--Labeled Cells Under the Tongue Epithelium Serve as Progenitors for Taste Bud Cells That Are Mainly Type III and Keratin 8-Low.

Taste bud cells are specialized epithelial cells that undergo continuous turnover, and thus require active progenitors for their renewal and an intact taste function. Our previous studies suggested that a population of taste bud cells originates from outside of the surrounding tongue epithelium-previously regarded sole source of taste bud progenitors. In this study, we demonstrated that (SRY-related HMG-box gene 10)-expressing cells, known to be in the migrating neural crest, were also distributed in taste bud-surrounding tissue compartments under the tongue epithelium, that is, the connective tissue core of taste papillae and von Ebner's glands. By lineage tracing of -expressing cells using , a model driven by the endogenous promoter, crossing with a reporter line R26-tdTomato (tdT), we found -labeled tdT cells within taste buds in all three types of taste papillae (fungiform, circumvallate, and foliate) as well as in the soft palate in postnatal mice. The tdT taste bud cells were progressively more abundant along the developmental stages, from virtually zero at birth to over 35% in adults. Most of tdT taste bud cells had a low intensity of immunosignals of Keratin 8 (a widely used taste bud cell marker). In circumvallate taste buds, tdT signals were co-localized principally with a type III taste bud cell marker, less so with type I and II cell makers. Together, our data demonstrate a novel progenitor source for taste buds of postnatal mice--labeled cells in the connective tissue core and/or von Ebner's glands.