Article body Our knowledge of RNA interference — popularly known as RNAi — has expanded dramatically in the short time since its discovery. Several types of small silencing RNAs have now been discovered, including small interfering RNAs (siRNAs), microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs). Small RNAs are involved in regulating gene expression in many ways, and RNAi is being harnessed by