RNA interference (RNAi) is a gene-silencing technique that inhibits gene expression by causing the intracellular degradation of mRNA molecules. Since first reported in 1998, RNAi has sparked a revolution in molecular biology and has been employed in a myriad of biological contexts for the systematic evaluation of gene function. The ability to selectively regulate the activity of specific genes within a given biological location represents a methodology by which researchers can upregulate or downregulate protein expression.