BMP-9 induces CV2 expression in endothelial cells. (A) Expression of CV2 after treatment of HAECs with BMP-0 (10 ng/mL) for 24 hours, as determined by real-time PCR and immunoblotting. β-actin is shown for comparison. (B) Expression of CV2 after transfection of scrambled siRNA (SCR) or siRNA to ALK1 or SMAD1 in HAECs followed by treatment with BMP-9 (0-10 ng/mL), as determined by real-time PCR and immunoblotting. Treatment was started 24 hours after transfection and lasted 24 hours. (C) Expression of ALK1 and CV2 in BAECs after transfection of an ALK1 expression vector and treatment with BMP-9 (10 ng/mL), as determined by immunoblotting. Treatment was started at the time of transfection and lasted 24 hours. (D-E) Expression of CV2 in lungs, aorta, kidney, and liver of (D) wild-type (WT) and Alk1^+/− mice, and (E)WT and Mgp^−/− mice, as determined by real-time PCR and immunoblotting (n = 3). (F) Vascular expression of CV2 (green fluorescence) in aorta and lungs of Alk1^+/−, WT, and Mgp^−/− mice, as determined by immunofluorescence. Nuclei are visualized by DAPI (blue fluorescence). Asterisks indicate statistically significant differences compared with (A) start time, (B) no BMP-9, or (D-E) WT tissue. *P < .05, ***P < .001, Tukey test.