Expression of green fluorescent protein in oligodendrocytes in a time- andlevel-controllable fashion with a tetracycline-regulated system

Developments in transgenic technology have greatly enhanced our ability to understand the functions of various genes in animal models and relevant hum an diseases. The tetracycline (tet)-regulated transactivation system for in ducing gene expression allowed us to control the expression of exogenous ge nes in a temporal and quantitative way. The ability to manipulate a cell-sp ecific promoter enabled us to express one particular protein in a single ty pe of cell. The combination of a tetracycline system and a tissue-specific promoter has led us to the development of an innovative gene expression sys tem, which is able to express genes in a cell type-specific and time- and l evel-controllable fashion. An oligodendrocyte-specific myelin basic protein (MBP) gene promoter controls the reversed tet-inducible transactivator. Th e green fluorescent protein (GFP) gene was placed under the control of the human cytomegalovirus (CMV) basic promoter in tandem with seven tet-respons ive elements (TRE), binding sites for the activated transactivator. Upon th e addition of doxycycline (DOX, a tetracycline derivative), tet transactiva tors became activated and bound to one or more TRE, leading to the activati on of the CMV promoter and the expression of GFP in oligodendrocytes. We ha ve successfully expressed GFP and luciferase at high levels in oligodendroc ytes in a time- and dose-dependent fashion. In the absence of DOX, there wa s almost no GFP expression in oligodendroglial cultures. Graded levels of G FP expression were observed after induction with DOX (0.5 to 12.5 mu g/ml). Our data indicate that this inducible gene expression system is useful for the study of gene function in vivo and for the development of transgenic a nimal models relevant to human diseases such as multiple sclerosis.