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A high-throughput method to monitor the expression of microRNA precursors.

ABSTRACT: microRNAs (miRNAs) are small, functional, non-coding RNAs. miRNAs are transcribed as long primary transcripts (primary precursors) that are processed to the approximately 75 nt precursors (pre-miRNAs) by the nuclear enzyme Drosha. The approximately 22 nt mature miRNA is processed from the pre-miRNA by the RNase III Dicer. The vast majority of published studies to date have used northern blotting to detect the expression of miRNAs. We describe here a sensitive, high throughput, real-time PCR assay to monitor the expression of miRNA precursors. Gene-specific primers and reverse transcriptase were used to convert the primary precursors and pre-miRNAs to cDNA. The expression of 23 miRNA precursors in six human cancer cell lines was assayed using the PCR assay. The miRNA precursors accumulated to different levels when compared with each other or when a single precursor is compared in the various cell lines. The precursor expression profile of three miRNAs determined by the PCR assay was identical to the mature miRNA expression profile determined by northern blotting. We propose that the PCR assay may be scaled up to include all of the 150+ known human miRNA genes and can easily be adaptable to other organisms such as plants, Caenorhabditis elegans and Drosophila.

SUBMITTER: Schmittgen TD

PROVIDER: S-EPMC390315 | biostudies-literature | 2004 Feb

REPOSITORIES: biostudies-literature

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A high-throughput method to monitor the expression of microRNA precursors.

Schmittgen Thomas D TD Jiang Jinmai J Liu Qian Q Yang Liuqing L

Nucleic acids research 20040225 4

microRNAs (miRNAs) are small, functional, non-coding RNAs. miRNAs are transcribed as long primary transcripts (primary precursors) that are processed to the approximately 75 nt precursors (pre-miRNAs) by the nuclear enzyme Drosha. The approximately 22 nt mature miRNA is processed from the pre-miRNA by the RNase III Dicer. The vast majority of published studies to date have used northern blotting to detect the expression of miRNAs. We describe here a sensitive, high throughput, real-time PCR assa ...[more]

PMID: 14985473

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Project description:BackgroundNormalization is critical for accurate gene expression analysis. A significant challenge in the quantitation of gene expression from biofluids samples is the inability to quantify RNA concentration prior to analysis, underscoring the need for robust normalization tools for this sample type. In this investigation, we evaluated various methods of normalization to determine the optimal approach for quantifying microRNA (miRNA) expression from biofluids and tissue samples when using the TaqMan® Megaplex™ high-throughput RT-qPCR platform with low RNA inputs.FindingsWe compared seven normalization methods in the analysis of variation of miRNA expression from biofluid and tissue samples. We developed a novel variant of the common mean-centering normalization strategy, herein referred to as mean-centering restricted (MCR) normalization, which is adapted to the TaqMan Megaplex RT-qPCR platform, but is likely applicable to other high-throughput RT-qPCR-based platforms. Our results indicate that MCR normalization performs comparable to or better than both standard mean-centering and other normalization methods. We also propose an extension of this method to be used when migrating biomarker signatures from Megaplex to singleplex RT-qPCR platforms, based on the identification of a small number of normalizer miRNAs that closely track the mean of expressed miRNAs.ConclusionsWe developed the MCR method for normalizing miRNA expression from biofluids samples when using the TaqMan Megaplex RT-qPCR platform. Our results suggest that normalization based on the mean of all fully observed (fully detected) miRNAs minimizes technical variance in normalized expression values, and that a small number of normalizer miRNAs can be selected when migrating from Megaplex to singleplex assays. In our study, we find that normalization methods that focus on a restricted set of miRNAs tend to perform better than methods that focus on all miRNAs, including those with non-determined (missing) values. This methodology will likely be most relevant for studies in which a significant number of miRNAs are not detected.

Project description:Background: Only a subset of radically-resected pancreatic ductal adenocarcinoma (PDAC) patients benefit from chemotherapy, and identification of novel prognostic factors is warranted. Recently miRNAs emerged as diagnostic biomarkers and innovative therapeutic targets, while high-throughput arrays are opening new opportunities to evaluate whether they can also predict clinical outcome. The present study evaluated whether comprehensive miRNA expression profiling correlated with overall survival (OS) in resected PDAC patients. Methodology/Principal Findings: High-resolution miRNA profiles were obtained with the Toray’s 3D-GeneTM miRNA chip, detecting more than 1200 types of human miRNA. RNA was isolated from paraffin-embedded primary tumors of 26 radically resected stage-pT3N1 homogeneously treated patients (adjuvant gemcitabine 1000mg/m2/day, days-1/8/15, every 28days), carefully selected according to their outcome (OS<12 vs. OS>30 months, i.e. short/long-OS). Highly stringent statistics included t-test, distance matrix with Spearman-ranked correlation, and iterative approaches. Unsupervised hierarchical analysis revealed that PDAC specimens clustered according to their short/long-OS classification, while the feature selection algorithm RELIEF identified the top-4 discriminating miRNAs between the two groups. These miRNAs target more than 1500 transcripts, including 169 targeted by two or more of these miRNAs. MiR-211 emerged as the best discriminating miRNA, with significantly higher expression in long- vs. short-OS patients. The expression of this miRNA was subsequently assessed by quantitative-PCR in an independent cohort of laser microdissected tumors from 60 resected stage-pT3N1 PDAC patients treated with the same gemcitabine regimen. Patients with low miR-211 expression according to median value had a significantly shorter median OS (14.8, 95%CI=13.1-16.5, vs. 25.7 months, 95%CI=16.2-35.1, log-rank P=0.004). Multivariate analysis demonstrated that low miR-211 expression was an independent factor of poor prognosis (hazard ratio 2.3, P=0.03) after adjusting for all the factors influencing outcome. 19 samples, duplicated gene spots

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A high-throughput method to monitor the expression of microRNA precursors.

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A high-throughput method to monitor the expression of microRNA precursors.

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