Cell surface GPI-bound ligand for Eph receptors, a family of receptor tyrosine kinases which are crucial for migration, repulsion and adhesion during neuronal, vascular and epithelial development. Binds promiscuously Eph receptors residing on adjacent cells, leading to contact-dependent bidirectional signaling into neighboring cells. Induces compartmentalized signaling within a caveolae-like membrane microdomain when bound to the extracellular domain of its cognate receptor. This signaling event requires the activity of the Fyn tyrosine kinase. Activates the epha3 receptor to regulate cell-cell adhesion and cytoskeletal organization. With the receptor epha2 may regulate lens fiber cells shape and interactions and be important for lens transparency maintenance. May function actively to stimulate axon fasciculation (By similarity). Controls axon growth and may be involved in the creation of the retino-tectal map. Widespread expression in the embryo. Expressed in the presumptive midbrain of developing embryos from the six-somite stage. By 24 hours, strongly expressed in the midbrain caudal to the presumptive tectum. At later stages, maintained at the posterior margin of the tectum. Belongs to the ephrin family.