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 (PubMed:17332925, PubMed:18794797). Involved in angiogenesis, regulating vascular endothelial cell differentiation and migration through activation of EPHA2. Acts as a ligand for EPHA3, inhibiting epithelial-to-mesenchymal transition of cardiac cells and playing a role in heart development (PubMed:12794130). May also contribute to dendritic spine morphogenesis (By similarity). {ECO:0000250|UniProtKB:P52793, ECO:0000269|PubMed:12794130, ECO:0000269|PubMed:17332925, ECO:0000269|PubMed:18794797}. This is the function of EFNA1 (ephrin A1, Ensembl gene identifier ENSG00000169242).