Eph receptor deficiencies lead to altered cochlear function

Ephrins and Eph receptors are a family of molecules that have been implicated in many developmental processes including neuronal network formation, guidance of cell migration, and axonal pathfinding. These molecules exhibit the ability to send bidirectional signals following ligand-receptor interactions resulting from cell-cell contacts. Gene-targeted knockout mice of B-class ephrins and Eph receptors have been shown to display phenotypic responses that correlate with anatomical defects. For example, disruption of the EphB2 receptor leads to defects of the vestibular system, including pathfinding abnormalities in efferent axons and reduced endolymph production. Such developmental distortions lead to deficiencies in ionic homeostasis and repetitive circling behaviors. The present study demonstrates that B-class ephrins and Eph receptors are expressed in cochlear tissues, suggesting that they may play some role in auditory function. To determine whether ephrins and Eph receptors have a functional role in the peripheral auditory system, distortion-product otoacoustic emission (DPOAE) levels, collected across a broad frequency range, were compared between groups of mice expressing different Eph receptor genotypes. In particular, EphB1 and EphB3 receptor knockout mice exhibited significantly diminished DPOAE levels as compared to wild-type littermates, indicating that these specific Eph receptors are necessary for normal cochlear function.