Simultaneous Cre-mediated conditional knockdown of two genes in mice.

One of the most promising techniques to manipulate gene expression in vivo is the use of RNA interference (RNAi). Various approaches were developed to use RNAi in the mouse, including vector-based expression of short hairpin RNAs and the Cre/loxP recombination system. We combined these two approaches to create a vector system that allows the time- and tissue-specific control of two genes at the same time. For this purpose two independent conditional shRNA expression cassettes are combined into a single construct. By the use of different, incompatible pairs of lox sites that flank transcriptional stop cassettes, Cre recombinase can independently activate both short hairpins. Here, we show that Cre simultaneously activates both shRNAs in vitro and in vivo. We applied this technique to silence the widely coexpressed gene pairs Gsk-3 alpha/Gsk-3 beta and Erk1/Erk2 in murine embryonic stem cells and in the mouse brain