Hair cell replacement in avian vestibular epithelium: supporting cell to type I hair cell

Previous investigations have demonstrated that the sensory epithelium of the avian vestibular system possesses the capacity to replace hair cells both on an ongoing basis and following severe damage. Supporting cells, within the sensory epithelium, are believed to be the progenitors of the regenerated hair cells. In the present study we describe the series of events leading to the formation of a regenerated vestibular hair cell in post-hatched birds. Young chickens received injections of streptomycin sulfate in order to damage the sensory epithelium of the vestibular system. These injections were followed by injections of the cell proliferation marker tritiated-thymidine. At predetermined intervals, the animals were killed, and the vestibular organs were processed for tissue autoradiography. Our results confirm that hair cells originate from supporting cells. The data also indicate that postmitotic cells migrate towards the lumen of the epithelium where they differentiate into Type II hair cells. At a later time, some of the new Type II hair cells further differentiate into Type I hair cells. These results suggest that both types of avian vestibular hair cells have a common ancestor. The data also provide evidence in support of the hypothesis that calyx enclosed Type I hair cells, only present in birds and mammals, are a more differentiated stage of Type II hair cells.