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Gene Silencing Passes Test in Human Cells
Edward R. Winstead

Scientists planning to test the functions of every human gene have cleared an important hurdle by demonstrating that RNA can silence a single gene in human cells without causing any other disruptions to the cell.

Detail from image showing gene expression changes. View full

The technique for silencing genes, called RNA interference, is one of the hottest research tools in biology because it allows scientists to assess the functions of genes by turning them off and seeing what happens to a cell.

Gene silencing in theory could be used in cancer medicine to silence an overactive tumor-causing gene. But the therapeutic potential of RNA interference depends on its specificity—and whether it can disable a gene target without affecting other genes.

To address this issue on a genomic scale, researchers at Stanford University School of Medicine in California silenced individual genes in human cells in culture. Then, using “gene chips,” they monitored the activity of some 30,000 other genes in the cells and found that none had been affected.

“This technology seems to be very, very specific,” says Jen-Tsan Chi, a member of the Stanford team led by Patrick O. Brown. “And that’s good news for the whole scientific community.”

The precision of RNA interference is equivalent to that of techniques for “knocking out” genes in laboratory organisms such as the mouse, the researchers found. But introducing RNA into cells takes considerably less time than breeding generations of genetically modified mice.

Indeed, the efficiency of RNA interference is appealing to researchers. And the new data suggest, more than previous studies, that it can be used investigate the functions of the 35,000 or so human genes.

“The power of this technology is that once you know the sequence of a gene, you can design [a molecule] to silence the gene,” says Howard Y. Chang, also part of the Stanford team.

“We’re interested in applying this technology on a genome-wide scale, so it’s important that the silencing be very specific,” says Chang. Otherwise, one could not know whether cellular changes are due to a single gene or multiple genes.

Though still very much in the experimental stages, RNA interference has shown promise in the laboratory. Researchers have silenced genes in HIV to prevent the virus from entering human cells in culture. In another study, mice injected with short RNAs were protected against a form of hepatitis.

These studies suggest that the technology acts on specific targets. The new study is perhaps the first to assess the specificity in human cells on a genomic scale using gene chips. These are glass slides or microchips containing DNA from thousands of genes, and they indicate which genes are active in the cell at a particular moment.

To silence the genes, the team introduced “short interfering” RNAs, or siRNAs, which prevented the genes from producing proteins. The gene silenced in this study was a jellyfish gene that coded for a green fluorescent protein. It was added to the human cells as a biochemical marker to indicate whether the silencing worked.

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Chi, J. T. et al. Genome-wide view of gene silencing by small interfering RNAs. Proc Natl Acad Sci USA. Published online May 2, 2003.

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