Down-regulation of Lyn kinase in confluent endothelial cells disrupts AJ. (A) HUVECs were transfected with control or Lyn siRNA together with DY-547–labeled siGLO RISC-free control siRNA to allow visualization of siRNA transfected cells. Forty-eight hours after transfection, cells were fixed and immunostained for VE-cadherin. In control siRNA transfected HUVECs, VE-cadherin staining was continuous along cell borders indicative of its presence at the AJs. In Lyn siRNA-transfected cells, VE-cadherin was lost from AJs, resulting in formation of interendothelial gaps, as pointed by the arrows. (B) Quantification of gaps and (C) cell numbers in 4 random images (mean ± SD).