The Timing of α-Gustducin Expression during Cell Renewal in Rat Vallate Taste Buds

The G protein subunita α-gustducin is expressed in a subset of light (Type II) but not in dark (Type I) cells in rat vallate taste buds. The thymidine analogue 5-bromo-2′-deoxyuridine (BrdU) is incorporated into DNA during the S-phase of the cell cycle and can be used to determine the time of origin of a cell. In this study, 31 rats were injected with BrdU (50 mg/kg i.p.) and perfused at various times, from 2.5 to 10.5 days, following BrdU administration. Vallate papillae were embedded in polyester wax, cut into 4 μm transverse sections, and characterized with antibodies to BrdU and α-gustducin. Sections were processed for indirect immunofluorescence or with an immunoperoxidase procedure. From immunoperoxidase material on 21 rats, counts of α-gustducin- and BrdU-labeled cells were obtained from 300–800 taste bud profiles at each survival time; a total of 4122 taste bud profiles were examined. Cells with nuclei immunoreactive for BrdU occurred within the taste buds at 2.5 days and double-labeled cells were clearly evident at 3.5 days; a small number of double-labeled cells were seen as early as 2.5 days. Double-labeled cells reached a peak at 6.5 days and did not decline significantly by 10.5 days. Cells labeled for BrdU but not α-gustducin peaked at 5.5 days and showed a significant decline by 8.5 days. These latter cells included light cells not expressing α-gustducin and dark cells, which have previously been shown to have a shorter life span than light cells. These data suggest that expression of a-gustducin appears very early in a cell's life span and that these cells are longer lived than many of the cells that do not express this G protein.