Figure 1. Dual recombinase technology enables VE-Cadherin-Cre to delete Atm in primary sarcoma endothelial cells.

(A) Recombinase expression in KP^FRT; VE-Cadherin-Cre mice injected with adeno-FlpO to generate sarcomas. (B) Reporter expression in KP^FRT; VE-Cadherin-Cre; mTmG mice. All cells initially express tdTomato, and VE-Cadherin-Cre deletes tdTomato and turns on eGFP expression in endothelial cells (green). (C) Fluorescence images of CD31-stained soft tissue sarcomas initiated with adeno-FlpO in KP^FRT; VE-Cadherin-Cre; mTmG mice in the absence of radiation (No IR) and 2 weeks after irradiation with 20 Gy. Images are representative of 3 mice per group. (D) Representative immunofluorescence images of a sarcoma in a KP^loxP; LSL-eYFP mouse initiated with adeno-Cre and stained with GS-IB₄. (E) Genetic strategy to activate Kras and delete p53 in tumor cells and delete Atm in endothelial cells. Control mice retained 1 WT allele of Atm in endothelial cells. (F) Expression of Atm mRNA in FACS-isolated tumor endothelial cells (CD45^–CD34⁺CD31⁺) from the indicated mice (n = 3 per group). (G and H) Immunofluorescence (G) and quantification (H) of CD31⁺pATM⁺ cells in sarcomas from KP^FRTVAtm^fl/+ and KP^FRTVAtm^fl/fl mice 4 hours after irradiation with 20 Gy (n = 4 per group). A pATM⁺ endothelial cell in the KP^FRTVAtm^fl/+ mouse (arrows) and a pATM^– endothelial cell in the KP^FRTVAtm^fl/fl mouse (arrowheads) are shown at higher magnification in the insets. Data are mean ± SEM. Scale bars: 100 μm (C, D, and G); 25 μm (G, insets) *P < 0.05.