Conditional transgene expression in endothelial cells

The ability to tightly control transgene expression in vivo provides an opp ortunity to determine the role of certain gene products at different times during development and/or in response to different stimuli. We have charact erized and evaluated a tetracycline-responsive endothelial-specific binary system during mouse development, by engineering several transgenic lines wh ich drive the expression of a tetracycline-controlled transactivator (tTA) under the control of either the Tek or Tie promoters (driver lines). We hav e also generated a responder line which carries multiple copies of the tTA DNA binding element (tet(os)) upstream of a reporter gene coding for a nucl ear targeted beta-galactosidase (responder lines). No expression of the tar get transgene was detected in mice homozygous for the reporter transgene. O n mating the driver lines with the responder line, expression of beta-galac tosidase from the reporter transgene was detected within the endothelium. R esponder transgene expression was repressed rapidly upon addition of doxycy cline to the drinking water. Importantly, this repression was reversible up on withdrawal of the drug. This approach should be useful to deliver the ex pression of potentially toxic gene products or rescue embryonic mutations t hat affect either the endothelial lineage or production of growth factors w hich are secreted systemically.