Lectin-binding patterns in the developing tooth

Protein–Protein Interactions of the Developing Enamel Matrix

Extracellular matrix proteins control the formation of the inorganic component of hard tissues including bone, dentin, and enamel. The structural proteins expressed primarily in the enamel matrix are amelogenin, ameloblastin, enamelin, and amelotin. Other proteins, like biglycan, are also present in the enamel matrix as well as in other mineralizing and nonmineralizing tissues of mammals. In addition, the presence of sulfated enamel proteins, and "tuft" proteins has been examined and discussed in relation to enamel formation. The structural proteins of the enamel matrix must have specific protein-protein interactions to produce a matrix capable of directing the highly ordered structure of the enamel crystallites. Protein-protein interactions are also likely to occur between the secreted enamel proteins and the plasma membrane of the enamel producing cells, the ameloblasts. Such protein-protein interactions are hypothesized to influence the secretion of enamel proteins, establish short-term order of the forming matrix, and to mediate feedback signals to the transcriptional machinery of these cells. Membrane-bound proteins identified in ameloblasts, and which interact with the structural enamel proteins, include Cd63 (cluster of differentiation 63 antigen), annexin A2 (Anxa2), and lysosomal-associated glycoprotein 1 (Lamp1). These and related data help explain the molecular and cellular mechanisms responsible for the removal of the organic enamel matrix during the events of enamel mineralization, and how the enamel matrix influences its own fate through signaling initiated at the cell surface. The knowledge gained from enamel developmental studies may lead to better dental and nondental materials, or materials inspired by Nature. These data will be critical to scientists, engineers, and dentists in their pursuits to regenerate an entire tooth. For tooth regeneration to become a reality, the protein-protein interactions involving the key dental proteins must be identified and understood. The scope of this review is to discuss the current understanding of protein-protein interactions of the developing enamel matrix, and relate this knowledge to enamel biomineralization.

Developmentally regulated changes in phospholipid composition in murine molar tooth

In order to explore the possibility that phospholipids are differently expressed during the cascade of events leading to tooth formation, we decided to carry out simultaneous biochemical, histological and electron histochemical studies. High performance thin-layer chromatography and gas-liquid chromatography were used to compare the composition of embryonic mouse first molar tooth germs at day 18 of gestation (E18) and at birth (D1), erupting teeth at day 7 (D7) and erupted molars at day 21 (D21). For the latter, non-demineralized and EDTA-demineralized lipid extracts were analysed separately. Moreover, an ultrahistochemical study was carried out using the iodoplatinate reaction which retains and visualizes phospholipids. Developmentally regulated changes occurred and were closely correlated with an increase in cell membrane phospholipids. Gradual accumulation of phospholipids was identified in the extracellular matrix, at an early stage of tooth germ development within the basement membrane and later, as predentine/dentine and enamel components participating in mineralization processes. Matrix vesicles transiently present in dentine were partly responsible for the lipids that were detected. A first group of phospholipids including phosphatidylcholine as the major membrane-associated phospholipid and phosphatidylinositol as the intracellular second messenger increased by a factor of 2.3 between E18 and D21. This increase is probably associated with cell lengthening and was relatively modest compared with the higher increase detected for a second group of phospholipids, namely phosphatidylethanolamine (x4.8), phosphatidylserine (x 5.9) and sphingomyelin (x5.4). This second group of extracellular matrix-associated phospholipids constituted 68% of the demineralized lipid extract and, therefore, contributes to the mineralization of dental tissues.

A histopathological study of the effects of low-power laser irradiation on wound healing of exposed dental pulp tissues in dogs, with special reference to lectins and collagens

This study investigated the effects of low-power laser irradiation on exposed pulp tissue in dogs. Gallium-aluminium-arsenide diode laser (300 mW) irradiation was applied to the exposed surface of the pulp, and histopathological changes were observed at 1, 3, and 7 wk after the operation. In addition, the lectin (concanavalin A, Dolichos biflorus agglutinin, peanut agglutinin, Ricinus communis agglutinin I, soybean agglutinin, Ulex europeus agglutinin I, and wheat germ agglutinin) binding pattern and distribution of collagens (type I, III, and V) were examined to determine the histochemical and immunohistochemical nature of wound healing. The fibrous matrix formation and the continuing changes in the dentin bridge formation of the irradiation group were observed earlier (1 wk after the operation) than in the nonirradiation control group. Lectin histochemistry and collagen immunohistochemistry showed that concanavalin A, peanut agglutinin, wheat germ agglutinin, and collagens (types I, III, and V) were distributed in the fibrous matrix and dentin bridge. The expression of these lectins and collagens occurred earlier in the laser irradiation group than in the control group. These results suggest that laser irradiation accelerates wound healing of the pulp and the expression of the lectins and collagens. Furthermore, D-glucose-, D-mannose-, N-acetyl-D-galactosamine-, and N-acetyl-neuraminic acid-binding sugars and type I, III, and V collagens play an important role in the healing of pulp wounds.

Immunolocalization of CD44 and the ezrin-radixin-moesin (ERM) family in the stratum intermedium and papillary layer of the mouse enamel organ

We studied the immunohistochemical localization of CD44 and the ezrin-radixin-moesin (ERM) family of actin binding proteins in mouse enamel organ, using confocal laser scanning microscopy and transmission electron microscopy to clarify their role in cytoskeletal organization. At the differentiation stage of ameloblasts, immunoreactivity to CD44 was detected on the plasma membrane of the inner enamel epithelium, the stellate reticulum, the stratum intermedium, and the external enamel epithelium. In accordance with the differentiation of preameloblasts into secretory ameloblasts, immunoreactivity increased in the stratum intermedium cells. At the maturation stage, intense immunoreactivity was observed on the papillary layer cells. For the ERM family, the stratum intermedium and the papillary layer cells were stained with anti-ezrin and -radixin monoclonal antibodies but not with the anti-moesin antibody. Electron microscopic observations revealed that CD44, ezrin, and radixin were localized in the region at which preameloblasts came into contact with the stratum intermedium at the differentiation stage. At the secretory and maturation stages, they were concentrated in the microvilli of the stratum intermedium and the papillary layer cells. These findings suggest that the CD44-ezrin-radixin-actin filament system is involved in cell-cell interaction between preameloblasts and the stratum intermedium, and in the cytoskeletal organization of the cells in the stratum intermedium and the papillary layer.

Effect of growth hormone on the distribution of decorin and biglycan during odontogenesis in the rat incisor

Previous studies have shown that growth hormone can influence the expression of N-acetylgalactosamine-containing molecules in the extracellular matrix of developing rat incisors. N-acetylgalactosamine is a principal component of proteoglycans containing chondroitin sulfate and dermatan sulfate, as well as of some glycoproteins. Since chondroitin sulfate proteoglycans are identifiable components in enamel, dentin, and cementum, we have tested the hypothesis that growth hormone modulates their expression in developing rat incisors. The distribution of the chondroitin-sulfate-rich proteoglycans, decorin and biglycan, was investigated. We used the Lewis dwarf rat as a model because their circulating growth hormone levels are markedly reduced. Polyclonal antibodies against decorin and biglycan were used to localize these two proteoglycans. Semi-quantitative assessments of the staining patterns and intensities were made for each proteoglycan within compartments of the developing teeth. In normal Lewis rats, decorin and biglycan differentially expressed throughout the enamel organ, dental papilla, and dental follicle. Decorin displayed a wide distribution throughout all three regions and was closely associated with different cellular components. In contrast, biglycan showed little association with cells and was identified in the predentin and osteoid matrices. The expression of both proteoglycans was dramatically decreased in the growth-hormone-deficient animals. Administration of growth hormone to the dwarf rats markedly elevated the expression of both proteoglycans, approximating the distribution and intensity of staining seen in normal animals. These findings confirm that growth hormone status can modulate the expression of decorin and biglycan, and hence matrix deposition, in the rat tooth.

Growth hormone regulates an N-acetylgalactosamine component in odontogenesis: a specific lectin-binding study in the Lewis dwarf rat

Dental organs of incisors from normal, dwarf and growth hormone-treated dwarf rats were analysed histochemically using a panel of lectins. A distinctive pattern of differential staining was obtained with Helix pomatia agglutinin, a lectin specific for N-acetylgalactosamine. In Bouin's perfused and paraffin-embedded undecalcified tissues from normal rats, reaction product for N-acetylgalactosamine was visible in the odontogenic cells and some extracellular matrices. In the growth hormone-deficient dwarf rats, the N-acetylgalactosamine reaction was consistently minimal in the odontoblasts, predentin, cementoblasts, cementoid, osteoblasts and osteoid matrices, although the staining of ameloblasts and osteoclasts was similar to normal. Administration of growth hormone to dwarf rats for six days (66 micrograms/100 g rat b.i.d.) restored the reaction for N-acetylgalactosamine in the affected matrices. Thus, an N-acetylgalactosamine rich matric component is differentially expressed during odontogensis. Growth hormone may regulate this component in these matrices, which may be a proteoglycan or a glycoprotein, essential for normal growth of the teeth.

Immunofluorescent lectin binding patterns and glycoprotein co-localization in the developing murine molar tooth

Fluorescein-conjugated lectins were used in conjunction with antibodies to laminin, tenascin and amelogenin to investigate saccharide expression in the developing tooth germ. At the bud stage, peanut agglutinin (PNA) binding demonstrated residues that may be D-galactose-(beta 1----3)DGalNAc, and this staining occurred after the expression of tenascin. Only the cap-stage enamel organ suprabasal cells and the enamel knot stained intensely with Ulex europeus agglutinin-I, but not Lotus tetragonolobus agglutinin, implying the transient presence of blood group H type I oligosaccharides. At the late stages of amelogenesis, enamel synthesis is preceded by en bloc loss of inner enamel basement membrane components. Before this, Bandeiraea (Griffonia) simplicifolia--I (BSL-I) staining was lost from postmitotic ameloblasts, suggesting that a glycosylated species is initially removed. Additionally, PNA was co-localized with amelogenin protein, suggesting that it may express beta-D-galactosyl sequences. These results indicate that the glycosylation patterns of matrix components during odontogenesis may be important as they vary in a manner similar to that of the well-known glycoproteins.

Changes in glycoconjugates revealed by lectin staining in the developing airways of Syrian golden hamsters

Lectin binding was studied in the developing airways of Syrian golden hamsters on gestational days 11-16 (day 16 is the day of birth). The trachea and lungs were fixed in 4% formaldehyde-1% glutaraldehyde, 6% mercuric chloride-1% sodium acetate-0.1% glutaraldehyde, and 95% ethanol; embedded in paraffin; and stained with eight lectin-horseradish peroxidase conjugates: Triticum vulgare (WGA), Dolichos biflorus (DBA), Helix pomatia (HPA), Maclura pomifera (MPA), Griffonia simplicifolia I-B4 (GSA I-B4), Arachis hypogaea (PNA), Ulex europeus I (UEA I), and Limulus polyphemus (LPA). Each lectin yielded a characteristic staining pattern, which modulated throughout development. In general, changes in staining characteristics of the tracheal epithelium preceded similar changes in the lobar bronchus, bronchiole, and alveolus. In the case of UEA I, MPA, WGA, and HPA, staining increased with time uniformly over the luminal surface of all epithelial cells. However, in the case of PNA, GSA I-B4, and LPA, after the differentiation of ciliated and secretory cells, the apical surfaces of the ciliated cells stained more intensely than the apical surfaces of the secretory cells. Neuraminidase pretreatment enhanced PNA and GSA I-B4 staining in both cell types. In the case of PNA, these light microscopic observations were confirmed by ultrastructural study. Unlike the other lectins, the pattern of staining with DBA was unusual. Staining was moderate at first, then decreased (days 13 and 14), then increased at all airway levels. This study shows that different glycoconjugates modulate in airway epithelial cells throughout fetal development.

Influence of colchicine on the addition of a sugar to the enamel protein in secretory ameloblasts of cultured germs of rat molar tooth by 3H-galactose radioautography

The influence of colchicine on the addition of 3H-galactose to the enamel protein in secretory ameloblasts of cultured germs of rat molar tooth was investigated by light- and electron-microscopic radioautography. In tooth germs cultured without colchicine, the reaction products of 3H-galactose were observed over Golgi cisternae at early chase times and then localized over the enamel with time. In tooth germs cultured with colchicine, the silver grains were seen over the Golgi cisternae, condensing granules and accumulated secretory granules. Some grains also appeared with time over the pale granular material precipitated in the intercellular space with colchicine treatment. In quantitative analysis with light microscopic radioautography, values of silver grain counts over the unit area (100 microns2) on ameloblasts and enamel of colchicine-treated tooth germs were significantly lower at both 0 min and 30 min chase after 30 min pulse than those of control tooth germs, respectively. This finding indicates that colchicine diminished the incorporation of 3H-galactose into the secretory ameloblast of cultured tooth germs. It is suggested that colchicine decreases the activity of the Golgi apparatus with regard to the addition of sugar to the synthesizing glycoprotein in the secretory ameloblast.

Binding of Ricinus communis I lectin to developing dystrophic muscle in human fetus

In previous studies it was shown that a D-galactose-specific lectin, Ricinus communis I (RCA I), does not bind to the plasma membrane of muscle fibres from patients with Duchenne muscular dystrophy (DMD) in contrast to normal muscle. We have now studied RCA I binding to the membranes of developing human fetal muscle in fetuses at 95% risk of DMD (n = 6) and normal controls (n = 5) with a developmental range of 12-20 weeks of gestation. The results were compared to the membrane appearance with conventional ultrastructure. Binding of RCA I to the muscle basement membrane was consistently strong from the early stages of myogenesis, such as in fusing myoblasts/myocytes. RCA I binding to the plasma membrane was weak but detectable in both DMD and normal fetuses at 12-14 weeks of gestation. Both the normal and diseased condition showed an increase of RCA I labelling of the muscle plasma membrane at 15-17 weeks and strong labelling at 18-20 weeks of gestation. No difference was observed in the RCA I localization of normal and diseased human fetal muscle plasma membrane. It is concluded that (a) the plasma membrane in developing fetal muscle undergoes a maturation process between 12 and 20 weeks gestational age leading to an increase in expression of RCA I binding carbohydrate moieties; and (b) that the absence of RCA I binding glycoprotein in mature DMD muscle plasma membrane reflects a change acquired during the course of disease.

The carbohydrate moiety of mineral-bound proteins from fetal enamel: a basis for enamelins heterogeneity

Enamelins were prepared from the soft enamel of bovine fetuses. They were purified on synthetic hydroxyapatite and separated in two fractions by affinity chromatography on a ConA-ultrogel column. The two fractions were different with respect to their electrophoretic behavior, stainability, amino acid composition, phosphorylation, and glycosylation. The ConA-binding fraction, consisting of three molecular species with apparent molecular weights of 33, 37, and 45 kD, contained organic phosphorus and high levels of sugars. The Gal/Man ratio suggested a biantennary structure. The ConA-unbound fraction contained two major molecular species with molecular weights of 70 and 56 kD, and represented 70% of the total enamelin preparation. The amino acid composition of this fraction showed a higher level of alanine and a lower level of proline when compared with that of total enamelins. Its sugar composition was unusual, being principally constituted of N-acetyl galactosamine and N-acetyl glucosamine.

Light-microscopic studies on spatial and temporal binding of the lectins concanavalin A, wheat-germ agglutinin and peanut agglutinin in early rat odontogenesis

The spatial distribution and temporal expression of alpha-D-mannosyl(glucosyl)-, N-acetyl-D-glucosaminyl- and beta-D-galactosyl residues as detected by peroxidase-conjugated lectins correlated with early odontogenic events in six principal developmental stages (fetal days 13.5, 14, 15, 17, 18.5 and 19.5). The odontogenic epithelium of 13.5- and 14-day-old fetuses was characterized by strong concanavalin A (Con A) binding and between days 17 and 19.5, the stellate reticulum displayed strong peanut agglutinin (PNA) binding. Between 15 and 19.5, differentiation of dental ectomesenchyme was characterized by a rhythmic expression of terminal galactosyl residues shown by PNA-binding. At the developing dental basement membrane, there were various carbohydrate-specific regions. At days 13.5 and 14, the odontogenic basement membrane was specific for N-acetyl-D-glucosamines detected by wheat-germ agglutinin (WGA). The results suggest that the carbohydrates present at the inner dental basement membrane at days 17 to 19.5 may be involved in cell-matrix interactions during cytodifferentiation.

Distribution profiles of keratin proteins during rat amelogenesis

We examined rat cells undergoing amelogenesis for the presence of three types of keratin proteins using a polyclonal antibody to keratin (against total keratins (TK) with molecular masses ranging from 41 to 65 kilodaltons (kd) and monoclonal antibodies keratins to KL1 and PKK1 (reactive with keratins with molecular masses of 55-57 and 41-56 kd, respectively). In normal oral epithelia from young rats, the TK, KL1, and PKK1 antibodies bound to all of the epithelial strata. The epithelial cap on the top of incisors and the dental lamina of molar teeth exhibited strong TK staining, moderate staining KL1, and little or no PKK1 staining. In developing molar enamel organs, both the outer and inner enamel epithelia, the stratum intermedium, and stellate reticulum cells were all positively stained by the TK immunoreagent. In developing incisors, TK only bound strongly to stratum-intermedium cells, and no KL1 and PKK1 staining antibodies was observed in ameloblasts or the stratum intermedium.