miRNA: licensed to kill the messenger.

Current developments have brought non-coding genes under limelight together with their better-known siblings, the coding genes or mRNA. The 2006 Nobel Prize in Physiology or Medicine was awarded to Andrew Fire and Craig Mello for their 1998 discovery that double-stranded RNA triggers suppression of gene activity in a homology-dependent manner, a process named RNA interference (RNAi). Post-transcriptional regulation of genes was generally regarded as an odd regulatory mechanism for several years until it was learnt that regulatory trans-acting antisense RNAs exist in several species. Identification of a large number of small RNA molecules called microRNAs (miRNAs) elevated the overall field of biomedical RNAi to the striking level of current recognition. miRNAs represent a class of endogenous small ( approximately 22 nucleotides) RNA molecules that can repress protein synthesis. It is estimated that there are over 600 miRNAs in mammalian cells, and that about 30% of all genes are regulated by miRNA. Current understanding of the molecular mechanism of any disease would be incomplete without factoring in the functional significance of miRNA. In the category of the futuristic RNAi drugs, miRNA-based therapies are promising. The field has progressed rapidly as it relates to cancer research (highlighted in DNA and Cell Biology Volume 26, Number 4), while development in most other areas (highlighted in DNA and Cell Biology Volume 26, Number 3) of biomedical research remains in its infancy, offering significant opportunity for researchers. Approaches to interfere with miRNA function in vivo offer novel therapeutic opportunities. Lessons in gene therapy have taught us that tinkering with the genetic machinery comes with its own set of risks, especially in a clinical setting. miRNA-based therapies are also subject to such risks, which need to be prudently managed. Having acknowledged the potential risk, we have to recognize that new knowledge about the functional roles of miRNA is revolutionizing cell biology and will have a major impact on biomedical research imminently.