SIALYLATION OF TERMINAL SACCHARIDES OF GLYCOCONJUGATES EXPRESSED BY MURINE MOLAR TOOTH GERMS DEVELOPING IN-VITRO AND IN-VIVO

During development of the mammalian tooth germ the pattern of terminal saccharides of glycoconjugates changes, with many structures losing l ectin reactivity in a consistent pattern. This study investigated whet her the epitopes are lost or become masked by terminal sialylation, us ing a combination of neuraminidase treatment of sections and sialic ac id-reactive lectins. The results suggested that most of the terminal g alactosamine and fucose sites in the epithelial enamel organ were remo ved during morphogenesis. Conversely, during condensation of the denta l mesenchyme, masked peanut agglutinin (PNA)-reactive galactose epitop es appeared. During differentiation and organisation of the mesenchyme into odontoblasts and a subodontoblastic layer the PNA-reactive sites became masked again. These regions also specifically expressed sialyl ated glucosamine. However, at the proliferating epithelial cervical lo op galactose sites appeared to be masked. This was more pronounced dur ing in vitro development when abnormal expression of PNA-reactive site s was found at the cervical loop. Additionally, fucosylated sites pers isted in the enamel organ, further indicating that the expression of t erminal saccharides was disrupted during development in the organ cult ure system. These data suggest that loss of terminal galactose and gal actosamine is related to differentiation of the cells. However, whethe r this loss occurs by removal or sialic acid masking is not dependent either on the origin of the cells or the epitope being lost.