Cre-Rux – improving mouse well-being with a refined approach for in vivo genetic manipulation

Biomedical research relies on genetic manipulation of animals, particularly mice, as experimental models to mimic human diseases and study their mechanisms. A widely used system relies on the use of the enzyme Cre recombinase. A variant of this enzyme, CreERT2, needs the drug tamoxifen to be active. However, it is increasingly apparent that tamoxifen administration can be problematic. Reports show that tamoxifen administration can be toxic in mice. The tamoxifen system has also been reported to have unspecific activity. Moreover, some experimental setups require forced oral administration of tamoxifen, which is a stressful procedure. An alternative that eliminates these issues would represent an important refinement step. In the proposed project we will test the suitability of the drug RU486 as an alternative to tamoxifen. Additionally, we will use a modified version of Cre, to reduce unspecific activity and thus increase experimental reproducibility and reliability. We will also test a protocol for voluntary oral administration of RU486 to eliminate the need of forced oral administration and the associated stress for the animals. Given the prevalence of tamoxifen-based systems, the establishment of a refined alternative system will immensely improve animal welfare in biomedical research.