Timing of molecular events in the chick basilar papilla during regeneration of hair cells

Loss of cochlear hair cells leads to a permanent sensory deficit in mammals. However, the hair cells of the chicken cochlea have been shown to regenerate and recover function following damage. In order to identify potential molecular pathways which are involved in regulating this cellular regeneration, semi-quantitative RT-PCR and fluorescence immunocytochemistry were used to study two cytoskeletal proteins and several growth factor and retinoic acid receptors. Studies were done on basilar papillae of both control birds and birds exposed to a 900 Hz pure tone at 123 dB SPL for 48 hours. The first molecular marker seen in the tissue following exposure to the 900 Hz pure tone was the appearance of heavy expression of fibroblast growth factor receptor (FGFR) on the apical surfaces of supporting cells in the damaged area of the basilar papilla. This novel expression of FGFR remained until 20 days after the onset of exposure (AOE). Both B-actin and flmbrin appeared in new regenerating hair cells approximately 96 hours AOE. In addition, semi-quantitative RTPCR experiments indicated an upregulation in the expression levels of βactin mRNA in the basilar papilla at 120 hours AOE. An understanding of the molecular events occurring during regeneration will hopefully lead to an understanding of the compensatory mechanism of chickens to recover loss of auditory function. Ultimately, this should provide a basis for efforts to induce hair cell regeneration in humans to treat deafness and restore hearine.