Seeing Is Believing: Visualizing Circular RNAs

Advancement in the RNA sequencing techniques has discovered hundreds of thousands of circular RNAs (circRNAs) in humans. However, the physiological function of most of the identified circRNAs remains unexplored. Recent studies have established that spliceosomal machinery and RNA-binding proteins modulate circRNA biogenesis. Furthermore, circRNAs have been implicated in regulating crucial cellular processes by interacting with various proteins and microRNAs. However, there are several challenges in understanding the mechanism of circRNA biogenesis, transport, and their interaction with cellular factors to regulate cellular events because of their low abundance and sequence similarity with linear RNA. Addressing these challenges requires systematic studies that directly visualize the circRNAs in cells at single-molecule resolution along with the molecular regulators. In this review, we present the design, benefits, and weaknesses of RNA imaging techniques such as single-molecule RNA fluorescence in situ hybridization and BaseScope in fixed cells and fluorescent RNA aptamers in live-cell imaging of circRNAs. Furthermore, we propose the potential use of molecular beacons, multiply labeled tetravalent RNA imaging probes, and Cas-derived systems to visualize circRNAs.

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Live Cell Imaging of Single RNA Molecules with Fluorogenic Mango II Arrays

10.1101/840082 ◽

2019 ◽

Author(s):

Adam D. Cawte ◽

Peter J. Unrau ◽

David S. Rueda

Keyword(s):

Single Molecule ◽

Signal To Noise Ratio ◽

Super Resolution ◽

Live Cell ◽

Rna Aptamers ◽

Live Cells ◽

Structured Illumination ◽

Rna Molecules ◽

Cellular Processes ◽

Rna Imaging

AbstractRNA molecules play vital roles in many cellular processes. Visualising their dynamics in live cells at single-molecule resolution is essential to elucidate their role in RNA metabolism. RNA aptamers, such as Spinach and Mango, have recently emerged as a powerful background-free technology for live-cell RNA imaging due to their fluorogenic properties upon ligand binding. Here, we report a novel array of Mango II aptamers for RNA imaging in live and fixed cells with high contrast and single-molecule sensitivity. Direct comparison of Mango II and MS2-tdMCP-mCherry dual-labelled mRNAs show marked improvements in signal to noise ratio using the fluorogenic Mango aptamers. Using both coding (β-actin mRNA) and long non-coding (NEAT1) RNAs, we show that the Mango array does not affect cellular localisation. Additionally, we can track single mRNAs for extended time periods, likely due to fluorophore exchange. This property makes the arrays readily compatible with structured illumination super-resolution microscopy.

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CircIMPACT: An R Package to Explore Circular RNA Impact on Gene Expression and Pathways

Genes ◽

10.3390/genes12071044 ◽

2021 ◽

Vol 12 (7) ◽

pp. 1044

Author(s):

Alessia Buratin ◽

Enrico Gaffo ◽

Anna Dal Molin ◽

Stefania Bortoluzzi

Keyword(s):

Gene Expression ◽

Rna Binding ◽

Rna Binding Proteins ◽

Experimental Studies ◽

R Package ◽

Circular Rna ◽

Circular Rnas ◽

Case Study Analysis ◽

Cellular Processes

Circular RNAs (circRNAs) are transcripts generated by back-splicing. CircRNAs might regulate cellular processes by different mechanisms, including interaction with miRNAs and RNA-binding proteins. CircRNAs are pleiotropic molecules whose dysregulation has been linked to human diseases and can drive cancer by impacting gene expression and signaling pathways. The detection of circRNAs aberrantly expressed in disease conditions calls for the investigation of their functions. Here, we propose CircIMPACT, a bioinformatics tool for the integrative analysis of circRNA and gene expression data to facilitate the identification and visualization of the genes whose expression varies according to circRNA expression changes. This tool can highlight regulatory axes potentially governed by circRNAs, which can be prioritized for further experimental study. The usefulness of CircIMPACT is exemplified by a case study analysis of bladder cancer RNA-seq data. The link between circHIPK3 and heparanase (HPSE) expression, due to the circHIPK3-miR558-HPSE regulatory axis previously determined by experimental studies on cell lines, was successfully detected. CircIMPACT is freely available at GitHub.

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CRAFT: a bioinformatics software for custom prediction of circular RNA functions

10.1101/2021.11.17.468947 ◽

2021 ◽

Author(s):

Anna Dal Molin ◽

Enrico Gaffo ◽

Valeria Difilippo ◽

Alessia Buratin ◽

Caterina Tretti Parenzan ◽

...

Keyword(s):

Regulatory Networks ◽

Rna Binding ◽

Rna Binding Proteins ◽

Enrichment Analysis ◽

Functional Enrichment Analysis ◽

Circular Rna ◽

Functional Enrichment ◽

Circular Rnas ◽

Cellular Processes ◽

Functional Investigation

Circular RNAs (circRNAs), transcripts generated by backsplicing, are particularly stable and pleiotropic molecules, whose dysregulation drives human diseases and cancer by modulating gene expression and signaling pathways. CircRNAs can regulate cellular processes by different mechanisms, including interaction with microRNAs (miRNAs) and RNA-binding proteins (RBP), and encoding specific peptides. The prediction of circRNA functions is instrumental to interpret their impact in diseases, and to prioritize circRNAs for functional investigation. Currently, circRNA functional predictions are provided by web databases that do not allow custom analyses, while self-standing circRNA prediction tools are mostly limited to predict only one type of function, mainly focusing on the miRNA sponge activity of circRNAs. To solve these issues, we developed CRAFT (CircRNA Function prediction Tool), a freely available computational pipeline that predicts circRNA sequence and molecular interactions with miRNAs and RBP, along with their coding potential. Analysis of a set of circRNAs with known functions has been used to appraise CRAFT predictions and to optimize its setting. CRAFT provides a comprehensive graphical visualization of the results, links to several knowledge databases, and extensive functional enrichment analysis. Moreover, it originally combines the predictions for different circRNAs. CRAFT is a useful tool to help the user explore the potential regulatory networks involving the circRNAs of interest and generate hypotheses about the cooperation of circRNAs into the modulation of biological processes.

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The Biomarker and Therapeutic Potential of Circular Rnas in Schizophrenia

Cells ◽

10.3390/cells9102238 ◽

2020 ◽

Vol 9 (10) ◽

pp. 2238

Author(s):

Artem Nedoluzhko ◽

Natalia Gruzdeva ◽

Fedor Sharko ◽

Sergey Rastorguev ◽

Natalia Zakharova ◽

...

Keyword(s):

Gene Expression ◽

Rna Binding ◽

Gene Expression Regulation ◽

Rna Binding Proteins ◽

Therapeutic Potential ◽

Expression Patterns ◽

Circular Rna ◽

Circular Rnas ◽

Cellular Processes ◽

Non Coding Rna

Circular RNAs (circRNAs) are endogenous, single-stranded, most frequently non-coding RNA (ncRNA) molecules that play a significant role in gene expression regulation. Circular RNAs can affect microRNA functionality, interact with RNA-binding proteins (RBPs), translate proteins by themselves, and directly or indirectly modulate gene expression during different cellular processes. The affected expression of circRNAs, as well as their targets, can trigger a cascade of events in the genetic regulatory network causing pathological conditions. Recent studies have shown that altered circular RNA expression patterns could be used as biomarkers in psychiatric diseases, including schizophrenia (SZ); moreover, circular RNAs together with other cell molecules could provide new insight into mechanisms of this disorder. In this review, we focus on the role of circular RNAs in the pathogenesis of SZ and analyze their biomarker and therapeutic potential in this disorder.

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C9orf72-associated arginine-rich dipeptide repeats induce RNA-dependent nuclear accumulation of Staufen in neurons

Human Molecular Genetics ◽

10.1093/hmg/ddab089 ◽

2021 ◽

Author(s):

Eun Seon Kim ◽

Chang Geon Chung ◽

Jeong Hyang Park ◽

Byung Su Ko ◽

Sung Soon Park ◽

...

Keyword(s):

Retinal Degeneration ◽

Rna Binding ◽

Rna Binding Proteins ◽

Nuclear Accumulation ◽

Heterozygous Mutation ◽

Pathological Feature ◽

Dependent Manner ◽

Cellular Processes ◽

Drosophila Model ◽

Post Transcriptional Regulation

Abstract RNA-binding proteins (RBPs) play essential roles in diverse cellular processes through post-transcriptional regulation of RNAs. The subcellular localization of RBPs is thus under tight control, the breakdown of which is associated with aberrant cytoplasmic accumulation of nuclear RBPs such as TDP-43 and FUS, well-known pathological markers for amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD). Here, we report in Drosophila model for ALS/FTD that nuclear accumulation of a cytoplasmic RBP, Staufen, may be a new pathological feature. We found that in Drosophila C4da neurons expressing PR36, one of the arginine-rich dipeptide repeat proteins (DPRs), Staufen accumulated in the nucleus in Importin- and RNA-dependent manner. Notably, expressing Staufen with exogenous NLS—but not with mutated endogenous NLS—potentiated PR-induced dendritic defect, suggesting that nuclear-accumulated Staufen can enhance PR toxicity. PR36 expression increased Fibrillarin staining in the nucleolus, which was enhanced by heterozygous mutation of stau (stau+/−), a gene that codes Staufen. Furthermore, knockdown of fib, which codes Fibrillarin, exacerbated retinal degeneration mediated by PR toxicity, suggesting that increased amount of Fibrillarin by stau+/− is protective. Stau+/− also reduced the amount of PR-induced nuclear-accumulated Staufen and mitigated retinal degeneration and rescued viability of flies expressing PR36. Taken together, our data show that nuclear accumulation of Staufen in neurons may be an important pathological feature contributing to the pathogenesis of ALS/FTD.

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Identification of Novel RNA Binding Proteins Influencing Circular RNA Expression in Hepatocellular Carcinoma

International Journal of Molecular Sciences ◽

10.3390/ijms22147477 ◽

2021 ◽

Vol 22 (14) ◽

pp. 7477

Author(s):

Rok Razpotnik ◽

Petra Nassib ◽

Tanja Kunej ◽

Damjana Rozman ◽

Tadeja Režen

Keyword(s):

Hepatocellular Carcinoma ◽

Binding Proteins ◽

Rna Binding ◽

Rna Binding Proteins ◽

Regulatory Protein ◽

Circular Rna ◽

Differentially Expressed ◽

Circular Rnas ◽

Bioinformatics Analyses ◽

Published Evidence

Circular RNAs (circRNAs) are increasingly recognized as having a role in cancer development. Their expression is modified in numerous cancers, including hepatocellular carcinoma (HCC); however, little is known about the mechanisms of their regulation. The aim of this study was to identify regulators of circRNAome expression in HCC. Using publicly available datasets, we identified RNA binding proteins (RBPs) with enriched motifs around the splice sites of differentially expressed circRNAs in HCC. We confirmed the binding of some of the candidate RBPs using ChIP-seq and eCLIP datasets in the ENCODE database. Several of the identified RBPs were found to be differentially expressed in HCC and/or correlated with the overall survival of HCC patients. According to our bioinformatics analyses and published evidence, we propose that NONO, PCPB2, PCPB1, ESRP2, and HNRNPK are candidate regulators of circRNA expression in HCC. We confirmed that the knocking down the epithelial splicing regulatory protein 2 (ESRP2), known to be involved in the maintenance of the adult liver phenotype, significantly changed the expression of candidate circRNAs in a model HCC cell line. By understanding the systemic changes in transcriptome splicing, we can identify new proteins involved in the molecular pathways leading to HCC development and progression.

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Comprehensive landscape and future perspectives of circular RNAs in colorectal cancer

Molecular Cancer ◽

10.1186/s12943-021-01318-6 ◽

2021 ◽

Vol 20 (1) ◽

Author(s):

Fei Long ◽

Zhi Lin ◽

Liang Li ◽

Min Ma ◽

Zhixing Lu ◽

...

Keyword(s):

Colorectal Cancer ◽

Molecular Mechanisms ◽

Rna Binding ◽

Rna Binding Proteins ◽

Circular Rnas ◽

Future Perspectives ◽

Cis Acting ◽

New Class ◽

Functional Peptides ◽

Mirna Sponges

AbstractColorectal cancer (CRC) is a common hereditary tumor that is often fatal. Its pathogenesis involves multiple genes, including circular RNAs (circRNAs). Notably, circRNAs constitute a new class of noncoding RNAs (ncRNAs) with a covalently closed loop structure and have been characterized as stable, conserved molecules that are abundantly expressed in tissue/development-specific patterns in eukaryotes. Based on accumulating evidence, circRNAs are aberrantly expressed in CRC tissues, cells, exosomes, and blood from patients with CRC. Moreover, numerous circRNAs have been identified as either oncogenes or tumor suppressors that mediate tumorigenesis, metastasis and chemoradiation resistance in CRC. Although the regulatory mechanisms of circRNA biogenesis and functions remain fairly elusive, interesting results have been obtained in studies investigating CRC. In particular, the expression of circRNAs in CRC is comprehensively modulated by multiple factors, such as splicing factors, transcription factors, specific enzymes and cis-acting elements. More importantly, circRNAs exert pivotal effects on CRC through various mechanisms, including acting as miRNA sponges or decoys, interacting with RNA binding proteins, and even translating functional peptides. Finally, circRNAs may serve as promising diagnostic and prognostic biomarkers and potential therapeutic targets in the clinical practice of CRC. In this review, we discuss the dysregulation, functions and clinical significance of circRNAs in CRC and further discuss the molecular mechanisms by which circRNAs exert their functions and how their expression is regulated. Based on this review, we hope to reveal the functions of circRNAs in the initiation and progression of cancer and highlight the future perspectives on strategies targeting circRNAs in cancer research.

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Current Understanding of Circular RNAs in Systemic Lupus Erythematosus

Frontiers in Immunology ◽

10.3389/fimmu.2021.628872 ◽

2021 ◽

Vol 12 ◽

Author(s):

Hongjiang Liu ◽

Yundong Zou ◽

Chen Chen ◽

Yundi Tang ◽

Jianping Guo

Keyword(s):

Systemic Lupus Erythematosus ◽

Lupus Erythematosus ◽

Rna Binding ◽

Rna Binding Proteins ◽

Protein Complexes ◽

Expression Patterns ◽

Regulation Of Gene Expression ◽

Current Understanding ◽

Circular Rnas ◽

Systemic Lupus

Systemic lupus erythematosus (SLE) is a common and potentially fatal autoimmune disease that affects multiple organs. To date, its etiology and pathogenesis remains elusive. Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNAs with covalently closed loop structure. Growing evidence has demonstrated that circRNAs may play an essential role in regulation of gene expression and transcription by acting as microRNA (miRNA) sponges, impacting cell survival and proliferation by interacting with RNA binding proteins (RBPs), and strengthening mRNA stability by forming RNA-protein complexes duplex structures. The expression patterns of circRNAs exhibit tissue-specific and pathogenesis-related manner. CircRNAs have implicated in the development of multiple autoimmune diseases, including SLE. In this review, we summarize the characteristics, biogenesis, and potential functions of circRNAs, its impact on immune responses and highlight current understanding of circRNAs in the pathogenesis of SLE.

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The effective function of circular RNA in colorectal cancer

Cancer Cell International ◽

10.1186/s12935-021-02196-0 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Mandana Ameli-Mojarad ◽

Melika Ameli-Mojarad ◽

Mahrooyeh Hadizadeh ◽

Chris Young ◽

Hosna Babini ◽

...

Keyword(s):

Colorectal Cancer ◽

Molecular Mechanisms ◽

Rna Binding ◽

Rna Binding Proteins ◽

Circular Rna ◽

Circular Rnas ◽

Colorectal Tumorigenesis ◽

Non Coding Rnas ◽

Mirna Sponges ◽

Mechanisms Of Development

AbstractColorectal cancer (CRC) is the 3rd most common type of cancer worldwide. Late detection plays role in one-third of annual mortality due to CRC. Therefore, it is essential to find a precise and optimal diagnostic and prognostic biomarker for the identification and treatment of colorectal tumorigenesis. Covalently closed, circular RNAs (circRNAs) are a class of non-coding RNAs, which can have the same function as microRNA (miRNA) sponges, as regulators of splicing and transcription, and as interactors with RNA-binding proteins (RBPs). Therefore, circRNAs have been investigated as specific targets for diagnostic and prognostic detection of CRC. These non-coding RNAs are also linked to metastasis, proliferation, differentiation, migration, angiogenesis, apoptosis, and drug resistance, illustrating the importance of understanding their involvement in the molecular mechanisms of development and progression of CRC. In this review, we present a detailed summary of recent findings relating to the dysregulation of circRNAs and their potential role in CRC.

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Insights into the multifaceted role of circular RNAs: implications for Parkinson’s disease pathogenesis and diagnosis

npj Parkinson s Disease ◽

10.1038/s41531-021-00265-9 ◽

2022 ◽

Vol 8 (1) ◽

Author(s):

Epaminondas Doxakis

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Rna Binding ◽

Rna Binding Proteins ◽

Clinical Manifestations ◽

Alpha Synuclein ◽

Circular Rnas ◽

Age Related ◽

And Function ◽

The Brain

AbstractParkinson’s disease (PD) is a complex, age-related, neurodegenerative disease whose etiology, pathology, and clinical manifestations remain incompletely understood. As a result, care focuses primarily on symptoms relief. Circular RNAs (circRNAs) are a large class of mostly noncoding RNAs that accumulate with aging in the brain and are increasingly shown to regulate all aspects of neuronal and glial development and function. They are generated by the spliceosome through the backsplicing of linear RNA. Although their biological role remains largely unknown, they have been shown to regulate transcription and splicing, act as decoys for microRNAs and RNA binding proteins, used as templates for translation, and serve as scaffolding platforms for signaling components. Considering that they are stable, diverse, and detectable in easily accessible biofluids, they are deemed promising biomarkers for diagnosing diseases. CircRNAs are differentially expressed in the brain of patients with PD, and growing evidence suggests that they regulate PD pathogenetic processes. Here, the biogenesis, expression, degradation, and detection of circRNAs, as well as their proposed functions, are reviewed. Thereafter, research linking circRNAs to PD-related processes, including aging, alpha-synuclein dysregulation, neuroinflammation, and oxidative stress is highlighted, followed by recent evidence for their use as prognostic and diagnostic biomarkers for PD.

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