<ORIGINAL ARTICLE>Study on apoptosis in oral cells and tissues : Induction of apoptosis in vitro and observation of physiological cell death in vivo

P(論文)Programmed cell death during tissue development has been believed to indicate morphologically apoptotic features. However, few investigations have been reported regarding apoptosis in vivo because the method had not been established to prove apoptosis in situ before a TUNEL method was introduced. Therefore, the purpose of the present study was to establish an in vitro system of apoptosis in oral carcinoma cell-line, and to investigate the apoptosis during oral development using a TUNEL method and an electron microscopic (EM) observation. An addition of anti-Fas antibody in medium induced apoptosis in the human oral carcinoma cell-line SAS, which was proved by a DNA ladder pattern on agarose gel electrophoresis and an apoptotic feature under EM. These cells showing TUNEL-positives confirmed that the TUNEL method was a useful for proof of apoptosis in situ. TUNEL positive reactions were observed at the area of dental papilla, enamel organ, palatal fusion, circumference of Meckel's cartilage and oral developmental epithelium in fetal tissues of rats Prior to the tooth emerging in the oral cavity, the positive reactions were seen at the connective tissue intervening between reduced enamel epithelium and oral epithelium, the fusion of those epithelia and the reduced enamel epithelium. EM findings showed apoptotic bodies featuring nuclear fragmentation with condensedchromatm in the tooth buds The circumference of Meckel's cartilage revealed rather necrotic feature than apoptotic feature. The cells in oral epithelium indicating TUNEL positives possessed flatten nuclei with condensed chromatm and scant organelles During tooth eruption, apoptotic bodies and phagocytosis of apoptotic bodies by macrophages or epithelial cells were observed in the reduced enamel epithelium. These results indicated that physiological cell death via apoptotic processes might play an important role in the development and the maintenance of homeostasis in oral tissues.departmental bulletin pape