Exon circularization requires canonical splice signals

The role of circRNA in insulin resistance and its progression induced by adipose inflammation

CircRNAs refer to a type of closed circular non-coding RNA without a 5' cap or a 3' poly (A) structure. They are largely distributed in the cytoplasm or localized in exosomes and cannot be easily degraded by RNA exonuclease activity. Their stable expression is broadly observed across eukaryotic species. Insulin resistance (IR) refers to the inability of insulin to exert its normal biological function, as manifested by the impairment of glucose utilization in peripheral tissues (e.g., muscle and fat tissues). IR is a key factor in the pathogenesis of Type 2 diabetes (T2D) and is closely associated with obesity. Recent studies have shown that certain circRNAs play critical roles in obesity-induced diabetes by regulating IR and participating in inflammatory processes. CircRNAs, with their multiple microRNA (miRNA) binding sites, act as miRNA sponges to eliminate the inhibitory actions of miRNAs and up-regulate the expression of target genes. CircRNAs play a significant role in regulating obesity-induced diabetes through their interactions with disease-related miRNAs. In the present study, we explored the biological characteristics of circRNAs and extensively discussed the role of circRNAs in the development of inflammation and IR in adipocytes, highlighting their potential as therapeutic targets for obesity-induced diabetes. Specific circRNAs (e.g., circARF3 and circ-ZNF609) have been identified as key players in modulating IR and inflammatory responses in adipose tissue. CircRNAs are emerging as important regulators of IR and inflammation in adipocytes, with significant potential for therapeutic intervention in obesity-induced diabetes. Further research is needed to elucidate the mechanisms underlying their actions and to explore strategies for targeting circRNAs in clinical applications.

Structural determinants of inverted Alu-mediated backsplicing revealed by -MaP and -JuMP

Biogenesis of circular RNA usually involves a backsplicing reaction where the downstream donor site is ligated to the upstream acceptor site by the spliceosome. For this reaction to occur, these sites must be in proximity. Inverted repeat sequences, such as Alu elements, if positioned in the upstream and downstream introns, can base pair and represent one mechanism for inducing proximity. Here, we investigate the pre-mRNA structure of the human HIPK3 gene at exon 2, which forms a circular RNA via backsplicing. We leverage multiple chemical probing approaches, including the recently developed SHAPE-JuMP (selective 2'-hydroxyl acylation analyzed by primer extension and juxtaposed merged pairs) strategy, to characterize secondary and tertiary interactions in the pre-mRNA that govern backsplicing. Our data confirm that the antisense Alu elements AluSz(-) and AluSq2(+), in the upstream and downstream introns, form a highly paired interaction. Circularization requires formation of long-range Alu-mediated base pairs but does not require the full-length AluSq2(+). In addition to confirming long-range base pairs, our SHAPE-JuMP data identified multiple long-range interactions between non-pairing nucleotides. Genome-wide analysis of inverted repeats flanking circular RNAs confirms that the presence of these elements favors circularization, but with modest predictive power. Together, our study suggests that secondary structure considerations alone do not fully explain backsplicing and that additional interactions are involved.

Impacts of Circular RNAs on the Osteogenic Differentiation of Dental Stem Cells

Dental stem cells are widely viewed as good options for bone regeneration because of their ease of acquisition, innate ability to renew themselves, and ability to differentiate into different types of cells. However, the process of osteogenic differentiation of dental stem cells is orchestrated by an intricate system of regulatory mechanisms. Recent studies have demonstrated the critical impacts of circular RNAs (circRNAs) on osteogenic differentiation of dental stem cells. Exploring the roles and regulatory pathways of circRNAs in dental stem cells could identify novel targets and approaches for utilizing dental stem cell therapy in clinical settings. This review provides a comprehensive overview of the functions and mechanisms of circRNAs, with a particular focus on their expression patterns and regulatory roles in osteogenic differentiation of various dental stem cell types. Furthermore, this review discusses current research challenges in this field and proposes future directions for advancing our understanding of circRNA-mediated regulation in dental stem cell biology.

Biogenesis of circular RNAs in vitro and in vivo from the Drosophila Nk2.1/scarecrow gene

The scarecrow (scro) gene encodes a fly homolog of mammalian Nkx2.1, which is vital for early fly development and for optic lobe development. Previously, scro was reported to produce a circular RNA in addition to traditional mRNAs. In this study, we report 12 different scro circular RNAs, which are either mono or multiexonic forms. The most abundant ones are circScro(2) carrying the second exon (E2) only and bi-exonic circScro(3,4) having both the third (E3) and fourth exon (E4). Levels of circScro(2) show an age-dependent increase in adult heads, supporting a general trend of high accumulation of circular RNAs in aged fly brains. In silico analysis of the introns flanking circular RNA exons predicts 2 pairs of intronic complementary sequences; 1 pair residing in introns 1 and 2 and the other in introns 2 and 4. The first pair was demonstrated to be essential for the circScro(2) production in cell-based assays; furthermore, deletion of the region including intronic complementary sequence components in the intron-2 reduces in vivo production of both circScro(2) and circScro(3,4) by 80%, indicating them to be essential for the biogenesis of the 2 circular RNAs. Besides the intronic complementary sequence, the intron regions immediately abutting exons seem to be responsible for a basal level of circular RNA formation. Moreover, ectopic intronic complementary sequence derived from the laccase2 locus is comparably effective in circScro production, buttressing the importance of the hairpin loop structure formed by intronic complementary sequence for the biogenesis of circular RNA. Last, overexpressed scro alters outcomes of both linear and circular RNAs from the endogenous scro locus, suggesting that Scro plays a direct or indirect role in regulating the expression levels of either or both forms.

Developmental Regulation of circRNAs in Normal and Diseased Mammary Gland: A Focus on circRNA-miRNA Networks

Circular RNAs (circRNAs) have emerged as critical regulators in various biological processes including diseases. In the mammary gland (MG), which undergoes most of its development postnatally, circRNAs play pivotal roles in both physiological and pathological contexts. This review highlights the involvement of circRNAs during key developmental stages of the MG, with particular emphasis on lactation, where circRNA-miRNA networks significantly influence milk secretion and composition. CircRNAs exhibit stage-, breed- and species-specific expression patterns during lactation, which underscores their complexity. This intricate regulation also plays a significant role in pathological conditions of the MG, where dysregulated circRNA expression contributes to disease progression such as mastitis, early breast cancer (BC) stages, and epithelial-to-mesenchymal transition in BC (EMT). In mastitis, altered circRNA expression disrupts immune responses and compromises epithelial integrity. During early BC progression, circRNAs drive cell proliferation, while in EMT, they facilitate metastatic processes. By focusing on the circRNA-miRNA interactions underlying these processes, this review highlights their potential use as biomarkers for MG development, disease progression, and as therapeutic targets.

Transcriptome-scale analysis of functional alternative back-splicing events in colorectal cancer

BACKGROUND

Circular RNAs (circRNAs) are a class of non-polyadenylated RNAs generated from back-splicing of genes. Multiple circRNAs can be generated at a single gene locus through alternative back-splicing events (ABS), sharing the same 5' or 3' back-splice site. To date, how prevalent ABS events are and how they are participated in carcinogenesis of human colorectal cancer (CRC) remains unexplored.

METHODS

To explore the functional roles of ABS events in CRC carcinogenesis, we analyzed ribosomal RNA-depleted transcriptome sequencing data of 176 CRC samples and characterized the landscape of ABS events in CRC. CRC cancer-related ABS events were identified by comparing paired CRC tumor tissues and adjacent normal tissues. Then, univariate and multivariate Cox regression was used to find prognostic ABS events. Moreover, in vitro and in vivo assays were used to exploring the functional roles of circXPO1-1 and circXPO1-2 in CRC.

RESULTS

We totally identified 19,611 high confidence circRNAs in CRC, among which 17,874 (91·1%) of circRNAs were found recurrently. The number of ABS circRNAs accounted for 68.8% of all identified high confidence circRNAs, which suggested that ABS events are prevalent in CRC transcriptome. Particularly, 552 ABS circRNAs were found to be aberrantly expressed between paired CRC tumor tissues and adjacent normal tissues, and their parent genes are closely associated with cancer-related hallmarks. In addition, 13 differential ABS circRNAs were identified to be associated with CRC patient survival and could act as independent prognostic indicators. Furthermore, we identified two ABS circRNAs of XPO1 gene (circXPO1-1 and circXPO1-2). The result showed that overexpression of circXPO1-2 inhibited CRC cell proliferation, migration, and invasion in vitro and in vivo, whereas circXPO1-1 is not, indicating that the circularization isoforms of XPO1 gene have different functions in CRC.

CONCLUSIONS

In conclusion, our work provides the landscape of ABS events in CRC transcriptome and the close association of ABS circRNAs with tumorigenesis offers a new set of targets with potential clinical benefit.

Circular RNAs exhibit exceptional stability in the aging brain and serve as reliable age and experience indicators

Circular RNAs (circRNAs) increase in the brain with age across various animal systems. To elucidate the reasons behind this phenomenon, we profile circRNAs from fly heads at six time points throughout their lifespan. Our results reveal a linear increase in circRNA levels with age, independent of changes in mRNA levels, overall transcription, intron retention, or host gene splicing, demonstrating that the age-related accumulation is due to high stability rather than increased biogenesis. This remarkable stability suggests that circRNAs can serve as markers of environmental experience. Indeed, flies exposed to a 10-day regimen at 29°C exhibit higher levels of specific circRNAs even 6 weeks after returning to standard conditions, indicating that circRNAs can reveal past environmental stimuli. Moreover, half-life measurements show circRNA stability exceeding 20 days, with some displaying virtually no degradation. These findings underscore the remarkable stability of circRNAs in vivo and their potential as markers for stress and life experiences.

Deciphering the Contribution of Circular RNAs to Age-Related Decline in Sertoli Cell Survivor

Male fertility declines during aging. This process mainly affects spermatogonia and Sertoli cells, leading to impaired spermatogenesis and poor-quality sperm production. Circular RNAs (circRNAs) are covalently closed RNA molecules produced by backsplicing. In the field of male reproduction, circRNAs boast great potential in the regulation of spermatogenesis and sperm morpho-functional skills. However, their potential role in age-related male reproductive anomalies remains largely elusive. Here, we analyzed the reproductive phenotype of the aged male mouse experimental model, pointing our attention to a putative functional link between circRNAs and Sertoli cell survival. Our results confirm several testicular age-related defects including: (i) altered morphology of the seminiferous epithelium; (ii) affected spermatogenesis; and (iii) decreased sperm production. In particular, aged spermatozoa (SPZ) were decreased in number in association with low motility and abnormal morphology (sperm head anomalies and tail bents). The expression analysis of selective spermatic circRNAs demonstrated a de-regulated expression profile in Aged versus Young SPZ. Among them, we turned the lens on circAbcb9 as a spermatic circRNA potentially involved in the Sertoli cell senescence pathway via the circRNA/miRNA/mRNA network (ceRNET). Indeed, a significant shutdown of circAbcb9-dependent network associated with a prominent increase in Sertoli cell senescence occurred in Aged testis. Interestingly, circAbcb9 was also expressed in human SPZ at decreased levels in Aged men, suggesting a conserved role. Collectively, our study stimulates greater interest in circRNAs as involved in the molecular mechanisms behind the age-related effect on Sertoli cell survival, also providing new implications for fused protein in sarcoma (FUS) protein in sertolian circRNA biogenesis.

Decoding the complex journeys of RNAs along neurons

Neurons are highly polarized, specialized cells that must overcome immense challenges to ensure the health and survival of the organism in which they reside. They can spread over meters and persist for decades yet communicate at sub-millisecond and millimeter scales. Thus, neurons require extreme levels of spatial-temporal control. Neurons employ molecular motors to transport coding and noncoding RNAs to distal synapses. Intracellular trafficking of RNAs enables neurons to locally regulate protein synthesis and synaptic activity. The way in which RNAs get loaded onto molecular motors and transported to their target locations, particularly following synaptic plasticity, is explored below.

Global dysregulation of circular RNAs in frontal cortex and whole blood from DM1 and DM2

Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are autosomal dominant neuromuscular disorders associated with expansions of microsatellites, respectively, in DMPK and CNBP. Their pathogenesis is linked to the global aberrant alternative splicing (AAS) of many genes and marks mostly muscular and neuronal tissues, while blood is the least affected. Recent data in DM1 skeletal muscles indicated that abnormalities in RNA metabolism also include global upregulation of circular RNAs (circRNAs). CircRNAs are a heterogeneous group considered splicing errors and by-products of canonical splicing. To elucidate whether circRNA dysregulation is an inherent feature of the myotonic environment, we perform their analysis in the frontal cortex and whole blood of DM1 and DM2 patients. We find a global elevation of circRNAs in both tissues, and its magnitude is neither correlated with the differences in their parental gene expression nor is associated with AAS published earlier. Aberrantly spliced cassette exons of linear transcripts affected in DM1 and DM2 are not among the circularized exons, which unique genomic features prerequisite back-splicing. However, the blueprint of the AAS of linear RNAs is found in a variety of circRNA isoforms. The heterogeneity of circRNAs also originates from the utilization of exonic and intronic cryptic donors/acceptors in back splice junctions, and intron-containing circRNAs are more characteristic of the blood. Overall, this study reveals circRNA dysregulation in various tissues from DM1 and DM2; however, their levels do not correlate with the AAS in linear RNAs, suggesting a potential independent regulatory mechanism underlying circRNA upregulation in myotonic dystrophy.

Non-coding RNAs and regulation of the PI3K signaling pathway in lung cancer: Recent insights and potential clinical applications

Lung cancer (LC) is one of the most common causes of cancer-related death worldwide. It has been demonstrated that the prognosis of current drug treatments is affected by a variety of factors, including late stage, tumor recurrence, inaccessibility to appropriate treatments, and, most importantly, chemotherapy resistance. Non-coding RNAs (ncRNAs) contribute to tumor development, with some acting as tumor suppressors and others as oncogenes. The phosphoinositide 3-kinase (PI3Ks)/AKT serine/threonine kinase pathway is one of the most important common targets of ncRNAs in cancer, which is widely applied to modulate the cell cycle and a variety of biological processes, including cell growth, mobility survival, metabolic activity, and protein production. Discovering the biology of ncRNA-PI3K/AKT signaling may lead to advances in cancer diagnosis and treatment. As a result, we investigated the expression and role of PI3K/AKT-related ncRNAs in clinical characteristics of lung cancer, as well as their functions as potential biomarkers in lung cancer diagnosis, prognosis, and treatment.

Circular RNAs in neurological conditions - computational identification, functional validation, and potential clinical applications

Non-coding RNAs (ncRNAs) have gained significant attention in recent years due to advancements in biotechnology, particularly high-throughput total RNA sequencing. These developments have led to new understandings of non-coding biology, revealing that approximately 80% of non-coding regions in the genome possesses biochemical functionality. Among ncRNAs, circular RNAs (circRNAs), first identified in 1976, have emerged as a prominent research field. CircRNAs are abundant in most human cell types, evolutionary conserved, highly stable, and formed by back-splicing events which generate covalently closed ends. Notably, circRNAs exhibit high expression levels in neural tissue and perform diverse biochemical functions, including acting as molecular sponges for microRNAs, interacting with RNA-binding proteins to regulate their availability and activity, modulating transcription and splicing, and even translating into functional peptides in some cases. Recent advancements in computational and experimental methods have enhanced our ability to identify and validate circRNAs, providing valuable insights into their biological roles. This review focuses on recent developments in circRNA research as they related to neuropsychiatric and neurodegenerative conditions. We also explore their potential applications in clinical diagnostics, therapeutics, and future research directions. CircRNAs remain a relatively underexplored area of non-coding biology, particularly in the context of neurological disorders. However, emerging evidence supports their role as critical players in the etiology and molecular mechanisms of conditions such as schizophrenia, bipolar disorder, major depressive disorder, Alzheimer's disease, and Parkinson's disease. These findings suggest that circRNAs may provide a novel framework contributing to the molecular dysfunctions underpinning these complex neurological conditions.

Noncanonical circRNA biogenesis driven by alpha and gamma herpesviruses

Herpesviruses require the host transcriptional machinery, inducing significant changes in gene expression to prioritize viral transcripts. We examined alpha- and gamma-herpesvirus alterations to a type of alternative splicing, namely circular RNA (circRNA) synthesis. We developed "Circrnas in Host And viRuses anaLysis pIpEline" (CHARLIE) to facilitate viral profiling. This method identified thousands of back-splicing variants, including circRNA common to lytic and latent phases of infection. Ours is the first report of Herpes Simplex Virus-1 circRNAs, including species derived from ICP0 and the latency-associated transcript. We characterized back-splicing cis- and trans-elements, and found viral circRNAs resistant to spliceosome perturbation and lacking canonical splice donor-acceptors. Subsequent loss-of-function studies of host RNA ligases (RTCB, RLIG1) revealed instances of decreased viral back splicing. Using eCLIP and 4sU-Sequencing, we determined that the KSHV RNA-binding protein, ORF57, enhanced synthesis for a subset of viral and host circRNAs. Our work explores unique splicing mechanisms driven by lytic infection, and identifies a class of transcripts with the potential to function in replication, persistence, or tumorigenesis.

Estrogen-induced circFAM171A1 regulates sheep myoblast proliferation through the oar-miR-485-5p/MAPK15/MAPK pathway

Estrogen is an important hormone that affects muscle development in female animals. Previous studies have shown that estrogen can protect muscle cells from apoptosis by inhibiting the MAPK signaling pathway. However, the molecular mechanisms by which estrogen-induced MAPK signaling regulates myoblast growth and development remain unclear. In this study, RNA-seq was performed on ovariectomized small-tailed Han (OR-STH) sheep and sham surgery small-tailed Han (STH) sheep to analyze the effects of estrogen on muscle growth and development in female animals. There were 8721 differentially expressed circRNAs (DECs), 143 differentially expressed miRNAs (DEMs) and 2238 differentially expressed mRNAs (DEGs) in the longissimus dorsi between the OR-STH and STH groups. Bioinformatics analysis revealed that the differentially expressed gene MAPK15 was significantly enriched in the MAPK signaling pathway, which is important for muscle development. Therefore, we constructed the ceRNA network circFAM171A1/oar-miR-485-5p/MAPK15 and explored its effect on muscle growth and development. The results of the molecular mechanism experiments indicated that circFAM171A1 can sponge oar-miR-485-5p to regulate MAPK15. The addition of the exogenous hormone estradiol (E2) to sheep myoblasts could induce circFAM171A1, regulate the expression of oar-miR-485-5p and MAPK15, and promote the proliferation of sheep myoblasts. The results showed that MAPK15 and circFAM171A1 significantly promoted the proliferation of myoblasts and inhibited the apoptosis of myoblasts in sheep, whereas oar-miR-485-5p inhibited the expression of MAPK15 and circFAM171A1, inhibited myoblast proliferation and promoted apoptosis. Furthermore, circFAM171A1 attenuated the inhibitory effect of oar-miR-485-5p on myoblasts. In summary, estrogen induced the expression of circFAM171A1 in sheep myoblasts, and circFAM171A1 can act as a sponge for oar-miR-485-5p to promote the expression of the target gene MAPK15 and ultimately regulate the proliferation of sheep myoblasts. This study provides new insights into the molecular mechanism of estrogen regulation of muscle growth and development in female animals.

Mechanism of Action of circRNA/miRNA Network in DLBCL

Circular RNAs (circRNAs) make up approximately 10% of the human transcriptome. CircRNAs belong to the broad group of non-coding RNAs and characteristically are formed by backsplicing into a stable circular loop. Their main role is to regulate transcription through the inhibition of miRNAs' expression, termed miRNA sponging. CircRNAs promote tumorigenesis/lymphomagenesis by competitively binding to miRNAs at miRNA binding sites. In diffuse large B-cell lymphoma (DLBCL), several circRNAs have been identified and their expression is related to both progression and response to therapy. DLBCL is the most prevalent and aggressive subtype of B-cell lymphomas and accounts for about 25% to 30% of all non-Hodgkin lymphomas. DLBCL displays great heterogeneity concerning histopathology, biology, and genetics. Patients who have relapsed or have refractory disease after first-line therapy have a very poor prognosis, demonstrating an important unmet need for new treatment options. As more circRNAs are identified in the future, we will better understand their biological roles and potential use in treating cancer, including DLBCL. For example, circAmotl1 promotes nuclear translocation of MYC and upregulation of translational targets of MYC, thus enhancing lymphomagenesis. Another example is circAPC, which is significantly downregulated in DLBCL and correlates with disease aggressiveness and poor prognosis. CircAPC increases expression of the host gene adenomatous polyposis coli (APC), and in doing so inactivates the canonical Wnt/β-catenin signaling and restrains DLBCL growth. MiRNAs belong to the non-coding regulatory molecules that significantly contribute to lymphomagenesis through their target mRNAs. In DLBCL, among the highly expressed miRNAs, are miR-155-5p and miR-21-5p, which regulate NF-ĸB and PI3K/AKT signaling pathways. The aim of this review is to describe the function and mechanism of regulation of circRNAs on miRNAs' expression in DLBCL. This will help us to better understand the regulatory network of circRNA/miRNA/mRNA, and to propose novel therapeutic targets to treat DLBCL.

Post-Transcriptional Regulation of Gene Expression and the Intricate Life of Eukaryotic mRNAs

In recent years, there has been a growing appreciation for how regulatory events that occur either co- or post-transcriptionally contribute to the control of gene expression. Messenger RNAs (mRNAs) are extensively regulated throughout their metabolism in a precise spatiotemporal manner that requires sophisticated molecular mechanisms for cell-type-specific gene expression, which dictates cell function. Moreover, dysfunction at any of these steps can result in a variety of human diseases, including cancers, muscular atrophies, and neurological diseases. This review summarizes the steps of the central dogma of molecular biology, focusing on the post-transcriptional regulation of gene expression.

CircNIPBLL modulates the inflammatory response against Eimeria tenella infection via sponging gga-miR-2954

Coccidiosis, a parasitic disease caused by Eimeria protozoa that parasitizes intestinal tissues of chicken, poses a challenge to the development of the poultry industry. circRNAs are a class of circular RNA macromolecules crucial in the immune response to pathogens. Previous studies have shown that gga-miR-2954 inhibits the inflammatory response to Eimeria tenella (E. tenella) infection. In this study, we screened the key circRNA (circNIPBLL) regulating gga-miR-2954 using a co-expression network. The RNase R and Actinomycin D assays showed that the circular structure of the circNIPBLL was stable. Besides, the circNIPBLL expression was mainly distributed in the cytoplasm but did not have coding capacity. Overexpression of circNIPBLL significantly promoted the production of the IL-6, IL-1β, TNF-α, and IL-8 in sporozoite-stimulated DF-1 cells, whereas circNIPBLL knockdown significantly inhibited these effects. Moreover, circNIPBLL induced apoptosis of DF-1 cells stimulated by sporozoites. Mechanistically, circNIPBLL functioned as a sponge for gga-miR-2954, and overexpression of circNIPBLL rescued the effect of gga-miR-2954 mimic on the inflammatory response of DF-1 cells stimulated with sporozoites. Taken together, this study suggested that circNIPBLL modulated the inflammatory response against E. tenella infection by sponging gga-miR-2954, which may provide novel insights into the immune mechanisms of chicken resistance to E. tenella.

Role of circular RNAs in cancer therapy resistance

Over the past decade, circular RNAs (circRNAs) have gained recognition as a novel class of genetic molecules, many of which are implicated in cancer pathogenesis via different mechanisms, including drug resistance, immune escape, and radio-resistance. ExosomalcircRNAs, in particular, facilitatecommunication between tumour cells and micro-environmental cells, including immune cells, fibroblasts, and other components. Notably, micro-environmental cells can reportedly influence tumour progression and treatment resistance by releasing exosomalcircRNAs. circRNAs often exhibit tissue- and cancer-specific expression patterns, and growing evidence highlights their potential clinical relevance and utility. These molecules show strong promise as potential biomarkers and therapeutic targets for cancer diagnosis and treatment. Therefore, this review aimed to briefly discuss the latest findings on the roles and resistance mechanisms of key circRNAs in the treatment of various malignancies, including lung, breast, liver, colorectal, and gastric cancers, as well as haematological malignancies and neuroblastoma.This review will contribute to the identification of new circRNA biomarkers for the early diagnosis as well as therapeutic targets for the treatment of cancer.

Correlation of local and serum CircHIPK3 expressions with the progression of liver fibrosis/cirrhosis

BACKGROUND AND STUDY AIMS

This study was aimed to validate the correlation of circular RNA HIPK3 (CircHIPK3) expression in serum and tissues with the progression of liver fibrosis (LF) and liver cirrhosis (LC).

PATIENTS AND METHODS

Serum CircHIPK3 expressions were detected in 120 patients with LF/LC and 120 healthy controls (HCs). CircHIPK3 expression in tissues was detected in 120 fibrotic liver tissues and compared to 57 healthy liver tissues from patients with hepatic hemangioma. The expressions of CircHIPK3, TGF-β1, and CollA1 mRNAs were assessed by qRT-PCR. The Child-Pugh (CP) classification was used to evaluate disease severity. The Ishak score was applied to assess LF/LC in liver biopsy samples. The levels of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were also investigated. Receiver operating characteristic (ROC) analysis was conducted to assess the diagnostic value of CircHIPK3 expressions in serum and tissues.

RESULTS

CircHIPK3 expressions in serum and tissues were upregulated in patients with LF/LC compared to HCs. The patient group comprised 39 with CP class A (CP-A), 45 with CP class B (CP-B), and 36 with CP class B (CP-C). Patients with CP-C had markedly increased serum and local CircHIPK3 levels compared to those with CP-B and CP-A. Patients with CP-B showed upregulated CircHIPK3 expressions in serum and tissues compared to CP-A with statistical significance. ROC curve analysis indicated that CircHIPK3 expressions in both serum and tissues may serve as potential diagnostic indicators for the progression of LF/LC. Moreover, serum CircHIPK3 expressions were positively associated with serum ALT and AST levels. Tissue CircHIPK3 expressions were positively correlated with tissue TGF-β1 and CollA1 mRNA expressions. In addition, both serum and tissue CircHIPK3 expressions were positively associated with the Ishak score.

CONCLUSIONS

For the first time, this study demonstrated the positive correlation of CircHIPK3 expressions in both serum and tissues with the progression of LF/LC, regardless of etiology. CircHIPK3 might play a significant role in the development of LF/LC and act as a potential therapeutic target for these conditions.

The role of the circ_DOCK1-miR-1297-HOXA9 regulatory network in the development of oral squamous cell carcinoma

OBJECTIVE

Oral squamous cell carcinoma (OSCC) is a public health concern. The current study aimed to explore the role of circRNA Dedicator of Cytokinesis 1 (circ_DOCK1) and associated action mode in OSCC.

METHODS

The expression of circ_DOCK1 and microRNA-1297 (miR-1297) was measured by quantitative real-time polymerase chain reaction (qRT-PCR). EdU assay, colony formation assay, transwell assay and glycolysis stress test were applied for functional analyses. The expression level of Homeobox A9 (HOXA9) was detected by western blot. The interaction between miR-1297 and circ_DOCK1 or HOXA9 was verified by dual-luciferase reporter assay. Xenograft model was established to determine the role of circ_DOCK1 in vivo.

RESULTS

Circ_DOCK1 was highly expressed in OSCC tumor tissues and cell lines. Circ_DOCK1 knockdown suppressed colony formation, migration, invasion and glycolysis of OSCC cells. MiR-1297 was targeted by circ_DOCK1, and its inhibition reversed the anticancer effects of circ_DOCK1 knockdown. HOXA9 was a target of miR-1297, and its overexpression recovered miR-1297 reintroduction-evoked inhibition of colony formation, migration, invasion and glycolysis in OSCC cells. Furthermore, circ_DOCK1 knockdown repressed tumor growth in vivo.

CONCLUSION

Circ_DOCK1 exerted its carcinogenic role in OSCC partially via the circ_DOCK1-miR-1297-HOXA9 regulatory network, which will broaden our insights to understand the pathogenesis of OSCC and provide promising biomarkers for the diagnosis and treatment of OSCC.

Non-Coding RNA in Schwann Cell and Peripheral Nerve Injury: A Review

Peripheral nerve injury (PNI) can result in severe disabilities, profoundly impacting patients' quality of life and potentially endangering their lives. Therefore, understanding the potential molecular mechanisms that facilitate the regeneration of damaged nerves is crucial. Evidence indicates that Schwann cells (SCs) play a pivotal role in repairing peripheral nerve injuries. Previous studies have shown that RNA, particularly non-coding RNA (ncRNA), plays a crucial role in nerve regeneration, including the proliferation and dedifferentiation of SCs. In this review, the individual roles of ncRNA in SCs and PNI are analyzed. This review not only enhances the understanding of ncRNA's role in nerve injury repair but also provides a significant theoretical foundation and inspiration for the development of new therapeutic strategies.

CircRNA regulates lung cancer metastasis

Lung cancer stands prominently among the foremost contributors to human mortality, distinguished by its elevated fatality rate and the second-highest incidence rate among malignancies. The metastatic dissemination of lung cancer stands as a primary determinant of its elevated mortality and recurrence rates, underscoring the imperative for comprehensive investigation into its metastatic pathways. Circular RNAs (circRNAs), a subclass of non-coding RNA (ncRNA) molecules, have garnered attention for their pivotal involvement in the genesis and advancement of lung cancer. Emerging evidence highlights the indispensable functions of circRNAs in orchestrating the metastatic cascade of lung cancer. This review primarily discusses the mechanisms by which circRNAs act as competitive endogenous RNAs (ceRNAs) and modulate various signaling pathways to regulate lung cancer metastasis. CircRNAs influence critical cellular processes including angiogenesis, autophagy, and glycolysis, thereby exerting influence over the metastatic cascade in lung cancer. These discoveries offer innovative perspectives and therapeutic avenues for the diagnosis and management of lung cancer.

CircUCK2(2,3) promotes cancer progression and enhances synergistic cytotoxicity of lenvatinib with EGFR inhibitors via activating CNIH4-TGFα-EGFR signaling

BACKGROUND

Circular (circ)RNAs have emerged as crucial contributors to cancer progression. Nonetheless, the expression regulation, biological functions, and underlying mechanisms of circRNAs in mediating hepatocellular carcinoma (HCC) progression remain insufficiently elucidated.

METHODS

We identified circUCK2(2,3) through circRNA sequencing, RT-PCR, and Sanger sequencing. CircUCK2(2,3) levels were measured in two independent HCC cohorts using quantitative real-time PCR (qRT-PCR). We explored the functions of circUCK2(2,3) using gain- and loss-of-function assays. Techniques such as RNA-sequencing, RNA immunoprecipitation (RIP), polysome fractionation, RNA pulldown, dual luciferase reporter assay, inhibitors of EGFR downstream signaling, CRISPR-Cas9, and medium transfer assays were employed to investigate the regulatory mechanisms and the protumoral activities of circUCK2(2,3). Additionally, in vitro cytotoxic assays and patient-derived xenograft (PDX) models assessed the effects of circUCK2(2,3) on the cytotoxic synergy of lenvatinib and EGFR inhibitors.

RESULTS

CircUCK2(2,3) is upregulated in HCC tissues and serves as an independent risk factor for poor recurrence-free survival. The expression of circUCK2(2,3) is independent on its host gene, UCK2, but is regulated by its upstream promoter and flanking inverted complementary sequences. Functionally, circUCK2(2,3) enhances HCC proliferation, migration, and invasion, both in vitro and in vivo. Mechanistically, by sponging miR-149-5p, circUCK2(2,3) increases CNIH4 levels, which in turn amplifies TGFα secretion, resulting in the activation of EGFR and downstream pAKT and pERK signaling pathways. Moreover, circUCK2(2,3) overexpression sensitizes HCC cells to EGFR inhibitors, and increases the synergistic cytotoxicity of combined lenvatinib and EGFR inhibitor treatment.

CONCLUSIONS

CircUCK2(2,3) regulates a novel oncogenic pathway, miR-149-5p-CNIH4-TGFα-EGFR, in HCC, presenting a viable therapeutic target and biomarker for the precision treatment of HCC.

Circular RNA Formation and Degradation Are Not Directed by Universal Pathways

Circular RNAs (circRNAs) are a class of unique transcripts characterized by a covalently closed loop structure, which differentiates them from conventional linear RNAs. The formation of circRNAs occurs co-transcriptionally and post-transcriptionally through a distinct type of splicing known as back-splicing, which involves the formation of a head-to-tail splice junction between a 5' splice donor and an upstream 3' splice acceptor. This process, along with exon skipping, intron retention, cryptic splice site utilization, and lariat-driven intron processing, results in the generation of three main types of circRNAs (exonic, intronic, and exonic-intronic) and their isoforms. The intricate biogenesis of circRNAs is regulated by the interplay of cis-regulatory elements and trans-acting factors, with intronic Alu repeats and RNA-binding proteins playing pivotal roles, at least in the formation of exonic circRNAs. Various hypotheses regarding pathways of circRNA turnover are forwarded, including endonucleolytic cleavage and exonuclease-mediated degradation; however, similarly to the inconclusive nature of circRNA biogenesis, the process of their degradation and the factors involved remain largely unclear. There is a knowledge gap regarding whether these processes are guided by universal pathways or whether each category of circRNAs requires special tools and particular mechanisms for their life cycles. Understanding these factors is pivotal for fully comprehending the biological significance of circRNAs. This review provides an overview of the various pathways involved in the biogenesis and degradation of different types of circRNAs and explores key factors that have beneficial or adverse effects on the formation and stability of these unique transcripts in higher eukaryotes.

PlantCircRNA: a comprehensive database for plant circular RNAs

Circular RNAs (circRNAs) represent recently discovered novel regulatory non-coding RNAs. While they are present in many eukaryotes, there has been limited research on plant circRNAs. We developed PlantCircRNA (https://plant.deepbiology.cn/PlantCircRNA/) to fill this gap. The two most important features of PlantCircRNA are (i) it incorporates circRNAs from 94 plant species based on 39 245 RNA-sequencing samples and (ii) it imports the original AtCircDB and CropCircDB databases. We manually curated all circRNAs from published articles, and imported them into the database. Furthermore, we added detailed information of tissue as well as abiotic stresses to the database. To help users understand these circRNAs, the database includes a detection score to measure their consistency and a naming system following the guidelines recently proposed for eukaryotes. Finally, we developed a comprehensive platform for users to visualize, analyze, and download data regarding specific circRNAs. This resource will serve as a home for plant circRNAs and provide the community with unprecedented insights into these mysterious molecule.

Architects and Partners: The Dual Roles of Non-coding RNAs in Gene Fusion Events

Extensive research into gene fusions in cancer and other diseases has led to the discovery of novel biomarkers and therapeutic targets. Concurrently, various bioinformatics tools have been developed for fusion detection in RNA sequencing data, which, in the age of increasing affordability of sequencing, have delivered a large-scale identification of transcriptomic abnormalities. Historically, the focus of fusion transcript research was predominantly on coding RNAs and their resultant proteins, often overlooking non-coding RNAs (ncRNAs). This chapter discusses how ncRNAs are integral players in the landscape of gene fusions, detailing their contributions to the formation of gene fusions and their presence in chimeric transcripts. We delve into both linear and the more recently identified circular fusion RNAs, providing a comprehensive overview of the computational methodologies used to detect ncRNA-involved gene fusions. Additionally, we examine the inherent biases and limitations of these bioinformatics approaches, offering insights into the challenges and future directions in this dynamic field.

Non-coding RNAs to treat vascular smooth muscle cell dysfunction

Vascular smooth muscle cell (vSMC) dysfunction is a critical contributor to cardiovascular diseases, including atherosclerosis, restenosis and vein graft failure. Recent advances have unveiled a fascinating range of non-coding RNAs (ncRNAs) that play a pivotal role in regulating vSMC function. This review aims to provide an in-depth analysis of the mechanisms underlying vSMC dysfunction and the therapeutic potential of various ncRNAs in mitigating this dysfunction, either preventing or reversing it. We explore the intricate interplay of microRNAs, long-non-coding RNAs and circular RNAs, shedding light on their roles in regulating key signalling pathways associated with vSMC dysfunction. We also discuss the prospects and challenges associated with developing ncRNA-based therapies for this prevalent type of cardiovascular pathology. LINKED ARTICLES: This article is part of a themed issue Non-coding RNA Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v182.2/issuetoc.

A Review on Circular RNA Translation and Its Implications in Disease

The mRNA vaccine has emerged as a powerful tool against viral infection during the coronavirus disease 2019 (COVID-19) pandemic. In the post-COVID-19 era, the applications of mRNA-based therapy continue to expand and evolve. Circular RNA (circRNA), long assumed to be a noncoding RNA, has been proven to be translatable and subsequently developed as a next-generation mRNA modality due to its higher stability and wider therapeutic window. Nonetheless, the studies of circRNA translation and its application in diseases still present numerous technical features and challenges. In this chapter, we provide a summary and discussion on the mechanisms of circRNA translation and its applications in medicine development, aiming to serve as a reference and inspiration for readers interested in circRNA-based therapy.

The Emerging Roles of CircPVT1 in Cancer Progression

CircRNA is stable due to its ring structure and is abundant in humans, which not only exists in various tissues and biofluids steadily but also plays a significant role in the physiology and pathology of human beings. CircPVT1, an endogenous circRNA, has recently been identified from the PVT1 gene located in the cancer risk region 8q24. CircPVT1 is reported to be highly expressed in many different tumors, where it affects tumor cell proliferation, apoptosis, invasion, and migration. We summarize the biosynthesis and biological functions of circPVT1 and analyze the relationship between circPVT1 and tumors as well as its significance to tumors. Further, it's noteworthy for the diagnosis, treatment, and prognosis of cancer patients. Therefore, circPVT1 is likely to become an innovative tumor marker.

Structural determinants of inverted Alu-mediated backsplicing revealed by -MaP and -JuMP

Biogenesis of circular RNA usually involves a backsplicing reaction where the downstream donor site is ligated to the upstream acceptor site by the spliceosome. For this reaction to occur, it is hypothesized that these sites must be in proximity. Inverted repeat sequences, such as Alu elements, in the upstream and downstream introns are predicted to base-pair and represent one mechanism for inducing proximity. Here, we investigate the pre-mRNA structure of the human HIPK3 gene at exon 2, which forms a circular RNA via backsplicing. We leverage multiple chemical probing techniques, including the recently developed SHAPE- JuMP strategy, to characterize secondary and tertiary interactions in the pre- mRNA that govern backsplicing. Our data confirm that the antisense Alu elements, AluSz(-) and AluSq2(+) in the upstream and downstream introns, form a highly- paired interaction. Circularization requires formation of long-range Alu-mediated base pairs but does not require the full-length AluSq2(+). In addition to confirming long-range base pairs, our SHAPE-JuMP data identified multiple long-range interactions between non-pairing nucleotides. Genome-wide analysis of inverted repeats flanking circular RNAs confirm that their presence favors circularization, but the overall effect is modest. Together these results suggest that secondary structure considerations alone cannot fully explain backsplicing and additional interactions are key.

The landscape of circRNAs in gliomas temozolomide resistance: Insights into molecular pathways

As the deadliest type of primary brain tumor, gliomas represent a significant worldwide health concern. Circular RNA (circRNA), a unique non-coding RNA molecule, seems to be one of the most alluring target molecules involved in the pathophysiology of many kinds of cancers. CircRNAs have been identified as prospective targets and biomarkers for the diagnosis and treatment of numerous disorders, particularly malignancies. Recent research has established a clinical link between temozolomide (TMZ) resistance and certain circRNA dysregulations in glioma tumors. CircRNAs may play a therapeutic role in controlling or overcoming TMZ resistance in gliomas and may provide guidance for a novel kind of individualized glioma therapy. To address the biological characteristics of circRNAs and their potential to induce resistance to TMZ, this review has highlighted and summarized the possible roles that circRNAs may play in molecular pathways of drug resistance, including the Ras/Raf/ERK PI3K/Akt signaling pathway and metabolic processes in gliomas.

Evaluation of circANKLE2 & circL3MBTL4 -RNAs Expression in Fertile and Infertile Men

There are many factors that affect male fertility such as chronic health problems, psychological factors, and illnesses. Male infertility can be caused abnormal sperm function, low sperm production or even blockages that prevent the delivery of sperm. The aim of the work is to determine the expression pattern of the circularANKLE2 and circularL3MBTL4 RNA in spermatozoa from fertile and infertile males, as well as the relationship between these circRNA transcripts and sperm quality. The study involved two groups: a control group comprising 40 healthy, fertile men and an experimental group of 90 infertile males. Semen samples were collected and processed for analysis using computer-assisted semen analysis. Following RNA extraction from sperm samples, reverse transcription and real-time PCR were performed to assess the levels of circular ANKLE2 and circular L3MBTL4 RNA. There was a significant up-regulation of circularANKLE2 RNA expression (p < 0.05), and a significant down-regulation of circularL3MBTL4 RNA expression (p < 0.05) in asthenozoospermia, astheno-teratozoospermia, and oligo-astheno-teratozoospermia groups, as well as, in immature spermatozoa separated from normozoospermic samples. Moreover, the altered expression of both circular L3MBTL4 and circular ANKLE2 RNA showed significant correlations with the associated sperm parameters. In conclusion, the expression of circular ANKLE2 RNA and circular L3MBTL4 RNA may play a significant role in male fertility and could serve as potential biomarkers of sperm quality, warranting further investigation for their application in infertility diagnostics.

ZC3H14 facilitates backsplicing by binding to exon-intron boundary and 3' UTR

Circular RNAs (circRNAs) are natural outputs of eukaryotic transcription and RNA processing and have emerged as critical regulators in physiology and diseases. Although multiple cis-elements and trans-factors are reported to modulate the backsplicing of circRNA biogenesis, most of these regulations play roles in flanking introns of circRNAs. Here, using a genome-wide CRISPR knockout screen, we have identified an evolutionarily conserved RNA-binding protein ZC3H14 in regulating circRNA biogenesis. ZC3H14 binds to 3' and 5' exon-intron boundaries and 3' UTRs of cognate mRNAs to promote circRNA biogenesis through dimerization and the association with spliceosome. Yeast knockout of the ZC3H14 ortholog Nab2 has significantly lower levels of circRNAs. Zc3h14-/- mice exhibit disrupted spermatogenesis and reduced testicular circRNA levels. Additionally, expression levels of human ZC3H14 are associated with non-obstructive azoospermia. Our findings reveal a conserved requirement for ZC3H14 in the modulation of backsplicing and link ZC3H14 and circRNA biogenesis to male fertility.

Hsa_circ_0010023 promotes the development of papillary thyroid carcinoma by sponging miR-1250-5p

BACKGROUND

Papillary thyroid cancer (PTC) is the most common thyroid tumor (TC). However, there is still a lack of effective indicators for PTC detection and prognosis. We intended to find a novel tumor marker for the progression of PTC.

METHODS

The expression of circRNAs was measured by quantitative real-time polymerase chain reaction (qRT-PCR). SiRNA transfection was used to knockdown the expression of hsa_circ_0010023 in K1 cells. Cell proliferation was evaluated using cell counting and CCK8. Cell apoptosis was analyzed using flow cytometry. Hsa_circ_0010023 downstream pathways were predicted with bio-informatics analysis. The miR-1250-5p and MAPK1 were measured by qRT-PCR. The interaction between miR-1250-5p and hsa_circ_0010023 was vertified by dual-luciferase reporter assay.

RESULTS

Among the four circRNAs screened, only hsa_circ_0010023 and hsa_circ_0128482 were highly expressed in PTC (P < 0.05). The expression of hsa_circ_0010023 was significantly correlated with lymph node metastasis and extrathyroid infiltration (P < 0.05). Compared with the control group, the cell proliferation of the si-circ-0010023 group was significantly inhibited (P < 0.05). Knockdown of hsa_circ_0010023 promotes apoptosis of K1 cells (P < 0.001). The expression of hsa_circ_0010023 was negatively correlated with miR-1250-5p and positively correlated with MAPK1. MiR-1250-5p overexpression significantly reduced the luciferase activity of wild type plasmid (hsa_circ_0010023 WT), but not that of mutant type plasmid (hsa_circ_0010023 MUT).

CONCLUSION

The expression level of hsa_circ_0010023 was positive related to the progression of PTC, and hsa_circ_0010023 may promote PTC through sponging miR-1250-5p. Hsa_circ_0010023 may be a potential bio-marker for the diagnosis of PTC.

Comprehensive circular RNA profiling in various sheep tissues

Despite the scientific relevance of circular RNAs (circRNAs), the study of these RNAs in non-model organisms, especially in sheep, is still in its infancy. On the other hand, while some studies have focused on sheep circRNA identification in a limited number of tissues, there is a lack of comprehensive analysis that profile circRNA expression patterns across the tissues not yet investigated. In this study, 61 public RNA sequencing datasets from 12 different tissues were uniformly analyzed to identify circRNAs, profile their expression and investigate their various characteristics. We reported for the first time a circRNA expression landscape with functional annotation in sheep tissues not yet investigated including hippocampus, BonMarrowMacrophage, left-ventricle, thymus, ileum, reticulum and 23-day-embryo. A stringent computational pipeline was employed and 8919 exon-derived circRNAs with high confidence were identified, including 88 novel circRNAs. Tissue-specificity analysis revealed that 3059 circRNAs were tissue-specific, which were also more specific to the tissues than linear RNAs. The highest number of tissue-specific circRNAs was found in kidney, hippocampus and thymus, respectively. Co-expression analysis revealed that expression of circRNAs may not be affected by their host genes. While most of the host genes produced more than one isoform, only one isoform had dominant expression across the tissues. The host genes of the tissue-specific circRNAs were significantly enriched in biological/pathways terms linked to the important functions of their corresponding tissues, suggesting potential roles of circRNAs in modulating physiological activity of those tissues. Interestingly, functional terms related to the regulation and various signaling pathways were significantly enriched in all tissues, suggesting some common regulatory mechanisms of circRNAs to modulate the physiological functions of tissues. Finding of the present study provide a valuable resource for depicting the complexity of circRNAs expression across tissues of sheep, which can be useful for the field of sheep genomic and veterinary research.

A Representation Learning Approach for Predicting circRNA Back-Splicing Event via Sequence-Interaction-Aware Dual Encoder

Circular RNAs (circRNAs) play a crucial role in gene regulation and association with diseases because of their unique closed continuous loop structure, which is more stable and conserved than ordinary linear RNAs. As fundamental work to clarify their functions, a large number of computational approaches for identifying circRNA formation have been proposed. However, these methods fail to fully utilize the important characteristics of back-splicing events, i.e., the positional information of the splice sites and the interaction features of its flanking sequences, for predicting circRNAs. To this end, we hereby propose a novel approach called SIDE for predicting circRNA back-splicing events using only raw RNA sequences. Technically, SIDE employs a dual encoder to capture global and interactive features of the RNA sequence, and then a decoder designed by the contrastive learning to fuse out discriminative features improving the prediction of circRNAs formation. Empirical results on three real-world datasets show the effectiveness of SIDE. Further analysis also reveals that the effectiveness of SIDE.

m6A modification in non-coding RNAs: Mechanisms and potential therapeutic implications in fibrosis

N6-methyladenosine (m6A) is one of the most prevalent and reversible forms of RNA methylation, with increasing evidence indicating its critical role in numerous physiological and pathological processes. m6A catalyzes messenger RNA(mRNA) as well as regulatory non-coding RNAs (ncRNAs), such as microRNAs, long non-coding RNAs, and circular RNAs. This modification modulates ncRNA fate and cell functions in various bioprocesses, including ncRNA splicing, maturity, export, and stability. Key m6A regulators, including writers, erasers, and readers, have been reported to modify the ncRNAs involved in fibrogenesis. NcRNAs affect fibrosis progression by targeting m6A regulators. The interactions between m6A and ncRNAs can influence multiple cellular life activities. In this review, we discuss the impact of the interaction between m6A modifications and ncRNAs on the pathological mechanisms of fibrosis, revealing the possibility of these interactions as diagnostic markers and therapeutic targets in fibrosis.

Circular RNAs as novel biomarkers in glomerular diseases

Circular RNAs (circRNAs) regulate gene expression and biological procedures by controlling target genes or downstream pathways by sponging their related miRNA (s). Three types of circRNAs have been identified; exonic circRNAs (ecircRNAs), intronic RNAs (ciRNAs), and exon-intron circRNAs (ElciRNAs). It is clarified that altered levels of circRNAs have dynamic pathological and physiological functions in kidney diseases. Evidence suggests that circRNAs can be considered novel diagnostic biomarkers and therapeutic targets for renal diseases. Glomerulonephritis (GN) is a general term used to refer to a wide range of glomerular diseases. GN is an important cause of chronic kidney diseases. Here, we review the biogenesis of circRNAs, and their molecular and physiological functions in the kidney. Moreover, the dysregulated expression of circRNAs and their biological functions are discussed in primary and secondary glomerulonephritis. Moreover, diagnostic and therapeutic values of circRNAs in distinguishing or treating different types of GN are highlighted.

Drought-induced circular RNAs in maize roots: Separating signal from noise

Circular RNAs (circRNAs) play an important role in diverse biological processes; however, their origin and functions, especially in plants, remain largely unclear. Here, we used 2 maize (Zea mays) inbred lines, as well as 14 of their derivative recombination inbred lines with different drought sensitivity, to systematically characterize 8,790 circRNAs in maize roots under well-watered (WW) and water-stress (WS) conditions. We found that a diverse set of circRNAs expressed at significantly higher levels under WS. Enhanced expression of circRNAs was associated with longer flanking introns and an enrichment of long interspersed nuclear element retrotransposable elements. The epigenetic marks found at the back-splicing junctions of circRNA-producing genes were markedly different from canonical splicing, characterized by increased levels of H3K36me3/H3K4me1, as well as decreased levels of H3K9Ac/H3K27Ac. We found that genes expressing circRNAs are subject to relaxed selection. The significant enrichment of trait-associated sites along their genic regions suggested that genes giving rise to circRNAs were associated with plant survival rate under drought stress, implying that circRNAs play roles in plant drought responses. Furthermore, we found that overexpression of circMED16, one of the drought-responsive circRNAs, enhances drought tolerance in Arabidopsis (Arabidopsis thaliana). Our results provide a framework for understanding the intricate interplay of epigenetic modifications and how they contribute to the fine-tuning of circRNA expression under drought stress.

The importance of the circRNA/Wnt axis in gliomas: Biological functions and clinical opportunities

Gliomas are among the most common cancers in the central nervous system, arising through various signaling pathways. One significant pathway is Wnt signaling, a tightly regulated process that plays a crucial role in gliomagenesis and development. The current study aims to explore the relationship between circular RNAs (circRNAs) and the Wnt/β-catenin signaling pathway in gliomas, considering the growing recognition of circRNAs in disease pathogenesis. A comprehensive review of recent research was conducted to investigate the roles of circRNAs in gliomas, focusing on their expression patterns and interactions with the Wnt signaling pathway. The analysis included studies examining circRNAs' function as microRNA sponges and their impact on glioma biology. The findings reveal that circRNAs are differentially expressed in gliomas and significantly influence the occurrence, growth, and metastasis of these tumors. Specifically, circRNAs interact with the Wnt signaling pathway, affecting glioma development and progression. This interaction highlights the importance of circRNAs in glioma pathophysiology. Understanding the regulatory network involving circRNAs and Wnt signaling offers valuable insights into glioma pathophysiology. CircRNAs hold promise as diagnostic and prognostic biomarkers and may serve as targets for novel therapeutic strategies in glioma treatment.

The potential role of circular RNAs in regulating p53 in different types of cancers

P53 tumor suppressor is a major regulator of various cellular processes and functions. It has been reported that mutation or inactivation of p53 plays a crucial role in tumorigenesis in different types of cancers. Circular RNAs (circRNAs) are single-stranded non-coding RNAs that have significant post-transcriptional effects on the regulation of gene expression in various ways. These molecules can alter the expression and function of multiple genes and proteins. In the present study, we aimed to review circRNAs that regulate the expression, function, and stability of p53 and the possible interactions between these molecules and p53. Considering the importance of p53 in cancer and the network between p53 and circRNAs, future clinical trials targeting these circRNAs as therapeutic agents deserve worthy of attention.

Role and Regulatory Mechanism of circRNA_14820 in the Proliferation and Differentiation of Goat Skeletal Muscle Satellite Cells

Skeletal muscle satellite cells (SMSCs), a type of myogenic stem cell, play a pivotal role in postnatal muscle regeneration and repair in animals. Circular RNAs (circRNAs) are a distinct class of non-coding RNA molecules capable of regulating muscle development by modulating gene expression, acting as microRNAs, or serving as protein decoys. In this study, we identified circ_14820, an exonic transcript derived from adenosine triphosphatase family protein 2 (ATAD2), through initial RNA-Seq analysis. Importantly, overexpression of circ_14820 markedly enhanced the proliferation of goat SMSCs while concomitantly suppressing their differentiation. Moreover, circ_14820 exhibited predominant localization in the cytoplasm of SMSCs. Subsequent small RNA and mRNA sequencing of circ_14820-overexpressing SMSCs systematically elucidated the molecular regulatory mechanisms associated with circ_14820. Our preliminary findings suggest that the circ_14820-miR-206-CCND2 regulatory axis may govern the development of goat SMSCs. These discoveries contribute to a deeper understanding of circRNA-mediated mechanisms in regulating skeletal muscle development, thereby advancing our knowledge of muscle biology.

Advanced strategies of targeting circular RNAs as therapeutic approaches in colorectal cancer drug resistance

Colorectal cancer (CRC) stands second in terms of mortality and third among the highest prevalent kinds of cancer globally. CRC prevalence is rising in moderately and poorly developed regions and is greater in economically advanced regions. Despite breakthroughs in targeted therapy, resistance to chemotherapeutics remains a significant challenge in the long-term management of CRC. Circular RNAs (circRNAs) have been involved in growing cancer therapy resistance, particularly in CRC, according to an increasing number of studies in recent years. CircRNAs are one of the novel subclasses of non-coding RNAs, previously thought of as viroid. According to studies, circRNAs have been recommended as biological markers for therapeutic targets and diagnostic and prognostic purposes. That is particularly notable given that the expression of circRNAs has been linked to the hallmarks of CRC since they are responsible for drug resistance in CRC patients; thereby, circRNAs are significant for chemotherapy failure. Moreover, knowledge concerning circRNAs remains relatively unclear despite using all these advanced techniques. Here, in this study, we will go over the most recent published work to highlight the critical roles of circRNAs in CRC development and drug resistance and highlight the main strategies to overcome drug resistance to improve clinical outcomes.

A Comprehensive Insight and In Silico Analysis of CircRNAs in Hepatocellular Carcinoma: A Step toward ncRNA-Based Precision Medicine

Circular RNAs (circRNAs) are cardinal players in numerous physiological and pathological processes. CircRNAs play dual roles as tumor suppressors and oncogenes in different oncological contexts, including hepatocellular carcinoma (HCC). Their roles significantly impact the disease at all stages, including initiation, development, progression, invasion, and metastasis, in addition to the response to treatment. In this review, we discuss the biogenesis and regulatory functional roles of circRNAs, as well as circRNA-protein-mRNA ternary complex formation, elucidating the intricate pathways tuned by circRNAs to modulate gene expression and cellular processes through a comprehensive literature search, in silico search, and bioinformatics analysis. With a particular focus on the interplay between circRNAs, epigenetics, and HCC pathology, the article sets the stage for further exploration of circRNAs as novel investigational theranostic agents in the dynamic realm of HCC.

circHIPK3 nucleates IGF2BP2 and functions as a competing endogenous RNA

Circular RNAs represent a class of endogenous RNAs that regulate gene expression and influence cell biological decisions with implications for the pathogenesis of several diseases. Here, we disclose a novel gene-regulatory role of circHIPK3 by combining analyses of large genomics datasets and mechanistic cell biological follow-up experiments. Using time-course depletion of circHIPK3 and specific candidate RNA-binding proteins, we identify several perturbed genes by RNA sequencing analyses. Expression-coupled motif analyses identify an 11-mer motif within circHIPK3, which also becomes enriched in genes that are downregulated upon circHIPK3 depletion. By mining eCLIP datasets and combined with RNA immunoprecipitation assays, we demonstrate that the 11-mer motif constitutes a strong binding site for IGF2BP2 in bladder cancer cell lines. Our results suggest that circHIPK3 can sequester IGF2BP2 as a competing endogenous RNA (ceRNA), leading to target mRNA stabilization. As an example of a circHIPK3-regulated gene, we focus on the STAT3 mRNA as a specific substrate of IGF2BP2 and validate that manipulation of circHIPK3 regulates IGF2BP2-STAT3 mRNA binding and, thereby, STAT3 mRNA levels. Surprisingly, absolute copy number quantifications demonstrate that IGF2BP2 outnumbers circHIPK3 by orders of magnitude, which is inconsistent with a simple 1:1 ceRNA hypothesis. Instead, we show that circHIPK3 can nucleate multiple copies of IGF2BP2, potentially via phase separation, to produce IGF2BP2 condensates. Our results support a model where a few cellular circHIPK3 molecules can induce IGF2BP2 condensation, thereby regulating key factors for cell proliferation.

Investigation of the Circular Transcriptome in Alzheimer's Disease Brain

Circular RNAs (circRNAs) are a subclass of non-coding RNAs which have demonstrated potential as biomarkers for Alzheimer's disease (AD). In this study, we conducted a comprehensive exploration of the circRNA transcriptome within AD brain tissues. Specifically, we assessed circRNA expression patterns in the dorsolateral prefrontal cortex collected from nine AD-afflicted individuals and eight healthy controls. Utilising two circRNA detection tools, CIRI2 and CIRCexplorer2, we detected thousands of circRNAs and performed a differential expression analysis. CircRNAs which exhibited statistically significantly differential expression were identified as AD-specific differentially expressed circRNAs. Notably, our investigation revealed 120 circRNAs with significant upregulation and 1325 circRNAs displaying significant downregulation in AD brains when compared to healthy brain tissue. Additionally, we explored the expression profiles of the linear RNA counterparts corresponding to differentially expressed circRNAs in AD-afflicted brains and discovered that the linear RNA counterparts exhibited no significant changes in the levels of expression. We used CRAFT tool to predict that circUBE4B had potential to target miRNA named as hsa-miR-325-5p, ultimately regulated CD44 gene. This study provides a comprehensive overview of differentially expressed circRNAs in the context of AD brains, underscoring their potential as molecular biomarkers for AD. These findings significantly enhance our comprehension of AD's underlying pathophysiological mechanisms, offering promising avenues for future diagnostic and therapeutic developments.

Hsa_circRNA_0000284 acts as a ceRNA to participate in coronary heart disease progression by sponging miRNA-338-3p via regulating the expression of ETS1

Coronary heart disease (CHD) is a prevalent global cause of death. Research suggests that circular RNAs (circRNAs) play a role in the development of CHD. In this study, we investigated the expression of hsa_circRNA_0000284 in peripheral blood leukocytes (PBLs) obtained from a cohort of 94 CHD patients aged over 50 years, as well as 126 age-matched healthy controls (HC). An in vitro inflammatory and oxidative injury cell model that simulates CHD was used to evaluate changes in hsa_ circRNA _0000284 under stress. CRISPR/Cas9 technology was used to evaluate changes in hsa_circRNA_0000284 expression. An hsa_ circRNA_0000284 overexpression and silencing cell model was used to analyze the biological functions of hsa_circRNA_0000284. Bioinformatics, qRT-PCR, viral transfection technology, and luciferase assays were used to evaluate the potential hsa_circRNA_0000284/miRNA-338-3p/ETS1 axis. Western blotting analysis was performed to detect protein expression. Herein, PBLs from CHD patients exhibited downregulation of hsa_circRNA_0000284 expression. Exposure to oxidative stress and inflammation can induce damage to human umbilical endothelial cells, resulting in the downregulation of hsa_circRNA_0000284 expression. The expression of hsa_circRNA_0000284 in EA-hy926 cells was significantly reduced after the AluSq2 element of hsa_circRNA_0000284 had been knocked out. The expression of hsa_circRNA_0000284 affected proliferation, cycle distribution, aging, and apoptosis in EA-hy926 cells. Consistent with the results of cell transfection experiments and luciferase assays, Western blotting showed that hsa_circRNA_0000284 plays a role in the regulation of hsa-miRNA-338-3p expression. Subsequently, hsa-miRNA-338-3p was found to be involved in the regulation of ETS1 expression.Communicated by Ramaswamy H. Sarma.

circIARS: a potential plasma biomarker for diagnosing non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is one of the most prevalent cancers in the world, and early diagnosis can effectively improve patient survival. Here, differentially expressed circIARS genes are screened from the sequencing results, and their molecular characteristics are examined by Sanger sequencing, RNase R assay, agarose gel electrophoresis (AGE), and fluorescence in situ hybridization (FISH). Real-time fluorescence quantitative polymerase chain reaction (qRT-PCR) is performed to detect the expression level of circIARS. The diagnostic value of the signature is analyzed using a subject operating characteristic (ROC) curve. Moreover, plasma is collected from postsurgical, chemotherapy, and relapse patients to investigate the prognostic value of circIARS in NSCLC. The expression of circIARS is greater in both the plasma and tissues of NSCLC patients than in those of healthy individuals, and could be used to distinguish NSCLC patients from patients with benign pulmonary disease (BPD), small cell lung cancer (SCLC) patients, and healthy individuals. The expression level of circIARS relatively decreases after antitumor therapy, such as chemotherapy, and relatively increases after recurrence. ROC analysis reveals that circIARS has better detection efficiency than traditional markers. In addition, circIARS expression level is strongly correlated with several clinicopathological parameters. Finally, we tentatively predict the downstream miRNAs or RBP that might bind to circIARS. Plasma circIARS is significantly greater in NSCLC patients and has good stability and specificity as a diagnostic marker, which could aid in the adjuvant diagnosis and dynamic monitoring of NSCLC.