New mechanisms for oral epithelial basal stem cell plasticity during re-epithelialization after injury

The oral mucosa undergoes daily insults and stem cells in the epithelial basal cell layer are required to regenerate gingiva tissue to maintain oral health. The Iroquois Homeobox 1 (IRX1/Irx1) protein is expressed in the stem cell niches in human/mouse oral epithelium and mesenchyme under homeostasis. We found that Irx1+/- heterozygous (Het) mice have delayed wound closure, delayed morphological changes of regenerated epithelium, as well as defective keratinocyte proliferation and differentiation during wound healing. RNA-seq analyses between wildtype and Irx1+/- mice at 3 days post injury (dpi), found impaired epithelial migration and decreased keratinocyte-related genes upon injury. Irx1 expressing cells are found in the gingival epithelial basal cell layer, a stem cell niche for gingival maintenance. Irx1 expressing cells are also found in cell niches in the underlying stroma. Irx1 activates Sox9 in the transient amplifying layer to increase cell proliferation and EGF signaling is activated to induce cell migration. Krt14CreERT lineage tracing experiments reveal defects in the stratification of the Irx1+/- heterozygous mouse oral epithelium. Irx1 is primed at the base of the gingiva in the basal cell layer of the oral epithelium, facilitating rapid and scarless wound healing through activating Sox9 and the EGF signaling pathway.