Know-how of RNA interference and its applications in research and therapy

Double stranded RNA (dsRNA) mediates gene silencing in a sequence specific manner. Originally recognized in plants and lower organisms, it was recently extended to higher eukaryotes and established as an important evolutionary conserved phenomenon. It has been established that the double stranded short interfering RNAs (siRNAs) originate by the activity of a dsRNA-specific endonuclease, Dicer. siRNA in conjunction with a multiple enzyme complex called RNA-induced silencing complex (RISC) locates to the specific sites on mRNA and degrades it by endonuclease and exonuclease activities. In addition to gene silencing at transcript level (degradation of messenger RNA), siRNA was also shown to reduce the expression of protein by silencing of gene promoters via de novo methylation. By virtue of their specific gene silencing activity and owing to the recent discoveries on their plasmid and virus driven expression, small dsRNAs are being widely adopted in research and therapeutics. They are rapidly replacing the conventional gene knock-out technologies. siRNA libraries are also being recruited as a new tool in genome wide functional screenings. There is no doubt that further progress in understanding the mechanism of their action as well as strategies to achieve their tightly regulated and tissue specific expression will revolutionize basic and applied biomedical research. (C) 2004 Elsevier B.V. All rights reserved.