Control of siRNA expression utilizing Cre-loxP recombination system.

Vector-mediated systems for specific siRNA expression in mammalian cells using pol III promoters allowing high level of transcription activity have been developed in the past years, widening the usage of RNA interference (RNAi). In this study, we controlled the pol III promoter (U6 promoter)-driven expression of siRNA using the Cre-loxP system. Our "Cre-On" siRNA-expression vector against firefly luciferase activity could be switched on only in the presence of Cre recombinase, which, in this study, was delivered directly from the medium into the cells as TAT-NLS-Cre, a fusion protein with TAT peptide (an Arg rich peptide derived from HIV) and nuclear localizing signal (NLS). Upon the addition of TAT-NLS-Cre, complete and functional siRNAs were generated and reporter activity was suppressed.