Neuroscience

'Hunger hormone' enhances memory

A team of neuroscience researchers at the University of Southern California have identified a surprising new role for the "hunger hormone" ghrelin. Ghrelin has previously been recognized for its unique role in sending hunger ...

Genetics

Tissue model reveals how RNA will act on the liver

Novel therapies based on a process known as RNA interference (RNAi) hold great promise for treating a variety of diseases by blocking specific genes in a patient's cells. Many of the earliest RNAi treatments have focused ...

Medications

Promising results for new acute porphyria treatment

Acute porphyria is a group of uncommon diseases that can cause severe, potentially life-threatening attacks of abdominal pain, nausea, vomiting and paralysis. Liver transplantation is currently the only effective treatment ...

Diseases, Conditions, Syndromes

Promising new drug for hepatitis B tested

Research at the Southwest National Primate Research Center (SNPRC) on the campus of Texas Biomedical Research Institute helped advance a new treatment now in human trials for chronic hepatitis B virus (HBV) infection. Testing ...

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RNA interference

RNA interference (RNAi) is a system within living cells that helps to control which genes are active and how active they are. Two types of small RNA molecules – microRNA (miRNA) and small interfering RNA (siRNA) – are central to RNA interference. RNAs are the direct products of genes, and these small RNAs can bind to specific other RNAs and either increase or decrease their activity, for example by preventing a messenger RNA from producing a protein. RNA interference has an important role in defending cells against parasitic genes – viruses and transposons – but also in directing development as well as gene expression in general.

The RNAi pathway is found in many eukaryotes including animals and is initiated by the enzyme Dicer, which cleaves long double-stranded RNA (dsRNA) molecules into short fragments of ~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, which occurs when the guide strand base pairs with a complementary sequence of a messenger RNA molecule and induces cleavage by Argonaute, the catalytic component of the RISC complex. This process is known to spread systemically throughout the organism despite initially limited molar concentrations of siRNA.

The selective and robust effect of RNAi on gene expression makes it 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. RNAi may also be used for large-scale screens that systematically shut down each gene in the cell, which can help identify the components necessary for a particular cellular process or an event such as cell division. Exploitation of the pathway is also a promising tool in biotechnology and medicine.

Historically, RNA interference was known by other names, including post transcriptional gene silencing, and quelling. Only after these apparently unrelated processes were fully understood did it become clear that they all described the RNAi phenomenon. In 2006, Andrew Fire and Craig C. Mello shared the Nobel Prize in Physiology or Medicine for their work on RNA interference in the nematode worm C. elegans, which they published in 1998.

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