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E C Lau

Publications and source records attributed to E C Lau.

27 records · Page 2Linked to original sources
PubMed1988

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.

Ameloblastoma↗
PubMed1988

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 x 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.

Amelogenin↗
PubMed1987

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.

Amelogenin↗
PubMed1985

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.

Amelogenin↗
PubMed1983

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.

Animals↗
PubMed1983

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.

Animals↗
PubMed1983

[35S]autoradiographic study of sulfated GAG accumulation and turnover in embryonic mouse tooth germs.

The accumulation of sulfated GAG in embryonic mouse molars before, during, and after terminal differentiation of odontoblasts was localized by [35S]autoradiography combined with the use of chondroitin ABC lyase. Much more sulfated GAG were accumulated in the dental papilla than in the dental epithelium. High incorporation of [35S]sulfate occurred at the epithelio-mesenchymal junction, which is the site of dental basement membrane and predentin. Before terminal differentiation of odontoblasts, the distribution of sulfated GAG was uniform at the basement membrane. After the onset of terminal differentiation of odontoblasts, much more sulfated GAG accumulated at the tip of principal cusps than at the apical (inferior) parts of cusps, and sulfated GAG were then found to be degraded more rapidly at the epithelio-mesenchymal junction than at other parts of the tooth germ. Thus regional variation in the rate of degradation of GAG exists in the tooth germs. Trypsin-isolated dental epithelia cultured in vitro synthesized a new basement membrane that could be labeled with [3H]glucosamine but not with 35SO4(-2). The epithelial-derived basal lamina contains little or no sulfatated GAG.

Animals↗
PubMedDate not supplied

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.

Amelogenin↗