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Estrem B, Davis R, Wang J. End resection and telomere healing of DNA double-strand breaks during nematode programmed DNA elimination. Nucleic Acids Res 2024; 52:8913-8929. [PMID: 38953168 PMCID: PMC11347171 DOI: 10.1093/nar/gkae579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2024] [Revised: 05/24/2024] [Accepted: 06/24/2024] [Indexed: 07/03/2024] Open
Abstract
Most DNA double-strand breaks (DSBs) are harmful to genome integrity. However, some forms of DSBs are essential to biological processes, such as meiotic recombination and V(D)J recombination. DSBs are also required for programmed DNA elimination (PDE) in ciliates and nematodes. In nematodes, the DSBs are healed with telomere addition. While telomere addition sites have been well characterized, little is known regarding the DSBs that fragment nematode chromosomes. Here, we used embryos from the human and pig parasitic nematode Ascaris to characterize the DSBs. Using END-seq, we demonstrate that DSBs are introduced before mitosis, followed by extensive end resection. The resection profile is unique for each break site, and the resection generates 3'-overhangs before the addition of neotelomeres. Interestingly, telomere healing occurs much more frequently on retained DSB ends than on eliminated ends. This biased repair of the DSB ends may be due to the sequestration of the eliminated DNA into micronuclei, preventing neotelomere formation at their ends. Additional DNA breaks occur within the eliminated DNA in both Ascaris and Parascaris, ensuring chromosomal breakage and providing a fail-safe mechanism for PDE. Overall, our data indicate that telomere healing of DSBs is specific to the break sites responsible for nematode PDE.
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Affiliation(s)
- Brandon Estrem
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Richard E Davis
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, CO 80045, USA
| | - Jianbin Wang
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
- UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996, USA
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Simmons JR, Estrem B, Zagoskin MV, Oldridge R, Zadegan SB, Wang J. Chromosome fusion and programmed DNA elimination shape karyotypes of nematodes. Curr Biol 2024; 34:2147-2161.e5. [PMID: 38688284 PMCID: PMC11111355 DOI: 10.1016/j.cub.2024.04.022] [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: 11/30/2023] [Revised: 02/21/2024] [Accepted: 04/09/2024] [Indexed: 05/02/2024]
Abstract
An increasing number of metazoans undergo programmed DNA elimination (PDE), where a significant amount of DNA is selectively lost from the somatic genome during development. In some nematodes, PDE leads to the removal and remodeling of the ends of all germline chromosomes. In several species, PDE also generates internal breaks that lead to sequence loss and increased numbers of somatic chromosomes. The biological significance of these karyotype changes associated with PDE and the origin and evolution of nematode PDE remain largely unknown. Here, we assembled the single germline chromosome of the nematode Parascaris univalens and compared the karyotypes, chromosomal gene organization, and PDE features among other nematodes. We show that PDE in Parascaris converts an XX/XY sex-determination system in the germline into an XX/XO system in the somatic cells. Comparisons of Ascaris, Parascaris, and Baylisascaris ascarid chromosomes suggest that PDE existed in the ancestor of these nematodes, and their current distinct germline karyotypes were derived from fusion events of smaller ancestral chromosomes. The DNA breaks involved in PDE resolve these fused germline chromosomes into their pre-fusion karyotypes. These karyotype changes may lead to alterations in genome architecture and gene expression in the somatic cells. Cytological and genomic analyses further suggest that satellite DNA and the heterochromatic chromosome arms are dynamic and may play a role during meiosis. Overall, our results show that chromosome fusion and PDE have been harnessed in these ascarids to sculpt their karyotypes, altering the genome organization and serving specific functions in the germline and somatic cells.
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Affiliation(s)
- James R Simmons
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Brandon Estrem
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Maxim V Zagoskin
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Ryan Oldridge
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Sobhan Bahrami Zadegan
- UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996, USA
| | - Jianbin Wang
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA; UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996, USA.
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3
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Estrem B, Davis RE, Wang J. End resection and telomere healing of DNA double-strand breaks during nematode programmed DNA elimination. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.15.585292. [PMID: 38559121 PMCID: PMC10980081 DOI: 10.1101/2024.03.15.585292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Most DNA double-strand breaks (DSBs) are harmful to genome integrity. However, some forms of DSBs are essential to biological processes, such as meiotic recombination and V(D)J recombination. DSBs are also required for programmed DNA elimination (PDE) in ciliates and nematodes. In nematodes, the DSBs are healed with telomere addition. While telomere addition sites have been well-characterized, little is known regarding the DSBs that fragment nematode chromosomes. Here, we used embryos from the nematode Ascaris to study the timing of PDE breaks and examine the DSBs and their end processing. Using END-seq, we characterize the DSB ends and demonstrate that DNA breaks are introduced before mitosis, followed by extensive end resection. The resection profile is unique for each break site, and the resection generates 3' overhangs before the addition of telomeres. Interestingly, telomere healing occurs much more frequently on retained DSB ends than on eliminated ends. This biased repair of the DSB ends in Ascaris may be due to the sequestration of the eliminated DNA into micronuclei, preventing their ends from telomere healing. Additional DNA breaks occur within the eliminated DNA in both Ascaris and Parascaris, ensuring chromosomal breakage and providing a fail-safe mechanism for nematode PDE.
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Affiliation(s)
- Brandon Estrem
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA
| | - Richard E. Davis
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, CO, 80045, USA
| | - Jianbin Wang
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA
- UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, TN, 37996, USA
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4
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Simmons JR, Estrem B, Zagoskin MV, Oldridge R, Zadegan SB, Wang J. Chromosome fusion and programmed DNA elimination shape karyotypes of parasitic nematodes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.21.572835. [PMID: 38187595 PMCID: PMC10769430 DOI: 10.1101/2023.12.21.572835] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
A growing list of metazoans undergo programmed DNA elimination (PDE), where a significant amount of DNA is selectively lost from the somatic genome during development. In some nematodes, PDE leads to the removal and remodeling of the ends of all germline chromosomes. In several species, PDE also generates internal breaks that lead to sequence loss and an increased number of somatic chromosomes. The biological significance of these karyotype changes associated with PDE and the origin and evolution of nematode PDE remain largely unknown. Here, we assembled the single germline chromosome of the horse parasite Parascaris univalens and compared the karyotypes, chromosomal gene organization, and PDE features among ascarid nematodes. We show that PDE in Parascaris converts an XX/XY sex-determination system in the germline into an XX/XO system in the somatic cells. Comparisons of Ascaris, Parascaris, and Baylisascaris ascarid chromosomes suggest that PDE existed in the ancestor of these parasites, and their current distinct germline karyotypes were derived from fusion events of smaller ancestral chromosomes. The DNA breaks involved in PDE resolve these fused germline chromosomes into their pre-fusion karyotypes, leading to alterations in genome architecture and gene expression in the somatic cells. Cytological and genomic analyses further suggest that satellite DNA and the heterochromatic chromosome arms play a dynamic role in the Parascaris germline chromosome during meiosis. Overall, our results show that chromosome fusion and PDE have been harnessed in these ascarids to sculpt their karyotypes, altering the genome organization and serving specific functions in the germline and somatic cells.
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Affiliation(s)
- James R. Simmons
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Brandon Estrem
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Maxim V. Zagoskin
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Ryan Oldridge
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Sobhan Bahrami Zadegan
- UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, Tennessee, 37996, USA
| | - Jianbin Wang
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, 37996, USA
- UT-ORNL Graduate School of Genome Science and Technology, University of Tennessee, Knoxville, Tennessee, 37996, USA
- Lead Contact
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Abstract
In most organisms, the whole genome is maintained throughout the life span. However, exceptions occur in some species where the genome is reduced during development through a process known as programmed DNA elimination (PDE). In the human and pig parasite Ascaris, PDE occurs during the 4 to 16 cell stages of embryogenesis, when germline chromosomes are fragmented and specific DNA sequences are reproducibly lost in all somatic cells. PDE was identified in Ascaris over 120 years ago, but little was known about its molecular details until recently. Genome sequencing revealed that approximately 1,000 germline-expressed genes are eliminated in Ascaris, suggesting PDE is a gene silencing mechanism. All germline chromosome ends are removed and remodeled during PDE. In addition, PDE increases the number of chromosomes in the somatic genome by splitting many germline chromosomes. Comparative genomics indicates that these germline chromosomes arose from fusion events. PDE separates these chromosomes at the fusion sites. These observations indicate that PDE plays a role in chromosome karyotype and evolution. Furthermore, comparative analysis of PDE in other parasitic and free-living nematodes illustrates conserved features of PDE, suggesting it has important biological significance. We summarize what is known about PDE in Ascaris and its relatives. We also discuss other potential functions, mechanisms, and the evolution of PDE in these parasites of humans and animals of veterinary importance.
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Dedukh D, Krasikova A. Delete and survive: strategies of programmed genetic material elimination in eukaryotes. Biol Rev Camb Philos Soc 2022; 97:195-216. [PMID: 34542224 PMCID: PMC9292451 DOI: 10.1111/brv.12796] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Revised: 08/31/2021] [Accepted: 09/02/2021] [Indexed: 02/06/2023]
Abstract
Genome stability is a crucial feature of eukaryotic organisms because its alteration drastically affects the normal development and survival of cells and the organism as a whole. Nevertheless, some organisms can selectively eliminate part of their genomes from certain cell types during specific stages of ontogenesis. This review aims to describe the phenomenon of programmed DNA elimination, which includes chromatin diminution (together with programmed genome rearrangement or DNA rearrangements), B and sex chromosome elimination, paternal genome elimination, parasitically induced genome elimination, and genome elimination in animal and plant hybrids. During programmed DNA elimination, individual chromosomal fragments, whole chromosomes, and even entire parental genomes can be selectively removed. Programmed DNA elimination occurs independently in different organisms, ranging from ciliate protozoa to mammals. Depending on the sequences destined for exclusion, programmed DNA elimination may serve as a radical mechanism of dosage compensation and inactivation of unnecessary or dangerous genetic entities. In hybrids, genome elimination results from competition between parental genomes. Despite the different consequences of DNA elimination, all genetic material destined for elimination must be first recognised, epigenetically marked, separated, and then removed and degraded.
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Affiliation(s)
- Dmitrij Dedukh
- Saint‐Petersburg State University7/9 Universitetskaya EmbankmentSaint‐Petersburg199034Russia
| | - Alla Krasikova
- Saint‐Petersburg State University7/9 Universitetskaya EmbankmentSaint‐Petersburg199034Russia
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Chromosome Healing Is Promoted by the Telomere Cap Component Hiphop in Drosophila. Genetics 2017; 207:949-959. [PMID: 28942425 DOI: 10.1534/genetics.117.300317] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 09/21/2017] [Indexed: 11/18/2022] Open
Abstract
The addition of a new telomere onto a chromosome break, a process termed healing, has been studied extensively in organisms that utilize telomerase to maintain their telomeres. In comparison, relatively little is known about how new telomeres are constructed on broken chromosomes in organisms that do not use telomerase. Chromosome healing was studied in somatic and germline cells of Drosophila melanogaster, a nontelomerase species. We observed, for the first time, that broken chromosomes can be healed in somatic cells. In addition, overexpression of the telomere cap component Hiphop increased the survival of somatic cells with broken chromosomes, while the cap component HP1 did not, and overexpression of the cap protein HOAP decreased their survival. In the male germline, Hiphop overexpression greatly increased the transmission of healed chromosomes. These results indicate that Hiphop can stimulate healing of a chromosome break. We suggest that this reflects a unique function of Hiphop: it is capable of seeding formation of a new telomeric cap on a chromosome end that lacks a telomere.
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Koroleva AG, Evtushenko EV, Maximova NV, Vershinin AV, Sitnikova TY, Kirilchik SV. Length and structure of telomeric DNA in three species of Baikal gastropods (Caenogastropoda: Hydrobioidea: Benedictiidae). RUSS J GENET+ 2015. [DOI: 10.1134/s1022795415030060] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Ribeyre C, Shore D. Regulation of telomere addition at DNA double-strand breaks. Chromosoma 2013; 122:159-73. [DOI: 10.1007/s00412-013-0404-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Revised: 02/28/2013] [Accepted: 03/04/2013] [Indexed: 12/11/2022]
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Wang J, Mitreva M, Berriman M, Thorne A, Magrini V, Koutsovoulos G, Kumar S, Blaxter ML, Davis RE. Silencing of germline-expressed genes by DNA elimination in somatic cells. Dev Cell 2012; 23:1072-80. [PMID: 23123092 PMCID: PMC3620533 DOI: 10.1016/j.devcel.2012.09.020] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Revised: 09/05/2012] [Accepted: 09/21/2012] [Indexed: 02/02/2023]
Abstract
Chromatin diminution is the programmed elimination of specific DNA sequences during development. It occurs in diverse species, but the function(s) of diminution and the specificity of sequence loss remain largely unknown. Diminution in the nematode Ascaris suum occurs during early embryonic cleavages and leads to the loss of germline genome sequences and the formation of a distinct genome in somatic cells. We found that ∼43 Mb (∼13%) of genome sequence is eliminated in A. suum somatic cells, including ∼12.7 Mb of unique sequence. The eliminated sequences and location of the DNA breaks are the same in all somatic lineages from a single individual and between different individuals. At least 685 genes are eliminated. These genes are preferentially expressed in the germline and during early embryogenesis. We propose that diminution is a mechanism of germline gene regulation that specifically removes a large number of genes involved in gametogenesis and early embryogenesis.
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Affiliation(s)
- Jianbin Wang
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, 80045
| | - Makedonka Mitreva
- The Genome Institute, Washington University School of Medicine, St. Louis, 63108
- Department of Genetics, Washington University School of Medicine, St. Louis, 63108
| | - Matthew Berriman
- The Wellcome Trust Sanger Institute, Genome Campus, Hinxton, CB10 1SA, UK
| | - Alicia Thorne
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, 80045
| | - Vincent Magrini
- The Genome Institute, Washington University School of Medicine, St. Louis, 63108
- Department of Genetics, Washington University School of Medicine, St. Louis, 63108
| | | | - Sujai Kumar
- Institute of Evolutionary Biology, University of Edinburgh, EH9 3JT UK
| | - Mark L. Blaxter
- Institute of Evolutionary Biology, University of Edinburgh, EH9 3JT UK
| | - Richard E. Davis
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, 80045
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Babizhayev MA, Vishnyakova KS, Yegorov YE. Telomere-dependent senescent phenotype of lens epithelial cells as a biological marker of aging and cataractogenesis: the role of oxidative stress intensity and specific mechanism of phospholipid hydroperoxide toxicity in lens and aqueous. Fundam Clin Pharmacol 2011; 25:139-62. [DOI: 10.1111/j.1472-8206.2010.00829.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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12
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Yang C, Przyborski S, Cooke MJ, Zhang X, Stewart R, Anyfantis G, Atkinson SP, Saretzki G, Armstrong L, Lako M. A key role for telomerase reverse transcriptase unit in modulating human embryonic stem cell proliferation, cell cycle dynamics, and in vitro differentiation. Stem Cells 2008; 26:850-63. [PMID: 18203676 DOI: 10.1634/stemcells.2007-0677] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Embryonic stem cells (ESC) are a unique cell population with the ability to self-renew and differentiate into all three germ layers. Human ESC express the telomerase reverse transcriptase (TERT) gene and the telomerase RNA (TR) and show telomerase activity, but TERT, TR, and telomerase are all downregulated during the differentiation process. To examine the role of telomerase in human ESC self-renewal and differentiation, we modulated the expression of TERT. Upregulation of TERT and increased telomerase activity enhanced the proliferation and colony-forming ability of human ESC, as well as increasing the S phase of the cell cycle at the expense of a reduced G1 phase. Upregulation of TERT expression was associated with increases in CYCLIN D1 and CDC6 expression, as well as hyperphosphorylation of RB. The differentiated progeny of control ESC showed shortening of telomeric DNA as a result of loss of telomerase activity. In contrast, the differentiated cells from TERT-overexpressing ESC maintained high telomerase activity and accumulated lower concentrations of peroxides than wild-type cells, implying greater resistance to oxidative stress. Although the TERT-overexpressing human ESC are able to form teratoma composed of three germ layers in vivo, their in vitro differentiation to all primitive and embryonic lineages was suppressed. In contrast, downregulation of TERT resulted in reduced ESC proliferation, increased G1, and reduced S phase. Most importantly, downregulation of TERT caused loss of pluripotency and human ESC differentiation to extraembryonic and embryonic lineages. Our results indicate for the first time an important role for TERT in the maintenance of human ESC pluripotency, cell cycle regulation, and in vitro differentiation capacity.
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Affiliation(s)
- Chunbo Yang
- North East Institute for Stem Cell Research, Newcastle upon Tyne NE1 3BZ, United Kingdom
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13
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Endings in the middle: current knowledge of interstitial telomeric sequences. Mutat Res 2007; 658:95-110. [PMID: 17921045 DOI: 10.1016/j.mrrev.2007.08.006] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2007] [Revised: 08/28/2007] [Accepted: 08/30/2007] [Indexed: 01/24/2023]
Abstract
Interstitial telomeric sequences (ITSs) consist of tandem repeats of the canonical telomeric repeat and are common in mammals. They are localized at intrachromosomal sites, including those repeats located close to the centromeres and those found at interstitial sites, i.e., between the centromeres and the telomeres. ITSs might originate from ancestral intrachromosomal rearrangements (inversions and fusions), from differential crossing-over or from the repair of double-strand break during evolution. Three classes of ITSs have been described in the human genome, namely, short ITSs, long subtelomeric ITSs and fusion ITSs. The fourth class of ITSs, pericentromeric ITSs, has been found in other species. The function of ITSs can be inferred from the association of heritable diseases with ITS polymorphic variants, both in copy number and sequence. This is one of the most attractive aspects of ITS studies because it leads to new and useful markers for genetic linkage studies, forensic applications, and detection of genetic instability in tumors. Some ITSs also might be hotspots of chromosome breakage, rearrangement and amplification sites, based on the type of clastogens and the nature of ITSs. This study will contribute new knowledge with respect to ITSs' biology and mechanism, prevalence of diseases, risk evaluation and prevention of related diseases, thus facilitates the design of early detection markers for diseases caused by genomic instability.
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Pennaneach V, Putnam CD, Kolodner RD. Chromosome healing byde novotelomere addition inSaccharomyces cerevisiae. Mol Microbiol 2006; 59:1357-68. [PMID: 16468981 DOI: 10.1111/j.1365-2958.2006.05026.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The repair of spontaneous or induced DNA damage by homologous recombination (HR) in Saccharomyces cerevisiae will suppress chromosome rearrangements. Alternative chromosome healing pathways can result in chromosomal instability. One of these pathways is de novo telomere addition where the end of a broken chromosome is stabilized by telomerase-dependent addition of telomeres at non-telomeric sites. De novo telomere addition requires the recruitment of telomerase to chromosomal targets. Subsequently, annealing of the telomerase reverse transcriptase RNA-template (guide RNA) at short regions of homology is followed by extension of the nascent 3'-end of the broken chromosome to copy a short region of the telomerase guide RNA; multiple cycles of this process yield the new telomere. Proteins including Pif1 helicase, the single-stranded DNA-binding protein Cdc13 and the Ku heterocomplex are known to participate in native telomere functions and also regulate the de novo telomere addition reaction. Studies of the sequences added at de novo telomeres have lead to a detailed description of the annealing-extension-dissociation cycles that copy the telomerase guide RNA, which can explain the heterogeneity of telomeric repeats at de novo and native telomeres in S. cerevisiae.
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Affiliation(s)
- Vincent Pennaneach
- Ludwig Institute for Cancer Research, Department of Medicine, University of California, San Diego School of Medicine, 9500 Gilman Drive, La Jolla, 92093-0669, USA
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15
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Abstract
Trypanosomatid parasite infections have a devastating impact on human health. Little is known about the requirements for parasite growth during any stage of their complex, multi-host life cycle. In most eukaryotic organisms, sustained cell proliferation requires telomerase-dependent telomere length maintenance. Here we investigate the regulation and biochemical features of telomerase from Trypanosoma cruzi, the causative agent of Chagas disease. We found that T.cruzi telomerase is active in extracts from multiple developmental stages of the parasite life cycle. Detailed characterization of the enzymatic properties of telomerase using epimatigote-stage extract revealed a unique combination of substrate specificities, consistent with the evolutionary divergence of trypanosomes from previously established model systems for telomerase biochemical characterization. Results from partial purification of T.cruzi telomerase suggest that the catalytically active enzyme is a large ribonucleoprotein complex and that the internal RNA template has an atypical, cytosine-rich permutation. These results expand our understanding of telomerase enzymology and should encourage the development of parasite-specific telomerase inhibitors as a method for disease therapy.
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Affiliation(s)
- Denise P Muñoz
- Department of Molecular and Cell Biology, 16 Barker Hall, University of California at Berkeley, Berkeley, CA 94720-3204, USA.
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16
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Bachmann-Waldmann C, Jentsch S, Tobler H, Müller F. Chromatin diminution leads to rapid evolutionary changes in the organization of the germ line genomes of the parasitic nematodes A. suum and P. univalens. Mol Biochem Parasitol 2004; 134:53-64. [PMID: 14747143 DOI: 10.1016/j.molbiopara.2003.11.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Chromatin diminution in the parasitic nematodes Ascaris suum and Parascaris univalens represents a rather complex molecular phenomenon that includes chromosomal breakage, DNA degradation and new telomere formation. At a given elimination site, DNA breakage and new telomere addition does not take place at a single chromosomal locus but at many different places within a several kilobase long chromosomal region, referred to as chromosomal breakage region (CBR). Here we describe the cloning and the characterisation of seven CBRs from A. suum and P. univalens and we show that the process has been conserved between the two species. A detailed sequence comparison provides evidence that the sequences of the CBRs and their flanking regions are not directly important for the specification of the elimination sites. Six out of the seven CBRs are conserved between the two nematode species, suggesting that they have already existed in a common ancestor. We present a hypothesis stating that the elimination process ensures the maintenance of a functional somatic genome and concomitantly allows extremely rapid and profound changes in the germ line genome, thereby allowing the development of new germ line specific functions and thus providing a selective advantage for the chromatin eliminating nematodes during further evolution.
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Affiliation(s)
- Christa Bachmann-Waldmann
- Departement of Biology, Zoology, University of Fribourg, Chemin du Musée 10, Fribourg CH-1700, Switzerland
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17
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Bousman S, Schneider G, Shampay J. Telomerase activity is widespread in adult somatic tissues of Xenopus. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART B, MOLECULAR AND DEVELOPMENTAL EVOLUTION 2003; 295:82-6. [PMID: 12548544 DOI: 10.1002/jez.b.7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Chromosome ends, or telomeres, are maintained by telomerase. Work in selected vertebrates has implied that telomerase is often repressed in differentiated cells, and telomere erosion results in senescence of cultured cells. Tissues from mature Xenopus laevis frogs were examined for telomerase enzymatic activity with the TRAP (telomere repeat amplification protocol) assay. All tissues contained active telomerase, most abundantly in testis, spleen, liver, and embryos; activity was less abundant but still readily detectable with < 100 ng of protein extract from brain and muscle tissues. Activity in somatic tissues of the diploid Xenopus tropicalis suggests this condition is not limited to the polyploid members of the genus, and that extensive differentiation-linked telomerase repression does not occur in Xenopus.
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Affiliation(s)
- Sylvia Bousman
- Kleinholz Biological Laboratories, Department of Biology, Reed College, Portland, Oregon 97202, USA
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18
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Xiang H, Wang J, Mao Y, Liu M, Reddy VN, Li DWC. Human telomerase accelerates growth of lens epithelial cells through regulation of the genes mediating RB/E2F pathway. Oncogene 2002; 21:3784-91. [PMID: 12032846 DOI: 10.1038/sj.onc.1205455] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2001] [Revised: 02/15/2002] [Accepted: 02/21/2002] [Indexed: 11/09/2022]
Abstract
Telomerase is a specialized reverse transcriptase that extends telomeres of eukaryotic chromosomes. The catalytic core of human telomerase is composed of an RNA template known as hTER (human telomerase RNA) and a protein subunit named hTERT (human telomerase reverse transcriptase). We have been studying other functions of the telomerase besides its major role in telomere maintenance. In our previous work, we have demonstrated that the hTERT can functionally interact with a rabbit TER to regulate expression of other genes and also attenuate the induced apoptosis. Here we report that overexpression of hTERT in a human lens epithelial cell line accelerates growth of the transfected lens epithelial cells. Associated with the acceleration of cell growth, expression of p53, p21 and GCIP (Grap2 cyclin-D interacting protein) is downregulated in the hTERT-transfected cells. With the downregulation of p21 and GCIP, the retinoblastoma protein (RB) is completely hyperphosphorylated in the hTERT-transfected cells. As expected, in the presence of RB hyperphosphorylation, the E2F transactivity is upregulated. Inhibition of telomerase activity abolishes the observed growth acceleration and also the related molecular changes. Furthermore, expression of hTERT in telomerase-negative human lens epithelial cells derived from primary cultures also accelerates growth of the transfected cells. Taken together, our results suggest that hTERT, when overexpressed in human lens epithelial cells, accelerates cell growth rate through regulation of RB/E2F pathway and possibly other genes.
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Affiliation(s)
- Hua Xiang
- Department of Molecular Biology, University of Medicine and Dentistry of New Jersey School of Osteopathic Medicine, Stratford, New Jersey, NJ 08084, USA
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Fitzgerald MS, Shakirov EV, Hood EE, McKnight TD, Shippen DE. Different modes of de novo telomere formation by plant telomerases. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2001; 26:77-87. [PMID: 11359612 DOI: 10.1046/j.1365-313x.2001.01010.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The telomerase reverse transcriptase can recognize broken chromosome ends and add new telomeres de novo in a reaction termed "chromosome healing". Here we investigate new telomere formation in vitro by telomerases from a variety of flowering plant species. Comparing the electrophoretic mobilities and nucleotide sequences of the products, we uncovered three different modes of new telomere formation. The soybean telomerase, designated a Class I enzyme, only elongated DNA primers ending in telomeric nucleotides. Arabidopsis and maize telomerases, designated Class II enzymes, efficiently extended completely non-telomeric sequences by positioning the 3' terminus at a preferred site on the RNA template. Silene latifolia and sorghum telomerases constituted class III enzymes that elongated non-telomeric DNA primers by annealing them at alternative sites on the RNA template. For all enzymes, errors were prevalent during synthesis of the first two repeats, likely reflecting lateral instability of the primer 3' terminus on the template during the initial rounds of elongation. Class III telomerases, however, were five- to 13-fold more error prone than class II, generating more mistakes in distal repeats added to the primers. This remarkable variability in enzyme-DNA interactions among plant telomerases does not reflect phylogenetic relationships, and therefore implies that the telomerase active site can evolve rapidly.
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Affiliation(s)
- M S Fitzgerald
- Department of Biochemistry and Biophysics, 2128 TAMU, Texas A & M University, College Station, Texas 77843-2128, USA
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20
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Müller F, Tobler H. Chromatin diminution in the parasitic nematodes ascaris suum and parascaris univalens. Int J Parasitol 2000; 30:391-9. [PMID: 10731562 DOI: 10.1016/s0020-7519(99)00199-x] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Chromatin diminution in Parascaris univalens and Ascaris suum undoubtedly represents an interesting case of developmentally programmed DNA rearrangement in higher eukaryotes. It is a complex mechanism involving chromosomal breakage, new telomere addition and DNA degradation, and occurs in all presomatic cells. The process is rather specific with respect to its developmental timing and the chromosomal regions that are eliminated. The functional significance of chromatin diminution still remains an enigma. The fact, however, that single-copy, protein-coding genes are contained in the eliminated DNA demonstrates that in P. univalens and A. suum, there is a qualitative difference between germ-line and somatic genomes, and suggests that chromatin diminution may be used as a "throw-away" approach to gene regulation. We present a hypothesis as to how, during evolution, a partial genome duplication might have been linked to the process of chromatin diminution, in order to provide a selective advantage to parasitic DNA-eliminating nematodes.
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Affiliation(s)
- F Müller
- Institute of Zoology, University of Fribourg, CH-1700, Fribourg, Switzerland.
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21
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Liu JP. Telomerase: not just black and white, but shades of gray. MOLECULAR CELL BIOLOGY RESEARCH COMMUNICATIONS : MCBRC 2000; 3:129-35. [PMID: 10860859 DOI: 10.1006/mcbr.2000.0203] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Telomerase, the telomeric DNA reverse transcriptase, plays a key role in the maintenance of telomeres in mammals and is required for immortalization of primary cells. Inexplicably, telomerase activation is sometimes associated with telomere shortening and inhibition leads not only to apoptosis but also increased tumorigenicity in rapidly renewing tissues of mouse and man. This article reviews the current evidence, both in vitro and in vivo, for telomerase function and the potential mechanisms, downstream of telomerase, in telomere signaling involving both the tumor-suppressor p53-dependent and independent pathways.
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Affiliation(s)
- J P Liu
- Baker Medical Research Institute, Commercial Road, Prahran, Victoria, Australia.
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