Figure 3.

The VE-cadherin-tTA transgene drives responder expression only in the endocardium, not the cardiac cushion mesenchyme. (A) E11.5 VE-cadherin:tTA/TET:myrAkt embryos stained with phospho-Akt showed increased Akt activation in the endocardium. (B) LacZ staining of E11.5 VE-cadherin:tTA/TET:LacZ embryos confirmed the endothelial specificity of the VE-cadherin promoter. (C) In ex vivo heart cushion explants (e), endothelial layer monolayer (m) outgrowth expressed lacZ but the mesenchymal outgrowth cells (red arrowheads) did not, again confirming the VE-cadherin-tTA gene would not be expressed and thus not drive TET-promoter expression in the mesenchyme. The figures shown are representative images from n>5 double transgenic explants assessed. Each litter gives 25% double transgenic offspring.