Post-transcriptional gene silencing by double-stranded RNA

Key Points RNA interference (RNAi) is the process by which double-stranded RNA specifically silences the expression of homologous genes through degradation of their cognate mRNA. Silencing is therefore a post-transcriptional phenomenon. The genetic silencing that occurs by RNAi is highly specific and is based on the sequence of the double-stranded RNA. Post-transcriptional gene silencing in plants and fungi is mechanistically related to RNAi in animals. The destruction of mRNA is accomplished by a multi-component nuclease, called the RNA-induced silencing complex, or RISC. The input double-stranded RNA is processed into short (∼22-nucleotide) RNAs, which are incorporated into the RISC. Here they act as 'guide RNAs' to confer target specificity to the nuclease. A number of likely molecules that participate in RNAi have been identified in many model systems by genetic analysis. The proposed biological roles of RNAi include resistance to viruses, transposon silencing and regulation of endogenous gene expression, particularly during development. RNAi has become a valuable experimental tool for investigating gene function in Caenorhabditis elegans, Drosophila melanogaster and plants. Once the mechanism of RNAi is better understood, it may become a powerful technology to study a broader range of systems, including mammalian organisms and cultured cells. Imagine being able to knock out your favourite gene with only a day's work. Not just in one model system, but in virtually any organism: plants, flies, mice or cultured cells. This sort of experimental dream might one day become reality as we learn to harness the power of RNA interference, the process by which double-stranded RNA induces the silencing of homologous endogenous genes. How this phenomenon works is slowly becoming clear, and might help us to develop an effortless tool to probe gene function in cells and animals.