Project Summary
The circumvallate papilla (CVP) and von Ebner's minor salivary glands (VEG) form a complex at the
posterior midline of the tongue. The epithelial trenches of the CVP contain hundreds of taste buds (TBs) which
each contain taste receptor cells (TRCs) that transduce taste information that is conveyed to the brain. Taste
perception is affected by salivation through tastant dissolution and subsequent clearing from the oral
epithelium. Serous saliva produced by VEG acinar cells is transported through salivary ducts that connect to
the ventral region of the CVP trenches. Cancer patients undergoing therapy often experience dysgeusia or taste
dysfunction, and can experience xerostomia due to reduced salivary gland function. Further, clinical data show
that dysgeusia is detrimental to patient quality of life, potentially leading to poor survival outcomes. Therefore,
understanding the maintenance of the CVP/VEG epithelium will allow the development of therapies to mitigate
the effects of cancer treatments on taste and salivary gland function.
CVP homeostasis occurs through the proliferation and differentiation of LGR5+ progenitor cells that
generate TRCs in TBs as well as cells of the surrounding keratinized non-taste epithelium that supports TB
structure. Though CVP epithelial renewal has been well characterized, progenitor cells involved in VEG
homeostasis have yet to be identified. However, our lab performed single-cell RNA sequencing (scRNA-seq) on
murine CVP/VEG epithelium, revealing that CVP and VEG lineages may arise from a common progenitor
population. Differential gene expression analysis reveals SOX9 marks this common progenitor, and
pseudotime analysis suggests SOX9+ progenitors give rise to LGR5+ progenitor cells. Preliminary lineage
tracing and immunostaining of Sox9CreERT2;TdTomato mice shows that SOX9+ cells contribute to CVP TBs and
non-taste epithelium, although this technique did not allow me to assess contributions to VEG. However,
organoids generated from single SOX9+ cells express markers of CVP and VEG, supporting a model where
SOX9+ cells are multipotent CVP/VEG progenitors. Together, these findings lead to my hypothesis that SOX9
marks a basal multipotent stem population that gives rise to CVP and VEG epithelia. To test
this, in Aim 1 I will use genetic barcoding and scRNAseq of SOX9+ progenitors and their progeny to determine
lineage relationships across the CVP/VEG complex. In Aim 2, I will generate organoids from LGR5+-only,
SOX9+-only, and LGR5+/SOX9+ double positive cells using CVP or VEG organoid protocols to assess if LGR5 vs
SOX9 expression restricts CVP and VEG lineage production. Further, I will ablate LGR5+ cells from
heterogenous organoid cultures to determine if single SOX9+ cells are truly multipotent or if they coordinate
with LGR5+ cells to maintain the CVP/VEG complex. Together, these findings will contribute to our
understanding of CVP/VEG homeostasis.
