Cell-type specific occurrence of apoptosis in taste buds of the rat circumvallate papilla.

The present study employed immunohistochemistry for single-stranded DNA (ssDNA) to detect apoptotic cells in taste buds of the rat circumvallate papilla. Double-labeling of ssDNA and markers for each cell type - phospholipase C beta2 (PLCbeta2) and alpha-gustducin for type II cells, neural cell adhesion molecule (NCAM) for type III cells, and Jacalin for type IV cells - was also performed to reveal which types of cells die by apoptosis. We detected approximately 16.8% and 14.0% of ssDNA-immunoreactive nuclei among PLCbeta2-immunoreactive and alpha-gustducinimmunoreactive cells, respectively, but rarely found ssDNA-immunoreactive cells among NCAM-immunoreactive or Jacalin-labeled cells, indicating that type II cells die by apoptosis. We also applied double labeling of ssDNA and human blood group antigen H (AbH) - which mostly labels type I cells as well as other cell types - and found that approximately 78% of ssDNA-immunoreactive cells were labeled with AbH, indicating that apoptosis also occurs in type I cells. The present results revealed that apoptosis occurs in both type I cells (dark cells) and type II cells (light cells), suggesting that there are two major cell lineages (dark cell and light cell lineages) for the differentiation of taste bud cells. In summury, type IV cells differentiate into dark and light cells and type III cells differentiate to type II cells within the light cell line.