Tetracycline activator and tet promoter targeted to first exon such that expression can be turned off with doxycycline. The TK-Neo and Ura3 genes from the tetracycline cassette were removed by breeding with Mox2-cre mice. In the absence of doxycyline, there is approximately 4-fold more mRNA and increased protein expression in the brain. Doxycycline treatment for 10 days reduces protein expression by about 50%.