Abstract

If using in vivo RNAi has you down for the count, here's what you need to know. For those frustrated by the brute force of knockout mice when studying gene function, in vivo RNA interference (RNAi) would seem to have come to the rescue. In theory, in vivo RNAi promises a more nuanced approach that gives researchers temporal and spatial control in knocking down genes. That doesn't mean, however, that it's easy to use. The notorious challenge with RNAi, even in cell culture, is delivery. "With in vivo, the problems are exactly the same, except ten times as hard," says Mark Behlke of Integrated DNA Technologies in Coralville, Iowa. Users struggle with getting RNA to their target organ or cell type, efficiently transfecting cells, and managing toxicity and off-target effects. A handful of tricks can remedy these problems. For synthetic small interfering RNAs, for example, there are cationic lipid reagents to neutralize RNA's negative charge and ease it through the cell membrane; chemical modifications to protect RNA from nucleases and block immune and other off-target effects; and 27mers (longer strands of RNA), which may be taken up more efficiently. Encoding siRNA in short hairpin construct for delivery in