Andrew Fire and colleagues first described RNA interference (RNAi) in Caenorhabditis elegans in 1998.1 Exogenous double-stranded RNA (dsRNA) injected into cells effectively induced silencing of an endogenous gene complementary to the injected RNA. Since then, scientists have used RNAi to silence genes in several organisms, and biotech companies have introduced products to assist them.2,3 In recent months, a number of groups have published data linking the RNAi pathway to a newly discovered class of small RNAs, called microRNAs (miRNAs), the functions of which are largely unknown.
The discovery of these small RNAs in a variety of organisms has led researchers to speculate if and how the biologies of RNAi and miRNAs intersect. "How closely related are they, and what determines the distinction between them?" asks Victor Ambros of Dartmouth Medical School, relating two of the main questions currently under investigation. "Also, what pathways are these miRNAs involved in, and can ...
