Prostak K S, Skobe Z
Department of Electron Microscopy, Forsyth Dental Center, Boston, Massachusetts 02115.
Am J Anat. 1988 May;182(1):59-72. doi: 10.1002/aja.1001820106.
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.
利用透射电子显微镜研究了板鳃亚纲（Raja erinacae）牙胚中内釉上皮细胞（IDE）和成牙本质细胞的超微结构，以确定每种细胞类型对类釉质基质形成的贡献。在第二排早期，IDE细胞含有很少与蛋白质合成相关的细胞器，而成牙本质细胞前体细胞似乎有能力启动细胞外基质的产生。第三排IDE细胞也缺乏与分泌蛋白合成相关的细胞器，尽管这些IDE细胞积累了大量的细胞内糖原。糖原似乎被包装成小泡，并通过胞吐作用进入朝向类釉质基质形成的外侧细胞外空间。第三排的成牙本质细胞具有与活跃的蛋白质分泌细胞一致的形态。然而，成牙本质细胞内没有前胶原颗粒，在类釉质基质中也没有观察到许多胶原纤维。相反，具有17.5纳米周期性横纹的非胶原“巨型”纤维与成牙本质细胞突起的内陷有关。巨型纤维跨越成牙本质细胞附近的透明区，在类釉质基质内终止。较细的25纳米宽的“单位”纤维从巨型纤维尖端发出，构成类釉质基质的主体。在早期将成牙本质细胞与类釉质基质分隔开的透明区，在后期尺寸减小，直到成牙本质细胞突起完全嵌入类釉质基质中。仅在完全形成的类釉质基质下方沉积一层未矿化的前期牙本质后，才观察到新生的类釉质微晶。结果表明，鳐鱼中类釉质基质的主要成分是一种源自成牙本质细胞的非胶原蛋白。内釉上皮细胞似乎为形成中的类釉质基质贡献了大量碳水化合物。
