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Fluorescent Platforms for RNA Chemical Biology Research. Genes (Basel) 2022; 13:genes13081348. [PMID: 36011259 PMCID: PMC9407474 DOI: 10.3390/genes13081348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 07/21/2022] [Accepted: 07/22/2022] [Indexed: 12/03/2022] Open
Abstract
Efficient detection and observation of dynamic RNA changes remain a tremendous challenge. However, the continuous development of fluorescence applications in recent years enhances the efficacy of RNA imaging. Here we summarize some of these developments from different aspects. For example, single-molecule fluorescence in situ hybridization (smFISH) can detect low abundance RNA at the subcellular level. A relatively new aptamer, Mango, is widely applied to label and track RNA activities in living cells. Molecular beacons (MBs) are valid for quantifying both endogenous and exogenous mRNA and microRNA (miRNA). Covalent binding enzyme labeling fluorescent group with RNA of interest (ROI) partially overcomes the RNA length limitation associated with oligonucleotide synthesis. Forced intercalation (FIT) probes are resistant to nuclease degradation upon binding to target RNA and are used to visualize mRNA and messenger ribonucleoprotein (mRNP) activities. We also summarize the importance of some fluorescence spectroscopic techniques in exploring the function and movement of RNA. Single-molecule fluorescence resonance energy transfer (smFRET) has been employed to investigate the dynamic changes of biomolecules by covalently linking biotin to RNA, and a focus on dye selection increases FRET efficiency. Furthermore, the applications of fluorescence assays in drug discovery and drug delivery have been discussed. Fluorescence imaging can also combine with RNA nanotechnology to target tumors. The invention of novel antibacterial drugs targeting non-coding RNAs (ncRNAs) is also possible with steady-state fluorescence-monitored ligand-binding assay and the T-box riboswitch fluorescence anisotropy assay. More recently, COVID-19 tests using fluorescent clustered regularly interspaced short palindromic repeat (CRISPR) technology have been demonstrated to be efficient and clinically useful. In summary, fluorescence assays have significant applications in both fundamental and clinical research and will facilitate the process of RNA-targeted new drug discovery, therefore deserving further development and updating.
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Gu Y, Huang LJ, Zhao W, Zhang TT, Cui MR, Yang XJ, Zhao XL, Chen HY, Xu JJ. Living-Cell MicroRNA Imaging with Self-Assembling Fragments of Fluorescent Protein-Mimic RNA Aptamer. ACS Sens 2021; 6:2339-2347. [PMID: 34028262 DOI: 10.1021/acssensors.1c00453] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
As the cellular roles of RNA abundance continue to increase, there is an urgent need for the corresponding tools to elucidate native RNA functions and dynamics, especially those of short, low-abundance RNAs in live cells. Fluorescent RNA aptamers provide a useful strategy to create the RNA tag and biosensor devices. Corn, which binds with 3,5-difluoro-4-hydroxybenzylidene-imidazolinone-2-oxime (DFHO), is a good candidate for the RNA tag because of its enhanced photostability and red-shifted spectrum. Herein, we report for the first time the utilization of Corn as a split aptamer system, combined with RNA-initiated fluorescence complementation (RIFC), for monitoring RNA self-assembly and sensing microRNA. In this platform, the 28-nt Corn was divided into two nonfunctional halves (named probe I and probe II), and an additional target RNA recognition and stem part was introduced in each probe. The target RNA can trigger the self-assembly reconstitution of the Corn's G-quadruplex scaffold for DFHO binding and turn-on fluorescence. These probes can be transfected stably into mammalian cells and deliver the light-up fluorescent response to microRNA-21 (miR-21). Significantly, the probes have good photostability, with minimal fluorescence loss after continuous irradiation, and can be used for imaging of miR-21 in living mammalian cells. The proposed method is universal and could be applied to the sensing of other tumor-associated RNAs, including messenger RNA and noncoding RNA, as well as for monitoring RNA/RNA interactions. The Corn-based splitting aptamers show promising potential in the real-time visualization and mechanistic analysis of nucleic acids.
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Affiliation(s)
- Yu Gu
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
- Institute for Materials Science and Engineering, School of Materials Sciences and Engineering, Suzhou University of Science and Technology, Suzhou 215011, China
| | - Li-Juan Huang
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Wei Zhao
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Ting-Ting Zhang
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Mei-Rong Cui
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Xue-Jiao Yang
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Xue-Li Zhao
- College of Chemistry and Molecular Engineering, Zheng-Zhou University, Zhengzhou 450001, China
| | - Hong-Yuan Chen
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Jing-Juan Xu
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
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Abstract
Technologies for RNA imaging in live cells play an important role in understanding the function and regulatory process of RNAs. One approach for genetically encoded fluorescent RNA imaging involves fluorescent light-up aptamers (FLAPs), which are short RNA sequences that can bind cognate fluorogens and activate their fluorescence greatly. Over the past few years, FLAPs have emerged as genetically encoded RNA-based fluorescent biosensors for the cellular imaging and detection of various targets of interest. In this review, we first give a brief overview of the development of the current FLAPs based on various fluorogens. Then we further discuss on the photocycles of the reversibly photoswitching properties in FLAPs and their photostability. Finally, we focus on the applications of FLAPs as genetically encoded RNA-based fluorescent biosensors in biosensing and bioimaging, including RNA, non-nucleic acid molecules, metal ions imaging and quantitative imaging. Their design strategies and recent cellular applications are emphasized and summarized in detail.
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Affiliation(s)
- Huangmei Zhou
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, China
| | - Sanjun Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, China.,Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi, China.,NYU-ECNU Institute of Physics at NYU Shanghai, Shanghai, China
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Ryckelynck M. Development and Applications of Fluorogen/Light-Up RNA Aptamer Pairs for RNA Detection and More. Methods Mol Biol 2021; 2166:73-102. [PMID: 32710404 DOI: 10.1007/978-1-0716-0712-1_5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The central role of RNA in living systems made it highly desirable to have noninvasive and sensitive technologies allowing for imaging the synthesis and the location of these molecules in living cells. This need motivated the development of small pro-fluorescent molecules called "fluorogens" that become fluorescent upon binding to genetically encodable RNAs called "light-up aptamers." Yet, the development of these fluorogen/light-up RNA pairs is a long and thorough process starting with the careful design of the fluorogen and pursued by the selection of a specific and efficient synthetic aptamer. This chapter summarizes the main design and the selection strategies used up to now prior to introducing the main pairs. Then, the vast application potential of these molecules for live-cell RNA imaging and other applications is presented and discussed.
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Affiliation(s)
- Michael Ryckelynck
- Université de Strasbourg, CNRS, Architecture et Réactivité de l'ARN, UPR 9002, Strasbourg, France.
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Gerhard L, Hennig S. FRET Analysis of RNA -Protein Interactions Using Spinach Aptamers. Methods Mol Biol 2021; 2323:171-197. [PMID: 34086281 DOI: 10.1007/978-1-0716-1499-0_13] [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: 06/12/2023]
Abstract
The method development to analyze direct RNA-protein interaction is of high importance as not many homogeneous assay formats are available.The discovery of fluorescent light-up aptamers (FLAPs), short RNA aptamers that switch the fluorescence of small, cell-permeable, and nontoxic organic chromophores on, paved the road for their utilization in direct RNA -protein interactions. The combination with fluorescent proteins as biological fluorophores enabled the development of homogeneous assays that are in principle even encodable on genomic level.Here the rules and methods to design a homogeneous in vitro assay for the detection and quantification of a direct RNA -protein interaction will be described. The design and application of a homogeneous assay to observe and quantify the interaction of the Pseudomonas aeruginosa bacteriophage coat protein 7 (PP7) with its binding RNA sequence (pp7-RNA) will be shown. For this, the Spinach-DFHBI aptamer as RNA fusion and the red fluorescent mCherry as protein fusion was used.The methods presented here do not require any chemical modification of proteins or RNAs which make them relatively easy to use and to adopt on other systems. As all fluorophores are fusion tags to the according biomolecules, standard cloning strategies and molecular biology technologies are sufficient and make this method available for a broad community of researchers.
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Affiliation(s)
- Laura Gerhard
- Division of Organic Chemistry, Department of Chemistry and Pharmaceutical Sciences, Vrije Universiteit Amsterdam, Amsterdam, Noord-Holland, The Netherlands
| | - Sven Hennig
- Division of Organic Chemistry, Department of Chemistry and Pharmaceutical Sciences, Vrije Universiteit Amsterdam, Amsterdam, Noord-Holland, The Netherlands.
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Steinmetzger C, Bessi I, Lenz AK, Höbartner C. Structure-fluorescence activation relationships of a large Stokes shift fluorogenic RNA aptamer. Nucleic Acids Res 2020; 47:11538-11550. [PMID: 31740962 PMCID: PMC7145527 DOI: 10.1093/nar/gkz1084] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Revised: 10/13/2019] [Accepted: 11/01/2019] [Indexed: 12/21/2022] Open
Abstract
The Chili RNA aptamer is a 52 nt long fluorogen-activating RNA aptamer (FLAP) that confers fluorescence to structurally diverse derivatives of fluorescent protein chromophores. A key feature of Chili is the formation of highly stable complexes with different ligands, which exhibit bright, highly Stokes-shifted fluorescence emission. In this work, we have analyzed the interactions between the Chili RNA and a family of conditionally fluorescent ligands using a variety of spectroscopic, calorimetric and biochemical techniques to reveal key structure–fluorescence activation relationships (SFARs). The ligands under investigation form two categories with emission maxima of ∼540 or ∼590 nm, respectively, and bind with affinities in the nanomolar to low-micromolar range. Isothermal titration calorimetry was used to elucidate the enthalpic and entropic contributions to binding affinity for a cationic ligand that is unique to the Chili aptamer. In addition to fluorescence activation, ligand binding was also observed by NMR spectroscopy, revealing characteristic signals for the formation of a G-quadruplex only upon ligand binding. These data shed light on the molecular features required and responsible for the large Stokes shift and the strong fluorescence enhancement of red and green emitting RNA–chromophore complexes.
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Affiliation(s)
- Christian Steinmetzger
- Institute of Organic Chemistry, Julius-Maximilians-University Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Irene Bessi
- Institute of Organic Chemistry, Julius-Maximilians-University Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Ann-Kathrin Lenz
- Institute of Organic Chemistry, Julius-Maximilians-University Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Claudia Höbartner
- Institute of Organic Chemistry, Julius-Maximilians-University Würzburg, Am Hubland, 97074 Würzburg, Germany
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Truong L, Ferré-D'Amaré AR. From fluorescent proteins to fluorogenic RNAs: Tools for imaging cellular macromolecules. Protein Sci 2019; 28:1374-1386. [PMID: 31017335 DOI: 10.1002/pro.3632] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 04/23/2019] [Indexed: 01/01/2023]
Abstract
The explosion in genome-wide sequencing has revealed that noncoding RNAs are ubiquitous and highly conserved in biology. New molecular tools are needed for their study in live cells. Fluorescent RNA-small molecule complexes have emerged as powerful counterparts to fluorescent proteins, which are well established, universal tools in the study of proteins in cell biology. No naturally fluorescent RNAs are known; all current fluorescent RNA tags are in vitro evolved or engineered molecules that bind a conditionally fluorescent small molecule and turn on its fluorescence by up to 5000-fold. Structural analyses of several such fluorescence turn-on aptamers show that these compact (30-100 nucleotides) RNAs have diverse molecular architectures that can restrain their photoexcited fluorophores in their maximally fluorescent states, typically by stacking between planar nucleotide arrangements, such as G-quadruplexes, base triples, or base pairs. The diversity of fluorogenic RNAs as well as fluorophores that are cell permeable and bind weakly to endogenous cellular macromolecules has already produced RNA-fluorophore complexes that span the visual spectrum and are useful for tagging and visualizing RNAs in cells. Because the ligand binding sites of fluorogenic RNAs are not constrained by the need to autocatalytically generate fluorophores as are fluorescent proteins, they may offer more flexibility in molecular engineering to generate photophysical properties that are tailored to experimental needs.
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Affiliation(s)
- Lynda Truong
- Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, Bethesda, Maryland, 20892-8012
| | - Adrian R Ferré-D'Amaré
- Biochemistry and Biophysics Center, National Heart, Lung, and Blood Institute, Bethesda, Maryland, 20892-8012
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Neubacher S, Hennig S. RNA Structure and Cellular Applications of Fluorescent Light-Up Aptamers. Angew Chem Int Ed Engl 2019; 58:1266-1279. [PMID: 30102012 PMCID: PMC6391945 DOI: 10.1002/anie.201806482] [Citation(s) in RCA: 74] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Indexed: 12/16/2022]
Abstract
The cellular functions of RNA are not limited to their role as blueprints for protein synthesis. In particular, noncoding RNA, such as, snRNAs, lncRNAs, miRNAs, play important roles. With increasing numbers of RNAs being identified, it is well known that the transcriptome outnumbers the proteome by far. This emphasizes the great importance of functional RNA characterization and the need to further develop tools for these investigations, many of which are still in their infancy. Fluorescent light-up aptamers (FLAPs) are RNA sequences that can bind nontoxic, cell-permeable small-molecule fluorogens and enhance their fluorescence over many orders of magnitude upon binding. FLAPs can be encoded on the DNA level using standard molecular biology tools and are subsequently transcribed into RNA by the cellular machinery, so that they can be used as fluorescent RNA tags (FLAP-tags). In this Minireview, we give a brief overview of the fluorogens that have been developed and their binding RNA aptamers, with a special focus on published crystal structures. A summary of current and future cellular FLAP applications with an emphasis on the study of RNA-RNA and RNA-protein interactions using split-FLAP and Förster resonance energy transfer (FRET) systems is given.
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Affiliation(s)
- Saskia Neubacher
- Department of Chemistry & Pharmaceutical SciencesVU University AmsterdamDe Boelelaan 11081081HZAmsterdamThe Netherlands
| | - Sven Hennig
- Department of Chemistry & Pharmaceutical SciencesVU University AmsterdamDe Boelelaan 11081081HZAmsterdamThe Netherlands
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Neubacher S, Hennig S. RNA Structure and Cellular Applications of Fluorescent Light-Up Aptamers. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201806482] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Saskia Neubacher
- Department of Chemistry & Pharmaceutical Sciences; VU University Amsterdam; De Boelelaan 1108 1081 HZ Amsterdam The Netherlands
| | - Sven Hennig
- Department of Chemistry & Pharmaceutical Sciences; VU University Amsterdam; De Boelelaan 1108 1081 HZ Amsterdam The Netherlands
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