The emerging world of microRNAs.

MicroRNAs (miRNAs) are a family of naturally occurring, evolutionary conserved, small (approximately 19-23 nucleotides), non-protein-coding RNA molecules that generally negatively regulate post-transcriptional gene expression. miRNAs are estimated to account for >3% of all human genes and to control expression of thousands of target mRNAs, with multiple miRNAs targeting each mRNA. A role for miRNAs has been identified in both normal physiological and pathological conditions, including metabolism, proliferation, cell death, differentiation and development, insulin secretion from pancreatic beta cells, viral infection and cancer. Antisense technologies have been successfully used to control miRNA expression in vitro and in vivo. Further analysis of this interesting class of small RNAs, in normal and pathological conditions, will enable us determine their potential to be exploited as therapeutic targets in disease.