Repulsion or adhesion: receptors make the call

Repulsive signaling plays a prominent role in regulating cell–cell interactions and is fundamental to multiple developmental processes. A proper balance between repulsion from and adhesion to other cells or the extracellular matrix is also important. Semaphorin–Plexin and ephrin–Eph ligand–receptor pairs compose two major repulsive signaling systems. Recent advances have elucidated mechanisms by which Semaphorin–Plexin and ephrin–Eph signaling control repulsion versus adhesion. Semaphorins act through a complex signaling pathway to inhibit integrin-mediated adhesion, allowing cell repulsion. Ephrin–Eph interactions can directly mediate cell adhesion and several mechanisms control whether ephrin–Eph binding and signaling induces repulsion or adhesion.