The GH-rtTA transgene was designed with a 1.7 kb promoter sequence from the rat growth hormone (Gh1) gene, a reverse tetracycline-regulated transactivator (rtTA) gene, and an SV40 intron/polyA sequence. This 4.5 kb transgene was microinjected into one-cell (C57BL/6 x SJL) mouse zygotes. Mice from founder line 4-3 were bred with C57BL/6;SJL wildtype mice to establish the colony. (J:68692)