Expression of the basal cell markers of taste buds in the anterior tongue and soft palate of the mouse embryo.

Although embryonic expression of Shh in the fungiform papilla placodes has a critical role in fungiform papilla patterning, it remains unclear whether its appearance indicates the differentiation of the basal cells of taste buds. To examine the embryonic development of the basal cells, the expression of Shh, Prox1, and Mash1 was determined in the anterior tongue and soft palate in mouse embryos by in situ hybridization. In the anterior tongue, Prox1 was coexpressed with Shh from the beginning of Shh expression in the fungiform papilla placodes at E12.5. Shh was expressed in the soft palate in a band-like pattern in the anteriormost region and in a punctate pattern in the posterior region at E14.5. The number (21.4 +/- 4.3, at E14.5) of locations where Shh was observed (i.e., spots) rapidly increased and reached a peak level (54.8 +/- 4.0 at E15.5). Also in the soft palate, Prox1 was coexpressed with Shh from the beginning of Shh expression. These results suggest that basal cell differentiation occurs synchronously with the patterning of Shh spots both in the anterior tongue and in the soft palate. In contrast, Mash1 expression lagged behind the expression of Shh and Prox1 and began after the number of Shh spots had reached its peak level in the soft palate. Furthermore, immunohistochemistry of PGP9.5 and Shh revealed that epithelial innervation slightly preceded Mash1 expression both in the tongue and in the soft palate. This is the first report describing the time courses of the embryonic expression of basal cell markers of taste buds.