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Sakamoto Y, Zaha S, Suzuki Y, Seki M, Suzuki A. Application of long-read sequencing to the detection of structural variants in human cancer genomes. Comput Struct Biotechnol J 2021; 19:4207-4216. [PMID: 34527193 PMCID: PMC8350331 DOI: 10.1016/j.csbj.2021.07.030] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 07/20/2021] [Accepted: 07/25/2021] [Indexed: 01/02/2023] Open
Abstract
In recent years, the so-called long-read sequencing technology has had a substantial impact on various aspects of genome sciences. Here, we introduce recent studies of cancerous structural variants (SVs) using long-read sequencing technologies, namely Pacific Biosciences (PacBio) sequencers, Oxford Nanopore Technologies (ONT) sequencers, and linked-read methods. By taking advantage of long-read lengths, these technologies have enabled the precise detection of SVs, including long insertions by transposable elements, such as LINE-1. In addition to SV detection, the epigenome status (including DNA methylation and haplotype information) surrounding SV loci has also been unveiled by long-read sequencing technologies, to identify the effects of SVs. Among the various research fields in which long-read sequencing has been applied, cancer genomics has shown the most remarkable advances. In fact, many studies are beginning to shed light on the detection of SVs and the elucidation of their complex structures in various types of cancer. In the particular case of cancers, we summarize the technical limitations of the application of this technology to the analysis of clinical samples. We will introduce recent achievements from this viewpoint. However, a similar approach will be started for other applications in the near future. Therefore, by complementing the current short-read sequencing analysis, long-read sequencing should reveal the complex nature of human genomes in their healthy and disease states, which will open a new opportunity for a better understanding of disease development and for a novel strategy for drug development.
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Affiliation(s)
- Yoshitaka Sakamoto
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Suzuko Zaha
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Yutaka Suzuki
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Masahide Seki
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
| | - Ayako Suzuki
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
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Structural variation and its potential impact on genome instability: Novel discoveries in the EGFR landscape by long-read sequencing. PLoS One 2020; 15:e0226340. [PMID: 31940362 PMCID: PMC6961855 DOI: 10.1371/journal.pone.0226340] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Accepted: 11/25/2019] [Indexed: 12/29/2022] Open
Abstract
Structural variation (SV) is typically defined as variation within the human genome that exceeds 50 base pairs (bp). SV may be copy number neutral or it may involve duplications, deletions, and complex rearrangements. Recent studies have shown SV to be associated with many human diseases. However, studies of SV have been challenging due to technological constraints. With the advent of third generation (long-read) sequencing technology, exploration of longer stretches of DNA not easily examined previously has been made possible. In the present study, we utilized third generation (long-read) sequencing techniques to examine SV in the EGFR landscape of four haplotypes derived from two human samples. We analyzed the EGFR gene and its landscape (+/- 500,000 base pairs) using this approach and were able to identify a region of non-coding DNA with over 90% similarity to the most common activating EGFR mutation in non-small cell lung cancer. Based on previously published Alu-element genome instability algorithms, we propose a molecular mechanism to explain how this non-coding region of DNA may be interacting with and impacting the stability of the EGFR gene and potentially generating this cancer-driver gene. By these techniques, we were also able to identify previously hidden structural variation in the four haplotypes and in the human reference genome (hg38). We applied previously published algorithms to compare the relative stabilities of these five different EGFR gene landscape haplotypes to estimate their relative potentials to generate the EGFR exon 19, 15 bp canonical deletion. To our knowledge, the present study is the first to use the differences in genomic architecture between targeted cancer-linked phased haplotypes to estimate their relative potentials to form a common cancer-linked driver mutation.
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Roychowdhury T, Abyzov A. Chromatin organization modulates the origin of heritable structural variations in human genome. Nucleic Acids Res 2019; 47:2766-2777. [PMID: 30773596 PMCID: PMC6451188 DOI: 10.1093/nar/gkz103] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Revised: 02/06/2019] [Accepted: 02/14/2019] [Indexed: 12/11/2022] Open
Abstract
Structural variations (SVs) in the human genome originate from different mechanisms related to DNA repair, replication errors, and retrotransposition. Our analyses of 26 927 SVs from the 1000 Genomes Project revealed differential distributions and consequences of SVs of different origin, e.g. deletions from non-allelic homologous recombination (NAHR) are more prone to disrupt chromatin organization while processed pseudogenes can create accessible chromatin. Spontaneous double stranded breaks (DSBs) are the best predictor of enrichment of NAHR deletions in open chromatin. This evidence, along with strong physical interaction of NAHR breakpoints belonging to the same deletion suggests that majority of NAHR deletions are non-meiotic i.e. originate from errors during homology directed repair (HDR) of spontaneous DSBs. In turn, the origin of the spontaneous DSBs is associated with transcription factor binding in accessible chromatin revealing the vulnerability of functional, open chromatin. The chromatin itself is enriched with repeats, particularly fixed Alu elements that provide the homology required to maintain stability via HDR. Through co-localization of fixed Alus and NAHR deletions in open chromatin we hypothesize that old Alu expansion had a stabilizing role on the human genome.
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Affiliation(s)
- Tanmoy Roychowdhury
- Mayo Clinic, Department of Health Sciences Research, Center for Individualized Medicine, Rochester, MN 55905, USA
| | - Alexej Abyzov
- Mayo Clinic, Department of Health Sciences Research, Center for Individualized Medicine, Rochester, MN 55905, USA
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Wisse RPL, Kuiper JJW, Radstake TRD, Broen JCA. Quantification of Double Stranded DNA Breaks and Telomere Length as Proxies for Corneal Damage and Replicative Stress in Human Keratoconus Corneas. Transl Vis Sci Technol 2019; 8:10. [PMID: 31372311 PMCID: PMC6660185 DOI: 10.1167/tvst.8.4.10] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 05/17/2019] [Indexed: 12/17/2022] Open
Abstract
Purpose The pathogenesis of keratoconus (KC) is multifactorial, and associated with oxidative stress and subsequent DNA damage. We investigate differences in DNA damage and replicative stress in patients with KC, and in healthy and diseased controls. Methods We obtained 64 corneal buttons from 27 patients with KC after corneal transplant surgery, 21 with a decompensated graft (DG), and 16 healthy controls (HC). The amount of intact Alu elements per genome copy as measured by quantitative polymerase chain reaction (qPCR) was used to quantify intact DNA. Telomere length was measured as a proxy for replicative stress. In addition, telomerase reverse transcriptase (hTERT) gene expression level was assessed. Results Mean (± standard deviation [SD]) DNA damage was similar between the KC (5.56 ± 14.08), DG (3.16 ± 8.22), and HC (3.51 ± 6.66) groups (P = 0.807). No associations were found between DNA damage and patient age (P = 0.523), atopic constitution (P = 0.240), or contact lens wear (P = 0.393). Telomere length differed (P = 0.034), most notably in the KC group, and hTERT was not detected in any corneal sample. Three cross-linked (CXL) KC corneas did not contain significantly more DNA damage (×2.6, P = 0.750). Conclusions Based on these findings, differences in actual corneal DNA damage in KC could not be identified, and the longer telomere length in KC did not support replicative stress as a major etiologic factor in the pathogenesis of KC. Future longitudinal investigations on KC etiology should assess progressively early cases to better comprehend the cellular and molecular processes preceding the archetypical morphologic changes. Translational Relevance The standard treatment for progressive keratoconus promotes the crosslinking of collagen fibers through ultraviolet radiation and the subsequent formation of reactive oxygen species. Our study helps to underline the safety of this treatment approach.
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Affiliation(s)
- Robert P L Wisse
- Department of Ophthalmology, University Medical Center Utrecht, The Netherlands
| | - Jonas J W Kuiper
- Department of Ophthalmology, University Medical Center Utrecht, The Netherlands.,Ophthalmo-Immunology group, Laboratory of Translational Immunology, Department of Immunology, University Medical Center Utrecht, The Netherlands
| | - Timothy R D Radstake
- Department of Rheumatology & Clinical Immunology, Laboratory of Translational Immunology, Department of Immunology, University Medical Center Utrecht, The Netherlands
| | - Jasper C A Broen
- Department of Rheumatology & Clinical Immunology, Laboratory of Translational Immunology, Department of Immunology, University Medical Center Utrecht, The Netherlands
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Ramakrishnan S, Kockler Z, Evans R, Downing BD, Malkova A. Single-strand annealing between inverted DNA repeats: Pathway choice, participating proteins, and genome destabilizing consequences. PLoS Genet 2018; 14:e1007543. [PMID: 30091972 PMCID: PMC6103520 DOI: 10.1371/journal.pgen.1007543] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Revised: 08/21/2018] [Accepted: 07/06/2018] [Indexed: 11/19/2022] Open
Abstract
Double strand DNA breaks (DSBs) are dangerous events that can result from various causes including environmental assaults or the collapse of DNA replication. While the efficient and precise repair of DSBs is essential for cell survival, faulty repair can lead to genetic instability, making the choice of DSB repair an important step. Here we report that inverted DNA repeats (IRs) placed near a DSB can channel its repair from an accurate pathway that leads to gene conversion to instead a break-induced replication (BIR) pathway that leads to genetic instabilities. The effect of IRs is explained by their ability to form unusual DNA structures when present in ssDNA that is formed by DSB resection. We demonstrate that IRs can form two types of unusual DNA structures, and the choice between these structures depends on the length of the spacer separating IRs. In particular, IRs separated by a long (1-kb) spacer are predominantly involved in inter-molecular single-strand annealing (SSA) leading to the formation of inverted dimers; IRs separated by a short (12-bp) spacer participate in intra-molecular SSA, leading to the formation of fold-back (FB) structures. Both of these structures interfere with an accurate DSB repair by gene conversion and channel DSB repair into BIR, which promotes genomic destabilization. We also report that different protein complexes participate in the processing of FBs containing short (12-bp) versus long (1-kb) ssDNA loops. Specifically, FBs with short loops are processed by the MRX-Sae2 complex, whereas the Rad1-Rad10 complex is responsible for the processing of long loops. Overall, our studies uncover the mechanisms of genomic destabilization resulting from re-routing DSB repair into unusual pathways by IRs. Given the high abundance of IRs in the human genome, our findings may contribute to the understanding of IR-mediated genomic destabilization associated with human disease. Efficient and accurate repair of double-strand DNA breaks (DSBs), resulting from the exposure of cells to ionizing radiation or various chemicals, is crucial for cell survival. Conversely, faulty DSB repair can generate genomic instability that can lead to birth defects or cancer in humans. Here we demonstrate that inverted DNA repeats (IRs) placed in the vicinity of a DSB, interfere with the accurate repair of DSBs and promote genomic rearrangements and chromosome loss. This results from annealing between inverted repeats, located either in different DNA molecules or in the same molecule. In addition, we describe a new role for the Rad1-Rad10 protein complex in processing fold-back (FB) structures formed by intra-molecular annealing involving IRs separated by long spacers. In contrast, FBs with short spacers are processed by the Mre11-Rad50-Xrs2/-Sae2 complex. Overall, we describe several pathways of DSB promoted interaction between IRs that can lead to genomic instability. Given the large number of IRs in the human genome, our findings are relevant to the mechanisms driving genomic destabilization in humans contributing to the development of cancer and other diseases.
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Affiliation(s)
- Sreejith Ramakrishnan
- Department of Biology, University of Iowa, Iowa City, IA, United States of America
- Indiana University Purdue University Indianapolis, Indianapolis, IN, United States of America
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA, United States of America
| | - Zachary Kockler
- Department of Biology, University of Iowa, Iowa City, IA, United States of America
| | - Robert Evans
- Indiana University Purdue University Indianapolis, Indianapolis, IN, United States of America
| | - Brandon D. Downing
- Indiana University Purdue University Indianapolis, Indianapolis, IN, United States of America
| | - Anna Malkova
- Department of Biology, University of Iowa, Iowa City, IA, United States of America
- Indiana University Purdue University Indianapolis, Indianapolis, IN, United States of America
- * E-mail:
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Navarrete HP, Soler LH, Mares RE, Ramos MA. Frequency of Alu insertions within the ACE and PR loci in Northwestern Mexicans. BMC Res Notes 2017; 10:339. [PMID: 28750672 PMCID: PMC5530943 DOI: 10.1186/s13104-017-2673-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 07/22/2017] [Indexed: 11/10/2022] Open
Abstract
OBJECTIVE Presently, non-LTR retrotransposons are the most active mobile elements in the human genome. Among these, Alu elements are highly represented in the modern population. Worldwide, distribution of Alu polymorphisms (insertion/deletion; I/D) shows variability between different populations. Two Alu insertion loci, ACE and PR, are significant biomarkers that have served in several genotype-phenotype association studies. In Mexico, studies concerning the frequency of these biomarkers have been conducted mainly in subpopulations from central and southern regions. Here, we screened a population sample of the northwestern region to gain further knowledge regarding the prevalence of Alu polymorphisms within ACE and PR loci. RESULTS For ACE locus, the observed genotype frequencies were 26.5, 51.0 and 22.5% for II, ID, and DD, respectively; and allelic frequencies for I and D were 52 and 48%. Whereas respective genotype frequencies for PR locus were 2.7, 26.5 and 70.8%, and the corresponding allele frequencies were 16 and 84%. Furthermore, the insertion frequency within ACE locus was similar between central, western and northwestern subpopulations, and rather higher in southeastern subpopulation (p < 0.05). Although the occurrence of Alu polymorphisms within PR locus has not been widely examined, the insertion frequency was higher in northwestern subpopulation, as compared with western and southeastern subpopulations (p < 0.05). Based on the frequency of Alu insertions found in ACE and PR loci, subpopulations from the northwestern, western and central regions share a common genetic origin, but apparently not with the subpopulation from the southeastern region, in accordance with the notion that assumes the existence of a broad genomic diversity in the Mexican population. In addition, the high prevalence of Alu insertions reveals their potential application as biomarkers with prognostic value for the associated diseases; e.g., as part of the standard protocols for clinical diagnosis.
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Affiliation(s)
- Hilda P Navarrete
- Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California, Calzada Universidad 14418, Parque Industrial Internacional, 22390, Tijuana, BCN, Mexico
| | - Linda H Soler
- Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California, Calzada Universidad 14418, Parque Industrial Internacional, 22390, Tijuana, BCN, Mexico
| | - Rosa E Mares
- Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California, Calzada Universidad 14418, Parque Industrial Internacional, 22390, Tijuana, BCN, Mexico
| | - Marco A Ramos
- Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California, Calzada Universidad 14418, Parque Industrial Internacional, 22390, Tijuana, BCN, Mexico.
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Yang JF, Ding XF, Chen L, Mat WK, Xu MZ, Chen JF, Wang JM, Xu L, Poon WS, Kwong A, Leung GKK, Tan TC, Yu CH, Ke YB, Xu XY, Ke XY, Ma RC, Chan JC, Wan WQ, Zhang LW, Kumar Y, Tsang SY, Li S, Wang HY, Xue H. Copy number variation analysis based on AluScan sequences. J Clin Bioinforma 2014; 4:15. [PMID: 25558350 PMCID: PMC4273479 DOI: 10.1186/s13336-014-0015-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Accepted: 11/12/2014] [Indexed: 01/08/2023] Open
Abstract
BACKGROUND AluScan combines inter-Alu PCR using multiple Alu-based primers with opposite orientations and next-generation sequencing to capture a huge number of Alu-proximal genomic sequences for investigation. Its requirement of only sub-microgram quantities of DNA facilitates the examination of large numbers of samples. However, the special features of AluScan data rendered difficult the calling of copy number variation (CNV) directly using the calling algorithms designed for whole genome sequencing (WGS) or exome sequencing. RESULTS In this study, an AluScanCNV package has been assembled for efficient CNV calling from AluScan sequencing data employing a Geary-Hinkley transformation (GHT) of read-depth ratios between either paired test-control samples, or between test samples and a reference template constructed from reference samples, to call the localized CNVs, followed by use of a GISTIC-like algorithm to identify recurrent CNVs and circular binary segmentation (CBS) to reveal large extended CNVs. To evaluate the utility of CNVs called from AluScan data, the AluScans from 23 non-cancer and 38 cancer genomes were analyzed in this study. The glioma samples analyzed yielded the familiar extended copy-number losses on chromosomes 1p and 9. Also, the recurrent somatic CNVs identified from liver cancer samples were similar to those reported for liver cancer WGS with respect to a striking enrichment of copy-number gains in chromosomes 1q and 8q. When localized or recurrent CNV-features capable of distinguishing between liver and non-liver cancer samples were selected by correlation-based machine learning, a highly accurate separation of the liver and non-liver cancer classes was attained. CONCLUSIONS The results obtained from non-cancer and cancerous tissues indicated that the AluScanCNV package can be employed to call localized, recurrent and extended CNVs from AluScan sequences. Moreover, both the localized and recurrent CNVs identified by this method could be subjected to machine-learning selection to yield distinguishing CNV-features that were capable of separating between liver cancers and other types of cancers. Since the method is applicable to any human DNA sample with or without the availability of a paired control, it can also be employed to analyze the constitutional CNVs of individuals.
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Affiliation(s)
- Jian-Feng Yang
- Division of Life Science and Applied Genomics Centre, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Xiao-Fan Ding
- Division of Life Science and Applied Genomics Centre, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Lei Chen
- National Center for Liver Cancer Research and Eastern Hepatobiliary Surgery Hospital, 225 Changhai Road, Shanghai, 200438 China
| | - Wai-Kin Mat
- Division of Life Science and Applied Genomics Centre, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Michelle Zhi Xu
- Department of Oncology, Nanjing First Hospital, No. 68 Changle Road, Nanjing, 210006 China
| | - Jin-Fei Chen
- Department of Oncology, Nanjing First Hospital, No. 68 Changle Road, Nanjing, 210006 China
| | - Jian-Min Wang
- Department of Hematology, Changhai Hospital, Second Military Medical University, 174 Changhai Road, Shanghai, 200433 China
| | - Lin Xu
- Department of Thoracic Surgery, Jiangsu Key Laboratory of Molecular and Translational Cancer Research, Nanjing Medical University Affiliated Cancer Hospital, Cancer Institute of Jiangsu Province, Baiziting 42, Nanjing, 210009 China
| | - Wai-Sang Poon
- Division of Neurosurgery, Department of Surgery, Prince of Wales Hospital, Chinese University of Hong Kong, 30-32 Ngan Shing Street, Sha Tin, Hong Kong, China
| | - Ava Kwong
- Division of Neurosurgery, Department of Surgery, Li Ka Shing Faculty of Medicine, University of Hong Kong, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong, China
| | - Gilberto Ka-Kit Leung
- Division of Neurosurgery, Department of Surgery, Li Ka Shing Faculty of Medicine, University of Hong Kong, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong, China
| | - Tze-Ching Tan
- Department of Neurosurgery, Queen Elizabeth Hospital, 30 Gascoigne Road, Kowloon, Hong Kong, China
| | - Chi-Hung Yu
- Department of Neurosurgery, Queen Elizabeth Hospital, 30 Gascoigne Road, Kowloon, Hong Kong, China
| | - Yue-Bin Ke
- Shenzhen Center for Disease Control and Prevention, No 8 Longyuan Road, Nanshan district, Shenzhen City, 518055 China
| | - Xin-Yun Xu
- Shenzhen Center for Disease Control and Prevention, No 8 Longyuan Road, Nanshan district, Shenzhen City, 518055 China
| | - Xiao-Yan Ke
- Nanjing Brain Hospital and Nanjing Institute of Neuropsychiatry, Nanjing Medical University, Nanjing, 210029 China
| | - Ronald Cw Ma
- Department of Medicine and Therapeutics, 9th floor, Clinical Sciences Building, The Prince of Wales Hospital, Shatin, Hong Kong
| | - Juliana Cn Chan
- Department of Medicine and Therapeutics, 9th floor, Clinical Sciences Building, The Prince of Wales Hospital, Shatin, Hong Kong
| | - Wei-Qing Wan
- Department of Neurosurgery, Beijing Tiantan Hospital, 6 Tiantan Xili, Dongcheng District, Capital Medical University, Beijing, 100050 China
| | - Li-Wei Zhang
- Department of Neurosurgery, Beijing Tiantan Hospital, 6 Tiantan Xili, Dongcheng District, Capital Medical University, Beijing, 100050 China
| | - Yogesh Kumar
- Division of Life Science and Applied Genomics Centre, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Shui-Ying Tsang
- Division of Life Science and Applied Genomics Centre, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Shao Li
- MOE Key Laboratory of Bioinformatics and Bioinformatics Division, TNLIST, Department of Automation, Tsinghua University, Beijing, 100084 China
| | - Hong-Yang Wang
- National Center for Liver Cancer Research and Eastern Hepatobiliary Surgery Hospital, 225 Changhai Road, Shanghai, 200438 China.,International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Hospital, 225 Changhai Road, Shanghai, 200438 China
| | - Hong Xue
- Division of Life Science and Applied Genomics Centre, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
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Dynamic Alu methylation during normal development, aging, and tumorigenesis. BIOMED RESEARCH INTERNATIONAL 2014; 2014:784706. [PMID: 25243180 PMCID: PMC4163490 DOI: 10.1155/2014/784706] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 08/16/2014] [Indexed: 12/15/2022]
Abstract
DNA methylation primarily occurs on CpG dinucleotides and plays an important role in transcriptional regulations during tissue development and cell differentiation. Over 25% of CpG dinucleotides in the human genome reside within Alu elements, the most abundant human repeats. The methylation of Alu elements is an important mechanism to suppress Alu transcription and subsequent retrotransposition. Decades of studies revealed that Alu methylation is highly dynamic during early development and aging. Recently, many environmental factors were shown to have a great impact on Alu methylation. In addition, aberrant Alu methylation has been documented to be an early event in many tumors and Alu methylation levels have been associated with tumor aggressiveness. The assessment of the Alu methylation has become an important approach for early diagnosis and/or prognosis of cancer. This review focuses on the dynamic Alu methylation during development, aging, and tumor genesis. The cause and consequence of Alu methylation changes will be discussed.
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Separate quality-control measures are necessary for estimation of RNA and methylated DNA from formalin-fixed, paraffin-embedded specimens by quantitative PCR. J Mol Diagn 2014; 16:253-60. [PMID: 24412525 DOI: 10.1016/j.jmoldx.2013.11.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2013] [Revised: 11/13/2013] [Accepted: 11/25/2013] [Indexed: 01/10/2023] Open
Abstract
Estimations of RNA abundance and DNA methylation by quantitative PCR (qPCR) from formalin-fixed, paraffin-embedded (FFPE) tissue specimens are not yet routine in clinical laboratory practice. Excluding specimens with poorly preserved nucleic acids is an important quality-control step for avoiding unreliable results. Because the assays for RNA abundance and DNA methylation have different critical limiting factors, we examined the extent of overlap of excluded specimens for RNA abundance versus methylated DNA. The transcript abundance of three reference genes and of the test gene, estrogen receptor 1 (ESR1), was estimated by SYBR Green qPCR in 250 breast cancer specimens. The estrogen receptor (ER) protein was identified by IHC, and concordance between ESR1 and ER was estimated by Cohen's κ. TaqMan PCR for the ALU-C4 sequence was performed with bisulfite-treated DNA to determine usability in the MethyLight assay. Excluding specimens with mean reference gene CT values exceeding the group mean by >1 SD led to significant improvement of the concordance of ESR1 and ER. Specimens with usable DNA after bisulfite treatment likewise had ALU-C4 CT values of less than the group mean + 1 SD. Samples with low-quality RNA and DNA were partly nonoverlapping. RNA and DNA extracted from the same FFPE block need separate exclusion criteria for qPCR assays of transcript abundance and methylated DNA.
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McLain AT, Carman GW, Fullerton ML, Beckstrom TO, Gensler W, Meyer TJ, Faulk C, Batzer MA. Analysis of western lowland gorilla (Gorilla gorilla gorilla) specific Alu repeats. Mob DNA 2013; 4:26. [PMID: 24262036 PMCID: PMC4177385 DOI: 10.1186/1759-8753-4-26] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Accepted: 10/23/2013] [Indexed: 02/07/2023] Open
Abstract
Background Research into great ape genomes has revealed widely divergent activity levels over time for Alu elements. However, the diversity of this mobile element family in the genome of the western lowland gorilla has previously been uncharacterized. Alu elements are primate-specific short interspersed elements that have been used as phylogenetic and population genetic markers for more than two decades. Alu elements are present at high copy number in the genomes of all primates surveyed thus far. The AluY subfamily and its derivatives have been recognized as the evolutionarily youngest Alu subfamily in the Old World primate lineage. Results Here we use a combination of computational and wet-bench laboratory methods to assess and catalog AluY subfamily activity level and composition in the western lowland gorilla genome (gorGor3.1). A total of 1,075 independent AluY insertions were identified and computationally divided into 10 subfamilies, with the largest number of gorilla-specific elements assigned to the canonical AluY subfamily. Conclusions The retrotransposition activity level appears to be significantly lower than that seen in the human and chimpanzee lineages, while higher than that seen in orangutan genomes, indicative of differential Alu amplification in the western lowland gorilla lineage as compared to other Homininae.
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Affiliation(s)
- Adam T McLain
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
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