This site has a user-friendly procedure and information can be accessed by two ways.

First: User can go to Database search section and by selecting category, organism and main feature of databases can reach the appropriate databases Fig. 1.

Figure 1: Database search

Second: user can click on each resource category and can access all the databases in this category Fig. 1.

Figure 2: miRNA category resources

miRNAs clamp down on gene expression by cleavage or translational inhibition of mRNAs through binding to complementary regions in the 3′-untranslated region (3’-UTR) of their targets. Although, greatest studies into miRNA function has located for sites in 3′ UTRs, some investigations show that targeting can happen in 5′ UTRs and coding sequence (CDS)[1, 2].

miRNA biosynthesis is mainly mediated by two RNase III-proteins; the initially transcribed pri-miRNA is processed by Drosha to pre-miRNA that is next exported to the cytoplasm to be further processed to double-stranded 21-23 nt long mature miRNA by Dicer. In some cases, only one of the two strands of the mature miRNA, known as guide strand, associates with the RNA-induced silencing complex (RISC) and directs it to target mRNAs by base pairing; whereas, in other cases both strands can do this (Figure 1). In plants, the homology between miRNA and mRNA is extensive and leads to mRNA degradation. However, in animals, the complementarity is mostly located to nucleotides 2-8 at the 5’ end of miRNA (seed region)[3-5]. Concepts of miRNA function are summarized in Figure.



miRNA gene transcription, biogenesis and function. Several transcription factors (TF) control miRNA gene transcription positively or negatively. miRNAs are transcribed by RNA polymerase II to yield pri-miRNA which is processed by Drosha to pre-miRNA. Pri-miRNAs are  then exported to the cytoplasm to be further processed into double-stranded 21-23 nt long mature miRNA by Dicer. Mature miRNA associates with the RNA-induced silencing complex (RISC) and directs it to target mRNAs by base pairing.

A single miRNA can suppress the expression of hundreds of genes, therefore controlling several molecular processes. Multiplicity of miRNA targets, a routine process of miRNA function includes the limited suppression of numerous mRNAs in a biological pathway by a single miRNA. This mechanism decreases the requirement on a single miRNA-mRNA interaction and rises the strength of the gene controlling system. miRNA buffering effect, miRNAs may target factors which activate or inhibit a certain process, thus protecting that process from environmental oscillations.


1.    Kloosterman WP, Wienholds E, Ketting RF et al. Substrate requirements for let-7 function in the developing zebrafish embryo, Nucleic Acids Res 2004;32:6284-6291.
2.    Lytle JR, Yario TA, Steitz JA. Target mRNAs are repressed as efficiently by microRNA-binding sites in the 5' UTR as in the 3' UTR, Proc Natl Acad Sci U S A 2007;104:9667-9672.
3.    Davis-Dusenbery BN, Hata A. Mechanisms of control of microRNA biogenesis, J Biochem 2010;148:381-392.
4.    Krol J, Loedige I, Filipowicz W. The widespread regulation of microRNA biogenesis, function and decay, Nat Rev Genet 2010;11:597-610.
5.    Treiber T, Treiber N, Meister G. Regulation of microRNA biogenesis and function, Thromb Haemost 2012;107:605-610.

 MicroRNAs (miRNAs) are a class of 21–23 nucleotides(nt), non- coding RNAs that regulate gene expression network post-transcriptionally[1]. Studies in different organisms have shown the role of miRNAs as critical components of gene regulatory networks in eukaryotes and they are estimated to regulate at least 50% of the human gene expression[2]. Recent studies have verified the significant role of miRNAs in a broad range of biological activities, such as cell proliferation, differentiation, senescence, metabolism, apoptosis, and life span[2, 3]. miRNA research has attracted a lot of attention among biomedical researchers focusing on human diseases. These studies have uncovered the critical regulatory functions of miRNAs in varieties of human disorders ranging from cancers[4], autoimmune[5] and infectious diseases[6] to cardiac[7] and neurological disorders[8]. miRNAs are expected to be clinically valuable as therapeutic agents[9, 10], biomarkers for diagnosis, assessment of disease progression and response to drugs[11-15]. Consequently, miRNA research is crucial to fully comprehend the molecular underpinnings of human diseases as well as the basic aspects of eukaryotic physiology.



1.            Bartel DP. MicroRNAs: target recognition and regulatory functions, Cell 2009;136:215-233.

2.            Huntzinger E, Izaurralde E. Gene silencing by microRNAs: contributions of translational repression and mRNA decay, Nat Rev Genet 2011;12:99-110.

3.            Dai R, Ahmed SA. MicroRNA, a new paradigm for understanding immunoregulation, inflammation, and autoimmune diseases, Transl Res 2011;157:163-179.

4.            Jansson MD, Lund AH. MicroRNA and cancer, Mol Oncol 2012;6:590-610.

5.            Quintero-Ronderos P, Montoya-Ortiz G. Epigenetics and autoimmune diseases, Autoimmune Dis 2012;2012:593720.

6.            Kumar A. MicroRNA in HCV infection and liver cancer, Biochim Biophys Acta 2011;1809:694-699.

7.            Yu S, Li G. MicroRNA expression and function in cardiac ischemic injury, J Cardiovasc Transl Res 2010;3:241-245.

8.            Salta E, De Strooper B. Non-coding RNAs with essential roles in neurodegenerative disorders, Lancet Neurol 2012;11:189-200.

9.            Fiedler J, Gupta SK, Thum T. MicroRNA-based therapeutic approaches in the cardiovascular system, Cardiovasc Ther 2012;30:e9-e15.

10.          Jackson A, Linsley PS. The therapeutic potential of microRNA modulation, Discov Med 2010;9:311-318.

11.          Rukov JL, Shomron N. MicroRNA pharmacogenomics: post-transcriptional regulation of drug response, Trends Mol Med 2011;17:412-423.

12.          Du L, Pertsemlidis A. microRNA regulation of cell viability and drug sensitivity in lung cancer, Expert Opin Biol Ther 2012;12:1221-1239.

13.          Kosaka N, Iguchi H, Ochiya T. Circulating microRNA in body fluid: a new potential biomarker for cancer diagnosis and prognosis, Cancer Sci 2010;101:2087-2092.

14.          Luo X, Burwinkel B, Tao S et al. MicroRNA signatures: novel biomarker for colorectal cancer?, Cancer Epidemiol Biomarkers Prev 2011;20:1272-1286.

15.          Zen K, Zhang CY. Circulating microRNAs: a novel class of biomarkers to diagnose and monitor human cancers, Med Res Rev 2012;32:326-348.