The loss of epithelial cells by apoptosis was investigated in the fused area of the palatal shelves during secondary palate development in ICR mice. The results were as follows:
1) Sec ondary palate development, from palatal contact to fusion, was divided into five stages as follows:
(1) no palatal co ntact, (2) palatal contact, (3) early palatal fusion, (4) late palatal fusion, and (5) complete palatal fusion.
2) During the early and late palatal fusion stages, the morphological findings were as follows: reduced cell size, condensed chromatin, spreaded intercellular space caused by reduction in cell size, and apoptotic bodies.
3) The appearance of Fas and Fas ligand positive cells was marked during the early andlate palatal fusion phases, suggesting that apoptosis is mediated by Fas/Fas ligand.
4) The appearance of TUNEL positive cells, which exhibit DNA fragmentation, was marked during the early and late palatal fusion phases. However, cells with DNA fragmentation were not seen in the areas of disappearence of epithelial cells.
5) Shedding periderm, which has been seen in the nasal and oral cavities, is thought to be one of the mechanisms by which apoptotic cells are eliminated into the lumen.
6) Apoptosis was responsible for most of the epithelial cell loss in th e fused area during secondary palate development.
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