FigS4F. Copyright: Reprinted with permission from Elsevier from [doi:10.1016/j.ydbio.2007.03.004] Dev Biol 305: 599-614, Kalin RE; Kretz MP; Meyer AM; Kispert A; Heppner FL; Brandli AW, Paracrine and autocrine mechanisms of apelin signaling govern embryonic and tumor angiogenesis. Copyright 2007