Ephrin A4 is a member of the ephrin (EPH) family. Ephrins and EPH-related receptors comprise the largest subfamily of receptor protein-tyrosine kinases. Based upon their structures and sequence relationships, ephrins are divided into the ephrin-A (EFNA) class, which are attached to the membrane by a glycosylphosphatidylinositol linkage, and the ephrin-B (EFNB) class, which are transmembrane proteins. Class A ephrins are linked to the membrane by a GPI linkage and bind primarily to EphA receptors; Class B ephrins contain a membrane-spanning region and bind primarily to EphB receptors. Both ephrins and Eph receptors are largely expressed throµghout the ectoderm, mesoderm, and endoderm of vertebrate embryos.EFNA binds to the EPHA2, EPHA4, EPHA5, EPHA6, and EPHA7 receptors. Two transcript variations which encode different isoforms were identified throµgh sequence analysis. During development the Eph receptor and their membrane-attached ligands, ephrins, show diverse expression patterns.The ephrins and EPH-related receptors mediate developmental events, principally in the nervous system and in erythropoiesis. The critical roles of Eph and ephrins during development imply involvement of these genes in congenital disorders affecting the nervous system and other tissues. Ephrins and Eph receptors are possibly involved in carcinogenesis.