Pax9 Is Required for Filiform Papilla Development and Suppresses Skin-Specific Differentiation of the Mammalian Tongue Epithelium

The study demonstrated that Pax9 was essential for the development of filiform papillae (FP) on the mouse tongue and for suppressing skin-specific differentiation in the tongue epithelium. In Pax9-deficient mice, the tongue's surface was smoother, with FP lacking normal polarity and a cornified layer, indicating abnormal morphology. Gene expression analysis showed down-regulation of keratin genes associated with 'hard' orthokeratin and up-regulation of those linked to 'soft' orthokeratin, suggesting the tongue epithelium developed skin-like characteristics. The study highlighted Pax9's crucial role in FP morphogenesis and the regulation of epithelial differentiation pathways, with delayed expression of Hoxc13 and other genes in the epidermal differentiation complex contributing to defects in FP development and barrier formation.