Study on a cause of hearing defect in Vlgr1 mutated mice

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1) Study on the functional domain of Vlgr1We collaborated on this theme with the group of French. We revealed that Vlgr1 was related to the proteins that consist of the ankle link of stereocilia.2) Study on the hearing defect of Vlgr1 knockout miceWe revealed that Vlgr1-knockout mice suffered from a hearing defect because of inner ear dysfunction, as indicated by auditory brainstem response and distortion product oto-acoustic emissions. The expression of Vlgr1 was identified in the developing hair cells from embryonic day 17 to postnatal day 10. Vlgr1 was localized in the base of stereocilia on hair cells using confocal microscopy. This Vlgr1 localization was limited to the base of stereocilia within approximately 200-400 nm from the apical surface of hair cells using immunoelectron microscopy. This localization of Vlgr1 was disappeared under the calcium free condition. Under the SEM studies, the Vlgr1 knockout mice showed malformation of the stereocilia of cochlear hair cells. At postnatal day 0, the appearance of hair bundles was almost normal in the Vlgr1 knockout mice. The cochlear hair bundles of Vlgr1 knockout mice became disarranged at postnatal day 8. Furthermore, the stereocilia in the Vlgr1 knockout mice became slanted and disarranged thereafter. These results indicate that loss of Vlgr1 resulted in abnormal development of stereocilia formation and the Vlgr1 was related to the formation of ankle link.