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Lee U, Mozeika SM, Zhao L. A Synergistic, Cultivator Model of De Novo Gene Origination. Genome Biol Evol 2024; 16:evae103. [PMID: 38748819 PMCID: PMC11152449 DOI: 10.1093/gbe/evae103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/12/2024] [Indexed: 06/07/2024] Open
Abstract
The origin and fixation of evolutionarily young genes is a fundamental question in evolutionary biology. However, understanding the origins of newly evolved genes arising de novo from noncoding genomic sequences is challenging. This is partly due to the low likelihood that several neutral or nearly neutral mutations fix prior to the appearance of an important novel molecular function. This issue is particularly exacerbated in large effective population sizes where the effect of drift is small. To address this problem, we propose a regulation-focused, cultivator model for de novo gene evolution. This cultivator-focused model posits that each step in a novel variant's evolutionary trajectory is driven by well-defined, selectively advantageous functions for the cultivator genes, rather than solely by the de novo genes, emphasizing the critical role of genome organization in the evolution of new genes.
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Affiliation(s)
- UnJin Lee
- Laboratory of Evolutionary Genetics and Genomics, The Rockefeller University, New York, NY, USA
| | - Shawn M Mozeika
- Laboratory of Evolutionary Genetics and Genomics, The Rockefeller University, New York, NY, USA
| | - Li Zhao
- Laboratory of Evolutionary Genetics and Genomics, The Rockefeller University, New York, NY, USA
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2
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Yahsi B, Palaz F, Dincer P. Applications of CRISPR Epigenome Editors in Tumor Immunology and Autoimmunity. ACS Synth Biol 2024; 13:413-427. [PMID: 38298016 DOI: 10.1021/acssynbio.3c00524] [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] [Indexed: 02/02/2024]
Abstract
Over the past decade, CRISPR-Cas systems have become indispensable tools for genetic engineering and have been used in clinical trials for various diseases. Beyond genome editing, CRISPR-Cas systems can also be used for performing programmable epigenetic modifications. Recent efforts in enhancing CRISPR-based epigenome modifiers have yielded potent tools enabling targeted DNA methylation/demethylation capable of sustaining epigenetic memory through numerous cell divisions. Moreover, it has been understood that during chronic inflammatory states, including cancer, T cells encounter a state called T cell exhaustion that involves elevated inhibitory receptors (e.g., LAG-3, TIM3, PD-1, CD39) and reduced effector T cell-related protein levels (IFN-γ, granzyme B, and perforin). Importantly, epigenetic dysregulation has been identified as one of the key drivers of T cell exhaustion, and it remains one of the biggest obstacles in the field of immunotherapy and decreases the efficiency of chimeric antigen receptor T (CAR-T) cell therapy. Similarly, autoimmune diseases exhibit epigenetically dysfunctional regulatory T (Treg) cells. For instance, FOXP3 intronic regions, known as conserved noncoding sequences, display hypomethylation in healthy states but hypermethylation in pathological contexts. Therefore, the reversal of epigenetic dysregulation in cancer and autoimmune diseases using CRISPR-based epigenome modifiers has important therapeutic implications. In this review, we outline the progressive refinement of CRISPR-based epigenome modifiers and explore their potential therapeutic applications in tumor immunology and autoimmunity.
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Affiliation(s)
- Berkay Yahsi
- Hacettepe University School of Medicine, Ankara 06100, Turkey
| | - Fahreddin Palaz
- Faculty of Medicine, Hacettepe University, Ankara 06100, Turkey
| | - Pervin Dincer
- Department of Medical Biology, Faculty of Medicine, Hacettepe University, Ankara 06100, Turkey
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3
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Nepal C, Andersen JB. Alternative promoters in CpG depleted regions are prevalently associated with epigenetic misregulation of liver cancer transcriptomes. Nat Commun 2023; 14:2712. [PMID: 37169774 PMCID: PMC10175279 DOI: 10.1038/s41467-023-38272-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Accepted: 04/24/2023] [Indexed: 05/13/2023] Open
Abstract
Transcriptional regulation is commonly governed by alternative promoters. However, the regulatory architecture in alternative and reference promoters, and how they differ, remains elusive. In 100 CAGE-seq libraries from hepatocellular carcinoma patients, here we annotate 4083 alternative promoters in 2926 multi-promoter genes, which are largely undetected in normal livers. These genes are enriched in oncogenic processes and predominantly show association with overall survival. Alternative promoters are narrow nucleosome depleted regions, CpG island depleted, and enriched for tissue-specific transcription factors. Globally tumors lose DNA methylation. We show hierarchical retention of intragenic DNA methylation with CG-poor regions rapidly losing methylation, while CG-rich regions retain it, a process mediated by differential SETD2, H3K36me3, DNMT3B, and TET1 binding. This mechanism is validated in SETD2 knockdown cells and SETD2-mutated patients. Selective DNA methylation loss in CG-poor regions makes the chromatin accessible for alternative transcription. We show alternative promoters can control tumor transcriptomes and their regulatory architecture.
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Affiliation(s)
- Chirag Nepal
- Biotech Research and Innovation Centre (BRIC), Department of Health and Medical Sciences, University of Copenhagen, Ole Maaløes Vej 5, Copenhagen N, DK-2200, Denmark.
- Center for Genomics, School of Medicine, Loma Linda University, Loma Linda, CA, 92350, USA.
| | - Jesper B Andersen
- Biotech Research and Innovation Centre (BRIC), Department of Health and Medical Sciences, University of Copenhagen, Ole Maaløes Vej 5, Copenhagen N, DK-2200, Denmark.
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Alkhayer R, Ponath V, Frech M, Adhikary T, Graumann J, Neubauer A, von Strandmann EP. KLF4-mediated upregulation of the NKG2D ligand MICA in acute myeloid leukemia: a novel therapeutic target identified by enChIP. Cell Commun Signal 2023; 21:94. [PMID: 37143070 PMCID: PMC10157933 DOI: 10.1186/s12964-023-01118-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2023] [Accepted: 03/27/2023] [Indexed: 05/06/2023] Open
Abstract
The immunoreceptor NKG2D, which is expressed on NK cells and T cell subsets is critically involved in tumor immune surveillance. This applies in particular to acute myeloid leukemia (AML), which evades immune detection by downregulation of NKG2D ligands (NKG2D-L), including MICA. The absence of NKG2D-L on AML cells is moreover associated with leukemia stem cell characteristics. The NKG2D/NKG2D-L system thus qualifies as an interesting and promising therapeutic target.Here we aimed to identify transcription factors susceptible to pharmacological stimulation resulting in the expression of the NKG2D-L MICA in AML cells to restore anti-tumor activity. Using a CRISPR-based engineered ChIP (enChIP) assay for the MICA promoter region and readout by mass spectrometry-based proteomics, we identified the transcription factor krüppel-like factor 4 (KLF4) as associated with the promoter. We demonstrated that the MICA promoter comprises functional binding sites for KLF4 and genetic as well as pharmacological gain- and loss-of-function experiments revealed inducible MICA expression to be mediated by KLF4.Furthermore, induction in AML cells was achieved with the small compound APTO253, a KLF4 activator, which also inhibits MYC expression and causes DNA damage. This induction in turn yielded increased expression and cell surface presentation of MICA, thus rendering AML cells more susceptible to NK cell-mediated killing. These data unravel a novel link between APTO253 and the innate anti-tumor immune response providing a rationale for targeting AML cells via APTO253-dependent KFL4/MICA induction to allow elimination by endogenous or transplanted NK and T cells in vivo. Video Abstract.
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Affiliation(s)
- Reem Alkhayer
- Institute for Tumor Immunology, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany
- Clinic for Hematology, Oncology, and Immunology, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany
| | - Viviane Ponath
- Institute for Tumor Immunology, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany
- Clinic for Hematology, Oncology, and Immunology, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany
| | - Miriam Frech
- Clinic for Hematology, Oncology, and Immunology, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany
| | - Till Adhikary
- Institute for Molecular Biology and Tumor Research, Institute for Medical Bioinformatics and Biostatistics, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany
| | - Johannes Graumann
- Institute of Translational Proteomics, Philipps University of Marburg, Marburg, Germany
| | - Andreas Neubauer
- Clinic for Hematology, Oncology, and Immunology, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany
| | - Elke Pogge von Strandmann
- Institute for Tumor Immunology, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany.
- Clinic for Hematology, Oncology, and Immunology, Center for Tumor Biology and Immunology, Philipps University of Marburg, Marburg, Germany.
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Abstract
Transcription start site (TSS) selection influences transcript stability and translation as well as protein sequence. Alternative TSS usage is pervasive in organismal development, is a major contributor to transcript isoform diversity in humans, and is frequently observed in human diseases including cancer. In this review, we discuss the breadth of techniques that have been used to globally profile TSSs and the resulting insights into gene regulation, as well as future prospects in this area of inquiry.
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Affiliation(s)
| | - Gabriel E. Zentner
- Department of Biology, Indiana University, Bloomington, IN 47401, USA
- Indiana University Melvin and Bren Simon Comprehensive Cancer Center, Indianapolis, IN 46202, USA
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Alves E, Taifour S, Dolcetti R, Chee J, Nowak AK, Gaudieri S, Blancafort P. Reprogramming the anti-tumor immune response via CRISPR genetic and epigenetic editing. Mol Ther Methods Clin Dev 2021; 21:592-606. [PMID: 34095343 PMCID: PMC8142043 DOI: 10.1016/j.omtm.2021.04.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Precise clustered regularly interspaced short palindromic repeats (CRISPR)-mediated genetic and epigenetic manipulation of the immune response has become a promising immunotherapeutic approach toward combating tumorigenesis and tumor progression. CRISPR-based immunologic reprograming in cancer therapy comprises the locus-specific enhancement of host immunity, the improvement of tumor immunogenicity, and the suppression of tumor immunoevasion. To date, the ex vivo re-engineering of immune cells directed to inhibit the expression of immune checkpoints or to express synthetic immune receptors (chimeric antigen receptor therapy) has shown success in some settings, such as in the treatment of melanoma, lymphoma, liver, and lung cancer. However, advancements in nuclease-deactivated CRISPR-associated nuclease-9 (dCas9)-mediated transcriptional activation or repression and Cas13-directed gene suppression present novel avenues for the development of tumor immunotherapies. In this review, the basis for development, mechanism of action, and outcomes from recently published Cas9-based clinical trial (genetic editing) and dCas9/Cas13-based pre-clinical (epigenetic editing) data are discussed. Lastly, we review cancer immunotherapy-specific considerations and barriers surrounding use of these approaches in the clinic.
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Affiliation(s)
- Eric Alves
- School of Human Sciences, The University of Western Australia, Perth, WA 6009, Australia
- Cancer Epigenetics Laboratory, The Harry Perkins Institute of Medical Research, Perth, WA 6009, Australia
| | - Shahama Taifour
- School of Human Sciences, The University of Western Australia, Perth, WA 6009, Australia
- Cancer Epigenetics Laboratory, The Harry Perkins Institute of Medical Research, Perth, WA 6009, Australia
| | - Riccardo Dolcetti
- Diamantina Institute, The University of Queensland, Brisbane, QLD 4102, Australia
- Sir Peter MacCallum Centre for Cancer Immunotherapy, University of Melbourne, Melbourne, VIC 3000, Australia
| | - Jonathan Chee
- National Centre for Asbestos Related Diseases, Institute of Respiratory Health, The University of Western Australia, Perth, WA 6009, Australia
- School of Biomedical Sciences, The University of Western Australia, Perth, WA 6009, Australia
| | - Anna K. Nowak
- National Centre for Asbestos Related Diseases, Institute of Respiratory Health, The University of Western Australia, Perth, WA 6009, Australia
- School of Medicine, The University of Western Australia, Perth, WA 6009, Australia
| | - Silvana Gaudieri
- School of Human Sciences, The University of Western Australia, Perth, WA 6009, Australia
- Institute for Immunology and Infectious Diseases, Murdoch University, Perth, WA 6150, Australia
- Division of Infectious Diseases, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Pilar Blancafort
- School of Human Sciences, The University of Western Australia, Perth, WA 6009, Australia
- Cancer Epigenetics Laboratory, The Harry Perkins Institute of Medical Research, Perth, WA 6009, Australia
- The Greehey Children’s Cancer Research Institute, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
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Chia M, Li C, Marques S, Pelechano V, Luscombe NM, van Werven FJ. High-resolution analysis of cell-state transitions in yeast suggests widespread transcriptional tuning by alternative starts. Genome Biol 2021; 22:34. [PMID: 33446241 PMCID: PMC7807719 DOI: 10.1186/s13059-020-02245-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 12/15/2020] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND The start and end sites of messenger RNAs (TSSs and TESs) are highly regulated, often in a cell-type-specific manner. Yet the contribution of transcript diversity in regulating gene expression remains largely elusive. We perform an integrative analysis of multiple highly synchronized cell-fate transitions and quantitative genomic techniques in Saccharomyces cerevisiae to identify regulatory functions associated with transcribing alternative isoforms. RESULTS Cell-fate transitions feature widespread elevated expression of alternative TSS and, to a lesser degree, TES usage. These dynamically regulated alternative TSSs are located mostly upstream of canonical TSSs, but also within gene bodies possibly encoding for protein isoforms. Increased upstream alternative TSS usage is linked to various effects on canonical TSS levels, which range from co-activation to repression. We identified two key features linked to these outcomes: an interplay between alternative and canonical promoter strengths, and distance between alternative and canonical TSSs. These two regulatory properties give a plausible explanation of how locally transcribed alternative TSSs control gene transcription. Additionally, we find that specific chromatin modifiers Set2, Set3, and FACT play an important role in mediating gene repression via alternative TSSs, further supporting that the act of upstream transcription drives the local changes in gene transcription. CONCLUSIONS The integrative analysis of multiple cell-fate transitions suggests the presence of a regulatory control system of alternative TSSs that is important for dynamic tuning of gene expression. Our work provides a framework for understanding how TSS heterogeneity governs eukaryotic gene expression, particularly during cell-fate changes.
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Affiliation(s)
- Minghao Chia
- The Francis Crick Institute, London, UK
- Genome Institute of Singapore, 60 Biopolis Street, Genome, #02-01, Singapore, 138672, Singapore
| | - Cai Li
- The Francis Crick Institute, London, UK
- School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Sueli Marques
- SciLifeLab, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Solna, Sweden
| | - Vicente Pelechano
- SciLifeLab, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Solna, Sweden
| | - Nicholas M Luscombe
- The Francis Crick Institute, London, UK
- Okinawa Institute of Science & Technology Graduate University, Okinawa, 904-0495, Japan
- UCL Genetics Institute, University College London, London, WC1E 6BT, UK
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8
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Gowthaman U, García-Pichardo D, Jin Y, Schwarz I, Marquardt S. DNA Processing in the Context of Noncoding Transcription. Trends Biochem Sci 2020; 45:1009-1021. [DOI: 10.1016/j.tibs.2020.07.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 07/17/2020] [Accepted: 07/30/2020] [Indexed: 12/14/2022]
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du Mee DJM, Bak M, Østergaard E, Rasmussen LJ. Mitochondrial dysfunction induced by variation in the non-coding genome - A proposed workflow to improve diagnostics. Mitochondrion 2020; 53:255-259. [PMID: 32497723 DOI: 10.1016/j.mito.2020.05.013] [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: 04/07/2020] [Accepted: 05/26/2020] [Indexed: 11/18/2022]
Abstract
Mitochondrial disorders are one of the most common inherited metabolic disorders and are caused by variants in nuclear genes or the mitochondrial genome. Additionally, there is a large group of patients displaying clinical symptoms, where the genetic background is unknown. Mitochondrial disorders have a huge variety in their clinical presentation, making diagnostics challenging. Genomes of higher organisms contain around 95% non-protein-coding DNA. Recently, non-protein-coding sequences have been shown to affect gene expression in many cellular processes, including mitochondrial functioning. As these insights are not frequently incorporated in diagnostics we propose a workflow utilizing this knowledge for faster diagnostics of patients lacking a molecular diagnosis.
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Affiliation(s)
- Dorine Jeanne Mariëtte du Mee
- Department of Plant and Environmental Sciences, Copenhagen Plant Science Centre, University of Copenhagen, Frederiksberg, Denmark
| | - Mads Bak
- Department of Clinical Genetics, Copenhagen University Hospital Rigshospitalet and Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Elsebet Østergaard
- Department of Clinical Genetics, Copenhagen University Hospital Rigshospitalet and Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Lene Juel Rasmussen
- Center for Healthy Aging, Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark.
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10
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McCarthy MT, Lin D, Soga T, Adam J, O'Callaghan CA. Inosine pranobex enhances human NK cell cytotoxicity by inducing metabolic activation and NKG2D ligand expression. Eur J Immunol 2020; 50:130-137. [PMID: 31434164 PMCID: PMC6972573 DOI: 10.1002/eji.201847948] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 07/29/2019] [Accepted: 08/20/2019] [Indexed: 02/06/2023]
Abstract
Inosine pranobex (IP) is a synthetic immunomodulating compound, indicated for use in the treatment of human papillomavirus-associated warts and subacute sclerosing panencephalitis. Previous studies demonstrate that the immunomodulatory activity of IP is characterized by enhanced lymphocyte proliferation, cytokine production, and NK cell cytotoxicity. The activation of NKG2D signaling on NK cells, CD8+ T cells, and γδ T cells also produces these outcomes. We hypothesized that IP alters cellular immunity through the induction of NKG2D ligand expression on target cells, thereby enhancing immune cell activation through the NKG2D receptor. We tested this hypothesis and show that exposure of target cells to IP leads to increased expression of multiple NKG2D ligands. Using both targeted metabolic interventions and unbiased metabolomic studies, we found that IP causes an increase in intracellular concentration of purine nucleotides and tricarboxylic acid (TCA) cycle intermediates and NKG2D ligand induction. The degree of NKG2D ligand induction was functionally significant, leading to increased NKG2D-dependent target cell immunogenicity. These findings demonstrate that the immunomodulatory properties of IP are due to metabolic activation with NKG2D ligand induction.
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Affiliation(s)
- Michael T. McCarthy
- Wellcome Trust Centre for Human Genetics, Nuffield Department of MedicineUniversity of OxfordOxfordOX3 7BNUK
| | - Da Lin
- Wellcome Trust Centre for Human Genetics, Nuffield Department of MedicineUniversity of OxfordOxfordOX3 7BNUK
| | - Tomoyoshi Soga
- Institute for Advanced BiosciencesKeio UniversityTsuruokaYamagata997‐0052Japan
| | - Julie Adam
- Wellcome Trust Centre for Human Genetics, Nuffield Department of MedicineUniversity of OxfordOxfordOX3 7BNUK,Target Discovery InstituteNuffield Department of MedicineUniversity of OxfordOxfordOX3 7FZUK
| | - Christopher A. O'Callaghan
- Wellcome Trust Centre for Human Genetics, Nuffield Department of MedicineUniversity of OxfordOxfordOX3 7BNUK
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11
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Hou Y, Zhang R, Sun X. Enhancer LncRNAs Influence Chromatin Interactions in Different Ways. Front Genet 2019; 10:936. [PMID: 31681405 PMCID: PMC6807612 DOI: 10.3389/fgene.2019.00936] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 09/05/2019] [Indexed: 12/14/2022] Open
Abstract
More than 98% of the human genome does not encode proteins, and the vast majority of the noncoding regions have not been well studied. Some of these regions contain enhancers and functional non-coding RNAs. Previous research suggested that enhancer transcripts could be potent independent indicators of enhancer activity, and some enhancer lncRNAs (elncRNAs) have been proven to play critical roles in gene regulation. Here, we identified enhancer–promoter interactions from high-throughput chromosome conformation capture (Hi-C) data. We found that elncRNAs were highly enriched surrounding chromatin loop anchors. Additionally, the interaction frequency of elncRNA-associated enhancer–promoter pairs was significantly higher than the interaction frequency of other enhancer–promoter pairs, suggesting that elncRNAs may reinforce the interactions between enhancers and promoters. We also found that elncRNA expression levels were positively correlated with the interaction frequency of enhancer–promoter pairs. The promoters interacting with elncRNA-associated enhancers were rich in RNA polymerase II and YY1 transcription factor binding sites. We clustered enhancer–promoter pairs into different groups to reflect the different ways in which elncRNAs could influence enhancer–promoter pairs. Interestingly, G-quadruplexes were found to potentially mediate some enhancer–promoter interaction pairs, and the interaction frequency of these pairs was significantly higher than that of other enhancer–promoter pairs. We also found that the G-quadruplexes on enhancers were highly related to the expression of elncRNAs. G-quadruplexes located in the promoters of elncRNAs led to high expression of elncRNAs, whereas G-quadruplexes located in the gene bodies of elncRNAs generally resulted in low expression of elncRNAs.
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Affiliation(s)
- Yue Hou
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, China
| | - Rongxin Zhang
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, China
| | - Xiao Sun
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, China
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12
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Transcription-driven chromatin repression of Intragenic transcription start sites. PLoS Genet 2019; 15:e1007969. [PMID: 30707695 PMCID: PMC6373976 DOI: 10.1371/journal.pgen.1007969] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Revised: 02/13/2019] [Accepted: 01/16/2019] [Indexed: 12/31/2022] Open
Abstract
Progression of RNA polymerase II (RNAPII) transcription relies on the appropriately positioned activities of elongation factors. The resulting profile of factors and chromatin signatures along transcription units provides a “positional information system” for transcribing RNAPII. Here, we investigate a chromatin-based mechanism that suppresses intragenic initiation of RNAPII transcription. We demonstrate that RNAPII transcription across gene promoters represses their function in plants. This repression is characterized by reduced promoter-specific molecular signatures and increased molecular signatures associated with RNAPII elongation. The conserved FACT histone chaperone complex is required for this repression mechanism. Genome-wide Transcription Start Site (TSS) mapping reveals thousands of discrete intragenic TSS positions in fact mutants, including downstream promoters that initiate alternative transcript isoforms. We find that histone H3 lysine 4 mono-methylation (H3K4me1), an Arabidopsis RNAPII elongation signature, is enriched at FACT-repressed intragenic TSSs. Our analyses suggest that FACT is required to repress intragenic TSSs at positions that are in part characterized by elevated H3K4me1 levels. In sum, conserved and plant-specific chromatin features correlate with the co-transcriptional repression of intragenic TSSs. Our insights into TSS repression by RNAPII transcription promise to inform the regulation of alternative transcript isoforms and the characterization of gene regulation through the act of pervasive transcription across eukaryotic genomes. Genes represent DNA elements that are transcribed into mRNA. However, the position where transcription actually starts can be dynamically regulated to expand the diversity of RNA isoforms produced from a single gene. Functionally, alternative Transcription Start Sites (TSSs) may generate protein isoforms with differing N-terminal regions and distinct cellular functions. In plants, light signaling regulates protein isoforms largely through regulated TSS selection, emphasizing the biological significance of this mechanism. Despite the importance of alternative TSS selection, little is known about the underlying molecular mechanisms. Here, we characterize for the first time how transcription initiation from an upstream promoter represses alternative downstream promoter activity in plants. This repression mechanism is associated with chromatin changes that are required to maintain precise gene expression control. Specific chromatin signatures are established during transcription via dynamic interactions between the transcription machinery and associated factors. The conserved histone chaperone complex FACT is one such factor involved in regulating the chromatin environment along genes during transcription. We find that mutant plants with reduced FACT activity specifically initiate transcription from thousands of intragenic positions, thus expanding RNA isoform diversity. Overall, our study reveals conserved and plant-specific chromatin features associated with the co-transcriptional repression of downstream intragenic TSSs. These findings promise to help inform the molecular mechanism underlying environmentally-triggered TSS regulation in plants.
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