Comparison of ephrin-A ligand and EphA receptor distribution in the developing inner ear

Members of the recently discovered Eph family appear to play important roles in a variety of developmental processes including tissue segmentation, cell migration and axonal guidance. To begin to understand the functions of the EphA subclass of receptors and their corresponding GPI-linked (ephrin-A) ligands in the inner ear, a developmental immunohistochemical analysis was completed. The results indicated that the ligands ephrin-A1 and ephrin-A2 were localized mainly at cellular boundaries in the inner ear. Ephrin-A1 was detected mainly in the epithelial cells lining the fluid filled ducts of the inner ear, whereas ephrin-A2 was prominently expressed in connective tissue regions. The receptor EphA4 was detected in vestibular hair cells. EphA5 and EphA7 were detected mainly in cochlear and vestibular supporting cells. These results suggest that these Eph molecules play a role in establishing the formation and cellular organization of the complex inner ear labyrinth. Additionally, all of the ligands and receptors evaluated were expressed in vestibular and cochlear neurons at various developmental stages, suggesting they may play a role in establishing or maintaining innervation to the inner ear.