Expression of basement membrane components in the dental papilla mesenchyme of monkey tooth germs--an immunohistochemical study

Transmission and scanning electron microscopic observations of epithelial-mesenchymal interface of rat tooth germs using dithiothreitol separation

Aperiodic fibrils (AF) project from the interstitial side of the lamina densa of the basement membrane (BM) of the inner enamel epithelium (IE), and show remarkable changes in their morphology during development. The three-dimensional morphology of aperiodic fibrils during development has not been observed, because of the difficulty of exposing the interstitial surface of the BM of the inner enamel epithelium. In the present study, the dithiothreitol separation method was applied to expose the interstitial side of the inner enamel epithelial BM of rat tooth germs for the purpose of observing the exposed aperiodic fibrils by transmission and scanning electron microscopy (TEM and SEM, respectively). After dithiothreitol treatment, the enamel organ (EO) was mechanically separated from the dental papilla (DP). In the region with poorly-developed aperiodic fibrils, the separation occurred at the junction between the inner enamel epithelial BM and the dental papilla, and the aperiodic fibrils were exposed, showing the typical picture of dithiothreitol separation. SEM observation of this region revealed that the aperiodic fibrils were connected to each other and they formed networks. These networks resembled those formed by the anchoring fibrils of epidermal and mucosal epithelial BMs. TEM and SEM observations revealed that there were sidechain-like structures on the surface of the aperiodic fibrils. In the region with well-developed aperiodic fibrils, dithiothreitol treatment was not entirely effective, and some mesenchymal tissues remained on the BM. In this region, TEM observation revealed that the aperiodic fibrils were arranged in parallel with each other, and were connected by the sidechains. Several thin collagen fibrils, which were thought to be immature collagen fibrils (CF) of the predentine, were also connected to the aperiodic fibrils with these sidechains and arranged in parallel with them. Based on SEM and TEM observations, the aperiodic fibrils may be regarded as a kind of anchoring fibrils and they may play a role in connecting the BM with the mesenchymal tissue below. They are also thought to guide the arrangement of collagen fibrils in the surface layer of the predentin.

Ultrastructure and composition of basement membranes in the tooth

The tooth, the hardest organ in the body, is known to be formed through highly elaborate, unique processes of differentiation and development. Basement membranes play critical roles in fundamentally important biological processes such as growth and differentiation, and for better understanding of the mechanism of development and maintenance of the tooth, specializations of tooth basement membranes are reviewed in detail in relation to their roles. The basement membrane at such diverse locations in the tooth as the inner enamel epithelium, maturation-stage ameloblasts, and junctional epithelium at the dentogingival border are specialized in their own highly unique ways for anchoring, firm binding, or mediation in the transport of substances. Thus, the role of basement membranes in the developing and mature tooth is manifold and for these roles individual basement membranes are specialized in their own specific ways which are rare or not seen in nondental tissues, and these specializations are essential for successful development and maintenance of the tooth.

Possible role of monkey gingival fibroblasts in external basement membrane maintenance

Morphological and immunocytochemical investigations were made of the interface between the junctional epithelium and connective tissue in gingiva from young monkeys (Macaca fuscata). Some fibroblasts with conspicuous cytoplasmic organelles, including the elements of rough endoplasmic reticulum, the Golgi apparatus, and mitochondria, were found close to the external basement membrane in the connective tissue underlying the junctional epithelium. Occasionally, cytoplasmic cell processes either made contact with the lamina densa of the basement membrane or came into direct contact with the plasma membrane of the basal layer of junctional epithelium cells. Fragments of a structure like that of the basement membrane were observed between the process and the basal cells. Fibroblasts could be seen very close to the disrupted portion created by the passage of leukocytes migrating into the junctional epithelium through the external basement membrane. Immunoperoxidase methods demonstrated a positive reaction product for laminin on the external basement membrane. This product was observed in the rough endoplasmic reticulum of junctional epithelium cells and of gingival connective tissue fibroblasts located close to the junctional epithelium basement membrane. The cytoplasm of fibroblasts distant from the epithelium, however, demonstrated no immunoreactivity. These results suggest that, in cooperation with epithelial cells, some fibroblasts located near the junctional epithelium can produce such basement membrane components as laminin and that these components may serve to stabilize and/or restore previously assembled basement membrane.

Light and electron microscopical immunohistochemical localization of large proteoglycans in human tooth germs at the bell stage

The immunohistochemical localization of large hyaluronate-binding proteoglycans has been studied in human tooth germs at the bell stage using a monoclonal antibody, 5D5, which is derived from bovine sclera and specifically recognizes the core protein of large proteoglycans, such as versican, neurocan and brevican, but not that of aggrecan. In the early bell stage before predentine secretion, when the enamel organs consisted of the inner and outer enamel epithelia, stratum intermedium and stellate reticulum, the enamel organs were not stained by 5D5, but the dental papillae and follicles stained strongly. Concomitant with the secretion of predentine, dentine and subsequent enamel matrix, strong 5D5 immunostaining distributed over the entire cell surfaces of secretory ameloblasts was observed. The forming enamel matrix showed strong staining. While most of the inner and outer enamel epithelia and stratum intermedium lacked staining, the cervical loop region and stellate reticulum showed weak staining. Although the forming dentine and odontoblasts appeared to lack 5D5 affinity, the predentine, dental papilla and dental follicle demonstrated moderate to strong reactivity. At the ultrastructural level, specific immunoreaction by immunogold particle deposition was clearly detected over the basal lamina of presecretory ameloblasts, secretion granules of secretory ameloblasts and the forming enamel matrix. These results indicate that a marked increase in the large proteoglycan associated with secretory ameloblasts may correlate with cell differentiation and enamel matrix biosynthesis.

Effects of a functional agar surface on in vitro dentinogenesis induced in proteolytically isolated, agar-coated dental papillae in rat mandibular incisors

In an attempt to study the effects of a three-dimensional agar surface on in vitro dentinogenesis both in the growing end and in incisally cross-cut pulp, the possible expression of odontoblast phenotype was investigated morphologically, autoradiographically and immunohistochemically. Explants were incubated for 8 days. In the growing end, during the last 4 days, mitotic cells differentiated into [3H]-thymidine-labelled, tubular matrix-forming cells. In cross-cut pulp, however, during the first 4 days, mitotic cells differentiated into [3H]-thymidine-labelled, tubular matrix-forming cells. Electron microscopy demonstrated that, in both regions, tubular matrix-forming cells had characteristics similar to those of primary odontoblasts. When agar was incubated alone, exogenous fibronectin was deposited on it rapidly. After 12 h, endogenous fibronectin appeared on explant peripheral cells. Collagen and materials reacting positively to periodic acid-Schiff (PAS) were first interposed between agar and explant after 4 days. After 8 days, an inner immunonegative layer corresponding to materials reacting positively to PAS or toluidine blue and an outer immunopositive layer of fibronectin or collagen were visible adjacent to the rows of elongated columnar cells. In the presence of Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP), a competitive inhibitor of attachment of cells to fibronectin, explants became detached from the agar surface, and no dentinogenesis occurred. These results indicate that, when in contact with an agar surface that becomes modified by fibronectin and/or by a complex of fibronectin with deposited matrix, dental mesenchymal cells progressively differentiate into tubular matrix-forming cells. Possibly the functional agar surface has the important role of providing a foothold for cell attachment, which is the first step towards in vitro odontoblast differentiation. This system of inducing tubular matrix-forming cells constitutes a useful model for the study of in vitro dentinogenesis.