Tet System in Mice, brief description

Conditional Expression of Activated G Protein Alpha Subunits in Transgenic Mice

There are well defined point mutations in all G protein alpha subunits (G alpha) that lock the G alpha in the "on" position. These activated G proteins will signal constitutively in a receptor independent fashion from the time they are synthesized and delivered to the plasma membrane. These activated G proteins have been useful in dissecting signaling pathways, and have been implicated in several human genetic diseases. The recently described (1-5) tetracycline gene induction system (tTA system described below) now allows temporal and tissue-specific control constitutively activated alpha i and alpha q subunits in transgenic mice, while circumventing their possible developmental effects.

In the tTA system, gene expression is driven by a minimal promoter fused downstream of seven operator sequences (TRE) of the E. colitet operon (fig. 1) (1-2). Since the TRE promoter is bacterially derived, it is inactive in mammalian cells, unless the tTA protein is expressed in the same cell. The tTA system has been used successfully in cultured cells and in transgenic mice to drive expression of reporter and oncogenic genes(3-5). By using the tTA system, several groups have reported target gene induction of 500- to 1,000,000-fold in transgenic mice (3-5). In the tTAsystem, tissue specificity is generated by varying the promoter driving tTA gene transcription (fig. 1). Temporal control over transgene expression is generated by the presence or absence of tetracycline. Thus, by usingthe tTA system, gene expression can be studied in specific mouse tissues in adult mice or during specific developmental stages.

References

1. Gossen, M., Freundlieb, S., Bender, G., Muller, G., Hillen, W., and Bujard, H. (1995) Transcriptional activation by tetracyclines in mammalian cells. Science 268, 1766–1769.

2. Gossen, M., and Bujard, H. (1992) Tight control of gene expression in mammalian cells by tetracycline-responsive promoters. Proc.Natl. Acad. Sci. USA 89, 5547–5551.

3. Furth, P. A., St. Onge, L., Boger, H., Gruss, P., Gossen, M., Kistner, A., Bujard, H., and Hennighausen, L. (1994) Temporal control of gene expression in transgenic mice by a tetracycline-responsive promoter.Proc. Natl. Acad. Sci. USA 91, 9302–9306.

4. Kistner, A., Gossen, M., Zimmerman, F., Jerecic, J., Ullmer, C., Lubbert, H., and Bujard, H. (1996) Doxycycline-mediated quantitative and tissue-specific control of gene expression in transgenic mice. Proc. Natl. Acad. Sci. USA 93, 10933–10938.

5. Yu, Z., Redfern, C. S., and Fishman, G. I. (1996) Conditional transgene expression in the heart. Circ. Res. 79, 691–697.