NG2-positive cells were targeted by the Tbx4 -lung enhancer driven Tet-On system. Lung tissue sections of the triple transgenic mice (Tbx4-rtTA/TetO-Cre/mT-mG) with different Dox induction as indicated were co-immunostained by GFP, NG2, and SMA or PECAM-1. (A) In the E18.5 lung of the triple transgenic mice with Dox induction from E6.5 to E18.5, NG2-positive cells, including SMA-positive vasculature smooth muscle cells and SMA-negative pericytes, were all marked by GFP expression, suggesting that these cells were targeted by the Tet-On system in fetuses. (B-C) With Dox induction at either mid-gestation (E11.5 to E15.5) or late gestation (E15.5 to E18.5), most NG-2 positive cells of the triple transgenic mouse lungs at E15.5 (B) or E18.5 (C) were positive for GFP. These NG2-positive cells were adjacent to PECAM-1 positive endothelial cells. Dox, doxycycline; E, embryonic day; PECAM-1, platelet endothelial cell adhesion molecule; SMA, α-smooth muscle actin.