MicroRNA or miRNAs are small 21 base length non-coding oligonucleotides responsible for post-transcriptional regulators of messenger RNA transcripts (mRNAs). The way it regulates gene expression is not properly understood.
The miRNA is usually found in the non-coding introns while some are found in exons and transcribed by RNA polymerase II. It is estimated that there are about 1000 miRNAs or more. In recent years it has come to light that several of these miRNAs are implicated in diseases particularly cancer. The emergence of miRNA dysfunctions in cancers and other human diseases is of great therapeutic potential.
There is a difference between microRNA and siRNA, that siRNA can be synthetically made and can be transfected exogenously while the siRNA are endogenous in nature. However both work by blocking mRNA and the way it seems to act as RNA interference is similar. Another difference between siRNAs and miRNAs are that miRNAs are encoded by specific miRNA genes as short hairpin in the nucleus. In addition, the function of siRNA is the breakdown of mRNA while the function of miRNA is to inhibit expression of protein synthesis by blocking the translation of mRNAs. Currently a lot of research is being carried out to identify more miRNAs and its role in the pathogenesis of various diseases. For example it is know known that miR-21 is over-expressed in several cancers including breast tumors. This suggests the oncogenic potential of some miRNAs and its modulation in tumorigenesis.
As the association between miRNAs and disease are complex, more research is required to understand the importance of between the two. A database of such microRNAs will enable quick access of miRNAs associated with diseases.
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