A new technology developed by Harvard Medical School researchers in the laboratory of Yang Shi, associate professor of pathology, extends the range of possibilities of selective interference of gene expression without having to manipulate DNA in the egg or embryo. The new technology makes it possible to turn off genes in a highly specific manner, and its effect is persistent, unlike earlier RNA interference methods for human cells. Previously, to study mammalian protein function, many researchers had to go the laborious route of making “knockout” animals, a process that can take many months. The new technology complements knockout techniques and enables researchers to conduct a variety of experiments with cells grown in vitro, many of which represent differentiated cell types often difficult to obtain as primary cultures. The technology also may eventually be used as a platform for developing new therapies.