Outer Hair Cell Function is Normal in βV Spectrin Knockout Mice

Reports have proposed a putative role for {beta}V spectrin in outer hair cells (OHCs) of the cochlea. In an ongoing investigation of the role of the cytoskeleton in electromotility, we tested mice with a targeted exon deletion of {beta}V spectrin (Spnb5), and unexpectedly find that Spnb5(-/-) animals auditory thresholds are unaffected. Similarly, these mice have normal OHC electromechanical activity (otoacoustic emissions) and non-linear capacitance. In contrast, magnitudes of auditory brainstem response (ABR) wave 1-amplitudes are significantly reduced. Evidence of a synaptopathy was absent with normal hair cell CtBP2 counts. In Spnb5(-/-) mice, the number of afferent and efferent nerve fibers is decreased. Consistent with this data, Spnb5 mRNA is present in Type I and II spiral ganglion neurons, but undetectable in OHCs. Together, these data establish that {beta}V spectrin is important for hearing, affecting neuronal structure and function. Significantly, these data exclude {beta}V spectrin as functionally important to OHCs as has been previously suggested.