FGFR3 expression during development and regeneration of the chick inner ear sensory epithelia

Several studies suggest fibroblast growth factor receptor 3 (FGFR3) plays a role in the development of the auditory epithelium in mammals. We undertook a study of FGFR3 in the developing and mature chicken inner ear and during regeneration of this epithelium to determine whether FGFR3 shows a similar pattern of expression in birds. FGFR3 mRNA is highly expressed in most support cells in the mature chick basilar papilla but not in vestibular organs of the chick. The gene is expressed early in the development of the basilar papilla. Gentamicin treatment sufficient to destroy hair cells in the basilar papilla causes a rapid, transient downregulation of FGFR3 mRNA in the region of damage. In the initial stages of hair cell regeneration, the support cells that reenter the mitotic cycle in the basilar papilla do not express detectable levels of FGFR3 mRNA. However, once the hair cells have regenerated in this region, the levels of FGFR3 mRNA and protein expression rapidly return to approximate those in the undamaged epithelium. These results indicate that FGFR3 expression changes after drug-induced hair cell damage to the basilar papilla in an opposite way to that found in the mammalian cochlea and may be involved in regulating the proliferation of support cells.