The timing of alpha-gustducin expression during cell renewal in rat vallate taste buds

The G protein subunit alpha-gustducin is expressed in a subset of light(Type II) but not in dark (Type I) cells in rat vallate taste buds. Thethymidine analogue 5-bromo-2'-deoxyuridine (BrdU) is incorporated into DNAduring the S-phase of the cell cycle and can be used to determine the timeof origin of a cell. In this study, 31 rats were injected with BrdU (50mg/kg i.p.) and perfused at various times, from 2.5 to 10.5 days, followingBrdU administration. Vallate papillae were embedded in polyester wax, cutinto 4 microm transverse sections, and characterized with antibodies toBrdU and alpha-gustducin. Sections were processed for indirectimmunofluorescence or with an immunoperoxidase procedure. Fromimmunoperoxidase material on 21 rats, counts of alpha-gustducin- andBrdU-labeled cells were obtained from 300-800 taste bud profiles at eachsurvival time; a total of 4122 taste bud profiles were examined. Cells withnuclei immunoreactive for BrdU occurred within the taste buds at 2.5 daysand double-labeled cells were clearly evident at 3.5 days; a small numberof double-labeled cells were seen as early as 2.5 days. Double-labeledcells reached a peak at 6.5 days and did not decline significantly by 10.5days. Cells labeled for BrdU but not alpha-gustducin peaked at 5.5 days andshowed a significant decline by 8.5 days. These latter cells included lightcells not expressing alpha- gustducin and dark cells, which have previouslybeen shown to have a shorter life span than light cells. These data suggestthat expression of alpha-gustducin appears very early in a cell's life spanand that these cells are longer lived than many of the cells that do notexpress this G protein.