependent neoplasms which progress toward a hormone-independent phenotype during hormone-deprivation therapy. We evaluated nevirapine, a reverse transcriptase inhibitor, as a new treatment in hormone-refractory prostate carcinoma cells with the aim of restoring the androgen-dependency of tumor cells, the rationale being that endogenous reverse transcriptase is up-regulated in transformed cells and reverse transcriptase inhibitors exert a differentiating activity in human tumors. METHODS AND RESULTS Nevirapine induced extensive reprogramming of gene expression in vitro with up-regulation of genes that might be silenced during prostate tumor progression (i.e., K18, PSA and androgen receptor) and down-regulation of genes involved in the progression toward an androgen-independent phenotype (i.e., K5, EGFR1, EGF and VEGF-A). Furthermore, nevirapine down-regulated the growth of prostate carcinoma xenografts in athymic mice and induced a differentiated phenotype in vivo with increased K18 expression. Interestingly, the drug restored androgen signaling by enhancing the ability of tumor cells to respond to dihydrotestosterone stimulation and to the antiproliferative activity of the androgen receptor blocker bicalutamide. Finally, nevirapine pretreatment increased the susceptibility of tumor cells to docetaxel, by enhancing their ability to undergo apoptosis. CONCLUSIONS These data suggest that nevirapine may be clinically tested in human hormone-refractory prostate carcinoma to restore the susceptibility to androgen deprivation therapy or to docetaxel.
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Affiliation(s)
- Matteo Landriscina
- Clinical Oncology Unit, Department of Medical Sciences, University of Foggia, Viale Pinto, Foggia, Italy
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38
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Stefanidis K, Loutradis D, Vassiliou LV, Anastasiadou V, Kiapekou E, Nikas V, Patris G, Vlachos G, Rodolakis A, Antsaklis A. Nevirapine induces growth arrest and premature senescence in human cervical carcinoma cells. Gynecol Oncol 2008; 111:344-9. [DOI: 10.1016/j.ygyno.2008.08.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2008] [Revised: 07/25/2008] [Accepted: 08/01/2008] [Indexed: 10/21/2022]
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Soper SF, van der Heijden GW, Hardiman TC, Goodheart M, Martin SL, de Boer P, Bortvin A. Mouse maelstrom, a component of nuage, is essential for spermatogenesis and transposon repression in meiosis. Dev Cell 2008; 15:285-97. [PMID: 18694567 PMCID: PMC2546488 DOI: 10.1016/j.devcel.2008.05.015] [Citation(s) in RCA: 257] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2008] [Revised: 05/19/2008] [Accepted: 05/30/2008] [Indexed: 11/20/2022]
Abstract
Tight control of transposon activity is essential for the integrity of the germline. Recently, a germ-cell-specific organelle, nuage, was proposed to play a role in transposon repression. To test this hypothesis, we disrupted a murine homolog of a Drosophila nuage protein Maelstrom. Effects on male meiotic chromosome synapsis and derepression of transposable elements (TEs) were observed. In the adult Mael(-/-) testes, LINE-1 (L1) derepression occurred at the onset of meiosis. As a result, Mael(-/-) spermatocytes were flooded with L1 ribonucleoproteins (RNPs) that accumulated in large cytoplasmic enclaves and nuclei. Mael(-/-) spermatocytes with nuclear L1 RNPs exhibited massive DNA damage and severe chromosome asynapsis even in the absence of SPO11-generated meiotic double-strand breaks. This study demonstrates that MAEL, a nuage component, is indispensable for the silencing of TEs and identifies the initiation of meiosis as an important step in TE control in the male germline.
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Affiliation(s)
- Sarah F.C. Soper
- Biology Department, Johns Hopkins University, Baltimore, MD 21218, USA
| | | | - Tara C. Hardiman
- Department of Embryology, Carnegie Institution of Washington, Baltimore, MD 21218, USA
| | - Mary Goodheart
- Howard Hughes Medical Institute, Whitehead Institute, and Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142, USA
| | - Sandra L. Martin
- Department of Cell and Developmental Biology and Molecular Biology Program, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Peter de Boer
- Department of Obstetrics and Gynaecology, Radboud University Nijmegen Medical Centre, 6500 HB Nijmegen, The Netherlands
| | - Alex Bortvin
- Department of Embryology, Carnegie Institution of Washington, Baltimore, MD 21218, USA
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40
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Bonaccorsi I, Altieri F, Sciamanna I, Oricchio E, Grillo C, Contartese G, Galati EM. Endogenous reverse transcriptase as a mediator of ursolic acid's anti-proliferative and differentiating effects in human cancer cell lines. Cancer Lett 2008; 263:130-9. [PMID: 18282657 DOI: 10.1016/j.canlet.2007.12.026] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2007] [Revised: 12/07/2007] [Accepted: 12/16/2007] [Indexed: 11/16/2022]
Abstract
Ursolic acid (UA) is a pentacyclic triterpenoid compound that is widely distributed in the plant kingdom and has a broad range of biological effects. Here, we examined the effects of UA on the proliferation and differentiation of human tumor cell lines from melanoma (A375), glioblastoma (U87) and thyroid anaplastic carcinoma (ARO), and on the proliferation of a non-transformed human fibroblast cell line (WI-38). The results show that UA inhibits tumor cell proliferation in a dose- and time-dependent manner. Consistent with this finding, UA treatment promotes differentiation of all of the analyzed tumor cell lines. Interestingly, we found that UA inhibits the endogenous reverse transcriptase (RT) activity in tumor cells, which has recently been shown to be involved in the control of proliferation and differentiation of neoplastic cells. Considering these findings, we suggest that the observed anti-proliferative and differentiating effects of UA may be related to this target.
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Affiliation(s)
- Irene Bonaccorsi
- Pharmaco-Biological Department, School of Pharmacy, University of Messina, Vill. SS. Annunziata, 98168 Messina, Italy
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Garcia-Perez JL, Marchetto MCN, Muotri AR, Coufal NG, Gage FH, O'Shea KS, Moran JV. LINE-1 retrotransposition in human embryonic stem cells. Hum Mol Genet 2007; 16:1569-77. [PMID: 17468180 DOI: 10.1093/hmg/ddm105] [Citation(s) in RCA: 179] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
LINE-1 elements comprise approximately 17% of human DNA and their mobility continues to impact genome evolution. However, little is known about the types of non-transformed cells that can support LINE-1 retrotransposition. Here, we show that human embryonic stem cells express endogenous LINE-1 elements and can accommodate LINE-1 retrotransposition in vitro. The resultant retrotransposition events can occur into genes and can result in the concomitant deletion of genomic DNA at the target site. Thus, these data suggest that LINE-1 retrotransposition events may occur during early stages of human development.
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Affiliation(s)
- Jose L Garcia-Perez
- Departments of Human Genetics and Internal Medicine, University of Michigan Medical School, 1241 E. Catherine Street, Ann Arbor, MI 48109, USA
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Belancio VP, Whelton M, Deininger P. Requirements for polyadenylation at the 3' end of LINE-1 elements. Gene 2006; 390:98-107. [PMID: 17023124 DOI: 10.1016/j.gene.2006.07.029] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2006] [Revised: 07/13/2006] [Accepted: 07/18/2006] [Indexed: 10/24/2022]
Abstract
LINE-1 (L1) is the only active, autonomous, non-LTR, human retroelement. There are about 5x10(5) L1 copies in the human genome, the majority of which are truncated at their 5' ends. Both truncated and full-length L1 insertions contain a polyadenylation (polyA) signal at their 3' ends. A typical polyA site consists of the three main cis-acting elements: a conserved hexamer, cleavage site, and a GU-rich downstream region. A newly inserted L1 copy contains the conserved AATAAA hexamer at the end of its sequence. However, the GU-rich downstream region has to be provided by the neighboring genomic sequences and therefore it would vary for every L1 copy. Using northern blot analysis of transiently transfected L1 expression vectors we demonstrate that L1 element contain sequence that allow efficient polyadenylation at the L1 3' end upon retrotransposition into a new genomic location independent of the base composition downstream of the insertion site. The strategy of polyadenylation at the 3' end of L1 parallels the approach the element employs at its 5'UTR by having an unusual internal polymerase II promoter, making new insertions less dependent on the properties of the flanking sequences at the new locus.
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Affiliation(s)
- Victoria P Belancio
- Tulane Cancer Center, SL66, and Department of Epidemiology, Tulane University Health Sciences Center, 1430 Tulane Ave., New Orleans, LA 70112, United States
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Lucchinetti E, Feng J, Silva RD, Tolstonog GV, Schaub MC, Schumann GG, Zaugg M. Inhibition of LINE-1 expression in the heart decreases ischemic damage by activation of Akt/PKB signaling. Physiol Genomics 2006; 25:314-24. [PMID: 16418318 DOI: 10.1152/physiolgenomics.00251.2005] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Microarray analyses indicate that ischemic and pharmacological preconditioning suppress overexpression of the non-long terminal repeat retrotransposon long interspersed nuclear element 1 (LINE-1, L1) after ischemia-reperfusion in the rat heart. We tested whether L1 overexpression is mechanistically involved in postischemic myocardial damage. Isolated, perfused rat hearts were treated with antisense or scrambled oligonucleotides (ODNs) against L1 for 60 min and exposed to 40 min of ischemia followed by 60 min of reperfusion. Functional recovery and infarct size were measured. Effective nuclear uptake was determined by FITC-labeled ODNs, and downregulation of L1 transcription was confirmed by RT-PCR. Immunoblot analysis was used to assess changes in expression levels of the L1-encoded proteins ORF1p and ORF2p. Immunohistochemistry was performed to localize ORF1/2 proteins in cardiac tissue. Effects of ODNs on prosurvival protein kinase B (Akt/PKB) expression and activity were also determined. Antisense ODNs against L1 prevented L1 burst after ischemia-reperfusion. Inhibition of L1 increased Akt/PKBbeta expression, enhanced phosphorylation of PKB at serine 473, and markedly improved postischemic functional recovery and decreased infarct size. Antisense ODN-mediated protection was abolished by LY-294002, confirming the involvement of the Akt/PKB survival pathway. ORF1p and ORF2p were found to be expressed in rat heart. ORF1p showed a predominantly nuclear localization in cardiomyocytes, whereas ORF2p was exclusively present in endothelial cells. ORF1p levels increased in response to ischemia, which was reversed by antisense ODN treatment. No significant changes in ORF2p were noted. Our results demonstrate that L1 suppression favorably affects postischemic outcome in the heart. Modifying transcriptional activity of L1 may represent a novel anti-ischemic therapeutic strategy.
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Affiliation(s)
- Eliana Lucchinetti
- Cardiovascular Anesthesia Research Laboratory, Institute of Anesthesiology, University Hospital Zurich, Switzerland
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Basame S, Wai-lun Li P, Howard G, Branciforte D, Keller D, Martin SL. Spatial assembly and RNA binding stoichiometry of a LINE-1 protein essential for retrotransposition. J Mol Biol 2006; 357:351-7. [PMID: 16434051 DOI: 10.1016/j.jmb.2005.12.063] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2005] [Revised: 12/13/2005] [Accepted: 12/18/2005] [Indexed: 11/16/2022]
Abstract
LINE-1, or L1, is a highly successful retrotransposon in mammals, comprising 17% and 19% of the human and mouse genomes, respectively. L1 retrotransposition and hence amplification requires the protein products of its two open reading frames, ORF1 and ORF2. The sequence of the ORF1 protein (ORF1p) is not related to any protein with known function. ORF1p has RNA binding and nucleic acid chaperone activities that are both required for retrotransposition. Earlier studies have shown that ORF1p forms a homotrimer with an asymmetric dumbbell shape, in which a rod separates a large end from a small end. Here, we determine the topological arrangement of monomers within the homotrimer by comparing atomic force microscopy (AFM) images of the full ORF1p with those of truncations containing just the N or C-terminal regions. In addition, AFM images of ORF1p bound to RNA at high protein/RNA molar ratios show that ORF1p can form tightly packed clusters on RNA, with binding occurring at the C-terminal domain. The number of bound ORF1p trimers increases with increasing length of the RNA, revealing that the binding site size is about 50 nt, a value confirmed by nitrocellulose filter binding under stoichiometric conditions. These results are consistent with a role for ORF1p during L1 retrotransposition that includes both coating the RNA and acting as a nucleic acid chaperone. Furthermore, these in vitro L1 ribonucleoprotein particles provide insight into the structure of the L1 retrotransposition intermediate.
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Affiliation(s)
- Solomon Basame
- Molecular Machines Laboratory, Department of Chemistry, University of New Mexico, Albuquerque, NM 87131, USA
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Kulpa DA, Moran JV. Ribonucleoprotein particle formation is necessary but not sufficient for LINE-1 retrotransposition. Hum Mol Genet 2005; 14:3237-48. [PMID: 16183655 DOI: 10.1093/hmg/ddi354] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Long interspersed elements (LINE-1s or L1s) are abundant non-LTR retrotransposons that mobilize through an RNA intermediate by target site primed reverse transcription. The L1-encoded proteins (ORF1p and ORF2p) preferentially associate with their encoding transcript to form a ribonucleoprotein particle (RNP), which is a proposed retrotransposition intermediate. Here, we have used epitope tagging to discriminate the proteins encoded by engineered L1s from those encoded by endogenously expressed L1s. We demonstrate that an L1 containing an epitope tag at the carboxyl terminus of ORF1p remains retrotransposition-competent and that tagged ORF1p and its encoding RNA localize to cytoplasmic RNPs. We also identified two classes of ORF1p mutants, one that severely decreased RNP formation and blocked retrotransposition, and another that allows RNP formation but reduces retrotransposition by 100-fold. Thus, these data indicate that RNP formation is important but not sufficient for L1 retrotransposition and suggest that ORF1p also may function at downstream steps in the L1 retrotransposition pathway.
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Affiliation(s)
- Deanna A Kulpa
- Department of Human Genetics, University of Michigan Medical School, Ann Arbor, MI 48109-0618, USA
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Sinibaldi-Vallebona P, Lavia P, Garaci E, Spadafora C. A role for endogenous reverse transcriptase in tumorigenesis and as a target in differentiating cancer therapy. Genes Chromosomes Cancer 2005; 45:1-10. [PMID: 16175572 DOI: 10.1002/gcc.20266] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
An unexpected result emerging from completion of the genome sequencing project is that a large portion of mammalian genomes is constituted by retrotransposons. A large body of published data supports the conclusion that retrotransposons are biologically active elements and indicates that retrotransposition is an ongoing process in mammalian genomes. Retroelements can act as insertional mutagens altering the coding integrity of genes and, recently, have been found to also affect the expression of cellular genes at the epigenetic level: in this light, they are a potential threat in that these events can trigger the onset of several pathologies including cancer. Retroelement genes, and particularly the gene coding for reverse transcriptase (RT), are typically expressed at high levels in transformed cells and tumors. In recent work, we have found that drug-mediated inhibition of the endogenous RT activity, or silencing of expression of active retrotransposons of the LINE-1 family by RNA interference, down-regulate cell growth and induce the activation of differentiating functions in several cancer cell lines. Moreover, the inhibition of endogenous RT activity in vivo antagonizes the growth of human tumors in animal models. In this review, we discuss newly emerging concepts on the role of retrotransposons and suggest that an abnormally high level of the RT activity that they encode may contribute to the loss of control in the proliferation and differentiation programs typical of transformed cells. In this light, RT-coding elements may be regarded as promising targets in the development of novel, differentiation-inducing approaches to cancer therapy.
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Pittoggi C, Sciamanna I, Mattei E, Beraldi R, Lobascio AM, Mai A, Quaglia MG, Lorenzini R, Spadafora C. Role of endogenous reverse transcriptase in murine early embryo development. Mol Reprod Dev 2004; 66:225-36. [PMID: 14502601 DOI: 10.1002/mrd.10349] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
We report that a reverse transcriptase (RT) activity is present in early cleavage stage embryos as determined by a Polymerase chain reaction (PCR)-based detection assay. In an attempt to establish whether this activity plays a role in early embryonic development, we have blocked the endogenous RT by two independent approaches: (1) embryos were exposed to nevirapine, a highly specific nonnucleoside inhibitor of RT activity; (2) anti-RT antibody was microinjected into the nucleus of one blastomere of 2-cell embryos. When embryos were exposed to nevirapine in the developmental window between late 1-cell and 4-cell stages, development was arrested before the blastocyst stage. In contrast, development was not affected when embryos were exposed to nevirapine after the eight-cell stage. Developmental arrest was also induced when anti-RT antibody was microinjected in one blastomere of 2-cell embryos. Analysis of gene expression by RT-PCR in nevirapine-arrested 2-cell embryos revealed an extensive and specific reprogramming of gene expression, involving both developmentally regulated and constitutively expressed genes, compared to control embryos. These results support the conclusion that an endogenous RT activity is required in mouse early embryogenesis specifically between the late 1-cell and the 4-cell stage.
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Ergün S, Buschmann C, Heukeshoven J, Dammann K, Schnieders F, Lauke H, Chalajour F, Kilic N, Strätling WH, Schumann GG. Cell type-specific expression of LINE-1 open reading frames 1 and 2 in fetal and adult human tissues. J Biol Chem 2004; 279:27753-63. [PMID: 15056671 DOI: 10.1074/jbc.m312985200] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The LINE-1 (L1) family of non-long terminal repeat retrotransposons is a major force shaping mammalian genomes, and its members can alter the genome in many ways. Mutational analyses have shown that coexpression of functional proteins encoded by the two L1-specific open reading frames, ORF1 and ORF2, is an essential prerequisite for the propagation of L1 elements in the genome. However, all efforts to identify ORF2-encoded proteins have failed so far. Here, applying a novel antibody we report the presence of proteins encoded by ORF2 in a subset of cellular components of human male gonads. Immunohistochemical analyses revealed coexpression of ORF1 and ORF2 in prespermatogonia of fetal testis, in germ cells of adult testis, and in distinct somatic cell types, such as Leydig, Sertoli, and vascular endothelial cells. Coexpression of both proteins in male germ cells is necessary for the observed genomic expansion of the number of L1 elements. Peptide mass fingerprinting analysis of a approximately 130-kDa polypeptide isolated from cultured human dermal microvascular endothelial cells led to the identification of ORF2-encoded peptides. An isolated approximately 45-kDa polypeptide was shown to derive from nonfunctional copies of ORF2 coding regions. The presence of both ORF1- and ORF2-encoded proteins in vascular endothelial cells and its apparent association with certain stages of differentiation and maturation of blood vessels may have functional relevance for vasculogenesis and/or angiogenesis.
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Affiliation(s)
- Süleyman Ergün
- Institut für Anatomie, Universitätsklinikum Hamburg-Eppendorf, Germany
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Kolosha VO, Martin SL. High-affinity, non-sequence-specific RNA binding by the open reading frame 1 (ORF1) protein from long interspersed nuclear element 1 (LINE-1). J Biol Chem 2003; 278:8112-7. [PMID: 12506113 DOI: 10.1074/jbc.m210487200] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Long interspersed nuclear element 1 (LINE-1 or L1) is an interspersed repeated DNA found in mammalian genomes. L1 achieved its high copy number by retrotransposition, a process that requires the two L1-encoded proteins, ORF1p and ORF2p. The role of ORF1p in the retrotransposition cycle is incompletely understood, but it is known to bind single-stranded nucleic acids and act as a nucleic acid chaperone. This study assesses the nature and specificity of the interaction of ORF1p with RNA. Results of coimmunoprecipitation experiments demonstrate that ORF1p preferentially binds a single T1 nuclease digestion product of 38 nucleotides (nt) within the full-length mouse L1 transcript. The 38-nt fragment is localized within L1 RNA and found to be sufficient for binding by ORF1p but not necessary, because its complement is also efficiently coimmunoprecipitated, as are all sequences 38 nt or longer. Results of nitrocellulose filter-binding assays demonstrate that the binding of ORF1p to RNA does not require divalent cations but is sensitive to the concentration of monovalent cation. Both sense and antisense transcripts bind with apparent K(D)s in the low nanomolar range. The results of both types of assay unambiguously support the conclusion that purified ORF1p from mouse L1 is a high-affinity, non-sequence-specific RNA binding protein.
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Affiliation(s)
- Vladimir O Kolosha
- Department of Cellular and Structural Biology and Program in Molecular Biology, University of Colorado School of Medicine, Denver 80262, USA
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Abstract
L1 retrotransposons comprise 17% of the human genome. Although most L1s are inactive, some elements remain capable of retrotransposition. L1 elements have a long evolutionary history dating to the beginnings of eukaryotic existence. Although many aspects of their retrotransposition mechanism remain poorly understood, they likely integrate into genomic DNA by a process called target primed reverse transcription. L1s have shaped mammalian genomes through a number of mechanisms. First, they have greatly expanded the genome both by their own retrotransposition and by providing the machinery necessary for the retrotransposition of other mobile elements, such as Alus. Second, they have shuffled non-L1 sequence throughout the genome by a process termed transduction. Third, they have affected gene expression by a number of mechanisms. For instance, they occasionally insert into genes and cause disease both in humans and in mice. L1 elements have proven useful as phylogenetic markers and may find other practical applications in gene discovery following insertional mutagenesis in mice and in the delivery of therapeutic genes.
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Affiliation(s)
- E M Ostertag
- Department of Genetics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
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