Ultrastructural study of the relationship between the morphogenesis of filiform papillae and the keratinisation of the lingual epithelium in the rat

Tongues were removed from rat fetuses on d 16 of gestation (E16) and from n ewborn (PO) and juvenile rats on d 7 (P7) and d21 (P21) postnatally for exa mination by light and transmission electron microscopy. In the fetuses at E 16, no rudiments of filiform papillae were visible on the dorsal surface of the tongue. No evidence of keratinisation could be recognised over the ent ire dorsal lingual epithelium. At PO, rudiments of filiform papillae showed a similar distribution to that seen in the adult, but had a more rounded a ppearance. The columnar structure of cells in the epithelium, with the diff erent degrees of keratinisation as observed in the mature adult, was indist inct, but a keratinised layer was clearly located at the tip of each filifo rm papilla. In juveniles at P7, the filiform papillae on the anterior part of the tongue were long and slender, and the anterior and posterior cell co lumns of the filiform papillae and the interpapillary cell columns were cle arly distinguishable. In juveniles at P21, the structure of filiform papill ae was identical to that in the adult. These results indicate that, in rats , the morphogenesis of filiform papillae advances in parallel with keratini sation of the lingual epithelium from just before birth to a few weeks afte r birth.