Micro-RNAs (miRNAs): Genomic organisation, biogenesis and mode of action

Department of Biotechnology, University of Kashmir, Science Block, Hazratbal Campus, Srinagar, Kashmir 190006, India.
Cell and Tissue Research (Impact Factor: 3.57). 05/2012; 349(2):405-13. DOI: 10.1007/s00441-012-1438-0
Source: PubMed


MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression in animals and in plants. In recent years, miRNAs have been shown to be important biological molecules for regulating various cellular functions. miRNAs function post-transcriptionally usually by base-pairing to the mRNA 3'-untranslated regions of the mRNAs and repress protein synthesis by mechanisms that are not fully understood. Various miRNA genes have been mapped in the genome of a number of organisms and the list continues to grow. Details regarding the genomic organisation, transcriptional regulation and post-transcriptional maturation of miRNAs are still emerging. In this review, information regarding the genomic organisation, biogenesis and regulation of expression of miRNAs is discussed.

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    • "They post-transcriptionally regulate expression of target genes primarily by destabilizing target mRNAs that can lead to mRNA degradation and/or translational repression (Fabian et al., 2010; Ul Hussain, 2012). Increasing numbers of miRNAs have been shown to play key regulatory roles in cell proliferation, differentiation, apoptosis and hematopoiesis (Ul Hussain, 2012; Esteller, 2011). Aberrant expression of miRNA has been increasingly documented in various types of tumors, including lymphomas (Lawrie, 2013; Husby et al., 2013). "
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    ABSTRACT: Lymphoblastic lymphoma is an aggressive subtype of non-Hodgkin lymphoma. Identification of prognostic factors for these patients, especially for patients with T-cell lymphoblastic lymphoma (T-LBL), remains a challenge. This is largely due to relative rarity of the disease and lack of adequate samples for biological research. T-LBL is more common in Asia than in Western countries. In an attempt to explore novel prognostic markers for T-LBL, we conducted retrospective study of archived diagnostic specimens from 57 Chinese patients with well-defined diagnosis of T-LBL. Using quantitative real-time reverse transcription-PCR, we analyzed miR-17 and miR-19 expression levels in formalin-fixed and paraffin-embedded lymph node specimens from these patients, together with reactive lymph node controls. We correlated molecular findings to patients' immunophenotype and clinical follow-up information. MYC protein expression was also evaluated in these patients. We found that miR-17 and miR-19 levels were concordant and upregulated in T-LBL in comparison with controls. Statistical analysis showed that higher expression of miR-17 and miR-19, and positive MYC protein results were associated with a shorter overall survival of T-LBL. In addition, miR-17 and miR-19 appeared to be independent prognostic factors for T-LBL. We demonstrate here that upregulation of miR-17 and miR-19 correlates with poor clinical outcome of T-LBL, indicating that miR-17 and miR-19 may be considered as potential unfavorable prognostic markers for T-LBL. Copyright © 2015. Published by Elsevier Inc.
    Experimental and Molecular Pathology 07/2015; 99(2). DOI:10.1016/j.yexmp.2015.07.012 · 2.71 Impact Factor
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    • "They can increase or decrease protein expression by binding to the 3′-untranslated region (UTR) or to other regions (e.g., the 5′-UTR, coding sequences) of target mRNA transcripts [11] and thus play a central role in gene regulation in both health and disease. miRNA genes are located in inter- or intragenic regions of protein-coding gene introns and/or exons and are transcribed from DNA but not translated into proteins; they can exist individually or form clusters (reviewed in [12]). "
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    ABSTRACT: MicroRNAs are one class of small, endogenous, non-coding RNAs that are approximately 22 nucleotides in length; they are very numerous, have been phylogenetically conserved, and involved in biological processes such as development, differentiation, cell proliferation, and apoptosis. MicroRNAs contribute to modulating the expression levels of specific proteins based on sequence complementarity with their target mRNA molecules and so they play a key role in both health and disease. Angiogenesis is the process of new blood vessel formation from preexisting ones, which is particularly relevant to cancer and its progression. Over the last few years, microRNAs have emerged as critical regulators of signalling pathways in multiple cell types including endothelial and perivascular cells. This review summarises the role of miRNAs in tumour angiogenesis and their potential implications as therapeutic targets in cancer.
    BioMed Research International 08/2014; 2014:878450. DOI:10.1155/2014/878450 · 1.58 Impact Factor
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    • "Therefore, the occurrence of 18 R − pre-miRNA entirely by chance is very unlikely. Some authors describe mirtrons as tightly packed between exons [3], but in our analysis we have found that this is not the case. Most mirtrons are surrounded by intronic sequences not exons. "
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    ABSTRACT: Mirtrons are a special type of pre-miRNA which originate from intronic regions and are spliced directly from the transcript instead of being processed by Drosha. The splicing mechanism is better understood for the processing of mRNA for which was established that there is a characteristic CG content around splice sites. Here we analyse the CG-content ratio of pre-miRNAs and mirtrons and compare them with their genomic neighbourhood in an attempt to establish key properties which are easy to evaluate and to understand their biogenesis. We propose a simple log-ratio of the CG-content comparing the precursor sequence and is flanking region. We discovered that Caenorhabditis elegans and Drosophila melanogaster mirtrons, so far without exception, have smaller CG-content than their genomic neighbourhood. This is markedly different from usual pre-miRNAs which mostly have larger CG-content when compared to their genomic neighbourhood. We also analysed some mammalian and primate mirtrons which, in contrast the invertebrate mirtrons, have higher CG-content ratio.
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