Expression of CYP1B1 restores the capillary morphogenesis defect observed in CYP1B1^−/− EC. (A) Western blot analysis of whole cell lysates (20 μg) from CYP1B1^−/− ECs infected with the adenoviruses expressing empty vector or CYP1B1 at different virus input. β-catenin was used for loading control. (B) CYP1B1 activity assay of CYP1B1^+/+ (incubated with or without TCDD) and CYP1B1^−/− ECs infected with the adenoviruses expressing empty vector or CYP1B1. Data in each bar are the mean relative luminescence (error bars indicate the standard deviation, n = 3, *P [CYP1B1^+/+; control vs TCDD] and **P < .05 [CYP1B1^−/−; vector vs CYP1B1]). The CYP1B1^−/− ECs infected with adenovirus control (5 pfu/cell) (C), adenovirus expressing CYP1B1 (5 pfu/cell) (D), or CYP1B1^+/+ ECs with vector control (5 pfu/cell) (E) were plated on Matrigel as described in “Methods” (×40). The capillary morphogenesis by CYP1B1^+/+ cells infected with a retrovirus expressing control siRNA (F) or a mouse specific CYP1B1 siRNA 2015 (G) was similarly determined. The quantitative assessments of the data are shown in panels H and I. Data in each bar are the mean number of branches per 5 high-power fields (×100; error bars indicate SD). Note that the ability of CYP1B1^−/− ECs to organize in Matrigel was significantly improved with reexpression of CYP1B1, while its siRNA knockdown resulted in attenuation of capillary morphogenesis in CYP1B1^+/+ retinal ECs (n = 3, *P < .05). These experiments were repeated with 2 different preparations of ECs with similar results.