RNA interference (RNAi) is a ubiquitous pathway that regulates gene expression. It uses small, imperfectly paired, double-stranded RNAs approximately 21 nucleotides long, called microRNAs, that are processed from longer stem-loop transcripts.1 MicroRNAs are taken up by the cytoplasmic RNA-induced silencing complex (RISC), which removes 1 strand, leaving an unpaired strand that binds to messenger RNAs (mRNAs) with a partially complementary sequence. RISC suppresses the expression of bound mRNAs by accelerating their degradation and suppressing their translation into protein. MicroRNAs and the RNAi gene-silencing pathway were first discovered in the 1990s in plants, worms, and flies. In those organisms, microRNAs play an important role in regulating changes in gene expression that occur in development and in protection from viruses.
Lieberman J, Sharp PA. Harnessing RNA Interference for TherapyThe Silent Treatment. JAMA. 2015;313(12):1207-1208. doi:10.1001/jama.2015.1241