p53 and Bax: Putative death factors in taste cell turnover

The turnover of cells in renewing epithelia presents an opportunity to exam ine cell death pathways in adult vertebrates. In mouse lingual epithelium a typical taste receptor cell survives for 9 days, until it is killed by an unknown cascade of death factors. Apoptosis was implicated by the presence of fragmented DNA in about 8% of taste receptor cells in the vallate papill a. In using immunocytochemistry to seek putative dearth factors, we observe d that squamous epithelial cells of the tongue were negative for Bar, a dea th factor in the Bcl-2 family of survival/death factors, and were also nega tive for p53, a tumor-suppressor protein linked to apoptosis and Bar transc ription. In contrast, 8-10% of the taste receptor cells were Bax-positive, and 9-11% were p53 positive. These immunopositive taste receptor cells were more likely to display death-related morphologic defects than other recept or cells, and they frequently coexpressed p53 and Bar. In both neonatal and adult mice, the labeling of dividing cells with 5-bromo-2'-deoxyuridine in dicated that all Bar-positive taste cells were at least 5 days old. On post natal day 7, when few taste cells were old, no more than 1% of taste cells were immunopositive for either p53 or Bar. We inferred that old taste recep tor cells employ p53 and Bar as part of their apoptotic death pathway. The routine expression of p53 by postmitotic, aged taste cells broadens the con ventional View that p53 is restricted to mitotic cells that have stress-dam aged DNA. Furthermore, the scattered distribution of aged receptor cells wi thin the taste bud excludes some explanations for stable taste signals duri ng receptor cell turnover. J. Comp. Neurol. 413:168-180, 1999. (C) 1999 Wil ey-Liss, Inc.