1. What is this powerful tool?


Courtesy of Sirna Therapeutics

RNA interference (RNAi) is a type of posttranscriptional genetic regulation that occurs naturally in the cytoplasm to protect the cell against excess and foreign RNAs. Double-stranded RNA (dsRNA), an unusual type of nucleic acid encoded in viral genomes and transposable elements, triggers a process that regulates gene expression without touching the genome.

2. What do we know about it?

Scientists know that RNAi protects the cell against viral infections and genomic instability, but no one knows exactly how dsRNA triggers RNAi's defense mechanism. Scientists do know the chain of events that the dsRNA initiates, which ultimately rids the cell of mRNA.

3. How does it work?

Dicers, a class of RNase III enzymes, recognize dsRNA molecules and cut them into short (~21–25) nucleotide segments called small interfering RNAs (siRNAs). These segments hook up with an RNA-induced silencing complex (RISC), and...

4. Where does RNAi normally occur?

So far, researchers have found RNAi in every organism they have studied, from fungi to humans; the proteins involved are highly conserved. RNAi regulates flower color in petunias and developmental timing in nematodes, and it acts as an antiviral agent in mammals.

5. Why are researchers excited about RNAi?

Partly because it is simple (no genome manipulation is necessary), and partly because it's so specific. Investigators can use it as an experimental tool for sequence-specific silencing and high-throughput screening: By introducing a particular dsRNA, scientists can inactivate specific mRNAs and quickly assess gene function. UK researchers have produced entire libraries of dsRNAs for Caenorhabditis elegans, and others are working on a similar library for humans. Other studies in plants, worms, and mice have shown that RNAi's silencing effects can spread throughout an entire organism during development. Now drug companies are investigating RNAi's potential clinical applications, such as a treatment for macular degeneration and other diseases, an antiviral agent, and a possible gene therapy.

- Maria W. Anderson

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