RNA InterferencePrinciples and Applications

RNA interference (RNAi) is a term used to describe a series of mechanisms in eukaryotic cells that utilize small RNA duplexes of 21 to 25 nucleotides in length for regulation of gene expression. RNAi pathways exist in all higher eukaryotic organisms as well as in many lower eukaryotes. The types... read moreof gene regulation initiated by small RNA duplexes range from transcriptional gene silencing to inhibition of translation.

A common feature of all RNAi related mechanisms is the need for cells to produce the short RNA duplexes via an RNAse III family enzyme termed Dicer. Dicer generates short duplexes with a recessed 5’ phosphate group and protruding 2 base 3’ overhangs. The Dicer produced RNAs can enter into one or more pathways in the cell wherein one of the two strands may be selected to guide a complex of proteins to a target RNA (or DNA) sequence that is the substrate for cleavage, translational inhibition, or chromatin modification. Naturally occurring small RNAs are termed micro RNAs, or miRNAs.

These miRNAs are produced from primary Pol II transcripts as precursors, often poly miRNA containing precursors, which are subsequently processed via two independent cleavage events into short duplexes. Although there are over 250 known miRNAs in humans, the targets and functions for only a handful are known. The cellular proteins that process and utilize endogenous miRNAs can be programmed to with synthetic or vector expressed short RNA duplexes to mediate transcriptional or post-transcriptional silencing of selected target genes or mRNAs.

The world of small RNAs and their involvement in a variety of critical cellular processes is currently one of the hottest areas of biology. In addition to understanding the functional roles that endogenous small RNAs play in regulating expression of mRNAs or proteins, there is great interest in exploiting these molecules for target identification and validation in human disease, as well as applying small RNAs as target specific therapeutic agents. This series will examine the biogenesis and functioning of endogenous small RNAs, explore the biochemistry of the complexes of small RNAs and proteins involved in the various RNAi pathways, and finally present applications of small RNAs in functional genomics and as therapeutic agents.