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At least 19 recordsLinked to original sources
PubMed1988

H+-K+-ATPase activity in the rat incisor enamel organ during enamel formation.

The enamel organ of growing rat incisors was perfusion-fixed with a mixture of formaldehyde and glutaraldehyde and processed for ultracytochemical demonstration of ouabain-resistant, K+-stimulated p-nitrophenylphosphatase representing the second dephosphorylative step of H-K-ATPase by use of the one-step lead method. Throughout the stages of amelogenesis, the enzymatic activity was found in the plasma membranes, mitochondrial membranes, and lysosomal structures of the cells of stratum intermedium, papillary layer, and ameloblast layer. Gap junctions and desmosomes between these cells were, however, free of reaction product or showed slight precipitates of reaction. The stellate reticulum and the outer enamel epithelium at the stage of enamel secretion were usually negative for reaction. Although secretory, transition, and ruffle-ended maturation ameloblasts showed enzymatic activity at their basolateral cell surfaces, their distal cell surfaces facing the enamel were always free of reaction product. On the other hand, the smooth-ended maturation ameloblasts seldom showed a positive reaction, except in lysosomes and along their basal cell surfaces. An energy-dispersive X-ray microanalysis of reaction products of H-K-ATPase in unosmicated tissue sections demonstrated that they were composed of lead and phosphorus, which had been released during the dephosphorylation of substrate. In cytochemical controls, the enzymatic activity was completely dependent on substrate and potassium ion, resistant to ouabain and levamisole, and inhibited by nolinium bromide, a specific inhibitor of H-K-ATPase. In addition, inorganic trimetaphosphatase as enzymatic marker of lysosome was localized in dark and pale lysosomes, phagosomes, multivesicular bodies, and ferritin-containing vesicles of the ameloblasts and the cells of stratum intermedium and papillary layer. These membrane-bound structures were also positive for H-K-ATPase reaction. These results suggest that: 1) H-K-ATPase functions to maintain an acidic internal pH of lysosomes in the enamel organ cells; and 2) H-K-ATPase localization in the plasma membranes of enamel organ cells is concerned with efflux of protons derived from cytoplasmic water.

4-Nitrophenylphosphatase↗
PubMed1986

Penetration of various molecular-weight proteins into the enamel organ and enamel of the rat incisor.

During enamel maturation, most of the organic matrix is removed as the mineral content increases; it is postulated that proteolytic enzymes within enamel break down large proteins into more mobile fragments. To predict how such fragments might leave the enamel, the entry and penetration of various proteins into it was examined. Rats (100 g) were injected via the external jugular vein with 125I-iodinated calcitonin (3600), insulin (5700), epidermal growth factor (EGF; 6100) and albumin (68,000). They were killed after 10 min and radioautographs made to visualize these molecules in the incisor enamel organ and enamel. In addition, dissected incisors were wiped free of their enamel organs, dipped in the iodinated protein solutions for 10 min, and processed for radioautography. In all dipped teeth, except those exposed to albumin, there was a gradient of silver-grain density over the entire thickness of enamel in both the secretion and maturation zones. In all injected animals, enamel labelling in the secretion zone was only slightly above background. In the maturation zone of animals injected with calcitonin and insulin, many grains were over enamel adjacent to smooth-ended ameloblasts but not ruffle-ended ones. Animals injected with EGF and albumin had no labelled enamel in the maturation zone. Thus dipped rat incisor enamel was permeable to proteins with molecular weights as high as 6100. Localization of injected proteins indicates that the enamel organ restricts their passage into enamel, but proteins with molecular weights as high as 5700 may pass into enamel through or between smooth-ended ameloblasts. As exogenous proteins readily diffused into the enamel, it seems likely that enamel proteins of similar size can leave enamel by a similar route.

Animals↗
PubMed1984

Histological, macroscopic and microhardness observations of fluoride-induced changes in the enamel organ and enamel of sheep incisor teeth.

When aged 8.5 months, 10 sheep born in the same week were given 4 mg fluoride (F)/kg body weight orally for 26 days. Three sheep received no F. Sheep were killed at the end of the treatment period and later at selected stages of tooth development. The macroscopic changes in the enamel of one incisor were related to the cellular changes in the enamel organ of the contralateral tooth. A break in enamel continuity, hypoplasia, was seen on the labial enamel of 9 of the 10 F-treated sheep. Pitting of the enamel was associated with shortening of some ameloblasts and aggregations of cysts affecting cells late in their secretory phase in the first-killed sheep. In sheep killed later, these changes were associated with cells which had progressed into their maturation phase. A more extensive absence of enamel with ledge formation cervically, seen in one sheep, was associated with displacement or death of almost all the cells in their secretory phase during F treatment and consequent retention of the organic matrix. The hypoplastic lesions resulted from secretory-cell reaction during the period of F dosing. Diffuse patchy opacities, characterized by an irregular hypomineralized surface zone, were only apparent in the enamel of the later-killed sheep and were associated in one sheep with abnormal ameloblast regression in the contralateral tooth. These defects possibly resulted from the long-continued release of F stored in the bones during the period of F dosing.

Animals↗
PubMed1983

A morphological, tracer and cytochemical study of the role of the papillary layer of the rat-incisor enamel organ during enamel maturation.

Thin-section, freeze-fracture, tracer and cytochemical methods showed that papillary cells were characterized by the presence of numerous mitochondria and microvilli. The cytoplasms contained Golgi apparatus, multivesicular bodies (MVB), tubular structures and coated vesicles. In freeze-fracture replicas, some tubular structures and vesicles were continuous with the cell surfaces. Intravenously-injected horseradish peroxidase (HRP) was rapidly incorporated into the papillary cells via coated vesicles and tubular structures. Horseradish peroxidase-labelled coated vesicles and tubular structures then fused with endocytic vacuoles and MVB. These endocytic vacuoles and MVB showed HRP-labelling of various degrees. Acid-phosphatase activity was demonstrated in the Golgi apparatus, endocytic vacuoles and MVB of papillary cells. Enzymic activity sometimes took place in tubular structures but never occurred in coated vesicles. These results indicate that absorptive and digestive activities of papillary cells are closely related to loss of organic materials from the enamel matrix during enamel maturation.

Acid Phosphatase↗
PubMed1980

Effect of glutaraldehyde and decalcifying agents on acid phosphomonoester hydrolase activity in the enamel organ of the rat incisor: a biochemical study comparing enamel organ with liver.

Enamel organs were dissected from the labial surface of unfixed and glutaraldehyde-fixed rat incisors and assayed biochemically at pH 5.0 for acid phosphomonoester hydrolase activity using cytidine 5'-monophosphate (5'-CMP), beta-glycerophosphate (beta GP), phosphorylcholine (PC), and phosphoserine (PS) as substrates. Whole homogenates from unfixed enamel organs showed substantial enzyme activity toward 5'-CMP and beta GP, but 1/4 and 1/8 less activity toward PC and PS, respectively. Perfusion fixation with 2% glutaraldehyde resulted in a net loss of 80% of the enzyme activity toward each substrate. Lineweaver-Burk plots revealed that the fixative depressed the rate of hydrolysis of substrate (decrease in Vmax) and it also lowered the affinity of enzymes for substrate (increase in KM). Hence, fixed tissue generally required two or three times as much substrate to saturate the enzymes, but less substrate was hydrolyzed, as compared to unfixed tissue. Decalcification of fixed incisors with either formic citric acid, ethylenediaminetetraacetic acid (EDTA), or ethyleneglycoltetacetic acid (EGTA) did not further alter enzyme activity in the enamel organ as determined by Lineweaver-Burk plots, However, EDTA and EGTA were found to increase the susceptibility of fixed enzymes to inhibition by lead ions. This chelator-enhanced lead inhibition was greatest following decalcification with EGTA and using PC as substrate. Similar results were obtained for liver.

Acid Phosphatase↗
PubMed1992

Presence of multinucleate cells in the papillary layer of the Macaca fuscata enamel organ.

The enamel organ of Macaca fuscata from post-secretory transition to the early maturation stage of was investigated by means of light and electron microscopy. Unusual, large multinucleated cells were observed in the papillary layer. These cells contained organelles characteristic of the maturation stage ameloblast and often extended to the enamel surface, suggesting a possible origin from the ameloblast layer.

Ameloblasts↗
PubMed1983

Scanning electron microscopy of the papillary layer of the rat-incisor enamel organ.

The enamel organ isolated from the maturation zone was treated with hydrochloric acid to remove such extracellular materials as collagen fibrils and basal lamina covering the papillary layer. Two types of the ridges were classified on the basis of their morphology and distribution: (1) globular and irregularly arranged ridges at the periphery of the early maturation zone, (2) elliptical and parallel ridges in the central part of this zone and over the whole of the late maturation zone. The fine surface structures of the ridges were characterized by numerous interdigitating cell processes.

Animals↗
PubMed1986

Ultracytochemical demonstration of ATP-dependent calcium pump in ameloblasts of rat incisor enamel organ.

The enamel organ of the growing rat incisor was fixed with a mixture of formaldehyde and glutaraldehyde and processed for ultracytochemical demonstration of Ca- and Mg-activated membrane ATPase by a one-step lead technique at alkaline pH. To inhibit nonspecific alkaline phosphatase, 5 mM levamisole was added to the incubation media. Intense Ca- and Mg-ATPase activity was demonstrated in the cell surfaces of the secretory ameloblasts, except at the proximal and distal junctional complexes and the gap junctions in the lateral and basal cell surfaces. Deep plasma membrane invaginations at the proximal and distal parts of Tomes processes facing interrod- and rod-enamel growth regions exhibited the strongest enzymatic reaction. Mg-ATPase activity was also shown to be present in the plasma membranes of secretory ameloblasts but it was less intense than Ca-ATPase. Except for a slight reaction in the Golgi membranes, all other cell organelles of the secretory ameloblasts and the adjacent enamel matrix were free of enzymatic reaction. However, when the tissues were incubated in media lacking levamisole, a prominent enzymatic reaction was observed in the newly secreted enamel matrix of the rod and interrod growth regions as well as on the plasma membranes of the cells. In maturation ameloblasts of both ruffle-ended and smooth-ended types, a weak reaction for Ca- and Mg-ATPase was restricted to basal cell surfaces facing the papillary cell layer. In tissues incubated in media lacking levamisole, a variable deposition of reaction products was observed in the Golgi membranes, mitochondrial membranes, tubular elements of smooth endoplasmic reticulum in the ruffled border zone, and along the plasma membranes of the ruffled border. Throughout the secretory and maturation stages, a moderate and/or weak enzymatic reaction for both Ca- and Mg-ATPase was seen in the plasma membranes of the cells of the stratum intermedium and the papillary layer when incubated in media with levamisole. Omission of substrate ATP and/or the enzyme activator CaCl2 from the incubation media for Ca-ATPase produced a negative reaction in the tissues examined. When the calmodulin blocker trifluoperazine was administered to the rats intravenously, Ca-ATPase activity was almost completely abolished from the plasma membranes of secretory ameloblasts, but not of other cell types.

Ameloblasts↗
PubMed1980

Ultrastructure of the human enamel organ. I. External enamel epithelium, stellate reticulum, and stratum intermedium.

The fine structure of external enamel epithelium, stellate reticulum and stratum intermedium in primary tooth germs (bell stage) from four human foetuses was investigated. Characteristically, the cells of the differentiated external enamel epithelium, stellate reticulum and stratum intermedium exhibit many free ribosomes, few rough endoplasmic reticulum cisterns, well-developed Golgi complexes, many coated and smooth vesicles, often in relation to the cell membranes, and many bundles of tonofilaments. The cells are connected by numerous desmosomes and gap junctions. A parallel differentiation of stratum intermedium - external enamel epithelium, and the ameloblast layer is demonstrated. The morphology of the cells of the three layers indicates that these have secretory, transport and supporting functions.

Cell Membrane↗
PubMed1980

Ultrastructure of the human enamel organ. II. Internal enamel epithelium, preameloblasts, and secretory ameloblasts.

The fine structure of internal enamel epithelium, preameloblasts and secretory ameloblasts in primary tooth germs (bell stage) from four human foetuses was investigated. The characteristics of the differentiation of internal enamel epithelium via preameloblasts to secretory ameloblasts are described. The internal enamel epithelium consists of a row of low differentiated prismatic cells separated from the dental papilla by a distinct even basal lamina. In the preameloblasts the rough endoplasmic reticulum cisterns and mitochondria increase in number, the Golgi complexes become extensive and take up a distal position, and secretory granules are formed. Furthermore, the basal lamina is removed by coated vesicles, and proximally and distally in the cells a complex of zonulae adhaerentes, terminal webs and gap junctions is formed. The secretory ameloblasts make up a layer of highly differentiated cells demonstrating typical merocrine secretion.

Ameloblasts↗
PubMed1996

Dendritic cells: a novel cellular component of the rat incisor enamel organ appearing in the late stages of enamel maturation.

Immunocompetent cells in the enamel organ of rat incisors were examined immunohistochemically using OX6, ED1, and ED2 monoclonal antibodies known to recognize the Class II MHC molecules, a monocyte-macrophage lineage, and residential macrophages, respectively. The OX6 immunopositive cells (MHC cells) were located exclusively in the enamel maturation zone. MHC cells increased in number in the incisal direction and occasionally extended cytoplasmic processes deep into the ameloblast layer. Migration of MHC cells in the ameloblast layer were also encountered. MHC cells lacked phagolysosomes and could be distinguished from typical macrophages. ED2 immunopositive cells were not seen in the enamel organ. ED1 positive cells displayed identical localization to MHC cells except that some appeared in the transitional zone. MHC cells could not be seen in the enamel organ of rat molar tooth germs. Our data confirmed the presence of a large population of "dendritic" immunocompetent cells in the enamel organ of rat incisors and characterized the ultrastructural features of these cells. Biological significance of the immunocompetent cells in the enamel organ during amelogenesis needs to be clarified.

Amelogenesis↗
PubMed1981

Histology of enamel organ and chemical composition of adjacent enamel in rat incisors.

By avoiding chemical fixation and using a freeze-drying technique, it proved possible to examine the enamel organ of rat mandibular incisors histologically while retaining the adjacent enamel of the same tooth for chemical analysis. The dramatic alterations which occur in enamel organ histology, such as ameloblast shortening and the development of hte papillary layer, could then be compared directly with mineral uptake and mineral content of the adjacent enamel. Both enamel and adjacent enamel organ were sampled as a continuous series of pieces, 0.5 mm in width, from youngest (apical) to oldest (incisal) tissue. Short ameloblasts were associated directly with the beginning of a rapid uptake of phosphate ions during the maturation phase and also coincided with the beginning of a steep rise in mineral content. By implication, some loss of matrix may also occur at this point. Development of the highly vascular papillary layer preceded ameloblast shortening and may be associated with changes in the organic matrix prior to its disappearance from the tissue. Further development of this layer was associated with ameloblast shortening. This may also therefore be associated with mineral uptake during maturation.

Animals↗
PubMed1998

Protein-to-protein interactions: criteria defining the assembly of the enamel organic matrix.

Enamel crystallites form in a protein matrix located proximal to the ameloblast cell layer. This unique organic extracellular matrix is constructed from structural protein components biosynthesized and secreted by ameloblasts. To date, three distinct classes of enamel matrix proteins have been cloned. These are the amelogenins, tuftelin, and ameloblastin, with recent data implicating ameloblastin gene expression during cementogenesis. The organic enamel extracellular matrix undergoes assembly to provide a three-dimensional array of protein domains that carry out the physiologic function of guiding enamel hydroxyapatite crystallite formation. Using the yeast two-hybrid system, we have surveyed these three known enamel gene products for their ability to direct self-assembly. We measured the capacity of the enamel gene products to direct protein-to-protein interactions, a characteristic of enamel proteins predicated to be required for self-assembly. We provide additional evidence for the self-assembly nature of amelogenin and tuftelin. Ameloblastin self-assembly could not be demonstrated, nor were protein-to-protein interactions observed between ameloblastin and either amelogenin or tuftelin. Within the limits of the yeast two-hybrid assay, these findings constrain the emerging model of enamel matrix assembly by helping to define the limits of enamel matrix protein-protein interactions that are believed to guide enamel mineral crystallite formation.

Amelogenesis↗
PubMed2006

Evidence by signal peptide trap technology for the expression of carbonic anhydrase 6 in rat incisor enamel organs.

During screening of a rat incisor enamel organ cDNA library by signal peptide trap technology, we identified a DNA fragment matching a predicted translation sequence for rat carbonic anhydrase 6 (CA6). This result was unexpected because CA6, to date, has been associated primarily with secretions from glandular tissues. To further characterize this observation, reverse transcription-polymerase chain reaction (RT-PCR) amplifications were carried out on total RNA extracted from freeze-dried secretory and maturation-stage rat incisor enamel organs. A cDNA fragment of the expected size was detected in control samples from rat salivary glands as well as within maturation-stage enamel organ samples. This CA6 RT-PCR fragment was further cloned and sequenced and found to match the nucleotide sequence 770-1079 from clone XM_216584 of GenBank. Northern blot analyses with the rat CA6 cDNA fragment confirmed its expression relative to maturation-stage enamel organ samples. It is at present unclear whether the CA6 expressed by enamel organ cells is secreted into the enamel layer or into the intercellular spaces of the enamel organ itself to assist in neutralizing excess protons arising from the growth of apatite crystals during the maturation stage of amelogenesis.

Amelogenesis↗