Murine primary endothelial cells were isolated from the lungs of CAGGFP-Spry4 and Spry4f/f mice. Cells were then transduced with AdLacZ or AdCre to either overexpress (A, B) or delete (C, D) Spry4. The expression of integrin subunits αV and β3 were analyzed by immunoblotting. The images were quantified by ImageJ and normalized to tubulin levels; n = 3; data are means ± S.D. * p < 0.05. Conditional CAGGFP-Spry4 transgenic (E, F) or Spry4f/f (G, H) knockout female mice were mated with male Tie2-Cre transgenic mice. Both embryos and yolk sacs at E9.5 were dissociated into single cell suspensions and analyzed by flow cytometry. The level of integrin β3 in PECAM-positive cells was quantified; n = 5; data are geometric means ± S.D. * p < 0.05. Spry4 transgene significantly inhibits integrin β3 protein levels in both embryos and yolk sacs, whereas Spry4 deletion increases integrin β3 protein levels.