1
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Carvajal-Maldonado D, Li Y, Returan M, Averill AM, Doublié S, Wood RD. Dynamic stem loop extension by Pol θ and templated insertion during DNA repair. J Biol Chem 2024:107461. [PMID: 38876299 DOI: 10.1016/j.jbc.2024.107461] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2024] [Revised: 05/26/2024] [Accepted: 05/28/2024] [Indexed: 06/16/2024] Open
Abstract
Theta-mediated end-joining (TMEJ) is critical for survival of cancer cells when other DNA double-stranded break repair pathways are impaired. Human DNA polymerase theta (Pol θ) can extend single-stranded DNA oligonucleotides, but little is known about preferred substrates and mechanism. We show that Pol θ can extend both single-stranded DNA and RNA substrates by unimolecular stem loop synthesis initiated by only two 3' terminal base-pairs. Given sufficient time, Pol θ uses alternative pairing configurations that greatly expand the repertoire of sequence outcomes. Further primer-template adjustments yield low-fidelity outcomes when the nucleotide pool is imbalanced. Unimolecular stem loop synthesis competes with bimolecular end-joining, even when a longer terminal microhomology for end-joining is available. Both reactions are partially suppressed by the ssDNA binding protein RPA. Protein-primer grasp residues that are specific to Pol θ are needed for rapid stem-loop synthesis. The ability to perform stem-loop synthesis from a minimally paired primer is rare amongst human DNA polymerases but we show that human DNA polymerases Pol η and Pol λ can catalyze related reactions. Using purified human Pol θ, we reconstituted in vitro TMEJ incorporating an insertion arising from a stem loop extension. These activities may help explain TMEJ repair events that include inverted repeat sequences.
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Affiliation(s)
- Denisse Carvajal-Maldonado
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Center, Houston, Texas, USA
| | - Yuzhen Li
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Center, Houston, Texas, USA
| | - Mark Returan
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Center, Houston, Texas, USA
| | - April M Averill
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont, USA
| | - Sylvie Doublié
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont, USA.
| | - Richard D Wood
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Center, Houston, Texas, USA.
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2
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Menck CFM, Galhardo RS, Quinet A. The accurate bypass of pyrimidine dimers by DNA polymerase eta contributes to ultraviolet-induced mutagenesis. Mutat Res 2024; 828:111840. [PMID: 37984186 DOI: 10.1016/j.mrfmmm.2023.111840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2023] [Revised: 10/23/2023] [Accepted: 11/02/2023] [Indexed: 11/22/2023]
Abstract
Human xeroderma pigmentosum variant (XP-V) patients are mutated in the POLH gene, responsible for encoding the translesion synthesis (TLS) DNA polymerase eta (Pol eta). These patients suffer from a high frequency of skin tumors. Despite several decades of research, studies on Pol eta still offer an intriguing paradox: How does this error-prone polymerase suppress mutations? This review examines recent evidence suggesting that cyclobutane pyrimidine dimers (CPDs) are instructional for Pol eta. Consequently, it can accurately replicate these lesions, and the mutagenic effects induced by UV radiation stem from the deamination of C-containing CPDs. In this model, the deamination of C (forming a U) within CPDs leads to the correct insertion of an A opposite to the deaminated C (or U)-containing dimers. This intricate process results in C>T transitions, which represent the most prevalent mutations detected in skin cancers. Finally, the delayed replication in XP-V cells amplifies the process of C-deamination in CPDs and increases the burden of C>T mutations prevalent in XP-V tumors through the activity of backup TLS polymerases.
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Affiliation(s)
- C F M Menck
- Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo (USP), São Paulo, SP, Brazil.
| | - R S Galhardo
- Department of Microbiology, Institute of Biomedical Sciences, University of São Paulo (USP), São Paulo, SP, Brazil
| | - A Quinet
- Université Paris Cité, Inserm, CEA, Stabilité Génétique Cellules Souches et Radiations, LRS/iRCM/IBFJ, F-92265 Fontenay-aux-Roses, France; Université Paris-Saclay, Inserm, CEA, Stabilité Génétique Cellules Souches et Radiations, LRS/iRCM/IBFJ, F-92265 Fontenay-aux-Roses, France
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3
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Steele EJ, Franklin A, Lindley RA. Somatic mutation patterns at Ig and Non-Ig Loci. DNA Repair (Amst) 2024; 133:103607. [PMID: 38056368 DOI: 10.1016/j.dnarep.2023.103607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Revised: 11/17/2023] [Accepted: 11/21/2023] [Indexed: 12/08/2023]
Abstract
The reverse transcriptase (RT) model of immunoglobulin (Ig) somatic hypermutation (SHM) has received insufficient scientific attention. This is understandable given that DNA deamination mediated by activation-induced deaminase (AID), the initiating step of Ig SHM, has dominated experiments since 2002. We summarise some key history of the RT Ig SHM model dating to 1987. For example, it is now established that DNA polymerase η, the sole DNA repair polymerase involved in post-replication short-patch repair, is an efficient cellular RT. This implies that it is potentially able to initiate target site reverse transcription by RNA-directed DNA repair at AID-induced lesions. Recently, DNA polymerase θ has also been shown to be an efficient cellular RT. Since DNA polymerase θ plays no significant role in Ig SHM, it could serve a similar RNA-dependent DNA polymerase role as DNA polymerase η at non-Ig loci in the putative RNA-templated nucleotide excision repair of bulky adducts and other mutagenic lesions on the transcribed strand. A major yet still poorly recognised consequence of the proposed RT process in Ig SHM is the generation of significant and characteristic strand-biased mutation signatures at both deoxyadenosine/deoxythymidine and deoxyguanosine/deoxycytidine base pairs. In this historical perspective, we highlight how diagnostic strand-biased mutation signatures are detected in vivo during SHM at both Ig loci in germinal centre B lymphocytes and non-Ig loci in cancer genomes. These strand-biased signatures have been significantly obscured by technical issues created by improper use of the polymerase chain reaction technique. A heightened awareness of this fact should contribute to better data interpretation and somatic mutation pattern recognition both at Ig and non-Ig loci.
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Affiliation(s)
- Edward J Steele
- Melville Analytics Pty Ltd, 2/102 Duke St, Kangaroo Point, Brisbane 4169, Qld, Australia.
| | - Andrew Franklin
- Novartis Pharmaceuticals UK Limited, The WestWorks Building, White City Place, 195 Wood Lane, W12 7FQ London, United Kingdom
| | - Robyn A Lindley
- GMDxgenomics, Suite 201, 697 Burke Rd, Camberwell, Melbourne 3124, Vic, Australia; Department of Clinical Pathology, Faculty of Medicine, Dentistry & Health Sciences, University of Melbourne, Vic, Australia
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4
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Feltes BC, Menck CFM. Current state of knowledge of human DNA polymerase eta protein structure and disease-causing mutations. MUTATION RESEARCH. REVIEWS IN MUTATION RESEARCH 2022; 790:108436. [PMID: 35952573 DOI: 10.1016/j.mrrev.2022.108436] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 06/29/2022] [Accepted: 07/31/2022] [Indexed: 01/01/2023]
Abstract
POLη, encoded by the POLH gene, is a crucial protein for replicating damaged DNA and the most studied specialized translesion synthesis polymerases. Mutations in POLη are associated with cancer and the human syndrome xeroderma pigmentosum variant, which is characterized by extreme photosensitivity and an increased likelihood of developing skin cancers. The myriad of structural information about POLη is vast, covering dozens of different mutants, numerous crucial residues, domains, and posttranslational modifications that are essential for protein function within cells. Since POLη is key vital enzyme for cell survival, and mutations in this protein are related to aggressive diseases, understanding its structure is crucial for biomedical sciences, primarily due to its similarities with other Y-family polymerases and its potential as a targeted therapy-drug for tumors. This work provides an up-to-date review on structural aspects of the human POLη: from basic knowledge about critical residues and protein domains to its mutant variants, posttranslational modifications, and our current understanding of therapeutic molecules that target POLη. Thus, this review provides lessons about POLη's structure and gathers critical discussions and hypotheses that may contribute to understanding this protein's vital roles within the cells.
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Affiliation(s)
- Bruno César Feltes
- Department of Theoretical Informatics, Institute of Informatics, Department of Theoretical Informatics, Federal University of Rio Grande do Sul, Porto Alegre, RS Brazil; Department of Genetics, Institute of Bioscience, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil; Department of Biophysics, Institute of Bioscience, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil
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5
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Carvajal-Maldonado D, Drogalis Beckham L, Wood RD, Doublié S. When DNA Polymerases Multitask: Functions Beyond Nucleotidyl Transfer. Front Mol Biosci 2022; 8:815845. [PMID: 35071329 PMCID: PMC8782244 DOI: 10.3389/fmolb.2021.815845] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Accepted: 12/13/2021] [Indexed: 11/13/2022] Open
Abstract
DNA polymerases catalyze nucleotidyl transfer, the central reaction in synthesis of DNA polynucleotide chains. They function not only in DNA replication, but also in diverse aspects of DNA repair and recombination. Some DNA polymerases can perform translesion DNA synthesis, facilitating damage tolerance and leading to mutagenesis. In addition to these functions, many DNA polymerases conduct biochemically distinct reactions. This review presents examples of DNA polymerases that carry out nuclease (3'-5' exonuclease, 5' nuclease, or end-trimming nuclease) or lyase (5' dRP lyase) extracurricular activities. The discussion underscores how DNA polymerases have a remarkable ability to manipulate DNA strands, sometimes involving relatively large intramolecular movement.
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Affiliation(s)
- Denisse Carvajal-Maldonado
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Center, Houston, TX, United States
| | - Lea Drogalis Beckham
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT, United States
| | - Richard D Wood
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Center, Houston, TX, United States
| | - Sylvie Doublié
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT, United States
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6
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Franklin A, Steele EJ. RNA-directed DNA repair and antibody somatic hypermutation. Trends Genet 2021; 38:426-436. [PMID: 34740453 DOI: 10.1016/j.tig.2021.10.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 10/03/2021] [Accepted: 10/04/2021] [Indexed: 10/19/2022]
Abstract
Somatic hypermutation at antibody loci affects both deoxyadenosine-deoxythymidine (A/T) and deoxycytidine-deoxyguanosine (C/G) pairs. Deamination of C to deoxyuridine (U) by activation-induced deaminase (AID) explains how mutation at C/G pairs is potentiated. Mutation at A/T pairs is triggered during the initial stages of repair of AID-generated U lesions and occurs through an as yet unknown mechanism in which polymerase η has a major role. Recent evidence confirms that human polymerase η can act as a reverse transcriptase. Here, we compare the popular suggestion of mutation at A/T pairs through nucleotide mispairing (owing to polymerase error) during short-patch repair synthesis with the alternative proposal of mutation at A/T pairs through RNA editing and RNA-directed DNA repair.
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Affiliation(s)
- Andrew Franklin
- Novartis Pharma AG, Novartis Campus, 4056, Basel, Switzerland.
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7
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Steele EJ, Gorczynski RM, Lindley RA, Liu Y, Temple R, Tokoro G, Wickramasinghe DT, Wickramasinghe NC. The efficient Lamarckian spread of life in the cosmos. ADVANCES IN GENETICS 2020; 106:21-43. [PMID: 33081924 PMCID: PMC7340397 DOI: 10.1016/bs.adgen.2020.03.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In this Chapter we discuss the various mechanisms that are available for the possible transfer of cosmic microbial living systems from one cosmic habitat to another. With the 100 or so habitable planets that are now known to exist in our galaxy alone transfers of cometary dust carrying life including fragments of icy planetoids/asteroids would be expected to occur on a routine basis. It is thus easy to view the galaxy as a single connected "biosphere" of which our planet Earth is a minor component. The Hoyle-Wickramasinghe Panspermia paradigm provides a cogent biological rationale for the actual widespread existence of Lamarckian modes of inheritance in terrestrial systems (which we review here). Thus the Panspermia paradigm provides the raison d'etre for Lamarckian Inheritance. Under a terrestrially confined neoDarwinian viewpoint such an association may have been thought spurious in the past. Our aim here is to outline the main evidence for rapid terrestrial-based Lamarckian-based evolutionary hypermutation processes dependent on reverse transcription-coupled mechanisms among others. Such rapid adaptation mechanisms would be consistent with the effective cosmic spread of living systems. For example, a viable, or cryo-preserved, living system traveling through space in a protective matrix will of necessity need to adapt rapidly and proliferate on landing in a new cosmic niche. Lamarckian mechanisms thus come to the fore and supersede the slow (blind and random) genetic processes expected under neoDarwinian Earth centred theories.
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Affiliation(s)
- Edward J Steele
- C.Y.O'Connor ERADE Village Foundation, Piara Waters, Perth, WA, Australia; Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka; Melville Analytics Pty Ltd, Melbourne, VIC, Australia.
| | | | - Robyn A Lindley
- Department of Clinical Pathology, Faculty of Medicine, Dentistry & Health Sciences, University of Melbourne, Melbourne, VIC, Australia; GMDx Group Ltd, Melbourne, VIC, Australia
| | - Yongsheng Liu
- Henan Collaborative Innovation Center of Modern Biological Breeding, Henan Institute of Science and Technology, Xinxiang, China
| | - Robert Temple
- The History of Chinese Science and Culture Foundation, Conway Hall, London, United Kingdom
| | - Gensuke Tokoro
- Institute for the Study of Panspermia and Astroeconomics, Gifu, Japan
| | - Dayal T Wickramasinghe
- College of Physical and Mathematical Sciences, Australian National University, Canberra, ACT, Australia
| | - N Chandra Wickramasinghe
- Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka; Institute for the Study of Panspermia and Astroeconomics, Gifu, Japan; University of Buckingham, Buckingham, United Kingdom; National Institute of Fundamental Studies, Kandy, Sri Lanka.
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8
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Blood and saliva-derived exomes from healthy Caucasian subjects do not display overt evidence of somatic mosaicism. Mutat Res 2020; 821:111705. [PMID: 32569906 DOI: 10.1016/j.mrfmmm.2020.111705] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Revised: 04/07/2020] [Accepted: 04/27/2020] [Indexed: 02/07/2023]
Abstract
Somatic mosaicism is a normal occurrence during development in the tissues and organs. As part of establishing a "healthy population "(HP) background or base-line, we investigated whether such mosaicism can be routinely detected in the circulating DNA secured from a rigorously designed healthy human liquid biopsy clinical trial (saliva, blood). We deployed next generation (NG) whole exome sequencing (WES) at median exome coverage rates of 97.2 % (-to-30x) and 70.0 % (-to-100x). We found that somatic mosaicism is not detectable by such standard bulk WES sequencing assays in saliva and blood DNA in 24 normal healthy Caucasians of both sexes from 18 to 60 years of age. We conclude that for circulating DNA using standard WES no novel somatic mutational variants can be detected in protein-coding regions of normal healthy subjects. This implies that the extent within normal tissues of somatic mosaicism must be at a lower level, below the detection threshold, for these circulating DNA WES read depths.
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9
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Ghodke PP, Guengerich FP. Impact of 1, N 6-ethenoadenosine, a damaged ribonucleotide in DNA, on translesion synthesis and repair. J Biol Chem 2020; 295:6092-6107. [PMID: 32213600 DOI: 10.1074/jbc.ra120.012829] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 03/23/2020] [Indexed: 01/02/2023] Open
Abstract
Incorporation of ribonucleotides into DNA can severely diminish genome integrity. However, how ribonucleotides instigate DNA damage is poorly understood. In DNA, they can promote replication stress and genomic instability and have been implicated in several diseases. We report here the impact of the ribonucleotide rATP and of its naturally occurring damaged analog 1,N 6-ethenoadenosine (1,N 6-ϵrA) on translesion synthesis (TLS), mediated by human DNA polymerase η (hpol η), and on RNase H2-mediated incision. Mass spectral analysis revealed that 1,N 6-ϵrA in DNA generates extensive frameshifts during TLS, which can lead to genomic instability. Moreover, steady-state kinetic analysis of the TLS process indicated that deoxypurines (i.e. dATP and dGTP) are inserted predominantly opposite 1,N 6-ϵrA. We also show that hpol η acts as a reverse transcriptase in the presence of damaged ribonucleotide 1,N 6-ϵrA but has poor RNA primer extension activities. Steady-state kinetic analysis of reverse transcription and RNA primer extension showed that hpol η favors the addition of dATP and dGTP opposite 1,N 6-ϵrA. We also found that RNase H2 recognizes 1,N 6-ϵrA but has limited incision activity across from this lesion, which can lead to the persistence of this detrimental DNA adduct. We conclude that the damaged and unrepaired ribonucleotide 1,N 6-ϵrA in DNA exhibits mutagenic potential and can also alter the reading frame in an mRNA transcript because 1,N 6-ϵrA is incompletely incised by RNase H2.
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Affiliation(s)
- Pratibha P Ghodke
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37323-0146
| | - F Peter Guengerich
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37323-0146.
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10
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Franklin A, Steele EJ, Lindley RA. A proposed reverse transcription mechanism for (CAG)n and similar expandable repeats that cause neurological and other diseases. Heliyon 2020; 6:e03258. [PMID: 32140575 PMCID: PMC7044655 DOI: 10.1016/j.heliyon.2020.e03258] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 09/26/2019] [Accepted: 01/15/2020] [Indexed: 12/12/2022] Open
Abstract
The mechanism of (CAG)n repeat generation, and related expandable repeat diseases in non-dividing cells, is currently understood in terms of a DNA template-based DNA repair synthesis process involving hairpin stabilized slippage, local error-prone repair via MutSβ (MSH2-MSH3) hairpin protective stabilization, then nascent strand extension by DNA polymerases-β and -δ. We advance a very similar slipped hairpin-stabilized model involving MSH2-MSH3 with two key differences: the copying template may also be the nascent pre-mRNA with the repair pathway being mediated by the Y-family error-prone enzymes DNA polymerase-η and DNA polymerase-κ acting as reverse transcriptases. We argue that both DNA-based and RNA-based mechanisms could well be activated in affected non-dividing brain cells in vivo. Here, we compare the advantages of the RNA/RT-based model proposed by us as an adjunct to previously proposed models. In brief, our model depends upon dysregulated innate and adaptive immunity cascades involving AID/APOBEC and ADAR deaminases that are known to be involved in normal locus-specific immunoglobulin somatic hypermutation, cancer progression and somatic mutations at many off-target non-immunoglobulin sites across the genome: we explain how these processes could also play an active role in repeat expansion diseases at RNA polymerase II-transcribed genes.
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Affiliation(s)
- Andrew Franklin
- Medical Department, Novartis Pharmaceuticals UK Limited, 200 Frimley Business Park, Frimley, Surrey, GU16 7SR, United Kingdom
| | - Edward J. Steele
- Melville Analytics Pty Ltd, Melbourne, Vic, 3004, Australia
- CYO’Connor ERADE Village Foundation, Perth, WA, Australia
| | - Robyn A. Lindley
- GMDxgenomics, Melbourne, Vic, Australia
- Department of Clinical Pathology, Faculty of Medicine, Dentistry & Health Sciences, University of Melbourne, Vic, Australia
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11
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Steele EJ, Lindley RA. Regulatory T cells and co-evolution of allele-specific MHC recognition by the TCR. Scand J Immunol 2019; 91:e12853. [PMID: 31793005 PMCID: PMC7064991 DOI: 10.1111/sji.12853] [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: 09/17/2019] [Accepted: 11/27/2019] [Indexed: 12/13/2022]
Abstract
What is the evolutionary mechanism for the TCR-MHC-conserved interaction? We extend Dembic's model (Dembic Z. In, Scand J Immunol e12806, 2019) of thymus positive selection for high-avidity anti-self-MHC Tregs among double (CD4 + CD8+)-positive (DP) developing thymocytes. This model is based on competition for self-MHC (+ Pep) complexes presented on cortical epithelium. Such T cells exit as CD4 + CD25+FoxP3 + thymic-derived Tregs (tTregs). The other positively selected DP T cells are then negatively selected on medulla epithelium removing high-avidity anti-self-MHC + Pep as T cells commit to CD4 + or CD8 + lineages. The process is likened to the competitive selection and affinity maturation in Germinal Centre for the somatic hypermutation (SHM) of rearranged immunoglobulin (Ig) variable region (V[D]Js) of centrocytes bearing antigen-specific B cell receptors (BCR). We now argue that the same direct SHM processes for TCRs occur in post-antigenic Germinal Centres, but now occurring in peripheral pTregs. This model provides a potential solution to a long-standing problem previously recognized by Cohn and others (Cohn M, Anderson CC, Dembic Z. In, Scand J Immunol e12790, 2019) of how co-evolution occurs of species-specific MHC alleles with the repertoire of their germline TCR V counterparts. We suggest this is not by 'blind', slow, and random Darwinian natural selection events, but a rapid structured somatic selection vertical transmission process. The pTregs bearing somatic TCR V mutant genes then, on arrival in reproductive tissues, can donate their TCR V sequences via soma-to-germline feedback as discussed in this journal earlier. (Steele EJ, Lindley RA. In, Scand J Immunol e12670, 2018) The high-avidity tTregs also participate in the same process to maintain a biased, high-avidity anti-self-MHC germline V repertoire.
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Affiliation(s)
- Edward J Steele
- Melville Analytics Pty Ltd, Melbourne, Vic, Australia.,CYO'Connor ERADE Village Foundation, Perth, WA, Australia
| | - Robyn A Lindley
- GMDxCo Pty Ltd, Melbourne, Vic, Australia.,Department of Clinical Pathology, Faculty of Medicine, Dentistry & Health Sciences, University of Melbourne, Melbourne, Vic, Australia
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12
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Steele EJ, Gorczynski RM, Lindley RA, Liu Y, Temple R, Tokoro G, Wickramasinghe DT, Wickramasinghe NC. Lamarck and Panspermia - On the Efficient Spread of Living Systems Throughout the Cosmos. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 149:10-32. [PMID: 31445944 DOI: 10.1016/j.pbiomolbio.2019.08.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2019] [Revised: 08/14/2019] [Accepted: 08/21/2019] [Indexed: 02/06/2023]
Abstract
We review the main lines of evidence (molecular, cellular and whole organism) published since the 1970s demonstrating Lamarckian Inheritance in animals, plants and microorganisms viz. the transgenerational inheritance of environmentally-induced acquired characteristics. The studies in animals demonstrate the genetic permeability of the soma-germline Weismann Barrier. The widespread nature of environmentally-directed inheritance phenomena reviewed here contradicts a key pillar of neo-Darwinism which affirms the rigidity of the Weismann Barrier. These developments suggest that neo-Darwinian evolutionary theory is in need of significant revision. We argue that Lamarckian inheritance strategies involving environmentally-induced rapid directional genetic adaptations make biological sense in the context of cosmic Panspermia allowing the efficient spread of living systems and genetic innovation throughout the Universe. The Hoyle-Wickramasinghe Panspermia paradigm also developed since the 1970s, unlike strictly geocentric neo-Darwinism provides a cogent biological rationale for the actual widespread existence of Lamarckian modes of inheritance - it provides its raison d'être. Under a terrestrially confined neo-Darwinian viewpoint such an association may have been thought spurious in the past. Our aim is to outline the conceptual links between rapid Lamarckian-based evolutionary hypermutation processes dependent on reverse transcription-coupled mechanisms among others and the effective cosmic spread of living systems. For example, a viable, or cryo-preserved, living system travelling through space in a protective matrix will need of necessity to rapidly adapt and proliferate on landing in a new cosmic niche. Lamarckian mechanisms thus come to the fore and supersede the slow (blind and random) genetic processes expected under a traditional neo-Darwinian evolutionary paradigm.
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Affiliation(s)
- Edward J Steele
- C.Y.O'Connor ERADE Village Foundation, Piara Waters, Perth, 6112, WA, Australia; Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka; Melville Analytics Pty Ltd, Melbourne, Vic, Australia.
| | | | - Robyn A Lindley
- Department of Clinical Pathology, Faculty of Medicine, Dentistry & Health Sciences, University of MelbourneVic, Australia; GMDx Group Ltd, Melbourne, Vic, Australia
| | - Yongsheng Liu
- Henan Collaborative Innovation Center of Modern Biological Breeding, Henan Institute of Science and Technology, Xinxiang, 453003, China
| | - Robert Temple
- The History of Chinese Science and Culture Foundation, Conway Hall, London, UK
| | - Gensuke Tokoro
- Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka; Institute for the Study of Panspermia and Astrobiology, Gifu, Japan
| | - Dayal T Wickramasinghe
- Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka; College of Physical and Mathematical Sciences, Australian National University, Canberra, Australia
| | - N Chandra Wickramasinghe
- Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka; Institute for the Study of Panspermia and Astrobiology, Gifu, Japan; Buckingham Centre for Astrobiology, University of Buckingham, UK
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13
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Pilzecker B, Jacobs H. Mutating for Good: DNA Damage Responses During Somatic Hypermutation. Front Immunol 2019; 10:438. [PMID: 30915081 PMCID: PMC6423074 DOI: 10.3389/fimmu.2019.00438] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 02/19/2019] [Indexed: 11/13/2022] Open
Abstract
Somatic hypermutation (SHM) of immunoglobulin (Ig) genes plays a key role in antibody mediated immunity. SHM in B cells provides the molecular basis for affinity maturation of antibodies. In this way SHM is key in optimizing antibody dependent immune responses. SHM is initiated by targeting the Activation-Induced Cytidine Deaminase (AID) to rearranged V(D)J and switch regions of Ig genes. The mutation rate of this programmed mutagenesis is ~10-3 base pairs per generation, a million-fold higher than the non-AID targeted genome of B cells. AID is a processive enzyme that binds single-stranded DNA and deaminates cytosines in DNA. Cytosine deamination generates highly mutagenic deoxy-uracil (U) in the DNA of both strands of the Ig loci. Mutagenic processing of the U by the DNA damage response generates the entire spectrum of base substitutions characterizing SHM at and around the initial U lesion. Starting from the U as a primary lesion, currently five mutagenic DNA damage response pathways have been identified in generating a well-defined SHM spectrum of C/G transitions, C/G transversions, and A/T mutations around this initial lesion. These pathways include (1) replication opposite template U generates transitions at C/G, (2) UNG2-dependent translesion synthesis (TLS) generates transversions at C/G, (3) a hybrid pathway comprising non-canonical mismatch repair (ncMMR) and UNG2-dependent TLS generates transversions at C/G, (4) ncMMR generates mutations at A/T, and (5) UNG2- and PCNA Ubiquitination (PCNA-Ub)-dependent mutations at A/T. Furthermore, specific strand-biases of SHM spectra arise as a consequence of a biased AID targeting, ncMMR, and anti-mutagenic repriming. Here, we review mammalian SHM with special focus on the mutagenic DNA damage response pathways involved in processing AID induced Us, the origin of characteristic strand biases, and relevance of the cell cycle.
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Affiliation(s)
- Bas Pilzecker
- Division of Tumor Biology & Immunology, The Netherlands Cancer Institute, Amsterdam, Netherlands
| | - Heinz Jacobs
- Division of Tumor Biology & Immunology, The Netherlands Cancer Institute, Amsterdam, Netherlands
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Steele EJ, Al-Mufti S, Augustyn KA, Chandrajith R, Coghlan JP, Coulson SG, Ghosh S, Gillman M, Gorczynski RM, Klyce B, Louis G, Mahanama K, Oliver KR, Padron J, Qu J, Schuster JA, Smith WE, Snyder DP, Steele JA, Stewart BJ, Temple R, Tokoro G, Tout CA, Unzicker A, Wainwright M, Wallis J, Wallis DH, Wallis MK, Wetherall J, Wickramasinghe DT, Wickramasinghe JT, Wickramasinghe NC, Liu Y. Cause of Cambrian Explosion - Terrestrial or Cosmic? PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 136:3-23. [PMID: 29544820 DOI: 10.1016/j.pbiomolbio.2018.03.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
We review the salient evidence consistent with or predicted by the Hoyle-Wickramasinghe (H-W) thesis of Cometary (Cosmic) Biology. Much of this physical and biological evidence is multifactorial. One particular focus are the recent studies which date the emergence of the complex retroviruses of vertebrate lines at or just before the Cambrian Explosion of ∼500 Ma. Such viruses are known to be plausibly associated with major evolutionary genomic processes. We believe this coincidence is not fortuitous but is consistent with a key prediction of H-W theory whereby major extinction-diversification evolutionary boundaries coincide with virus-bearing cometary-bolide bombardment events. A second focus is the remarkable evolution of intelligent complexity (Cephalopods) culminating in the emergence of the Octopus. A third focus concerns the micro-organism fossil evidence contained within meteorites as well as the detection in the upper atmosphere of apparent incoming life-bearing particles from space. In our view the totality of the multifactorial data and critical analyses assembled by Fred Hoyle, Chandra Wickramasinghe and their many colleagues since the 1960s leads to a very plausible conclusion - life may have been seeded here on Earth by life-bearing comets as soon as conditions on Earth allowed it to flourish (about or just before 4.1 Billion years ago); and living organisms such as space-resistant and space-hardy bacteria, viruses, more complex eukaryotic cells, fertilised ova and seeds have been continuously delivered ever since to Earth so being one important driver of further terrestrial evolution which has resulted in considerable genetic diversity and which has led to the emergence of mankind.
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Affiliation(s)
- Edward J Steele
- CY O'Connor ERADE Village Foundation, Piara Waters, WA, Australia; Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka.
| | - Shirwan Al-Mufti
- Buckingham Centre for Astrobiology, University of Buckingham, UK
| | - Kenneth A Augustyn
- Center for the Physics of Living Organisms, Department of Physics, Michigan Technological University, Michigan, United States
| | | | - John P Coghlan
- University of Melbourne, Office of the Dean, Faculty Medicine, Dentistry and Health Sciences, 3rd Level, Alan Gilbert Building, Australia
| | - S G Coulson
- Buckingham Centre for Astrobiology, University of Buckingham, UK
| | - Sudipto Ghosh
- Metallurgical & Materials Engineering IIT, Kanpur, India
| | - Mark Gillman
- South African Brain Research Institute, 6 Campbell Street, Waverly, Johannesburg, South Africa
| | - Reginald M Gorczynski
- University Toronto Health Network, Toronto General Hospital, University of Toronto, Canada
| | - Brig Klyce
- Buckingham Centre for Astrobiology, University of Buckingham, UK
| | - Godfrey Louis
- Department of Physics, Cochin University of Science and Technology Cochin, India
| | | | - Keith R Oliver
- School of Veterinary and Life Sciences Murdoch University, Perth, WA, Australia
| | - Julio Padron
- Studio Eutropi, Clinical Pathology and Nutrition, Via Pompei 46, Ardea, 00040, Rome, Italy
| | - Jiangwen Qu
- Department of Infectious Disease Control, Tianjin Center for Disease Control and Prevention, China
| | - John A Schuster
- School of History and Philosophy of Science, Faculty of Science, University of Sydney, Sydney, Australia
| | - W E Smith
- Institute for the Study of Panspermia and Astrobiology, Gifu, Japan
| | - Duane P Snyder
- Buckingham Centre for Astrobiology, University of Buckingham, UK
| | - Julian A Steele
- Centre for Surface Chemistry and Catalysis, KU Leuven, Celestijnenlaan 200F, 3001, Leuven, Belgium
| | - Brent J Stewart
- CY O'Connor ERADE Village Foundation, Piara Waters, WA, Australia
| | - Robert Temple
- The History of Chinese Culture Foundation, Conway Hall, London, UK
| | - Gensuke Tokoro
- Institute for the Study of Panspermia and Astrobiology, Gifu, Japan
| | - Christopher A Tout
- Institute of Astronomy, The Observatories, Madingley Road, Cambridge, CB3 0HA, UK
| | | | - Milton Wainwright
- Buckingham Centre for Astrobiology, University of Buckingham, UK; Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka
| | - Jamie Wallis
- Buckingham Centre for Astrobiology, University of Buckingham, UK
| | - Daryl H Wallis
- Buckingham Centre for Astrobiology, University of Buckingham, UK
| | - Max K Wallis
- Buckingham Centre for Astrobiology, University of Buckingham, UK
| | - John Wetherall
- School of Biomedical Sciences, Perth, Curtin University, WA, Australia
| | - D T Wickramasinghe
- College of Physical and Mathematical Sciences, Australian National University, Canberra, Australia
| | | | - N Chandra Wickramasinghe
- Buckingham Centre for Astrobiology, University of Buckingham, UK; Centre for Astrobiology, University of Ruhuna, Matara, Sri Lanka; Institute for the Study of Panspermia and Astrobiology, Gifu, Japan
| | - Yongsheng Liu
- Henan Collaborative Innovation Center of Modern Biological Breeding, Henan Institute of Science and Technology, Xinxiang, 453003, China; Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
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Steele EJ. Reverse Transcriptase Mechanism of Somatic Hypermutation: 60 Years of Clonal Selection Theory. Front Immunol 2017; 8:1611. [PMID: 29218047 PMCID: PMC5704389 DOI: 10.3389/fimmu.2017.01611] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Accepted: 11/07/2017] [Indexed: 01/24/2023] Open
Abstract
The evidence for the reverse transcriptase mechanism of somatic hypermutation is substantial and multifactorial. In this 60th anniversary year of the publication of Sir MacFarlane Burnet's Clonal Selection Theory, the evidence is briefly reviewed and updated.
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Affiliation(s)
- Edward J. Steele
- CYO’Connor ERADE Village Foundation Inc., Piara Waters, WA, Australia
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Steele EJ, Lindley RA. ADAR deaminase A-to-I editing of DNA and RNA moieties of RNA:DNA hybrids has implications for the mechanism of Ig somatic hypermutation. DNA Repair (Amst) 2017; 55:1-6. [PMID: 28482199 DOI: 10.1016/j.dnarep.2017.04.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Revised: 04/14/2017] [Accepted: 04/14/2017] [Indexed: 11/16/2022]
Abstract
The implications are discussed of recently published biochemical studies on ADAR-mediated A-to-I DNA and RNA deamination at RNA:DNA hybrids. The significance of these data are related to previous work on strand-biased and codon-context mutation signatures in B lymphocytes and cancer genomes. Those studies have established that there are two significant strand biases at A:T and G:C base pairs, A-site mutations exceed T-site mutations (A>>T) by 2.9 fold and G-site mutations exceed C-site mutations (G>>C) by 1.7 fold. Both these strand biases are inconsistent with alternative "DNA Deamination" mechanisms, yet are expected consequences of the RNA/RT-based "Reverse Transcriptase" mechanism of immunoglobulin (Ig) somatic hypermutation (SHM). The A-to-I DNA editing component at RNA:DNA hybrids that is likely to occur in Transcription Bubbles, while important, is of far lower A-to-I editing efficiency than in dsRNA substrates. The RNA moiety of RNA:DNA hybrids is also edited at similar lower frequencies relative to the editing rate at dsRNA substrates. Further, if the A-to-I DNA editing at RNA:DNA hybrids were the sole cause of A-to-I (read as A-to-G) mutation events for Ig SHM in vivo then the exact opposite strand biases at A:T base pairs (T>>A) of what is actually observed (A>>T) would be predicted. It is concluded that the strand-biased somatic mutation patterns at both A:T and G:C base pairs in vivo are best interpreted by the sequential steps of the RNA/RT-based mechanism. Further, the direct DNA A-to-I deamination at Transcription Bubbles is expected to contribute to the T-to-C component of the strand-biased Ig SHM spectrum.
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Affiliation(s)
- Edward J Steele
- CYO'Connor ERADE Village Foundation Inc., Piara Waters, WA, Australia.
| | - Robyn A Lindley
- GMDxCo Pty Ltd., Hawthorn Vic, Australia; Department of Pathology, Faculty of Medicine, Dentistry & Health Sciences, University of Melbourne Vic, Australia
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Lee DW, Khavrutskii IV, Wallqvist A, Bavari S, Cooper CL, Chaudhury S. BRILIA: Integrated Tool for High-Throughput Annotation and Lineage Tree Assembly of B-Cell Repertoires. Front Immunol 2017; 7:681. [PMID: 28144239 PMCID: PMC5239784 DOI: 10.3389/fimmu.2016.00681] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Accepted: 12/21/2016] [Indexed: 11/13/2022] Open
Abstract
The somatic diversity of antigen-recognizing B-cell receptors (BCRs) arises from Variable (V), Diversity (D), and Joining (J) (VDJ) recombination and somatic hypermutation (SHM) during B-cell development and affinity maturation. The VDJ junction of the BCR heavy chain forms the highly variable complementarity determining region 3 (CDR3), which plays a critical role in antigen specificity and binding affinity. Tracking the selection and mutation of the CDR3 can be useful in characterizing humoral responses to infection and vaccination. Although tens to hundreds of thousands of unique BCR genes within an expressed B-cell repertoire can now be resolved with high-throughput sequencing, tracking SHMs is still challenging because existing annotation methods are often limited by poor annotation coverage, inconsistent SHM identification across the VDJ junction, or lack of B-cell lineage data. Here, we present B-cell repertoire inductive lineage and immunosequence annotator (BRILIA), an algorithm that leverages repertoire-wide sequencing data to globally improve the VDJ annotation coverage, lineage tree assembly, and SHM identification. On benchmark tests against simulated human and mouse BCR repertoires, BRILIA correctly annotated germline and clonally expanded sequences with 94 and 70% accuracy, respectively, and it has a 90% SHM-positive prediction rate in the CDR3 of heavily mutated sequences; these are substantial improvements over existing methods. We used BRILIA to process BCR sequences obtained from splenic germinal center B cells extracted from C57BL/6 mice. BRILIA returned robust B-cell lineage trees and yielded SHM patterns that are consistent across the VDJ junction and agree with known biological mechanisms of SHM. By contrast, existing BCR annotation tools, which do not account for repertoire-wide clonal relationships, systematically underestimated both the size of clonally related B-cell clusters and yielded inconsistent SHM frequencies. We demonstrate BRILIA’s utility in B-cell repertoire studies related to VDJ gene usage, mechanisms for adenosine mutations, and SHM hot spot motifs. Furthermore, we show that the complete gene usage annotation and SHM identification across the entire CDR3 are essential for studying the B-cell affinity maturation process through immunosequencing methods.
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Affiliation(s)
- Donald W Lee
- Biotechnology HPC Software Applications Institute (BHSAI), Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command , Fort Detrick, MD , USA
| | - Ilja V Khavrutskii
- Biotechnology HPC Software Applications Institute (BHSAI), Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command , Fort Detrick, MD , USA
| | - Anders Wallqvist
- Biotechnology HPC Software Applications Institute (BHSAI), Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command , Fort Detrick, MD , USA
| | - Sina Bavari
- Molecular and Translational Sciences, U.S. Army Medical Research Institute of Infectious Diseases , Frederick, MD , USA
| | - Christopher L Cooper
- Molecular and Translational Sciences, U.S. Army Medical Research Institute of Infectious Diseases , Frederick, MD , USA
| | - Sidhartha Chaudhury
- Biotechnology HPC Software Applications Institute (BHSAI), Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Materiel Command , Fort Detrick, MD , USA
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Somatic hypermutation in immunity and cancer: Critical analysis of strand-biased and codon-context mutation signatures. DNA Repair (Amst) 2016; 45:1-24. [DOI: 10.1016/j.dnarep.2016.07.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Accepted: 07/01/2016] [Indexed: 01/01/2023]
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19
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Steele EJ. Commentary: Past, present, and future of epigenetics applied to livestock breeding - Hard versus Soft Lamarckian Inheritance Mechanisms. Front Genet 2016; 7:29. [PMID: 26941780 PMCID: PMC4763540 DOI: 10.3389/fgene.2016.00029] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2015] [Accepted: 02/13/2016] [Indexed: 12/24/2022] Open
Affiliation(s)
- Edward J Steele
- CY O'Connor ERADE Village Foundation Piara Waters, WA, Australia
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20
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Mönttinen HAM, Ravantti JJ, Stuart DI, Poranen MM. Automated structural comparisons clarify the phylogeny of the right-hand-shaped polymerases. Mol Biol Evol 2014; 31:2741-52. [PMID: 25063440 DOI: 10.1093/molbev/msu219] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Polymerases are essential for life, being responsible for replication, transcription, and the repair of nucleic acid molecules. Those that share a right-hand-shaped fold and catalytic site structurally similar to the DNA polymerase I of Escherichia coli may catalyze RNA- or DNA-dependent RNA polymerization, reverse transcription, or DNA replication in eukarya, archaea, bacteria, and their viruses. We have applied novel computational methods for structure-based clustering and phylogenetic analyses of this functionally diverse polymerase superfamily, which currently comprises six families. We identified a structural core common to all right-handed polymerases, composed of 57 amino acid residues, harboring two positionally and chemically conserved residues, the catalytic aspartates. The structural conservation within each of the six families is considerable, for example, the structural core shared by family Y DNA polymerases covers over 90% of the polymerase domain of the Sulfolobus solfataricus Dpo4. Our phylogenetic analyses propose an early separation of RNA-dependent polymerases that use primers from those that are primer-independent. Furthermore, the exchange of polymerase genes between viruses and their hosts is evident. Because of this horizontal gene transfer, the phylogeny of polymerases does not always reflect the evolutionary history of the corresponding organisms.
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Affiliation(s)
- Heli A M Mönttinen
- Department of Biosciences, Viikki Biocenter, University of Helsinki, Helsinki, Finland
| | - Janne J Ravantti
- Department of Biosciences, Viikki Biocenter, University of Helsinki, Helsinki, Finland Institute of Biotechnology, Viikki Biocenter, University of Helsinki, Helsinki, Finland
| | - David I Stuart
- Division of Structural Biology and the Oxford Protein Production Facility, The Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom Diamond Light Source Limited, Harwell Science and Innovation Campus, Oxfordshire, United Kingdom
| | - Minna M Poranen
- Department of Biosciences, Viikki Biocenter, University of Helsinki, Helsinki, Finland
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Critical Analysis of Strand-Biased Somatic Mutation Signatures in TP53 versus Ig Genes, in Genome-Wide Data and the Etiology of Cancer. ACTA ACUST UNITED AC 2013. [DOI: 10.1155/2013/921418] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Previous analyses of rearranged immunoglobulin (Ig) variable genes (VDJs) concluded that the mechanism of Ig somatic hypermutation (SHM) involves the Ig pre-mRNA acting as a copying template resulting in characteristic strand biased somatic mutation patterns at A:T and G:C base pairs. We have since analysed cancer genome data and found the same mutation strand-biases, in toto or in part, in nonlymphoid cancers. Here we have analysed somatic mutations in a single well-characterised gene TP53. Our goal is to understand the genesis of the strand-biased mutation patterns in TP53—and in genome-wide data—that may arise by “endogenous” mechanisms as opposed to adduct-generated DNA-targeted strand-biased mutations caused by well-characterised “external” carcinogenic influences in cigarette smoke, UV-light, and certain dietary components. The underlying strand-biased mutation signatures in TP53, for many non-lymphoid cancers, bear a striking resemblance to the Ig SHM pattern. A similar pattern can be found in genome-wide somatic mutations in cancer genomes that have also mutated TP53. The analysis implies a role for base-modified RNA template intermediates coupled to reverse transcription in the genesis of many cancers. Thus Ig SHM may be inappropriately activated in many non-lymphoid tissues via hormonal and/or inflammation-related processes leading to cancer.
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Steele EJ, Williamson JF, Lester S, Stewart BJ, Millman JA, Carnegie P, Lindley RA, Pain GN, Dawkins RL. Genesis of ancestral haplotypes: RNA modifications and reverse transcription-mediated polymorphisms. Hum Immunol 2010; 72:283-293.e1. [PMID: 21156194 DOI: 10.1016/j.humimm.2010.12.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2010] [Revised: 11/15/2010] [Accepted: 12/06/2010] [Indexed: 11/30/2022]
Abstract
Understanding the genesis of the block haplotype structure of the genome is a major challenge. With the completion of the sequencing of the Human Genome and the initiation of the HapMap project the concept that the chromosomes of the mammalian genome are a mosaic, or patchwork, of conserved extended block haplotype sequences is now accepted by the mainstream genomics research community. Ancestral Haplotypes (AHs) can be viewed as a recombined string of smaller Polymorphic Frozen Blocks (PFBs). How have such variant extended DNA sequence tracts emerged in evolution? Here the relevant literature on the problem is reviewed from various fields of molecular and cell biology particularly molecular immunology and comparative and functional genomics. Based on our synthesis we then advance a testable molecular and cellular model. A critical part of the analysis concerns the origin of the strand biased mutation signatures in the transcribed regions of the human and higher primate genome, A-to-G versus T-to-C (ratio ∼ 1.5 fold) and C-to-T versus G-to-A (≥ 1.5 fold). A comparison and evaluation of the current state of the fields of immunoglobulin Somatic Hypermutation (SHM) and Transcription-Coupled DNA Repair focused on how mutations in newly synthesized RNA might be copied back to DNA thus accounting for some of the genome-wide strand biases (e.g., the A-to-G vs T-to-C component of the strand biased spectrum). We hypothesize that the genesis of PFBs and extended AHs occurs during mutagenic episodes in evolution (e.g., retroviral infections) and that many of the critical DNA sequence diversifying events occur first at the RNA level, e.g., recombination between RNA strings resulting in tandem and dispersed RNA duplications (retroduplications), RNA mutations via adenosine-to-inosine pre-mRNA editing events as well as error prone RNA synthesis. These are then copied back into DNA by a cellular reverse transcription process (also likely to be error-prone) that we have called "reverse transcription-mediated long DNA conversion." Finally we suggest that all these activities and others can be envisaged as being brought physically under the umbrella of special sites in the nucleus involved in transcription known as "transcription factories."
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Affiliation(s)
- Edward J Steele
- C.Y O'Connor ERADE Village Foundation, Canning Vale, Western Australia, Australia.
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Polak P, Querfurth R, Arndt PF. The evolution of transcription-associated biases of mutations across vertebrates. BMC Evol Biol 2010; 10:187. [PMID: 20565875 PMCID: PMC2927911 DOI: 10.1186/1471-2148-10-187] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2009] [Accepted: 06/18/2010] [Indexed: 02/03/2024] Open
Abstract
Background The interplay between transcription and mutational processes can lead to particular mutation patterns in transcribed regions of the genome. Transcription introduces several biases in mutational patterns; in particular it invokes strand specific mutations. In order to understand the forces that have shaped transcripts during evolution, one has to study mutation patterns associated with transcription across animals. Results Using multiple alignments of related species we estimated the regional single-nucleotide substitution patterns along genes in four vertebrate taxa: primates, rodents, laurasiatheria and bony fishes. Our analysis is focused on intronic and intergenic regions and reveals differences in the patterns of substitution asymmetries between mammals and fishes. In mammals, the levels of asymmetries are stronger for genes starting within CpG islands than in genes lacking this property. In contrast to all other species analyzed, we found a mutational pressure in dog and stickleback, promoting an increase of GC-contents in the proximity to transcriptional start sites. Conclusions We propose that the asymmetric patterns in transcribed regions are results of transcription associated mutagenic processes and transcription coupled repair, which both seem to evolve in a taxon related manner. We also discuss alternative mechanisms that can generate strand biases and involves error prone DNA polymerases and reverse transcription. A localized increase of the GC content near the transcription start site is a signature of biased gene conversion (BGC) that occurs during recombination and heteroduplex formation. Since dog and stickleback are known to be subject to rapid adaptations due to population bottlenecks and breeding, we further hypothesize that an increase in recombination rates near gene starts has been part of an adaptive process.
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Affiliation(s)
- Paz Polak
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany.
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Steele EJ, Lindley RA. Somatic mutation patterns in non-lymphoid cancers resemble the strand biased somatic hypermutation spectra of antibody genes. DNA Repair (Amst) 2010; 9:600-3. [PMID: 20418189 DOI: 10.1016/j.dnarep.2010.03.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2010] [Accepted: 03/24/2010] [Indexed: 10/19/2022]
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Abstract
We are in the midst of a revolution in the genomic sciences that will forever change the way we view biology and medicine, particularly with respect to brain form, function, development, evolution, plasticity, neurological disease pathogenesis and neural regenerative potential. The application of epigenetic principles has already begun to identify and characterize previously unrecognized molecular signatures of disease latency, onset and progression, mechanisms underlying disease pathogenesis, and responses to new and evolving therapeutic modalities. Moreover, epigenomic medicine promises to usher in a new era of neurological therapeutics designed to promote disease prevention and recovery of seemingly lost neurological function via reprogramming of stem cells, redirecting cell fate decisions and dynamically modulating neural network plasticity and connectivity.
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Affiliation(s)
- Mark F Mehler
- Institute for Brain Disorders and Neural Regeneration, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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Steele EJ. Mechanism of somatic hypermutation: critical analysis of strand biased mutation signatures at A:T and G:C base pairs. Mol Immunol 2008; 46:305-20. [PMID: 19062097 DOI: 10.1016/j.molimm.2008.10.021] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Accepted: 10/14/2008] [Indexed: 12/17/2022]
Abstract
The DNA sequence data of the somatic hypermutation (SHM) field published since 1984 has been critically reviewed. The analysis has revealed three strand biased mutation signatures. The first concerns the mutations generated at G:C base pairs in mice genetically deficient in uracil-DNA glycosylase and MSH2-MSH6-mediated mismatch repair. Such mice display the AID deaminase footprint and here C mutations exceed G mutations at least 1.5-fold. This supports earlier and more recent studies claiming that dC-to-dU deaminations occur preferentially in the single stranded DNA regions of the displaced nontranscribed strand (NTS) during transcription. The second concerns the signature generated in immunised mice where G mutations exceed C mutations by at least 1.7-fold. This is a newly identified strand bias which has previously gone undetected. It is consistent with the polynucleotide polymerisation signature of RNA polymerase II copying the template DNA strand carrying AID-mediated lesions generated at C bases, viz. uracils and abasic sites. A reverse transcription step would then need to intervene to fix the mutation pattern in DNA. The third concerns the long recognised strand biased signature generated in normal aged or actively immunised mice whereby A mutations exceed T mutations by two- to three-fold. It is argued that this pattern is best understood as a combination of adenosine-to-inosine (A-to-I) RNA editing followed by a reverse transcription step fixing the A-to-G, as well as A-to-T and A-to-C, as strand biased mutation signatures in DNA. The reasons why the AID-linked RNA polymerase II mutation signature had previously gone undetected are discussed with regard to limitations of standard PCR-based SHM assay techniques. It is concluded that the most economical SHM mechanism involves both DNA and RNA deaminations coupled to a reverse transcription process, most likely involving DNA polymerase eta acting in its reverse transcriptase mode. Experimental approaches to differentiate this RNA-based model from the standard DNA deamination model are discussed.
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Affiliation(s)
- Edward J Steele
- Genomic Interactions Group and CILR, Research School of Biological Sciences, The Institute of Advanced Studies, Australian National University, Canberra, ACT 2601, Australia.
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Human DNA polymerase eta activity and translocation is regulated by phosphorylation. Proc Natl Acad Sci U S A 2008; 105:16578-83. [PMID: 18946034 DOI: 10.1073/pnas.0808589105] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Human DNA polymerase eta (pol eta) can replicate across UV-induced pyrimidine dimers, and defects in the gene encoding pol eta result in a syndrome called xeroderma pigmentosum variant (XP-V). XP-V patients are prone to the development of cancer in sun-exposed areas, and cells derived from XP-V patients demonstrate increased sensitivity to UV radiation and a higher mutation rate compared with wild-type cells. pol eta has been shown to replicate across a wide spectrum of DNA lesions introduced by environmental or chemotherapeutic agents, or during nucleotide starvation, suggesting that the biological roles for pol eta are not limited to repair of UV-damaged DNA. The high error rate of pol eta requires that its intracellular activity be tightly regulated. Here, we show that the phosphorylation of pol eta increased after UV irradiation, and that treatment with caffeine, siRNA against ATR, or an inhibitor of PKC (calphostin C), reduced the accumulation of pol eta at stalled replication forks after UV irradiation or treatment with cisplatin and gemcitabine. Site-specific mutagenesis (S587A and T617A) of pol eta at two putative PKC phosphorylation sites located in the protein-protein interaction domain prevented nuclear foci formation induced by UV irradiation or treatment with gemcitabine/cisplatin. In addition, XP-V cell lines stably expressing either the S587A or T617A mutant form of pol eta were more sensitive to UV radiation and gemcitabine/cisplatin than control cells expressing wild-type pol eta. These results suggest that phosphorylation is one mechanism by which the cellular activity of pol eta is regulated.
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Mattick JS, Mehler MF. RNA editing, DNA recoding and the evolution of human cognition. Trends Neurosci 2008; 31:227-33. [PMID: 18395806 DOI: 10.1016/j.tins.2008.02.003] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2007] [Revised: 02/10/2008] [Accepted: 02/12/2008] [Indexed: 01/09/2023]
Abstract
RNA editing appears to be the major mechanism by which environmental signals overwrite encoded genetic information to modify gene function and regulation, particularly in the brain. We suggest that the predominance of Alu elements in the human genome is the result of their evolutionary co-adaptation as a modular substrate for RNA editing, driven by selection for higher-order cognitive function. We show that RNA editing alters transcripts from loci encoding proteins involved in neural cell identity, maturation and function, as well as in DNA repair, implying a role for RNA editing not only in neural transmission and network plasticity but also in brain development, and suggesting that communication of productive changes back to the genome might constitute the molecular basis of long-term memory and higher-order cognition.
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Affiliation(s)
- John S Mattick
- ARC Special Research Centre for Functional and Applied Genomics, Institute for Molecular Bioscience, University of Queensland, St. Lucia, QLD 4072, Australia
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Storici F, Bebenek K, Kunkel TA, Gordenin DA, Resnick MA. RNA-templated DNA repair. Nature 2007; 447:338-41. [PMID: 17429354 PMCID: PMC2121219 DOI: 10.1038/nature05720] [Citation(s) in RCA: 172] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2006] [Accepted: 02/28/2007] [Indexed: 01/05/2023]
Abstract
RNA can act as a template for DNA synthesis in the reverse transcription of retroviruses and retrotransposons and in the elongation of telomeres. Despite its abundance in the nucleus, there has been no evidence for a direct role of RNA as a template in the repair of any chromosomal DNA lesions, including DNA double-strand breaks (DSBs), which are repaired in most organisms by homologous recombination or by non-homologous end joining. An indirect role for RNA in DNA repair, following reverse transcription and formation of a complementary DNA, has been observed in the non-homologous joining of DSB ends. In the yeast Saccharomyces cerevisiae, in which homologous recombination is efficient, RNA was shown to mediate recombination, but only indirectly through a cDNA intermediate generated by the reverse transcriptase function of Ty retrotransposons in Ty particles in the cytoplasm. Although pairing between duplex DNA and single-strand (ss)RNA can occur in vitro and in vivo, direct homologous exchange of genetic information between RNA and DNA molecules has not been observed. We show here that RNA can serve as a template for DNA synthesis during repair of a chromosomal DSB in yeast. The repair was accomplished with RNA oligonucleotides complementary to the broken ends. This and the observation that even yeast replicative DNA polymerases such as alpha and delta can copy short RNA template tracts in vitro demonstrate that RNA can transfer genetic information in vivo through direct homologous interaction with chromosomal DNA.
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Affiliation(s)
- Francesca Storici
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences (NIH, DHHS), Research Triangle Park, North Carolina 27709, USA
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Franklin A, Blanden RV. Potential inhibition of somatic hypermutation by nucleoside analogues. Mol Immunol 2007; 44:666-9. [PMID: 16581133 DOI: 10.1016/j.molimm.2006.02.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2006] [Revised: 02/19/2006] [Accepted: 02/20/2006] [Indexed: 12/28/2022]
Abstract
Somatic hypermutation, which occurs in antigen-activated germinal centre B lymphocytes, diversifies the genes that encode immunoglobulin variable regions and leads to the 'affinity maturation' of the humoral immune response. Hypermutation affects dC/dG and dA/dT pairs with approximately equal frequency in vivo. DNA polymerase-theta contributes to hypermutagenesis at dC/dG pairs and DNA polymerase-eta is substantially involved in the generation of hypermutations at dA/dT pairs. The biochemical properties of polymerases-theta and -eta indicate that their DNA synthetic activities are potentially susceptible to inhibition by nucleoside analogues, so it is feasible that nucleoside analogues reduce the accumulation of dC/dG- and dA/dT-targeted hypermutations in vivo. Nucleoside analogues could hence impair the humoral adaptive immune response of HIV-infected patients who are prescribed these chemotherapeutic agents.
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Affiliation(s)
- Andrew Franklin
- Biocontrol Group, School of Botany and Zoology, Australian National University, Daley Road, Acton, 0200 ACT, Australia.
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Steele EJ, Lindley RA, Wen J, Weiller GF. Computational analyses show A-to-G mutations correlate with nascent mRNA hairpins at somatic hypermutation hotspots. DNA Repair (Amst) 2006; 5:1346-63. [PMID: 16884961 DOI: 10.1016/j.dnarep.2006.06.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2006] [Accepted: 06/06/2006] [Indexed: 12/24/2022]
Abstract
Activation-induced cytidine deaminase (AID) initiates Phase I somatic hypermutation (SHM) of antibody genes by deaminating deoxy-cytosine to deoxy-uracil (C-to-U). These lesions trigger Phase II, a poorly understood process of error-prone repair targeting A-T pairs by DNA polymerase eta (Pol eta). Since Pol eta is also a reverse transcriptase, Phase II could involve copying off RNA as well as DNA templates. We explore this idea further since in an RNA-based pathway it is conceivable that adenosine-to-inosine (A-to-I) RNA editing causes A-to-G transitions since I like G pairs with C. Adenosine deaminases (ADARs) are known to preferentially edit A nucleotides that are preceded by an A or U (W) in double-stranded RNA substrates. On this assumption and using a theoretical bioinformatics approach we show that a significant and specific correlation (P<0.002) exists between the frequency of WA-to-WG mutations and the number of mRNA hairpins that could potentially form at the mutation site. This implies roles for both RNA editing and reverse transcription during SHM in vivo and suggests definitive genetic experiments targeting the appropriate ADAR1 isoform (gammaINF-ADAR1) and/or Ig pre-mRNA templates.
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Affiliation(s)
- Edward J Steele
- Genomic Interactions Group & CILR, Research School of Biological Sciences, Australian National University, Canberra, Australia.
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Franklin A, Blanden RV. A/T-targeted somatic hypermutation: critique of the mainstream model. Trends Biochem Sci 2006; 31:252-8. [PMID: 16616496 DOI: 10.1016/j.tibs.2006.03.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2006] [Revised: 02/14/2006] [Accepted: 03/24/2006] [Indexed: 12/25/2022]
Abstract
The "affinity maturation" of the humoral immune response is driven by antigen-activated somatic hypermutation (SHM) of the genes that encode antibody variable regions and the subsequent antigenic selection of mutant clones. The molecular mechanism of SHM is yet to be completely elucidated. SHM affects cytosine-guanine (C/G) and adenine-thymine (A/T) pairs with approximately equal frequency in vivo. The proposition that error-prone DNA-dependent DNA synthesis explains A/T-targeted hypermutagenesis seems to have mainstream support within the hypermutation research community at present. A major feature of SHM in vivo is that C/G hypermutation is strand unbiased, whereas A/T hypermutation is strand biased. We show that the "DNA-based polymerase error" model of A/T-targeted hypermutagenesis does not explain this important aspect of SHM.
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Affiliation(s)
- Andrew Franklin
- Biocontrol Group, School of Botany and Zoology, Australian National University, Daley Road, Acton, ACT 0200, Australia.
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Franklin A, Blanden RV. Hypothesis: biological role for J-C intronic matrix attachment regions in the molecular mechanism of antigen-driven somatic hypermutation. Immunol Cell Biol 2005; 83:383-91. [PMID: 16033533 DOI: 10.1111/j.1440-1711.2005.01327.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
A major function of J-C intronic matrix attachment regions (MAR) during immune diversification via somatic hypermutation (SHM) at immunoglobulin loci may be to manipulate the topology of DNA within the upstream target domain. The suggestion that SHM induction requires MAR-induced torsional strain, in conjunction with DNA remodelling at the J-C intron, completes the definition of a cogent paradigm within which all extant molecular data on the issue may be interpreted. Moreover, the suggestion that a mutagenic mechanism relieves MAR-generated superhelicity could provide an indication as to the evolutionary basis of SHM.
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Affiliation(s)
- Andrew Franklin
- Division of Immunology and Genetics, The John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia.
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Abstract
Nucleotide-excision repair diseases exhibit cancer, complex developmental disorders and neurodegeneration. Cancer is the hallmark of xeroderma pigmentosum (XP), and neurodegeneration and developmental disorders are the hallmarks of Cockayne syndrome and trichothiodystrophy. A distinguishing feature is that the DNA-repair or DNA-replication deficiencies of XP involve most of the genome, whereas the defects in CS are confined to actively transcribed genes. Many of the proteins involved in repair are also components of dynamic multiprotein complexes, transcription factors, ubiquitylation cofactors and signal-transduction networks. Complex clinical phenotypes might therefore result from unanticipated effects on other genes and proteins.
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Affiliation(s)
- James E Cleaver
- Auerback Melanoma Laboratory, Room N431, UCSF Cancer Center, University of California, 94143-0808, USA.
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36
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Diaz M, Lawrence C. An update on the role of translesion synthesis DNA polymerases in Ig hypermutation. Trends Immunol 2005; 26:215-20. [PMID: 15797512 DOI: 10.1016/j.it.2005.02.008] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Several years have passed since the discovery of activation-induced cytosine deaminase (AID), the molecule responsible for triggering hypermutation of Ig genes. We now know that AID deaminates cytosines in the DNA encoding the variable portion of the Ig receptor, although an additional role in deaminating a regulatory mRNA transcript has not been ruled out. A major question that remains unanswered is how AID, a cytosine deaminase, causes mutations at both G:C and A:T base pairs. Mounting evidence suggests the involvement of a group of error-prone DNA polymerases known to bypass DNA lesions: the translesion synthesis (TLS) DNA polymerases. In this Review, we discuss the evidence for a role of TLS DNA polymerases in Ig hypermutation and argue that a major remaining challenge in our understanding of this mechanism is the recruitment of TLS DNA polymerases to the Ig locus following AID-mediated cytosine deamination.
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Affiliation(s)
- Marilyn Diaz
- Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, 111 TW Alexander Drive, Research Triangle Park, NC 27709, USA.
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Steele EJ. DNA polymerase-eta as a reverse transcriptase: implications for mechanisms of hypermutation in innate anti-retroviral defences and antibody SHM systems. DNA Repair (Amst) 2004; 3:687-92. [PMID: 15177177 DOI: 10.1016/j.dnarep.2004.03.040] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Franklin A, Blanden RV. On the molecular mechanism of somatic hypermutation of rearranged immunoglobulin genes. Immunol Cell Biol 2004; 82:557-67. [PMID: 15550113 DOI: 10.1111/j.1440-1711.2004.01289.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Somatic hypermutation (SHM) diversifies the genes that encode immunoglobulin variable regions in antigen-activated germinal centre B lymphocytes. Available evidence strongly suggests that DNA deamination potentiates phase I SHM and subsequently triggers phase II SHM. A concise review of this evidence is followed by a detailed critique of two possible models which suggest that polymerase-eta potentiates phase II SHM via either its DNA-dependent or its RNA-dependent DNA synthetic activity. Quantitative analysis, in the context of extant data that define the features of SHM, favours the RNA-dependent mechanism.
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Affiliation(s)
- Andrew Franklin
- Division of Immunology and Genetics, The John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia.
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Processed switch-region transcripts and retrotranscripts as possible generators of heteroduplex 'R-loop' targets for AID deamination. Nat Rev Immunol 2004. [DOI: 10.1038/nri1395-c1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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40
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Blanden RV, Franklin A, Steele EJ. The boundaries of the distribution of somatic hypermutation of rearranged immunoglobulin variable genes. Immunol Cell Biol 2004; 82:205-8. [PMID: 15061775 DOI: 10.1046/j.0818-9641.2004.01226.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Available evidence about the mechanisms and distribution of somatic hypermutation (SHM) of rearranged immunoglobulin (IgV) genes is reviewed with particular emphasis on the 5' boundary. In heavy (H) chain genes, the 5' boundary of SHM is the transcription start site; in contrast to kappa light (L) chain genes, it is located in the leader (L) intron. DNA-based models of SHM cannot account for this difference. However, an updated reverse transcriptase (RT)-based model invoking error-prone RT activity of DNA polymerase eta copying IgV pre-mRNA templates to produce cDNA of the transcribed strand (TS) of IgV DNA, which then replaces the corresponding section of the original TS, can explain the difference. This explanation incorporates recent knowledge of pre-mRNA processing, in particular, binding of the splicing-associated protein termed U2AF to a pyrimidine-rich tract in the L intron of pre-mRNA of kappa L chains that may block RT progression further upstream to the end of the pre-mRNA template (transcription start site). Reasons why this block may not occur in H chains and other aspects of the updated RT-model are discussed.
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Affiliation(s)
- Robert V Blanden
- Division of Immunology and Genetics, John Curtin School of Medical Research, Australian National University, GPO Box 334, Canberra City, ACT 2601, Australia.
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