Factors influencing the expression of dental extracellular matrix biomineralization

The forming tooth organ provides a number of opportunities to investigate the cellular and molecular biology of cell-mediated extracellular matrix (ECM) biomineralization. Regulatory processes associated with tooth formation are being investigated by identifying when and where cell adhesion molecules (CAMs), substrate adhesion molecules (SAMs), dentine phosphoprotein and enamel gene products are expressed during sequential developmental stages. In vitro organotypic culture studies in serumless, chemically-defined medium, have shown that instructive and permissive signalling are required for both morphogenesis and cytodifferentiation. Intrinsic developmental instructions (autocrine and paracrine factors) act independently of long-range hormonal or exogenous growth factors and mediate morphogenesis from the initiation of the dental lamina to the crown stages of tooth development. This review summarizes the results of studies using experimental embryology, recombinant DNA technology and immunocytology to elucidate mechanisms responsive to instructive epithelial-mesenchymal interactions associated with ameloblast differentiation, odontoblast differentiation, and dentine and enamel ECM biomineralization.

Factors associated with osteoarthritis of the hip and knee in Hong Kong Chinese: obesity, joint injury, and occupational activities

In 1998, a case-control study was conducted in Hong Kong on hospital patients with osteoarthritis of the hip (n = 138) and osteoarthritis of the knee (n = 658). Age- and sex-matched controls were recruited consecutively from general practice clinics in the same region. The following three risk factors were found to be associated with osteoarthritis of both the hip and the knee: first, a history of joint injury: for osteoarthritis of the hip, the odds ratio = 25.1 (95% confidence interval (CI): 3.5, 181) in men and 43.3 (95% CI: 11.7, 161) in women; for osteoarthritis of the knee, the odds ratio = 12.1 (95% CI: 3.4, 42.5) in men and 7.6 (95% CI: 3.8, 15.2) in women; second, climbing stairs frequently: for osteoarthritis of the hip, the odds ratio = 12.5 (95% CI: 1.5, 104.3) in men and 2.3 (95% CI: 0.6, 8.1) in women; for osteoarthritis of the knee, the odds ratio = 2.5 (95% CI: 1.0, 6.4) in men and 5.1 (95% CI: 2.5, 10.2) in women; third, lifting heavy weight frequently: for osteoarthritis of the hip, the odds ratio = 3.1 (95% CI: 0.7, 14.3) in men and 2.4 (95% CI: 1.1, 5.3) in women; for osteoarthritis of the knee, the odds ratio = 5.4 (95% CI: 2.4, 12.4) in men and 2.0 (95% CI: 1.2, 3.1) in women. In addition, subjects whose height and weight were in the highest quartile were at increased risk of osteoarthritis of the hip and knee, respectively (p < 0.05).

Protection of mice from teratogen-induced cleft palate by exogenous methionine

A major challenge for biomedical research is the reduction and/or prevention of congenital craniofacial abnormalities which can be induced by some extrinsic toxicants such as retinoic acids (e.g. isotretinoin, Accutane) and glucocorticoids (corticosteroid hormones) during embryonic craniofacial morphogenesis. Our present studies using a genetically susceptible mouse strain (B10.A) indicate that the teratogenic actions of exogenous retinoic acid or glucocorticoid in secondary cleft palate induction can be largely reduced or even completely rescued by subsequent administration of methionine. The greatest reduction in frequency of all-trans retinoic acid- or triamcinolone-induced secondary cleft palate was obtained by a single-dose IP administration of methionine at 187 mg/kg to pregnant mice on E13 21 hr. It appears that detrimental toxic effects were not observed in mice treated with this therapeutic level of methionine. Our present findings support the need for further research into the role of exogenous methionine in cleft palate reduction, that will provide a biological rationale for considering methionine as a therapeutic agent.

A review of the aggregation properties of a recombinant amelogenin

The present paper reviews some recent data on the aggregation properties of a recombinant amelogenin using dynamic light scattering, transmission electron microscopy, atomic force microscopy, and size exclusion chromatography. It was found that the recombinant amelogenin M179 molecules in solution form spherical monodisperse aggregates (15-20 nm) which are predominantly stabilized by intermolecular hydrophobic interactions while their surfaces are charged, carrying the hydrophilic carboxy-terminal sequence. We concluded that the spherical aggregates represent the "stippled materials" secreted by the ameloblasts at the mineralization front. We further speculate that the self-assembly process in the formation of amelogenin aggregates may play a primary role in the structural organization of mineralizing enamel.

Alternative splicing of the mouse amelogenin primary RNA transcript

A heterogeneous mixture of amelogenins can be extracted from developing tooth enamel matrix. In an attempt to discover the extent to which alternative splicing of the amelogenin primary RNA transcript can generate unique isoforms, we have conducted a thorough search for cDNAs amplified by reverse transcription-polymerase chain reaction (RT-PCR). Over 2400 colonies were screened by colony hybridization. Seven different alternatively spliced amelogenin mRNAs were isolated. The predicted translation products of the messages are 194, 180, 156, 141, 74, 59, and 44 amino acids in length. RT-PCR amplification products not predicted by these seven amelogenin cDNAs were characterized. The intron separating exons 5 and 6 was cloned and sequenced. Using rapid amplification of cDNA ends (RACE) techniques, the 5' ends of the amelogenin mRNAs were cloned and characterized. The finding that the same exon 1 is common to all of the cloned mRNAs indicates that mouse amelogenin is transcribed from a single promoter. The mouse amelogenin transcription and translation initiation sites, the 5' untranslated leader, and the segment encoding the signal peptide were determined. The distinctly nonamelogenin-like exon 4, first observed in human amelogenin cDNAs, has also been found in mice. Antibodies were raised to synthetic exon 4-encoded polypeptides and used to immunostain Western transfers and histologic tooth sections.

Detection of monodisperse aggregates of a recombinant amelogenin by dynamic light scattering

Recombinant murine amelogenins M179 and M166 were expressed in Escherichia coli and purified. The aggregation properties of these amelogenins have been investigated in aqueous solutions as well as acetonitrile-containing solutions using dynamic light scattering. Dynamic light scattering provides direct measurement of the translational diffusion coefficient and hydrodynamic radius, and of an estimate of the molecular weight. Polydispersity and statistical parameters of how to interpret the analysis are also provided. Amelogenin aggregation was examined in solutions of a range of pH, ionic strengths, and protein concentrations. It was shown that at pH 7.8-8 and ionic strength of 0.02-0.05M the M179 molecules form monodispersed aggregates with hydrodynamic radii ranging from 15 to 19 nm. Analysis of hydrodynamic radii and size distribution of M179 aggregates in acetonitrile-containing solvents compared to that in aqueous solutions indicated a primary role for hydrophobic interactions in the association process of amelogenin molecules to form aggregates. Comparison between the aggregates formed by M179 and M166, which lacks the hydrophilic carboxy-terminal 13 residue sequence of M179, suggested that the self-assembly of amelogenin molecules to form stable and monodisperse aggregates requires the presence of the hydrophilic carboxy-terminal sequence of M179.

Isolation and characterization of a mouse amelogenin expressed in Escherichia coli

A mouse cDNA encoding a 180 amino acid amelogenin was subcloned into the pET expression plasmid (Novagen, Madison, WI) for production in Escherichia coli. A simple growth and purification protocol yields 20-50 mg of 95-99% pure recombinant amelogenin from a 4.5-liter culture. This is the first heterologous expression of an enamel protein. The expressed protein was characterized by partial Edman sequencing, amino acid composition analysis, SDS-PAGE, Western blotting, laser desorption mass spectrometry, and hydroxyapatite binding. The recombinant amelogenin is 179 amino acids in length, has a molecular weight of 20,162 daltons, and hydroxyapatite binding properties similar to the porcine 173 residue amelogenin. Solubility analyses showed that the bacterially expressed protein is only sparingly soluble in the pH range of 6.4-8.0 or in solutions 20% saturated with ammonium sulfate. The purified protein was used to generate rabbit polyclonal anti-amelogenin antibodies which show specific reaction to amelogenins in both Western blot analyses of enamel extracts and in immunostaining of developing mouse molars.

Self-assembly of a recombinant amelogenin protein generates supramolecular structures

Amelogenin proteins are the principal constituents of the extracellular organic matrix associated with the nucleation and growth of the carbonated calcium hydroxyapatite (HAP)-containing mineral phase of dental enamel. Amelogenins are believed to function in controlling the sizes and organization of the developing enamel crystals. Previous studies have shown that enamel proteins exhibit unusual reversible aggregation properties. The present studies were designed to test the hypothesis that self-assembly of recombinant amelogenin generates supramolecular structures that are indistinguishable from the electron-dense particles associated with HAP crystal growth in vivo. A recombinant amelogenin analog of the murine 180-residue protein was analyzed by high-resolution size exclusion chromatography, atomic force (AFM), and transmission electron (TEM) microscopy. It was found that the amelogenin formed supramolecular aggregates which were in a concentration-dependent equilibrium with protein monomers. Imaging of the amelogenin by both AFM and TEM techniques revealed spherical aggregate structures of about 18 nm diameter which were seen to be similar to electron-dense enamel structures observed in vivo. We interpret these results to suggest that, in vivo, the amelogenin protein self-assembles through functional motifs of the protein primary structure, generating specific supramolecular aggregates which we hypothesize function to control the ultrastructural organization of the developing enamel crystallites.

Messenger RNA phenotyping for semi-quantitative comparison of glucocorticoid receptor transcript levels in the developing embryonic mouse palate

A specific complex of glucocorticoid and receptor interacts with responsive genes in target tissues of developing palate and controls its morphogenesis. In order to examine developmental changes in glucocorticoid receptor gene expression during embryonic palate formation, variations in transcript levels have been determined using a simple semi-quantitative reverse transcription-polymerase chain reaction (PCR) procedure. Oligo (dT)16 was used as the primer for reverse transcription, and the amount of PCR product for glucocorticoid receptor was normalized against those for glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and beta-actin. We found that either GAPDH or beta-actin were suitable internal standards, and that the mRNA levels of glucocorticoid receptor undergoes a significant decrease of 30% at the developmental stage of embryonic mouse palatal shelf re-orientation. Immunolocalization of the receptor demonstrated a significant change in the distribution pattern of glucocorticoid receptor during the re-orientation stage of secondary palate formation. Our present data suggest that developmental variations in glucocorticoid receptor level control morphogenetic events of secondary palate formation.

Alternative splicing of the mouse amelogenin primary RNA transcript contributes to amelogenin heterogeneity

A heterogeneous population of amelogenin proteins is derived from a single copy of the mouse amelogenin gene. To investigate the one gene--multiple protein enigma, we designed a study to distinguish between alternative splicing and proteolytic cleavage models. A pulse of [35S]methionine labeling demonstrated that multiple amelogenins are synthesized concurrently, a result consistent with an alternative splicing mechanism. Using reverse transcription and polymerase chain reaction we cloned a segment from the 5' end of a mouse amelogenin mRNA and connected it to a previously isolated abbreviated cDNA clone. Four additional cDNAs derived from alternatively spliced amelogenin mRNAs have been cloned and characterized. The five transcripts encode amelogenins 180, 156, 141, 74, and 59 amino acids in length.

Autosomal localization of the amelogenin gene in monotremes and marsupials: implications for mammalian sex chromosome evolution

We have determined by Southern blot analysis that DNA sequences homologous to the AMG gene probe are present in the genomes of both marsupial and monotreme mammals, although adult monotremes lack teeth. In situ hybridization and Southern analysis of cell hybrids demonstrate that AMG homologues are located on autosomes. In the Tammar Wallaby, AMG homologues are located on chromosomes 5q and 1q and in the Platypus, on chromosomes 1 and 2. The autosomal location of the AMG homologues provides additional support for the hypothesis that an autosomal region equivalent to the human Xp was translocated to the X chromosome in the Eutheria after the divergence of the marsupials 150 million years ago. The region containing the AMG gene is therefore likely to have been added 80-150 million years ago to a pseudoautosomal region shared by the ancestral eutherian X and Y chromosome; the X and Y alleles must have begun diverging after this date.

Human ameloblastoma tumors express the amelogenin gene

Instructive signals are responsible for the regulation of the expression of gene products characteristic of many cell lineages during normal development and potentially during neoplasia. The odontogenic origin of ameloblastomas is based largely on the similarity in histologic appearance between the tumor and the developing tooth organ. A pathognomonic pattern for odontogenic tissue-specific gene expression in ameloblastomas has not been previously shown. In these studies, the gene expression parameters for human ameloblastomas have been characterized with the techniques of messenger RNA phenotyping in combination with Northern and in situ hybridization analysis of messenger RNA. The results of these studies confirm that amelogenin, a gene transcribed solely by differentiated ameloblasts, was expressed by epithelial cells from human ameloblastomas. This observation suggests that the instructive signals required for ameloblast differentiation are shared during normal development and tumorigenesis of odontogenic epithelium.

Linkage of amelogenin (Amel) to the distal portion of the mouse X chromosome

Amelogenins are hydrophobic, proline-rich proteins that are the primary biosynthetic products of ameloblasts. These cells are responsible for the formation of tooth enamel, and amelogenins play an important role in the process of biomineralization. A cDNA, corresponding to the mouse 26-kDa amelogenin, has been molecularly cloned and sequenced. Southern blot analysis of genomic DNA from the mouse using this cDNA as a probe indicates that there is only one mouse amelogenin (Amel) gene. This paper describes restriction site variation for the Amel gene that we have identified between C57BL/6 and M. spretus and the segregation of that variation as an X-chromosome gene. The position of the amelogenin locus (Amel) relative to the loci for alpha-galactosidase (Ags), proteolipoprotein (Plp), and the random genomic probe DXWas31 has been determined. Amel is established as: (1) the most distal locus in the genetic map of the mouse X chromosome, (2) lying proximal to the X:Y pairing region, and (3) being restricted to the mouse X chromosome.

Human developing enamel proteins exhibit a sex-linked dimorphism

The amelogenin protein of developing dental enamel is generally accepted to mediate the regulation of the form and size of the hydroxyapatite crystallites during enamel biomineralization (1). A genetic disorder of enamel development (amelogenesis imperfecta) has been linked to the amelogenin gene AMEL(2-3), and loci regulating enamel thickness and tooth size have been mapped to the human sex chromosomes (4). In the human genome there are two AMEL loci with one copy of the gene on each of the sex chromosomes (AMELX and AMELY), whereas in the mouse only an AMELX locus is present (5). It is presently unknown if human AMELY is transcriptionally active. These observations prompted us to examine specimens of human developing enamel for sexual dimorphism at the protein level. We report here, for the first time, a diagnosis of differences in human enamel proteins which permits the distinction of specimens according to the sex of the individual.

Amelogenin post-secretory processing during biomineralization in the postnatal mouse molar tooth

The primary structures, molecular genetics and biosynthesis of the amelogenin protein of the developing tooth are established, but knowledge of their subsequent post-secretory processing and its relation to enamel biomineralization is fragmentary. Preparations of tooth matrix proteins were isolated from molars (M1) of mice from birth to 15 days and analysed by SDS-PAGE and immunochemical methods. Amelogenin proteins, isolated and partially purified by HPLC, were characterized by amino acid analysis and SDS-PAGE. At birth a 26 kDa amelogenin was present that during subsequent developmental stages generated a series of 20-25 kDa amelogenins differing in apparent size by approximately 1 kDa. Amino acid analyses showed that all these amelogenins have amino-terminal TRAP sequences; analyses for both glycosylation and phosphorylation were negative. It is suggested that these post-secretory amelogenins are generated by a sequence of specific carboxy-terminal cleavages, and that the observed post-secretory processing of amelogenin is functionally linked to the structure of the enamel matrix and the control of crystallite development.

Analysis of human enamel genes: insights into genetic disorders of enamel

A number of inherited craniofacial diseases are known to be associated with gene mutations. Inherited genetic disorders of enamel formation called amelogenesis imperfecta (AI) affect the human population with a prevalence of 1 in 14,000 in the United States. Amelogenins, the major proteins in developing enamel matrix of mammalian teeth, have been suggested to participate in normal enamel matrix biomineralization, as well as with abnormal biomineralization such as seen in AI. The complementary DNA for mouse amelogenin gene (AMEL) has been cloned, characterized, and used as a probe to establish the chromosomal locations of AMEL for mouse and man. The human AMEL gene sequences have been located to the distal short arm p22.1----p22.3 region of the X chromosome, and the pericentromeric region of the Y chromosome. An assignment of human AMEL gene to the X chromosome p22 region together with a recent assignment of the X-linked AI disease locus to the Xp22.2 region support the association of the AMEL-X gene with AI. This also leads us to propose that a mutated AMEL-X gene produces altered amelogenin polypeptide, which is defective in its ability to participate in mineralization of enamel matrix, thus giving rise to the X-linked phenotypes of AI.

Human and mouse amelogenin gene loci are on the sex chromosomes

Enamel is the outermost covering of teeth and is the hardest tissue in the vertebrate body. The enamel matrix is composed of enamelin and amelogenin classes of protein. We have determined the chromosomal locations for the human and mouse amelogenin (AMEL) loci using Southern blot analyses of DNA from human, mouse, or somatic cell hybrids by hybridization to a characterized mouse amelogenin cDNA. We have determined that human AMEL sequences are located on the distal short arm of the X chromosome in the p22.1----p22.3 region and near the centromere on the Y chromosome, possibly at the proximal long arm (Yq11) region. These chromosomal assignments are consistent with the hypothesis that perturbation of the amelogenin gene is involved in X-linked types of amelogenesis imperfecta, as well as with the Y-chromosomal locations for genes that participate in regulating tooth size and shape. Unlike the locus in humans, the mouse AMEL locus appears to be assigned solely to the X chromosome. Finally, together with the data on other X and Y chromosome sequences, these data for AMEL mapping support the notion of a pericentric inversion occurring in the human Y chromosome during primate evolution.

In situ hybridization analysis of keratin gene expression in human ameloblastomas

Complementary DNA (cDNA) clones corresponding to the 55 kDa (K 14) and 59 kDa (K 10) keratins were used as probes for in situ hybridization analysis for the expression of keratin genes in human ameloblastomas and in oral mucosa. Transcripts for either the K 14 keratin or the K 10 keratin were restricted in their spatial distribution within stratified epithelia consistent with the stage of differentiation of the keratinocyte: the K 14 keratin gene transcript was restricted to the basal cell layers of the mucosa, while the K 10 keratin transcript was expressed predominantly in suprabasal cells, within the granular and prickle layers. In contrast, only the K 14 keratin transcript could be identified within the epithelial cells of human ameloblastomas. The differentiation-specific keratin transcript (K 10) was not present at detectable levels in this type of odontogenic tumors. In an atypical, infiltrating ameloblastoma, neither the K 10 nor the K 14 transcript could be identified. Granular cells within one ameloblastoma expressed the K 14 transcript. A detailed examination of the pattern of gene expression in these unique tumors may lead to a better understanding of their pathogenesis.

Spatial- and temporal-restricted pattern for amelogenin gene expression during mouse molar tooth organogenesis

Position- and time-restricted amelogenin gene transcription was analysed in developing tooth organs using in situ hybridization with asymmetric complementary RNA probes produced from a cDNA specific to the mouse 26 × 10(3) Mr amelogenin. In situ analysis was performed on developmentally staged fetal and neonatal mouse mandibular first (M1) and maxillary first (M1) molar tooth organs using serial sections and three-dimensional reconstruction. Amelogenin mRNA was first detected in a cluster of ameloblasts along one cusp of the M1 molar at the newborn stage of development. In subsequent developmental stages, amelogenin transcripts were detected within foci of ameloblasts lining each of the five cusps comprising the molar crown form. The number of amelogenin transcripts appeared to be position-dependent, being more abundant on one cusp surface while reduced along the opposite surface. Amelogenin gene transcription was found to be bilaterally symmetric between the developing right and left M1 molars, and complementary between the M1 and M1 developing molars; indicating position-restricted gene expression resulting in organ stereoisomerism. The application of in situ hybridization to forming tooth organ geometry provides a novel strategy to define epithelial-mesenchymal signal(s) which are believed to be responsible for organ morphogenesis, as well as for temporal- and spatial-restricted tissue-specific expression of enamel extracellular matrix.

Examining the possible molecular origins for enamel protein complexity

Our strategy was to examine each of the three loci capable of contributing to the observed complexity 0 of mouse amelogenin proteins recovered from forming enamel: the genome (gene); the transcription apparatus (messenger RNA); and the translation apparatus (proteins). Our approach was based on recombinant DNA technology and a complementary DNA (cDNA) clone, pMa5-5, specific to the predominant mouse amelogenin protein. An "artificial ameloblast" was engineered based on pMa5-5 and the resulting synthetic products compared to those from authentic ameloblasts. First, the genome probably is not responsible for amelogenin complexity: Southern analysis indicates that the amelogenin gene exists as a single copy in either differentiated dental tissue or germ line tissue. Thus, ectomesenchymal-derived instructive signals for ameloblast differentiation do not lead to re-arrangement or amplification of the amelogenin gene. Next, using nucleic acid hybridization techniques, we examined messenger RNA from mouse ameloblasts. Northern analysis of authentic mRNA from mouse ameloblasts, with either the intact or 3'-end of pMa 5-5 used as the reporter molecule, indicates that only one size class of mRNA was detectable. We conclude that at the sensitivity of this assay there is no evidence for multiple mRNAs. Last, "artificial ameloblasts" were engineered so that the translation apparatus could be examined as a source of amelogenin complexity. Capped, artificial mRNAs were constructed to the pMa 5-5 template and used to program the synthesis of amelogenin polypeptides by translation in a cell-free system. When the resulting total translation products were immunoprecipitated with the rabbit anti-mouse amelogenin antibody, we observed multiple polypeptides, suggesting that the utilization of alternative start sites may also contribute to the observed complexity of amelogenin proteins, at least for artificial mRNAs translated in vitro.

Amelogenin antigenic domain defined by clonal epitope selection

To experimentally examine the participation of amelogenins in controlled mineral-phase maturation of mammalian enamel, the identification of the individual proteins and their corresponding gene(s) is required. For this purpose, cDNAs were constructed from polyadenylated RNA from 2-day postnatal murine teeth, molecularly cloned into lambda-gt11 expression vectors and transfected into E. coli. The cDNA library was screened for amelogenin gene(s) by using either antibody or nucleic acid probes. An amelogenin cDNA clone encoding 79 carboxy-terminal amino acid residues and 100 nucleotides of the 3' noncoding sequence was demonstrated to contain a major antigenic site for amelogenin protein by immunostaining of specific amelogenin proteins from total extracted enamel protein blots using clonal epitope selected antibody. This is the first report linking amelogenin epitope(s) to a defined DNA sequence, and consequently a defined portion of the amino acid sequence for amelogenins. Secondary structure analysis, based on the relative average linear hydropathy of the amino acid sequence of amelogenin, predicted epitopes in the amino terminus of the molecule rather than the carboxy terminus. Our present data suggest that the carboxy terminus of the amelogenins is sufficiently externalized to be an antigenic domain. These data may be useful in subsequent structural analysis of amelogenin proteins and enhancing our understanding of their physicochemical participation in biomineralization.

DNA sequence for cloned cDNA for murine amelogenin reveal the amino acid sequence for enamel-specific protein

Enamel is the unique and highly mineralized extracellular matrix that covers vertebrate teeth. Amelogenin proteins represent the predominate subfamily of gene products found in developing mammalian enamel, and are implicated in the regulation of the formation of the largest hydroxyapatite crystals in the vertebrate body. Previous attempts to isolate, purify and characterize amelogenins extracted from developing matrix have proven difficult. We now have determined the DNA sequence for a cDNA for the 26-kDa class of murine amelogenin and deduced its corresponding amino acid sequence. The murine amino acid sequence is homologous to bovine or porcine amelogenins extracted from developing enamel matrices. However, an additional 10-residues were found at the carboxy terminus of the murine amelogenin. This is the most complete sequence database for amelogenin peptides and the only DNA sequence for enamel specific genes.

Chromatography on DEAE-cellulose microcolumns: a quantitative method for the fractionation of small quantities of glycosaminoglycans

A simple, sensitive, and efficient method is described for qualitative and quantitative determination of glycosaminoglycans (GAG) synthesized by embryonic mouse teeth. After release from proteoglycan aggregates by enzymatic treatment, a mixture of different GAG was absorbed on a DEAE-cellulose microcolumn (Whatman DE-52 microgranular) at low salt concentration. The different types of GAG were eluted by stepwise increases in the concentration of NaCl. Glycopeptides, which generally contaminate the extract, can be completely removed prior to the elution of GAG. The eluate fractions were analyzed by rechromatography on the same column, using gradient elution. The stepwise elution is suitable for analysis as well as preparation of labeled GAG, the supply of which is limited in amount. The scale of chromatography can easily be stepped up. Quantitative analysis of GAG from embryonic mouse teeth is presented to demonstrate the usefulness of this method.

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.