Regulation of VEGFR2 and NRP1 expression in Dll4-transduced endothelial cells. (A) Quantitative RT-PCR analysis of VEGF-A, VEGFR1, VEGFR2, FGFR1, and NRP1 expression in HUVECs transduced with vector only or Dll4. The results reflect relative mRNA levels (normalized to GAPDH) in Dll4-transduced and control HUVECs and are expressed as the fold mRNA change in Dll4 versus control HUVECs. The results represent the mean (± SEM) from 4 to 9 independent determinations. ^*P < .05. (B) Surface levels of CD31, VEGFR2, and NRP1 expression in vector-only (Vector) and Dll4-transduced (Dll4) HUVECs measured by flow cytometry. Control reflects background surface fluorescence staining with appropriate controls.