1
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Berteli TS, Wang F, Navarro PA, Kohlrausch FB, Keefe DL. A pilot study of LINE-1 copy number and telomere length with aging in human sperm. J Assist Reprod Genet 2023; 40:1845-1854. [PMID: 37382785 PMCID: PMC10371944 DOI: 10.1007/s10815-023-02857-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Accepted: 06/03/2023] [Indexed: 06/30/2023] Open
Abstract
PURPOSE Unlike other cells in the body, in sperm, telomere length (TL) increases with age. TL can regulate nearby genes, and the subtelomeric region is rich in retrotransposons. We hypothesized that age-related telomere lengthening in sperm might suppress Long Interspersed Element 1 (LINE-1/L1), the only competent retrotransposon in humans. METHODS We measured L1 copy number (L1-CN) and sperm telomere length (STL) from young and older men to evaluate the relationship between age, TL and L1-CN. We also evaluated L1-CN and TL in individual sperm to determine whether these variables influence sperm morphology. STL was assayed by Multiplex quantitative polymerase chain reaction method (mmqPCR) and L1-CN by Quantitative polymerase chain reaction (qPCR). RESULTS We found that STL increased, and L1-CN decreased significantly with paternal age. STL in normal single sperm was significantly higher than in abnormal sperm. L1-CN did not differ between normal and abnormal sperm. Furthermore, morphologically normal sperm have longer telomeres than abnormal sperm. CONCLUSIONS Elongation of telomeres in the male germline could repress retrotransposition, which tends to increase with cellular aging. More studies in larger cohorts across a wide age span are needed to confirm our conclusions and explore their biological and clinical significance.
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Affiliation(s)
- Thalita S Berteli
- Department of Obstetrics and Gynecology, Langone Medical Center, New York University, 462, 1st Avenue, New York, NY, 10016, USA.
- Human Reproduction Division, Department of Gynecology and Obstetrics, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
| | - Fang Wang
- Department of Obstetrics and Gynecology, Langone Medical Center, New York University, 462, 1st Avenue, New York, NY, 10016, USA
| | - Paula A Navarro
- Human Reproduction Division, Department of Gynecology and Obstetrics, Ribeirao Preto Medical School, University of Sao Paulo, Ribeirao Preto, SP, Brazil
| | - Fabiana B Kohlrausch
- Department of Obstetrics and Gynecology, Langone Medical Center, New York University, 462, 1st Avenue, New York, NY, 10016, USA
- Human Genetics Laboratory, Fluminense Federal University, Niteroi, RJ, Brazil
| | - David L Keefe
- Department of Obstetrics and Gynecology, Langone Medical Center, New York University, 462, 1st Avenue, New York, NY, 10016, USA
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2
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Jedlička P, Tokan V, Kejnovská I, Hobza R, Kejnovský E. Telomeric retrotransposons show propensity to form G-quadruplexes in various eukaryotic species. Mob DNA 2023; 14:3. [PMID: 37038191 PMCID: PMC10088271 DOI: 10.1186/s13100-023-00291-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Accepted: 03/07/2023] [Indexed: 04/12/2023] Open
Abstract
BACKGROUND Canonical telomeres (telomerase-synthetised) are readily forming G-quadruplexes (G4) on the G-rich strand. However, there are examples of non-canonical telomeres among eukaryotes where telomeric tandem repeats are invaded by specific retrotransposons. Drosophila melanogaster represents an extreme example with telomeres composed solely by three retrotransposons-Het-A, TAHRE and TART (HTT). Even though non-canonical telomeres often show strand biased G-distribution, the evidence for the G4-forming potential is limited. RESULTS Using circular dichroism spectroscopy and UV absorption melting assay we have verified in vitro G4-formation in the HTT elements of D. melanogaster. Namely 3 in Het-A, 8 in TART and 2 in TAHRE. All the G4s are asymmetrically distributed as in canonical telomeres. Bioinformatic analysis showed that asymmetric distribution of potential quadruplex sequences (PQS) is common in telomeric retrotransposons in other Drosophila species. Most of the PQS are located in the gag gene where PQS density correlates with higher DNA sequence conservation and codon selection favoring G4-forming potential. The importance of G4s in non-canonical telomeres is further supported by analysis of telomere-associated retrotransposons from various eukaryotic species including green algae, Diplomonadida, fungi, insects and vertebrates. Virtually all analyzed telomere-associated retrotransposons contained PQS, frequently with asymmetric strand distribution. Comparison with non-telomeric elements showed independent selection of PQS-rich elements from four distinct LINE clades. CONCLUSION Our findings of strand-biased G4-forming motifs in telomere-associated retrotransposons from various eukaryotic species support the G4-formation as one of the prerequisites for the recruitment of specific retrotransposons to chromosome ends and call for further experimental studies.
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Affiliation(s)
- Pavel Jedlička
- Department of Plant Developmental Genetics, Institute of Biophysics of the Czech Academy of Sciences, Kralovopolska 135, 61200, Brno, Czech Republic
| | - Viktor Tokan
- Department of Plant Developmental Genetics, Institute of Biophysics of the Czech Academy of Sciences, Kralovopolska 135, 61200, Brno, Czech Republic.
| | - Iva Kejnovská
- Department of Biophysics of Nucleic Acids, Institute of Biophysics of the Czech Academy of Sciences, Kralovopolska 135, 61200, Brno, Czech Republic
| | - Roman Hobza
- Department of Plant Developmental Genetics, Institute of Biophysics of the Czech Academy of Sciences, Kralovopolska 135, 61200, Brno, Czech Republic
| | - Eduard Kejnovský
- Department of Plant Developmental Genetics, Institute of Biophysics of the Czech Academy of Sciences, Kralovopolska 135, 61200, Brno, Czech Republic.
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3
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Takeuchi C, Yokoshi M, Kondo S, Shibuya A, Saito K, Fukaya T, Siomi H, Iwasaki Y. Mod(mdg4) variants repress telomeric retrotransposon HeT-A by blocking subtelomeric enhancers. Nucleic Acids Res 2022; 50:11580-11599. [PMID: 36373634 PMCID: PMC9723646 DOI: 10.1093/nar/gkac1034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 10/17/2022] [Accepted: 10/22/2022] [Indexed: 11/16/2022] Open
Abstract
Telomeres in Drosophila are composed of sequential non-LTR retrotransposons HeT-A, TART and TAHRE. Although they are repressed by the PIWI-piRNA pathway or heterochromatin in the germline, the regulation of these retrotransposons in somatic cells is poorly understood. In this study, we demonstrated that specific splice variants of Mod(mdg4) repress HeT-A by blocking subtelomeric enhancers in ovarian somatic cells. Among the variants, we found that the Mod(mdg4)-N variant represses HeT-A expression the most efficiently. Subtelomeric sequences bound by Mod(mdg4)-N block enhancer activity within subtelomeric TAS-R repeats. This enhancer-blocking activity is increased by the tandem association of Mod(mdg4)-N to repetitive subtelomeric sequences. In addition, the association of Mod(mdg4)-N couples with the recruitment of RNA polymerase II to the subtelomeres, which reinforces its enhancer-blocking function. Our findings provide novel insights into how telomeric retrotransposons are regulated by the specific variants of insulator proteins associated with subtelomeric sequences.
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Affiliation(s)
- Chikara Takeuchi
- Department of Molecular Biology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Moe Yokoshi
- Laboratory of Transcription Dynamics, Research Center for Biological Visualization, Institute for Quantitative Biosciences, The University of Tokyo, Tokyo 113-0032, Japan
| | - Shu Kondo
- Department of Chromosome Science, National Institute of Genetics, Research Organization of Information and Systems (ROIS), Shizuoka 411-8540, Japan
| | - Aoi Shibuya
- Department of Molecular Biology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Kuniaki Saito
- Department of Chromosome Science, National Institute of Genetics, Research Organization of Information and Systems (ROIS), Shizuoka 411-8540, Japan
| | - Takashi Fukaya
- Laboratory of Transcription Dynamics, Research Center for Biological Visualization, Institute for Quantitative Biosciences, The University of Tokyo, Tokyo 113-0032, Japan,Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 113-0032, Japan
| | | | - Yuka W Iwasaki
- To whom correspondence should be addressed. Tel: +81 3 5363 3529; Fax: +81 3 5363 3266;
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4
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Gržan T, Despot-Slade E, Meštrović N, Plohl M, Mravinac B. CenH3 distribution reveals extended centromeres in the model beetle Tribolium castaneum. PLoS Genet 2020; 16:e1009115. [PMID: 33125365 PMCID: PMC7598501 DOI: 10.1371/journal.pgen.1009115] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 09/14/2020] [Indexed: 11/18/2022] Open
Abstract
Centromeres are chromosomal domains essential for kinetochore assembly and correct chromosome segregation. Inconsistent in their underlying DNA sequences, centromeres are defined epigenetically by the presence of the centromere-specific histone H3 variant CenH3. Most of the analyzed eukaryotes have monocentric chromosomes in which CenH3 proteins deposit into a single, primary constriction visible at metaphase chromosomes. Contrary to monocentrics, evolutionary sporadic holocentric chromosomes lack a primary constriction and have kinetochore activity distributed along the entire chromosome length. In this work, we identified cCENH3 protein, the centromeric H3 histone of the coleopteran model beetle Tribolium castaneum. By ChIP-seq analysis we disclosed that cCENH3 chromatin assembles upon a repertoire of repetitive DNAs. cCENH3 in situ mapping revealed unusually elongated T. castaneum centromeres that comprise approximately 40% of the chromosome length. Being the longest insect regional centromeres evidenced so far, T. castaneum centromeres are characterized by metapolycentric structure composed of several individual cCENH3-containing domains. We suggest that the model beetle T. castaneum with its metapolycentromeres could represent an excellent model for further studies of non-canonical centromeres in insects.
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Affiliation(s)
- Tena Gržan
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | | | - Nevenka Meštrović
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
| | - Miroslav Plohl
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
- * E-mail: (MP); (BM)
| | - Brankica Mravinac
- Division of Molecular Biology, Ruđer Bošković Institute, Zagreb, Croatia
- * E-mail: (MP); (BM)
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5
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Bryan TM. G-Quadruplexes at Telomeres: Friend or Foe? Molecules 2020; 25:molecules25163686. [PMID: 32823549 PMCID: PMC7464828 DOI: 10.3390/molecules25163686] [Citation(s) in RCA: 86] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 08/09/2020] [Accepted: 08/10/2020] [Indexed: 12/28/2022] Open
Abstract
Telomeres are DNA-protein complexes that cap and protect the ends of linear chromosomes. In almost all species, telomeric DNA has a G/C strand bias, and the short tandem repeats of the G-rich strand have the capacity to form into secondary structures in vitro, such as four-stranded G-quadruplexes. This has long prompted speculation that G-quadruplexes play a positive role in telomere biology, resulting in selection for G-rich tandem telomere repeats during evolution. There is some evidence that G-quadruplexes at telomeres may play a protective capping role, at least in yeast, and that they may positively affect telomere maintenance by either the enzyme telomerase or by recombination-based mechanisms. On the other hand, G-quadruplex formation in telomeric DNA, as elsewhere in the genome, can form an impediment to DNA replication and a source of genome instability. This review summarizes recent evidence for the in vivo existence of G-quadruplexes at telomeres, with a focus on human telomeres, and highlights some of the many unanswered questions regarding the location, form, and functions of these structures.
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Affiliation(s)
- Tracy M Bryan
- Children's Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, NSW 2145, Australia
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6
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Essential factors involved in the precise targeting and insertion of telomere-specific non-LTR retrotransposon, SART1Bm. Sci Rep 2020; 10:8963. [PMID: 32488018 PMCID: PMC7265360 DOI: 10.1038/s41598-020-65925-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Accepted: 05/04/2020] [Indexed: 11/09/2022] Open
Abstract
Telomere length maintenance is essential for most eukaryotes to ensure genome stability and integrity. A non-long terminal repeat (LTR) retrotransposon, SART1Bm, targets telomeric repeats (TTAGG)n of the silkworm Bombyx mori and is presumably involved in telomere length maintenance. However, how many telomeric repeats are required for its retrotransposition and how reverse transcription is initiated at the target site are not well understood. Here, using an ex vivo and trans-in vivo recombinant baculovirus retrotransposition system, we demonstrated that SART1Bm requires at least three (TTAGG) telomeric repeats and a longer poly(A) tail for its accurate retrotransposition. We found that SART1Bm retrotransposed only in the third (TTAGG) tract of three repeats and that the A residue of the (TTAGG) unit was essential for its retrotransposition. Interestingly, SART1Bm also retrotransposed into telomeric repeats of other species, such as human (TTAGGG)n repeats, albeit with low retrotransposition efficiency. We further showed that the reverse transcription of SART1Bm occurred inaccurately at the internal site of the 3' untranslated region (UTR) when using a short poly(A) tail but at the accurate site when using a longer poly(A) tail. These findings promote our understanding of the general mechanisms of site-specific retrotransposition and aid the development of a site-specific gene knock-in tool.
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7
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Markova DN, Christensen SM, Betrán E. Telomere-Specialized Retroelements in Drosophila: Adaptive Symbionts of the Genome, Neutral, or in Conflict? Bioessays 2019; 42:e1900154. [PMID: 31815300 DOI: 10.1002/bies.201900154] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 10/31/2019] [Indexed: 12/17/2022]
Abstract
Linear chromosomes shorten in every round of replication. In Drosophila, telomere-specialized long interspersed retrotransposable elements (LINEs) belonging to the jockey clade offset this shortening by forming head-to-tail arrays at Drosophila telomere ends. As such, these telomeric LINEs have been considered adaptive symbionts of the genome, protecting it from premature decay, particularly as Drosophila lacks a conventional telomerase holoenzyme. However, as reviewed here, recent work reveals a high degree of variation and turnover in the telomere-specialized LINE lineages across Drosophila. There appears to be no absolute requirement for LINE activity to maintain telomeres in flies, hence the suggestion that the telomere-specialized LINEs may instead be neutral or in conflict with the host, rather than adaptive.
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Affiliation(s)
- Dragomira N Markova
- Department of Biology, University of Texas at Arlington, Arlington, TX, 76019, USA
| | - Shawn M Christensen
- Department of Biology, University of Texas at Arlington, Arlington, TX, 76019, USA
| | - Esther Betrán
- Department of Biology, University of Texas at Arlington, Arlington, TX, 76019, USA
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8
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Saint-Leandre B, Nguyen SC, Levine MT. Diversification and collapse of a telomere elongation mechanism. Genome Res 2019; 29:920-931. [PMID: 31138619 PMCID: PMC6581046 DOI: 10.1101/gr.245001.118] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Accepted: 05/14/2019] [Indexed: 12/18/2022]
Abstract
In most eukaryotes, telomerase counteracts chromosome erosion by adding repetitive sequence to terminal ends. Drosophila melanogaster instead relies on specialized retrotransposons that insert exclusively at telomeres. This exchange of goods between host and mobile element-wherein the mobile element provides an essential genome service and the host provides a hospitable niche for mobile element propagation-has been called a "genomic symbiosis." However, these telomere-specialized, jockey family retrotransposons may actually evolve to "selfishly" overreplicate in the genomes that they ostensibly serve. Under this model, we expect rapid diversification of telomere-specialized retrotransposon lineages and, possibly, the breakdown of this ostensibly symbiotic relationship. Here we report data consistent with both predictions. Searching the raw reads of the 15-Myr-old melanogaster species group, we generated de novo jockey retrotransposon consensus sequences and used phylogenetic tree-building to delineate four distinct telomere-associated lineages. Recurrent gains, losses, and replacements account for this retrotransposon lineage diversity. In Drosophila biarmipes, telomere-specialized elements have disappeared completely. De novo assembly of long reads and cytogenetics confirmed this species-specific collapse of retrotransposon-dependent telomere elongation. Instead, telomere-restricted satellite DNA and DNA transposon fragments occupy its terminal ends. We infer that D. biarmipes relies instead on a recombination-based mechanism conserved from yeast to flies to humans. Telomeric retrotransposon diversification and disappearance suggest that persistently "selfish" machinery shapes telomere elongation across Drosophila rather than completely domesticated, symbiotic mobile elements.
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Affiliation(s)
- Bastien Saint-Leandre
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.,Epigenetics Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Son C Nguyen
- Epigenetics Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.,Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Mia T Levine
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.,Epigenetics Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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9
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Aksenova AY, Mirkin SM. At the Beginning of the End and in the Middle of the Beginning: Structure and Maintenance of Telomeric DNA Repeats and Interstitial Telomeric Sequences. Genes (Basel) 2019; 10:genes10020118. [PMID: 30764567 PMCID: PMC6410037 DOI: 10.3390/genes10020118] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2019] [Revised: 01/30/2019] [Accepted: 01/30/2019] [Indexed: 02/07/2023] Open
Abstract
Tandem DNA repeats derived from the ancestral (TTAGGG)n run were first detected at chromosome ends of the majority of living organisms, hence the name telomeric DNA repeats. Subsequently, it has become clear that telomeric motifs are also present within chromosomes, and they were suitably called interstitial telomeric sequences (ITSs). It is well known that telomeric DNA repeats play a key role in chromosome stability, preventing end-to-end fusions and precluding the recurrent DNA loss during replication. Recent data suggest that ITSs are also important genomic elements as they confer its karyotype plasticity. In fact, ITSs appeared to be among the most unstable microsatellite sequences as they are highly length polymorphic and can trigger chromosomal fragility and gross chromosomal rearrangements. Importantly, mechanisms responsible for their instability appear to be similar to the mechanisms that maintain the length of genuine telomeres. This review compares the mechanisms of maintenance and dynamic properties of telomeric repeats and ITSs and discusses the implications of these dynamics on genome stability.
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Affiliation(s)
- Anna Y Aksenova
- Laboratory of Amyloid Biology, St. Petersburg State University, 199034 St. Petersburg, Russia.
| | - Sergei M Mirkin
- Department of Biology, Tufts University, Medford, MA 02421, USA.
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10
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Morozov SY, Lezzhov AA, Lazareva EA, Erokhina TN, Solovyev AG. Potential Role of Accessory Domains in Polyproteins Encoded by Retrotransposons in Anti-viral Defense of Host Cells. Front Microbiol 2019; 9:3193. [PMID: 30687243 PMCID: PMC6338049 DOI: 10.3389/fmicb.2018.03193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Accepted: 12/10/2018] [Indexed: 11/30/2022] Open
Affiliation(s)
- Sergey Y Morozov
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.,Department of Virology, Biological Faculty, Moscow State University, Moscow, Russia
| | - Alexander A Lezzhov
- Faculty of Bioengineering and Bioinformatics, Moscow State University, Moscow, Russia
| | - Ekaterina A Lazareva
- Department of Virology, Biological Faculty, Moscow State University, Moscow, Russia
| | - Tatiana N Erokhina
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - Andrey G Solovyev
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.,Department of Virology, Biological Faculty, Moscow State University, Moscow, Russia.,Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Moscow, Russia
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11
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Drosophila: Retrotransposons Making up Telomeres. Viruses 2017; 9:v9070192. [PMID: 28753967 PMCID: PMC5537684 DOI: 10.3390/v9070192] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Revised: 07/14/2017] [Accepted: 07/17/2017] [Indexed: 12/27/2022] Open
Abstract
Drosophila and extant species are the best-studied telomerase exception. In this organism, telomere elongation is coupled with targeted retrotransposition of Healing Transposon (HeT-A) and Telomere Associated Retrotransposon (TART) with sporadic additions of Telomere Associated and HeT-A Related (TAHRE), all three specialized non-Long Terminal Repeat (non-LTR) retrotransposons. These three very special retroelements transpose in head to tail arrays, always in the same orientation at the end of the chromosomes but never in interior locations. Apparently, retrotransposon and telomerase telomeres might seem very different, but a detailed view of their mechanisms reveals similarities explaining how the loss of telomerase in a Drosophila ancestor could successfully have been replaced by the telomere retrotransposons. In this review, we will discover that although HeT-A, TART, and TAHRE are still the only examples to date where their targeted transposition is perfectly tamed into the telomere biology of Drosophila, there are other examples of retrotransposons that manage to successfully integrate inside and at the end of telomeres. Because the aim of this special issue is viral integration at telomeres, understanding the base of the telomerase exceptions will help to obtain clues on similar strategies that mobile elements and viruses could have acquired in order to ensure their survival in the host genome.
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12
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Integration site selection by retroviruses and transposable elements in eukaryotes. Nat Rev Genet 2017; 18:292-308. [PMID: 28286338 DOI: 10.1038/nrg.2017.7] [Citation(s) in RCA: 145] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Transposable elements and retroviruses are found in most genomes, can be pathogenic and are widely used as gene-delivery and functional genomics tools. Exploring whether these genetic elements target specific genomic sites for integration and how this preference is achieved is crucial to our understanding of genome evolution, somatic genome plasticity in cancer and ageing, host-parasite interactions and genome engineering applications. High-throughput profiling of integration sites by next-generation sequencing, combined with large-scale genomic data mining and cellular or biochemical approaches, has revealed that the insertions are usually non-random. The DNA sequence, chromatin and nuclear context, and cellular proteins cooperate in guiding integration in eukaryotic genomes, leading to a remarkable diversity of insertion site distribution and evolutionary strategies.
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13
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Both the Exact Target Site Sequence and a Long Poly(A) Tail Are Required for Precise Insertion of the 18S Ribosomal DNA-Specific Non-Long Terminal Repeat Retrotransposon R7Ag. Mol Cell Biol 2016; 36:1494-508. [PMID: 26976636 DOI: 10.1128/mcb.00970-15] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2015] [Accepted: 03/02/2016] [Indexed: 11/20/2022] Open
Abstract
Ribosomal elements (R elements) are site-specific non-long terminal repeat (LTR) retrotransposons that target ribosomal DNA (rDNA). To elucidate how R elements specifically access their target sites, we isolated and characterized the 18S rDNA-specific R element R7Ag from Anopheles gambiae Using an in vivo and ex vivo recombinant baculovirus retrotransposition system, we found that the exact host 18S rDNA sequence at the target site is essential for the precise insertion of R7Ag. In addition, a long poly(A) tail is necessary for the accurate initiation of R7Ag reverse transcription, a novel mechanism found in non-LTR elements. We further compared the subcellular localizations of proteins in R7Ag as well as R1Bm, another R element that targets 28S rDNA. Although the open reading frame 1 proteins (ORF1ps) of both R7Ag and R1Bm localized predominantly in the cytoplasm, ORF2 proteins (ORF2ps) colocalized in the nucleus with the nucleolar marker fibrillarin. The ORF1ps and ORF2ps of both R elements colocalized largely in the nuclear periphery and to a lesser extent within the nucleus. These results suggest that R7Ag and R1Bm proteins may access nucleolar rDNA targets in an ORF2p-dependent manner.
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14
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Abstract
Although most of non-long terminal repeat (non-LTR) retrotransposons are incorporated in the host genome almost randomly, some non-LTR retrotransposons are incorporated into specific sequences within a target site. On the basis of structural and phylogenetic features, non-LTR retrotransposons are classified into two large groups, restriction enzyme-like endonuclease (RLE)-encoding elements and apurinic/apyrimidinic endonuclease (APE)-encoding elements. All clades of RLE-encoding non-LTR retrotransposons include site-specific elements. However, only two of more than 20 APE-encoding clades, Tx1 and R1, contain site-specific non-LTR elements. Site-specific non-LTR retrotransposons usually target within multi-copy RNA genes, such as rRNA gene (rDNA) clusters, or repetitive genomic sequences, such as telomeric repeats; this behavior may be a symbiotic strategy to reduce the damage to the host genome. Site- and sequence-specificity are variable even among closely related non-LTR elements and appeared to have changed during evolution. In the APE-encoding elements, the primary determinant of the sequence- specific integration is APE itself, which nicks one strand of the target DNA during the initiation of target primed reverse transcription (TPRT). However, other factors, such as interaction between mRNA and the target DNA, and access to the target region in the nuclei also affect the sequence-specificity. In contrast, in the RLE-encoding elements, DNA-binding motifs appear to affect their sequence-specificity, rather than the RLE domain itself. Highly specific integration properties of these site-specific non-LTR elements make them ideal alternative tools for sequence-specific gene delivery, particularly for therapeutic purposes in human diseases.
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15
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Deng Z, Wang Z, Lieberman PM. Telomeres and viruses: common themes of genome maintenance. Front Oncol 2012; 2:201. [PMID: 23293769 PMCID: PMC3533235 DOI: 10.3389/fonc.2012.00201] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 12/08/2012] [Indexed: 12/14/2022] Open
Abstract
Genome maintenance mechanisms actively suppress genetic instability associated with cancer and aging. Some viruses provoke genetic instability by subverting the host's control of genome maintenance. Viruses have their own specialized strategies for genome maintenance, which can mimic and modify host cell processes. Here, we review some of the common features of genome maintenance utilized by viruses and host chromosomes, with a particular focus on terminal repeat (TR) elements. The TRs of cellular chromosomes, better known as telomeres, have well-established roles in cellular chromosome stability. Cellular telomeres are themselves maintained by viral-like mechanisms, including self-propagation by reverse transcription, recombination, and retrotransposition. Viral TR elements, like cellular telomeres, are essential for viral genome stability and propagation. We review the structure and function of viral repeat elements and discuss how they may share telomere-like structures and genome protection functions. We consider how viral infections modulate telomere regulatory factors for viral repurposing and can alter normal host telomere structure and chromosome stability. Understanding the common strategies of viral and cellular genome maintenance may provide new insights into viral-host interactions and the mechanisms driving genetic instability in cancer.
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Affiliation(s)
- Zhong Deng
- The Wistar Institute Philadelphia, PA, USA
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Zhang L, Rong YS. Retrotransposons at Drosophila telomeres: host domestication of a selfish element for the maintenance of genome integrity. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1819:771-5. [PMID: 22342531 DOI: 10.1016/j.bbagrm.2012.01.018] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 01/25/2012] [Accepted: 01/30/2012] [Indexed: 01/18/2023]
Abstract
Telomere serves two essential functions for the cell. It prevents the recognition of natural chromosome ends as DNA breaks (the end capping function). It counteracts incomplete end replication by adding DNA to the ends of chromosomes (the end elongation function). In most organisms studied, telomerase fulfills the end elongation function. In Drosophila, however, telomere specific retrotransposons have been coerced into performing this essential function for the host. In this review, we focus our discussion on transposition mechanisms and transcriptional regulation of these transposable elements, and present provocative models for the purpose of spurring new interests in the field. This article is part of a Special Issue entitled: Chromatin in time and space.
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Affiliation(s)
- Liang Zhang
- Laboatory of Biochechemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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