A strong nerve dependence of sonic hedgehog expression in basal cells in mouse taste bud and an autonomous transcriptional control of genes in differentiated taste cells.

The nerve-dependency of gene expression in mouse taste bud was examined through an analysis of changes in gene expression in and around the taste buds in circumvallate papillae after surgery of cranial nerve IXth (glossopharyngeal nerve). The number of cells expressing T1r3, gustducin, Mash1 and Nkx2.2 gradually decreased after denervation. However, the expression intensity of these genes was barely influenced by denervation, and strong expression was observed at 6 days after denervation. In contrast, the basal cell-specific Sonic hedgehog (Shh) expression in the taste buds was decreased markedly at 6 h after denervation. In the regeneration process of taste buds, Shh expression was observed during a very early phase before taste bud formation. These results indicate the autonomous transcriptional control of genes in differentiated taste cells and the strong nerve-dependency of Shh expression in basal cells. Furthermore, in order to reveal the mitotic activity of Shh-expressing cells in taste buds, the BrdU-labeling experiments were performed using a combination of BrdU-immunohistochemistry and in situ hybridization. BrdU-signal was very rarely observed in Shh-expressing cells immediately after BrdU injection, and the signals were noted mainly in Ptc-expressing cells. BrdU signals rapidly increased in Shh-expressing cells in following 12 h and began to decrease after 2 days post-injection. These results suggest that most Shh-expressing cells are not mitotically active, but that Shh-expressing cells may be in the early transient developmental state of taste cells in taste buds.