RNA interference
Introduction
RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules. It has been known to be vital for the regulation of gene expression, defense against viral infection, and in the development of organisms.
Discovery and History
The phenomenon of RNAi was first observed by plant researchers in the early 1990s. It was not until 1998 that Andrew Fire and Craig C. Mello described the mechanism in the nematode Caenorhabditis elegans, for which they were awarded the 2006 Nobel Prize in Physiology or Medicine.
Mechanism of RNA interference
RNAi is initiated by the enzyme Dicer, which cleaves long double-stranded RNA (dsRNA) molecules into short fragments of about 20 nucleotides. One of the two strands of each fragment, known as the guide strand, is then incorporated into the RNA-induced silencing complex (RISC). The most well-studied outcome is post-transcriptional gene silencing (PTGS), which occurs when the guide strand pairs with a complementary sequence in a messenger RNA molecule and induces cleavage by Argonaute, the catalytic component of the RISC. In some organisms, this process spreads systemically, despite the initial triggering being localized.
Types of RNA molecules involved in RNAi
There are several types of RNA molecules involved in RNAi, including microRNA (miRNA), small interfering RNA (siRNA), and Piwi-interacting RNA (piRNA). Each of these RNAs is distinct in origin, biogenesis, and mechanism of action, but they all function within the RNAi pathway.
RNAi in different organisms
RNAi is a widespread process that occurs in many different organisms, including animals, plants, and fungi. It plays a crucial role in development, genome stability, and antiviral defense.
RNAi in medicine and research
RNAi has potential therapeutic applications, such as in the treatment of cancer, viral infections, and other diseases. It is also a valuable research tool, both in cell culture and in living organisms, because synthetic dsRNA introduced into cells can induce suppression of specific genes of interest.