Ultrastructural study of the relationship between the morphogenesis of filiform papillae and the keratinization of the lingual epithelium in the mouse

Tongues were removed from fetuses of mice on the 15th day of gestation (E15 ), from newborns (PO), and from juveniles on the 7th day (p7) and on the 21 st day (P21) after birth for examination by light microscopy and transmissi on electron microscopy. In the fetuses at E15, no rudiments of filiform pap illae were visible on the dorsal surface of the tongue. No evidence of kera tinization was recognized throughout the entire dorsal lingual epithelium. At PO, rudiments of filiform papillae were compactly distributed over the d orsal surface, as are the filiform papillae in the adult, but their tips we re rounder than those of the filiform papillae in the adult. Cell columns i n the epithelium, with different deg rees of keratinization of the type obs erved in the matured adult were indistinct. However, a keratinized layer wa s clearly visible on the tip of each filiform papilla. In juveniles at P7,t he filiform papillae on the anterior part of the tongue were long and slend er, and the anterior and posterior cell columns of the filiform papillae we re identical to those in the adult. These results indicate th at, in mice, the morphogenesis of filiform papillae advances in parallel with keratiniza tion of the lingual epithelium from the stage just before birth to a stage a few weeks after birth.