Inducible gene inactivation in neurons of the adult mouse forebrain

Background: The analysis of the role of genes in important brain functions like learning, memory and synaptic plasticity requires gene inactivation at the adult stage to exclude developmental effects, adaptive changes or even lethality. In order to achieve temporally controlled somatic mutagenesis, the Cre/IoxP-recombination system has been complemented with the tamoxifen-inducible fusion protein consisting of Cre recombinase and the mutated ligand binding domain of the human estrogen receptor ( CreER(T2)). To induce recombination of conditional alleles in neurons of the adult forebrain, we generated a bacterial artificial chromosome-derived transgene expressing the CreERT2 fusion protein under control of the regulatory elements of the CaMKII alpha gene ( CaMKCreER(T2) transgene). Results: We established three mouse lines harboring one, two and four copies of the CaMKCreERT2 transgene. The CaMKCreERT2 transgene displayed reliable and copy number-dependent expression of Cre recombinase specifically in neurons of the adult forebrain. Using Cre reporter mice we show very low background activity of the transgene in absence of the ligand and efficient induction of recombination upon tamoxifen treatment in all three lines. In addition, we demonstrate in mice harboring two conditional glucocorticoid receptor ( GR) alleles and the CaMKCreERT2 transgene spatially restricted loss of GR protein expression in neurons of the adult forebrain upon tamoxifen treatment. Conclusion: This is to our knowledge the first approach allowing highly efficient inducible gene inactivation in neurons of the adult mouse forebrain. This new approach will be a useful tool to dissect the function of specific genes in the adult forebrain. Effects of gene inactivation on pre- and postnatal brain development and compensatory mechanisms elicited by an early onset of gene inactivation can now be excluded.