IDENTIFICATION OF HAIR CELL PROGENITORS AND INTERMITOTIC MIGRATION OFTHEIR NUCLEI IN THE NORMAL AND REGENERATING AVIAN INNER-EAR

Postembryonic production of sensory hair cells occurs in both normal a nd aminoglycoside-damaged avian inner ears. The cellular source and me chanism that results in new differentiated hair cells were investigate d in the avian vestibular epithelia using three distinct cell-cycle-sp ecific labeling methods to identify proliferating sensory epithelial c ells. First, immunocytochemical detection of the proliferating cell nu clear antigen, an auxiliary protein of DNA polymerase, allowed labelin g of cells in late G1, S, and early G2 phases of the cell cycle. Secon d, a pulse-fix tritiated thymidine autoradiographic protocol was used to identify cells in S phase of the cell cycle. Finally, Hoechst 33342 , a fluorescent DNA stain, was used to identify epithelial cells in mi tosis. The distribution of cells active in the cell cycle within the n ormal and ototoxin-damaged vestibular epithelium suggests that support ing cells within the sensory epithelia are the cellular precursors to the regenerated hair cells. Differences between the proliferation mark er densities in control and damaged end organs indicate that the upreg ulation of mitotic activity observed after streptomycin treatment is d ue primarily to an increase in the number of dividing progenitor cells . The differences between the extent of ototoxic damage and the level of reparative proliferative response suggest a generalized stimulus, s uch as a soluble chemical factor, plays a role in initiating regenerat ion. Finally, after DNA replication is initiated, progenitor cell nucl ei migrate from their original location close to the basement membrane to the lumenal surface, where cell division occurs. This pattern of i ntermitotic nuclear migration is analogous to that observed in the dev eloping inner ear and neural epithelium.