p63-Dependent Homeostatic and Reactive Differentiation Program of Salivary Myoepithelial Cells

Objectives: The mouse salivary gland (mSG) is composed of several epithelial cell types of distinct lineages that are established by coordinated differentiation programs of resident stem cells. Using scRNA-seq and lineage tracing analyses, we recently generated a detailed cell fate trajectory map of the basal and myoepithelial cell (MEC) populations of the mSG. We have also shown that ΔNp63, a master transcriptional regulator of stem and progenitor cells, is enriched in the basal and MEC compartments and that ΔNp63^+ve cells beget and maintain all the epithelial cell lineages of the adult mSG. Although the pivotal role of ΔNp63 in establishing the broader epithelial cell fate and identity in the mSG has been demonstrated, a molecular understanding of ΔNp63 function in commitment and differentiation, specifically in the MEC population, is limited.
Methods: We have utilized Acta2^CreERT2/ΔNp63^fl/fl alleles to conditionally ablate ΔNp63 in the MECs of adult mSGs and assessed alterations in stem and progenitor cell differentiation. In parallel, we have investigated the contribution of the ΔNp63^+ve MECs in mSG regeneration after injury. To assess the molecular basis of its function, we have performed a comprehensive ChIP-seq based identification of the ΔNp63-driven target gene circuitry in the mSG.
Results: Ablation of ΔNp63 results in dramatic skewing of epithelial cell differentiation accompanied by a marked loss of the mSG stem and progenitor cell populations including the MECs. Furthermore, this loss is epitomized by accompanying functional defects in SG regeneration. Interestingly, our studies have unearthed a vast trove of ΔNp63 direct target genes including Acta2, which are specifically enriched in the MEC population and are likely to mediate the cell autonomous functions of ΔNp63.
Conclusions: Our multipronged biochemical and genetic approach has revealed a crucial role for ΔNp63 in establishing and maintaining the MEC population and in governing differentiation programs in the mSG.