Abstract
Cell adhesion molecules (CAMs) are involved in cell migration, morphogenesis, and cell differentiation within the embryo, and later in the maintenance of the multicellular organism. The aim of the present investigation was to analyze and compare the distribution of the CAMs, E-cadherin and C-CAM, during odontogenesis and palate formation, and furthermore, to analyze the expression of the intermediate filament (IF), nestin, in odontogenesis. Mice and rats of different ages (ranging from embryonic day 13, E13, to adult) were used. The expression of the molecules was detected by immunohistochemistry and in situ hybridization.
In general, E-cadherin was expressed by most epitehelia of the oral and nasal cavity. With terminal differentiation, the oral epithelium displayed a higher CAMs expression than the nasal epithelium. In the craniofacial complex E-cadherin was expressed already at E14, while C-CAM was detected first at E16. During palatal closure at E15, the forming epithelial fusion zones (seams and triangles) showed, in the center, a high E-cadherin expression. The peripheral cells of the epithelial seam were less E-cadherin positive. This may indicate that E-cadherin is involved in the fusion of the epithelia and its expression has to be down-regulated in order for the epithelium to disintegrate and form mesenchymal continuity in the palate. There were no differences, with respect to CAM expression, between embryos with the retinoic acid (RA) induced cleft palate and normal embryos, indicating that RA does not affect the expression of CAMs. In odontogenesis, E-cadherin was present in the dental lamina, presecretory ameloblasts and cementoblasts. C-CAM was detected first in the reduced enamel epithelium prior to tooth eruption. Later, C-CAM was confined to the junctional epithelium (JE) of the gingival sulcus. Nestin was expressed in both mesenchymal and epithelial derived tissues during early tooth developmental stages and remained to be expressed exclusively in the odontoblasts.
In conclusion, the findings indicate that both E-cadherin and C-CAM are involved in the formation of the epithelial structures of the craniofacial complex in a specific spatio-temporal pattern. E-cadherin may be involved in early tooth initiation, and differentiation and repolarization of ameloblasts, while C-CAM may be important for the formation and integrity of the JE. Nestin may be involved in early epithelial mesenchymal interactions during tooth development and later in the maintenance of the dynamic odontoblasts.
