1
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Keniry A, Blewitt ME. Chromatin-mediated silencing on the inactive X chromosome. Development 2023; 150:dev201742. [PMID: 37991053 DOI: 10.1242/dev.201742] [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] [Indexed: 11/23/2023]
Abstract
In mammals, the second X chromosome in females is silenced to enable dosage compensation between XX females and XY males. This essential process involves the formation of a dense chromatin state on the inactive X (Xi) chromosome. There is a wealth of information about the hallmarks of Xi chromatin and the contribution each makes to silencing, leaving the tantalising possibility of learning from this knowledge to potentially remove silencing to treat X-linked diseases in females. Here, we discuss the role of each chromatin feature in the establishment and maintenance of the silent state, which is of crucial relevance for such a goal.
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Affiliation(s)
- Andrew Keniry
- Epigenetics and Development Division, The Walter and Eliza Hall Institute for Medical Research, 1G Royal Parade, Parkville, VIC 3052, Australia
- The Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia
| | - Marnie E Blewitt
- Epigenetics and Development Division, The Walter and Eliza Hall Institute for Medical Research, 1G Royal Parade, Parkville, VIC 3052, Australia
- The Department of Medical Biology, University of Melbourne, Parkville, VIC 3010, Australia
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2
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Jiang T, Zhang XO, Weng Z, Xue W. Deletion and replacement of long genomic sequences using prime editing. Nat Biotechnol 2022; 40:227-234. [PMID: 34650270 PMCID: PMC8847310 DOI: 10.1038/s41587-021-01026-y] [Citation(s) in RCA: 86] [Impact Index Per Article: 43.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Accepted: 07/19/2021] [Indexed: 12/21/2022]
Abstract
Genomic insertions, duplications and insertion/deletions (indels), which account for ~14% of human pathogenic mutations, cannot be accurately or efficiently corrected by current gene-editing methods, especially those that involve larger alterations (>100 base pairs (bp)). Here, we optimize prime editing (PE) tools for creating precise genomic deletions and direct the replacement of a genomic fragment ranging from ~1 kilobases (kb) to ~10 kb with a desired sequence (up to 60 bp) in the absence of an exogenous DNA template. By conjugating Cas9 nuclease to reverse transcriptase (PE-Cas9) and combining it with two PE guide RNAs (pegRNAs) targeting complementary DNA strands, we achieve precise and specific deletion and repair of target sequences via using this PE-Cas9-based deletion and repair (PEDAR) method. PEDAR outperformed other genome-editing methods in a reporter system and at endogenous loci, efficiently creating large and precise genomic alterations. In a mouse model of tyrosinemia, PEDAR removed a 1.38-kb pathogenic insertion within the Fah gene and precisely repaired the deletion junction to restore FAH expression in liver.
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Affiliation(s)
- Tingting Jiang
- RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA, USA
| | - Xiao-Ou Zhang
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA, USA
- School of Life Sciences and Technology, Tongji University, Shanghai, China
| | - Zhiping Weng
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester, MA, USA
| | - Wen Xue
- RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA, USA.
- Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, MA, USA.
- Department of Molecular Medicine, University of Massachusetts Medical School, Worcester, MA, USA.
- Li Weibo Institute for Rare Diseases Research, University of Massachusetts Medical School, Worcester, MA, USA.
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3
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The tandem repeat modules of Xist lncRNA: a swiss army knife for the control of X-chromosome inactivation. Biochem Soc Trans 2021; 49:2549-2560. [PMID: 34882219 PMCID: PMC8786293 DOI: 10.1042/bst20210253] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 11/19/2021] [Accepted: 11/23/2021] [Indexed: 12/16/2022]
Abstract
X-inactive-specific transcript (Xist) is a long non-coding RNA (lncRNA) essential for X-chromosome inactivation (XCI) in female placental mammals. Thirty years after its discovery, it is still puzzling how this lncRNA triggers major structural and transcriptional changes leading to the stable silencing of an entire chromosome. Recently, a series of studies in mouse cells have uncovered domains of functional specialization within Xist mapping to conserved tandem repeat regions, known as Repeats A-to-F. These functional domains interact with various RNA binding proteins (RBPs) and fold into distinct RNA structures to execute specific tasks in a synergistic and coordinated manner during the inactivation process. This modular organization of Xist is mostly conserved in humans, but recent data point towards differences regarding functional specialization of the tandem repeats between the two species. In this review, we summarize the recent progress on understanding the role of Xist repetitive blocks and their involvement in the molecular mechanisms underlying XCI. We also discuss these findings in the light of the similarities and differences between mouse and human Xist.
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4
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S. Zibitt M, Hartford CCR, Lal A. Interrogating lncRNA functions via CRISPR/Cas systems. RNA Biol 2021; 18:2097-2106. [PMID: 33685382 PMCID: PMC8632070 DOI: 10.1080/15476286.2021.1899500] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Revised: 03/01/2021] [Accepted: 03/02/2021] [Indexed: 12/13/2022] Open
Abstract
Long noncoding RNAs (lncRNAs) are an increasing focus of investigation due to their implications in diverse biological processes and disease. Nevertheless, the majority of lncRNAs are low in abundance and poorly conserved, posing challenges to functional studies. The CRISPR/Cas system, an innovative technology that has emerged over the last decade, can be utilized to further understand lncRNA function. The system targets specific DNA and/or RNA sequences via a guide RNA (gRNA) and Cas nuclease complex. We and others have utilized this technology in various applications such as lncRNA knockout, knockdown, overexpression, and imaging. In this review, we summarize how the CRISPR/Cas technology provides new tools to investigate the roles and therapeutic implications of lncRNAs.
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Affiliation(s)
- Meira S. Zibitt
- Regulatory RNAs and Cancer Section, Genetics Branch, Center for Cancer Research (CCR), National Cancer Institute (NCI), National Institutes of Health (NIH), Bethesda, MD, USA
| | - Corrine Corrina R. Hartford
- Regulatory RNAs and Cancer Section, Genetics Branch, Center for Cancer Research (CCR), National Cancer Institute (NCI), National Institutes of Health (NIH), Bethesda, MD, USA
| | - Ashish Lal
- Regulatory RNAs and Cancer Section, Genetics Branch, Center for Cancer Research (CCR), National Cancer Institute (NCI), National Institutes of Health (NIH), Bethesda, MD, USA
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5
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Trotman JB, Braceros KCA, Cherney RE, Murvin MM, Calabrese JM. The control of polycomb repressive complexes by long noncoding RNAs. WILEY INTERDISCIPLINARY REVIEWS. RNA 2021; 12:e1657. [PMID: 33861025 PMCID: PMC8500928 DOI: 10.1002/wrna.1657] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 01/12/2021] [Accepted: 03/19/2021] [Indexed: 02/06/2023]
Abstract
The polycomb repressive complexes 1 and 2 (PRCs; PRC1 and PRC2) are conserved histone-modifying enzymes that often function cooperatively to repress gene expression. The PRCs are regulated by long noncoding RNAs (lncRNAs) in complex ways. On the one hand, specific lncRNAs cause the PRCs to engage with chromatin and repress gene expression over genomic regions that can span megabases. On the other hand, the PRCs bind RNA with seemingly little sequence specificity, and at least in the case of PRC2, direct RNA-binding has the effect of inhibiting the enzyme. Thus, some RNAs appear to promote PRC activity, while others may inhibit it. The reasons behind this apparent dichotomy are unclear. The most potent PRC-activating lncRNAs associate with chromatin and are predominantly unspliced or harbor unusually long exons. Emerging data imply that these lncRNAs promote PRC activity through internal RNA sequence elements that arise and disappear rapidly in evolutionary time. These sequence elements may function by interacting with common subsets of RNA-binding proteins that recruit or stabilize PRCs on chromatin. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Recognition RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.
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Affiliation(s)
- Jackson B. Trotman
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Keean C. A. Braceros
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
- Curriculum in Mechanistic, Interdisciplinary Studies of Biological Systems, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Rachel E. Cherney
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - McKenzie M. Murvin
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - J. Mauro Calabrese
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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6
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Decoding LncRNAs. Cancers (Basel) 2021; 13:cancers13112643. [PMID: 34072257 PMCID: PMC8199187 DOI: 10.3390/cancers13112643] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 05/23/2021] [Accepted: 05/25/2021] [Indexed: 02/07/2023] Open
Abstract
Non-coding RNAs (ncRNAs) have been considered as unimportant additions to the transcriptome. Yet, in light of numerous studies, it has become clear that ncRNAs play important roles in development, health and disease. Long-ignored, long non-coding RNAs (lncRNAs), ncRNAs made of more than 200 nucleotides have gained attention due to their involvement as drivers or suppressors of a myriad of tumours. The detailed understanding of some of their functions, structures and interactomes has been the result of interdisciplinary efforts, as in many cases, new methods need to be created or adapted to characterise these molecules. Unlike most reviews on lncRNAs, we summarize the achievements on lncRNA studies by taking into consideration the approaches for identification of lncRNA functions, interactomes, and structural arrangements. We also provide information about the recent data on the involvement of lncRNAs in diseases and present applications of these molecules, especially in medicine.
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7
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Westervelt N, Yoest A, Sayed S, Von Zimmerman M, Kaps K, Chadwick BP. Deletion of the XIST promoter from the human inactive X chromosome compromises polycomb heterochromatin maintenance. Chromosoma 2021; 130:177-197. [PMID: 33745031 DOI: 10.1007/s00412-021-00754-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 02/01/2021] [Accepted: 02/21/2021] [Indexed: 10/21/2022]
Abstract
Silencing most gene expression from all but one X chromosome in female mammals provides a means to overcome X-linked gene expression imbalances with males. Central to establishing gene silencing on the inactivated X chromosome are the actions of the long non-coding RNA XIST that triggers the repackaging of the chosen X into facultative heterochromatin. While understanding the mechanisms through which XIST expression is regulated and mediates its affects has been a major focus of research since its discovery, less is known about the role XIST plays in maintaining chromatin at the human inactive X chromosome (Xi). Here, we use genome engineering to delete the promoter of XIST to knockout expression from the Xi in non-cancerous diploid human somatic cells. Although some heterochromatin features exhibit limited change at the Xi, two of those assessed showed significant reductions including histone H2A monoubiquitylation at lysine 119 and histone H3 trimethylation at lysine 27, both of which are covalent histone modifications catalyzed by the polycomb repressive complexes 1 and 2 respectively. Coupled with these reductions, we observed an occasional gain of euchromatin signatures on Xp, but despite these signs of chromatin instability, we did not observe appreciable changes in the reactivation of genes from the Xi. Collectively, these data are consistent with maintenance of dosage compensation at the Xi involving multiple redundant layers of gene silencing.
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Affiliation(s)
- Natalia Westervelt
- Department of Biological Science, Florida State University, 319 Stadium Drive, King 3076, Tallahassee, FL, 32306-4295, USA
| | - Andrea Yoest
- Department of Biological Science, Florida State University, 319 Stadium Drive, King 3076, Tallahassee, FL, 32306-4295, USA
| | - Sadia Sayed
- Department of Biological Science, Florida State University, 319 Stadium Drive, King 3076, Tallahassee, FL, 32306-4295, USA
| | - Marina Von Zimmerman
- Department of Biological Science, Florida State University, 319 Stadium Drive, King 3076, Tallahassee, FL, 32306-4295, USA
| | - Kelly Kaps
- Department of Biological Science, Florida State University, 319 Stadium Drive, King 3076, Tallahassee, FL, 32306-4295, USA
| | - Brian P Chadwick
- Department of Biological Science, Florida State University, 319 Stadium Drive, King 3076, Tallahassee, FL, 32306-4295, USA.
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8
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Dixon-McDougall T, Brown CJ. Independent domains for recruitment of PRC1 and PRC2 by human XIST. PLoS Genet 2021; 17:e1009123. [PMID: 33750950 PMCID: PMC8016261 DOI: 10.1371/journal.pgen.1009123] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 04/01/2021] [Accepted: 03/07/2021] [Indexed: 01/08/2023] Open
Abstract
XIST establishes inactivation across its chromosome of origin, even when expressed from autosomal transgenes. To identify the regions of human XIST essential for recruiting heterochromatic marks we generated a series of overlapping deletions in an autosomal inducible XIST transgene present in 8p of the HT1080 male fibrosarcoma cell line. We examined the ability of each construct to enrich its unified XIST territory with the histone marks established by PRC1 and PRC2 as well as the heterochromatin factors MacroH2A and SMCHD1. Chromatin enrichment of ubH2A by PRC1 required four distinct regions of XIST, and these were completely distinct from the two domains crucial for enrichment of H3K27me3 by PRC2. Both the domains required, as well as the impact of PRC1 and PRC2 inhibitors, suggest that PRC1 is required for SMCHD1 while PRC2 function is necessary for MacroH2A recruitment, although incomplete overlap of regions implicates roles for additional factors. This cooperativity between factors contributes to the requirement for multiple separate domains being required for each feature examined. The independence of the PRC1/PRC2 pathways was observed when XIST was expressed both autosomally or from the X chromosome suggesting that these observations are not purely a result of the context in which XIST operates. Although independent domains were required for the PRC1 and PRC2 pathways overall all regions tested were important for some aspect of XIST functionality, demonstrating both modularity and cooperativity across the XIST lncRNA.
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Affiliation(s)
- Thomas Dixon-McDougall
- Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Carolyn J. Brown
- Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada
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9
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Chou HC, Bhalla K, Demerdesh OE, Klingbeil O, Hanington K, Aganezov S, Andrews P, Alsudani H, Chang K, Vakoc CR, Schatz MC, McCombie WR, Stillman B. The human origin recognition complex is essential for pre-RC assembly, mitosis, and maintenance of nuclear structure. eLife 2021; 10:61797. [PMID: 33522487 PMCID: PMC7877914 DOI: 10.7554/elife.61797] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 01/30/2021] [Indexed: 12/23/2022] Open
Abstract
The origin recognition complex (ORC) cooperates with CDC6, MCM2-7, and CDT1 to form pre-RC complexes at origins of DNA replication. Here, using tiling-sgRNA CRISPR screens, we report that each subunit of ORC and CDC6 is essential in human cells. Using an auxin-inducible degradation system, we created stable cell lines capable of ablating ORC2 rapidly, revealing multiple cell division cycle phenotypes. The primary defects in the absence of ORC2 were cells encountering difficulty in initiating DNA replication or progressing through the cell division cycle due to reduced MCM2-7 loading onto chromatin in G1 phase. The nuclei of ORC2-deficient cells were also large, with decompacted heterochromatin. Some ORC2-deficient cells that completed DNA replication entered into, but never exited mitosis. ORC1 knockout cells also demonstrated extremely slow cell proliferation and abnormal cell and nuclear morphology. Thus, ORC proteins and CDC6 are indispensable for normal cellular proliferation and contribute to nuclear organization.
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Affiliation(s)
- Hsiang-Chen Chou
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States.,Graduate Program in Molecular and Cellular Biology, Stony Brook University, Stony Brook, United States
| | - Kuhulika Bhalla
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Olaf Klingbeil
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Sergey Aganezov
- Department of Computer Science, Whiting School of Engineering, Johns Hopkins University, Baltimore, United States
| | - Peter Andrews
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | - Habeeb Alsudani
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | - Kenneth Chang
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
| | | | - Michael C Schatz
- Department of Computer Science, Whiting School of Engineering, Johns Hopkins University, Baltimore, United States
| | | | - Bruce Stillman
- Cold Spring Harbor Laboratory, Cold Spring Harbor, United States
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10
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Trotman JB, Lee DM, Cherney RE, Kim SO, Inoue K, Schertzer MD, Bischoff SR, Cowley DO, Calabrese J. Elements at the 5' end of Xist harbor SPEN-independent transcriptional antiterminator activity. Nucleic Acids Res 2020; 48:10500-10517. [PMID: 32986830 PMCID: PMC7544216 DOI: 10.1093/nar/gkaa789] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 08/20/2020] [Accepted: 09/12/2020] [Indexed: 12/22/2022] Open
Abstract
The Xist lncRNA requires Repeat A, a conserved RNA element located in its 5' end, to induce gene silencing during X-chromosome inactivation. Intriguingly, Repeat A is also required for production of Xist. While silencing by Repeat A requires the protein SPEN, how Repeat A promotes Xist production remains unclear. We report that in mouse embryonic stem cells, expression of a transgene comprising the first two kilobases of Xist (Xist-2kb) causes transcriptional readthrough of downstream polyadenylation sequences. Readthrough required Repeat A and the ∼750 nucleotides downstream, did not require SPEN, and was attenuated by splicing. Despite associating with SPEN and chromatin, Xist-2kb did not robustly silence transcription, whereas a 5.5-kb Xist transgene robustly silenced transcription and read through its polyadenylation sequence. Longer, spliced Xist transgenes also induced robust silencing yet terminated efficiently. Thus, in contexts examined here, Xist requires sequence elements beyond its first two kilobases to robustly silence transcription, and the 5' end of Xist harbors SPEN-independent transcriptional antiterminator activity that can repress proximal cleavage and polyadenylation. In endogenous contexts, this antiterminator activity may help produce full-length Xist RNA while rendering the Xist locus resistant to silencing by the same repressive complexes that the lncRNA recruits to other genes.
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Affiliation(s)
- Jackson B Trotman
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599, USA
| | - David M Lee
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599, USA
- Curriculum in Genetics and Molecular Biology, Chapel Hill, NC 27599, USA
| | - Rachel E Cherney
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599, USA
- Curriculum in Genetics and Molecular Biology, Chapel Hill, NC 27599, USA
| | - Susan O Kim
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599, USA
| | - Kaoru Inoue
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599, USA
| | - Megan D Schertzer
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599, USA
- Curriculum in Genetics and Molecular Biology, Chapel Hill, NC 27599, USA
| | - Steven R Bischoff
- Animal Models Core, University of North Carolina at Chapel Hill, 120 Mason Farm Road, Chapel Hill, NC 27599, USA
| | - Dale O Cowley
- Animal Models Core, University of North Carolina at Chapel Hill, 120 Mason Farm Road, Chapel Hill, NC 27599, USA
| | - J Mauro Calabrese
- Department of Pharmacology and Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599, USA
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11
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García-García JD, Joshi J, Patterson JA, Trujillo-Rodriguez L, Reisch CR, Javanpour AA, Liu CC, Hanson AD. Potential for Applying Continuous Directed Evolution to Plant Enzymes: An Exploratory Study. Life (Basel) 2020; 10:E179. [PMID: 32899502 PMCID: PMC7555113 DOI: 10.3390/life10090179] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 08/31/2020] [Accepted: 09/01/2020] [Indexed: 12/22/2022] Open
Abstract
Plant evolution has produced enzymes that may not be optimal for maximizing yield and quality in today's agricultural environments and plant biotechnology applications. By improving enzyme performance, it should be possible to alleviate constraints on yield and quality currently imposed by kinetic properties or enzyme instability. Enzymes can be optimized more quickly than naturally possible by applying directed evolution, which entails mutating a target gene in vitro and screening or selecting the mutated gene products for the desired characteristics. Continuous directed evolution is a more efficient and scalable version that accomplishes the mutagenesis and selection steps simultaneously in vivo via error-prone replication of the target gene and coupling of the host cell's growth rate to the target gene's function. However, published continuous systems require custom plasmid assembly, and convenient multipurpose platforms are not available. We discuss two systems suitable for continuous directed evolution of enzymes, OrthoRep in Saccharomyces cerevisiae and EvolvR in Escherichia coli, and our pilot efforts to adapt each system for high-throughput plant enzyme engineering. To test our modified systems, we used the thiamin synthesis enzyme THI4, previously identified as a prime candidate for improvement. Our adapted OrthoRep system shows promise for efficient plant enzyme engineering.
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Affiliation(s)
| | - Jaya Joshi
- Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, USA;
| | - Jenelle A. Patterson
- Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, USA;
| | - Lidimarie Trujillo-Rodriguez
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32603, USA; (L.T.-R.); (C.R.R.)
| | - Christopher R. Reisch
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32603, USA; (L.T.-R.); (C.R.R.)
| | - Alex A. Javanpour
- Department of Biomedical Engineering, University of California, Irvine, CA 92617, USA; (A.A.J.); (C.C.L.)
| | - Chang C. Liu
- Department of Biomedical Engineering, University of California, Irvine, CA 92617, USA; (A.A.J.); (C.C.L.)
- Department of Chemistry, University of California, Irvine, CA 92617, USA
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, USA
| | - Andrew D. Hanson
- Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, USA;
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12
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Garland W, Jensen TH. Nuclear sorting of RNA. WILEY INTERDISCIPLINARY REVIEWS-RNA 2019; 11:e1572. [PMID: 31713323 DOI: 10.1002/wrna.1572] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/30/2019] [Accepted: 10/08/2019] [Indexed: 12/27/2022]
Abstract
The majority of the mammalian genome is transcribed by RNA polymerase II, yielding a vast amount of noncoding RNA (ncRNA) in addition to the standard production of mRNA. The typical nuclear biogenesis of mRNA relies on the tightly controlled coupling of co- and post-transcriptional processing events, which ultimately results in the export of transcripts into the cytoplasm. These processes are subject to surveillance by nuclear RNA decay pathways to prevent the export of aberrant, or otherwise "non-optimal," transcripts. However, unlike mRNA, many long ncRNAs are nuclear retained and those that maintain enduring functions must employ precautions to evade decay. Proper sorting and localization of RNA is therefore an essential activity in eukaryotic cells and the formation of ribonucleoprotein complexes during early stages of RNA synthesis is central to deciding such transcript fate. This review details our current understanding of the pathways and factors that direct RNAs towards a particular destiny and how transcripts combat the adverse conditions of the nucleus. This article is categorized under: RNA Export and Localization > Nuclear Export/Import RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.
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Affiliation(s)
- William Garland
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus C., Denmark
| | - Torben Heick Jensen
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus C., Denmark
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13
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Bousard A, Raposo AC, Żylicz JJ, Picard C, Pires VB, Qi Y, Gil C, Syx L, Chang HY, Heard E, da Rocha ST. The role of Xist-mediated Polycomb recruitment in the initiation of X-chromosome inactivation. EMBO Rep 2019; 20:e48019. [PMID: 31456285 PMCID: PMC6776897 DOI: 10.15252/embr.201948019] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Revised: 07/29/2019] [Accepted: 08/06/2019] [Indexed: 12/22/2022] Open
Abstract
Xist RNA has been established as the master regulator of X-chromosome inactivation (XCI) in female eutherian mammals, but its mechanism of action remains unclear. By creating novel Xist-inducible mutants at the endogenous locus in male mouse embryonic stem (ES) cells, we dissect the role of the conserved A-B-C-F repeats in the initiation of XCI. We find that transcriptional silencing can be largely uncoupled from Polycomb repressive complex 1 and complex 2 (PRC1/2) recruitment, which requires B and C repeats. Xist ΔB+C RNA specifically loses interaction with PCGF3/5 subunits of PRC1, while binding of other Xist partners is largely unaffected. However, a slight relaxation of transcriptional silencing in Xist ΔB+C indicates a role for PRC1/2 proteins in early stabilization of gene repression. Distinct modules within the Xist RNA are therefore involved in the convergence of independent chromatin modification and gene repression pathways. In this context, Polycomb recruitment seems to be of moderate relevance in the initiation of silencing.
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Affiliation(s)
- Aurélie Bousard
- Mammalian Developmental Epigenetics GroupInstitut CurieCNRS UMR3215, INSERM U934PSL UniversityParisFrance
| | - Ana Cláudia Raposo
- Instituto de Medicina MolecularJoão Lobo AntunesFaculdade de MedicinaUniversidade de LisboaLisboaPortugal
| | - Jan Jakub Żylicz
- Mammalian Developmental Epigenetics GroupInstitut CurieCNRS UMR3215, INSERM U934PSL UniversityParisFrance
- Department of Physiology, Development and NeuroscienceUniversity of CambridgeCambridgeUK
| | - Christel Picard
- Mammalian Developmental Epigenetics GroupInstitut CurieCNRS UMR3215, INSERM U934PSL UniversityParisFrance
| | - Vanessa Borges Pires
- Instituto de Medicina MolecularJoão Lobo AntunesFaculdade de MedicinaUniversidade de LisboaLisboaPortugal
- Instituto de Ciências Biomédicas Abel SalazarUniversidade do PortoPortoPortugal
| | - Yanyan Qi
- Center for Dynamic Personal RegulomesStanford UniversityStanfordCAUSA
| | - Cláudia Gil
- Instituto de Medicina MolecularJoão Lobo AntunesFaculdade de MedicinaUniversidade de LisboaLisboaPortugal
| | - Laurène Syx
- Mammalian Developmental Epigenetics GroupInstitut CurieCNRS UMR3215, INSERM U934PSL UniversityParisFrance
| | - Howard Y Chang
- Center for Dynamic Personal RegulomesStanford UniversityStanfordCAUSA
- Howard Hughes Medical InstituteStanford UniversityStanfordCAUSA
| | - Edith Heard
- Mammalian Developmental Epigenetics GroupInstitut CurieCNRS UMR3215, INSERM U934PSL UniversityParisFrance
| | - Simão Teixeira da Rocha
- Mammalian Developmental Epigenetics GroupInstitut CurieCNRS UMR3215, INSERM U934PSL UniversityParisFrance
- Instituto de Medicina MolecularJoão Lobo AntunesFaculdade de MedicinaUniversidade de LisboaLisboaPortugal
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