Ephrin A2 may play a role in axon guidance during hair cell regeneration

Objective: Hair cell regeneration in the avian cochlea is accompanied by frequency specific reinnervation and recovery of physiologic function. The molecular cues that guide ganglion cells to tonotopically appropriate new hair cells have not been identified. We investigated the potential of ephrin A2 in this process. Study Design: Ephrin A2 expression was characterized in acoustic ganglion cells of normal and gentamicin-treated early post hatch chicks. Methods: Ephrin A2 expression was determined by Western analysis of total protein isolated from acoustic ganglia in normal animals. Protein localization was characterized by fluorescence immunohistochemisty in sections of acoustic ganglia of normal and gentamicin treated animals. Patterns of ephrin A2 expression in acoustic ganglia were determined and quantified during hair cell regeneration. Results: Ephrin A2 expression was found in acoustic ganglia by Western analysis. Localization of this protein by immunofluoresence revealed its presence in acoustic ganglion cells in normal chicks. After gentamicin treatment, ephrin A2 expression was lost in a subset of acoustic ganglion cells. The spatial and temporal pattern of ephrin A2 loss coincides with the pattern of hair cell loss and regeneration. Conclusions: The changes in ephrin A2 immunoreactivity in acoustic ganglion cells during cochlear damage and regeneration suggests that ephrin A2 may be involved in the guidance of ganglion cells to tonotopically appropriate hair cell targets during regeneration. Ephrin A2 in hair cell regeneration.