Semaphorin-RhoA signaling regulates HERS maintenance by acting against TGF-β-induced EMT

Background and ObjectivesHertwig's epithelial root sheath (HERS) plays a role in root dentin formation. It produces the epithelial rests of Malassez (ERM) for the induction of periodontal tissue development during root formation. Although ERM is thought to be caused by epithelial-mesenchymal transition (EMT), the mechanism by which HERS is maintained as epithelium is unknown. Here, we aimed to elucidate the molecular mechanisms regulating the relationship between HERS maintenance and ERM development. MethodsTo understand the relationship between HERS and ERM development during root formation, we observed the developing molar root using cytokeratin14 (CK14) Cre/tdTomato mice via stereomicroscopy. The relationship between semaphorin and transforming growth factor (TGF) signaling in the maintenance of HERS and ERM development was examined using CK14cre/R26-tdTomato mice and a HERS cell line. ResultstdTomato-positive cells were observed on HERS and the migrating cells from HERS. The migrating cells showed reduced E-cadherin expression. In contrast, HERS cells expressed semaphorin receptors and active RhoA. Semaphorin signaling was associated with RhoA activation and cell-cell adhesion, while TGF-beta induced decreased E-cadherin and active RhoA expression, and consequently enhanced cell migration. ConclusionHERS induces root formation by controlling epithelial maintenance and EMT through the opposing effects of semaphorin and TGF-beta signaling.

Automated summary

This study investigates the molecular mechanisms underlying the maintenance of Hertwig's epithelial root sheath (HERS) and the development of epithelial rests of Malassez (ERM) during root dentin formation. The researchers observed the expression of semaphorin receptors in HERS cells and the activation of RhoA signaling pathway, while TGF-beta signaling pathway promoted cell migration and reduced E-cadherin expression. These findings provide insights into the opposing effects of semaphorin and TGF-beta signaling in controlling HERS maintenance and EMT during root formation.