Inducible Overexpression of Angiopoietin-2 in Mice

Mice were maintained in the Laboratory Animal Centre of the University of Helsinki. The National Animal Experiment Board in Finland approved animal experiments used in this study. We used the VEC-tTA/Tet-OS-Ang2 mouse line, which expresses mouse Ang2 under an inducible endothelial cell promoter19 (link). The driver VEC-tTA and responder transgenic mouse lines were bred together to obtain double-transgenic VEC-tTA/Tet-OS-Ang2 offspring. To overcome the embryonic lethality due to endothelial Ang2 overexpression in double-transgenic embryos, Ang2 expression was repressed during the entire pregnancy. Tetracycline (Sigma-Aldrich) at 2 mg ml⁻¹ in 5% sucrose was added to the drinking water of pregnant females, starting at the time of mating and until birth, when Ang2 expression was induced by discontinuation of Tetracycline administration. Single-transgenic or WT littermates were used as controls for double-transgenic mice, both designated as WT. None of the control mice displayed any obvious phenotype.