Generation of shRNA transgenic mice.

RNA interference (RNAi)-mediated gene knockdown has developed into a routine method to assess gene function in cultured mammalian cells in a fast and easy manner. For the use of RNAi in mice, short hairpin (sh) RNAs expressed stably from the genome are a faster alternative to conventional knockout approaches. Here, we describe an advanced strategy for complete or conditional gene knockdown in mice, where the Cre/loxP system is used to activate RNAi in a time- and tissue-dependent manner. Single-copy RNAi constructs are placed into the Rosa26 locus of ES cells by recombinase-mediated cassette exchange and transmitted through the germline of chimaeric mice. The shRNA transgenic offspring can be either directly used for phenotypic analysis or are further crossed to a Cre transgenic strain to activate conditional shRNA vectors. The site-specific insertion of single-copy shRNA vectors allows the expedite and reproducible production of knockdown mice and provides an easy and fast approach to assess gene function in vivo.

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-3alpha/Gsk-3beta and Erk1/Erk2 in murine embryonic stem cells and in the mouse brain.