These mice contain the rtTAS*M2, or rtTA2S-M2, an optimized form of reverse tetracycline regulated transactivator, gene inserted into the Gt(ROSA)26Sor locus. Expression of the rtTAS*M2 is blocked by a loxP-flanked STOP fragment placed between the rtTAS*M2 sequence and the Gt(ROSA)26Sor promoter. When these mutant mice are bred to mice that express Cre recombinase, the resulting offspring will express rtTAS*M2, reverse tetracycline regulated transactivator, in the cre expressing cells. When bred to mice that also carry a gene of interest under the regulatory control of a tetracycline-responsive promoter element (tetO), expression of the gene of interest may be regulated by the tetracycline analog, doxycycline (dox). In the presence of dox, transcription of the target gene is induced in cells where rtTA is expressed. Mice that are homozygous for the targeted mutation are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities.
