Intracellular localization and routing of miRNA and RNAi pathway components.

Several different pathways, generally termed RNA silencing pathways, utilize small RNA molecules guiding sequence-specific silencing effects of ribonucleoprotein effector complexes, traditionally termed RNA-induced silencing complex (RISC). Three RNA silencing pathways were recognized in mammalian cells: RNA interference (RNAi), where short RNAs produced from long double-stranded RNA guide cleavage of cognate mRNAs, microRNA (miRNA) pathway, where endogenously-encoded miRNAs typically induce translational repression, and piRNA pathway, where piRNAs (PIWI-associated RNAs) guide repression of repetitive sequences in the germline. Originally, RNAi and miRNA pathways were thought to act in the cytoplasm, however, there is a growing body of evidence that these pathways also have a nuclear component.