Biomedical subjects

C C Bessem

Publications and source records attributed to C C Bessem.

5 recordsLinked to original sources

PubMed1991

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.

Ameloblasts↗

PubMed1989

Amelogenesis in vitro: a model for studies of epithelial postsecretory processing during tissue-specific extracellular matrix biomineralization.

The extracellular matrix (ECM) of developing mammalian enamel comprises a complex of unusual epithelial-derived proteins, which appear to function in concert to initiate and propagate tissue-specific biomineralization. Following enamel protein synthesis by ameloblast cells within the enamel organ, the subsequent steps of posttranslational modification, secretion, postsecretory processing and eventual removal of these proteins from forming enamel are largely unknown. To address this issue we have designed studies to investigate the hypothesis that enamel proteins are removed from enamel and translocated into the vasculature as relatively high-molecular-weight components. We examined enamel proteins recovered from serumless medium during prolonged organ culture of mouse capstage mandibular first molars. By 21 days in vitro the tooth crown formed and dentine and enamel biomineralization were apparent. At 31 days, explants retained metabolic activity and the enamel matrix showed extensive transformation. Immunologically identified enamel proteins of 26-18 k Da were produced by cultured tooth organs, translocated from tooth explants to the culture medium, recovered from the medium and then compared to control enamel protein from in vivo preparations. Comparable postsecretory processing of the 26-k Da amelogenin protein was observed in vitro and in vivo. We speculate that the pathway reported in the present studies is comparable to the processing of the enamel protein polypeptides of the maturing enamel which occurs in vivo. The in vitro organ culture model described in this report provides an approach with which to investigate the molecular events associated with epithelial-derived postsecretory processing of ECM molecules associated with tissue-specific biomineralization.

Ameloblasts↗

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↗

PubMed1984

Total poly(A+)-messenger RNA from bovine lens cofractionates with sucrose purified fiber cell plasma membrane.

Poly(A+)-messenger RNA was isolated from bovine lens as well as poly(A+)-mRNA from crude and sucrose-purified plasma membrane. Bovine lens MP26 antisera was also propagated in rabbits, from which anti-MP26 IgG was partially purified and used to assay for the specific synthesis of MP26 during in vitro translation of the isolated poly(A+)-mRNAs. We found that membrane-associated poly(A+)-mRNA supported the synthesis of proteins which were identical to those translated from total lens fiber cell poly(A+)-mRNA. These proteins included MP26, as assayed by immunoprecipitation of [35S]-labeled MP26.

Animals↗

PubMed1981

Possible functions of mesenchyme cell-derived fibronectin during formation of basal lamina.

Epithelial synthesis and secretion of basal lamina has been considered to be a general feature of various vertebrate epithelium-mesenchyme interacting systems (e.g., salivary gland, mammary gland, feather, hair, and tooth morphogenesis). It has been repeatedly assumed that embryonic ectoderm and ectodermal derivatives, such as epithelial tissues associated with tooth morphogenesis, synthesize and secrete basal lamina. Basal lamina of embryonic mouse tooth organs contain laminin, type IV collagen, glycosaminoglycans, and possibly fibronectin. Ectodermally derived epithelia produce laminin, collagens, and glycosaminoglycans but they do not appear to produce fibronectin. Mesenchyme can effect basal lamina formation in vitro by releasing mesenchyme-derived fibronectin. Theiler stage 25 molar tooth mesenchymal and epithelial tissues were enzymatically separated and cultured in chemically defined media without serum, embryonic extracts, or antibiotics for periods not exceeding 24 hr. Isolated epithelia did not reconstitute a basal lamina. Mesenchymepreconditioned media, fibronectin substrata, or addition of 10% fetal calf serum induced reconstitution of epithelium-derived basal lamina. Dental mesenchyme-preconditioned medium contained, as a major component, a protein of M(r) approximately 2.3 x 10(5) identified as fibronectin by the criteria of gelatin binding and subunit molecular weight. Fibronectin was not produced by isolated epithelia. These results support the hypothesis that basal lamina ultrastructural organization results from supramolecular interactions between epithelium-derived macromolecules (e.g., type IV collagen, proteoglycans, glycosaminoglycans, and laminin) with mesenchyme-derived cell surface fibronectin.

Animals↗