Determining how Sox9 taste progenitors are established embryonically and contribute adult taste buds

About This Grant

Project Summary Hundreds of taste buds (TBs) are located in the epithelial trenches of the circumvallate taste papilla (CVP) at the posterior midline of the tongue. Each TB contains taste receptor cells (TRCs) that transduce taste information to the brain and are continually replaced from stem/progenitor cells outside of TBs. Cancer patients undergoing chemo- or radiotherapy often experience dysgeusia, or taste dysfunction, likely due to perturbation to TRC renewal. Patients experiencing dysgeusia have increased risk of depression, malnutrition, and poor treatment outcomes. Therefore, understanding the mechanisms regulating maintenance of taste epithelium and TRC renewal will inform development of treatments to prevent or restore taste loss in these patients. CVP homeostasis occurs through proliferation and differentiation of progenitor cells that generate both TRCs and the surrounding non-taste epithelium. Our lab has recently identified new, long-term SOX9+ progenitors that, as a population, generate TRCs and non-taste epithelium (NTE); however, the potential of individual SOX9+ progenitors is unexplored. SOX9+ progenitors are located distant from taste buds, in the epithelial junction linking CVP trenches to the ducts of the underlying von Ebner's minor salivary glands (VEG). Each CVP contains a dozen or more junctions containing SOX9+ cells, suggesting that multiple independent progenitor reservoirs contribute to taste epithelium. Additionally, in contrast to the highly proliferative CVP, the junction contains few proliferative cells, indicating SOX9+ cells are slow cycling. These findings lead to my hypothesis that individual SOX9+ progenitors from multiple junctions produce progeny that move into local CVP trench epithelium, become highly proliferative, and differentiate into TRCs and NTE. Thus, in Aim 1, I will use sparse SOX9 lineage trace, whole-tissue clearing, and EdU birth dating, to determine the lineage and proliferative potential of individual progenitors from multiple junctions. Our previous work has focused on SOX9+ progenitor contribution in adult homeostasis, but if and when these taste stem cells are established embryonically is unknown. Embryonic immunostaining reveals SOX9+ cells are present during initial formation of the CVP and have overlapping expression with Ptch, the Shh signaling receptor. Shh is necessary for anterior tongue taste bud development, and proper CVP trench invagination in the posterior tongue. These findings lead to my second hypothesis that embryonic Shh signaling is required to establish adult SOX9+ taste progenitors. In Aim 2, I will use embryonic lineage tracing and genetic deletion of Shh signaling in SOX9+ cells to determine when SOX9+ cells are established, begin contributing to TBs, and if Shh signaling is required in these processes. Overall, this work may lead to approaches to leverage concentrated pools of taste stem cells to restore taste function in patients.