microRNA  (miRNA)   &   quantitative real-time RT-PCR (5)
microRNA  (miRNA)   &   quantitative real-time RT-PCR (1)
microRNA  (miRNA)   &   quantitative real-time RT-PCR (2)
microRNA  (miRNA)   &   quantitative real-time RT-PCR (3)
microRNA  (miRNA)   &   quantitative real-time RT-PCR (4)
microRNA  REVIEWS (6)
microRNA normalisation (7)
mirtrons  (8)
latest microRNA papers (9)  ... NEW

RNA interference (RNAi)        small inhibiting RNA  (siRNA)       small activating RNA  (saRNA)

Quantitative real-time RT-PCR applications for microRNA quantification:

Editorial - The microRevolution


Glimpses of a Tiny RNA World.
SCIENCE VOL 294    26 OCTOBER 2001
Gary Ruvkun

Functions of microRNAs and related small RNAs in plants.
Allison C Mallory & Hervé Vaucheret
MicroRNAs (miRNAs) and short interfering RNAs (siRNAs), 20- to 27-nt in length, are essential regulatory molecules that act as sequence-specific guides in several processes in most eukaryotes (with the notable exception of the yeast Saccharomyces cerevisiae). These processes include DNA elimination, heterochromatin assembly, mRNA cleavage and translational repression. This review focuses on the regulatory roles of plant miRNAs during development, in the adaptive response to stresses and in the miRNA pathway itself. This review also covers the regulatory roles of two classes of endogenous plant siRNAs, ta-siRNAs and nat-siRNAs, which participate in post-transcriptional control of gene expression.

Evidence that microRNAs are associated with translating messenger RNAs in human cells.
Patricia A Maroney, Yang Yu, Jesse Fisher & Timothy W Nilsen
MicroRNAs (miRNAs) regulate gene expression post-transcriptionally by binding the 3¢ untranslated regions of target mRNAs. We examined the subcellular distribution of three miRNAs in exponentially growing HeLa cells and found that the vast majority are associated with mRNAs in polysomes. Several lines of evidence indicate that most of these mRNAs, including a known miRNA-regulated target (KRAS mRNA), are actively being translated.

How microRNAs control cell division, differentiation and death.
Eric A Miska
Current Opinion in Genetics & Development 2005, 15: 563–568
After the milestone discovery of the first microRNA in 1993, the past five years have seen a phenomenal surge of interest in these short, regulatory RNAs. Given that 2% of all known human genes encode microRNAs, one main goal is to uncover microRNA function. Although it has been more difficult to assign function to microRNAs in animals than it has been in plants, important roles are emerging: in invertebrates, microRNAs control developmental timing, neuronal differentiation, tissue growth and programmed cell death. Functional studies in zebrafish and mice point toward important roles for microRNAs during morphogenesis and organogenesis. Finally, microRNAs might regulate viral infection and human cancer.

microRNA target predictions in animals.
Nikolaus Rajewsky
In recent years, microRNAs (miRNAs) have emerged as a major class of regulatory genes, present in most metazoans and important for a diverse range of biological functions. Because experimental identification of miRNA targets is difficult, there has been an explosion of computational target predictions. Although the initial round of predictions resulted in very diverse results, subsequent computational and experimental analyses suggested that at least a certain class of conserved miRNA targets can be confidently predicted and that this class of targets is large, covering, for example, at least 30% of all human genes when considering about 60 conserved vertebrate miRNA gene families. Most recent approaches have also shown that there are correlations between domains of miRNA expression and mRNA levels of their targets. Our understanding of miRNA function is still extremely limited, but it may be that by integrating mRNA and miRNA sequence and expression data with other comparative genomic data, we will be able to gain global and yet specific insights into the function and evolution of a broad layer of post-transcriptional control.

Human let-7a miRNA blocks protein production on actively translating polyribosomes.
Stephanie Nottrott, Martin J Simard & Joel D Richter
MicroRNAs (miRNAs) regulate gene expression at a post-transcriptional level through base-pairing to 3¢ untranslated regions (UTRs) of messenger RNAs. The mechanism by which human let-7a miRNA regulates mRNA translation was examined in HeLa cells expressing reporter mRNAs containing the Caenorhabditis elegans lin-41 3¢ UTR. let-7a miRNA strongly repressed translation, yet the majority of control and lin-41–bearing RNAs sedimented with polyribosomes in sucrose gradients; these polyribosomes, together with let-7a miRNA and the miRISC protein AGO, were released from those structures by puromycin. RNA containing the lin-41 3¢ UTR and an iron response element in the 5¢ UTR sedimented with polysomes when cells were incubated with iron, but showed ribosome run-off when the iron was chelated. These data indicate that let-7a miRNA inhibits actively translating polyribosomes. Nascent polypeptide coimmunoprecipitation experiments further suggest that let-7a miRNA interferes with the accumulation of growing polypeptides.

Computational identification of microRNA targets.
Developmental Biology 267 (2004) 529– 535
Nikolaus Rajewskya, and Nicholas D. Soccib,
  Department of Biology, New York University, New York, NY 10003-6688, USA;  Department of Pathology, and Seaver Foundation for Bioinformatics, Albert Einstein College of Medicine, Bronx, NY 10461, USA;  Computational Biology Center, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA
Recent experiments have shown that the genomes of organisms such as worm, fly, human, and mouse encode hundreds of microRNA genes. Many of these microRNAs are thought to regulate the translational expression of other genes by binding to partially complementary sites in messenger RNAs. Phenotypic and expression analysis suggests an important role of microRNAs during development. Therefore, it is of fundamental importance to identify microRNA targets. However, no experimental or computational high-throughput method for target site identification in animals has been published yet. Our main result is a new computational method that is designed to identify microRNA target sites. This method recovers with high specificity known microRNA target sites that have previously been defined experimentally. Based on these results, we present a simple model for the mechanism of microRNA target site recognition. Our model incorporates both kinetic and thermodynamic components of target recognition. When we applied our method to a set of 74 Drosophila melanogaster microRNAs, searching 3V UTR sequences of a predefined set of fly mRNAs for target sites which were evolutionary conserved between D. melanogaster and Drosophila pseudoobscura, we found that many key developmental body patterning genes such as hairy and fushi-tarazu are likely to be translationally regulated by microRNAs.

Incorporating structure to predict microRNA targets.
PNAS  2005 vol. 102 no. 11, 4006–4009
Harlan Robins*†, Ying Li‡, and Richard W. Padgett‡
*Institute for Advanced Study, Olden Lane, Princeton, NJ 08540; and ‡Department of Molecular Biology and Biochemistry, Waksman Institute, Cancer Institute of New Jersey, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-1020

MicroRNAs (miRNAs) are a recently discovered set of regulatory genes that constitute up to an estimated 1% of the total number of genes in animal genomes, including Caenorhabditis elegans, Drosophila, mouse, and humans [Lagos-Quintana, M., Rauhut, R., Lendeckel, W. & Tuschl, T. (2001) Science 294, 853–858; Lai, E. C., Tomancak, P., Williams, R. W. & Rubin, G.M. (2003) Genome Biol. 4, R42; Lau, N. C., Lim, L. P., Weinstein, E. G. & Bartel, D. P. (2001) Science 294, 858–862; Lee, R. C. & Ambros, V. (2001) Science 294, 862-8644; and Lee, R. C., Feinbaum, R. L. & Ambros, V. (1993) Cell 115, 787–798]. In animals, miRNAs regulate genes by attenuating protein translation through imperfect base pair binding to 3 UTR sequences of target genes. A major challenge in understanding the regulatory role of miRNAs is to accurately predict regulated targets. We have developed an algorithm for predicting targets that does not rely on evolutionary conservation. As one of the features of this algorithm, we incorporate the folded structure of mRNA. By using Drosophila miRNAs as a test case, we have validated our predictions in 10 of 15 genes tested. One of these validated genes is mad as a target for bantam. Furthermore, our computational and experimental data suggest that miRNAs have fewer targets than previously reported.

Intronic microRNA precursors that bypass Drosha processing.
Nature Letters Vol 448:5 2007
J. Graham Ruby1,2*, Calvin H. Jan1,2* & David P. Bartel1,2
MicroRNAs (miRNAs) are 22-nucleotide endogenous RNAs that often repress the expression of complementary messenger RNAs1. In animals, miRNAs derive from characteristic hairpins in primary transcripts through two sequential RNase III-mediated cleavages; Drosha cleaves near the base of the stem to liberate a 60-nucleotide pre-miRNA hairpin, then Dicer cleaves near the loop to generate a miRNA:miRNA* duplex2,3. From that duplex, the mature miRNA is incorporated into the silencing complex. Here we identify an alternative pathway for miRNA biogenesis, in which certain debranched introns mimic the structural features of pre-miRNAs to enter the miRNA-processing pathway without Drosha-mediated cleavage. We call these pre-miRNAs/introns ‘mirtrons’, and have identified 14 mirtrons in Drosophila melanogaster and another four in Caenorhabditis elegans (including the reclassification of mir-62). Some of these have been selectively maintained during evolution with patterns of sequence conservation suggesting important regulatory functions in the animal. The abundance of introns comparable in size to pre-miRNAs appears to have created a context favourable for the emergence of mirtrons in flies and nematodes. This suggests that other lineages with many similarly sized introns probably also have mirtrons, and that the mirtron pathway could have provided an early avenue for the emergence of miRNAs before the advent of Drosha.

MicroInspector: a web tool for detection of miRNA binding sites in an RNA sequence.
Nucleic Acids Research, 2005, Vol. 33, Web Server issue W696–W700
Ventsislav Rusinov1,2, Vesselin Baev1,2, Ivan Nikiforov Minkov2 and Martin Tabler1,*
1Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology—Hellas, PO Box 1527, GR -71110 Heraklion /Crete, Greece and 2 Depar tment of Pla nt Phys iology and Mole cular Biology, Universit y of Plo vdiv 24, Tsar Assen St, 4000 Plovdiv, Bulgaria
Regulation ofpost-transcriptionalgeneexpressionby microRNAs (miRNA) has so far been validated for only a few mRNA targets. Based on the large number of miRNA genes and the possibility that one miRNA might influence gene expression of several targets simultaneously, the quantity of ribo-regulated genes is expected to be much higher. Here, we describe the web tool MicroInspector that will analyse a userdefined RNA sequence, which is typically an mRNA or a part of an mRNA, for the occurrence of binding sites for known and registered miRNAs. The program allows variation of temperature, the setting of energy values as well as the selection of different miRNA databases to identify miRNA-binding sites of different strength. MicroInspector could spot the correct sites for miRNA-interaction in known target mRNAs. Using other mRNAs, for which such an interaction has not yet been described, we discovered frequently potential miRNA binding sites of similar quality, which can now be analysed experimentally. The MicroInspector program is easy to use and does not require specific computer skills. The service can be accessed via the MicroInspector web server at  http://www.imbb.forth.gr/microinspector

Target labelling for the detection and profiling of microRNAs expressed in CNS tissue using microarrays.
BMC Biotechnology 2006, 6:47
Reuben Saba1,2 and Stephanie A Booth*1,2
1Division of Host Genetics & Prion Diseases, National Microbiology Laboratory, 1015 Arlington Street, Public Health Agency of Canada, Winnipeg, MB, R3E 3R2, Canada and 2Department of Medical Microbiology and Infectious Diseases, Faculty of Medicine, University of Manitoba, Winnipeg, MB, R3B 1Y6, Canada
Background: MicroRNAs (miRNA) are a novel class of small, non-coding, gene regulatory RNA molecules that have diverse roles in a variety of eukaryotic biological processes. High-throughput detection and differential expression analysis of these molecules, by microarray technology, may contribute to a greater understanding of the many biological events regulated by these molecules. In this investigation we compared two different methodologies for the preparation of labelled miRNAs from mouse CNS tissue for microarray analysis. Labelled miRNAs were prepared either by a procedure involving linear amplification of miRNAs (labelled-aRNA) or using a direct labelling strategy (labelled-cDNA) and analysed using a custom miRNA microarray platform. Our aim was to develop a rapid, sensitive methodology to profile miRNAs that could be adapted for use on limited amounts of tissue. Results: We demonstrate the detection of an equivalent set of miRNAs from mouse CNS tissues using both amplified and non-amplified labelled miRNAs. Validation of the expression of these miRNAs in the CNS by multiplex real-time PCR confirmed the reliability of our microarray platform. We found that although the amplification step increased the sensitivity of detection of miRNAs, we observed a concomitant decrease in specificity for closely related probes, as well as increased variation introduced by dye bias. Conclusion: The data presented in this investigation identifies several important sources of systematic bias that must be considered upon linear amplification of miRNA for microarray analysis in comparison to directly labelled miRNA.

A brain-specific microRNA regulates dendritic spine development.
Gerhard M. Schratt1,2,3, Fabian Tuebing4, Elizabeth A. Nigh1,2,3, Christina G. Kane1,2,3, Mary E. Sabatini3,
Michael Kiebler4 & Michael E. Greenberg1,2,3
Nature Vol 439:19  January 2006

MicroRNAs are small, non-coding RNAs that control the translation of target messenger RNAs, thereby regulating critical aspects of plant and animal development. In the mammalian nervous system, the spatiotemporal control of mRNA translation has an important role in synaptic development and plasticity. Although a number of microRNAs have been isolated from the mammalian brain, neither the specific microRNAs that regulate synapse function nor their target mRNAs have been identified. Here we show that a brain-specific microRNA, miR-134, is localized to the synaptodendritic compartment of rat hippocampal neurons and negatively regulates the size of dendritic spines-postsynaptic sites of excitatory synaptic transmission. This effect is mediated by miR-134 inhibition of the translation of an mRNA encoding a protein kinase, Limk1, that controls spine development. Exposure of neurons to extracellular stimuli such as brain-derived neurotrophic factor relieves miR-134 inhibition of Limk1 translation and in this way may contribute to synaptic development, maturation and/or plasticity.

SHORT COMMUNICATION:  miR-21-mediated tumor growth.
Oncogene (2006), 1–5
M-L Si, S Zhu, H Wu, Z Lu, F Wu and Y-Y Mo
Department of Medical Microbiology, Immunology and Cell Biology, Southern Illinois University School of Medicine, Springfield,

MicroRNAs (miRNAs) are B22 nucleotide non-coding RNA molecules that regulate gene expression post-transcriptionally. Although aberrant expression of miRNAs in various human cancers suggests a role for miRNAs in tumorigenesis, it remains largely unclear as to whether knockdown of a specific miRNA affects tumor growth. In this study, we profiled miRNA expression in matched normal breast tissue and breast tumor tissues by TaqMan real-time polymerase chain reaction miRNA array methods. Consistent with previous findings, we found that miR-21 was highly overexpressed in breast tumors compared to the matched normal breast tissues among 157 human miRNAs analysed. To better evaluate the role of miR-21 in tumorigenesis, we
transfected breast cancer MCF-7 cells with anti-miR-21 oligonucleotides and found that anti-miR-21 suppressed both cell growth in vitro and tumor growth in the xenograft mouse model. Furthermore, this anti-miR-21-mediated cell growth inhibition was associated with increased apoptosis and decreased cell proliferation, which could be in part owing to downregulation of the antiapoptotic Bcl-2 in anti-miR-21- treated tumor cells. Together, these results suggest that miR-21 functions as an oncogene and modulates tumorigenesis through regulation of genes such as bcl-2 and thus, it may serve as a novel therapeutic target.

Discovering microRNAs from deep sequencing data using miRDeep
Friedländer MR, Chen W, Adamidi C, Maaskola J, Einspanier R, Knespel S, Rajewsky N.
Nat Biotechnol. 2008 Apr;26(4):407-15. doi: 10.1038/nbt1394.
Max Delbrück Centrum für Molekulare Medizin, Robert-Rössle-Strasse 10, D-13125 Berlin-Buch, Germany
The capacity of highly parallel sequencing technologies to detect small RNAs at unprecedented depth suggests their value in systematically identifying microRNAs (miRNAs). However, the identification of miRNAs from the large pool of sequenced transcripts from a single deep sequencing run remains a major challenge. Here, we present an algorithm, miRDeep, which uses a probabilistic model of miRNA biogenesis to score compatibility of the position and frequency of sequenced RNA with the secondary structure of the miRNA precursor. We demonstrate its accuracy and robustness using published Caenorhabditis elegans data and data we generated by deep sequencing human and dog RNAs. miRDeep reports altogether approximately 230 previously unannotated miRNAs, of which four novel C. elegans miRNAs are validated by northern blot analysis.

miRNA profiling for biomarker discovery in multiple sclerosis: from microarray to deep sequencing
Guerau-de-Arellano M, Alder H, Ozer HG, Lovett-Racke A, Racke MK.
Neurology Department, The Ohio State University Medical Center, 460 W 12th Ave Room 0705, Columbus, OH 43210, USA
J Neuroimmunol. 2012 Jul 15;248(1-2): 32-39
MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level. miRNAs are highly expressed in cells of the immune and nervous system, attesting to their importance in Neuroimmunology. Besides their involvement in modulation of physiological and pathological processes, miRNAs hold high promise as disease biomarkers, therapeutic agents and/or drug targets. Several studies have recently explored the involvement of miRNAs in Multiple Sclerosis (MS) using a variety of miRNA profiling techniques. In this review, we discuss basic miRNA biology and nomenclature, the techniques available for miRNA profiling research and recent miRNA profiling studies in Multiple Sclerosis.

MicroRNAs accurately identify cancer tissue origin
Rosenfeld N, Aharonov R, Meiri E, Rosenwald S, Spector Y, Zepeniuk M, Benjamin H, Shabes N, Tabak S, Levy A, Lebanony D, Goren Y, Silberschein E, Targan N, Ben-Ari A, Gilad S, Sion-Vardy N, Tobar A, Feinmesser M, Kharenko O, Nativ O, Nass D, Perelman M, Yosepovich A, Shalmon B, Polak-Charcon S, Fridman E, Avniel A, Bentwich I, Bentwich Z, Cohen D, Chajut A, Barshack I.
Rosetta Genomics Ltd., Rehovot 76706, Israel.
Nat Biotechnol. 2008 Apr;26(4):462-9. doi: 10.1038/nbt1392
MicroRNAs (miRNAs) belong to a class of noncoding, regulatory RNAs that is involved in oncogenesis and shows remarkable tissue specificity. Their potential for tumor classification suggests they may be used in identifying the tissue in which cancers of unknown primary origin arose, a major clinical problem. We measured miRNA expression levels in 400 paraffin-embedded and fresh-frozen samples from 22 different tumor tissues and metastases. We used miRNA microarray data of 253 samples to construct a transparent classifier based on 48 miRNAs. Two-thirds of samples were classified with high confidence, with accuracy >90%. In an independent blinded test-set of 83 samples, overall high-confidence accuracy reached 89%. Classification accuracy reached 100% for most tissue classes, including 131 metastatic samples. We further validated the utility of the miRNA biomarkers by quantitative RT-PCR using 65 additional blinded test samples. Our findings demonstrate the effectiveness of miRNAs as biomarkers for tracing the tissue of origin of cancers of unknown primary origin.

Pre-microRNA and mature microRNA in human mitochondria
Barrey E, Saint-Auret G, Bonnamy B, Damas D, Boyer O, Gidrol X.
Unité de Biologie Intégrative des Adaptations à l'Exercice-INSERM U902, Genopole Evry, France
PLoS One. 2011;6(5):e20220. doi: 10.1371/journal.pone.0020220
BACKGROUND: Because of the central functions of the mitochondria in providing metabolic energy and initiating apoptosis on one hand and the role that microRNA (miRNA) play in gene expression, we hypothesized that some miRNA could be present in the mitochondria for post-transcriptomic regulation by RNA interference. We intend to identify miRNA localized in the mitochondria isolated from human skeletal primary muscular cells.
METHODOLOGY/PRINCIPAL FINDINGS: To investigate the potential origin of mitochondrial miRNA, we in-silico searched for microRNA candidates in the mtDNA. Twenty five human pre-miRNA and 33 miRNA aligments (E-value<0.1) were found in the reference mitochondrial sequence and some of the best candidates were chosen for a co-localization test. In situ hybridization of pre-mir-302a, pre-let-7b and mir-365, using specific labelled locked nucleic acids and confocal microscopy, demonstrated that these miRNA were localized in mitochondria of human myoblasts. Total RNA was extracted from enriched mitochondria isolated by an immunomagnetic method from a culture of human myotubes. The detection of 742 human miRNA (miRBase) were monitored by RT-qPCR at three increasing mtRNA inputs. Forty six miRNA were significantly expressed (2(nd) derivative method Cp>35) for the smallest RNA input concentration and 204 miRNA for the maximum RNA input concentration. In silico analysis predicted 80 putative miRNA target sites in the mitochondrial genome (E-value<0.05).
CONCLUSIONS/SIGNIFICANCE: The present study experimentally demonstrated for the first time the presence of pre-miRNA and miRNA in the human mitochondria isolated from skeletal muscular cells. A set of miRNA were significantly detected in mitochondria fraction. The origin of these pre-miRNA and miRNA should be further investigate to determine if they are imported from the cytosol and/or if they are partially processed in the mitochondria.

Toward the blood-borne miRNome of human diseases
Keller A, Leidinger P, Bauer A, Elsharawy A, Haas J, Backes C, Wendschlag A, Giese N, Tjaden C, Ott K, Werner J, Hackert T, Ruprecht K, Huwer H, Huebers J, Jacobs G, Rosenstiel P, Dommisch H, Schaefer A, Müller-Quernheim J, Wullich B, Keck B, Graf N, Reichrath J, Vogel B, Nebel A, Jager SU, Staehler P, Amarantos I, Boisguerin V, Staehler C, Beier M, Scheffler M, Büchler MW, Wischhusen J, Haeusler SF, Dietl J, Hofmann S, Lenhof HP, Schreiber S, Katus HA, Rottbauer W, Meder B, Hoheisel JD, Franke A, Meese E.
Biomarker Discovery Center, Heidelberg, Germany
Nat Methods. 2011 Sep 4;8(10): 841-843
In a multicenter study, we determined the expression profiles of 863 microRNAs by array analysis of 454 blood samples from human individuals with different cancers or noncancer diseases, and validated this 'miRNome' by quantitative real-time PCR. We detected consistently deregulated profiles for all tested diseases; pathway analysis confirmed disease association of the respective microRNAs. We observed significant correlations (P = 0.004) between the genomic location of disease-associated genetic variants and deregulated microRNAs.

Evaluation of two commercial global miRNA expression profiling platforms for detection of less abundant miRNAs
Jensen SG, Lamy P, Rasmussen MH, Ostenfeld MS, Dyrskjøt L, Orntoft TF, Andersen CL.
Department of Molecular Medicine (MOMA), Aarhus University Hospital-Skejby, DK-8200 Aarhus N, Denmark.
BMC Genomics. 2011 Aug 26;12: 435
BACKGROUND: microRNAs (miRNA) are short, endogenous transcripts that negatively regulate the expression of specific mRNA targets. miRNAs are found both in tissues and body fluids such as plasma. A major perspective for the use of miRNAs in the clinical setting is as diagnostic plasma markers for neoplasia. While miRNAs are abundant in tissues, they are often scarce in plasma. For quantification of miRNA in plasma it is therefore of importance to use a platform with high sensitivity and linear performance in the low concentration range. This motivated us to evaluate the performance of three commonly used commercial miRNA quantification platforms: GeneChip miRNA 2.0 Array, miRCURY Ready-to-Use PCR, Human panel I+II V1.M, and TaqMan Human MicroRNA Array v3.0.
RESULTS: Using synthetic miRNA samples and plasma RNA samples spiked with different ratios of 174 synthetic miRNAs we assessed the performance characteristics reproducibility, recovery, specificity, sensitivity and linearity. It was found that while the qRT-PCR based platforms were sufficiently sensitive to reproducibly detect miRNAs at the abundance levels found in human plasma, the array based platform was not. At high miRNA levels both qRT-PCR based platforms performed well in terms of specificity, reproducibility and recovery. At low miRNA levels, as in plasma, the miRCURY platform showed better sensitivity and linearity than the TaqMan platform.
CONCLUSION: For profiling clinical samples with low miRNA abundance, such as plasma samples, the miRCURY platform with its better sensitivity and linearity would probably be superior.

An alternative mode of microRNA target recognition
Chi SW, Hannon GJ, Darnell RB.
Laboratory of Neuro-Oncology, The Rockefeller University, Howard Hughes Medical Institute, New York, New York, USA
Nat Struct Mol Biol. 2012 19(3): 321-327
MicroRNAs (miRNAs) regulate mRNA targets through perfect pairing with their seed region (positions 2-7). Recently, a precise genome-wide map of miRNA interaction sites in mouse brain was generated by high-throughput sequencing and analysis of clusters of ~50-nucleotide mRNA tags cross-linked to Argonaute (Ago HITS-CLIP). By analyzing Ago HITS-CLIP 'orphan clusters'-Ago binding regions from HITS-CLIP that cannot be explained by canonical seed matches-we have now identified an alternative binding mode used by miRNAs. Specifically, G-bulge sites (positions 5-6) are often bound and regulated by miR-124 in brain. More generally, bulged sites comprise ≥15% of all Ago-miRNA interactions in mouse brain and are evolutionarily conserved. We call position 6 the 'pivot' nucleotide and suggest a model in which a transitional 'nucleation bulge' leads to functional bulge mRNA-miRNA interactions, expanding the number of potential miRNA regulatory sites.

Small non-coding RNAs in animal development
Giovanni Stefani & Frank J. Slack
Nature Reviews Molecular Cell Biology 9, 219-230 (2008)
The modulation of gene expression by small non-coding RNAs is a recently discovered level of gene regulation in animals and plants. In particular, microRNAs (miRNAs) and Piwi-interacting RNAs (piRNAs) have been implicated in various aspects of animal development, such as neuronal, muscle and germline development. During the past year, an improved understanding of the biological functions of small non-coding RNAs has been fostered by the analysis of genetic deletions of individual miRNAs in mammals. These studies show that miRNAs are key regulators of animal development and are potential human disease loci.

MicroRNAs in metabolism and metabolic disorders
Rottiers V, Näär AM.
Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129, USA.
Nat Rev Mol Cell Biol. 2012 13(4): 239-250
MicroRNAs (miRNAs) have recently emerged as key regulators of metabolism. For example, miR-33a and miR-33b have a crucial role in controlling cholesterol and lipid metabolism in concert with their host genes, the sterol-regulatory element-binding protein (SREBP) transcription factors. Other metabolic miRNAs, such as miR-103 and miR-107, regulate insulin and glucose homeostasis, whereas miRNAs such as miR-34a are emerging as key regulators of hepatic lipid homeostasis. The discovery of circulating miRNAs has highlighted their potential as both endocrine signalling molecules and disease markers. Dysregulation of miRNAs may contribute to metabolic abnormalities, suggesting that miRNAs may potentially serve as therapeutic targets for ameliorating cardiometabolic disorders.

Virus-encoded microRNAs: an overview and a look to the future
Kincaid RP, Sullivan CS.
The University of Texas at Austin, Molecular Genetics & Microbiology, Austin, Texas, United States of America.
PLoS Pathog. 2012 8(12): e1003018
MicroRNAs (miRNAs) are small RNAs that play important roles in the regulation of gene expression. First described as posttranscriptional gene regulators in eukaryotic hosts, virus-encoded miRNAs were later uncovered. It is now apparent that diverse virus families, most with DNA genomes, but at least some with RNA genomes, encode miRNAs. While deciphering the functions of viral miRNAs has lagged behind their discovery, recent functional studies are bringing into focus these roles. Some of the best characterized viral miRNA functions include subtle roles in prolonging the longevity of infected cells, evading the immune response, and regulating the switch to lytic infection. Notably, all of these functions are particularly important during persistent infections. Furthermore, an emerging view of viral miRNAs suggests two distinct groups exist. In the first group, viral miRNAs mimic host miRNAs and take advantage of conserved networks of host miRNA target sites. In the larger second group, viral miRNAs do not share common target sites conserved for host miRNAs, and it remains unclear what fraction of these targeted transcripts are beneficial to the virus. Recent insights from multiple virus families have revealed new ways of interacting with the host miRNA machinery including noncanonical miRNA biogenesis and new mechanisms of posttranscriptional cis gene regulation. Exciting challenges await the field, including determining the most relevant miRNA targets and parlaying our current understanding of viral miRNAs into new therapeutic strategies. To accomplish these goals and to better grasp miRNA function, new in vivo models that recapitulate persistent infections associated with viral pathogens are required.

A versatile method to design stem-loop primer-based quantitative PCR assays for detecting small regulatory RNA molecules
Czimmerer Z, Hulvely J, Simandi Z, Varallyay E, Havelda Z, Szabo E, Varga A, Dezso B, Balogh M, Horvath A, Domokos B, Torok Z, Nagy L, Balint BL.
Department of Biochemistry and Molecular Biology, Research Center for Molecular Medicine, University of Debrecen Medical and Health Science Center, Debrecen, Hungary.
PLoS One. 2013;8(1): e55168
Short regulatory RNA-s have been identified as key regulators of gene expression in eukaryotes. They have been involved in the regulation of both physiological and pathological processes such as embryonal development, immunoregulation and cancer. One of their relevant characteristics is their high stability, which makes them excellent candidates for use as biomarkers. Their number is constantly increasing as next generation sequencing methods reveal more and more details of their synthesis. These novel findings aim for new detection methods for the individual short regulatory RNA-s in order to be able to confirm the primary data and characterize newly identified subtypes in different biological conditions. We have developed a flexible method to design RT-qPCR assays that are very sensitive and robust. The newly designed assays were tested extensively in samples from plant, mouse and even human formalin fixed paraffin embedded tissues. Moreover, we have shown that these assays are able to quantify endogenously generated shRNA molecules. The assay design method is freely available for anyone who wishes to use a robust and flexible system for the quantitative analysis of matured regulatory RNAs.

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