Engineering elements for gene silencing: the artificial microRNAs technology.

Small RNA (sRNA)-mediated gene silencing constitutes a powerful tool for the molecular characterization- of a given gene. The RNAi technology has been largely used for this purpose. This approach is based on the cloning of an inverted repeated fragment of the gene to be silenced. Even when this approach -produces a strong repression of the target gene it also involves the production of multiple small RNAs species that can easily lead to off targeting. Taking advantage of the latest insights into the new post-biogenesis layer of regulation in microRNA (miRNA) activity, it is possible to overcome the above-mentioned limitation. Artificial microRNAs (amiRNAs) are 21mer small RNAs, which can be genetically engineered and they function to specifically silence single or multiple genes of interest. Since generally just one miRNA molecule is generated from each precursor, the specificity of this technology is much higher than longer inverted repeats. Application of this technology results in highly specific mRNA downregulation by computationally designed sequences programmed to target one or a set of custom-selected transcripts.