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 progenit ors of the regenerated hair cells. In the present study we describe th e series of events leading to the formation of a regenerated vestibula r hair cell in post-hatched birds. Young chickens received injections of streptomycin sulfate in order to damage the sensory epithelium of t he vestibular system. These injections were followed by injections of the cell proliferation marker tritiated-thymidine. At predetermined in tervals, the animals were killed, and the vestibular organs were proce ssed for tissue autoradiography. Our results confirm that hair cells o riginate from supporting cells. The data also indicate that postmitoti c cells migrate towards the lumen of the epithelium where they differe ntiate 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 resu lts suggest that both types of avian vestibular hair cells have a comm on ancestor. The data also provide evidence in support of the hypothes is that calyx enclosed Type I hair cells, only present in birds and ma mmals, are a more differentiated stage of Type II hair cells.