A Network of Noncoding Regulatory RNAs Acts in the Mammalian Brain

HIV-1 Tat-Induced Astrocytic Extracellular Vesicle miR-7 Impairs Synaptic Architecture

Although combination antiretroviral therapy (cART) has improved the health of millions of those living with HIV-1 (Human Immunodeficiency Virus, Type 1), the penetration into the central nervous system (CNS) of many such therapies is limited, thereby resulting in residual neurocognitive impairment commonly referred to as NeuroHIV. Additionally, while cART has successfully suppressed peripheral viremia, cytotoxicity associated with the presence of viral Transactivator of transcription (Tat) protein in tissues such as the brain, remains a significant concern. Our previous study has demonstrated that both HIV-1 Tat as well as opiates such as morphine, can directly induce synaptic alterations via independent pathways. Herein, we demonstrate that exposure of astrocytes to HIV-1 protein Tat mediates the induction and release of extracellular vesicle (EV) microRNA-7 (miR-7) that is taken up by neurons, leading in turn, to downregulation of neuronal neuroligin 2 (NLGN2) and ultimately to synaptic alterations. More importantly, we report that these impairments could be reversed by pretreatment of neurons with a neurotrophic factor platelet-derived growth factor-CC (PDGF-CC).

Tagger-A Swiss army knife for multiomics to dissect cell type-specific mechanisms of gene expression in mice

A deep understanding of how regulation of the multiple levels of gene expression in mammalian tissues give rise to complex phenotypes has been impeded by cellular diversity. A handful of techniques were developed to tag-select nucleic acids of interest in specific cell types, thereby enabling their capture. We expanded this strategy by developing the Tagger knock-in mouse line bearing a quad-cistronic transgene combining enrichment tools for nuclei, nascent RNA, translating mRNA, and mature microRNA (miRNA). We demonstrate that Tagger can capture the desired nucleic acids, enabling multiple omics approaches to be applied to specific cell types in vivo using a single transgenic mouse line.

This Methods and Resources paper describes Tagger, a knock-in mouse line bearing a quad-cistronic transgene that enables the capture of translating mRNAs, mature miRNAs, pulse-labeled total RNA, and the nucleus, all from specific cells of complex tissues.

3' Uridylation Confers miRNAs with Non-canonical Target Repertoires

Many microRNAs (miRNAs) exist alongside abundant miRNA isoforms (isomiRs), most of which arise from post-maturation sequence modifications such as 3' uridylation. However, the ways in which these sequence modifications affect miRNA function remain poorly understood. Here, using human miR-27a in cell lines as a model, we discovered that a nonfunctional target site unable to base-pair extensively with the miRNA seed sequence can regain function when an upstream adenosine is able to base-pair with a post-transcriptionally added uridine in the miR-27a tail. This tail-U-mediated repression (TUMR) is abolished in cells lacking the uridylation enzymes TUT4 and TUT7, indicating that uridylation alters miRNA function by modulating target recognition. We identified a set of non-canonical targets in human cells that are specifically regulated by uridylated miR-27a. We provide evidence that TUMR expands the targets of other endogenous miRNAs. Our study reveals a function of uridylated isomiRs in regulating non-canonical miRNA targets.

Strategies for genetic inactivation of long noncoding RNAs in zebrafish

The number of annotated long noncoding RNAs (lncRNAs) continues to grow; however, their functional characterization in model organisms has been hampered by the lack of reliable genetic inactivation strategies. While partial or full deletions of lncRNA loci disrupt lncRNA expression, they do not permit the formal association of a phenotype with the encoded transcript. Here, we examined several alternative strategies for generating lncRNA null alleles in zebrafish and found that they often resulted in unpredicted changes to lncRNA expression. Removal of the transcription start sites (TSSs) of lncRNA genes resulted in hypomorphic mutants, due to the usage of either constitutive or tissue-specific alternative TSSs. Deletions of short, highly conserved lncRNA regions can also lead to overexpression of truncated transcripts. In contrast, knock-in of a polyadenylation signal enabled complete inactivation of malat1, the most abundant vertebrate lncRNA. In summary, lncRNA null alleles require extensive in vivo validation, and we propose insertion of transcription termination sequences as the most reliable approach to generate lncRNA-deficient zebrafish.

lncRNA XIST regulates proliferation and migration of hepatocellular carcinoma cells by acting as miR-497-5p molecular sponge and targeting PDCD4

BACKGROUND

MicroRNAs (miRNAs) play a pivotal role in hepatocellular carcinoma (HCC) progression and have been confirmed to participate in the carcinogenesis and development of HCC. However, the relationship between miR-497-5p and HCC remains unclear.

METHODS

Kaplan-Meier curve analysis and the log-rank test were used to investigate the efficacy of miR-497-5p on overall survival (OS) and disease-free survival (DFS) in patients with HCC. According to in vitro experiments, programmed cell death 4 (PDCD4) was a target of miR-497-5p by the dual-luciferase activity assay. The efficacy of PDCD4 on cell proliferation and metastasis in HCC was examined by transwell assays, CCK-8 assays and reverse transcription quantitative PCR (RT-qPCR). Additionally, we conducted a luciferase activity reporter assay to confirm the interaction between lncRNA XIST and miR-49-5p. Then, to evaluate the relationship between lncRNA XIST and miR-497-5p, several mechanistic experiments, including qRT-PCR, Western blotting, transwell assays and tumor xenograft assays, were performed.

RESULTS

miR-497-5p was upregulated in HCC tissues, and high expression of miR-497-5p resulted in increases in tumor size and tumor number and a higher tumor-node-metastasis (TNM) stage and Edmondson grade in patients with HCC. Silencing miR-497-5p inhibited the proliferation and migration of HCC cells. PDCD4, which was downregulated in HCC tissues, was shown to be a target of miR-497-5p and was negatively correlated with the expression of miR-497-5p. lncRNA XIST was found to act as a miR-497-5p sponge and to regulate the level of PDCD4, which is targeted by miR-497-5p. lncRNA XIST was observed to be downregulated in the HCC tissues and positively correlated with the expression of PDCD4.

CONCLUSIONS

Our findings reveal that the XIST/miR-497-5p/PDCD4 axis participates in HCC development and that XIST could be used as a biomarker of HCC.

Noncoding RNAs in development and teratology, with focus on effects of cannabis, cocaine, nicotine, and ethanol

Completion of the Human Genome Project has led to the identification of a large number of transcription start sites that are not paired with protein-coding genes, supporting the growing recognition of the abundance of encoded nonprotein-coding RNAs (ncRNAs) and their importance for speciation and species-specific development. Present in both plants and animals, ncRNAs vary in size, function, primary sequence, and secondary structure. While microRNAs (miRNAs) are the best known, there are a number of other ncRNAs (long[er] nonprotein-coding RNA, pseudogenes, circular RNAs, and so on) that have been shown to play an important role in the development either directly or via networks of proteins and other ncRNAs, including modulating the impact of miRNAs. Furthermore, these ncRNAs and their developmental regulatory networks are sensitive to teratogens such as ethanol, cannabis, cocaine, and nicotine. A better understanding of the developmental role of ncRNAs and their capacity to mediate teratogenesis is a necessary step in efforts to minimize the long-term consequences of developmental exposures to drugs-of-abuse. Moreover, with increasing awareness of the prevalence of polydrug use, experimental models will need to incorporate more complex drug exposure paradigms into meaningful assessments of developmental ncRNA function.

MyoD-induced circular RNA CDR1as promotes myogenic differentiation of skeletal muscle satellite cells

Many protein coding and non-coding genes interplay in governing skeletal muscle formation. Nevertheless, comparing with the linear transcripts, functions of covalently closed circular RNAs (circRNAs), the new frontier of regulatory non-coding RNA (ncRNAs) molecules, remain largely unknown. Here, we identify CDR1as (antisense to the cerebellar degeneration-related protein 1 transcript, also termed as ciRS-7), a well-known cancer and neuron circRNA, plays a significant role in virtually controlling muscle differentiation. CDR1as is highly expressed in muscles of the mid-embryonic goat foetus, and activated at the initiation of myogenic differentiation in vitro. MyoD (myogenic differentiation protein 1), a driven transcription factor for myogenesis, promotes CDR1as by binding on its 5' flank region (-646 to -634 bp, neighbouring the predicted transcription start site at -580 bp). Overexpression or knockdown of CDR1as dramatically induces or impedes muscle differentiation program, respectively. By competitively binding to miR-7 (microRNA 7), CDR1as relieves the downregulation of IGF1R (insulin like growth factor 1 receptor) caused by miR-7 and consequently activates muscle differentiation. These results unveil that CDR1as plays critical roles in myogenic differentiation, which extends the versatile functions of CDR1as in mammal development and disease.

Role of Long Noncoding RNAs and Circular RNAs in Nerve Regeneration

Nerve injuries may cause severe disability and affect the quality of life. It is of great importance to get a full understanding of the biological processes and molecular mechanisms underlying nerve injuries to find and target specific molecules for nerve regeneration. Numerous studies have shown that noncoding RNAs (ncRNAs) participate in diverse biological processes and diseases. Long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) are two major groups of ncRNAs, which attract growing attention. The altered expression patterns of lncRNAs and circRNAs following nerve injury suggest that these ncRNAs might be associated with nerve regeneration. This review will give a brief introduction of lncRNAs and circRNAs. We then summarize the current studies on lncRNAs and circRNAs following peripheral nerve injury and spinal cord injury (SCI). Typical lncRNAs and circRNAs are introduced to illustrate the diverse molecular mechanisms for nerve regeneration. In addition, we also discuss some issues to be addressed in future investigations on lncRNAs and circRNAs.

Extracellular RNAs as Biomarkers of Sporadic Amyotrophic Lateral Sclerosis and Other Neurodegenerative Diseases

Recent progress in the research for underlying mechanisms in neurodegenerative diseases, including Alzheimer disease (AD), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS) has led to the development of potentially effective treatment, and hence increased the need for useful biomarkers that may enable early diagnosis and therapeutic monitoring. The deposition of abnormal proteins is a pathological hallmark of neurodegenerative diseases, including β-amyloid in AD, α-synuclein in PD, and the transactive response DNA/RNA binding protein of 43kDa (TDP-43) in ALS. Furthermore, progression of the disease process accompanies the spreading of abnormal proteins. Extracellular proteins and RNAs, including mRNA, micro RNA, and circular RNA, which are present as a composite of exosomes or other forms, play a role in cell–cell communication, and the role of extracellular molecules in the cell-to-cell spreading of pathological processes in neurodegenerative diseases is now in the spotlight. Therefore, extracellular proteins and RNAs are considered potential biomarkers of neurodegenerative diseases, in particular ALS, in which RNA dysregulation has been shown to be involved in the pathogenesis. Here, we review extracellular proteins and RNAs that have been scrutinized as potential biomarkers of neurodegenerative diseases, and discuss the possibility of extracellular RNAs as diagnostic and therapeutic monitoring biomarkers of sporadic ALS.

Circular RNA circ-FoxO3 Inhibits Myoblast Cells Differentiation

CircRNA is a type of closed circular non-coding RNA formed by reverse splicing and plays an important role in regulating the growth and development of plants and animals. To investigate the function of circ-FoxO3 in mouse myoblast cells' (C2C12) differentiation and proliferation, we used RT-qPCR to detect the expression level of circ-FoxO3 in mouse myoblast cells at different densities and different differentiation stages, and the specific interference fragment was used to inhibit the expression level of circ-FoxO3 in myoblast cells to observe its effect on myoblast cells proliferation and differentiation. We found that the expression level of circ-FoxO3 in myoblast cells increased with the prolongation of myoblast cells differentiation time, and its expression level decreased with the proliferation of myoblast cells. At the same time, we found that the differentiation ability of the cells was significantly increased (p < 0.05), but the cell proliferation was unchanged (p > 0.05) after inhibiting the expression of circ-FoxO3 in myoblast cells. Combining the results of bioinformatics analysis and the dual luciferase reporter experiment, we found that circ-FoxO3 is a sponge of miR-138-5p, which regulates muscle differentiation. Our study shows that circ-FoxO3 can inhibit the differentiation of C2C12 myoblast cells and lay a scientific foundation for further study of skeletal muscle development at circRNA levels.

The clarified role of interleukin-19 in the inflammatory bowel disease and hypersensitivity: Insights from animal models and humans

The cytokine interleukin-19 (IL-19) is a member of the IL-10 family that includes IL-20, IL-22, IL-24, and IL-26. Previous studies indicated that IL-19 is produced by keratinocytes, epithelial cells, macrophages, and B-cells. Especially, the number of IL-4-producing T cells increased, whereas the number of IFN-γ-producing T cells decreased when naive T cells from healthy people were cultured in the presence of IL-19. There is an increasing body of data demonstrating that IL-19 is associated with the development of type 1 helper T cell-responses, although IL-19 was originally associated with the development of type 2 helper T cell-responses. In this review, we will attempt to discuss current knowledge about the role of IL-19 on several T cell response-mediated inflammatory diseases including inflammatory bowel disease and hypersensitivity.

MicroRNA based theranostics for brain cancer: basic principles

BACKGROUND

Because of the complexity of the blood-brain barrier (BBB), brain tumors, especially the most common and aggressive primary malignant tumor type arising from the central nervous system (CNS), glioblastoma, remain an essential challenge regarding diagnostic and treatment. There are no approved circulating diagnostic or prognostic biomarkers, nor novel therapies like immune checkpoint inhibitors for glioblastoma, and chemotherapy brings only minimal survival benefits. The development of molecular biology led to the discovery of new potential diagnostic tools and therapeutic targets, offering the premise to detect patients at earlier stages and overcome the current poor prognosis.

MAIN BODY

One potential diagnostic and therapeutic breakthrough might come from microRNAs (miRNAs). It is well-known that miRNAs play a role in the initiation and development of various types of cancer, including glioblastoma. The review aims to answer the following questions concerning the role of RNA theranostics for brain tumors: (1) which miRNAs are the best candidates to become early diagnostic and prognostic circulating biomarkers?; (2) how to deliver the therapeutic agents in the CNS to overcome the BBB?; (3) which are the best methods to restore/inhibit miRNAs?

CONCLUSIONS

Because of the proven roles played by miRNAs in gliomagenesis and of their capacity to pass from the CNS tissue into the blood or cerebrospinal fluid (CSF), we propose miRNAs as ideal diagnostic and prognostic biomarkers. Moreover, recent advances in direct miRNA restoration (miRNA mimics) and miRNA inhibition therapy (antisense oligonucleotides, antagomirs, locked nucleic acid anti-miRNA, small molecule miRNA inhibitors) make miRNAs perfect candidates for entering clinical trials for glioblastoma treatment.

Research progress on circularRNAs in pancreatic cancer: emerging but promising

There is currently no diagnostic modality for early-stage pancreatic cancer. Given that adjuvant therapies require further development, the overall survival of pancreatic cancer remains unsatisfactory. Circular RNAs (circRNAs) are a class of noncoding RNAs that play an important role in the progression of many diseases including cancer. CircRNAs mainly bind to microRNAs as microRNA sponges to restore the expression of targeted genes and regulate tumor invasion, metastasis, proliferation, and apoptosis. CircRNAs also play roles in the diagnosis and targeted therapy of tumors. Studies on the mechanisms of action of circRNAs in pancreatic cancer are still in their infancy, but it is anticipated that this field will gradually advance. In this review, we provide a brief introduction to circRNAs from four perspectives: biogenesis, functions, and mechanisms of action, tumor therapy with circRNAs, and circRNAs' roles in pancreatic cancer.

LncRNA-MEG3 inhibits cell proliferation and invasion by modulating Bmi1/RNF2 in cholangiocarcinoma

Cholangiocarcinoma (CCA) is a mortal cancer with gradually increasing incidences all over the world, whereas effective diagnosis and treatment for this disease are still lacking. As a classical long noncoding RNA (lncRNA), maternally expressed gene 3 (MEG3) has been reported to exhibit pivotal regulatory roles in the occurrence and development of various digestive system tumors. Nevertheless, the clinical relevance and biological function of MEG3 in CCA remain largely unclear. In this study, MEG3 expression was significantly downregulated in both CCA tissues and cells in comparison with that in nontumor controls, respectively, and this downexpression was prominently associated with advanced TNM stage, lymph node invasion, and poor survival. Moreover, decreased MEG3 was an independent forecaster of poor prognosis for CCA patients. Functionally, MEG3 overexpression inhibited CCA growth in vitro and in vivo. Enhanced MEG3 also suppressed migration and invasion of CCLP-1 and QBC939 cells by reversing epithelial-mesenchymal transition (EMT) process. On the contrary, the proliferation, metastasis, and EMT were facilitated via knocking down MEG3. In addition, the expression of B lymphoma Mo-MLV insertion region 1 (Bmi1) and RING finger protein 2 was impacted by gain or loss of MEG3, furthermore, the malignant processes induced by MEG3 knockdown were rescued by means of silencing Bmi1. These data suggested that MEG3 caused tumor suppressive effects partly through mediating polycomb repressive complex 1. Our findings elucidate that MEG3 exerts critical functions in CCA development and likely acts as a promising tumor indicator or intervention target for CCA.

Deep learning of the back-splicing code for circular RNA formation

Motivation

Circular RNAs (circRNAs) are a new class of endogenous RNAs in animals and plants. During pre-RNA splicing, the 5′ and 3′ termini of exon(s) can be covalently ligated to form circRNAs through back-splicing (head-to-tail splicing). CircRNAs can be conserved across species, show tissue- and developmental stage-specific expression patterns, and may be associated with human disease. However, the mechanism of circRNA formation is still unclear although some sequence features have been shown to affect back-splicing.

Results

In this study, by applying the state-of-art machine learning techniques, we have developed the first deep learning model, DeepCirCode, to predict back-splicing for human circRNA formation. DeepCirCode utilizes a convolutional neural network (CNN) with nucleotide sequence as the input, and shows superior performance over conventional machine learning algorithms such as support vector machine and random forest. Relevant features learnt by DeepCirCode are represented as sequence motifs, some of which match human known motifs involved in RNA splicing, transcription or translation. Analysis of these motifs shows that their distribution in RNA sequences can be important for back-splicing. Moreover, some of the human motifs appear to be conserved in mouse and fruit fly. The findings provide new insight into the back-splicing code for circRNA formation.

Availability and implementation

All the datasets and source code for model construction are available at https://github.com/BioDataLearning/DeepCirCode.

Supplementary information

Supplementary data are available at Bioinformatics online.

Cellular functions of long noncoding RNAs

A diverse catalog of long noncoding RNAs (lncRNAs), which lack protein-coding potential, are transcribed from the mammalian genome. They are emerging as important regulators in gene expression networks by controlling nuclear architecture and transcription in the nucleus and by modulating mRNA stability, translation and post-translational modifications in the cytoplasm. In this Review, we highlight recent progress in cellular functions of lncRNAs at the molecular level in mammalian cells.

Long noncoding RNAs in intestinal epithelium homeostasis

The epithelium of the mammalian intestinal mucosa is a rapidly self-renewing tissue in the body, and its homeostasis is preserved through well-controlled mechanisms. Long noncoding RNAs (lncRNAs) regulate a variety of biological functions and are intimately involved in the pathogenesis of diverse human diseases. Here we highlight the roles of several lncRNAs expressed in the intestinal epithelium, including uc.173, SPRY4-IT1, H19, and Gata6, in maintaining the integrity of the intestinal epithelium, focusing on the emerging evidence of lncRNAs in the regulation of intestinal mucosal regeneration and epithelial barrier function. We also discuss recent results that the interactions between lncRNAs with microRNAs and the RNA-binding protein HuR influence epithelial homeostasis. With rapidly advancing knowledge of lncRNAs, there is also growing recognition that lncRNAs in the intestinal epithelium might be promising therapeutic targets in our efforts to protect the integrity of the intestinal epithelium in response to stressful environments.

Non-Coding RNA Networks in ALK-Positive Anaplastic-Large Cell Lymphoma

Non-coding RNAs (ncRNAs) are essential regulators of gene expression. In recent years, it has become more and more evident that the different classes of ncRNAs, such as micro RNAs, long non-coding RNAs and circular RNAs are organized in tightly controlled networks. It has been suggested that deregulation of these networks can lead to disease. Several studies show a contribution of these so-called competing-endogenous RNA networks in various cancer entities. In this review, we highlight the involvement of ncRNA networks in anaplastic-large cell lymphoma (ALCL), a T-cell neoplasia. A majority of ALCL cases harbor the molecular hallmark of this disease, a fusion of the anaplastic lymphoma kinase (ALK) gene with the nucleophosmin (NPM, NPM1) gene leading to a permanently active kinase that promotes the malignant phenotype. We have focused especially on ncRNAs that are regulated by the NPM-ALK fusion gene and illustrate how their deregulation contributes to the pathogenesis of ALCL. Lastly, we summarize the findings and point out potential therapeutic implications.

Intriguing circles: Conflicts and controversies in circular RNA research

Circular RNAs (circRNAs) are covalently closed RNA circles without a 5' cap or 3' tail. Since the landmark discovery of ciRS-7/CDR1as functioning as a miR-7 sponge in 2013, circRNAs have become a hot topic in RNA research. CircRNAs have been found to play active roles in cancer, cardiovascular diseases, neurological disorders, and many other diseases. They can function as microRNA (miRNA) sponges, protein scaffolds, and even translation templates. However, as circRNA research expands, many divergent views have emerged. For example, are most circRNAs competent in serving as miRNA sponges? What kinds of circRNAs are most likely to sponge miRNAs? Apart from sponging miRNAs, what could the functions of most circRNAs be? What are the features of circRNAs that are translatable? Many researchers have claimed that circRNAs are abundant, stable, conserved, and specific molecules, which hold great potential in serving as biomarkers. However, circRNA abundance is variable and some circRNAs are abundant while others are not. In addition, their stability and conservation may vary under different circumstances. Furthermore, it is unclear whether circRNA biogenesis is more likely to be regulated by RNA binding proteins or transcription factors. All of these are open questions that remain to be answered by researchers in this field. Discussing and investigating these questions will advance the understanding of this class of novel molecules and may propel inspiring new ideas for future studies. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA in Disease and Development > RNA in Disease RNA Methods > RNA Analyses in Cells RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

Circbank: a comprehensive database for circRNA with standard nomenclature

Circular RNAs (circRNAs) represent a new type of regulatory RNA which forms a covalently closed continuous loop from back-splicing events, a process in which the downstream 5' splice site and the 3' splice site are covalently linked. Emerging evidence indicates that circRNAs exert a new layer of transcriptional and post-transcriptional regulation of gene expression. However, there is no standard nomenclature of circRNA, although the study of circRNAs has exploded in the past few years. Here we present circbank ( www.circbank.cn ), a comprehensive database for human circRNAs, where a novel naming system of circRNAs based on the host genes of circRNAs was implemented. In addition to the new naming system, circbank collected other five features of circRNAs including the miRNA binding site, conservation of circRNAs, m⁶A modification of circRNAs, mutation of circRNAs and protein-coding potential of circRNAs. Circbank is publicly available and allows users to query, browse and download circRNAs with all six features we provided, based on different search criteria. The database may serve as a resource to facilitate the research of function and regulation of circRNAs.

The emerging roles and functions of circular RNAs and their generation

Circular RNAs (circRNAs) are closed long non-coding RNAs, in which the 5’ and 3’ termini are covalently linked by back-splicing of exons from a single pre-mRNA. Emerging evidence indicates that circRNAs are broadly expressed in mammalian cells and show cell type- or tissue-specific expression patterns. Importantly, circRNAs have been shown to participate in regulating various biological processes. Functionally, circRNAs can influence cellular physiology through various molecular mechanisms, such as serving as a decoy for microRNAs or RNA-binding proteins to modulate gene expression or translation of regulatory proteins. The biogenesis of circRNAs is known to be tightly regulated by cis- (intronic complementary sequences) and/or trans-factors (splicing factors) that constitute a cell- and context-dependent regulatory layer in the control of gene expression. However, our understanding of the regulation and function of circRNAs is still limited. In this review, we summarize the current progress in elucidating the functional roles, mechanisms and biogenesis of circRNAs. We also discuss the relationship between regulation and formation of circRNAs.

CircDLST promotes the tumorigenesis and metastasis of gastric cancer by sponging miR-502-5p and activating the NRAS/MEK1/ERK1/2 signaling

Background

Accumulating evidence shows that, the dysregulation of circular RNAs (circRNAs) is associated with the progression of multiple malignancies. But, the underlying mechanisms by which has_circ_0032627 (circDLST) contributed to gastric cancer (GC) remain undocumented.

Methods

The expression and cellular localization of circDLST and its association with clinicopathological characteristics and prognosis in patients with GC was analysed by using fluorescence in situ hybridization. Gain- and loss-of-function experiments as well as a subcutaneous xenograft tumor model and a liver metastasis model from orthotopic implantation of GC tissues were conducted to assess the role of circDLST in GC cells. CircDLST specific binding with miR-502-5p was confirmed by dual luciferase gene report, RNA immunoprecipitation (RIP) assays and RIP-miRNA expression profiling. qRT-PCR and Western blot analysis was used to detect the effects of circDLST on miR-502-5p-mediated NRAS/MEK1/ERK1/2 signaling in GC cells.

Results

The expression levels of circDLST were dramatically elevated in GC tissues as compared with the adjacent normal tissues, and acted as an independent prognostic factor of poor survival in patients with GC. Knockdown of circDLST inhibited the cell viability, colony formation, DNA synthesis, cell invasion and liver metastasis in vitro and in vivo, whereas overexpression of circDLST had the opposite effects. Furthermore, circDLST was co-localized with miR-502-5p in the cytoplasm of GC cells, and acted as a sponge of miR-502-3p in GC cells, which abrogated the tumor promoting effects of circDLST by inactivating the NRAS/MEK1/ERK1/2 signaling in GC cells.

Conclusion

CircDLST promotes the tumorigenesis and metastasis of GC cells by sponging miR-502-5p to activate the NRAS/MEK1/ERK1/2 signaling.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-1015-1) contains supplementary material, which is available to authorized users.

Epigenetic Regulations in Neuropsychiatric Disorders

Precise genetic and epigenetic spatiotemporal regulation of gene expression is critical for proper brain development, function and circuitry formation in the mammalian central nervous system. Neuronal differentiation processes are tightly regulated by epigenetic mechanisms including DNA methylation, histone modifications, chromatin remodelers and non-coding RNAs. Dysregulation of any of these pathways is detrimental to normal neuronal development and functions, which can result in devastating neuropsychiatric disorders, such as depression, schizophrenia and autism spectrum disorders. In this review, we focus on the current understanding of epigenetic regulations in brain development and functions, as well as their implications in neuropsychiatric disorders.

A novel protein encoded by a circular RNA circPPP1R12A promotes tumor pathogenesis and metastasis of colon cancer via Hippo-YAP signaling

BACKGROUND

It has been well established that circular RNAs (circRNAs) play an important regulatory role during tumor progression. Recent studies have indicated that even though circRNAs generally regulate gene expression through miRNA sponges, they may encode small peptides in tumor pathogenesis. However, it remains largely unexplored whether circRNAs are involved in the tumorigenesis of colon cancer (CC).

METHODS

The expression profiles of circRNAs in CC tissues were assessed by circRNA microarray. Quantitative real-time PCR, RNase R digestion assay and tissue microarray were used to confirm the existence and expression pattern of circPPP1R12A. The subcellular distribution of circPPP1R12A was analyzed by nuclear mass separation assay and fluorescence in situ hybridization (FISH). SDS-PAGE and LC/MS were employed to evaluate the protein-coding ability of circPPP1R12A. CC cells were stably transfected with lentivirus approach, and cell proliferation, migration and invasion, as well as tumorigenesis and metastasis in nude mice were assessed to clarify the functional roles of circPPP1R12A and its encoded protein circPPP1R12A-73aa. RNA-sequencing and Western blotting analysis were furthered employed to identify the critical signaling pathway regulated by circPPP1R12A-73aa.

RESULTS

We firstly screened the expression profiles of human circRNAs in CC tissues and found that the expression of hsa_circ_0000423 (termed as circPPP1R12A) was significantly increased in CC tissues. We also found that circPPP1R12A was mostly localized in the cytoplasm of CC cells. Kaplan-Meier analysis showed that patients with higher levels of circPPP1R12A had a significantly shorter overall survival. By gain- and loss-of-function approaches, the results suggested that circPPP1R12A played a critical role in proliferation, migration and invasion of CC cells. Furthermore, we showed that circPPP1R12A carried an open reading frame (ORF), which encoded a functional protein (termed as circPPP1R12A-73aa). Next, we found that PPP1R12A-C, not circPPP1R12A, promoted the proliferation, migration and invasion abilities of CC in vitro and in vivo. Finally, we identified that circPPP1R12A-73aa promoted the growth and metastasis of CC via activating Hippo-YAP signaling pathway. In addition, the YAP specific inhibitor Peptide 17 dramatically alleviated the promotive effect of circPPP1R12A-73aa on CC cells.

CONCLUSIONS

In the present study, we illustrated the coding-potential of circRNA circPPP1R12A in the progression of CC. Moreover, we identified that circPPP1R12A-73aa promoted the tumor pathogenesis and metastasis of CC via activating Hippo-YAP signaling pathway. Our findings might provide valuable insights into the development of novel potential therapeutic targets for CC.

Functions and roles of long noncoding RNA in cholangiocarcinoma

Cholangiocarcinoma (CCA) is one of the most fatal cancers in humans, with a gradually increasing incidence worldwide. The efficient diagnostic and therapeutic measures for CCA to reduce mortality are urgently needed. Long noncoding RNAs (lncRNAs) may provide the potential diagnostic and therapeutic option for suppressing the CCA development. LncRNAs are a type of non-protein-coding RNAs, which are larger than 200 nucleotides in length. Increasing evidence reveals that lncRNAs exhibit critical roles in the carcinogenesis and development of CCA. Deregulation of lncRNAs impacts the proliferation, migration, invasion, and antiapoptosis of CCA cells by multiple sophisticated mechanisms. Consequently, lncRNAs likely represent promising biomarkers or intervention targets of CCA. In this review, we summarize current studies regarding the biological functions and regulatory mechanisms of diverse lncRNAs in CCA.

MicroRNAs in contusion spinal cord injury: pathophysiology and clinical utility

Spinal cord injury (SCI) in humans is a common central nervous system trauma. Pathophysiologically, SCI involves both primary and secondary damages. Therapeutically, targeting secondary damage including inflammation, neuropathic pain, apoptosis, demyelination, and glial reaction to promote functional benefits for SCI patients has long been considered a potential treatment strategy by neuroscientists and clinicians. As a type of small non-coding RNA, microRNAs (miRNAs) have been shown to play essential roles in the regulation of pathophysiologic processes of SCI and are considered to be an effective treatment method for SCI. Dysregulated expression of miRNAs is observed in SCI patients and animal models of SCI. Furthermore, miRNAs might also be used as biomarkers for diagnostic and prognostic purposes in SCI. Given contusion injury is the most clinically relevant type of SCI, this review mainly focuses on the role of miRNAs in the pathophysiology of contusion SCI and the putative utilization of miRNAs as diagnostic biomarkers and therapeutic targets for contusion SCI.

Biology of RNA Surveillance in Development and Disease

The 'RNA world', in which RNA molecules stored information and acquired enzymatic properties, has been proposed to have preceded organism life. RNA is now recognized for its central role in biology, with accumulating evidence implicating coding and noncoding (nc)RNAs in myriad mechanisms regulating cellular physiology and disequilibrium in transcriptomes resulting in pathological conditions. Nascently synthesized RNAs are subjected to stringent regulation by sophisticated RNA surveillance pathways. In this review, we integrate these pathways from a developmental viewpoint, proposing RNA surveillance as the convergence of mechanisms that ensure the exact titration of RNA molecules in a spatiotemporally controlled manner, leading to development without the onset of pathological conditions, including cancer.

Deregulation of Circular RNAs in Cancer From the Perspectives of Aberrant Biogenesis, Transport and Removal

CircRNAs (circular RNAs) are a class of RNAs generated from circularization with multiple novel functions. Recent studies have revealed the aberrant expression and aberrant functions of circRNAs in various tumors; thus, circRNAs have been recognized as promising cancer biomarkers. However, the underlying mechanisms behind their aberrant expression and functions remain unclear. In this review, we discuss at length the cancer-specific deregulation of circRNAs and the potential underlying aberrant events in circRNA biogenesis, localization and removal in cancer cells.

Rapid Generation of Long Noncoding RNA Knockout Mice Using CRISPR/Cas9 Technology

In recent years, long noncoding RNAs (lncRNAs) have emerged as multifaceted regulators of gene expression, controlling key developmental and disease pathogenesis processes. However, due to the paucity of lncRNA loss-of-function mouse models, key questions regarding the involvement of lncRNAs in organism homeostasis and (patho)-physiology remain difficult to address experimentally in vivo. The clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 platform provides a powerful genome-editing tool and has been successfully applied across model organisms to facilitate targeted genetic mutations, including Caenorhabditis elegans, Drosophila melanogaster, Danio rerio and Mus musculus. However, just a few lncRNA-deficient mouse lines have been created using CRISPR/Cas9-mediated genome engineering, presumably due to the need for lncRNA-specific gene targeting strategies considering the absence of open-reading frames in these loci. Here, we describe a step-wise procedure for the generation and validation of lncRNA loss-of-function mouse models using CRISPR/Cas9-mediated genome engineering. In a proof-of-principle approach, we generated mice deficient for the liver-enriched lncRNA Gm15441, which we found downregulated during development of metabolic disease and induced during the feeding/fasting transition. Further, we discuss guidelines for the selection of lncRNA targets and provide protocols for in vitro single guide RNA (sgRNA) validation, assessment of in vivo gene-targeting efficiency and knockout confirmation. The procedure from target selection to validation of lncRNA knockout mouse lines can be completed in 18–20 weeks, of which <10 days hands-on working time is required.

miRNA Targeting: Growing beyond the Seed

miRNAs are small RNAs that guide Argonaute proteins to specific target mRNAs to repress their translation and stability. Canonically, miRNA targeting is reliant on base pairing of the seed region, nucleotides 2-7, of the miRNA to sites in mRNA 3' untranslated regions. Recently, the 3' half of the miRNA has gained attention for newly appreciated roles in regulating target specificity and regulation. In addition, the extent of pairing to the miRNA 3' end can influence the stability of the miRNA itself. These findings highlight the importance of sequences beyond the seed in controlling the function and existence of miRNAs.

The novel roles of circRNAs in human cancer

Covalently closed single-stranded circular RNAs (circRNAs) consist of introns or exons and are widely present in eukaryotic cells. CircRNAs generally have low expression levels and relatively stable structures compared with messenger RNAs (mRNAs), most of which are located in the cytoplasm and often act in cell type and tissue-specific manners, indicating that they may serve as novel biomarkers. In recent years, circRNAs have gradually become a hotspot in the field of RNA and cancer research, but the functions of most circRNAs have not yet been discovered. Known circRNAs can affect the biogenesis of cancers in diverse ways, such as functioning as a microRNA (miRNA) sponges, combining with RNA binding proteins (RBPs), working as a transcription factor and translation of proteins. In this review, we summarize the characteristics and types of circRNAs, introduce the biogenesis of circRNAs, discuss the emerging functions and databases on circRNAs and present the current challenges of circRNAs studies.

Individual long non-coding RNAs have no overt functions in zebrafish embryogenesis, viability and fertility

Hundreds of long non-coding RNAs (lncRNAs) have been identified as potential regulators of gene expression, but their functions remain largely unknown. To study the role of lncRNAs during vertebrate development, we selected 25 zebrafish lncRNAs based on their conservation, expression profile or proximity to developmental regulators, and used CRISPR-Cas9 to generate 32 deletion alleles. We observed altered transcription of neighboring genes in some mutants, but none of the lncRNAs were required for embryogenesis, viability or fertility. Even RNAs with previously proposed non-coding functions (cyrano and squint) and other conserved lncRNAs (gas5 and lnc-setd1ba) were dispensable. In one case (lnc-phox2bb), absence of putative DNA regulatory-elements, but not of the lncRNA transcript itself, resulted in abnormal development. LncRNAs might have redundant, subtle, or context-dependent roles, but extrapolation from our results suggests that the majority of individual zebrafish lncRNAs have no overt roles in embryogenesis, viability and fertility.

Regulation of microRNA function in animals

Since their serendipitous discovery in nematodes, microRNAs (miRNAs) have emerged as key regulators of biological processes in animals. These small RNAs form complex networks that regulate cell differentiation, development and homeostasis. Deregulation of miRNA function is associated with an increasing number of human diseases, particularly cancer. Recent discoveries have expanded our understanding of the control of miRNA function. Here, we review the mechanisms that modulate miRNA activity, stability and cellular localization through alternative processing and maturation, sequence editing, post-translational modifications of Argonaute proteins, viral factors, transport from the cytoplasm and regulation of miRNA-target interactions. We conclude by discussing intriguing, unresolved research questions.

Modulation of Bacterial sRNAs Activity by Epigenetic Modifications: Inputs from the Eukaryotic miRNAs

Trans-encoded bacterial regulatory RNAs (sRNAs) are functional analogues of eukaryotic microRNAs (miRNAs). These RNA classes act by base-pairing complementarity with their RNA targets to modulate gene expression (transcription, half-life and/or translation). Based on base-pairing, algorithms predict binding and the impact of small RNAs on targeted-RNAs expression and fate. However, other actors are involved such as RNA binding proteins and epigenetic modifications of the targeted and small RNAs. Post-transcriptional base modifications are widespread in all living organisms where they lower undesired RNA folds through conformation adjustments and influence RNA pairing and stability, especially if remodeling their ends. In bacteria, sRNAs possess RNA modifications either internally (methylation, pseudouridinylation) or at their ends. Nicotinamide adenine dinucleotide were detected at 5′-ends, and polyadenylation can occur at 3′-ends. Eukaryotic miRNAs possess N⁶-methyladenosine (m⁶A), A editing into I, and non-templated addition of uridines at their 3′-ends. Biological functions and enzymes involved in those sRNA and micro RNA epigenetic modifications, when known, are presented and challenged.

microRNAs Sculpt Neuronal Communication in a Tight Balance That Is Lost in Neurological Disease

Since the discovery of the first microRNA 25 years ago, microRNAs (miRNAs) have emerged as critical regulators of gene expression within the mammalian brain. miRNAs are small non-coding RNAs that direct the RNA induced silencing complex to complementary sites on mRNA targets, leading to translational repression and/or mRNA degradation. Within the brain, intra- and extracellular signaling events tune the levels and activities of miRNAs to suit the needs of individual neurons under changing cellular contexts. Conversely, miRNAs shape neuronal communication by regulating the synthesis of proteins that mediate synaptic transmission and other forms of neuronal signaling. Several miRNAs have been shown to be critical for brain function regulating, for example, enduring forms of synaptic plasticity and dendritic morphology. Deficits in miRNA biogenesis have been linked to neurological deficits in humans, and widespread changes in miRNA levels occur in epilepsy, traumatic brain injury, and in response to less dramatic brain insults in rodent models. Manipulation of certain miRNAs can also alter the representation and progression of some of these disorders in rodent models. Recently, microdeletions encompassing MIR137HG, the host gene which encodes the miRNA miR-137, have been linked to autism and intellectual disability, and genome wide association studies have linked this locus to schizophrenia. Recent studies have demonstrated that miR-137 regulates several forms of synaptic plasticity as well as signaling cascades thought to be aberrant in schizophrenia. Together, these studies suggest a mechanism by which miRNA dysregulation might contribute to psychiatric disease and highlight the power of miRNAs to influence the human brain by sculpting communication between neurons.

Circular RNA hsa_circ_0076248 promotes oncogenesis of glioma by sponging miR-181a to modulate SIRT1 expression

Glioma is one of the most common primary malignancies of the central nervous system, which has aggressive clinical behavior and a poorer prognosis. MicroRNAs (miRs) are a class of small noncoding RNAs that function as mediators of gene expression, which can be sponged by circRNA provided with a closed circular structure. Dysregulations of circular RNAs (circRNAs) and miRs have been implicated in the development and progression of glioma. In the current study, we investigated the role of circular RNA hsa_circ_0076248 in mediating the oncogenesis of glioma by sponging miR‐181a to modulate silent information regulator 1 (SIRT1) expression in vitro and in vivo. The quantitative real‐time polymerase chain reaction results showed that the expression of miR‐181a was significantly decreased in glioma tissues and cell lines compared with normal brain tissues and normal gliocyte, respectively, and the expression of hsa_circ_0076248 and SIRT1 demonstrated the opposite. Bioinformatics analysis identified hsa_circ_0076248 could sponge miR‐181a, and miR‐181a could target the mRNA of SIRT1. Our results verified that downregulating hsa_circ_0076248 or upregulating miR‐181a could depress the proliferation and invasion of glioma in vitro and in vivo. The experiment also showed that downregulating hsa_circ_0076248 or upregulating miR‐181a could remarkably promote the temozolomide chemotherapy sensitivity. Furthermore, Western blot analysis testified that downregulating hsa_circ_0076248 or upregulating miR‐181a could promote the expression of p53 and SIRT1. In summary, our study sheds light on the regulatory mechanism of hsa_circ_0076248 in glioma growth and invasion via sponging miR‐181a, which downregulates the SIRT1 expression and also suggests that hsa_circ_0076248, miR‐181a, and SIRT1 may serve as potential therapeutic targets for glioma.

Long noncoding RNA (lncRNA): a target in neuropathic pain

INTRODUCTION

Current treatments for neuropathic pain are limited in part due to the incomplete understanding of its underlying mechanisms. Recent evidence reveals the dysregulated expression of long non-coding RNAs (lncRNAs) in the damaged nerve, dorsal root ganglion (DRG), and spinal cord dorsal horn following peripheral nerve injury. However, the role of the majority of lncRNAs in neuropathic pain genesis is still elusive. Unveiling the mechanisms of how lncRNAs participate in neuropathic pain may develop new strategies to prevent and/or treat this disorder. Areas covered: This review focuses on the dysregulation of lncRNAs in the DRG, dorsal horn, and the injured nerves from preclinical models of neuropathic pain. We provide evidence of how peripheral nerve injury causes the dysregulation of lncRNAs in these pain-related regions. The potential mechanisms of how dysregulated lncRNAs contribute to the pathogenesis of neuropathic pain are discussed. Expert opinion: The investigation on the role of the dysregulated lncRNAs in neuropathic pain might open up a novel avenue for therapeutic treatment of this disorder. However, current investigation is at the infancy stage, which challenges the translation of preclinical findings. More intensive studies on lncRNAs are required before the preclinical findings are translated into therapeutic management for neuropathic pain.

Characteristics of plant circular RNAs

Circular RNA (circRNA) is a kind of covalently closed single-stranded RNA molecules that have been proved to play important roles in transcriptional regulation of genes in diverse species. With the rapid development of bioinformatics tools, a huge number (95143) of circRNAs have been identified from different plant species, providing an opportunity for uncovering the overall characteristics of plant circRNAs. Here, based on publicly available circRNAs, we comprehensively analyzed characteristics of plant circRNAs with the help of various bioinformatics tools as well as in-house scripts and workflows, including the percentage of coding genes generating circRNAs, the frequency of alternative splicing events of circRNAs, the non-canonical splicing signals of circRNAs and the networks involving circRNAs, miRNAs and mRNAs. All this information has been integrated into an upgraded online database, PlantcircBase 3.0 (http://ibi.zju.edu.cn/plantcircbase/). In this database, we provided browse, search and visualization tools as well as a web-based blast tool, BLASTcirc, for prediction of circRNAs from query sequences based on searching against plant genomes and transcriptomes.

Competing Endogenous RNA Regulations in Neurodegenerative Disorders: Current Challenges and Emerging Insights

The past decade has witnessed exciting breakthroughs that have contributed to the richness and complexity of a burgeoning modern RNA world, and one particular breakthrough-the competing endogenous RNA (ceRNA) hypothesis-has been described as the "Rosetta Stone" for decoding the RNA language used in regulating RNA crosstalk and modulating biological functions. The proposed far-reaching mechanism unites diverse RNA species and provides new insights into previously unrecognized RNA-RNA interactions and RNA regulatory networks that perhaps determine gene expression in an organized, hierarchical manner. The recently uncovered ceRNA regulatory loops and networks have emphasized the power of ceRNA regulation in a wide range of developmental stages and pathological contexts, such as in tumorigenesis and neurodegenerative disorders. Although the ceRNA hypothesis drastically enhanced our understanding of RNA biology, shortly after the hypothesis was proposed, disputes arose in relation mainly to minor discrepancies in the reported effects of ceRNA regulation under physiological conditions, and this resulted in ceRNA regulation becoming an extensively studied and fast-growing research field. Here, we focus on the evidence supporting ceRNA regulation in neurodegenerative disorders and address three critical points related to the ceRNA regulatory mechanism: the microRNA (miRNA) and ceRNA hierarchies in cross-regulations; the balance between destabilization and stable binding in ceRNA-miRNA interactions; and the true extent to which ceRNA regulatory mechanisms are involved in both health and disease, and the experimental shortcomings in current ceRNA studies.

Target RNAs Strike Back on MicroRNAs

MicroRNAs are extensively studied regulatory non-coding small RNAs that silence animal genes throughout most biological processes, typically doing so by binding to partially complementary sequences within target RNAs. A plethora of studies has described detailed mechanisms for microRNA biogenesis and function, as well as their temporal and spatial regulation during development. By inducing translational repression and/or degradation of their target RNAs, microRNAs can contribute to achieve highly specific cell- or tissue-specific gene expression, while their aberrant expression can lead to disease. Yet an unresolved aspect of microRNA biology is how such small RNA molecules are themselves cleared from the cell, especially under circumstances where fast microRNA turnover or specific degradation of individual microRNAs is required. In recent years, it was unexpectedly found that binding of specific target RNAs to microRNAs with extensive complementarity can reverse the outcome, triggering degradation of the bound microRNAs. This emerging pathway, named TDMD for Target RNA-Directed MicroRNA Degradation, leads to microRNA 3'-end tailing by the addition of A/U non-templated nucleotides, trimming or shortening from the 3' end, and highly specific microRNA loss, providing a new layer of microRNA regulation. Originally described in flies and known to be triggered by viral RNAs, novel endogenous instances of TDMD have been uncovered and are now starting to be understood. Here, we review our current knowledge of this pathway and its potential role in the control and diversification of microRNA expression patterns.

Circular RNAs: Characteristics, Function and Clinical Significance in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide. HCC patients are commonly diagnosed at an advanced stage, for which highly effective therapies are limited. Moreover, the five-year survival rate of HCC patients remains poor due to high frequency of tumor metastasis and recurrence. These challenges give rise to the emergent need to discover promising biomarkers for HCC diagnosis and identify novel targets for HCC therapy. Circular RNAs (circRNAs), a class of long-overlook non-coding RNA, have been revealed as multi-functional RNAs in recent years. Growing evidence indicates that circRNA expression alterations have a broad impact in biological characteristics of HCC. Most of these circRNAs regulate HCC progression by acting as miRNA sponges, suggesting that circRNAs may function as promising diagnostic biomarkers and ideal therapeutic targets for HCC. In this review, we summarize the current progress in studying the functional role of circRNAs in HCC pathogenesis and present their potential values as diagnostic biomarkers and therapeutic targets. In-depth investigations on the function and mechanism of circRNAs in HCC will enrich our knowledge of HCC pathogenesis and contribute to the development of effective diagnostic biomarkers and therapeutic targets for HCC.

Metazoan MicroRNAs

MicroRNAs (miRNAs) are ∼22 nt RNAs that direct posttranscriptional repression of mRNA targets in diverse eukaryotic lineages. In humans and other mammals, these small RNAs help sculpt the expression of most mRNAs. This article reviews advances in our understanding of the defining features of metazoan miRNAs and their biogenesis, genomics, and evolution. It then reviews how metazoan miRNAs are regulated, how they recognize and cause repression of their targets, and the biological functions of this repression, with a compilation of knockout phenotypes that shows that important biological functions have been identified for most of the broadly conserved miRNAs of mammals.