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胎子期にのみ歯芽が上下顎に存在するミンククジラBalaenoptera acutorostrata(鯨目ヒゲクジラ亜月)の, 歯芽の発生と生理学的退行に伴う細胞外基質分子であるフイブロネクチン, テネイシン, コラーゲンI, III, IV型及びラミニンの免疫組織学的分布を観察した. ミンククジラ歯芽の発生に伴うこれらの細胞外基質の消長は, 蕾状期から帽状期を経て象牙質の分泌が始まる鐘状期までは, テネイシンが発生初期のエナメル器に発現した他は, 陸生動物と大きな違いは見られなかった. しかしながら生理学的な退行期になると, 歯芽の未分化細胞の極性化に必要とされるフイブロネクチン, テネイシン, コラーゲンI, III型に対する免疫反応の発現は一様に弱くなり, これら細胞外基質の発現の停止と歯芽の退行の関連が示唆された. 一方, 退行する歯芽に隣接して新たに上顎に発生するヒゲ板原基においては, テネイシン, コラーゲンI, III型の強い免疫反応が観察され, これらの細胞外基質がこの器官の新生組織に再分布していることが示された.
The immunohistological distributions of fibronectin, tenascin, type I, III and IV collagens, and laminin were observed in the tooth buds of fetuses of minke whale, Balaenoptera acutorostrata. Distributions of extracellular matrices (ECMs) examined in this study except for tenascin were generally similar to those of terrestrial mammalian species during development of the tooth bud. Tenascin in the fetuses of minke whale showed characteristic distributions in the dental lamina and the enamel organ in the early tooth developmental stage. In the physiological degeneration stage of tooth bud development, immunoreactivity of the ECMs were very weakly and limitedly detected in the dental papilla and the surrounding mesenchyme. Immunoreactivity of tenascin and type I and III collagens were positively detected in the developing baleen plate germ which was associated with the degenerating tooth bud. These findings suggested that expressions of the ECMs were related to the formation of the tooth bud and baleen plate germ, and that the lack of the ECMs was related to the degeneration of the tooth bud in the fetal minke whale.
