Hearing development and spiral ganglion neurite growth in VASP deficient mice

Vasodilator-stimulated phosphoprotein (VASP) has been found to be involved in intracellular signalling pathways and to play an important role in the actin associated organization and formation of the cytoskeleton. Since differential VASP expression was noted in inner ear tissues, the present study was performed to investigate the hearing development in VASP deficient mice. Hearing development in VASP-/- mice and wild type animals was investigated by auditory brain stem (ABR) measurements. In addition, inner ear tissues of wild type animals were tested for VASP expression using PCR, Western blot analysis, in situ hybridisation, and immunohistochemistry. To compare spiral ganglion (SG) neurite growth, SG explants from VASP-/- and wild type mice were analyzed under cell culture conditions. The electroacoustical results of the present study indicate that VASP deficient mice present with a later onset of hearing during postnatal development compared to wild type animals. Transient VASP expression was detected in neonatal SG of wild type mice. Tissue culture experiments with SG explants from VASP-/- animals revealed significant alterations in SG neurite extension compared to wild types. The present findings suggest a role for VASP during neonatal development of the mammalian cochlea and allow speculation on a possible delayed innervation of cochlear hair cells due to changes in SG neurite growth in VASP-deficient mice. Temporary VASP deficits in the neonatal inner ear may be compensated by related proteins like MENA leading to a delayed but complete development of hearing function in VASP-/- animals.