Observations with the electron microscope on enameloid formation in the common eel ( Anguilla anguilla

• Published in: Proceedings of the Royal Society of London. Series B. Biological Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1976
• Subjects: Anguilla anguilla
• Online Access: http://dx.doi.org/10.1098/rspb.1976.0077; https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.1976.0077

In the eel, the very young tooth germ consisted of an invagination into the oral epithelium, filled with a papilla of mesenchymal cells. The basal layer of the epithelium surrounding the papilla became the inner dental epithelium (i. d. e.). Initially both the i. d. e. and the papilla cells were undifferentiated. Subsequently, the i. d. e. cells and the superficial cells of the papilla differentiated, the latter becoming odontoblasts, and the matrix of cap enameloid was laid down between the two cell layers. Differentiation of the i. d. e. cells and odontoblasts proceeded in parallel, both cell types acquiring the features of secretory cells, namely enlarged nucleoli, abundant rough endoplasmic reticulum, an active Golgi apparatus and numerous vesicles. Confluence of vesicles with the distal cell membranes was observed. These findings indicate that both the i. d. e. and odontoblasts synthesize protein and secrete it into the matrix of cap enameloid, in confirmation of previous studies with autoradiography (Shellis & Miles 1974). The matrix of cap enameloid reached its mature size and shape without becoming mineralized. It contained collagen fibres, odontoblast processes and vesicles. Mineralization of cap enameloid appeared to proceed centrifugally. The crystals were large and ribbon-like, as in enamel, and their orientation conformed with the pattern of collagen fibres of the matrix. The matrix protein, including the fibres, was, however, removed during mineralization, apparently by way of the i. d. e., which showed special features at this stage associated with transport of both protein and mineral. The collar enameloid in this fish was only about 2 μm thick and consisted of two hypermineralized layers. The inner layer appeared to be homologous with the cap enameloid, being formed by the joint activity of odontoblasts and the i. d. e. of Hertwig’s sheath. The outer, more heavily mineralized layer appeared to be produced entirely by the i. d. e. and a similar layer was laid down on the outer surface of the ...