RNA Interference and Gene Silencing

How double-stranded RNA triggers sequence-specific silencing of genes — a defence and regulatory pathway that is also a powerful laboratory tool.

Definition

RNA interference is a conserved gene-silencing pathway in which double-stranded RNA is processed into short guide RNAs that direct a protein complex to complementary messenger RNAs, leading to their cleavage or translational repression.

Scope

This topic covers RNA interference and related small-RNA silencing: the triggering of silencing by double-stranded RNA, its processing into small interfering RNAs, the action of the silencing effector complex, and the biological roles of the pathway in defence against viruses and transposons and in gene regulation. It also notes the use of RNAi as an experimental and therapeutic strategy. Endogenous microRNAs are covered more fully under non-coding RNA.

Core questions

• How does double-stranded RNA cause specific gene silencing?
• How is the trigger RNA processed into small interfering RNAs?
• What does the silencing complex do to a target mRNA?
• What are the natural roles of RNA interference, and how is it used in the lab?

Key theories

Double-stranded RNA as a silencing trigger

Fire and Mello showed that double-stranded RNA, far more potently than either strand alone, silences the matching gene in a sequence-specific way, revealing RNA interference as a defined regulatory pathway.

Guide-directed effector silencing

Long double-stranded RNA is diced into short duplexes whose guide strand programmes an effector complex to recognise complementary messages, coupling sequence specificity to mRNA cleavage or repression.

Mechanisms

An endonuclease processes long double-stranded RNA into short interfering RNA duplexes, one strand of which is loaded as a guide into the RNA-induced silencing complex containing an Argonaute protein. The guide RNA base-pairs with complementary messenger RNAs, directing their cleavage when pairing is extensive or repressing their translation when pairing is partial. The pathway overlaps mechanistically with endogenous microRNA silencing and can, in some organisms, direct chromatin-level silencing, providing defence against viruses and mobile elements as well as gene regulation.

Clinical relevance

RNA interference is a standard tool for knocking down genes in research and is the basis of approved small-RNA therapeutics; provided as significance, not clinical guidance.

History

The 1998 demonstration by Fire and Mello that double-stranded RNA triggers potent, specific silencing in C. elegans defined RNA interference and earned the 2006 Nobel Prize in Physiology or Medicine, after which the pathway's components and uses were rapidly developed.

Key figures

• Andrew Fire
• Craig Mello

Seminal works

• fire1998
• alberts2014

Frequently asked questions

What triggers RNA interference?

Double-stranded RNA matching a gene; it is processed into short guides that direct silencing of that gene's messenger RNA.

Why is RNA interference useful in the laboratory?

Introducing a matching double-stranded or small interfering RNA lets researchers specifically reduce the expression of a chosen gene to study its function.