Evidence for uptake of basement membrane by differentiating ameloblasts in the rat incisor enamel organ

Demonstration of type-IV collagen and acid phosphatase (ACPase) was carried out in the rat incisor enamel organ after the animals were fixed by perfusion with periodate-lysine-paraformaldehyde. Their incisors were dissected out, demineralized with EDTA, and prepared into 6-microns-thick frozen sections. The sections, which had been treated by means of antibody incubation for type-IV collagen, were washed with a Trismaleate buffer, incubated in Novikoff's medium for acid phosphatase (ACPase), and then incubated in a 3, 3'-diaminobenzidine solution. After osmification, the sections were embedded in epoxy resin for electron microscopy. The plasma membranes of the distal ends of the inner-enamel-epithelial cells were relatively even and were lined with a basement membrane. Type-IV collagen was localized both in the lamina densa and in the filaments attached to the lamina densa. In differentiating ameloblasts, the remarkably undulating distal plasma membranes formed irregular shallow and deep invaginations, and small cytoplasmic processes that penetrated the basement membrane. Coated pits occurred in various parts of these undulating plasma membranes. Positive reaction to type-IV collagen was observed in the invaginations and coated pits. ACPase-positive granules, present in inner-enamel-epithelial cells, increased in number and sometimes appeared close to both shallow and deep invaginations of differentiating ameloblasts. These results indicate that type-IV collagen in the basement membrane of the enamel organ is removed and degraded by differentiating ameloblasts by means of their engulfing system.

Immunohistochemical observations on bone morphogenetic protein in normal and abnormal conditions

Localization of bone morphogenetic protein (BMP) in human tissues and cells is important for investigating the mechanism of bone induction. A stable cell line secreting monoclonal antibody against bovine BMP (bBMP-McAb) was obtained by the hybridoma technique. The result of immunohistochemical staining (ABC method) showed that BMP is distributed along collagen fibers of normal bone, in periosteal cells, and in mesenchymal cells of marrow stroma. Little BMP can be found in bone cells of lamellar bone or in calcified bone matrix. BMP may be abundant in human tooth anlagen such as predentin, cells of the outer and inner enamel epithelium, and cells of dental sac generating bone. BMP is found in the cytoplasm of tumor cells of osteosarcoma and chondrosarcoma. Immunohistochemical staining showed that BMP plays a role in bone fracture healing. The ability of BMP-McAb to detect BMP and to inhibit the generation of new bone also makes it potentially useful in diagnosing, treating, and providing a prognosis for osteosarcoma and other bone diseases.

Human amelogenins: sequences of "TRAP" molecules

The extracellular protein matrix of developing enamel includes a major class of proteins, the amelogenins, which are believed to be concerned in regulating enamel biomineralization. Previous studies have shown the amelogenins of the extracellular matrix to be a complex of proline-rich hydrophobic proteins which, it is suggested, arise through posttranslational and postsecretory processing of a primary ameloblast gene product. More recently, it has been shown that the human amelogenin gene is located on both the X and Y chromosomes raising the possibility that polymorphism at the level of the gene may also contribute to the observed complexity of these enamel matrix proteins. To investigate such possible amelogenin polymorphism in developing human dental enamel, individual fractionated by size-exclusion and reversed-phase high pressure liquid chromatography (HPLC). Two tyrosine-rich amelogenin polypeptides (TRAPs) of approximately 5 kDa in size were isolated from an individual human dentition and characterized by automated gas-phase sequencing. These polypeptides were found to be of 42 (TRAP-2) and 44 (TRAP-1) amino acid residues in length; TRAP-2 lacked a carboxy-terminal -Gly-Trp sequence as has previously been described for analogous bovine TRAP molecules. However, residue #25 of the human TRAP-2 sequence was refractory to sequencing, apparently differing from the Trp-25 identified in TRAP-1. These findings suggest (1) two forms of TRAP molecules, differing only by cleavage of a carboxy-terminal dipeptide, are a general feature of human and other mammalian enamel proteins, probably being derived by postsecretory cleavage from the primary extracellular amelogenin; and (2) in human developing enamel four forms of TRAPs may arise either from polymorphism at the level of the gene, or by posttranscriptional alternative splicing of amelogenin mRNAs, coupled with specific post-secretory proteolytic processing.

Phylogenetic distribution of enamel proteins: immunohistochemical localization with monoclonal antibodies indicates the evolutionary appearance of enamelins prior to amelogenins

The hard covering tissues, enamel or enameloid, of representative vertebrate teeth were immunohistochemically stained using specific monoclonal antibodies against bovine amelogenins and bovine enamelins in order to determine the phylogenetic distribution of enamelin and amelogenin proteins. Immunohistochemically, only enamelin proteins were present in lower vertebrate (shark, bony fish, and larval amphibian) teeth and dermal denticles. Both enamelin and amelogenin proteins were present in higher vertebrate (mammal, reptile, and adult amphibian) teeth. Large hydroxyapatite crystal size and high levels of mineralization, characteristics common to both enamel and enameloid, are probably due to the presence of the common protein enamelin. The evolution of enamel from enameloid in the tetrapods seems to have involved the development of the gene for amelogenin.

Bovine tooth-derived bone morphogenetic protein

Eight groups of dental tissues were mechanically dissected from the mandibles of one-year-old steers; they were then defatted and decalcified in HCl. The noncollagenous proteins were extracted with various solvents from collections of tissue and bio-assayed for osteo-inductive activity. Collectively, the hard tissue (dentin, enamel, and cementum) noncollagenous proteins were fractionated by molecular sieve chromatography, hydroxyapatite affinity chromatography, and ion exchange chromatography. Osteo-inductive activity of each protein fraction was determined by implantation in the quadriceps muscle pouch of mice. The quantity of bone was measured by computerized image analysis. From 71% to 83% of 41 implants of dental hard tissues induced bone formation. The quantity of bone was greater from unerupted than from erupted teeth. Dental soft tissues that had no osteo-inductive activity were rich in a 14-kDa protein, presumably matrix gamma-carboxyglutamic acid-rich proteins. Proteins with Mr of from 15 to 28 kDa were associated with osteo-inductive activity. Components with Mr greater than 28 kDa had no activity. These observations suggest that bovine teeth have a selection of osteo-inductive proteins that is comparable in range of MW to bovine bone morphogenetic protein.

Calmodulin immunocytochemistry in rat incisor enamel organ through its life cycle

The enamel organ of the growing rat incisor was perfusion-fixed with a mixture of formaldehyde and glutaraldehyde and processed for indirect immunogold labeling of calmodulin on post-embedded ultrathin sections. Throughout the zones of presecretion, secretion, and maturation of enamel, specific protein A-immunogold labeling was localized on polyribosomes and those attached to endoplasmic reticulum, mitochondria, nuclear chromatin, phagolysosomes, and cytoplasm adjacent to the plasma membrane, and tonofilaments associated with desmosomes of ameloblasts and cells of outer layer of enamel organ. Golgi membranes, condensing vacuoles, secretion granules, primary lysosomes, and micropinocytotic coated vesicles were hardly labeled. In the presecretion zone, the basal lamina of the preameloblasts and the matrix vesicles and collagen fibrils of the predentin matrix were not immunoreactive. Tomes' process of secretory ameloblast and adjacent enamel crystals were labeled. In addition to the above immunoreactive structures, some phagolysosomes, ferritin granules, and the cytoplasm of the ruffled border zone of maturation ameloblast contained immunogold particles. In control sections incubated with either protein A-gold complex alone, or antiserum preabsorbed with an excess of calmodulin and protein A-gold complex, only a few gold particles were observed to be randomly associated with the tissues. These results indicate that calmodulin is present in the cells of the enamel organ through all stages of amelogenesis. Its wide distribution is consistent with its involvement in various cytoplasmic functions.

Distribution of intermediate-filament proteins in the human enamel organ: unusually complex pattern of coexpression of cytokeratin polypeptides and vimentin

We applied immunohistochemical techniques and gel electrophoresis to examine the distribution of intermediate filaments in human fetal oral epithelium and the epithelia of the human enamel organ. Both methods demonstrated that human enamel epithelia contain cytokeratins 5, 14, and 17, which are typical of the basal cells of stratified epithelia, as well as smaller quantities of cytokeratins 7, 8, 19, and in trace amounts 18, which are characteristic components of simple epithelial cells. In the external enamel epithelium and stellate-reticulum cells, most of these components appeared to be simultaneously expressed. In contrast, the parental oral epithelium was negative for cytokeratin 7, thus indicating possible "neoexpression" during the course of tooth formation. Immunohistochemical procedures using various monoclonal antibodies against vimentin revealed the transient coexpression of vimentin and cytokeratins in the external enamel epithelium and in stellate-reticulum cells during enamel development. The significance of the coexpression of cytokeratins and vimentin is discussed in relation to previous findings obtained in other normal tissues and in the light of the functional processes characteristic of these epithelia.

Patterns of expression of intermediate filaments in ameloblastoma and human fetal tooth germ

Monoclonal antibodies (Mab) were used to study the expression of cytokeratins and vimentin in various histological types of ameloblastoma and in human fetal tooth germ. The ameloblastoma and the tooth germ epithelia showed characteristics of both simple glandular and stratified squamous epithelial cells. Cytokeratin No. 18 was detected focally in most ameloblastomas studied but not in fetal odontogenic epithelia. Cytokeratins Nos. 8 and 19 were expressed in all epithelial elements of ameloblastomas and tooth germs. Only two tumors showed focally characteristics of keratinizing epithelia also seen in dental lamina but not in the enamel organ. All tumors except the granular cell ameloblastoma showed a variable coexpression of vimentin and cytokeratins in their neoplastic epithelia. A similar coexpression was detected in the stellate reticulum cells of the developing tooth. Ameloblastoma and human tooth germ epithelia share complex pattern of cytokeratin polypeptides together with coexpression of vimentin. The results strongly support the theory that ameloblastomas are of odontogenic origin and not direct derivatives of basal cells of oral epithelium or epidermis.

Micro-PIGE determination of fluorine distribution in developing hamster tooth germs

A micro-PIGE (Proton-Induced gamma-ray Emission) technique based on the delayed 5/2+----1/2+ nuclear transition of fluorine (E gamma = 197 keV, t1/2 = 87 ns) emitted after 19F(p,p', gamma)19F reaction was used to detect and study the distribution of fluorine in the developing enamel organ during pre-eruptive stages, i.e., the transitional to early maturation stages of enamel formation in neonatal hamsters administered a single IP dose of sodium fluoride (20 mg NaF/kg body weight). The aforementioned nuclear reaction is unique for fluorine, and therefore detection of gamma-rays emanating from this reaction in a biological specimen implies a positive identification of fluorine at that particular site. Calcium and phosphorus X-rays were also recorded and used as parameters for assessment of the relationship between the degree of mineralization and fluoride incorporation into the enamel organ. The highest fluorine concentration in the enamel organ was recorded in the dentin near the dentin-enamel junction (DEJ). In the enamel, the highest concentration of fluorine was found to be associated with the more mature areas of the enamel near the DEJ, but gradually decreased in the direction of the enamel surface. Fluorine was not detected in the control germs. These results suggest that administration of fluoride in high doses during the pre-eruptive stages of enamel formation leads to incorporation of the ion into the forming dentin and enamel mineral, and that the enamel matrix does not seem to bind fluoride avidly.

Cytokeratin expression of the odontogenic epithelia in dental follicles and developmental cysts

The patterns of cytokeratin expression in the epithelium of 5 dental follicles, 7 dentigerous cysts, 5 odontogenic keratocysts, 3 nasopalatine cysts and an epidermoid cyst have been studies using a panel of monoclonal antibodies. The epithelium of dental follicles and of developmental odontogenic cysts strongly expressed keratins 5 and 19 and showed weaker expression of keratins typical of stratified non-cornified and of simple epithelia. Staining with mAbs against the latter keratins varied with the degree of epithelial differentiation. Nasopalatine cysts strongly expressed simple epithelial keratins and the epidermoid cyst strongly expressed a marker of cornification. Odontogenic cysts thus appear to differ in their pattern of keratin expression from other oral developmental cysts and all derivatives of odontogenic epithelia appear to share similar basic patterns of cytokeratin expression.

Localization of lead and fluoride in cultured tooth germs by laser microprobe mass analysis

Trace elements can influence dental health, possibly by altering tooth resistance during preeruptive development. Therefore, it was investigated whether lead and fluoride would be incorporated into the calcifying matrices or the cellular parts of tooth germs in vitro. Using laser microprobe mass analysis, the localization of lead and fluoride was studied in the different layers or tooth germs that had been cultured in a medium to which PbCl2 of NaF had been added in different concentrations. Both elements could only be detected in the dentine layer. Hence, the enamel organ in the secretory stage of tooth development excludes lead and fluoride from the enamel, even when enamel formation by the ameloblasts is visibly disturbed. Furthermore, there seemed to be a process of saturation in the accumulation of lead and fluoride in the dentine.

Histochemical localization of calcium in the enamel organ of rat incisors in early-stage amelogenesis

The localization of calcium in the enamel organ of rapidly-frozen, freeze-substituted rat incisors in early-stage amelogenesis was examined by a histochemical calcium-staining method. In secretory ameloblasts, glyoxal bis(2-hydroxyanil) (GBHA) staining revealed intense red reactions in mitochondria and tubulovesicular structures located throughout the cytoplasm, while no reaction was seen in the nucleus and cytosol, nor along the plasma membranes of the respective cells. No significant GBHA reaction was observed in the intercellular compartment and other cells of the enamel organ. Some granular reactions were localized in the cells of the adjacent connective tissue. Control tests confirmed the specificity of GBHA reactions for calcium. Thus, the present observations provide histochemical evidence indicating an exclusive localization of calcium in mitochondria and tubulovesicular structures of the secretory ameloblast, and support their contributions to the translocation of calcium from the proximal to the distal pole of the cytoplasm.

Ultrastructural localization of dentine phosphoprotein in rat tooth germs by immunogold staining

Dentine phosphoprotein (DPP) was localized on thin frozen sections of fixed rat tooth germs by indirect immunogold staining. Antisera were directed against DPP and against glutaraldehyde-treated DPP and were characterized by immuno-electroblotting. In odontoblasts, DPP was found to be localized in the cisternae of the rough endoplasmic reticulum (RER) and the Golgi apparatus and in Golgi-associated vesicles. Odontoblastic processes were moderately positive for DPP and dentine was intensely labeled on frozen sections of unfixed tissue. Predentine showed a slight immunoreactivity. These results indicate the synthesis of DPP in the RER, its accumulation in the Golgi apparatus and its vesicular transport and secretion via the odontoblastic processes into dentine. The close association of the gold particles with the dentinal collagen fibres makes a role of DPP in linking mineral to collagen conceivable. Matrix vesicles were negative for DPP, suggesting that the protein is not present at the sites of matrix vesicle-associated nucleation.

A histochemical demonstration of calcium in the maturation stage enamel organ of rat incisors

The location of calcium in a rapid-frozen and freeze-substituted maturation stage enamel organ of the rat incisors was demonstrated by means of the glyoxal bis(2-hydroxyanil) (GBHA) staining method, which formed insoluble red precipitates of calcium-GBHA complex. In the ameloblast layer, highly GBHA-reactive tubulo-vesicular structures corresponding to mitochondria and some other membrane-bound structures were localized in both ruffle-ended and smooth-ended ameloblasts, although no significant GBHA reaction was localized in the nucleus, Golgi region, nor along the plasma membrane of these cells. In addition, numerous granular GBHA reactions appeared exclusively in association with the ruffled border of ruffle-ended ameloblasts. GBHA reactions were positive, but were considerably weaker in papillary cells than in the ameloblast. These observations provide a first published histochemical mapping of calcium in the maturation stage enamel organ, and suggest the active participation of mitochondria in maturation stage ameloblasts in calcium regulation.

Aspiration and characterization of predentin fluid in developing rat teeth by means of a micropuncture and micro-analytical technique

A fluid phase was aspirated in vivo and in vitro from predentin or pulp of developing rat teeth by means of a micropuncture technique. Pooled aspirates (approx. 2 nL) were analyzed for P, Na, K, Ca, Mg, and S by electron probe microtechniques (Lechene and Warner, 1979). Compared with pulp fluid, currently and previously studied cartilage fluids, as well as serum, predentin fluid showed elevated K, depressed Na, Cl, and Ca, as well as increased P. Statistical analysis was possible for only a few groups of comparisons among the elemental profiles. Ultrastructural examination of the aspiration site and of the aspirates showed no evidence of contamination with cell organelles or other formed elements. The micropuncture technique used was a critically precise and laborious procedure; possible contamination with intracellular fluid could not be avoided. The consistently low Mg concentration found in the aspirates, however, supports our view that the samples were primarily extracellular.

Ultrastructural localization of osteocalcin in rat tooth germs by immunogold staining

Osteocalcin was localized by indirect immunogold staining of thin frozen sections of rat tooth germs which had been fixed by different methods. Acrolein fixation proved to be satisfactory considering the preservation of fine structure and antigenicity. In odontoblasts, osteocalcin was found to be localized in the cisternae of the rough endoplasmic reticulum and Golgi apparatus. Few positive transport vesicles were found. Staining for osteocalcin in odontoblastic processes was only observed after strong fixation and was intense in odontoblasts engaged in early dentine formation. Predentine was slightly positive in the neighbourhood of positive processes. Matrix vesicles were negative and strong osteocalcin labeling of dentine seemed to appear after the onset of mineralization.

Proteins in the enamel fluid of immature porcine teeth

The fluid was separated from the immature soft enamel of porcine permanent teeth in the secretory stage according to procedures reported previously (Aoba and Moreno, 1987). The protein content of the fluid was about 2.8% w/v; its amino-acid composition was characterized by high contents of Pro, Glx, Leu, and His, showing composition similar to that of the 20 kilo-dalton (kd) amelogenin or its C-terminal segments. The two major protein species in the fluid had apparent molecular weights of 13 kd and 11 kd, as determined by SDS electrophoresis; the N-terminal residue of the former was Leu, while that of the latter was Ala. The C-terminal sequence of both of them was -Met-Phe-Ser. By comparison with the published sequence of 20-kd porcine amelogenin, it is concluded that the main fluid constituents were derived by cleavages of N-terminal segments from the 20-kd amelogenin.

A characterization of amelogenin messenger RNA in the bovine tooth germ

In order to study the nature of amelogenin mRNA, we isolated ameloblast-rich tissue from the unerupted permanent incisor tooth germs of 18-month-old steers and subjected it to guanidine HC1 solubilization for extraction of mRNA. When poly A+ ameloblast RNA was incubated with radioactive deoxynucleotides and reverse transcriptase, four major transcripts were detected with sizes of 1.9, 1.4, 0.7, and 0.4 kb in length. One of the transcripts (0.7 kb) corresponded precisely in length to that predicted from the size of the major in vitro translated amelogenin proteins (27,000 daltons). To determine whether the transcripts did indeed encode amelogenin mRNA, we constructed a λgt11 cDNA library and isolated several amelogenin cDNA's by screening with amelogenin antibody. Four clones were amplified and insert sizes determined by acrylamide gel electrophoresis. Two of the clones had insert sizes of ~ 0.7 kb (λAm 16, XAm 7), and two had insert sizes of ~ 0.4 kb (λAm 11, λAm 4). When the amelogenin cDNA was radiolabeled and used for northern analysis, two species of amelogenin message (0.75 and 0.45 kb) were evident, both of which showed extensive hybridization to λAm 16 (large) and λAm 11 (small) cDNA. These data indicate that: (1) Amelogenin mRNA is heterogeneous in the bovine tooth germ, having two major species 800 and 400 bases long; and (2) the major species of amelogenin share extensive sequence homology. Based on these data, we suggest that at least part of the heterogeneity of amelogenin matrix protein may arise from the production of heterogeneous amelogenin mRNA's that share some common nucleotide sequences.

Immunocytochemical localization of osteocalcin in developing rat teeth

Osteocalcin was purified by gel chromatography from a crude extract obtained after decalcification of rat incisors. The apparent molecular weight, as determined by 5-15% SDS-polyacrylamide gel electrophoresis, was 18,000, and amino acid analysis revealed 60 gamma-carboxyglutamic acid residues per 1000. Antisera against osteocalcin, raised in rabbits, reacted specifically with osteocalcin when investigated by immuno-electroblotting of dentin crude extract. 4-micron cryosections of formaldehyde-fixed tooth germs showed positive immunocytochemical staining for osteocalcin in dentin and odontoblasts. The staining of the mantle dentin at the coronal sides of the tooth germs was more intense than that of the adjacent circumpulpal dentin, while the odontoblasts involved in the formation of mantle dentin showed stronger immunoreactivity than did odontoblasts involved in circumpulpal dentin formation. This marked difference was not observed on the root sides of the tooth germs. In 1-micron cryosections, osteocalcin immunoreactivity was found evenly distributed throughout the entire cell body, with the exception of the Golgi region, which was less intensely stained, while the nucleus and the cell process were negative. The positive staining reaction with anti-osteocalcin antiserum was found in dentin from the very onset of its formation in the fetus. In conclusion, our results demonstrate the presence of osteocalcin in odontoblasts and dentin. Its immunocytochemical localization may be compatible with a distinct role in early dentinogenesis.

Immunofluorescence localization of type I and type III collagen and fibronectin in mouse dental tissues in late development and during molar eruption

Affinity-purified antibodies produced intense staining for type I collagen in alveolar bone matrix and predentine, and moderate staining in the dentine matrix, lamina propria, connective tissue invaginating into papillary layer of the enamel organ, dental sac and periodontal ligament. No staining occurred in oral epithelium, stellate reticulum, stratum intermedium, ameloblasts and odontoblasts. Fibronectin was distributed similarly except at the interface between the epithelial diaphragm and pre-odontoblasts where type I collagen was absent but fibronectin was present. In contrast, type III collagen showed strong staining in the periodontal ligament and lamina propria but no staining in bone matrix, predentine, dentine and at the interface between the epithelial diaphragm and pre-odontoblasts. The staining pattern for type III collagen was similar to that of type I and fibronectin in other tissues including endosteal reticular tissue, the connective tissue invaginating into papillary layer and the extracellular matrix of the pulp.

Monoclonal antibody and immunogold cytochemical localization of amelogenins in bovine secretory amelogenesis

Amelogenin enamel-protein epitopes in developing incisors were ultrastructurally localized with high specificity resolution. They formed clumps scattered over the enamel organic matrix between the hydroxyapatite crystals, and were also present over islands of stippled or granular material at the forming surface of the enamel matrix demonstrating that this material consists in part of amelogenin enamel protein. The amounts of amelogenin, as judged by labelling density, were not greater in the stippled or the surface crystal-containing matrix as compared to the enamel matrix up to 50 micron deep. Amelogenins were also localized in the rough endoplasmic reticulum. Golgi apparatus and secretory granules of the ameloblasts, which suggests they are merocrine secretions.

Immunochemical and biochemical studies of human enamel proteins during neonatal development

The present communication provides descriptions of the developmental, biochemical, and immunological properties of the human enamel extracellular matrix proteins. We report the isolation and partial characterization of the major human enamel proteins, the production of polyclonal antibodies directed against the human enamelins, and a comparison between the immunogenicity of enamelins and amelogenins from human and mouse enamel extracellular matrices. Our results indicate that although enamelins and amelogenins share some epitopes, each one of these proteins appears to invoke a different degree of immunogenicity.

mRNA characterization of human fetal enamel matrix

Preliminary characterization of the human enamel matrix at 16-18 weeks in utero was performed. Using an homogenizing buffer, the proteins were extracted and analysed by gel electrophoresis. Total cellular RNA was isolated and the cell-free mRNA translated. The major component was a 68,000 protein with an enamelin-like amino-acid composition. Other translation products included a 55,000 polypeptide and lower mol. wt components of 26,000, 22,000 and 20,000 size of amelogenin size. It is suggested that high mol. wt component in the enamelin range is the most prevalent at the early stage of human tooth development.

Effects of fluoride on protein secretion and removal during enamel development in the rat

Enamel maturation consists of a loss of the early secreted matrix proteins and an increase in mineralization. This study investigated the changes in enamel proteins of the rat incisor, caused by the ingestion of fluoride at various stages of enamel formation. Rats were given 0, 10, 25, 50, or 100 ppm fluoride in drinking water for five weeks. Changes in the protein composition of the secretory, early-maturation, and late-maturation enamel were investigated by means of gel filtration chromatography and polyacrylamide gel electrophoresis. No differences were found between fluorosed and control enamel proteins in secretory enamel. In fluorosed early-maturation enamel, amelogenins were retained in larger quantities than in control enamel in animals ingesting 25 ppm fluoride or greater. At the late-maturation stage of enamel formation, only enamel from animals ingesting 100 ppm fluoride in drinking water contained more protein, when compared with control enamel. This study suggests that fluoride ingestion levels resulting in enamel fluorosis inhibit the mechanisms involved in the removal of proteins during enamel maturation.

Correlated observations and analysis of maturation-ameloblast morphology and enamel mineralization

A combined HCl-collagenase digestion technique and scanning electron microscopy were used to isolate the enamel organ and to confirm the presence of maturation ameloblasts of both ruffle-ended (RA) and smooth-ended (SA) types on maturing enamel in kitten permanent tooth germs. EDTA perfusion of animals fixed with aldehyde produced two or three belt-like shallow grooves (from 30 to 100 micron wide) running horizontally through the maturing enamel surface, coinciding closely with the SA distribution pattern. In animals that had been perfusion-fixed with unbuffered osmium tetroxide containing 2.5% potassium pyroantimonate, SEM-EDX analysis detected K in a superficial enamel layer overlaid by the SA layer. Potassium concentration decreased gradually toward the deeper layers. Very little K penetrated the enamel under the RA layer. Energy-dispersive x-ray analysis of Ca and P concentrations in the enamel revealed an even distribution of these elements throughout the superficial layer of maturing enamel. These results suggest that the SA layer forms an access route for K and EDTA and that, in spite of the obvious morphological and functional differences between RA and SA, the maturing enamel surfaces overlaid by these two cell types show similar degrees of mineralization.

The relationship between the keratocyst antigen (KCA) and keratin

The relationship of the keratocyst antigen (KCA), the soluble component present in most keratocyst fluids, and keratin, was studied with immunofluorescence microscopy comparing their distribution in developing mouse embryonic teeth and in human ameloblastomas. In these tissues both molecules showed a strong codistribution in epithelial cells. In the embryonic teeth both molecules were present in the stratum intermedium cells between the stellate reticulum cells and ameloblasts, but the secretory ends of the ameloblasts showed fluorescent staining only for keratin. The relationship was further investigated by comparing the physicochemical characteristics of KCA and keratin. Results on immunoblotting and two-dimensional gel electrophoresis showed that KCA existed in keratocyst fluid as a 60-68,000 dalton polypeptide with an isoelectric point of pI 6.8. Immunoblotting analysis of various isolated keratins revealed a typical polypeptide pattern of each keratin when anti-KCA antiserum was used for staining. These findings suggest that KCA and keratin are related molecules and that KCA may be a soluble component of keratin.

Effects of different extraction media on the electrophoretic pattern of proteins from partly mineralized bovine enamel

Five different extraction solutions were used to isolate matrix proteins from immature bovine enamel, to evaluate the effect of this procedure on the pattern obtained after electrophoresis. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the dominating protein fraction in the ethylenediaminetetraacetic acid extract had a molecular weight of 67,000 daltons. The acetic acid and phosphate buffer extracts contained mostly low molecular weight proteins. Isoelectric focusing showed that most of the enamel proteins had isoelectric points below pH 7.0.

Immunohistochemical studies with a monoclonal antibody on the distribution of phosphophoryn in predentin and dentin

A monoclonal antibody was raised against phosphophoryn, a unique noncollagenous phosphoprotein in dentin. Mouse myeloma NS-I cells were fused with spleen cells obtained from BALB/c mice immunized with phosphophoryn from fetal calf tooth germs. Mice inoculated with the hybridoma produced ascites fluid containing the antibody and this reacted only with a band of phosphophoryn transblotted from polyacrylamide gel. Immunohistochemical studies with the antibody showed that phosphophoryn was present in odontoblasts, odontoblastic processes and dentin, but not in the matrix of predentin, and that the phosphophoryn content of the dentin layer was high at and around the predentin-dentin junction and gradually decreased toward the enamel layer. The area corresponding to mantle dentin was not stained with the antibody.

Localization of calcium in differentiating odontoblasts and ameloblasts before and during early dentinogenesis and amelogenesis in hamster tooth germs

Potassium pyroantimonate-osmium tetroxide cytochemistry has been used to study the distribution of ionic calcium in hamster tooth germs during cell differentiation and during early dentinogenesis and amelogenesis. Before the onset of mineralization, pyroantimonate (PA) reaction product was found in the nucleus of differentiating preameloblasts and preodontoblasts. In the predentin, it was preferentially located along striated collagen fibrils, lying perpendicular to the basal lamina. At the onset of mineralization, a pronounced increase of PA reaction product was evident in the predentin and on the plasma membrane and in mitochondria of both preodontoblasts and preameloblasts opposite the mineralizing mantle dentin. During early enamel mineralization, PA reaction product was present in the "growing" crystal ends, while in the secretory ameloblasts, most of the PA reaction product was localized on the cytoplasmic side of the apical plasma membranes and in mitochondria. When Tomes' processes developed, PA reaction product, both cytoplasmic and membrane bound, was low or absent deep in the processes, but gradually increased toward the apical terminal web. A corresponding gradient of PA reaction product was observed on the opposing enamel crystallites. From this study we conclude that both preodontoblasts and preameloblasts seem to be involved in calcium acquisition necessary for the early stages of mantle dentin mineralization. Tomes' processes seem to regulate the entry of calcium into the enamel mineralization front.

Ampicillin concentrations in human serum, gingiva, mandibular bone, dental follicle, and dental pulp following a single oral dose of talampicillin

Eighty-one patients who underwent the extraction of impacted mandibular third molars in the nonfasting state were given a single oral dose of talampicillin (500 mg) preoperatively. Specimens of venous blood (n = 132), gingiva (n = 70), mandibular bone (n = 78), dental follicle (n = 63), and dental pulp (n = 59) were obtained during the operation and assayed for ampicillin content. The mean peak concentrations in serum (9.64 micrograms/ml), gingiva (4.72 micrograms/mg), mandibular bone (1.77 micrograms/ml), dental follicle (3.46 micrograms/ml), and dental pulp (5.53 micrograms/mg) all occurred at approximately 150 minutes after administration of talampicillin. The ratios of the corresponding serum concentration to the peak concentrations in the various oral tissues when both were plotted as drug concentration curves were: gingiva, 0.50; mandibular bone, 0.16; dental follicle, 0.34; and dental pulp, 0.52. Talampicillin was absorbed well by the intestine, and sufficient concentrations of the resulting metabolite, ampicillin, were found in oral tissues.

Ultrastructural distribution of acidic glycosaminoglycans associated with matrix vesicle-mediated calcification in mouse progenitor predentine

The ultrastructural localization of acidic glycosaminoglycans, presumed to be proteoglycans, was examined during initial matrix vesicle-mediated calcification in dentine, by using ruthenium red (RR) staining, high iron diamine thiocarbohydrazide silver proteinate (HID-TCH-SP) staining, and an enzymatic digestion method. Progenitor predentine 2-10 micron width of developing mouse molar tooth germs was used throughout the present study. The outer surface membrane of the intact matrix vesicles had a strong affinity for RR. The RR positive materials appeared beaded and extended perpendicularly from the vesicle membrane. They tended to disappear with the disruption of the vesicular membrane, which resulted from overextension due to needle-like, crystal-like structures. The HID-TCH-SP stain deposits, approximately 10 nm in diameter, were densely distributed around the intact matrix vesicles, though few were found inside them. Some matrix vesicles that were presumably disrupted, however, contained smaller stain deposits. On the outer surface membrane of the disrupted vesicles, HID-TCH-SP stain deposits were fewer in number. The results obtained from enzymatic degradation studies showed that the anionic materials on the outer surface membrane of the matrix vesicles were represented by chondroitin-4-sulfate and/or chondroitin-6-sulfate. We suggest that chondroitin sulfates attached to the outer leaflet of the vesicular membrane play an important role during the incipient stage of the matrix vesicle-mediated calcification process.

Effects of maternal caffeine intake on the growth of rat tooth germs in protein-energy malnourished neonates

Fourteen rat dams with 8 pups each were fed either a 6, 12 or 20 per cent protein diet upon birth. Another group of 12 dams with the same number of pups was pair-fed either a 6, 12 or 20 per cent protein diet supplemented with caffeine (2 mg/100 g body weight). At day 15, randomly-selected pups were injected with [14C]-proline to determine collagen synthesis of the incisor and molar tooth germs. Another group of pups was used to determine calcium content of these tooth germs. Body weight, incisor weight and total calcium contents of tooth germs of pups from dams fed with 6 per cent protein diet were greater in the caffeine-supplemented group, whereas in the 20 per cent protein diet with caffeine group, these parameters were lower. The molar weights of the 12 per cent protein diet with caffeine animals were greater than the 12 per cent group without caffeine. The total hydroxyproline content of the incisor tooth germs from animals in the 12 per cent protein diet with caffeine was greater than is the non-caffeine group. However, total hydroxyproline of the molar tooth germs in the 20 per cent protein groups with caffeine was less than in the non-caffeine group. The rate of collagen synthesis of the incisor and molar tooth germs showed no difference in the presence or absence of caffeine in the 6, 12 and 20 per cent protein groups. Incisor and molar tooth germs are thus affected differently by the interaction of protein and caffeine, possibly due to differences in the pattern of tooth development.

An investigation of S-100 protein in embryonic dental papillae of rats

We attempted to identify S-100 protein, a marker of neural crest tissue, within cells of the developing dental papillae of 18-day rat fetuses by means of the immunoperoxidase technique. Although there is experimental evidence that dental papillae are derived from neural crest, no marker protein was identified in this study.

Glycosaminoglycans in embryonic mouse tooth germs. A histochemical analysis

Glycosaminoglycans (GAG) were localized in embryonic mouse molars by Alcian-blue staining in a critical-electrolyte-concentration (CEC) method (Scott and Dorling, 1965). Sulfated GAG were distinguished from hyaluronate (HA) by combining the binding specificity of Alcian blue and substrate specificity of GAG-lytic enzymes. The stratum reticulum was found to contain a small amount of HA, but no chondroitin sulfate (CS). The amount of HA decreased gradually during odontogenesis. No GAG were detected in the outer and inner dental epithelia. The basement membrane and the predentine were intensely stained, and shown to be rich in HA and CS. The preodontoblastic layer contained small amounts of HA and CS. These decreased progressively during odontogenesis. No GAG was found at the odontoblastic layer. The lower dental papilla contained a constant amount of HA (the major component) and CS.

Glycosaminoglycans in embryonic mouse teeth and the dissociated dental constituents

The nature, amounts and distribution of glycosaminoglycans (GAG) before and during odontoblast terminal differentiation were studied. GAG have been isolated from intact mouse tooth germs and from dissociated dental epithelia and dental papillae after labeling with [3H]glucosamine or 35SO2-(4) asd precursor. The kinds and relative amounts of 3H-labeled GAG were analyzed by chromatography on a DEAE-cellulose column and cellulose thin-layer sheets. The amounts of individual GAG relative to total GAG were determined from the elution profiles, whereas their nature was identified by the selective removal of chromatographic peaks after enzymatic or chemical degradation. We found hyaluronate and probably a minute quantity of heparan sulfate in the dental epithelium, while hyaluronate, heparan sulfate, and chondroitin sulfate were the main types of GAG in the dental papilla. The chondroitin sulfate recovered was further fractionated by cellulose thin-layer chromatography into two isomers, namely chondroitin-2-sulfate (the major component) and chondroitin-6-sulfate. Changes in the elution profile from DEAE-cellulose chromatography of tooth GAG extracted from different developmental stages suggest that modifications of GAG occur during odontogenesis. Alcian blue staining localized large amounts of hyaluronate and sulfated GAG along the epithelio-mesenchymal junction. Tissue specificity and changing patterns of GAG were demonstrated during odontogenesis.

Acid-soluble bovine fetal enamelins

High molecular weight enamelin proteins were recovered from conventional acetic acid extracts of fetal bovine enamel and were analyzed by gel filtration and ion-exchange chromatography. This procedure is simple and straightforward, and recovers approximately half of the total tissue enamelin content.

Calmodulin-like activity in a mineralising tissue: the rat molar tooth germ

Calmodulin, a calcium binding protein, has been implicated in the regulation of many calcium-dependent biological processes. Since calcium has an important role in hard tissue genesis, both at intra- and extracellular levels, we anticipate that calcium binding proteins may modulate this process. The present study investigated a mineralising tissue, the rat molar tooth germ, to determine the presence of calmodulin-like activity. A heat-treated cell-free extract of tooth germs provided enhancement of Ca2+-dependent Mg2+-ATPase and 3':5'-nucleotide phosphodiesterase activity. No enhancement occurred in the absence of calcium or in the presence of trifluoperazine. SDS-polyacrylamide gel electrophoresis of this extract revealed a protein band of approximately 18,000 mol. wt. These findings indicate the presence of calmodulin-like activity in rat molar tooth germs and support the proposal that calcium and calcium binding proteins, in particular calmodulin, have a major regulatory role in the biology of mineralising tissues.

Proteolytic enzyme in porcine immature enamel

A proteolytic enzyme cleaving the main component of enamel proteins obtained from immature enamel has been purified from a soluble extract of porcine immature enamel. It is optimally active around pH 6 against enamel protein. It is completely inhibited by phenylmethylsulfonyl fluoride and diisopropyl phosphofluoridate, and partially by benzamidine. EDTA does not affect its activity. The enzyme seems to sever initially its activity. The enzyme seems to sever initially enamel protein into two segments, one containing lysine, arginine and tyrosine and the other being free from these amino acids.

Mobility of concanavalin A receptors and distribution of cytoplasmic actin in odontogenic epithelial and mesenchymal cells

The distribution of concanavalin A (Con A) surface receptors and cytoplasmic actin in the same cell was studied in monolayer cultures of 2 odontogenic epithelial cells of different developmental age and in ecto-mesenchymal cells derived from the same tooth germ. Con A receptors were demonstrated by fluorescein-isothiocyanate-labelled Con A (FITC-Con A) and cytoplasmic actin by a specific anti-actin autoantibody (AAA) traced with a rhodamine-labelled goat anti-human globulin (R-AHG). All 3 cell types, incubated with FITC-Con A at 37 degrees C for increasing time periods, showed progressive changes in staining patterns from clusters, caps to perinuclear globules. Capping was seen in the majority of immature epithelial cells at 120–180 min, in cells of more mature epithelium at 180–240 min and in ecto-mesenchymal cells at 240–360 min. Binding of FITC-Con A to cell surfaces resulted in sequential changes in AAA staining from filamentous to an aggregated or diffuse pattern, co-capping of aggregated or diffusely stained areas with those capped by FITC-Con A, presence of aggregated or diffusely stained areas in sites similar to the perinuclear globules stained by FITC-Con A, to final re-emergence of filamentous staining. Prior treatment of cells with cytochalasin B or colchicine promoted capping in epithelial but not in ecto-mesenchymal cells while presence of either drug throughout the staining procedure inhibited capping. The results show that Con A receptors are more mobile in epithelial compared to ecto-mesenchymal cells and in immature epithelial cells compared to their more mature counterparts, and that binding and mobility of Con A receptors on the cell surface is associated with redistribution of cytoplasmic actin. The cytochalasin B and colchicine experiments suggest that both microfilaments and microtubules may have synergistic roles in the opposing functions of receptor anchorage and mobility, and that the relative receptor immobility of ectomesenchymal compared to epithelial cells may be attributed to firmer receptor anchorage to the cytoskeleton.

Ultrastructural and cytochemical studies on the matrix vesicle calcification in the teeth of the killifish, Oryzias latipes

Tooth germs of killifish were examined by both ultrastructural and cytochemical methods. The ultrastructure of the dentin in the early calcification stage of its development resembled that of mammals. Numerous extracellular membrane-bounded vesicles, matrix vesicles, were seen in the predentinal space, especially abundantly in the basal portion of the tooth germ. They were more numerous and more uniform in appearance than in any other higher vertebrates. Where calcification was going to start, slightly identifiable needles of apatite crystals were found in the vesicular structures. Crystals increase in number filling up the vesicles and then ther surroundings, finally to form many calcified spherules. Where calcification was more extensive, the matrix vesicles were no longer visible having been buried calcified among spherules. Contrary, to popular belief, there was no relationship seen between collagen fibrils and the initial deposits of minerals, that is, collagen fibrils did not seem to work as the initial site of calcification. Instead, matrix vesicles and plasma membranes of odontoblasts likely were involved in calcification as they both showed alkaline phosphatase activity. The ultrastructural and cytochemical findings from this study thus indicated that calcification of the killifish tooth germs was initiated not in the enamel, but in their dentin by the matrix vesicles which were liberated into the dentin matrix from odontoblasts mainly by way of fragmentation of cell processes.

Study on the biosynthesis of bovine enamel protein in vitro

Biosynthesis of enamel protein was investigated by incubating bovine tooth germs with 3H-proline containing medium. The radioactivity was incorporated into two protein fractions: one had a molecular weight of about 25,000, being secreted from the ameloblast to the enamel matrix, another having a higher molecular weight was supposed to be a cell associated protein.

The early mineralization of enamel. Fine structural observations on the cellular localization of calcium with the potassium pyroantimonate technique

The potassium pyronatimonate technique was used to study the cellular distribution of calcium during the early mineralization of enamel in rat molar tooth germs at the electron microscope level. Differing patterns of calcium distribution were observed in the ameloblast seemingly associated with the appearance of Tomes' process. In the early secretory ameloblast calcium pyroantimonate deposits were observed within the Golgi apparatus, within coated vesicles, within mitochondria and associated with the inner aspect of the cell membrane. However, with the development of Tomes' process the ameloblast no longer demonstrated these discrete deposits of calcium pyroantimonate. Instead they showed a diffuse cytoplasmic staining pattern with no preference for any particular organelle.

The effects of ascorbic acid deficiency on collagen synthesis by mouse molar tooth germs in organ culture

Second molar tooth germs from 2-day-old Swiss-Webster mice, grown in organ culture for 7 days in ascorbic-acid-deficient medium, synthesized about 65% as much protein (measured by incorporation of [14C]proline during a 24-h pulse) as did ascorbic-acid-supplemented controls. The newly synthesized proteins from ascorbic-acid-deficient cultures contained only about 7% of the hydroxyproline content of the controls. Collagenase digestion of the newly synthesized proteins showed that collagen comprised the same fraction of the total protein synthesized under both culture conditions. This result indicates that the ascorbate-deficient cultures made significant quantities of underhydroxylated collagen. Partial characterization of the collagen alpha chains on carboxymethyl cellulose columns showed an alpha1/alpha2 ratio of about 5, suggesting that at least two different species of collagen were synthesized. The alpha1/alpha2 ratio of the chains recovered from the ascorbate-deficient cultures was also about 5 but the chains were slightly underhydroxylated and the total amount of these chains which could be identified accounted for only a small fraction of the total collagen which was synthesized. A large fraction of the synthesized collagenous protein was found in the culture medium, mostly in the form of lower molecular weight peptides. It is concluded that most of the collagen which is synthesized by ascorbate-deficient tooth-bud cultures is not utilized by the component tissues, but is probably degraded and released into the medium.