Diversity of animal small RNA pathways and their biological utility

Higher eukaryotes employ extensive post‐transcriptional gene regulation to accomplish fine control of gene expression. The microRNA (miRNA) family plays important roles in the post‐transcriptional gene regulation of broad networks of target mRNA expression. Most miRNAs are generated by a conserved mechanism involving two RNase III enzymes Drosha and Dicer. However, work from the past few years has uncovered diverse noncanonical miRNA pathways, which exploit a variety of other RNA processing enzymes. In addition, the discovery of another abundant small RNA family, endogenous short interfering RNAs (endo‐siRNAs), has also broadened the catalogs of short regulatory RNAs. This review highlights recent studies that revealed novel small RNA biogenesis pathways, and discusses their relevance to gene regulatory networks. WIREs RNA 2012, 3:351–368. doi: 10.1002/wrna.113 This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > Biogenesis of Effector Small RNAs RNA Processing > Processing of Small RNAs Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs