Ultrastructure of odontogenic cells during enameloid matrix synthesis in tooth buds from an elasmobranch, Raja erinacae

Abstract

The ultrastructure of the inner dental epithelial cells (IDE) and odontoblasts in elasmobranch (Raja erinacae) tooth buds was investigated by transmission electron microscopy to determine what contribution each cell type makes to the forming enameloid matrix. Row II, early stage, IDE cells contained few organelles associated with protein synthesis, whereas preodontoblasts appeared competent to initiate extracellular matrix production. Row III IDE cells are also devoid of organelles related to secretory protein synthesis, although these IDE cells accumulated large pools of intracellular glycogen. The glycogen appeared to be packaged into vesicles and exocytosed into the lateral extracellular space toward the forming enameloid matrix. Row III odontoblasts had a morphology consistent with an active protein secretory cell. No procollagen granules were present within the odontoblasts, however, nor were many collagen fibers observed in the enameloid matrix. Instead, non-collagenous "giant" fibers having 17.5-nm periodic cross striations were associated with the invaginations of odontoblast cell processes. Giant fibers, which spanned a clear zone adjacent to the odontoblasts, terminated within the enameloid matrix. Smaller 25-nm-wide "unit" fibers emanated from the giant fiber tips to form the bulk of the enameloid matrix. The clear zone, which separated the odontoblasts from the enameloid matrix at early stages, diminished in size at later stages until the odontoblast processes were completely embedded in the enameloid matrix. Nascent enameloid crystallites were observed only after a layer of unmineralized predentin was deposited beneath fully formed enameloid matrix. The results suggest that the major constituent of the enameloid matrix in skates is a non-collagenous protein derived from the odontoblasts. The inner dental epithelial cells appear to contribute large quantities of carbohydrates to the forming enameloid matrix.

The effects of colchicine on the ultrastructure of odontogenic cells in the common skate, Raja erinacae

“…The results of this study corroborate the observation that elasmobranch IDE cells contain copious amounts of intracellular glycogen (Tomes, 1898;Kerr, 1955;Shellis, 1978;Nanci et al, 1983), which is secreted extracellularly during enameloid matrix formation (Goto, 1978;Prostak and Skobe, 1988). Colchicine treated skate IDE cells accumulated intracellular glycogen-rich granules, and intercellular glycogen and amorphous material.…”

“…"Giant" fibers of elasmobranch enameloid matrix appear to be aggregated forms of "unit" fibers (Kemp and Park, 1974;Prostak and Skobe, 1988). The present data suggest that "giant" fibers result from the secretion of electron-dense material observed in the Golgi cisternae of normal and treated enameloid-associated odontoblasts.…”

“…Elasmobranch enameloid matrix is composed of 25-nm-wide unit fibers, which are associated with "giant" fibers having 17.5-nm periodic cross-striations (Kemp and Park, 1974;Prostak and Skobe, 1988). "Giant" fibers were suggested to be a modified collagen similar to the actinotrichia found in teleost fins Park, 1970, 1974).…”

The homology and phylogeny of chondrichthyan tooth enameloid

“…The biomineralization of enameloid differs considerably from that of enamel, and also exhibits variation among gnathostome lineages (i.e., between chondrichthyans and actinopterygians). In chondrichthyans, enameloid crystallites precipitate almost exclusively upon odontoblast-derived tubular vesicles, delimited by a unit membrane, and although collagen and other ''electron-dense fibrils'' are present in the matrix, they do not serve as a crystallite nucleation structures (Prostak and Skobe, 1988;Sasagawa, 1989). In contrast, actinopterygian enameloid crystallites precipitate initially upon matrix vesicles, and accumulate subsequently along collagen fibers (Sasagawa, 1997).…”

The Origin and Evolution of Enamel Mineralization Genes

“…The enamel organic matrix is secreted by the ameloblasts, and contains enamel-specific proteins. In contrast, enameloid organic matrix is mostly deposited by odontoblasts and contains a large amount of collagen, but the ameloblasts contribute to its formation, too [Prostak and Skobe, 1984;Sasagawa, 1984;Prostak and Skobe, 1988;Prostak et al, 1993;Sasagawa, 1995Sasagawa, , 2002. However, in functional teeth, the structure of both tissues is similar, i.e.…”