Catalog of microRNA seed polymorphisms in vertebrates

Evaluating Single-Nucleotide Variants in MicroRNA Targeting Sites and Mature MicroRNA In Vitro Cell Culture by Luciferase Reporter Gene Assays

MicroRNAs (miRs) are small non-coding RNAs of 21-24 nucleotides in length that modulate gene expression by targeting the untranslated region (UTR) of mRNA. Single-nucleotide variants (SNVs) in primary miRs (pri-miRs), precursor miRs (pre-miRs), promoters of pri-miRs, and seed regions can affect miR stability or processing, may influence mature miR expression, and can affect target gene identification, respectively. The present protocol tests the binding and activity of miRs on 3'-UTR target sequences based on the expression of luciferase as a reporter gene fused to the UTR sequence in the presence of plasmids containing pre-miR of interest to test in vitro cell culture assay.

Challenging Cellular Homeostasis: Spatial and Temporal Regulation of miRNAs

Mature microRNAs (miRNAs) are single-stranded non-coding RNA (ncRNA) molecules that act in post-transcriptional regulation in animals and plants. A mature miRNA is the end product of consecutive, highly regulated processing steps of the primary miRNA transcript. Following base-paring of the mature miRNA with its mRNA target, translation is inhibited, and the targeted mRNA is degraded. There are hundreds of miRNAs in each cell that work together to regulate cellular key processes, including development, differentiation, cell cycle, apoptosis, inflammation, viral infection, and more. In this review, we present an overlooked layer of cellular regulation that addresses cell dynamics affecting miRNA accessibility. We discuss the regulation of miRNA local storage and translocation among cell compartments. The local amounts of the miRNAs and their targets dictate their actual availability, which determines the ability to fine-tune cell responses to abrupt or chronic changes. We emphasize that changes in miRNA storage and compactization occur under induced stress and changing conditions. Furthermore, we demonstrate shared principles on cell physiology, governed by miRNA under oxidative stress, tumorigenesis, viral infection, or synaptic plasticity. The evidence presented in this review article highlights the importance of spatial and temporal miRNA regulation for cell physiology. We argue that limiting the research to mature miRNAs within the cytosol undermines our understanding of the efficacy of miRNAs to regulate cell fate under stress conditions.

MicroRNAs in Genetic Etiology of Human Diseases

Since their first discovery more than 20 years ago, miRNAs have been subject to deliberate research and analysis for revealing their physiological or pathological involvement. Regulatory roles of miRNAs in signal transduction, gene expression, and cellular processes in development, differentiation, proliferation, apoptosis, and homeostasis also imply their critical role in disease pathogenesis. Their roles in cancer, neurodegenerative diseases, and other systemic diseases have been studied broadly. In these regulatory pathways, their mutations and target sequence variations play critical roles to determine their functional repertoire. In this chapter, we summarize studies that investigated the role of mutations, polymorphisms, and other variations of miRNAs in respect to pathological processes.

DISE/6mer seed toxicity-a powerful anti-cancer mechanism with implications for other diseases

micro(mi)RNAs are short noncoding RNAs that through their seed sequence (pos. 2-7/8 of the guide strand) regulate cell function by targeting complementary sequences (seed matches) located mostly in the 3' untranslated region (3' UTR) of mRNAs. Any short RNA that enters the RNA induced silencing complex (RISC) can kill cells through miRNA-like RNA interference when its 6mer seed sequence (pos. 2-7 of the guide strand) has a G-rich nucleotide composition. G-rich seeds mediate 6mer Seed Toxicity by targeting C-rich seed matches in the 3' UTR of genes critical for cell survival. The resulting Death Induced by Survival gene Elimination (DISE) predominantly affects cancer cells but may contribute to cell death in other disease contexts. This review summarizes recent findings on the role of DISE/6mer Seed Tox in cancer; its therapeutic potential; its contribution to therapy resistance; its selectivity, and why normal cells are protected. In addition, we explore the connection between 6mer Seed Toxicity and aging in relation to cancer and certain neurodegenerative diseases.

Evaluating the beneficial effects of dietary restrictions: A framework for precision nutrigeroscience

Dietary restriction (DR) has long been viewed as the most robust nongenetic means to extend lifespan and healthspan. Many aging-associated mechanisms are nutrient responsive, but despite the ubiquitous functions of these pathways, the benefits of DR often vary among individuals and even among tissues within an individual, challenging the aging research field. Furthermore, it is often assumed that lifespan interventions like DR will also extend healthspan, which is thus often ignored in aging studies. In this review, we provide an overview of DR as an intervention and discuss the mechanisms by which it affects lifespan and various healthspan measures. We also review studies that demonstrate exceptions to the standing paradigm of DR being beneficial, thus raising new questions that future studies must address. We detail critical factors for the proposed field of precision nutrigeroscience, which would utilize individualized treatments and predict outcomes using biomarkers based on genotype, sex, tissue, and age.

Application of the targeted sequencing approach reveals the single nucleotide polymorphism (SNP) repertoire in microRNA genes in the pig genome

MicroRNAs (miRNAs) are recognized as gene expression regulators, indirectly orchestrating a plethora of biological processes. Single nucleotide polymorphism (SNP), one of the most common genetic variations in the genome, is established to affect miRNA functioning and influence complex traits and diseases. SNPs in miRNAs have also been associated with important production traits in livestock. Thus, the aim of our study was to reveal the SNP variability of miRNA genes in the genome of the pig, which is a significant farm animal and large-mammal human model. To this end, we applied the targeted sequencing approach, enabling deep sequencing of specified genomic regions. As a result, 73 SNPs localized in 50 distinct pre-miRNAs were identified. In silico analysis revealed that many of the identified SNPs influenced the structure and energy of the hairpin precursors. Moreover, SNPs localized in the seed regions were shown to alter targeted genes and, as a result, enrich different biological pathways. The obtained results corroborate a significant impact of SNPs on the miRNA processing and broaden the state of knowledge in the field of animal genomics. We also report the targeted sequencing approach to be a promising alternative for the whole genome sequencing in miRNA genes focused studies.

MicroRNAs Regulating Autophagy in Neurodegeneration

Social and economic impacts of neurodegenerative diseases (NDs) become more prominent in our constantly aging population. Currently, due to the lack of knowledge about the aetiology of most NDs, only symptomatic treatment is available for patients. Hence, researchers and clinicians are in need of solid studies on pathological mechanisms of NDs. Autophagy promotes degradation of pathogenic proteins in NDs, while microRNAs post-transcriptionally regulate multiple signalling networks including autophagy. This chapter will critically discuss current research advancements in the area of microRNAs regulating autophagy in NDs. Moreover, we will introduce basic strategies and techniques used in microRNA research. Delineation of the mechanisms contributing to NDs will result in development of better approaches for their early diagnosis and effective treatment.

miR-499 rs3746444 and miR-196a-2 rs11614913 Are Associated with the Risk of Glioma, but Not the Prognosis

Previous studies of correlations of microRNA (miR)-499 rs3746444 and miR-196a-2 rs11614913 polymorphisms with glioma risk have yielded inconsistent results. In this study, relationships between these two polymorphisms and glioma risk and survival were evaluated. In total, 605 patients and 1,300 controls were genotyped. rs3746444 increased glioma risk in five genetic models (GA versus AA, odds ratio [OR], 95% confidence interval [CI] = 1.31 [1.05–1.66], p = 0.02; GG versus AA, OR [95% CI] = 10.70 [6.13–18.69], p < 0.0001; GA + GG versus AA, OR [95% CI] = 1.82 [1.47–2.24], p < 0.0001; GG versus AA + GA, OR [95% CI] = 9.99 [5.74–17.40], p < 0.0001; G versus A, OR [95% CI] = 2.18 [1.82–2.60], p < 0.0001). rs11614913 decreased glioma risk in a recessive model (OR [95% CI] = 0.79 [0.64–0.97], p = 0.03). No relationships between either SNP and survival were found. rs3746444 in the miR-499 seed region could affect target recognition. Bioinformatics analyses indicated that miR-499 rs3746444 is involved in various biological processes and pathways, including “cell adhesion molecule binding,” “positive regulation of catabolic process,” “NF-kappa B pathway,” and “PI3K-Akt pathway,” by targeting mRNAs. Our results suggested that miR-499 rs3746444 and miR-196a-2 rs11614913 have crucial roles in glioma susceptibility.

MicroRNA-224 (rs188519172 A>G) Gene Variability is Associated with a Decreased Susceptibility to Coronary Artery Disease: A Case-Control Study

AIM

The microRNAs regulate the expression of multiple genes involved in diseases such as cancer, diabetes and cardiovascular disease. In this study, we have investigated the association between the miR-224 gene polymorphism (rs188519172A>G) and susceptibility of coronary artery disease CAD.

METHODOLOGY

Hundred CAD patients and 100-matched healthy control were included. Genotyping of the miR-224 (rs188519172A>G) polymorphism was performed using Amplification refractory mutation system PCR method (ARMS-PCR).

RESULTS

A significant difference was observed in the genotype distribution among CAD patients and healthy controls (P=0.018). The frequencies of all three genotypes GG, GA, AA reported in the patient's samples were 33%, 66% and 01%, and in the healthy controls samples, were 16%, 82% and 2% respectively. A multivariate analysis based on logistic regression was conducted for each group to estimate the association between miR-224 rs188519172 genotypes and risk to coronary artery disease. Results show that the miR-224 (rs188519172 A>G) polymorphism was associated with a decreased risk to CAD in a codominant model, GA genotype vs. GG (OR = 0.39 (95 % CI, 0.19-0.76), RR 0.58 (0.38-0.90, P=0.006). In the dominant model, (GA+AA vs. GG), there was also a significant association with the OR=0.38 (95 % CI (0.19-0.76), RR 0.58 (0.38-0.89), and P=0.006. Whereas, in the recessive model, (GG+GA vs. AA), there was no significant association of CAD with OR=0.49 (95% CI (0.044-5.54), RR 0.74 (0.33-1.68), and P=0.48.

CONCLUSION

Our findings indicated that miR-224 (rs188519172) GA genotype is associated with a decreased susceptibility to CAD.

Genome-Wide Analysis of MicroRNA-related Single Nucleotide Polymorphisms (SNPs) in Mouse Genome

MicroRNAs are widely referred to as gene expression regulators for different diseases. The integration between single nucleotide polymorphisms (SNPs) and miRNAs has been associated with both human and animal diseases. In order to gain new insights on the effects of SNPs on miRNA and their related sequences, we steadily characterized a whole mouse genome miRNA related SNPs, analyzed their effects on the miRNA structural stability and target alteration. In this study, we collected 73643859 SNPs across the mouse genome, analyzed 1187 pre-miRNAs and 2027 mature miRNAs. Upon mapping the SNPs, 1700 of them were identified in 702 pre-miRNAs and 609 SNPs in mature miRNAs. We also discovered that SNP densities of the pre-miRNA and mature miRNAs are lower than the adjacent flanking regions. Also the flanking regions far away from miRNAs appeared to have higher SNP density. In addition, we also found that transitions were more frequent than transversions in miRNAs. Notably, 841 SNPs could change their corresponding miRNA's secondary structure from stable to unstable. We also performed target gain and loss analysis of 163 miRNAs and our results showed that few miRNAs remained unchanged and many miRNAs from wild mice gained target site. These results outline the first case of SNP variations in the mouse whole genome scale. Those miRNAs with changes in structure or target could be of interest for further studies.

MSDD: a manually curated database of experimentally supported associations among miRNAs, SNPs and human diseases

The MiRNA SNP Disease Database (MSDD, http://www.bio-bigdata.com/msdd/) is a manually curated database that provides comprehensive experimentally supported associations among microRNAs (miRNAs), single nucleotide polymorphisms (SNPs) and human diseases. SNPs in miRNA-related functional regions such as mature miRNAs, promoter regions, pri-miRNAs, pre-miRNAs and target gene 3′-UTRs, collectively called ‘miRSNPs’, represent a novel category of functional molecules. miRSNPs can lead to miRNA and its target gene dysregulation, and resulting in susceptibility to or onset of human diseases. A curated collection and summary of miRSNP-associated diseases is essential for a thorough understanding of the mechanisms and functions of miRSNPs. Here, we describe MSDD, which currently documents 525 associations among 182 human miRNAs, 197 SNPs, 153 genes and 164 human diseases through a review of more than 2000 published papers. Each association incorporates information on the miRNAs, SNPs, miRNA target genes and disease names, SNP locations and alleles, the miRNA dysfunctional pattern, experimental techniques, a brief functional description, the original reference and additional annotation. MSDD provides a user-friendly interface to conveniently browse, retrieve, download and submit novel data. MSDD will significantly improve our understanding of miRNA dysfunction in disease, and thus, MSDD has the potential to serve as a timely and valuable resource.

Computational Resources for Prediction and Analysis of Functional miRNA and Their Targetome

microRNAs are evolutionarily conserved, endogenously produced, noncoding RNAs (ncRNAs) of approximately 19-24 nucleotides (nts) in length known to exhibit gene silencing of complementary target sequence. Their deregulated expression is reported in various disease conditions and thus has therapeutic implications. In the last decade, various computational resources are published in this field. In this chapter, we have reviewed bioinformatics resources, i.e., miRNA-centered databases, algorithms, and tools to predict miRNA targets. First section has enlisted more than 75 databases, which mainly covers information regarding miRNA registries, targets, disease associations, differential expression, interactions with other noncoding RNAs, and all-in-one resources. In the algorithms section, we have compiled about 140 algorithms from eight subcategories, viz. for the prediction of precursor (pre-) and mature miRNAs. These algorithms are developed on various sequence, structure, and thermodynamic based features incorporated into different machine learning techniques (MLTs). In addition, computational identification of miRNAs from high-throughput next generation sequencing (NGS) data and their variants, viz. isomiRs, differential expression, miR-SNPs, and functional annotation, are discussed. Prediction and analysis of miRNAs and their associated targets are also evaluated under miR-targets section providing knowledge regarding novel miRNA targets and complex host-pathogen interactions. In conclusion, we have provided comprehensive review of in silico resources published in miRNA research to help scientific community be updated and choose the appropriate tool according to their needs.

Target gene identification and functional characterization of miR-1704 in chicken

MiRNAs are small non-coding RNAs that negatively regulate gene expression at the post-transcriptional level. SNPs in miRNA genes may lead to phenotypic variation by altering miRNA expression and their targets. In this study, miR-1704 expression profiles in nine tissues at 1 d, 6 weeks and 16 weeks old Gushi chickens were detected. MiR-1704 was widely expressed in the detection of tissues. The expression in 1 d and 6 weeks old was low abundance, while its expression at 16 weeks was very high. An rs14668705 (C > G) SNP was detected within the pre-miR-1704 in an F₂ resource population of Gushi chicken crossed with Anka broiler. Bioinformatic analysis indicated that the C > G mutation could introduce a base-pair mismatch and cause the change of free energy. Experiments further revealed that the rs14668705 in precursor miR-1704 could significantly affect mature miR-1704 biogenesis and was significantly associated with body weight at the age of 0, 6, 8, 10, and 12 weeks, shank circumference at 4, 8, and 12 weeks, carcass weight, and semi-evisceration weight (p < 0.05). Insulin receptor 2 (IRS2) gene, one of the potential targets of miR-1704 was identified and further confirmed. These data suggested that miR-1704 targeted IRS2 and have an effect on body weight in chicken.

Variants in vincristine pharmacodynamic genes involved in neurotoxicity at induction phase in the therapy of pediatric acute lymphoblastic leukemia

Vincristine is an important drug of acute lymphoblastic leukemia (ALL) treatment protocols that can cause neurotoxicity. Patients treated with LAL/SHOP protocols often suffer from vincristine-related neurotoxicity in early phases of treatment. A genetic variant in CEP72, a gene involved in vincristine pharmacodynamics, was recently associated with neurotoxicity after prolonged vincristine treatment. This association was not replicated in our Spanish population during induction phase. To test the possibility that other variants in genes involved in vincristine pharmacodynamics were associated with vincristine neuropathy in early phases of the treatment, we evaluated the correlation with toxicity of 24 polymorphisms in 9 key genes in a large cohort of 152 Spanish children with B-ALL homogeneously treated. Results showed no association between any genetic variant in the TUBB1, TUBB2A, TUBB2B, TUBB3, TUBB4, MAPT, MIR146a, MIR202, and MIR411 genes and vincristine-related neurotoxicity. These results are in line with the hypothesis that there are different mechanisms causing pheripheral neurotoxicity after prolonged and short-term vincristine treatments.

Noncoding RNAs Databases: Current Status and Trends

One of the most important resources for researchers of noncoding RNAs is the information available in public databases spread over the internet. However, the effective exploration of this data can represent a daunting task, given the large amount of databases available and the variety of stored data. This chapter describes a classification of databases based on information source, type of RNA, source organisms, data formats, and the mechanisms for information retrieval, detailing the relevance of each of these classifications and its usability by researchers. This classification is used to update a 2012 review, indexing now more than 229 public databases. This review will include an assessment of the new trends for ncRNA research based on the information that is being offered by the databases. Additionally, we will expand the previous analysis focusing on the usability and application of these databases in pathogen and disease research. Finally, this chapter will analyze how currently available database schemas can help the development of new and improved web resources.

Functional miRNA variants affect lung cancer susceptibility and platinum-based chemotherapy response

Background

Platinum-based chemotherapy is widely used as the first-line treatment of lung cancer. MicroRNAs have an important role in lung carcinogenesis and progression. Single-nucleotide polymorphisms (SNPs) in miRNA involved in miRNA biogenesis and structural alteration may affect miRNA expression. In this study, we aimed to investigate the association of functional miRNA variants with the lung cancer susceptibility and platinum-based chemotherapy response.

Methods

Nine genetic polymorphisms in miR-605, 146a, 149, 196a-2, 27a, 499, 30c-1, 5197 and let-7a-2 were selected with comprehensive collection strategy and genotyped by MALDI-TOF mass spectrometry in a total of 215 health control and 507 lung cancer patients (386 patients received at least two consecutive cycles of platinum-based chemotherapy).

Results

We found that an allele carriers of miR-146a rs2910164 (P=0.022, OR=1.315) and C allele carriers of miR-149 rs71428439 (P=0.042, OR=1.372) performance a high risk of lung cancer. Mir-30c-1 rs928508 (P=0.005, in recessive model) and let-7a-2 rs629367 (P=0.030 and P=0.021, in additive and dominant models, respectively) showed strong relationship with lung cancer risk in age under 57 years. The rs11614913 (miR-196a-2) C allele or rs9280508 (miR-30c-1) G allele carriers shown more sensitive to platinum both in additive (P=0.010, P=0.022, respectively) and dominant models (P=0.001, P=0.018, respectively).

Conclusions

These findings suggested that SNPs rs71428439 (miR-149), rs2910164 (miR-146a), rs928508 (mir-30c-1) and rs629367 (let-7a-2) were associated with the lung cancer prevalence, polymorphisms of rs11614913 (miR-196a-2) and rs9280508 (miR-30c-1) significantly influenced the patients' response to platinum-based chemotherapy, which may serve as potential clinical biomarkers to predict lung cancer risk and platinum-based chemotherapy response.

Classification of miRNA-related sequence variations

miRNA regulome is whole set of regulatory elements that regulate miRNA expression or are under control of miRNAs. Its understanding is vital for comprehension of miRNA functions. Classification of miRNA-related genetic variability is challenging because miRNA interact with different genomic elements and are studied at different omics levels. In the present study, miRNA-associated genetic variability is presented at three levels: miRNA genes and their upstream regulation, miRNA silencing machinery and miRNA targets. Several types of miRNA-associated genetic variations are known, including short and structural polymorphisms and epimutations. Differential expression can also affect miRNA regulome function. Classification of miRNA-associated genetic variability presents a baseline for complementing sequence variant nomenclature, planning of experiments, protocols for multi-omics data integration and development of biomarkers.

microRNAs in Cancer Susceptibility

microRNAs (miRNAs) are a small RNA species without protein-coding potential. However, they are key modulators of protein translation. Many studies have linked miRNAs with cancer initiation, progression, diagnosis, and prognosis, and recent studies have also linked them with cancer etiology and susceptibility, especially through single-nucleotide polymorphisms (SNPs). This review discusses some of the recent advances in miRNA-SNP literature-including SNPs in miRNA genes, miRNA target sites, and the processing machinery. In addition, we highlight some emerging areas of interest, including isomiRs and non-3'UTR focused miRNA-binding mechanisms that could provide further novel insight into the relationship between miR-SNPs and cancer. Finally, we note that additional epidemiological and experimental research is needed to close the gap in our understanding of the genotype-phenotype relationship between miRNA-SNPs and cancer.

MicroRNAs as biomarkers for psychiatric disorders with a focus on autism spectrum disorder: Current progress in genetic association studies, expression profiling, and translational research

MicroRNAs (miRNAs) are a group of small noncoding RNA molecules, 18-25 nucleotides in length, which can negatively regulate gene expression at the post-transcriptional level by binding to messenger RNAs. About half of all identified miRNAs in humans are expressed in the brain and display regulatory functions important for many biological processes related to the development of the central nervous system (CNS). Disruptions in miRNA biogenesis and miRNA-target interaction have been related to CNS diseases, including psychiatric disorders. In this review, we focus on the role of miRNAs in autism spectrum disorder (ASD) and summarize recent findings about ASD-associated genetic variants in miRNA genes, in miRNA biogenesis genes, and miRNA targets. We discuss deregulation of miRNA expression in ASD and functional validation of ASD-related miRNAs in animal models. Including miRNAs in studies of ASD will contribute to our understanding of its etiology and pathogenesis and facilitate the discrimination between different disease subgroups. Autism Res 2017. © 2017 International Society for Autism Research, Wiley Periodicals, Inc. Autism Res 2017, 10: 1184-1203. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

Effect of pre-miRNA-1658 gene polymorphism on chicken growth and carcass traits

Objective

Polymorphisms occurring in the precursor region of microRNAs (miRNAs) affect the target gene and alter the biogenesis of miRNAs, resulting in phenotypic variation. The purpose of the study was to investigate the genetic effects of rs16681031 (C>G) mutation in the precursor region of gga-miR-1658 on the economic traits of the Gushi-Anka chicken F2 resource population.

Methods

To explore the effect of miR-1658 polymorphisms on chicken economic traits, the SNP was genotyped by MassArray matrix-assisted laser desorption/ionization-time of flight mass spectrometry. The association between the SNP and chicken body size, growth and carcass traits was determined by linear mixed models.

Results

The SNP was not only significantly associated with body weight at the age of 6, 8, 10, 12 weeks, respectively, but also with the breadth of the chicken chest, body slanting length and pelvic breadth at 4 weeks, chest depth at 8 weeks of age, and body slanting length at 12 weeks (p<0.05), respectively.

Conclusion

Our data serve as a useful resource for further analysis of miRNA function, and represent a molecular genetic basis for poultry breeding.

Construction of an integrative regulatory element and variation map of the murine Tst locus

BACKGROUND

Given the abundance of new genomic projects and gene annotations, researchers trying to pinpoint causal genetic variants are faced with a challenging task of how to efficiently integrate all current genomic information. The objective of the study was to develop an approach to integrate various genomic annotations for a recently positionally-cloned Tst gene (Thiosulfate Sulfur Transferase, synonym Rhodanese) responsible for the Fob3b2 QTL effect on leanness and improved metabolic parameters. The second aim was to identify and prioritize Tst genetic variants that may be causal for the phenotypic effects.

RESULTS

A bioinformatics approach was developed to integrate existing knowledge of regulatory elements of the Tst gene. The entire Tst locus along with flanking segments was sequenced between our unique polygenic mouse Fat and Lean strains that were generated by divergent selection on adiposity for over 60 generations. The bioinformatics-generated regulatory element map of the Tst locus was then combined with genetic variants between the Fat and Lean mice and with comparative analyses of polymorphisms across 17 mouse strains in order to prioritise likely causal polymorphisms. Two candidate regulatory variants were identified, one overlapping an evolutionary constrained Tst intronic element and the other residing in the seed region of a predicted 3'UTR miRNA binding site.

CONCLUSIONS

This study developed a map of regulatory elements for the Tst locus in mice and identified candidate genetic variants with increased causal likelihood. This map provides a basis for experimental validation and functional analyses of this novel candidate leanness and antidiabetic gene. Our methodological approach is of general utility for analyzing regulation of loci that have limited annotations and experimental evidence and for identifying candidate causal regulatory genetic variants in post-GWAS or post-QTL- cloning studies.

Vincristine pharmacokinetics pathway and neurotoxicity during early phases of treatment in pediatric acute lymphoblastic leukemia

AIM

Vincristine is an important component of acute lymphoblastic leukemia (ALL) treatment protocols that can cause neurotoxicity. Patients treated with LAL/SHOP protocols often suffer from vincristine-related neurotoxicity in early phases of treatment. Recently, a genome-wide association study connected a SNP in CEP72, involved in vincristine pharmacodynamics, with neurotoxicity during later phases of therapy, which was not replicated during induction phase. These results, together with previous studies indicating that polymorphisms in pharmacokinetic genes are associated with drug toxicity, suggest that changes in the activity or levels of vincristine transporters or metabolizers could work as predictors of vincristine-related neurotoxicity in early phases of treatment in pediatric ALL.

PATIENTS & METHODS

We analyzed 150 SNPs in eight key genes involved in vincristine pharmacokinetics and in 13 miRNAs that regulate them. We studied their correlation with neurotoxicity during induction phase in 152 ALL patients treated with LAL/SHOP protocols.

RESULTS

The strongest associations with neurotoxicity were observed for two SNPs in ABCC2. The genotypes rs3740066 GG and rs12826 GG were associated with increased neurotoxicity.

CONCLUSION

Polymorphisms in ABCC2 could be novel markers for vincristine-related neurotoxicity in pediatric ALL in early phases.

In silico analysis of polymorphisms in microRNAs that target genes affecting aerobic glycolysis

BACKGROUND

Cancer cells preferentially metabolize glucose through aerobic glycolysis, an observation known as the Warburg effect. Recently, studies have deciphered the role of oncogenes and tumor suppressor genes in regulating the Warburg effect. Furthermore, mutations in glycolytic enzymes identified in various cancers highlight the importance of the Warburg effect at the molecular and cellular level. MicroRNAs (miRNAs) are non-coding RNAs that posttranscriptionally regulate gene expression and are dysregulated in the pathogenesis of various types of human cancers. Single nucleotide polymorphisms (SNPs) in miRNA genes may affect miRNA biogenesis, processing, function, and stability and provide additional complexity in the pathogenesis of cancer. Moreover, mutations in miRNA target sequences in target mRNAs can affect expression.

METHODS

In silico analysis and cataloguing polymorphisms in miRNA genes that target genes directly or indirectly controlling aerobic glycolysis was carried out using different publically available databases.

RESULTS

miRNA SNP2.0 database revealed several SNPs in miR-126 and miR-25 in the upstream and downstream pre-miRNA flanking regions respectively should be inserted after flanking regions and miR-504 and miR-451 had the fewest. These miRNAs target genes that control aerobic glycolysis indirectly. SNPs in premiRNA genes were found in miR-96, miR-155, miR-25 and miR34a by miRNASNP. Dragon database of polymorphic regulation of miRNA genes (dPORE-miRNA) database revealed several SNPs that modify transcription factor binding sites (TFBS) or creating new TFBS in promoter regions of selected miRNA genes as analyzed by dPORE-miRNA.

CONCLUSIONS

Our results raise the possibility that integration of SNP analysis in miRNA genes with studies of metabolic adaptations in cancer cells could provide greater understanding of oncogenic mechanisms.

SNP in pre-miR-1666 decreases mature miRNA expression and is associated with chicken performance

Polymorphisms in miRNA genes could potentially alter various biological processes by influencing the processing and (or) target selection of miRNAs. The rs14120863 (C > G) mutation, which we characterized in a Gushi-Anka F2 resource population, resides in the precursor region of miR-1666. Association analysis with chicken carcass and growth traits showed that the SNP was significantly associated with carcass weight, evisceration weight, breast muscle weight, leg muscle weight, and body weight at 8 weeks of age, as well as some body size indexes including shank girth, chest breadth, breast bone length, and body slanting length, in the Gushi-Anka F2 resource population. Quantitative RT-PCR results showed that miR-1666 expression levels in muscle tissues differed within various genotypes. Experiment in DF1 cells further confirmed that the SNP in miR-1666 could significantly alter mature miRNA production. Subsequently, using dual-luciferase report assay, we verified that miR-1666 could perform its function through targeting of the CBFB gene. In conclusion, the SNP in the precursor of miR-1666 could significantly reduce mature miR-1666 production. It may further affect the function of miR-1666 through the target gene CBFB, hence it is associated with chicken growth traits.

An update of miRNASNP database for better SNP selection by GWAS data, miRNA expression and online tools

MicroRNAs (miRNAs) are key regulators of gene expression involved in a broad range of biological processes. MiRNASNP aims to provide single nucleotide polymorphisms (SNPs) in miRNAs and genes that may impact miRNA biogenesis and/or miRNA target binding. Advanced miRNA research provided abundant data about miRNA expression, validated targets and related phenotypic variants. In miRNASNP v2.0, we have updated our previous database with several new data and features, including: (i) expression level and expression correlation of miRNAs and target genes in different tissues, (ii) linking SNPs to the results of genome-wide association studies, (iii) integrating experimentally validated miRNA:mRNA interactions, (iv) adding multiple filters to prioritize functional SNPs. In addition, as a supplement of the database, we have set up three flexible online tools to analyse the influence of novel variants on miRNA:mRNA binding. A new nice web interface was designed for miRNASNP v2.0 allowing users to browse, search and download. We aim to maintain the miRNASNP as a solid resource for function, genetics and disease studies of miRNA-related SNPs. Database URL: http://bioinfo.life. hust.edu.cn/miRNASNP2/.

Pre- and post-natal muscle microRNA expression profiles of two pig breeds differing in muscularity

miRNAs regulate the expression of target genes in diverse cellular processes and hence play important roles in physiological processes including developmental timing, patterning, embryogenesis, organogenesis, cell lineage, myogenesis and growth control. A comparative expression analysis of miRNAs expressed in the longissimus dorsi muscle at two prenatal stages (63 and 91 days post-conception (dpc)), and one adult stage (180 days post-natum) in both German Landrace (DL) and Pietrain (Pi) pig breeds was performed using a custom-designed array. During the prenatal stages, miR-199 and the miR-17 families were significantly up-regulated at 63 dpc, whereas miR-1 and miR-133a were overexpressed at 91 dpc. The abundance of several miRNAs was increased in the adult stage compared to 91 dpc including miR-1, miR-133, miR-22(a/b) and miR-29a. Some miRNAs were breed-specific, such as miR-199 and the miR-17 families which were all up-regulated in Pi pigs, while miR-133, miR-181 and miR-214 were up-regulated in DL pigs. Several pathways related to muscle development were enriched with predicted targets for the differentially expressed miRNAs. The dynamic expression and breed-associated regulation of porcine muscle miRNAs suggests a functional role for miRNA-mediated gene regulation during muscle development and phenotypic variations of muscle traits.

Genetic Variability of MicroRNA Genes in 15 Animal Species

MicroRNAs (miRNA) are a class of non-coding RNAs important in posttranscriptional regulation of target genes. Previous studies have proven that genetic variability of miRNA genes (miR-SNP) has an impact on phenotypic variation and disease susceptibility in human, mice and some livestock species. MicroRNA gene polymorphisms could therefore represent biomarkers for phenotypic traits also in other animal species. We upgraded our previously developed tool miRNA SNiPer to the version 4.0 which enables the search of miRNA genetic variability in 15 animal genomes: http://www.integratomics-time.com/miRNA-SNiPer. Genome-wide in silico screening (GWISS) of 15 genomes revealed that based on the current database releases, miRNA genes are most polymorphic in cattle, followed by human, fruitfly, mouse, chicken, pig, horse, and sheep. The difference in the number of miRNA gene polymorphisms between species is most probably not due to a biological reason and lack of genetic variability in some species, but to different stage of sequencing projects and differences in development of genomic resource databases in different species. Genome screening revealed several interesting genomic hotspots. For instance, several multiple nucleotide polymorphisms (MNPs) are present within mature seed region in cattle. Among miR-SNPs 46 are present on commercial whole-genome SNP chips: 16 in cattle, 26 in chicken, two in sheep and two in pig. The update of the miRNA SNiPer tool and the generated catalogs will serve researchers as a starting point in designing projects dealing with the effects of genetic variability of miRNA genes.

Revealing editing and SNPs of microRNAs in colon tissues by analyzing high-throughput sequencing profiles of small RNAs

Background

Editing and mutations in microRNAs (miRNAs) can change the stability of pre-miRNAs and/or complementarities between miRNAs and their targets. Small RNA (sRNA) high-throughput sequencing (HTS) profiles contain miRNAs that are originated from mutated DNAs or are edited during their biogenesis procedures. It is largely unknown whether miRNAs are edited in colon tissues since existing studies mainly focused their attention on the editing of miRNAs in brain tissues.

Results

Through comprehensive analysis of four high-throughput sequencing profiles of normal and cancerous colon tissues, we identified 548 editing and/or SNPs in miRNAs that are significant in at least one of the sequencing profiles used. Our results show that the most abundant editing events of miRNAs in colon tissues are 3'-A and 3'-U. In addition to four known A-to-I editing sites previously reported in brain tissues, four novel A-to-I editing sites are also identified in colon tissues.

Conclusions

This suggests that A-to-I editing of miRNAs potentially is a commonly existing mechanism in different tissues to diversify the possible functional roles of miRNAs, but only a small portion of different miRNAs are edited by the A-to-I mechanism at a significant level. Our results suggest that there are other types of editing in miRNAs through unknown mechanisms. Furthermore, several SNPs in miRNAs are also identified.

miR-146a polymorphism influences levels of miR-146a, IRAK-1, and TRAF-6 in young patients with coronary artery disease

Modulation of nuclear factor KappaB (NF-κB) activation may play a role in regulating inflammatory conditions associated with coronary artery disease (CAD). MicroRNA-146a (miR-146a) primarily targets interleukin-1 receptor-associated kinase 1 (IRAK-1) and tumour necrosis factor receptor associated factor 6 (TRAF-6), which results in inhibition of NF-κB via the TLR pathway. This study investigated the influence of the miR-146a GC rs2910164 on miR-146a expression in young South African Indians with CAD. CAD patients and controls were genotyped by PCR-RFLP and miRNA-146a levels were measured by qPCR. IRAK-1, TRAF-6 and NF-κB expression was determined by Western blot. No differences in genotypic frequency was found (GG: 45 vs. 47%, GC: 46 vs. 41%, CC: 9 vs. 12%) in controls and patients respectively (odds ratio = 1.025; 95% confidence interval 0.6782-1.550; p = 0.9164). Significantly higher levels of miR-146a was associated with CAD patients with the CC genotype (6.25-fold increase relative to controls and patients with the wildtype variant, p < 0.0001). Significantly lower levels of IRAK-1 (0.38 ± 0.02; p = 0.0072) and TRAF-6 (0.44 ± 0.02; p = 0.0146) was found in CAD patients with the CC genotype. The lowest levels of NF-κB and C-reactive protein were found in patients with the homozygous C allele compared to the heterozygous GC and wildtype variants. We propose a role for miR-146a in TLR signalling through a negative feedback mechanism involving the attenuation of NF-κB by down-regulation of IRAK-1 and TRAF-6. Our observations implicate miR-146a as a target for lowering inflammation in CAD patients.

Genetic variability of microRNA regulome in human

MicroRNAs are currently being extensively studied due to their important role as post-transcriptional regulators. During miRNA biogenesis, precursors undergo two cleavage steps performed by Drosha-DGCR8 (Microprocessor) cleaving of pri-miRNA to produce pre-miRNA and Dicer-mediated cleaving to create mature miRNA. Genetic variants within human miRNA regulome have been shown to influence miRNA expression, target interaction and to affect the phenotype. In this study, we reviewed the literature, existing bioinformatics tools and catalogs associated with polymorphic miRNA regulome, and organized them into four categories: (1) polymorphisms located within miRNA genes (miR-SNPs), (2) transcription factor-binding sites/miRNA regulatory regions (miR-rSNPs), (3) miRNA target sites (miR-TS-SNPs), and 4. miRNA silencing machinery (miR-SM-SNPs). Since the miR-SM-SNPs have not been systematically studied yet, we have collected polymorphisms associated with miRNA silencing machinery. We have developed two catalogs containing genetic variability within: (1) genes encoding three main catalytic components of the silencing machinery, DROSHA, DGCR8, and DICER1; (2) miRNA genes itself, overlapping Drosha and Dicer cleavage sites. The developed resource of polymorphisms is available online (http://www.integratomics-time.com/miRNA-regulome) and will be useful for further functional studies and development of biomarkers associated with diseases and phenotypic traits.

Identifying a polymorphic 'switch' that influences miRNAs' regulation of a myasthenia gravis risk pathway

The significant roles of genetic variants in myasthenia gravis (MG) pathogenesis have been demonstrated in many studies, and recently it has been revealed that aberrant level/regulation of microRNAs (miRNAs) might contribute to the initiation and progression of MG. However, the dysfunction of miRNA associated with single nucleotide polymorphisms (miRSNPs) has not been well investigated in MG. In this study, we created a contemporary catalog of 89 MG risk genes via manual literature-mining. Based on this risk gene catalog, we obtained 18 MG risk pathways. Furthermore, we identified 93 miRNAs that target MG risk pathways and revealed the miRSNPs ‘switches’ in miRNA regulation in the MG risk pathways by integrating the database information of miRSNPs. We also constructed a miRNA-mediated SNP switching pathway network (MSSPN) to intuitively analyze miRNA regulation of MG risk pathways and the relationship of the polymorphism ‘switch’ with these changes in regulation. Moreover, we carried out in-depth dissection on the correlation between hsa05200 (pathway in cancer) and MG development, and elaborated the significance of 4 high-risk genes. By network analysis and literature mining, we proposed a potential mechanism of miRSNPs→gene→pathway effects on MG pathogenesis, especially for rs28457673 (miR-15/16/195/424/497 family)→IGF1R→hsa05200 (pathway in cancer). Therefore, our studies have revealed a functional role for genetic modulators in MG pathogenesis at a systemic level, which could be informative for further miRNA and miRSNPs studies in MG.

Data integration of 104 studies related with microRNA epigenetics revealed that miR-34 gene family is silenced by DNA methylation in the highest number of cancer types

There is an increasing research interest regarding deregulation of microRNA (miRNA) expression by DNA methylation in cancer. The aim of this study was to integrate data from publications and identify miRNA genes shown to be silenced in the highest number of cancer types and thus facilitate biomarker and therapeutic development. We integrated relevant data from 104 published scientific articles. The following databases and bioinformatics tools were used for the analysis: miRBase, miRNA Genomic Viewer, MultAlin, miRNA SNiPer, TargetScan, Ensembl, MethPrimer, TarBase, miRecords, and ChIPBase. Among 2578 currently known human miRNAs and 158 known to be regulated by DNA methylation, miR-34 gene family (miR-34a, -34b, and -34c) was shown to be silenced by DNA methylation in the highest number of cancer types. Consequently, we developed the miR-34 gene family regulatory atlas, consisting of its upstream regulators and downstream targets including transcription factor binding sites (TFBSs), CpG islands, genetic variability and overlapping QTL. MicroRNA-34 gene family has a potential as a cancer biomarker and target for epigenetic drugs. This potential has already been recognized as MRX34 is well into phase I studies. The developed miR-34 gene family regulatory atlas presented in this study provides a starting point for further analyses and could thus facilitate development of therapeutics.

Identification of putative pathogenic SNPs implied in schizophrenia-associated miRNAs

Background

Schizophrenia is a severe brain disorder, and SNPs (Single nucleotide polymorphism) in schizophrenia-associated miRNAs are believed to be one of the important reasons for dysregulation which might contribute to the altered expression of genes and ultimately result in the disease. Identification of causal SNPs in associated miRNAs may have certain significance in understanding the mechanism of schizophrenia.

Results

For the above purposes, a method based on detection of free energy change is proposed for identification of causal SNPs in schizophrenia-associated miRNAs. A miRNA is firstly segmented, and free energy change is computed after adding an SNP into a segment. The method discovers successfully 6 out of 32 known SNPs and some artificial SNPs could cause significant change in free energy, and among which, 6 known SNPs are supposed to be responsible for most cases of schizophrenia in population.

Conclusions

The proposed method is not only a convenient way to discover causal SNPs in schizophrenia-associated miRNAs without any biochemical assay or sample comparison between cases and controls, but it also has high resolution for causal SNPs even if the SNPs are not reported for their very rare cases in the population. Moreover, the method can be applied to discover the causal SNPs in miRNAs associated with other diseases.

Single nucleotide polymorphism-specific regulation of matrix metalloproteinase-9 by multiple miRNAs targeting the coding exon

Microribonucleic acids (miRNAs) work with exquisite specificity and are able to distinguish a target from a non-target based on a single nucleotide mismatch in the core nucleotide domain. We questioned whether miRNA regulation of gene expression could occur in a single nucleotide polymorphism (SNP)-specific manner, manifesting as a post-transcriptional control of expression of genetic polymorphisms. In our recent study of the functional consequences of matrix metalloproteinase (MMP)-9 SNPs, we discovered that expression of a coding exon SNP in the pro-domain of the protein resulted in a profound decrease in the secreted protein. This missense SNP results in the N38S amino acid change and a loss of an N-glycosylation site. A systematic study demonstrated that the loss of secreted protein was due not to the loss of an N-glycosylation site, but rather an SNP-specific targeting by miR-671-3p and miR-657. Bioinformatics analysis identified 41 SNP-specific miRNA targeting MMP-9 SNPs, mostly in the coding exon and an extension of the analysis to chromosome 20, where the MMP-9 gene is located, suggesting that SNP-specific miRNAs targeting the coding exon are prevalent. This selective post-transcriptional regulation of a target messenger RNA harboring genetic polymorphisms by miRNAs offers an SNP-dependent post-transcriptional regulatory mechanism, allowing for polymorphic-specific differential gene regulation.

plantDARIO: web based quantitative and qualitative analysis of small RNA-seq data in plants

High-throughput sequencing techniques have made it possible to assay an organism's entire repertoire of small non-coding RNAs (ncRNAs) in an efficient and cost-effective manner. The moderate size of small RNA-seq datasets makes it feasible to provide free web services to the research community that provide many basic features of a small RNA-seq analysis, including quality control, read normalization, ncRNA quantification, and the prediction of putative novel ncRNAs. DARIO is one such system that so far has been focussed on animals. Here we introduce an extension of this system to plant short non-coding RNAs (sncRNAs). It includes major modifications to cope with plant-specific sncRNA processing. The current version of plantDARIO covers analyses of mapping files, small RNA-seq quality control, expression analyses of annotated sncRNAs, including the prediction of novel miRNAs and snoRNAs from unknown expressed loci and expression analyses of user-defined loci. At present Arabidopsis thaliana, Beta vulgaris, and Solanum lycopersicum are covered. The web tool links to a plant specific visualization browser to display the read distribution of the analyzed sample. The easy-to-use platform of plantDARIO quantifies RNA expression of annotated sncRNAs from different sncRNA databases together with new sncRNAs, annotated by our group. The plantDARIO website can be accessed at http://plantdario.bioinf.uni-leipzig.de/.

Obesity gene atlas in mammals

Obesity in humans has increased at an alarming rate over the past two decades and has become one of the leading public health problems worldwide. Studies have revealed a large number of genes/markers that are associated with obesity and/or obesity-related phenotypes, indicating an urgent need to develop a central database for helping the community understand the genetic complexity of obesity. In the present study, we collected a total of 1,736 obesity associated loci and created a freely available obesity database, including 1,515 protein-coding genes and 221 microRNAs (miRNAs) collected from four mammalian species: human, cattle, rat, and mouse. These loci were integrated as orthologs on comparative genomic views in human, cattle, and mouse. The database and genomic views are freely available online at: http://www.integratomics-time.com/fat_deposition. Bioinformatics analyses of the collected data revealed some potential novel obesity related molecular markers which represent focal points for testing more targeted hypotheses and designing experiments for further studies. We believe that this centralized database on obesity and adipogenesis will facilitate development of comparative systems biology approaches to address this important health issue in human and their potential applications in animals.

Comprehensive analysis of single nucleotide polymorphisms in human microRNAs

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that repress their targets at post transcriptional level. Single Nucleotide Polymorphisms (SNPs) in miRNAs can lead to severe defects to the functions of miRNAs and might result in diseases. Although several studies have tried to identify the SNPs in human miRNA genes or only in the mature miRNAs, there are only limited endeavors to explain the distribution of SNPs in these important genes. After a genome-wide scan for SNPs in human miRNAs, we totally identified 1899 SNPs in 961 out of the 1527 reported miRNA precursors of human, which is the most complete list of SNPs in human miRNAs to date. More importantly, to explain the distributions of SNPs existed in human miRNAs, we comprehensively and systematically analyzed the identified SNPs in miRNAs from several aspects. Our results suggest that conservation, genomic context, secondary structure, and functional importance of human miRNAs affect the accumulations of SNPs in these genes. Our results also show that the number of SNPs with significantly different frequencies among various populations in the HapMap and 1000 Genome Project data are consistent with the geographical distributions of these populations. These analyses provide a better insight of SNPs in human miRNAs and the spreading of the SNPs in miRNAs in different populations.

miRNAs and long noncoding RNAs as biomarkers in human diseases

Noncoding RNAs (ncRNAs) are transcripts that have no apparent protein-coding capacity; however, many ncRNAs have been found to play a major biological role in human physiology. Their deregulation is implicated in many human diseases, but their exact roles are only beginning to be elucidated. Nevertheless, ncRNAs are extensively studied as a novel source of biomarkers, and the fact that they can be detected in body fluids makes them extremely suitable for this purpose. The authors mainly focus on ncRNAs as biomarkers in cancer, but also touch on other human diseases such as cardiovascular diseases, autoimmune diseases, neurological disorders and infectious diseases. The authors discuss the established methods and provide a selection of emerging new techniques that can be used to detect and quantify ncRNAs. Finally, the authors discuss ncRNAs as a new strategy for therapeutic interventions.

Principles of miRNA-target regulation in metazoan models

MicroRNAs (miRs) are key post-transcriptional regulators that silence gene expression by direct base pairing to target sites of RNAs. They have a wide variety of tissue expression patterns and are differentially expressed during development and disease. Their activity and abundance is subject to various levels of control ranging from transcription and biogenesis to miR response elements on RNAs, target cellular levels and miR turnover. This review summarizes and discusses current knowledge on the regulation of miR activity and concludes with novel non-canonical functions that have recently emerged.

Prioritization of genetic variants in the microRNA regulome as functional candidates in genome-wide association studies

Comprehensive analyses of results from genome-wide association studies (GWAS) have demonstrated that complex disease/trait-associated loci are enriched in gene regulatory regions of the genome. The search for causal regulatory variation has focused primarily on transcriptional elements, such as promoters and enhancers. microRNAs (miRNAs) are now widely appreciated as critical posttranscriptional regulators of gene expression and are thought to impart stability to biological systems. Naturally occurring genetic variation in the miRNA regulome is likely an important contributor to phenotypic variation in the human population. However, the extent to which polymorphic miRNA-mediated gene regulation underlies GWAS signals remains unclear. In this study, we have developed the most comprehensive bioinformatic analysis pipeline to date for cataloging and prioritizing variants in the miRNA regulome as functional candidates in GWAS. We highlight specific findings, including a variant in the promoter of the miRNA let-7 that may contribute to human height variation. We also provide a discussion of how our approach can be expanded in the future. Overall, we believe that the results of this study will be valuable for researchers interested in determining whether GWAS signals implicate the miRNA regulome in their disease/trait of interest.

Genome-wide in silico screening for microRNA genetic variability in livestock species

MicroRNAs are a class of non-coding RNAs that post-transcriptionally regulate target gene expression. Previous studies have shown that microRNA gene variability can interfere with its function, resulting in phenotypic variation. Polymorphisms within microRNA genes present a source of novel biomarkers for phenotypic traits in animal breeding. However, little is known about microRNA genetic variability in livestock species, which is also due to incomplete data in genomic resource databases. Therefore, the aim of this study was to perform a genome-wide in silico screening of genomic sources and determine the genetic variability of microRNA genes in livestock species using mirna sniper 3.0 (http://www.integratomics-time.com/miRNA-SNiPer/), a new version of our previously developed tool. By examining Ensembl and miRBase genome builds, it was possible to design a tool-based generated search of 16 genomes including four livestock species: pig, horse, cattle and chicken. The analysis revealed 65 polymorphisms located within mature microRNA regions in these four species, including 28% within the seed region in cattle and chicken. Polymorphic microRNA genes in cattle and chicken were further examined for mapping to quantitative trait loci regions associated with production and health traits. The developed bioinformatics tool enables the analysis of polymorphic microRNA genes and prioritization of potential regulatory polymorphisms and therefore contributes to the development of microRNA-based biomarkers in livestock species. The assembled catalog and the developed tool can serve the animal science community to efficiently select microRNA SNPs for further quantitative and molecular genetic evaluations of their phenotypic effects and causal associations with livestock production traits.

Species-specific microRNA regulation influences phenotypic variability: perspectives on species-specific microRNA regulation

Phenotypic divergence among animal species may be due in part to species-specific (SS) regulation of gene expression by small, non-coding regulatory RNAs termed "microRNAs". This phenomenon can be modulated by several variables. First, microRNA genes vary by their level of conservation, many of them being SS, or unique to a particular evolutionary lineage. Second, microRNA expression levels vary spatially and temporally in different species. Lastly, while microRNAs bind the 3'UTR of target genes in order to silence their expression, the binding sites themselves are often non-conserved. The variability of the miRNA-target paradigm between different species is thus multifactorial, and this paradigm has only just started to gain attention from researchers in various fields. Here we present and discuss recent findings regarding the characteristics and implications of SS microRNA regulation.

Genome-wide and species-wide in silico screening for intragenic MicroRNAs in human, mouse and chicken

MicroRNAs (miRNAs) are non-coding RNAs (ncRNAs) involved in regulation of gene expression. Intragenic miRNAs, especially those exhibiting a high degree of evolutionary conservation, have been shown to be coordinately regulated and/or expressed with their host genes, either with synergistic or antagonistic correlation patterns. However, the degree of cross-species conservation of miRNA/host gene co-location is not known and co-expression information is incomplete and fragmented among several studies. Using the genomic resources (miRBase and Ensembl) we performed a genome-wide in silico screening (GWISS) for miRNA/host gene pairs in three well-annotated vertebrate species: human, mouse, and chicken. Approximately half of currently annotated miRNA genes resided within host genes: 53.0% (849/1,600) in human, 48.8% (418/855) in mouse, and 42.0% (210/499) in chicken, which we present in a central publicly available Catalog of intragenic miRNAs (http://www.integratomics-time.com/miR-host/catalog). The miRNA genes resided within either protein-coding or ncRNA genes, which include long intergenic ncRNAs (lincRNAs) and small nucleolar RNAs (snoRNAs). Twenty-seven miRNA genes were found to be located within the same host genes in all three species and the data integration from literature and databases showed that most (26/27) have been found to be co-expressed. Particularly interesting are miRNA genes located within genes encoding for miRNA silencing machinery (DGCR8, DICER1, and SND1 in human and Cnot3, Gdcr8, Eif4e, Tnrc6b, and Xpo5 in mouse). We furthermore discuss a potential for phenotype misattribution of miRNA host gene polymorphism or gene modification studies due to possible collateral effects on miRNAs hosted within them. In conclusion, the catalog of intragenic miRNAs and identified 27 miRNA/host gene pairs with cross-species conserved co-location, co-expression, and potential co-regulation, provide excellent candidates for further functional annotation of intragenic miRNAs in health and disease.

Single Nucleotide Polymorphisms Associated with MicroRNA Regulation

Since the discovery of microRNA (miRNA), the polymorphisms that affect miRNA regulation had been extensively investigated by many independent studies. Recently, researchers utilized bioinformatics and statistical approaches for genome-wide analysis on the human polymorphisms that reside in the miRNA genes, targets, and/or genes involved in miRNA processing. In this review, we will give an overview about the important findings of these studies from three perspectives: architecture of the polymorphisms within miRNAs or their targets, potential functional consequences of the polymorphisms on miRNA processing or targeting, and the associations of the polymorphisms with miRNA or target gene expression. The results of the previous studies demonstrated the signatures of natural selections on the miRNA genes and their targets, and proposed a collection of potentially functional, expression-associated, and/or positively selected polymorphisms that are promising for further investigations. In the meantime, a few useful resources about the polymorphic miRNA regulation have been developed and the different features of these databases were discussed in this review. Though recent research had benefited from these comprehensive studies and resources, there were still gaps in our knowledge about the polymorphisms involved in miRNA regulation, and future investigations were expected to address these questions.

RNA sequencing reveals small RNAs differentially expressed between incipient Japanese threespine sticklebacks

Background

Non-coding small RNAs, ranging from 20 to 30 nucleotides in length, mediate the regulation of gene expression and play important roles in many biological processes. One class of small RNAs, microRNAs (miRNAs), are highly conserved across taxa and mediate the regulation of the chromatin state and the post-transcriptional regulation of messenger RNA (mRNA). Another class of small RNAs is the Piwi-interacting RNAs, which play important roles in the silencing of transposons and other functional genes. Although the biological functions of the different small RNAs have been elucidated in several laboratory animals, little is known regarding naturally occurring variation in small RNA transcriptomes among closely related species.

Results

We employed next-generation sequencing technology to compare the expression profiles of brain small RNAs between sympatric species of the Japanese threespine stickleback (Gasterosteus aculeatus). We identified several small RNAs that were differentially expressed between sympatric Pacific Ocean and Japan Sea sticklebacks. Potential targets of several small RNAs were identified as repetitive sequences. Female-biased miRNA expression from the old X chromosome was also observed, and it was attributed to the degeneration of the Y chromosome.

Conclusions

Our results suggest that expression patterns of small RNA can differ between incipient species and may be a potential mechanism underlying differential mRNA expression and transposon activity.

Evolution of mir-92a underlies natural morphological variation in Drosophila melanogaster

Identifying the genetic mechanisms underlying phenotypic change is essential to understanding how gene regulatory networks and ultimately the genotype-to-phenotype map evolve. It is recognized that microRNAs (miRNAs) have the potential to facilitate evolutionary change [1-3]; however, there are no known examples of natural morphological variation caused by evolutionary changes in miRNA expression. Therefore, the contribution of miRNAs to evolutionary change remains unknown [1, 4]. Drosophila melanogaster subgroup species display a portion of trichome-free cuticle on the femur of the second leg called the "naked valley." It was previously shown that Ultrabithorax (Ubx) is involved in naked valley variation between D. melanogaster and D. simulans [5, 6]. However, naked valley size also varies among populations of D. melanogaster, ranging from 1,000 up to 30,000 μm(2). We investigated the genetic basis of intraspecific differences in the naked valley in D. melanogaster and found that neither Ubx nor shavenbaby (svb) [7, 8] contributes to this morphological difference. Instead, we show that changes in mir-92a expression underlie the evolution of naked valley size in D. melanogaster through repression of shavenoid (sha) [9]. Therefore, our results reveal a novel mechanism for morphological evolution and suggest that modulation of the expression of miRNAs potentially plays a prominent role in generating organismal diversity.