Genetic variation and RNA structure regulate microRNA biogenesis

The role of structure in regulatory RNA elements

Regulatory RNA elements fulfill functions such as translational regulation, control of transcript levels, and regulation of viral genome replication. Trans-acting factors (i.e., RNA-binding proteins) bind the so-called cis elements and confer functionality to the complex. The specificity during protein-RNA complex (RNP) formation often exploits the structural plasticity of RNA. Functional integrity of cis-trans pairs depends on the availability of properly folded RNA elements, and RNA conformational transitions can cause diseases. Knowledge of RNA structure and the conformational space is needed for understanding complex formation and deducing functional effects. However, structure determination of RNAs under in vivo conditions remains challenging. This review provides an overview of structured eukaryotic and viral RNA cis elements and discusses the effect of RNA structural equilibria on RNP formation. We showcase implications of RNA structural changes for diseases, outline strategies for RNA structure-based drug targeting, and summarize the methodological toolbox for deciphering RNA structures.

A transcription-independent role for HIF-1α in modulating microprocessor assembly

Microprocessor is an essential nuclear complex responsible for the initial RNase-mediated cleavage of primary miRNA, which is a tightly controlled maturation process that requires the proper assembly of Drosha and DGCR8. Unlike previously identified mechanisms directly targeting the enzymatic subunit Drosha, current knowledge about the biological ways of controlling miRNA nuclear maturation through DGCR8 is less addressed. In this study, we unveiled that the microprocessor assembly is governed by a master gene regulator HIF-1α irrespective of its canonical transcriptional activity. First, a widespread protein binding of HIF-1α with DGCR8 instead of Drosha was observed in response to biological stimulations. Similar protein interactions between their corresponding orthologues in model organisms were also observed. After dissecting the essential protein domains, we noticed that HIF-1α suppresses microprocessor assembly via binding to DGCR8. Furthermore, our results showed that HIF-1α hijacks monomeric DGCR8 thus reducing its dimer formation prior to microprocessor assembly, and consequently, the suppressed microprocessor formation and nuclear processing of primary miRNA were demonstrated. In conclusion, here we unveiled the mechanism of how microprocessor assembly is regulated by HIF-1α, which not only demonstrates a non-transcriptional function of nuclear HIF-1α but also provides new molecular insights into the regulation of microprocessor assembly through DGCR8.

microRNAs in action: biogenesis, function and regulation

Ever since microRNAs (miRNAs) were first recognized as an extensive gene family >20 years ago, a broad community of researchers was drawn to investigate the universe of small regulatory RNAs. Although core features of miRNA biogenesis and function were revealed early on, recent years continue to uncover fundamental information on the structural and molecular dynamics of core miRNA machinery, how miRNA substrates and targets are selected from the transcriptome, new avenues for multilevel regulation of miRNA biogenesis and mechanisms for miRNA turnover. Many of these latest insights were enabled by recent technological advances, including massively parallel assays, cryogenic electron microscopy, single-molecule imaging and CRISPR-Cas9 screening. Here, we summarize the current understanding of miRNA biogenesis, function and regulation, and outline challenges to address in the future.

Molecular characteristics and clinical implications of serine/arginine-rich splicing factors in human cancer

As critical splicing regulators, serine/arginine-rich splicing factors (SRSFs) play pivotal roles in carcinogenesis. As dysregulation of SRSFs may confer potential cancer risks, targeting SRSFs could provide important insights into cancer therapy. However, a global and comprehensive pattern to elaborate the molecular characteristics, mechanisms, and clinical links of SRSFs in a wide variety of human cancer is still lacking. In this study, a systematic analysis was conducted to reveal the molecular characteristics and clinical implications of SRSFs covering more than 10000 tumour samples of 33 human cancer types. We found that SRSFs experienced prevalent genomic alterations and expression perturbations in multiple cancer types. The DNA methylation, m6A modification, and miRNA regulation of SRSFs were all cancer context-dependent. Importantly, we found that SRSFs were strongly associated with cancer immunity, and were capable of predicting response to immunotherapy. And SRSFs had colossal potential for predicting survival in multiple cancer types, including those that have received immunotherapy. Moreover, we also found that SRSFs could indicate the drug sensitivity of targeted therapy and chemotherapy. Our research highlights the significance of SRSFs in cancer occurrence and development, and provides sufficient resources for understanding the biological characteristics of SRSFs, offering a new and unique perspective for developing cancer therapeutic strategies.

Association of microRNA Polymorphisms with Toxicities Induced by Methotrexate in Children with Acute Lymphoblastic Leukemia

Methotrexate (MTX), a structurally related substance to folic acid, is an important chemotherapeutic agent used for decades in the treatment of pediatric acute lymphoblastic leukemia (ALL) and other types of cancer as non-Hodgkin lymphomas and osteosarcomas. Despite the successful outcomes observed, the primary drawback is the variability in the pharmacokinetics and pharmacodynamics between patients. The main adverse events related to its use are nephrotoxicity, mucositis, and myelosuppression, especially when used in high doses. The potential adverse reactions and toxicities associated with MTX are a cause for concern and may lead to dose reduction or treatment interruption. Genetic variants in MTX transport genes have been linked to toxicity. Pharmacogenetic studies conducted in the past focused on single nucleotide polymorphisms (SNPs) in the coding and 5'-regulatory regions of genes. Recent studies have demonstrated a significant role of microRNAs (miRNAs) in the transport and metabolism of drugs and in the regulation of target genes. In the last few years, the number of annotated miRNAs has continually risen, in addition to the studies of miRNA polymorphisms and MTX toxicity. Therefore, the objective of the present study is to investigate the role of miRNA variants related to MTX adverse effects.

Noncoding RNA mutations in cancer

Cancer is driven by both germline and somatic genetic changes. Efforts have been devoted to characterizing essential genetic variations in cancer initiation and development. Most attention has been given to mutations in protein-coding genes and associated regulatory elements such as promoters and enhancers. The development of sequencing technologies and in silico and experimental methods has allowed further exploration of cancer predisposition variants and important somatic mutations in noncoding RNAs, mainly for long noncoding RNAs and microRNAs. Association studies including GWAS have revealed hereditary variations including SNPs and indels in lncRNA or miRNA genes and regulatory regions. These mutations altered RNA secondary structures, expression levels, and target recognition and then conferred cancer predisposition to carriers. Whole-exome/genome sequencing comparing cancer and normal tissues has revealed important somatic mutations in noncoding RNA genes. Mutation hotspots and somatic copy number alterations have been identified in various tumor-associated noncoding RNAs. Increasing focus and effort have been devoted to studying the noncoding region of the genome. The complex genetic network of cancer initiation is being unveiled. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Impact of microRNA polymorphisms on high-dose methotrexate-related hematological toxicities in pediatric acute lymphoblastic leukemia

Objectives

It is well known that transporter and enzyme genes could be regulated by microRNA (miRNA) at the post-transcriptional level, and single-nucleotide polymorphisms (SNPs) in miRNA, which are involved in the miRNA production and structure, may impact the miRNA expression level and then influence drug transport and metabolism. In this study, we aim to evaluate the association between miRNA polymorphisms and high-dose methotrexate (HD-MTX) hematological toxicities in Chinese pediatric patients with acute lymphoblastic leukemia (ALL).

Method

A total of 181 children with ALL were administered with 654 evaluable cycles of HD-MTX. Their hematological toxicities were evaluated according to the National Cancer Institute Common Terminology Criteria for Adverse Events v5. The association between 15 candidate SNPs of miRNA and hematological toxicities (leukopenia, anemia, and thrombocytopenia) was analyzed using Fisher's exact test. Further multiple backward logistic regression analysis was used to explore the independent risk factors for grade 3/4 hematological toxicities.

Result

Rs2114358 G>A in pre-hsa-miR-1206 was related to HD-MTX-related grade 3/4 leukopenia after multiple logistic regression [GA + AA vs. GG: odds ratio (OR): 2.308, 95% CI: 1.219-4.372, P = 0.010], and rs56103835 T > C in pre-hsa-mir-323b was associated with HD-MTX-related grade 3/4 anemia (TT + TC vs. CC: OR: 0.360, 95% CI: 0.239-0.541, P = 0.000); none of the SNPs were significantly associated with grade 3/4 thrombocytopenia. Bioinformatics tools predicted that rs2114358 G>A and rs56103835 T>C would impact the secondary structure of pre-miR-1206 and pre-miR-323b, respectively, and then probably influence the expression level of mature miRNAs and their target genes.

Conclusion

Rs2114358 G>A and rs56103835 T>C polymorphism may potentially influence HD-MTX-related hematological toxicities, which may serve as candidate clinical biomarkers to predict grade 3/4 hematological toxicities in pediatric patients with ALL.

Oncogenic SRSF3 in health and diseases

Serine/arginine rich splicing factor 3 (SRSF3) is an important multi-functional splicing factor, and has attracted increasing attentions in the past thirty years. The importance of SRSF3 is evidenced by its impressively conserved protein sequences in all animals and alternative exon 4 which represents an autoregulatory mechanism to maintain its proper cellular expression level. New functions of SRSF3 have been continuously discovered recently, especially its oncogenic function. SRSF3 plays essential roles in many cellular processes by regulating almost all aspects of RNA biogenesis and processing of many target genes, and thus, contributes to tumorigenesis when overexpressed or disregulated. This review updates and highlights the gene, mRNA, and protein structure of SRSF3, the regulatory mechanisms of SRSF3 expression, and the characteristics of SRSF3 targets and binding sequences that contribute to SRSF3's diverse molecular and cellular functions in tumorigenesis and human diseases.

SRSF7 and SRSF3 depend on RNA sequencing motifs and secondary structures to regulate Microprocessor

Human Microprocessor cleaves pri-miRNAs to initiate miRNA biogenesis. The accuracy and efficiency of Microprocessor cleavage ensure appropriate miRNA sequence and expression and thus its proper gene regulation. However, Microprocessor cleaves many pri-miRNAs incorrectly, so it requires assistance from many cofactors. For example, SRSF3 enhances Microprocessor cleavage by interacting with the CNNC motif in pri-miRNAs. However, whether SRSF3 can function with other motifs and/or requires the motifs in a certain secondary structure is unknown. In addition, the function of SRSF7 (a paralog of SRSF3) in miRNA biogenesis still needs to be discovered. Here, we demonstrated that SRSF7 could stimulate Microprocessor cleavage. In addition, by conducting high-throughput pri-miRNA cleavage assays for Microprocessor and SRSF7 or SRSF3, we demonstrated that SRSF7 and SRSF3 function with the CRC and CNNC motifs, adopting certain secondary structures. In addition, SRSF7 and SRSF3 affect the Microprocessor cleavage sites in human cells. Our findings demonstrate the roles of SRSF7 in miRNA biogenesis and provide a comprehensive view of the molecular mechanism of SRSF7 and SRSF3 in enhancing Microprocessor cleavage.

Differential analysis of RNA structure probing experiments at nucleotide resolution: uncovering regulatory functions of RNA structure

RNAs perform their function by forming specific structures, which can change across cellular conditions. Structure probing experiments combined with next generation sequencing technology have enabled transcriptome-wide analysis of RNA secondary structure in various cellular conditions. Differential analysis of structure probing data in different conditions can reveal the RNA structurally variable regions (SVRs), which is important for understanding RNA functions. Here, we propose DiffScan, a computational framework for normalization and differential analysis of structure probing data in high resolution. DiffScan preprocesses structure probing datasets to remove systematic bias, and then scans the transcripts to identify SVRs and adaptively determines their lengths and locations. The proposed approach is compatible with most structure probing platforms (e.g., icSHAPE, DMS-seq). When evaluated with simulated and benchmark datasets, DiffScan identifies structurally variable regions at nucleotide resolution, with substantial improvement in accuracy compared with existing SVR detection methods. Moreover, the improvement is robust when tested in multiple structure probing platforms. Application of DiffScan in a dataset of multi-subcellular RNA structurome and a subsequent motif enrichment analysis suggest potential links of RNA structural variation and mRNA abundance, possibly mediated by RNA binding proteins such as the serine/arginine rich splicing factors. This work provides an effective tool for differential analysis of RNA secondary structure, reinforcing the power of structure probing experiments in deciphering the dynamic RNA structurome.

The authors present DiffScan, an advanced tool for normalization and differential analysis of RNA structure probing experiments, combining their power in deciphering the dynamic RNA structurome and facilitating the discovery of RNA regulatory functions.

Dynamic Protein-RNA recognition in primary MicroRNA processing

MicroRNAs are prevalent regulators of gene expression, controlling most of the proteome in multicellular organisms. To generate the functional small RNAs, precise processing steps are required. In animals, microRNA biogenesis is initiated by Microprocessor that minimally consists of the Drosha enzyme and its partner, DGCR8. This first step is critical for selecting primary microRNAs, and many RNA-binding proteins and regulatory pathways target both the accuracy and efficiency of microRNA maturation. Structures of Drosha and DGCR8 in complex with primary microRNAs elucidate how RNA structural features rather than sequence provide the framework for substrate recognition. Comparing multiple states of Microprocessor and the closely related Dicer homologs shed light on the dynamic protein-RNA complex assembly and disassembly required to recognize RNAs with diverse sequences via common structural features.

Signatures of genetic variation in human microRNAs point to processes of positive selection and population-specific disease risks

The occurrence of natural variation in human microRNAs has been the focus of numerous studies during the last 20 years. Most of them have been focused on the role of specific mutations in disease, while a minor proportion seek to analyse microRNA diversity in the genomes of human populations. We analyse the latest human microRNA annotations in the light of the most updated catalogue of genetic variation provided by the 1000 Genomes Project. By means of the in silico analysis of microRNA genetic variation we show that the level of evolutionary constraint of these sequences is governed by the interplay of different factors, like their evolutionary age or genomic location. The role of mutations in the shaping of microRNA-driven regulatory interactions is emphasized with the acknowledgement that, while the whole microRNA sequence is highly conserved, the seed region shows a pattern of higher genetic diversity that appears to be caused by the dramatic frequency shifts of a fraction of human microRNAs. We highlight the participation of these microRNAs in population-specific processes by identifying that not only the seed, but also the loop, are particularly differentiated regions among human populations. The quantitative computational comparison of signatures of population differentiation showed that candidate microRNAs with the largest differences are enriched in variants implicated in gene expression levels (eQTLs), selective sweeps and pathological processes. We explore the implication of these evolutionary-driven microRNAs and their SNPs in human diseases, such as different types of cancer, and discuss their role in population-specific disease risk.

Regulatory Network of Serine/Arginine-Rich (SR) Proteins: The Molecular Mechanism and Physiological Function in Plants

Serine/arginine-rich (SR) proteins are a type of splicing factor. They play significant roles in constitutive and alternative pre-mRNA splicing, and are involved in post-splicing activities, such as mRNA nuclear export, nonsense-mediated mRNA decay, mRNA translation, and miRNA biogenesis. In plants, SR proteins function under a complex regulatory network by protein–protein and RNA–protein interactions between SR proteins, other splicing factors, other proteins, or even RNAs. The regulatory networks of SR proteins are complex—they are regulated by the SR proteins themselves, they are phosphorylated and dephosphorylated through interactions with kinase, and they participate in signal transduction pathways, whereby signaling cascades can link the splicing machinery to the exterior environment. In a complex network, SR proteins are involved in plant growth and development, signal transduction, responses to abiotic and biotic stresses, and metabolism. Here, I review the current status of research on plant SR proteins, construct a model of SR proteins function, and ask many questions about SR proteins in plants.

Exploring the multifunctionality of SR proteins

Members of the arginine–serine-rich protein family (SR proteins) are multifunctional RNA-binding proteins that have emerged as key determinants for mRNP formation, identity and fate. They bind to pre-mRNAs early during transcription in the nucleus and accompany bound transcripts until they are translated or degraded in the cytoplasm. SR proteins are mostly known for their essential roles in constitutive splicing and as regulators of alternative splicing. However, many additional activities of individual SR proteins, beyond splicing, have been reported in recent years. We will summarize the different functions of SR proteins and discuss how multifunctionality can be achieved. We will also highlight the difficulties of studying highly versatile SR proteins and propose approaches to disentangle their activities, which is transferrable to other multifunctional RBPs.

Biological function and molecular mechanism of SRSF3 in cancer and beyond

Serine/arginine-rich splicing factor 3 (SRSF3; also known as SRp20), an important member of the family of SRSFs, is abnormally expressed in tumors, resulting in aberrant splicing of hub genes, such as CD44, HER2, MDM4, Rac family small GTPase 1 and tumor protein p53. Under normal conditions, the splicing and expression of SRSF3 are strictly regulated. However, the splicing, expression and phosphorylation of SRSF3 are abnormal in tumors. SRSF3 plays important roles in the occurrence and development of tumors, including the promotion of tumorigenesis, cellular proliferation, the cell cycle and metastasis, as well as inhibition of cell senescence, apoptosis and autophagy. SRSF3-knockdown significantly inhibits the proliferation and metastatic characteristics of tumor cells. Therefore, SRSF3 may be suggested as a novel anti-tumor target. The other biological functions of SRSF3 and its regulatory mechanisms are also summarized in the current review.

Molecular mechanism of modulating miR482b level in tomato with botrytis cinerea infection

BACKGROUND

Plant miRNAs are involved in the response to biotic and abiotic stresses by altering their expression levels, and they play an important role in the regulation of plant resistance to stress. However, the molecular mechanism that regulates the expression levels of miRNAs in plants with biotic and abiotic stress still needs to be explored. Previously, we found that the expression of the miR482 family was changed in tomato infected by Botrytis cinerea. In this study, we investigated and uncovered the mechanism underlying the response of miR482 to B. cinerea infection in tomato.

RESULTS

First, RT-qPCR was employed to detect the expression patterns of miR482b in tomato infected by B. cinerea, and results showed that miR482b primary transcripts (pri-miR482b) were up-regulated in B. cinerea-infected leaves, but the mature miR482b was down-regulated. Subsequently, we used rapid amplification cDNA end method to amplify the full-length of pri-miR482b. Result showed that the pri-miR482b had two isoforms, with the longer one (consisting 300 bp) having an extra fragment of 53 bp in the 3'-end compared with the shorter one. In vitro Dicer assay indicated that the longer isoform pri-miR482b-x1 had higher efficiency in the post-transcriptional splicing of miRNA than the shorter isoform pri-miR482b-x2. In addition, the transcription level of mature miR482b was much higher in transgenic Arabidopsis overexpressing pri-miR482b-x1 than that in OE pri-miR482b-x2 Arabidopsis. These results confirmed that this extra 53 bp in pri-miR482b-x1 might play a key role in the miR482b biogenesis of post-transcription processing.

CONCLUSIONS

Extra 53 bp in pri-miR482b-x1 enhanced miR482b biogenesis, which elevated the transcription level of miR482b. This study clarified the response of miR482 to B. cinerea infection in tomato, thereby helping us further understand the molecular mechanisms that regulate the expression levels of other miRNAs.

Targeting Wnt/β-catenin signaling by microRNAs as a therapeutic approach in chemoresistant osteosarcoma

Osteosarcoma (OS) is an adolescent and young adult malignancy that mostly occurs in long bones. The treatment of OS is still a big challenge for clinicians due to increasing chemoresistance, and many efforts are being made today to find more beneficial treatments. In this regard, the use of microRNAs has shown a high capacity to develop promising therapies. By targeting cancer-involved signaling pathways, microRNAs reduce the cellular level of these protein pathways; thereby reducing the growth and invasion of tumors, and even leading cancer cells to apoptosis. One of these oncogenic pathways that play an important role in OS development and can be targeted by microRNAs is the Wnt/β-catenin signaling pathway. Hence, the first goal of this review article is to explain the cross-talk of microRNAs and the Wnt/β-catenin signaling in OS and then discussing recent findings of the use of microRNAs as a therapeutic approach in OS.

Comparative study of predicted miRNA between Indonesia and China (Wuhan) SARS-CoV-2: a bioinformatics analysis

BACKGROUND

Several reports on the discovery of SARS-CoV-2 mutations and variations in Indonesia COVID-19 cases led to genomic dysregulation with the first pandemic cases in Wuhan, China. MicroRNA (miRNA) plays an important role in this genetic regulation and contributes to the enhancement of viral RNA binding through the host mRNA.

OBJECTIVE

This research is aimed to detect miRNA targets of SARS-CoV-2 and examines their role in Indonesia cases against Wuhan cases.

METHODS

SARS-CoV-2 sequences were obtained from GISAID ( https://www.gisaid.org/ ), NCBI ( https://ncbi.nlm.nih.gov ), and National Genomics Data Center ( https://bigd.big.ac.cn/gwh/ ) databases. MiRDB ( https://github.com/gbnegrini/mirdb-custom-target-search ) was used to annotate and predict target human mature miRNAs. For statistical analysis, we utilized a series chi-square test to obtain significant miRNA. DIANA-miRPath v3.0 ( http://www.microrna.gr/miRPathv3 ) analyzed the Gene Ontology of mature miRNAs.

RESULT

The statistical results detected five significant miRNAs. Two miRNAs: hsa-miR-4778-5p and hsa-miR-4531 were consistently found in the majority of Wuhan samples, while they were only found in less than half of the Indonesia samples. The other three miRNA, hsa-miR-6844, hsa-miR-627-5p, and hsa-miR-3674, were discovered in most samples in both groups but with a significant difference ratio. Among these five significant miRNA targets, hsa-miR-6844 is the only miRNA that has an association with the ORF1ab gene of SARS-CoV-2.

CONCLUSION

The Gene Ontology analysis of five significant miRNA targets indicates a significant role in inflammation and the immune system. The specific detection of host miRNAs in this study shows that there are differences in the characteristics of SARS-CoV-2 between Indonesia and Wuhan.

Non-Coding Variants in Cancer: Mechanistic Insights and Clinical Potential for Personalized Medicine

The cancer genome is characterized by extensive variability, in the form of Single Nucleotide Polymorphisms (SNPs) or structural variations such as Copy Number Alterations (CNAs) across wider genomic areas. At the molecular level, most SNPs and/or CNAs reside in non-coding sequences, ultimately affecting the regulation of oncogenes and/or tumor-suppressors in a cancer-specific manner. Notably, inherited non-coding variants can predispose for cancer decades prior to disease onset. Furthermore, accumulation of additional non-coding driver mutations during progression of the disease, gives rise to genomic instability, acting as the driving force of neoplastic development and malignant evolution. Therefore, detection and characterization of such mutations can improve risk assessment for healthy carriers and expand the diagnostic and therapeutic toolbox for the patient. This review focuses on functional variants that reside in transcribed or not transcribed non-coding regions of the cancer genome and presents a collection of appropriate state-of-the-art methodologies to study them.

A quantitative map of human primary microRNA processing sites

Maturation of canonical microRNA (miRNA) is initiated by DROSHA that cleaves the primary transcript (pri-miRNA). More than 1,800 miRNA loci are annotated in humans, but it remains largely unknown whether and at which sites pri-miRNAs are cleaved by DROSHA. Here, we performed in vitro processing on a full set of human pri-miRNAs (miRBase version 21) followed by sequencing. This comprehensive profiling enabled us to classify miRNAs on the basis of DROSHA dependence and map their cleavage sites with respective processing efficiency measures. Only 758 pri-miRNAs are confidently processed by DROSHA, while the majority may be non-canonical or false entries. Analyses of the DROSHA-dependent pri-miRNAs show key cis-elements for processing. We observe widespread alternative processing and unproductive cleavage events such as "nick" or "inverse" processing. SRSF3 is a broad-acting auxiliary factor modulating alternative processing and suppressing unproductive processing. The profiling data and methods developed in this study will allow systematic analyses of miRNA regulation.

Variability in porcine microRNA genes and its association with mRNA expression and lipid phenotypes

BACKGROUND

Mature microRNAs (miRNAs) play an important role in repressing the expression of a wide range of mRNAs. The presence of polymorphic sites in miRNA genes and their corresponding 3'UTR binding sites can disrupt canonical conserved miRNA-mRNA pairings, and thus modify gene expression patterns. However, to date such polymorphic sites in miRNA genes and their association with gene expression phenotypes and complex traits are poorly characterized in pigs.

RESULTS

By analyzing whole-genome sequences from 120 pigs and wild boars from Europe and Asia, we identified 285 single nucleotide polymorphisms (SNPs) that map to miRNA loci, and 109,724 SNPs that are located in predicted 7mer-m8 miRNA binding sites within porcine 3'UTR. In porcine miRNA genes, SNP density is reduced compared with their flanking non-miRNA regions. By sequencing the genomes of five Duroc boars, we identified 12 miRNA SNPs that were subsequently genotyped in their offspring (N = 345, Lipgen population). Association analyses of miRNA SNPs with 38 lipid-related traits and hepatic and muscle microarray expression phenotypes recorded in the Lipgen population were performed. The most relevant detected association was between the genotype of the rs319154814 (G/A) SNP located in the apical loop of the ssc-miR-326 hairpin precursor and PPP1CC mRNA levels in the liver (q-value = 0.058). This result was subsequently confirmed by qPCR (P-value = 0.027). The rs319154814 (G/A) genotype was also associated with several fatty acid composition traits.

CONCLUSIONS

Our findings show a reduced variability of porcine miRNA genes, which is consistent with strong purifying selection, particularly in the seed region that plays a critical role in miRNA binding. Although it is generally assumed that SNPs mapping to the seed region are those with the most pronounced consequences on mRNA expression, we show that a SNP mapping to the apical region of ssc-miR-326 is significantly associated with hepatic mRNA levels of the PPP1CC gene, one of its predicted targets. Although experimental confirmation of such an interaction is reported in humans but not in pigs, this result highlights the need to further investigate the functional effects of miRNA polymorphisms that are located outside the seed region on gene expression in pigs.

Bulges control pri-miRNA processing in a position and strand-dependent manner

MicroRNAs (miRNAs) play critical roles in gene expression and numerous human diseases. The success of miRNA biogenesis is largely determined by the primary miRNA (pri-miRNA) processing by the DROSHA-DGCR8 complex, called Microprocessor. Here, we analysed the high-throughput pri-miRNA processing assays and secondary structures of pri-miRNAs to investigate the roles of bulges in the pri-miRNA processing. We found that bulges in multiple places control both the cleavage efficiency and accuracy of pri-miRNA processing. These bulges were shown to act on Microprocessor via its catalytic subunit, DROSHA, and function in a position and strand-dependent manner. Interestingly, we discovered that the enriched and conserved bulges, called midB, can correct DROSHA orientation on pri-miRNAs, thereby enhancing production of miRNAs. The revealed functions of the bulges help improve our understanding of pri-miRNA processing and suggest their potential roles in miRNA biogenesis regulation.

Genetic variability in noncoding RNAs: involvement of miRNAs and long noncoding RNAs in osteoporosis pathogenesis

The pathogenesis of osteoporosis is multifactorial and is the consequence of genetic, hormonal and lifestyle factors. Epigenetics, including noncoding RNA (ncRNA) deregulation, represents a link between susceptibility to develop the disease and environmental influences. The majority of studies investigated the expression of ncRNAs in osteoporosis patients; however, very little information is available on their genetic variability. In this review, we focus on two classes of ncRNAs: miRNAs and long noncoding RNAs (lncRNAs). We summarize recent findings on how polymorphisms in miRNAs and lncRNAs can perturb the lncRNA/miRNA/mRNA axis and may be involved in osteoporosis clinical outcome. We also provide a general overview on databases and bioinformatic tools useful for associating miRNAs and lncRNAs variability with complex genetic diseases.

Human disease-associated single nucleotide polymorphism changes the orientation of DROSHA on pri-mir-146a

The Microprocessor complex of DROSHA and DGCR8 initiates the biosynthesis of microRNAs (miRNAs) by processing primary miRNAs (pri-miRNAs). The Microprocessor can be oriented on pri-miRNAs in opposite directions to generate productive and unproductive cleavages at their basal and apical junctions, respectively. However, only the productive cleavage gives rise to miRNAs. A single nucleotide polymorphism (SNP, rs2910164) in pri-mir-146a is associated with various human diseases. Although this SNP was found to reduce the expression of miRNA, it is still not known if it affects the activity of the Microprocessor directly, and how it functions. In this study, we revealed that the SNP creates an unexpected mGHG motif at the apical junction of pri-mir-146a. This mGHG motif interacts with the double-stranded RNA-binding domain (dsRBD) of DROSHA, switching its orientation on pri-mir-146a from the basal to the apical junction. As a result, the SNP facilitates Microprocessor to cleave SNP-pri-mir-146a at its unproductive sites. Our findings help to elucidate the molecular mechanism that explains how the disease-associated SNP modulates the biogenesis of pri-mir-146a and thereby affects its cellular functions.

Emerging Roles of SRSF3 as a Therapeutic Target for Cancer

Ser/Arg-rich (SR) proteins are RNA-binding proteins known as constitutive and alternative splicing (AS) regulators that regulate multiple aspects of the gene expression program. Ser/Arg-rich splicing factor 3 (SRSF3) is the smallest member of the SR protein family, and its level is controlled by multiple factors and involves complex mechanisms in eukaryote cells, whereas the aberrant expression of SRSF3 is associated with many human diseases, including cancer. Here, we review state-of-the-art research on SRSF3 in terms of its function, expression, and misregulation in human cancers. We emphasize the negative consequences of the overexpression of the SRSF3 oncogene in cancers, the pathways underlying SRSF3-mediated transformation, and implications of potential anticancer drugs by downregulation of SRSF3 expression for cancer therapy. Cumulative research on SRSF3 provides critical insight into its essential part in maintaining cellular processes, offering potential new targets for anti-cancer therapy.

Select amino acids in DGCR8 are essential for the UGU-pri-miRNA interaction and processing

Microprocessor, composed of DROSHA and DGCR8, processes primary microRNAs (pri-miRNAs) in miRNA biogenesis. Its cleavage efficiency and accuracy are enhanced because DGCR8 interacts with the apical UGU motif of pri-miRNAs. However, the mechanism and influence of DGCR8–UGU interaction on cellular miRNA expression are still elusive. In this study, we demonstrated that Rhed (i.e., the RNA-binding heme domain, amino acids 285–478) of DGCR8 interacts with UGU. In addition, we identified three amino acids 461–463 in Rhed, which are critical for the UGU interaction and essential for Microprocessor to accurately and efficiently process UGU-pri-miRNAs in vitro and UGU-miRNA expression in human cells. Furthermore, we found that within the DGCR8 dimer, the amino acids 461–463 from one monomer are capable of discriminating between UGU- and noUGU-pri-miRNAs. Our findings improve the current understanding of the substrate-recognizing mechanism of DGCR8 and implicate the roles of this recognition in differentiating miRNA expression in human cells.

Thi Lieu Dang et al. study the mechanisms for the interaction between DGCR8 and the apical UGU motif of pri-miRNAs. They demonstrate that three amino acids in the Rhed domain of DGCR8 are critical to recognize and interact with UGU and to process pri-miRNAs. They further show amino acids 461–463 in one of the DGCR8 dimer are necessary to distinguish UGU- and noUGU-primiRNAs.

SRSF3: Newly discovered functions and roles in human health and diseases

The serine/arginine rich proteins (SR proteins) are members of a family of RNA binding proteins involved in regulating various features of RNA metabolism, including pre-mRNA constitutive and alternative splicing. In humans, a total of 12 SR splicing factors (SRSFs) namely SRSF1-SRSF12 have been reported. SRSF3, the smallest member of the SR family and the focus of this review, regulates critical steps in mRNA metabolism and has been shown to have mRNA-independent functions as well. Recent studies on SRSF3 have uncovered its role in a wide array of complex biological processes. We have also reviewed the involvement of SRSF3 in disease conditions like cancer, ageing, neurological and cardiac disorders. Finally, we have discussed in detail the autoregulation of SRSF3 and its implications in cancer and commented on the potential of SRSF3 as a therapeutic target, especially in the context of cancer.

MicroRNAs: From Mechanism to Organism

MicroRNAs (miRNAs) are short, regulatory RNAs that act as post-transcriptional repressors of gene expression in diverse biological contexts. The emergence of small RNA-mediated gene silencing preceded the onset of multicellularity and was followed by a drastic expansion of the miRNA repertoire in conjunction with the evolution of complexity in the plant and animal kingdoms. Along this process, miRNAs became an essential feature of animal development, as no higher metazoan lineage tolerated loss of miRNAs or their associated protein machinery. In fact, ablation of the miRNA biogenesis machinery or the effector silencing factors results in severe embryogenesis defects in every animal studied. In this review, we summarize recent mechanistic insight into miRNA biogenesis and function, while emphasizing features that have enabled multicellular organisms to harness the potential of this broad class of repressors. We first discuss how different mechanisms of regulation of miRNA biogenesis are used, not only to generate spatio-temporal specificity of miRNA production within an animal, but also to achieve the necessary levels and dynamics of expression. We then explore how evolution of the mechanism for small RNA-mediated repression resulted in a diversity of silencing complexes that cause different molecular effects on their targets. Multicellular organisms have taken advantage of this variability in the outcome of miRNA-mediated repression, with differential use in particular cell types or even distinct subcellular compartments. Finally, we present an overview of how the animal miRNA repertoire has evolved and diversified, emphasizing the emergence of miRNA families and the biological implications of miRNA sequence diversification. Overall, focusing on selected animal models and through the lens of evolution, we highlight canonical mechanisms in miRNA biology and their variations, providing updated insight that will ultimately help us understand the contribution of miRNAs to the development and physiology of multicellular organisms.

Significant Association between Microrna Gene Polymorphisms and Type 2 Diabetes Mellitus Susceptibility in Asian Population: A Meta-Analysis

BACKGROUND

The gene polymorphisms in microRNA might relate to susceptibility of type 2 diabetes mellitus (T2DM). However, the results of existing studies were inconsistent and obscure. To investigate the precise associations between microRNA gene polymorphisms and T2DM risk, the present meta-analysis was performed.

METHODS

The literatures were searched from four electronic databases, PubMed, Embase, CNKI and Wan-fang. Subsequently, odds ratios (ORs) and the corresponding 95% confidence intervals (CIs) were both used to evaluate the associations between two single nucleotide polymorphisms (SNPs) (microRNA146a rs2910164 (G>C), microRNA124a rs531564 (C>G)) and risk of T2DM in Asian population.

RESULTS

Totally, there were 4 studies included in our present analysis in the language of English and Chinese. There were partly significant associations between susceptibility of T2DM and SNPs (microRNA146a rs2910164 (G>C), microRNA124a rs531564 (C>G)). The G allele in microRNA146a rs2910164 (G>C) and C allele in microRNA124a rs531564 (C>G) both presented remarkably reduced risk of T2DM when compared with the healthy population.

CONCLUSION

The microRNA146a rs2910164 (G allele) and microRNA124a rs531564 (C allele) might function as protective factors in the pathogenetic process of T2DM in Asian population.

Mismatched and wobble base pairs govern primary microRNA processing by human Microprocessor

MicroRNAs (miRNAs) are small RNAs that regulate gene expression. miRNAs are produced from primary miRNAs (pri-miRNAs), which are cleaved by Microprocessor. Microprocessor, therefore, plays a crucial role in determining the efficiency and precision of miRNA production, and thus the function of the final miRNA product. Here, we conducted high-throughput enzymatic assays to investigate the catalytic mechanism of Microprocessor cleaving randomized pri-miRNAs. We identified multiple mismatches and wobble base pairs in the upper stem of pri-miRNAs, which influence the efficiency and accuracy of their processing. The existence of these RNA elements helps to explain the alternative cleavage of Microprocessor for some human pri-miRNAs. We also demonstrated that miRNA biogenesis can be altered via modification of the RNA elements by RNA-editing events or single nucleotide polymorphisms (SNPs). These findings improve our understanding of pri-miRNA processing mechanisms and provide a foundation for interpreting differential miRNA expression due to RNA modifications and SNPs.

MicroRNA genes are transcribed to long primary transcripts called primary microRNAs, which are cleaved by Microprocessor. Here the authors employ high-throughput sequencing and Microprocessor assay to show that mismatches and wobble base pairs in primary microRNAs affect the accuracy and efficiency of Microprocessor processing.

The internal loops in the lower stem of primary microRNA transcripts facilitate single cleavage of human Microprocessor

The human Microprocessor complex cleaves primary microRNA (miRNA) transcripts (pri-miRNAs) to initiate miRNA synthesis. Microprocessor consists of DROSHA (an RNase III enzyme), and DGCR8. DROSHA contains two RNase III domains, RIIIDa and RIIIDb, which simultaneously cleave the 3p- and 5p-strands of pri-miRNAs, respectively. In this study, we show that the internal loop located in the lower stem of numerous pri-miRNAs selectively inhibits the cleavage of Microprocessor on their 3p-strand, thereby, facilitating the single cleavage on their 5p-strand. This single cleavage does not lead to the production of miRNA but instead, it downregulates miRNA expression. We also demonstrate that by manipulating the size of the internal loop in the lower stem of pri-miRNAs, we can alter the ratio of single-cut to double-cut products resulted from the catalysis of Microprocessor, thus changing miRNA production in the in vitro pri-miRNA processing assays and in human cells. Therefore, the oscillating level of the single cleavage suggests another way of regulation of miRNA expression and offers an alternative approach to miRNA knockdown.

Association of microRNA-27a rs895819 polymorphism with the risk of cancer: An updated meta-analysis

BACKGROUND

MiR-27a rs895819 polymorphism is considered as a tumor- related susceptibility gene. Previous meta-analyses evaluated the association the association between miR-27a rs895819 and cancer risk, but the results were inconsistent. The present meta-analysis was carried out to better estimate the correlation of rs895819 and cancer susceptibility.

METHODS

We searched several databases to identify relevant studies, including PubMed, EMBASE and the Cochrane Controlled Trials Register. The odds ratios (ORs) with 95% confidence intervals (CIs) were used to estimate the association between miR-27a rs895819 and cancer risk.

RESULTS

The overall analysis showed the miR-27a rs895819 was not associated with cancer susceptibility in all models (dominant model: OR = 1.02, 95% CI:0.94-1.10, p = 0.632; recessive model: OR = 1.05, 95% CI: 0.92-1.76, p = 0.474; homozygote model: OR = 1.06, 95% CI: 0.91-1.23, p = 0.439; heterozygote model: OR = 1.00, 95% CI: 0.93-1.08, p = 0.934; and allele model: OR = 1.02, 95% CI: 0.96-1.09, p = 0.486). Interestingly, rs895819 A > G was significantly associated with colorectal cancer risk in recessive model (OR = 1.54, 95% CI: 1.29-1.83, p < 0.001), homozygote model (OR = 1.59, 95% CI: 1.31-1.92, p < 0.001), and allele model (OR = 1.22, 95% CI: 1.10-1.34, p < 0.001). In addition, rs895819 polymorphism was correlated with increased risk of breast cancer in the recessive model (OR = 0.81, 95% CI: 0.66-1.00, p = 0.046) and allele model (OR = 0.89, 95% CI: 0.80-0.98, p = 0.021).

CONCLUSIONS

Our results suggested that rs895819 polymorphism was correlated with increased risk of colorectal cancer and breast cancer, but not all types of cancer.

Inhibition of Microprocessor Function during the Activation of the Type I Interferon Response

Type I interferons (IFNs) are central components of the antiviral response. Most cell types respond to viral infections by secreting IFNs, but the mechanisms that regulate correct expression of these cytokines are not completely understood. Here, we show that activation of the type I IFN response regulates the expression of miRNAs in a post-transcriptional manner. Activation of IFN expression alters the binding of the Microprocessor complex to pri-miRNAs, reducing its processing rate and thus leading to decreased levels of a subset of mature miRNAs in an IRF3-dependent manner. The rescue of Microprocessor function during the antiviral response downregulates the levels of IFN-β and IFN-stimulated genes. All these findings support a model by which the inhibition of Microprocessor activity is an essential step to induce a robust type I IFN response in mammalian cells.

Degradation of splicing factor SRSF3 contributes to progressive liver disease

Serine rich splicing factor 3 (SRSF3) plays a critical role in liver function and its loss promotes chronic liver damage and regeneration. As a consequence, genetic deletion of SRSF3 in hepatocytes caused progressive liver disease and ultimately led to hepatocellular carcinoma. Here we show that SRSF3 is decreased in human liver samples with non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), or cirrhosis that was associated with alterations in RNA splicing of known SRSF3 target genes. Hepatic SRSF3 expression was similarly decreased and RNA splicing dysregulated in mouse models of NAFLD and NASH. We showed that palmitic acid-induced oxidative stress caused conjugation of the ubiquitin like NEDD8 protein to SRSF3 and proteasome mediated degradation. SRSF3 was selectively neddylated at lysine11 and mutation of this residue (SRSF3-K11R) was sufficient to prevent both SRSF3 degradation and alterations in RNA splicing. Finally prevention of SRSF3 degradation in vivo partially protected mice from hepatic steatosis, fibrosis and inflammation. These results highlight a neddylation-dependent mechanism regulating gene expression in the liver that is disrupted in early metabolic liver disease and may contribute to the progression to NASH, cirrhosis and ultimately hepatocellular carcinoma.

Functional polymorphism within miR-23a∼27a∼24-2 cluster confers clinical outcome of breast cancer in Pakistani cohort

AIM

MicroRNAs (miRNAs) are small regulatory RNA molecules that control gene activity by base pairing with target messenger RNA leading to their cleavage or translational repression. Previous studies show an involvement of miRNAs in various diseases including cancer. Members of the Mir-23a cluster (MIR23A, MIR24-2 and MIR27A) are involved in breast cancer (BC).

METHODS

In the present study, miR-23a/24-2/27a cluster was screened for genetic mutation in BC patients.

RESULTS

Heterozygous (A/G allele) as well as homozygous (G/G allele) variants were found in mir-27a gene in screened BC patients. RNA structural analysis revealed that the single nucleotide polymorphism (SNP) effects the size of the terminal loop in the precursor miRNA (pre-miRNA).

CONCLUSION

The altered (G allele) hairpin structure observed was two bases longer than the reference (A allele) hairpin.

Post-transcriptional control of miRNA biogenesis

MicroRNAs (miRNAs) are important regulators of gene expression that bind complementary target mRNAs and repress their expression. Precursor miRNA molecules undergo nuclear and cytoplasmic processing events, carried out by the endoribonucleases DROSHA and DICER, respectively, to produce mature miRNAs that are loaded onto the RISC (RNA-induced silencing complex) to exert their biological function. Regulation of mature miRNA levels is critical in development, differentiation, and disease, as demonstrated by multiple levels of control during their biogenesis cascade. Here, we will focus on post-transcriptional mechanisms and will discuss the impact of cis-acting sequences in precursor miRNAs, as well as trans-acting factors that bind to these precursors and influence their processing. In particular, we will highlight the role of general RNA-binding proteins (RBPs) as factors that control the processing of specific miRNAs, revealing a complex layer of regulation in miRNA production and function.

miRNAmotif-A Tool for the Prediction of Pre-miRNA⁻Protein Interactions

MicroRNAs (miRNAs) are short, non-coding post-transcriptional gene regulators. In mammalian cells, mature miRNAs are produced from primary precursors (pri-miRNAs) using canonical protein machinery, which includes Drosha/DGCR8 and Dicer, or the non-canonical mirtron pathway. In plant cells, mature miRNAs are excised from pri-miRNAs by the DICER-LIKE1 (DCL1) protein complex. The involvement of multiple regulatory proteins that bind directly to distinct miRNA precursors in a sequence- or structure-dependent manner adds to the complexity of the miRNA maturation process. Here, we present a web server that enables searches for miRNA precursors that can be recognized by diverse RNA-binding proteins based on known sequence motifs to facilitate the identification of other proteins involved in miRNA biogenesis. The database used by the web server contains known human, murine, and Arabidopsis thaliana pre-miRNAs. The web server can also be used to predict new RNA-binding protein motifs based on a list of user-provided sequences. We show examples of miRNAmotif applications, presenting precursors that contain motifs recognized by Lin28, MCPIP1, and DGCR8 and predicting motifs within pre-miRNA precursors that are recognized by two DEAD-box helicases—DDX1 and DDX17. miRNAmotif is released as an open-source software under the MIT License. The code is available at GitHub (www.github.com/martynaut/mirnamotif). The webserver is freely available at http://mirnamotif.ibch.poznan.pl.

MicroRNA-150 down Regulation in Acute Myeloid Leukaemia Patients and Its Prognostic Implication

BACKGROUND

MicroRNAs (miRNAs) are small, non-coding RNAs that are important for post-transcriptional gene regulation in both healthy and morbid conditions. Numerous miRNAs promote tumorigenesis, while others have a tumour suppressive effects. Acute myeloid leukaemia (AML) is a heterogeneous group of genetically diverse hematopoietic malignancies with variable response to treatment.

AIM

Our study aimed to investigate the possible role of miR-150 in de novo adult AML and the impact of its level on survival, and we used in the silicon analysis to predict the main target genes involved in miR-150 mediated cancer pathway.

MATERIAL AND METHODS

We evaluated miR-150 expression profiling assay using TaqMan primer probes RT-PCR in the plasma of 50 adult AML patients, before the start of treatment and at day 28 of treatment, along with 20 normal adult control samples. miR-16 was used as an endogenous reference for standardisation. Follow-up of patients during treatment at day 28 of induction chemotherapy and after one year was done.

RESULTS

In this study, we found a significantly lower level of miR-150 in AML patients when compared to controls (p = 0.005) with 0.62 fold change than in healthy controls. Patients were divided into two groups: the low miR-150 group (miR-150 < 1) and the high miR-150 group (miR-150 > 1). A statistically significant difference was found between the two groups regarding initial total leukocytic count and initial PB blast count while for the TLC, HB and PLT count at follow up. No difference in the overall survival between the low and the high miR-150 groups could be demonstrated.

CONCLUSION

Our results suggest that miR-150 functions as a tumour suppressor and gatekeeper in inhibiting cell transformation and that its downregulation is required for leukemogenesis.

Long Non-coding RNA Structure and Function: Is There a Link?

RNA has emerged as the prime target for diagnostics, therapeutics and the development of personalized medicine. In particular, the non-coding RNAs (ncRNAs) that do not encode proteins, display remarkable biochemical versatility. They can fold into complex structures and interact with proteins, DNA and other RNAs, modulating the activity, DNA targets or partners of multiprotein complexes. Thus, ncRNAs confer regulatory plasticity and represent a new layer of epigenetic control that is dysregulated in disease. Intriguingly, for long non-coding RNAs (lncRNAs, >200 nucleotides length) structural conservation rather than nucleotide sequence conservation seems to be crucial for maintaining their function. LncRNAs tend to acquire complex secondary and tertiary structures and their functions only impose very subtle sequence constraints. In the present review we will discuss the biochemical assays that can be employed to determine the lncRNA structural configurations. The implications and challenges of linking function and lncRNA structure to design novel RNA therapeutic approaches will also be analyzed.

Identification of key genes in cleft lip with or without cleft palate regulated by miR-199a-5p

BACKGROUND

Cleft lip with or without cleft palate (CL/P) is one of the most common congenital defects, which etiology involves both genetic and environmental factors. Previous studies have shown that miR-199a-5p may mediate the occurrence of CL/P. However, the key target genes regulated by miR-199a-5p are not clear. In this study, we employed a systematic bioinformatics analysis of target genes regulated by miR-199a-5p which may be involved in CL/P.

METHODS

The miRBase, Human miRNA tissue atlas, miRecords, miRpathDB, miRWalk, miRTarBase, DIANA-TarBase (v7.0), Literature search, DAVID software, Cytoscape plugin ClueGO + Cluepedia app, MalaCards, TargetScanhuman7.1, Venny 2.1, STRING and GEO databases were comprehensive employed to identify the key genes regulated by miR-199a-5p associated with CL/P.

RESULTS

Total 429 experimentally validated target genes were obtained from five miRNAs related databases. Expressions of miR-199a-5p and its experimentally validated target genes were elevated in bone, brain and skin. KEGG pathway analysis revealed that the target genes were enriched in focal adhesion, microRNAs in cancer and hippo signaling pathway. Biological process categorization revealed that significant portions of the target genes were grouped as transcription, DNA-templated. Total eight intersection genes were identified by using MalaCards and TargetScanhuman7.1. The target gene transforming growth factor alpha (TGFA) of miR-199a-5p involved in CL/P is screened and verified.

CONCLUSION

MiR-199a-5p may mediate CL/P by regulating key target gene TGFA. The study may contribute to a better understanding of the etiology of CL/P.

SRSF3 recruits DROSHA to the basal junction of primary microRNAs

The Microprocessor complex, consisting of an RNase III DROSHA and the DGCR8 dimer, cleaves primary microRNA transcripts (pri-miRNAs) to initiate microRNA (miRNA) maturation. Pri-miRNAs are stem-loop RNAs, and ∼79% of them contain at least one of the three major and conserved RNA motifs, UG, UGU, and CNNC. We recently demonstrated that the basal UG and apical UGU motifs of pri-miRNAs interact with DROSHA and DGCR8, respectively. They help orient Microprocessor on pri-miRNA in a proper direction in which DROSHA and DGCR8 localize to the basal and apical pri-miRNA junctions, respectively. In addition, CNNC, located at ∼17 nucleotides (nt) from the Microprocessor cleavage site, interacts with SRSF3 (SRp20) to stimulate Microprocessor to process pri-miRNAs. The mechanism underlying this stimulation, however, is unknown. In this study, we discovered that SRSF3 recruits DROSHA to the basal junction in a CNNC-dependent manner, thereby enhancing Microprocessor activity. Furthermore, by generating various pri-miRNA substrates containing CNNC at different locations, we demonstrated that such stimulation only occurs when CNNC is located at ∼17 nt from the Microprocessor cleavage site. Our findings reveal the molecular mechanism of SRSF3 in pri-miRNA processing and support the previously proposed explanation for the highly conserved position of CNNC in SRSF3-enhanced pri-miRNA processing.

Structural basis for terminal loop recognition and stimulation of pri-miRNA-18a processing by hnRNP A1

Post-transcriptional mechanisms play a predominant role in the control of microRNA (miRNA) production. Recognition of the terminal loop of precursor miRNAs by RNA-binding proteins (RBPs) influences their processing; however, the mechanistic basis for how levels of individual or subsets of miRNAs are regulated is mostly unexplored. We previously showed that hnRNP A1, an RBP implicated in many aspects of RNA processing, acts as an auxiliary factor that promotes the Microprocessor-mediated processing of pri-mir-18a. Here, by using an integrative structural biology approach, we show that hnRNP A1 forms a 1:1 complex with pri-mir-18a where both RNA recognition motifs (RRMs) bind to cognate RNA sequence motifs in the terminal loop of pri-mir-18a. Terminal loop binding induces an allosteric destabilization of base-pairing in the pri-mir-18a stem that promotes its downstream processing. Our results highlight terminal loop RNA recognition by RBPs as a potential general principle of miRNA biogenesis and regulation.

hnRNP A1 is an auxiliary factor that promotes the Microprocessor-mediated processing of pri-mir-18a, of the oncomiR-1 cluster. Here the authors employ an integrative structural biology approach and provide insights into the molecular mechanism of how hnRNP A1 facilitates pri-mir-18a biogenesis.

Polymorphism studies on microRNA targetome of thalassemia

Thalassemia is one of the most prevalent hemoglobin disorders. It is caused by the decreased or absent synthesis of one globin chain that leads to moderate to severe hemolytic anemia in clinical complications. Some genetic factors cause these phenotypic variations by the alteration of gene expression. MicroRNAs (miRNAs) are post-transcriptional regulators in gene expression. Therefore, variations in 3'-untranslated region (3'-UTR) of target genes may affect gene expression. It is of interest to evaluate the impact of noncoding SNPs in thalassemia related genes on miRNA: mRNA interactions in the severity of thalassemia. Polymorphisms that alter miRNA: mRNA interactions were predicted using PolymiRTS and Mirsnpscore tools. Then, the effect of predicted target SNPs on thermodynamic stability, local RNA structure and regulatory elements was investigated using RNAhybrid, RNAsnp and RegulomeDB, respectively. The molecular functions and the Biological process of candidate genes were extracted and interaction network was created. Forty-six SNPs were predicted to affect 188 miRNA interactions. These results suggest that 3'-UTR SNP may affect gene expression and cause phenotypic variation in thalassemia patients.