Tet repressor-based system for regulated gene expression in eukaryotic cells: Principles and advances

The tetracycline (Tc) responsive regulatory systems have been applied to control gene activities in eukaryotes. They are shown to function in cultured cells from mammals, plants, amphibians, and insects as well as in whole organisms including yeast, Drosophila, plants, mice, and rats. The basic regulatory circuits of the Tet systems and the elements constituting these circuits are based on simple principles. A number of parameters must be reconciled when setting up one of the systems for a particular purpose. When considering properties of the Tet system, such as degree (tightness) of control, expression levels, and regulation factors, it is crucial to distinguish among experimental situations in which the systems are stably inserted in the genome of cells in culture or of transgenic organisms and situations in which the respective regulatory elements are in a nonintegrated state, as in transient expression experiments or when contained in episomes.