Search

Odontoblasts are tall columnar cells located at the periphery of the dental pulp. They derive from ectomesenchymal cells originated by migration of neural crest cells during the early craniofacial development. Odontoblasts form the dentine, a collagen-based mineralized tissue, through secretion of its collagenous and noncollagenous organic matrix components and by control the mineralization process. A conspicuous cell process arises from the cell body of odontoblasts and penetrates into the mineralized dentine. After dentinogenesis, odontoblasts deposit new layers of dentine throughout life and might also form a type of reactionary/reparative dentine in response to dental caries and other external factors may affect teeth.

Little is known about the expression of associated proteins during the assembly of tight junctions (TJs). We studied the distribution of ZO-1, occludin, and claudin-1 between differentiating ameloblasts and odontoblasts in molar tooth germs from 1- to 3-day-old rats by confocal laser scanning microscopy. Immunoreactivity for ZO-1 was strong at proximal and distal junctional complexes of differentiating ameloblasts, while it was weak and punctuate at the distal region of differentiating odontoblasts. Occludin was immunoreactive at distal and proximal complexes of early differentiating ameloblasts and at distal regions of differentiating odontoblasts. However, in more advanced stages, occludin was only evident at the proximal complex of ameloblasts. Claudin-1 was strongly detected at the proximal complex but it was weak at distal complex of late differentiating ameloblasts. Thus, our results showed that ZO-1, occludin, and claudin-1 are differentially expressed as TJs assemble for regulating polarity and/or paracellular permeability in differentiating ameloblasts and odontoblasts., (Copyright 2004 Wiley-Liss, Inc.)

We studied the distribution of connexin (Cx) 43 and ZO-1 by confocal laser scanning microscopy at early stages of dentinogenesis and amelogenesis. Labeling for Cx43 was observed at early stages of differentiation in both the epithelial cells and differentiating odontoblasts. Immunolabeling was detected at the distal and medial regions of undifferentiated ameloblasts and between cells from stratum intermedium and stellate reticulum. Differentiating odontoblasts exhibited immunoreaction for this antibody at their distal end. Immunoreactivity for ZO-1 was observed at regions that correspond to the proximal and distal junctional complexes of differentiating ameloblasts. Staining for ZO-1 was observed at apical regions of odontoblasts with a punctate appearance. In more advanced stages, expression of Cx43 was more evident on ameloblasts, especially at the junctional complexes. Punctate immunolabeling for Cx43 was observed at the lateral sides of differentiating ameloblasts and between the other cells of the enamel organ. Immunoreaction for ZO-1 in ameloblasts was more evident than at the previous stage. It was also observed at the distal end of differentiated odontoblasts. The present study showed that differentiating ameloblasts and odontoblasts express Cx43 and ZO-1 as early as the start of the differentiation process. In addition, the expression of these junctional proteins increases as differentiation of cells continues.

We have examined freeze-fracture replicas of maxillary first molar tooth germs of newborn rats at early stages of dentinogenesis to study the development of tight junctions in the distal plasma membrane of differentiating odontoblasts. In addition, freeze-fracture was combined with filipin to observe the distribution of cholesterol on the distal plasma membrane of odontoblasts during differentiation. Only gap junctions were present in early differentiating odontoblasts. The distal plasma membrane exhibited low cholesterol content, which might indicate high fluidity. With the beginning of mineral deposition in matrix-vesicles, the first signs of tight junction formation were observed. Further development revealed increasingly complex focal tight junctions. In later stages, when mineralisation is observed progressing to the fibrillar and non-fibrillar constituents of the matrix, well developed focal tight junctions were detected. Concomitantly, cholesterol in distal portions of the odontoblast plasma membrane increased, indicating, probably, a higher rigidity. Thus, a distal plasma membrane domain is established, odontoblasts become fully differentiated, and partial compartmentalisation of matrix occurs. At this stage, odontoblasts may be able to secrete specific matrix molecules to ensure the progression of mineralisation.

Background: Mature odontoblasts possess junctional structures constituted by adherens, gap, and tight junctions. Although adherens and gap junctions appear early between odontoblasts, there is no information on the appearance and development of tight junctions between odontoblasts. In this study, we have examined freeze-fracture replicas of early dentinogenesis to study the development of tight junctions between odontoblasts and to determine whether these junctions are of zonular or macular type., Methods: Upper first molar tooth germs of Wistar rats between 1 and 3 days old were fixed in buffered 4% glutaraldehyde/4% formaldehyde and subsequently cryoprotected with cacodylate-buffered glycerol. Freeze-fracture replicas were obtained in a Balzers 301 apparatus, and early stages of dentinogenesis were examined in a Jeol 100 CX II electron microscope., Results: In the stage of early dentine matrix prior to mineralization, odontoblasts exhibit only gap junctions. With the progression of development, the distal plasma membranes of odontoblasts show numerous short tight junctions formed by fused particles and grooves. In the stage of advanced mineralization, branched and continuous rows of fused particles or grooves constitute tight junctions of the focal or macular type., Conclusions: The present study shows that tight junctions of focal or macular type appear on distal plasma membrane of early odontoblasts during differentiation. Formation of tight junctions indicates the establishment of a distal membrane domain and maturation of odontoblasts. These events occur as mantle dentine formation ceases and circumpulpar dentine formation begins.

Freeze-fracture replicas of rat molar tooth germs in conjunction with the 3-beta-hydroxysterol marker filipin were used to study the distribution of cholesterol in the distal portions of odontoblast plasma membrane. Filipin-sterol deformations (interactions) appeared as clusters interspersed with deformation-free regions on the distal plasma membrane of early differentiating odontoblasts. In fully differentiated odontoblasts, the whole distal membrane, including the process, was occupied by packed deformations with no free regions. It seems that early developing odontoblasts are poorer in cholesterol than the fully differentiated cells. As the content and/or distribution of 3-beta-hydroxysterols (cholesterol) is known to influence membrane fluidity, the low cholesterol content of early differentiating odontoblasts might be related to the fluidity required for the budding off of matrix vesicles.