Conditional transgene expression in endothelial cells.

The ability to tightly control transgene expression in vivo provides an opportunity to determine the role of certain gene products at different times during development and/or in response to different stimuli. We have characterized and evaluated a tetracycline-responsive endothelial-specific binary system during mouse development, by engineering several transgenic lines which drive the expression of a tetracycline-controlled transactivator (tTA) under the control of either the Tek or Tie promoters (driver lines). We have also generated a responder line which carries multiple copies of the tTA DNA binding element (tetOS) upstream of a reporter gene coding for a nuclear targeted beta-galactosidase (responder lines). No expression of the target transgene was detected in mice homozygous for the reporter transgene. On mating the driver lines with the responder line, expression of beta-galactosidase from the reporter transgene was detected within the endothelium. Responder transgene expression was repressed rapidly upon addition of doxycycline to the drinking water. Importantly, this repression was reversible upon withdrawal of the drug. This approach should be useful to deliver the expression of potentially toxic gene products or rescue embryonic mutations that affect either the endothelial lineage or production of growth factors which are secreted systemically.