The characteristic cellular organization and CEACAM1 expression in the junctional epithelium of rats and mice are genetically programmed and not influenced by the bacterial microflora.

BACKGROUND: The epithelial cell adhesion molecule CEACAM1 exhibits an interesting dynamic expression during tooth development. It is first expressed in the reduced enamel epithelium, its expression then increases in the orally faced reduced epithelium and the overlying oral epithelium that then fuse to give rise to the junctional epithelium. The expression of CEACAM1 remains at high levels in the junctional epithelium, in contrast to the surrounding oral sulcular epithelium which shows much lower expression levels. We investigated if the high expression levels of CEACAM1 and the loosely organized cells characteristic of the junctional epithelium are genetically programmed or result from bacterial infiltration. METHODS: Oral tissues from germ-free rats and mice and animals with conventional bacterial flora were analyzed by transmission electron microscopy and immunohistochemical staining for CEACAM1. RESULTS: The junctional epithelium of both germ-free and conventional animals was identical with respect to both CEACAM1 expression and morphology. Also the presence of leukocytes was the same in both types of animals. CONCLUSIONS: The results indicate that the characteristic morphology and the high expression levels of CEACAM1 in the junctional epithelium are genetically programmed and not a result of bacterial infiltration. This suggests that CEACAM1 has an important role for the structural integrity of the junctional epithelium. This conclusion was supported by the observation that the junctional epithelium does not express any E-cadherin, which is another abundant epithelial cell adhesion molecule.

Dynamic expression of E-cadherin in ameloblasts and cementoblasts in mice.

During embryonic development, E-cadherin mediates intercellular adhesion in a variety of epithelia in a spatio-temporal pattern. We have analyzed the distribution of this cell adhesion molecule in the mouse during odontogenesis, at both mRNA and protein levels, in the mandibular first molars and incisors. E-cadherin was strongly expressed at the bell stage by the cells of the dental organ, and by the pre-secretory ameloblasts and the cells of stratum intermedium at the early mineralization stage. At the onset of enamel secretion, E-cadherin disappeared from the apical pool of the ameloblasts and was later absent from the post-secretory ameloblasts. E-cadherin was also found in Hertwig's root sheath and later in the cells producing acellular cementum. These findings indicate that E-cadherin may be involved in the polarization of the ameloblasts and in the early stages of cementogenesis.

Expression of the intermediate filament nestin during rodent tooth development.

The developing tooth represents a suitable model for understanding the molecular mechanisms involved in induction, morphogenesis and differentiation of organs. It is conceivable that the developmental changes could be reflected in the distribution of different cytoskeletal components and in this report we analyze the expression of the intermediate filament nestin during rodent tooth development at the protein and mRNA levels (by immuno light and electron microscopy, and by in situ hybridization). Nestin is expressed at all stages of tooth development, but the expression levels increase after birth in both ectodermal and ectomesenchymal derivatives. The shift in nestin distribution, from the proliferating dental lamina to the dental mesenchyme, indicates that nestin may be involved in inductive phenomena. At early stages of mineralization, nestin is seen within the apical parts of the presecretory ameloblasts. Nestin is also expressed in odontoblasts, both during odontogenesis and after tooth eruption. The increase in nestin expression from early to late developmental stages and sustained expression in a differentiated cell type contrasts with previously observed patterns of nestin expression during nerve and muscle development. This suggests that nestin could be used as a specific marker for the odontoblast.