Immunohistochemical localization of syndecan-1 in the dental follicle of postnatal mouse teeth

Background: Syndecans are cell surface heparan sulfate proteoglycans that modulate the action of growth factors and extracellular matrix components. Syndecan-1 plays important roles during early tooth development, and it is expressed in the dental follicle of fetal tooth germ. However, no studies have followed its expression in the dental follicle during the postnatal period. We hypothesized that syndecan-1 protein expression in the dental follicle may be important for postnatal tooth development, and, thus, examined its expression patterns. Methods: Syndecan-1 protein expression in the dental follicle of the lower first molar was investigated by immunohistochemistry using embryonic day (E) 18.5 to 21 -day-old (d 21) mice. Immunoelectron microscopy was applied to the dental follicle and pulp cells to confirm its membrane localization in mesenchymal cells. Results: Strong syndecan-1 immunostaining was maintained in the dental follicle and the adjacent dental pulp surrounded by the Hertwig's epithelial root sheath (HERS) from d 4 to d 14, but reduced staining was noted at d 21 with the near-completion of tooth eruption. Three dimensionally, syndecan- 1 -positive areas plugged the apical foramina surrounded by HERS. However, immunostaining was detected constantly in the dental follicle and the dental pulp of the lower incisor at d 21. In addition, membrane localization of syndecan- I protein was confirmed for the first time in mesenchymal cells, including dental follicle and pulp cells, by immunoelectron microscopy. Conclusion: The spatial and temporal expression of syndecan-1 in the dental follicle suggests that this proteoglycan is important for the maintenance of proliferation and/or movement of cells in this region during tooth eruption.