[Jigok Lecture Series] ▶Subject: Establishing the tonotopy: sound frequency discrimination of the auditory neurosensory organ ▶Speaker: Prof. Jinwoong Bok (Department of Anatomy, Yonsei University College of Medicine) ▶Date: 4:30PM/May. 12(Thu.)/2016 ▶Place: Auditorium(1F), Postech Biotech Center *Abctract Sound frequency discrimination is crucial for daily activities throughout the animal kingdom. This process begins at the auditory peripheral organ known as the cochlea, which is tonotopically organized such that mechanosensory hair cells at the basal end respond to high frequency sound, whereas their counterparts at the apex respond to low frequencies. This frequency tuning is facilitated by specific anatomical and physiological properties, including gradual changes in the shape and physiology of the hair cells along the cochlea. However, the mechanisms for establishing the tonotopy remain obscure. Since the developing cochlea receives graded Shh signaling, it has been suggested that the gradient of Shh signaling may confer regional identities along the developing cochlea, contributing to the establishment of tonotopy. However, testing this hypothesis using a loss-of-function approach is not feasible because the cochlea fails to form in the absence of Shh. Thus, we examined the roles of Shh in development of the tonotopy by using gain-of-function models. Implanting Shh-soaked beads to the developing otocyst in chicken embryos causes basal hair cells to exhibit morphological features of their counterparts in the apex. These morphological changes are preceded by expansion of apically expressed genes toward the base of the cochlea. We also examined the cochleae from Pax2Cre/+; SmoM2/+ mice, in which the transducer of Shh (Smoothened) is constitutively activated in the inner ear epithelium. In this model we also observed expansion of apically associated genes toward the basal cochlea. Furthermore, we provide evidence that the regional cochlear identity is established early by Shh signaling emanating from the ventral midline. Together, these results suggest that Shh gradient provides regional identities along the developing cochlea, which prefigures the tonotopic organization of the mature cochlea. ▶Inquiry: Prof. Yoo, Joo-Yeon (279-2346) * This seminar will be given in English. please refrain from taking photos during seminars. *