Involvement of apoptosis in the detaching process of the epithelial primordium

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The present study was conducted to investigate to what extent apoptosis is involved in the process of detachment of the adenohypophysial primordium from the oral epithelium. For this purpose, sections including hypophysial rudiment of the 12- to 14-day-old rat fetuses was examined by using an in situ end labelling (TUNEL) method. Massive apoptosis was observed in the oral epithelium when the adenohypophysial primordium closes to form Rathke's pouch. Apoptotic cell death of the oral epithelium was not confined to the closing pouch but it was seen along the midline of the stomodeal roof. In observing closing Rathke's pouch, the apoptotic cells was frequently seen in the oral epithelium itself but it was less frequent in the adoral constricted part. Moreover, the incidence of cell death in the epithelial constriction was variable among individuals. In some fetuses, epithelial cells were found to be incorporated into the hypophysial primordium without degeneration. Such incomplete degenerative process of epithelial component is discussed in relation to the frequent presence of epithelial cysts in the adult rat adenohypophysis.