What's new about RNAi? Meeting on siRNAs and miRNAs.

Abstract

This Keystone meeting on siRNAs and miRNAs took place in Keystone, Colorado, USA, between April 14 and 19, 2004 and was organized by T. Tuschl and V. Ambros. ![][1] RNAi stands for ‘RNA interference’, which is the silencing of gene expression by the administration of double‐stranded RNA (dsRNA). Endogenous RNAi seems to be a primitive sort of immune system, the aim of which is to defend genomes against molecular parasites such as viruses and transposons. During the process of RNAi, the dsRNA is converted into a shorter form: siRNA. The term siRNA stands for ‘short interfering RNA’, and synthetic versions of these 21‐nucleotide molecules are widely used to induce RNAi in mammalian cell systems because they circumvent the aspecific interferon response of these cells to dsRNA. Then there is another species of small RNA molecule, the so‐called miRNA (micro RNA). It is important to note that miRNAs are always encoded by the genome itself as hairpin structures, whereas siRNAs can be both artificial and endogenous (Hamilton & Baulcombe, 1999; Aravin et al , 2001; Reinhart & Bartel, 2002; Ambros et al , 2003). Both molecules feed largely into one and the same process that can either lead to messenger RNA degradation or to the inhibition of protein synthesis. As a rule, siRNAs cause mRNA destruction, whereas miRNAs can cause both. In plants, the majority of miRNAs direct cleavage, whereas miRNAs in animals most often induce translation inhibition; however, examples of translation inhibition in plants and cleavage in animals have been found (Chen, 2004; Yekta et al , 2004). In this review, we follow the fate of these small molecules from their point of synthesis to the execution of their repressive effect (Fig 1) and the use of that effect in the lab. While doing this, we highlight the novel findings … [1]: /embed/graphic-1.gif