Model of ephrin-B2–EphB4 signals in vasculoangiogenesis.

(1) Ephrin-B2 on SMCs support proliferation and sprouting of arterial ECs. (2) Ephrin-B2⁺ ECs promote the recruitment of SMCs near ECs. Molecular cues for such induction are unknown; however, PDGF-BB and TGF-β may be involved in this process. (3) When the ephrin-B2⁺ ECs (arterial ECs) and EphB4⁺(venous ECs) face each other at the boundary of a capillary, cell proliferation of ECs may be suppressed, and the migratory ability may be arrested there.