Long dsRNA and silent genes strike back:RNAi in mouse oocytes and early embryos

RNA interference (RNAi) refers to the selective degradation of mRNA induced by double-stranded RNA (dsRNA), first discovered in Caenorhabditis elegans. Homology-dependent silencing phenomena related to RNAi have been observed in many species from all eukaryotic kingdoms. RNAi and related mechanisms share several conserved components. The hallmark of these phenomena is the presence of short dsRNA molecules (21-25 bp long), termed short interfering RNA (siRNA), which are generated from dsRNA by the activity of Dicer, a specific type III RNAse. These molecules serve as a template for the recognition and cleavage of the cognate mRNA. As it is beyond the scope of a single review to cover all aspects of RNAi, this review will focus on certain steps of the pathway relevant to mammals and on the use of long dsRNA to specifically silence genes in mammalian cells permissive to this technique, such as oocytes and early embryos.