Blockade of Notch signaling results in LEC sprouting. (A) Immunofluorescent PECAM-1 staining of LEC-coated microbeads subjected to Dll4-Fc– or HSA-conditioned medium with or without VEGF-C (100 ng/mL). (B) Quantification of the cumulative sprout lengths and number per bead in the experiment of panel A. (C) PECAM-1 staining of LEC-coated beads treated with the γ-secretase inhibitor Compound X (X, 30mM) or DMSO (vehicle). Scale bars, 100 μm. Data summarized from 2 independent experiments with conditioned media and a third independent experiment with purified Dll4-Fc (20 μg/mL), with similar results (n = 8-15 per group in each experiment) in panel B and 3 independent experiments in panel C. Error bars, SEM; ***P < .001; N.S., not significant.