Function and Localization of MicroRNAs in Mammalian Cells

Abstract

microRNAs (miRNAs) represent a large set of master regulators of gene expression. They constitute 1–4% of human genes andprobably regulate 30% of protein-encoding genes. These small regulatory RNAs act at a posttranscriptional level—mediatingtranslational repression and/or mRNA degradation—through their association with Argonaute protein and target mRNAs. Inthis paper, we discuss various mechanisms by which miRNAs regulate posttranscriptionally, including their subcellular localization.Recent results indicate that the majority of miRNA-targeted and thus translationally repressed mRNA is probably distributedin the diffuse cytoplasm, even though a small fraction is concentrated in subcellular compartments, such as processingbodies or stress granules; notably, the stress granule localization of Argonaute depends on the presence of miRNAs. Here wediscuss the structural requirement of these subcellular compartments in light of their potential miRNA functions.