SnapShot: Endogenous RNAi Pathways

Endogenous RNAi (endoRNAi) identifies a heterologous but interrelated array of small RNA-mediated phenomena triggered by and directing the silencing of endogenous sequences. EndoRNAi mechanisms target aberrant transcripts and repetitive and mobile RNA sequences, as well as bona fide messenger RNAs. In most endoRNAi mecha-nisms, the underlying molecular events remain poorly defined but appear to be almost as diverse as the targeted loci. A great variety of triggers can initiate endoRNAi in differ-ent cell types and species, each resulting in specific modes of small RNA biogenesis, response amplification, and gene silencing. In spite of such diversity, redundant themes prevail among the endoRNAi mechanisms. Our objective was to capture most of those themes. Note that, although it would conceptually fit within the continuum of endoRNAi mechanisms, canonical microRNA-mediated silencing is usually considered separately. This specific pathway has been extensively reviewed and is therefore not included in this SnapShot.In certain species of yeasts, protozoa (such as