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Angiogenesis is often initiated by the sprouting of endothelial cells from existing vessels. The leading cell in the sprout, the so-called tip cell, is characterized by filopodia extensions; the cells at the base of the sprout, the so-called stalk cells, are proliferating. VEGF/VEGFR2, the Notch ligands Delta4 and Notch signaling participate in orchestrating sprouting angiogenesis.
