siRNAs and shRNAs: skeleton keys to the human genome

The use of RNA interference (RNAi) to evoke gene silencing in mammalian cell systems is rapidly becoming a standard laboratory technique. Recent experiments have also proven the utility of RNAi in animals. The next few years will bear witness to the first RNAi-based genome-wide screens in mammals, breaking the barrier to the use of mammalian cells as a genetic system. In this review, some of the key features of RNAi in mammalian systems are discussed.