Tg(Rho-tTA)5Vmrg

The transgene contains ~4.4 kb of the mouse rhodopsin gene promoter immediately upstream of the initiating ATG, which has been replaced by that of the modified tetracycline transactivator tTA1 - which has lower toxicity than and >2-fold the activity of tTA - followed by the SV40 polyadenylation signal. RT-PCR of the retinas of transgenic mice reveals expression of tTA beginning on postnatal day (P)8, which increases over several days and and is maintained thereafter. In situ hybridization localizes expression to the photoreceptor cells of the outer nuclear layer of the retina. Mice bearing both this and a tetracyline operator (tetO) driven luciferase reporter transgene express luciferase from P8 in the same cells, reaching a plateau by P13. Luciferase assays of other tissues of these mice demonstrate that induction is specific to the retinal outer nuclear layer. Expression of luciferase, but not of tTA1, is abolished within 24 h by doxycycline (Dox) exposure via drinking water and remains so for at least 10 d with continued exposure; luciferase is again detectable 4 days after cessation of treatment. (J:172631, J:172632)