Functional Cell Types in Taste Buds Have Distinct Longevities

Abstract

Taste buds are clusters of polarized sensory cells embedded in stratified oral epithelium. In adult mammals, taste buds turn over continuously and are replenished through the birth of new cells in the basal layer of the surrounding non-sensory epithelium. The half-life of cells in mammalian taste buds has been estimated as 8–12 days on average. Yet, earlier studies did not address whether the now well-defined functional taste bud cell types all exhibit the same lifetime. We employed a recently developed thymidine analog, 5-ethynil-2′-deoxyuridine (EdU) to re-evaluate the incorporation of newly born cells into circumvallate taste buds of adult mice. By combining EdU-labeling with immunostaining for selected markers, we tracked the differentiation and lifespan of the constituent cell types of taste buds. EdU was primarily incorporated into basal extragemmal cells, the principal source for replenishing taste bud cells. Undifferentiated EdU-labeled cells began migrating into circumvallate taste buds within 1 day of their birth. Type II (Receptor) taste cells began to differentiate from EdU-labeled precursors beginning 2 days after birth and then were eliminated with a half-life of 8 days. Type III (Presynaptic) taste cells began differentiating after a delay of 3 days after EdU-labeling, and they survived much longer, with a half-life of 22 days. We also scored taste bud cells that belong to neither Type II nor Type III, a heterogeneous group that includes mostly Type I cells, and also undifferentiated or immature cells. A non-linear decay fit described these cells as two sub-populations with half-lives of 8 and 24 days respectively. Our data suggest that many post-mitotic cells may remain quiescent within taste buds before differentiating into mature taste cells. A small number of slow-cycling cells may also exist within the perimeter of the taste bud. Based on their incidence, we hypothesize that these may be progenitors for Type III cells.

Neuronal delivery of Hedgehog directs spatial patterning of taste organ regeneration

“…4B). Postmitotic TRCs are replaced every 8-24 d from surrounding epithelium (28), and this process can be tracked by marking of basal epithelial cells, which express K5 (Fig. S5C).…”

Single Lgr5- or Lgr6-expressing taste stem/progenitor cells generate taste bud cells ex vivo

“…Together, our data demonstrate that functional taste cells can be generated ex vivo from single Lgr5 + or Lgr6 + cells, validating the use of this model for the study of taste cell generation. (1,4,5). At present, the stem cell population and the regenerative process from adult taste stem/progenitor cells to mature taste bud cells are not well characterized.…”

The K + channel K IR 2.1 functions in tandem with proton influx to mediate sour taste transduction

“…Moreover because the Pkd2l1 Cre driver is expressed by mature neurons, it is only expected to excise the floxed allele at a time when there may already be significant expression of ion channels; under these circumstances, elimination of the current would only be observed if the existing protein has turned over and both alleles of Kcnj2 were inactivated. Given the short lifetime of taste cells (∼22 d) (45), the likelihood that all these events occur before a cell dies is low. Nonetheless, the significant reduction in the resting K + current in the tissuespecific KO mice, together with our pharmacological and expression profiling data, provide strong evidence that K IR 2.1 is required for the resting K + current in sour taste cells.…”