TEMPORAL CONTROL OF GENE-EXPRESSION IN TRANSGENIC MICE BY A TETRACYCLINE-RESPONSIVE PROMOTER

Promoters whose temporal activity can be directly manipulated in trans genic animals provide a tool for the study of gene functions in vivo, We have evaluated a tetracycline-responsive binary system for its abil ity to temporally control gene expression in transgenic mice. In this system, a tetracycline-controlled trans-activator protein (tTA), compo sed of the repressor of the tetracycline-resistance operon (tet from E scherichia coil transposon Tn10) and the activating domain of viral pr otein VP16 of herpes simplex virus, induces transcription from a minim al promoter (P-hCMV-1; see below) fused to seven tet operator sequenc es in the absence of tetracycline but not in its presence. Transgenic mice were generated that carried either a luciferase or a beta-galacto sidase reporter gene under the control of P-hCMV-1 Or a transgene con taining the tTA coding sequence under the control of the human cytomeg alovirus immediate early gene 1 (hCMV IE1) promoter/enhancer, Whereas little luciferase or beta-galactosidase activity was observed in tissu es of mice carrying only the reporter genes, the presence of tTA in do uble-transgenic mice induced expression of the reporter genes up to se veral thousand-fold, This induction was abrogated to basal levels upon administration of tetracycline. These findings can be used, for examp le, to design dominant gain-of-function experiments in which temporal control of transgene expression is required.