Spatial Regulation of Preameloblast Development in Response to Distal Mouse Incisor Injury.

Enamel, the outermost mineralized tissue of the tooth, is produced by specialized dental epithelial cells called ameloblasts. Unlike human enamel, which lacks regenerative capacity, the mouse incisor grows throughout life, driven by adult stem cells residing in the labial cervical loop (LaCl). To maintain tissue homeostasis, dental epithelial stem cells produce transit-amplifying cells (TACs) that commit to preameloblasts (PABs), migrate distally, and differentiate into enamel-forming ameloblasts. The full dental epithelial differentiation trajectory coexists within a single mouse incisor, making it an accessible model for studying adult tissue repair and regeneration. We have shown that the genome organizer SATB1 is enriched in PABs and is required for their differentiation into ameloblasts. Here, we investigated the injury response of PABs following mouse incisor tip trimming. Injured wild-type (wt) incisors exhibited an expanded PAB zone with intensive proliferation, reduced SATB1 in the ameloblast lineage, associated with a spatial delay in the deposition of the dentin/enamel matrix compared to uninjured controls. Trimming of Satb1 cKO mouse incisor failed to elicit this response, highlighting SATB1's role in PAB's response to injury. Compared with wt controls, injured wt incisors and both Satb1 cKO groups showed increased Ki67 immunoreactivity in LaCl mesenchymal and epithelial compartments, along with reduced Col1a1 expression in PAB microenvironment. In vitro, SATB1-transduced ameloblast lineage cells (ALCs) cultured on increasing concentrations of type I collagen exhibited reduced Ki67 but elevated Amelx/Ambn expression. There findings indicate that SATB1 is required for epithelial TACs to exit the cell cycle and transition toward PABs. Incisor tip injury delays PAB differentiation by stimulating LaCL mesenchymal proliferation and altering ECM remodeling within the PAB niche.