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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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Kojima KK. LINEs Contribute to the Origins of Middle Bodies of SINEs besides 3' Tails. Genome Biol Evol 2018; 10:370-379. [PMID: 29325122 PMCID: PMC5786205 DOI: 10.1093/gbe/evy008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/08/2018] [Indexed: 01/06/2023] Open
Abstract
Short interspersed elements (SINEs), which are nonautonomous transposable elements, require the transposition machinery of long interspersed elements (LINEs) to mobilize. SINEs are composed of two or more independently originating parts. The 5′ region is called the “head” and is derived mainly from small RNAs, and the 3′ region (“tail”) originates from the 3′ region of LINEs and is responsible for being recognized by counterpart LINE proteins. The origin of the middle “body” of SINEs is enigmatic, although significant sequence similarities among SINEs from very diverse species have been observed. Here, a systematic analysis of the similarities among SINEs and LINEs deposited on Repbase, a comprehensive database of eukaryotic repeat sequences was performed. Three primary findings are described: 1) The 5′ regions of only two clades of LINEs, RTE and Vingi, were revealed to have contributed to the middle parts of SINEs; 2) The linkage of the 5′ and 3′ parts of LINEs can be lost due to occasional tail exchange of SINEs; and 3) The previously proposed Ceph-domain was revealed to be a fusion of a CORE-domain and a 5′ part of RTE clade of LINE. Based on these findings, a hypothesis that the 5′ parts of bipartite nonautonomous LINEs, which possess only the 5′ and 3′ regions of the original LINEs, can contribute to the undefined middle part of SINEs is proposed.
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Affiliation(s)
- Kenji K Kojima
- Department of Life Sciences, National Cheng Kung University, Tainan, Taiwan.,Genetic Information Research Institute, Mountain View, California
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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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Macías F, López MC, Thomas MC. The Trypanosomatid Pr77-hallmark contains a downstream core promoter element essential for transcription activity of the Trypanosoma cruzi L1Tc retrotransposon. BMC Genomics 2016; 17:105. [PMID: 26861854 PMCID: PMC4748587 DOI: 10.1186/s12864-016-2427-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 02/01/2016] [Indexed: 01/11/2023] Open
Abstract
Background Trypanosomatid genomes are highly colonized by non-LTR retroelements that make up to 5 % of the nuclear genome. These elements are mainly accumulated in the strand switch regions (SSRs) where polycistronic transcription is initiated and have a 77 nt-long sequence - Pr77 - at their 5′ ends. L1Tc is the best represented retrotransposon in the Trypanosoma cruzi genome and is a potentially functional autonomous element that encodes its own retrotransposition machinery. The Pr77 of the T. cruzi L1Tc element activates gene transcription via RNA polymerase II, generating abundant, unspliced transcripts which are translated. Results The present manuscript describes the identification of a downstream core promoter element (DPE) in the L1Tc Pr77 sequence. Just four nucleotides long (CGTG), it covers in Pr77 positions +25 to +28 of the described L1Tc transcription start site. The Pr77-DPE motif is conserved in terms of sequence composition and position in the Pr77 of most trypanosomatid non-LTR retrotransposons, independent of the coding or non-coding capacity of these retroelements. Transcription assays in T. cruzi stable transfectants with vector containing point mutations at 17 locations of the Pr77 nucleotide sequence evidence that the DPE motif is essential for the promoter function of Pr77. Furthermore, the obtained data show that other nucleotides also contributed to the promoter function of Pr77. In addition, the presented results indicate that parasite nuclear proteins specifically bind to different regions of the Pr77 sequence although the strongest binding is to the DPE motif. Moreover, it is shown that the DPE sense single-stranded sequence is being required in DNA-protein recognition of nuclear factors. Conclusions The Pr77 sequence present in most of non-LTR retrotransposons of trypanosomatids contains a downstream core promoter element (DPE) which is conserved in terms of nucleotide composition and location. The Pr77-DPE motif is essential for the transcriptional activity of Pr77 although other nucleotides are also involved. DPE has a high affinity binding for nuclear proteins in T. cruzi. The wide retroelement-mediated distribution of Pr77 suggests that it may represent an important tool for regulating gene expression in trypanosomatids. Electronic supplementary material The online version of this article (doi:10.1186/s12864-016-2427-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Francisco Macías
- Instituto de Parasitología y Biomedicina López-Neyra, Consejo Superior de Investigaciones Científicas (IPBLN-CSIC), PTS Granada, Avda. del Conocimiento S/N, 18016, Granada, Spain.
| | - Manuel Carlos López
- Instituto de Parasitología y Biomedicina López-Neyra, Consejo Superior de Investigaciones Científicas (IPBLN-CSIC), PTS Granada, Avda. del Conocimiento S/N, 18016, Granada, Spain.
| | - M Carmen Thomas
- Instituto de Parasitología y Biomedicina López-Neyra, Consejo Superior de Investigaciones Científicas (IPBLN-CSIC), PTS Granada, Avda. del Conocimiento S/N, 18016, Granada, Spain.
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Servant G, Deininger PL. Insertion of Retrotransposons at Chromosome Ends: Adaptive Response to Chromosome Maintenance. Front Genet 2016; 6:358. [PMID: 26779254 PMCID: PMC4700185 DOI: 10.3389/fgene.2015.00358] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 12/10/2015] [Indexed: 01/30/2023] Open
Abstract
The telomerase complex is a specialized reverse transcriptase (RT) that inserts tandem DNA arrays at the linear chromosome ends and contributes to the protection of the genetic information in eukaryotic genomes. Telomerases are phylogenetically related to retrotransposons, encoding also the RT activity required for the amplification of their sequences throughout the genome. Intriguingly the telomerase gene is lost from the Drosophila genome and tandem retrotransposons replace telomeric sequences at the chromosome extremities. This observation suggests the versatility of RT activity in counteracting the chromosome shortening associated with genome replication and that retrotransposons can provide this activity in case of a dysfunctional telomerase. In this review paper, we describe the major classes of retroelements present in eukaryotic genomes in order to point out the differences and similarities with the telomerase complex. In a second part, we discuss the insertion of retroelements at the ends of chromosomes as an adaptive response for dysfunctional telomeres.
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Affiliation(s)
| | - Prescott L. Deininger
- Tulane Cancer Center, Department of Epidemiology, School of Public Health and Tropical Medicine, Tulane University, New Orleans, LAUSA
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Bire S, Rouleux-Bonnin F. Transgene Site-Specific Integration: Problems and Solutions. SITE-DIRECTED INSERTION OF TRANSGENES 2013. [DOI: 10.1007/978-94-007-4531-5_1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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Alexandrova EA, Olovnikov IA, Malakhova GV, Zabolotneva AA, Suntsova MV, Dmitriev SE, Buzdin AA. Sense transcripts originated from an internal part of the human retrotransposon LINE-1 5' UTR. Gene 2012; 511:46-53. [PMID: 22982412 DOI: 10.1016/j.gene.2012.09.026] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 08/29/2012] [Accepted: 09/04/2012] [Indexed: 10/27/2022]
Abstract
L1 (LINE-1) is one of the most abundant families of human transposable elements. Full-length human L1 has an ~900 bp long 5' untranslated region (5' UTR) which harbors an internal promoter for the RNA polymerase II. It is generally accepted that the first 100 bp of the 5' UTR function as a "minimal promoter" which directs transcription of the entire LINE-1 unit from the extreme 5' terminus. We re-investigated promoter activities of the different DNA fragments that cover the whole L1 5' UTR in cultured human cells by using the luciferase reporter system. Analysis of both mRNA expression and luciferase activity levels indicated that the very important region for the effective transcription is located within the internal part of the L1 5' UTR between nucleotide positions +390 and +526. 5' RACE analysis revealed that in the context of the complete 5' UTR, this part drives mRNA synthesis both from the canonical 5'-terminal transcription start site (TSS) and from within the internal region. In the absence of the first 100 bp, the L1 5' UTR efficiently directed transcription from aberrant TSSs located within its 3' proximal part or the ORF1. Finally, we analyzed transcripts originated from endogenous (genomic) L1 elements and identified two novel TSSs located at positions +525 and +570. We propose a model in which the internal part (390-526) of the L1 5' UTR plays a key role for recruitment of transcription initiation complex, which then may be either positioned onto the 5' terminally located "minimal promoter", or used proximately to direct 5' truncated RNA copy. Intriguingly, this internal regulatory element substantially overlaps with the region of the L1 5' UTR that is known to drive transcription in the opposite direction suggesting the existence of a common core for the bidirectional transcription.
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Affiliation(s)
- Elena A Alexandrova
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, 16/10 Miklukho-Maklaya, Moscow 117997, Russia
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The telomere-specific non-LTR retrotransposons SART1 and TRAS1 are suppressed by Piwi subfamily proteins in the silkworm, Bombyx mori. Cell Mol Biol Lett 2009; 15:118-33. [PMID: 19943120 PMCID: PMC6275988 DOI: 10.2478/s11658-009-0038-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2009] [Accepted: 11/24/2009] [Indexed: 01/22/2023] Open
Abstract
The telomere structures in Bombyx mori are thought to be maintained mainly by the transposition of the specialized telomeric retroelements SART and TRAS. The silkworm genome has telomeric TTAGG repeats and telomerase, but this telomerase displays little or no activity. Here, we report that the transcription of the telomeric retroelements SART1 and TRAS1 is suppressed by the silkworm Piwi subfamily proteins BmAgo3 and Siwi. The silkworm Piwi subfamily was found to be expressed predominantly in the gonads and early embryo, as in other model organisms, but in BmN4 cultured cells, these proteins formed granules that were separate from the nuage, which is a different behaviour pattern. The expression of TRAS1 was increased in BmN4 cells when BmAgo3 or Siwi were silenced by RNAi. Our results suggest that B. mori Piwi proteins are involved in regulating the transposition of telomeric retroelements, and that the functional piRNA pathway is conserved in BmN4 cultured cells.
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Olovnikov IA, Adyanova ZV, Galimov ER, Andreev DE, Terenin IM, Ivanov DS, Prassolov VS, Dmitriev SE. Key role of the internal 5′-UTR segment in the transcription activity of the human L1 retrotransposon. Mol Biol 2007. [DOI: 10.1134/s0026893307030119] [Citation(s) in RCA: 5] [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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Kawashima T, Osanai M, Futahashi R, Kojima T, Fujiwara H. A novel target-specific gene delivery system combining baculovirus and sequence-specific long interspersed nuclear elements. Virus Res 2007; 127:49-60. [PMID: 17498830 DOI: 10.1016/j.virusres.2007.03.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Revised: 03/16/2007] [Accepted: 03/17/2007] [Indexed: 11/26/2022]
Abstract
Transposable elements are valuable for somatic and germ-line transformation. However, long interspersed nuclear elements (LINEs) have not been used because of poor information on the transposition mechanism. We have developed a novel gene delivery system combining baculovirus AcNPV and two silkworm LINEs, SART1 and R1, which integrate into specific sequences of telomeric repeats and 28S ribosomal DNA, respectively. When two LINEs containing the enhanced green fluorescent protein gene recombined into AcNPV were infected into fifth instar larvae of the silkworm, we observed target-specific retrotransposition of LINEs at 72h post-infection, using polymerase chain reaction amplification and sequencing. Telomere- and 28S rDNA-specific transposition occurred in all nine tissues tested, including the ovary and testis. This is the first demonstration of site-specific gene delivery in living larvae. Insertion efficiencies were dependent on the virus titer for injection and the host strains of Bombyx mori. Using this system, we successfully detected the intergeneration transmission of retrotransposed sequences. In addition, AcNPV-mediated SART1 also transposed into telomere of another lepidopteran, Orgyia recens, suggesting that this system is useful for a wide variety of AcNPV-infectious insects. Site-specific gene delivery by virus-mediated LINE will be a potential gene therapy tool to avoid harmful unexpected insertions.
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Affiliation(s)
- Tomoko Kawashima
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Bioscience Bldg. 501, Kashiwa, Chiba 277-8562, Japan.
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Fu S, Zhang W, Guo A, Wang J. Identification of promoters of two dehydrogenase genes in Ketogulonicigenium vulgare DSM 4025 and their strength comparison in K. vulgare and Escherichia coli. Appl Microbiol Biotechnol 2007; 75:1127-32. [PMID: 17404730 DOI: 10.1007/s00253-007-0930-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2007] [Revised: 03/05/2007] [Accepted: 03/06/2007] [Indexed: 10/23/2022]
Abstract
Promoters of sorbose dehydrogenase gene sdh and sorbosone dehydrogenase gene sndh (Psdh and Psndh) in Ketogulonicigenium vulgare DSM 4025 were identified. The transcription initiation site (TIS) of Psdh was guanine 74 bp upstream of the start codon of sdh and the TIS of Psndh was adenine 113 bp upstream of the first codon of sndh. Comparing Psdh and Psndh, consensus sequences were found, which were TAVCVT (V=A, C or G) and THGAHC (H=A, C or T) for their putative -10 and -35 regions, respectively, and the spans between the 2 regions were 17 bp. Psdh and Psndh promoters may be constitutive in K. vulgare DSM 4025 when cultured in HJ medium. Semiquantitative RT-PCR analysis showed that the Psdh promoter was about 2.5 times stronger than Psndh in strength in K. vulgare DSM 4025. In Escherichia coli, Psdh and Psndh demonstrated strong activity with the former about two times stronger than the latter. DCIP decoloration method and reporter plasmids pSDH or pSNDH may be applied to discover promoters of genes in E. coli and to determine their strength in one step.
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Affiliation(s)
- Shulin Fu
- College of Life Science, Northwest Sci-Tec University of Agriculture and Forestry, Yangling, 712100, People's Republic of China
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Heras SR, López MC, Olivares M, Thomas MC. The L1Tc non-LTR retrotransposon of Trypanosoma cruzi contains an internal RNA-pol II-dependent promoter that strongly activates gene transcription and generates unspliced transcripts. Nucleic Acids Res 2007; 35:2199-214. [PMID: 17369274 PMCID: PMC1874656 DOI: 10.1093/nar/gkl1137] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
L1Tc is the best represented autonomous LINE of the Trypanosoma cruzi genome, throughout which several functional copies may exist. In this study, we show that the first 77 bp of L1Tc (Pr77) (also present in the T. cruzi non-autonomous retrotransposon NARTc, in the Trypanosoma brucei RIME/ingi elements, and in the T. cruzi, T. brucei and Leishmania major degenerate L1Tc/ingi-related elements [DIREs]) behave as a promoter element that activates gene transcription. The transcription rate promoted by Pr77 is 10–14-fold higher than that mediated by sequences located upstream from the T. cruzi tandemly repeated genes KMP11 and the GAPDH. The Pr77 promoter-derived mRNAs initiate at nucleotide +1 of L1Tc, are unspliced and translated. L1Tc transcripts show a moderate half life and are RNA pol II dependent. The presence of an internal promoter at the 5′ end of L1Tc favors the production of full-length L1Tc RNAs and reinforces the hypothesis that this mobile element may be naturally autonomous in its transposition.
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Affiliation(s)
| | - Manuel C. López
- *To whom correspondence should be addressed. +34 958 181 662+34 958 181 632 Correspondence may also be addressed to M. Carmen Thomas. +34 958 181 662+34 958 181
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Maxwell PH, Belote JM, Levis RW. Identification of multiple transcription initiation, polyadenylation, and splice sites in the Drosophila melanogaster TART family of telomeric retrotransposons. Nucleic Acids Res 2006; 34:5498-507. [PMID: 17020919 PMCID: PMC1636488 DOI: 10.1093/nar/gkl709] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The Drosophila non-long terminal repeat (non-LTR) retrotransposons TART and HeT-A specifically retrotranspose to chromosome ends to maintain Drosophila telomeric DNA. Relatively little is known, though, about the regulation of their expression and their retrotransposition to telomeres. We have used rapid amplification of cDNA ends (RACE) to identify multiple transcription initiation and polyadenylation sites for sense and antisense transcripts of three subfamilies of TART elements in Drosophila melanogaster. These results are consistent with the production of an array of TART transcripts. In contrast to other Drosophila non-LTR elements, a major initiation site for sense transcripts was mapped near the 3′ end of the TART 5′-untranslated region (5′-UTR), rather than at the start of the 5′-UTR. A sequence overlapping this sense start site contains a good match to an initiator consensus for the transcription start sites of Drosophila LTR retrotransposons. Interestingly, analysis of 5′ RACE products for antisense transcripts and the GenBank EST database revealed that TART antisense transcripts contain multiple introns. Our results highlight differences between transcription of TART and of other Drosophila non-LTR elements and they provide a foundation for testing the relationship between exceptional aspects of TART transcription and TART's specialized role at telomeres.
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Affiliation(s)
- Patrick H Maxwell
- Department of Biology, Syracuse University, 130 College Place, Syracuse, NY 13244, USA.
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Alcivar-Warren A, Meehan-Meola D, Wang Y, Guo X, Zhou L, Xiang J, Moss S, Arce S, Warren W, Xu Z, Bell K. Isolation and mapping of telomeric pentanucleotide (TAACC)n repeats of the Pacific whiteleg shrimp, Penaeus vannamei, using fluorescence in situ hybridization. MARINE BIOTECHNOLOGY (NEW YORK, N.Y.) 2006; 8:467-80. [PMID: 16729213 DOI: 10.1007/s10126-005-6031-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2005] [Accepted: 01/12/2006] [Indexed: 05/09/2023]
Abstract
To develop genetic and physical maps for shrimp, accurate information on the actual number of chromosomes and a large number of genetic markers is needed. Previous reports have shown two different chromosome numbers for the Pacific whiteleg shrimp, Penaeus vannamei, the most important penaeid shrimp species cultured in the Western hemisphere. Preliminary results obtained by direct sequencing of clones from a Sau3A-digested genomic library of P. vannamei ovary identified a large number of (TAACC/GGTTA)-containing SSRs. The objectives of this study were to (1) examine the frequency of (TAACC)n repeats in 662 P. vannamei genomic clones that were directly sequenced, and perform homology searches of these clones, (2) confirm the number of chromosomes in testis of P. vannamei, and (3) localize the TAACC repeats in P. vannamei chromosome spreads using fluorescence in situ hybridization (FISH). Results for objective 1 showed that 395 out of the 662 clones sequenced contained single or multiple SSRs with three or more repeat motifs, 199 of which contained variable tandem repeats of the pentanucleotide (TAACC/GGTTA)n, with 3 to 14 copies per sequence. The frequency of (TAACC)n repeats in P. vannamei is 4.68 kb for SSRs with five or more repeat motifs. Sequence comparisons using the BLASTN nonredundant and expressed sequence tag (EST) databases indicated that most of the TAACC-containing clones were similar to either the core pentanucleotide repeat in PVPENTREP locus (GenBank accession no. X82619) or portions of 28S rRNA. Transposable elements (transposase for Tn1000 and reverse transcriptase family members), hypothetical or unnamed protein products, and genes of known function such as 18S and 28S rRNAs, heat shock protein 70, and thrombospondin were identified in non-TAACC-containing clones. For objective 2, the meiotic chromosome number of P. vannamei was confirmed as N = 44. For objective 3, four FISH probes (P1 to P4) containing different numbers of TAACC repeats produced positive signals on telomeres of P. vannamei chromosomes. A few chromosomes had positive signals interstitially. Probe signal strength and chromosome coverage differed in the general order of P1>P2>P3>P4, which correlated with the length of TAACC repeats within the probes: 83, 66, 35, and 30 bp, respectively, suggesting that the TAACC repeats, and not the flanking sequences, produced the TAACC signals at chromosome ends and TAACC is likely the telomere sequence for P. vannamei.
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Affiliation(s)
- Acacia Alcivar-Warren
- Environmental and Comparative Genomics Section, Department of Environmental and Population Health, Cummings School of Veterinary Medicine at Tufts University, North Grafton, MA 01536, USA.
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Matsumoto T, Hamada M, Osanai M, Fujiwara H. Essential domains for ribonucleoprotein complex formation required for retrotransposition of telomere-specific non-long terminal repeat retrotransposon SART1. Mol Cell Biol 2006; 26:5168-79. [PMID: 16782900 PMCID: PMC1489159 DOI: 10.1128/mcb.00096-06] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Non-long terminal repeat (LTR) retrotransposons are major components of the higher eukaryotic genome. Most of them have two open reading frames (ORFs): ORF2 encodes mainly the endonuclease and reverse transcriptase domains, but the functional features of ORF1 remain largely unknown. We used telomere-specific non-LTR retrotransposon SART1 in Bombyx mori and clarified essential roles of the ORF1 protein (ORF1p) in ribonucleoprotein (RNP) formation by novel approaches: in vitro reconstitution and in vivo/in vitro retrotransposition assays using the baculovirus expression system. Detailed mutation analyses showed that each of the three CCHC motifs at the ORF1 C terminus are essential for SART1 retrotransposition and are involved in packaging the SART1 mRNA specifically into RNP. We also demonstrated that amino acid residues 555 to 567 and 285 to 567 in the SART1 ORF1p are crucial for the ORF1p-ORF1p and ORF1p-ORF2p interactions, respectively. The loss of these domains abolishes protein-protein interaction, leading to SART1 retrotransposition deficiency. These data suggest that systematic formation of RNP composed of ORF1p, ORF2p, and mRNA is mainly mediated by ORF1p domains and is a common, essential step for many non-LTR retrotransposons encoding the two ORFs.
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Affiliation(s)
- Takumi Matsumoto
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Bldg. 501, Kashiwa, Chiba 277-8562, Japan
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Fujiwara H, Osanai M, Matsumoto T, Kojima KK. Telomere-specific non-LTR retrotransposons and telomere maintenance in the silkworm, Bombyx mori. Chromosome Res 2005; 13:455-67. [PMID: 16132811 DOI: 10.1007/s10577-005-0990-9] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Most insects have telomeres that consist of pentanucleotide (TTAGG) telomeric repeats, which are synthesized by telomerase. However, all species in Diptera so far examined and several species in other orders of insect have lost the (TTAGG)n repeats, suggesting that some of them recruit telomerase-independent telomere maintenance. The silkworm, Bombyx mori, retains the TTAGG motifs in the chromosomal ends but expresses quite a low level of telomerase activity in all stages of various tissues. Just proximal to a 6-8-kb stretch of the TTAGG repeats in B. mori, more than 1000 copies of non-LTR retrotransposons, designated TRAS and SART families, occur among the telomeric repeats and accumulate. TRAS and SART are abundantly transcribed and actively retrotransposed into TTAGG telomeric repeats in a highly sequence-specific manner. They have three possible mechanisms to ensure specific integration into the telomeric repeats. This article focuses on the telomere structure and telomere-specific non-LTR retrotransposons in B. mori and discusses the mechanisms for telomere maintenance in this insect.
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Affiliation(s)
- Haruhiko Fujiwara
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Building 501, Kashiwano-ha, 277-8562 Kashiwa, Japan.
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17
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Zingler N, Weichenrieder O, Schumann GG. APE-type non-LTR retrotransposons: determinants involved in target site recognition. Cytogenet Genome Res 2005; 110:250-68. [PMID: 16093679 DOI: 10.1159/000084959] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2003] [Accepted: 02/05/2004] [Indexed: 10/25/2022] Open
Abstract
Non-long terminal repeat (Non-LTR) retrotransposons represent a diverse and widely distributed group of transposable elements and an almost ubiquitous component of eukaryotic genomes that has a major impact on evolution. Their copy number can range from a few to several million and they often make up a significant fraction of the genomes. The members of the dominating subtype of non-LTR retrotransposons code for an endonuclease with homology to apurinic/apyrimidinic endonucleases (APE), and are thus termed APE-type non-LTR retrotransposons. In the last decade both the number of identified non-LTR retrotransposons and our knowledge of biology and evolution of APE-type non-LTR retrotransposons has increased tremendously.
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Affiliation(s)
- N Zingler
- Paul-Ehrlich-Institut, Langen, Germany
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18
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Kojima KK, Matsumoto T, Fujiwara H. Eukaryotic translational coupling in UAAUG stop-start codons for the bicistronic RNA translation of the non-long terminal repeat retrotransposon SART1. Mol Cell Biol 2005; 25:7675-86. [PMID: 16107714 PMCID: PMC1190309 DOI: 10.1128/mcb.25.17.7675-7686.2005] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Most eukaryotic cellular mRNAs are monocistronic; however, many retroviruses and long terminal repeat (LTR) retrotransposons encode multiple proteins on a single RNA transcript using ribosomal frameshifting. Non-long terminal repeat (non-LTR) retrotransposons are considered the ancestor of LTR retrotransposons and retroviruses, but their translational mechanism of bicistronic RNA remains unknown. We used a baculovirus expression system to produce a large amount of the bicistronic RNA of SART1, a non-LTR retrotransposon of the silkworm, and were able to detect the second open reading frame protein (ORF2) by Western blotting. The ORF2 protein was translated as an independent protein, not as an ORF1-ORF2 fusion protein. We revealed by mutagenesis that the UAAUG overlapping stop-start codon and the downstream RNA secondary structure are necessary for efficient ORF2 translation. Increasing the distance between the ORF1 stop codon and the ORF2 start codon decreased translation efficiency. These results are different from the eukaryotic translation reinitiation mechanism represented by the yeast GCN4 gene, in which the probability of reinitiation increases as the distance between the two ORFs increases. The translational mechanism of SART1 ORF2 is analogous to translational coupling observed in prokaryotes and viruses. Our results indicate that translational coupling is a general mechanism for bicistronic RNA translation.
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MESH Headings
- Amino Acid Sequence
- Antigens, Neoplasm/chemistry
- Antigens, Neoplasm/genetics
- Base Sequence
- Codon, Initiator/genetics
- Codon, Terminator/genetics
- Frameshifting, Ribosomal
- Molecular Sequence Data
- Nucleic Acid Conformation
- Open Reading Frames/genetics
- Protein Biosynthesis/genetics
- RNA, Fungal/chemistry
- RNA, Fungal/genetics
- RNA, Fungal/metabolism
- Retroelements/genetics
- Ribonucleoproteins, Small Nuclear/chemistry
- Ribonucleoproteins, Small Nuclear/genetics
- Saccharomyces cerevisiae/genetics
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Affiliation(s)
- Kenji K Kojima
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Chiba, Japan
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19
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Osanai M, Takahashi H, Kojima KK, Hamada M, Fujiwara H. Essential motifs in the 3' untranslated region required for retrotransposition and the precise start of reverse transcription in non-long-terminal-repeat retrotransposon SART1. Mol Cell Biol 2004; 24:7902-13. [PMID: 15340053 PMCID: PMC515065 DOI: 10.1128/mcb.24.18.7902-7913.2004] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Non-long-terminal-repeat (non-LTR) retrotransposons amplify their copies by reverse transcribing mRNA from the 3' end, but the initial processes of reverse transcription are still unclear. We have shown that a telomere-specific non-LTR retrotransposon of the silkworm, SART1, requires the 3' untranslated region (3' UTR) for retrotransposition. With an in vivo retrotransposition assay, we identified several novel motifs within the 3' UTR involved in precise and efficient reverse transcription. Of 461 nucleotides (nt) of the 3' UTR, the central region, from nt 163 to nt 295, was essential for SART1 retrotransposition. Of five putative stem-loops formed in RNA for the SART1 3' UTR, the second stem-loop (nt 159 to 221) is included in this region. Loss of the 3' region (nt 296 to 461) in the 3' UTR and the poly(A) tract resulted in decreased and inaccurate reverse transcription, which starts mostly from several telomeric repeat-like GGUU sequences just downstream of the second stem-loop. These results suggest that short telomeric repeat-like sequences in the 3' UTR anneal to the bottom strand of (TTAGG)(n) repeats. We also demonstrated that the mRNA for green fluorescent protein (GFP) could be retrotransposed into telomeric repeats when the GFP coding region is fused with the SART1 3' UTR and SART1 open reading frame proteins are supplied in trans.
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Affiliation(s)
- Mizuko Osanai
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Building 501, Kashiwa, Chiba 277-8562, Japan
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20
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Maita N, Anzai T, Aoyagi H, Mizuno H, Fujiwara H. Crystal structure of the endonuclease domain encoded by the telomere-specific long interspersed nuclear element, TRAS1. J Biol Chem 2004; 279:41067-76. [PMID: 15247245 DOI: 10.1074/jbc.m406556200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The telomere-specific long interspersed nuclear element, TRAS1, encodes an endonuclease domain, TRAS1-EN, which specifically cleaves the telomeric repeat targets (TTAGG)n of insects and (TTAGGG)n of vertebrates. To elucidate the sequence-specific recognition properties of TRAS1-EN, we determined the crystal structure at 2.4-A resolution. TRAS1-EN has a four-layered alpha/beta sandwich structure; its topology is similar to apurinic/apyrimidinic endonucleases, but the beta-hairpin (beta10-beta11) at the edge of the DNA-binding surface makes an extra loop that distinguishes TRAS1-EN from cellular apurinic/apyrimidinic endonucleases. A protein-DNA complex model suggests that the beta10-beta11 hairpin fits into the minor groove, enabling interaction with the telomeric repeats. Mutational studies of TRAS1-EN also indicated that the Asp-130 and beta10-beta11 hairpin structure are involved in specific recognition of telomeric repeats.
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Affiliation(s)
- Nobuo Maita
- Department of Biochemistry, National Institute of Agrobiological Sciences, Tsukuba, 305-8602, Japan
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21
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Ohta Y, Noma K, Tsuchimoto S, Ohtsubo E, Ohtsubo H. Expression of Arabidopsis LINEs from two promoters. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 32:809-818. [PMID: 12472695 DOI: 10.1046/j.1365-313x.2002.01466.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Most Arabidopsis long interspersed elements (LINEs, called ATLNs) have two open reading frames, orf1 and orf2. In the 5' untranslated regions (UTRs) located upstream of orf1, the most proximal segments of tens of base pairs long are not homologous even in two ATLN members with almost identical sequences. In this study, we first show that RT-PCR products from ATLN39, a member of ATLN, can be detected only in total RNA from the hypomethylation mutant ddm1 or from suspension-cultured cells treated with a DNA methylation inhibitor 5-azacytidine, indicating that the expression of ATLN39 is negatively regulated by DNA methylation. We then show that orf1 fused in frame with the luciferase (luc) gene is expressed in suspension-cultured cells of A. thaliana when the 5' UTR is present in the region upstream of orf1. Analysis of deletion in the 5' UTR revealed that the 5' UTR has two promoters, designated here as P1 and P2. Analysis of transcripts by 5' RACE showed that their 5' ends were located at sites immediately upstream of the P1 region or at sites downstream of the P2 region. This observation and the fact that the P1 region contains no TATA sequence indicate that P1 is an internal promoter that initiates transcription from sites upstream of the promoter. A sequence containing GGCGA with a CpG methylatable site is conserved in the P1 regions in members closely related to ATLN39. The P2 region, however, contains the TATA sequence as well as another sequence with a CpG site. The TATA sequence is conserved in members closely related to ATLN39 but not in the other ATLN members, suggesting that P2 is the promoter uniquely present in the ATLN39-related members. Transcripts from promoter P1 can be used as templates to give new copies proficient in retroposition, but those from promoter P2 cannot because of the lack of the proximal half region of the 5' UTR sequence. Transcripts from promoter P2, as well as those from promoter P1 can, however, be used for the production of a sufficient amount of proteins for retroposition. Only a short sequence of the non-homologous region is present at the 5' ends of transcripts from promoter P1, thus suggesting that the non-homologous regions seen in the most proximal regions in ATLN elements are not generated in transcription.
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Affiliation(s)
- Yoshizu Ohta
- Institute of Molecular and Cellular Biosciences, the University of Tokyo, Bunkyo-ku, Japan
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22
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Takahashi H, Fujiwara H. Transplantation of target site specificity by swapping the endonuclease domains of two LINEs. EMBO J 2002; 21:408-17. [PMID: 11823433 PMCID: PMC125841 DOI: 10.1093/emboj/21.3.408] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Long interspersed elements (LINEs) are ubiquitous genomic elements in higher eukaryotes. Here we develop a novel assay to analyze in vivo LINE retrotransposition using the telomeric repeat-specific elements SART1 and TRAS1. We demonstrate by PCR that silkworm SART1, which is expressed from a recombinant baculovirus, transposes in Sf9 cells into the chromosomal (TTAGG)n sequences, at the same specific nucleotide position as in the silkworm genome. Thus authentic retrotransposition by complete reverse transcription of the entire RNA transcription unit and occasional 5' truncation is observed. The retrotransposition requires conserved domains in both open reading frames (ORFs), including the ORF1 cysteine- histidine motifs. In contrast to human L1, recognition of the 3' untranslated region sequence is crucial for SART1 retrotransposition, which results in efficient trans-complementation. Swapping the endonuclease domain from TRAS1 into SART1 converts insertion specificity to that of TRAS1. Thus the primary determinant of in vivo target selection is the endonuclease domain, suggesting that modified LINEs could be used as gene therapy vectors, which deliver only genes of interest but not retrotransposons themselves in trans to specific genomic locations.
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Affiliation(s)
- Hidekazu Takahashi
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Building 501, Kashiwa, Chiba 277-8562, Japan
Present address: Department of Molecular Biology and Genetics, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA Corresponding author e-mail:
| | - Haruhiko Fujiwara
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bioscience Building 501, Kashiwa, Chiba 277-8562, Japan
Present address: Department of Molecular Biology and Genetics, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA Corresponding author e-mail:
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23
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Kubo Y, Okazaki S, Anzai T, Fujiwara H. Structural and phylogenetic analysis of TRAS, telomeric repeat-specific non-LTR retrotransposon families in Lepidopteran insects. Mol Biol Evol 2001; 18:848-57. [PMID: 11319268 DOI: 10.1093/oxfordjournals.molbev.a003866] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
TRAS1 is a non-LTR retrotransposon inserted specifically into the telomeric repeat (TTAGG)(n) in the silkworm, Bombyx mori. To characterize the evolutionary origin of TRAS-like elements, we identified seven TRAS families (TRAS3, TRAS4, TRAS5, TRAS6, TRASY, TRASZ, and TRASW) from B. mori and four elements from two Lepidoptera, Dictyoploca japonica (TRASDJ) and Samia cynthia ricini (TRASSC3, TRASSC4, and TRASSC9). More than 2,000 copies of various Bombyx TRAS elements accumulated within (TTAGG)(n) sequences as unusual but orderly tandem repeats. The 5' and 3' regions were highly conserved within each class of Bombyx TRAS elements without truncation. This suggests that distinct classes of TRAS have been maintained independently by retrotransposition into (TTAGG)(n). The phylogenetic tree of site-specific retroelements showed that nine TRAS families in Lepidoptera constitute a single phylogenetic group that is closely related to the R1 family that inserts specifically into arthropod 28S rDNA. The higher amino acid sequence identity from endonuclease (EN) to reverse transcriptase (RT) domains between TRAS groups (about 37%-70%) than among TRAS elements and R1Bm (about 25%-30%), may reflect the presence of some DNA structure responsible for their target specificity. Sequence comparison from EN to RT domains among non-LTR elements revealed several regions conserved only within TRAS elements. We found a highly conserved region that resembles the Myb-like DNA-binding structure, between the EN and RT domains. These regions may be involved in site-specific integration of TRAS elements into the (TTAGG)(n) telomeric repeats.
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Affiliation(s)
- Y Kubo
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Tokyo, Japan
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24
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Abstract
Replication of eukaryotic linear chromosomes is incomplete and leaves terminal gaps. The evolutionary widely distributed solution to this "end replication" is twofold: chromosome ends are capped with telomeres, bearing multiple copies of redundant telomeric sequences, and the telomerase enzyme can add (lost) telomeric repeats. Telomerase in humans, as in all mammals, is ubiquitous in all embryonic tissues. In adults, telomerase remains active in germs cells, and, although down-regulated in most somatic tissues, telomerase is active in regenerative tissues and notably, in tumor cells. Telomerase activity is linked to cellular proliferation, and its activation seems to be a mandatory step in carcinogenesis. In contrast to mammals, indeterminately growing multicellular organisms, like fish and crustaceae, maintain unlimited growth potential or 'immortality' in all somatic tissues throughout their entire life. Also this cell immortalization is brought about by maintaining telomerase expression. Disease prognosis for human tumors includes evaluation of cell proliferation, based on the detection of proliferation markers with monoclonal antibodies. The significance of the classical marker Ki-67, and of a novel marker repp-86 are compared with semiquantitative telomerase assays. For tumor therapy, telomerase inhibitors are attractive tools. Results with telomerase knock-out mice have revealed promise, but also risk of this approach. On the other side, telomerase stimulation is attractive for expanding the potential of cellular proliferation in vitro, with possible applications for transplantation of in vitro expanded human cells, for immortalizing primary human cells as improved tissue models, and for the isolation of otherwise intractable products, like genuine human monoclonal antibodies.
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Affiliation(s)
- G Krupp
- Institute for Hematopathology, Center for Pathology and Applied Cancer Research, Christian-Albrechts-University, Kiel, Germany.
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25
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Anzai T, Takahashi H, Fujiwara H. Sequence-specific recognition and cleavage of telomeric repeat (TTAGG)(n) by endonuclease of non-long terminal repeat retrotransposon TRAS1. Mol Cell Biol 2001; 21:100-8. [PMID: 11113185 PMCID: PMC88784 DOI: 10.1128/mcb.21.1.100-108.2001] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The telomere of the silkworm Bombyx mori consists of (TTAGG/CCTAA)(n) repeats and harbors a large number of telomeric repeat-specific non-long terminal repeat retrotransposons, such as TRAS1 and SART1. To understand how these retrotransposons recognize and integrate into the telomeric repeat in a sequence-specific manner, we expressed the apurinic-apryrimidinic endonuclease-like endonuclease domain of TRAS1 (TRAS1 EN), which is supposed to digest the target DNA, and characterized its enzymatic properties. Purified TRAS1 EN could generate specific nicks on both strands of the telomeric repeat sequence between T and A of the (TTAGG)(n) strand (bottom strand) and between C and T of the (CCTAA)(n) strand (top strand). These sites are consistent with insertion sites expected from the genomic structure of boundary regions of TRAS1. Time course studies of nicking activities on both strands revealed that the cleavages on the bottom strand preceded those on the top strand, supporting the target-primed reverse transcription model. TRAS1 EN could cleave the telomeric repeats specifically even if it was flanked by longer tracts of nontelomeric sequence, indicating that the target site specificity of the TRAS1 element was mainly determined by its EN domain. Based on mutation analyses, TRAS1 EN recognizes less than 10 bp around the initial cleavage site (upstream 7 bp and downstream 3 bp), and the GTTAG sequence especially is essential for the cleavage reaction on the bottom strand (5'. TTAGGTT downward arrow AGG. 3'). TRAS1 EN, the first identified endonuclease digesting telomeric repeats, may be used as a genetic tool to shorten the telomere in insects and some other organisms.
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Affiliation(s)
- T Anzai
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
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26
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Sasaki T, Fujiwara H. Detection and distribution patterns of telomerase activity in insects. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:3025-31. [PMID: 10806402 DOI: 10.1046/j.1432-1033.2000.01323.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Telomeres of most insects consist of pentanucleotide (TTAGG)n repeats, although the repeats are absent in Diptera and some other insect species, where the telomere regions are perhaps maintained without telomerase. To understand various and unusual telomere formation in insects, we have studied the characteristic features of a putative insect telomerase that has not been previously described. Using a modified telomeric repeat amplification protocol (TRAP), we first detected the telomerase activity in crickets, cockroaches and two Lepidopteran insects. The telomerase from crickets and cockroaches required dATP, dGTP and dTTP but not dCTP as a substrate and sequence analyses of the products of TRAP revealed that the (TTAGG)n repeats are synthesized by telomerase. The cockroach telomerase was detected both in somatic (fat body, muscle and neural tissues) and germ line (testis) cells, suggesting that expression of this enzyme is not regulated in a tissue-specific manner at an adult stage. While we detected high levels of telomerase activity in crickets and cockroaches, we could not detect activity in all tissues and cell cultures of the silkworm, Bombyx mori and in two Drosophila and one Sarcophaga cell lines. This supports the theory that Dipteran insects maintain their telomeres without telomerase.
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Affiliation(s)
- T Sasaki
- Graduate School of Frontier Sciences, University of Tokyo, Japan
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