Observations on early development of the murine fetal oral vestibule

Morphological and immuno/histochemical studies were performed on the vestibular lamina (VL) of gestational day 13 murine fetuses, using light microscopy (LM), confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM), in an effort to elucidate the early development of the oral vestibule. Histochemistry employing LM demonstrated some PAS-positive glycogen particles in embryonic cells of the VL, dental lamina (DL), the primary epithelial band connecting the VL and DL, and the related stomodaeal simple epithelium. On the other hand, Gomori's aldehyde fuchsine method stained certain cystine-containing intracellular granules and intercellular amorphous substances, particularly in the central VL. Intense immunoreactivity for CK-10 intermediate-sized filament proteins was demonstrated in suprabasal and superficial cells of the VL stratified keratinized epithelium. Conversely, reactions for CK-19 filaments were found diffusely in both VL and DL cells retaining the cytokeratin characteristic of the simple epithelium. TEM of the VL revealed an increment in keratinosomes, tonofilaments and desmosomes in the suprabasal layers shifting toward superficial flat parakeratinized cells. The TUNEL method using CLSM detected programmed cell death in the VL, while TEM provided no morphological evidence of necrosis or typical apoptotic features during VL development. The present results indicate that physiological (naturally occurring) cell death and exfoliation of the oral-gingival type multilayered keratinizing epithelium are essential for degeneration and separation of the VL, ultimately leading to formation of the oral vestibule.