Search

Sea urchin teeth grow continuously and develop a complex mineralized structure consisting of spatially separate but crystallographically aligned first stage calcitic elements of high Mg content (5-15 mol% mineral). These become cemented together by epitaxially oriented second stage very high Mg calcite (30-40 mol% mineral). In the tooth plumula, ingressing preodontoblasts create layered cellular syncytia. Mineral deposits develop within membrane-bound compartments between cellular syncytial layers. We seek to understand how this complex tooth architecture is developed, how individual crystalline calcitic elements become crystallographically aligned, and how their Mg composition is regulated. Synchrotron microbeam X-ray scattering was performed on live, freshly dissected teeth. We observed that the initial diffracting crystals lie within independent syncytial spaces in the plumula. These diffraction patterns match those of mature tooth calcite. Thus, the spatially separate crystallites grow with the same crystallographic orientation seen in the mature tooth. Mineral-related proteins from regions with differing Mg contents were isolated, sequenced, and characterized. A tooth cDNA library was constructed, and selected matrix-related proteins were cloned. Antibodies were prepared and used for immunolocaliztion. Matrix-related proteins are acidic, phosphorylated, and associated with the syncytial membranes. Time-of-flight secondary ion mass spectroscopy of various crystal elements shows unique amino acid, Mg, and Ca ion distributions. High and very high Mg calcites differ in Asp content. Matrix-related proteins are phosphorylated. Very high Mg calcite is associated with Asp-rich protein, and it is restricted to the second stage mineral. Thus, the composition at each part of the tooth is related to architecture and function., (Copyright © 2011 S. Karger AG, Basel.)

Sea urchins have a set of five continuously growing teeth, each of which has a very complex structure. The mineral phase is calcite of varying Mg content, depending on the location within a tooth. The calcium carbonate is present in amorphous, plate-like and rod-like forms. It has been hypothesized that the mineral deposition is a matrix-mediated process, similar to that in vertebrate bone and tooth, wherein certain macromolecules within the organic matrix of the mineralized tissue play an important role in nucleating and controlling the growth habit of the mineral crystals. It has also been hypothesized that the mineral-related macromolecules involved in urchin teeth might bear a direct evolutionary relationship to those of the vertebrate tooth. These hypotheses are explored here by examining the pattern and nature of the mineral distribution, using microCT of intact teeth, and the nature of the mineral-related matrix proteins. The mineral-related proteins were extracted and fractionated by anion exchange chromatography. The relationship of certain fractions to vertebrate matrix proteins was established by immunoblots using antibodies to vertebrate tooth proteins. The antibodies were then used to localize the proteins within the teeth, by immunocytochemistry and histology with specific staining. The microCT data on mineral density has been correlated with the patterns of cellular migration and mineral deposition within the tooth as it grows. It appears that the mineralization within the different tooth compartments might take place under the influence of different matrix proteins. Further studies are in progress to more completely describe the vertebrate-invertebrate immunologically cross-reactive proteins of the urchin teeth., (Copyright 2002 Wiley-Liss, Inc.)

The article discusses the influence of phosphoproteins of the matrix on the formation and growth of crystals in two systems. The first system is the small, platelike crystals and crystal aggregates of carbonated apatite found in bone, dentin and cementum. The second system is the large, high-axial-ratio rodlike crystal aggregates found in dental enamel.

Recombinant amelogenin gene splice products A+4 and A-4, implanted in the pulp, induce the recruitment, proliferation, and differentiation of reparative cells. Our aim was to investigate the precocious events occurring in the pulp 1 d and 3 d after implantation of agarose beads alone or loaded with A+4 or A-4. Proliferation and cell recruitment towards an odonto/osteogenic phenotype were visualized by detection of the proliferation cell nuclear antigen (PCNA) and RP59. After implantation of beads alone or loaded with A+4, at day 3, pulp cells were moderately immunopositive for osteopontin (OP), whereas labeling was strongly positive upon treatment with A-4. Dentin sialoprotein (DSP) labeling was not detectable. Parallel in vitro studies were carried out on odontoblastic and mesenchymal progenitor cells in order to evaluate the effect of the amelogenin peptides on the expression of a series of marker genes involved in the odontoblastic/osteogenic/chondrogenic differentiation pathways. Altogether, our results suggest that the ‘signaling’ effects of the amelogenin peptides A+4 and A-4 may differ according to the type of target cells, their stage of differentiation, the time of treatment, and the type of amelogenin peptide (A+4 or A-4). [ABSTRACT FROM AUTHOR]

Bone and dentin formation are interesting examples of matrix-mediated mineralization. However, factors and mechanisms regulating this process are poorly understood. Dentin matrix protein 1 (DMP1) is an acidic extracellular matrix protein found in dentin and bone, and based on its amino acid composition it could be postulated to play an important role in mineralization. Our present study examines the ability of recombinant DMP1 to initiate apatite formation in vitro. A 45 Ca-binding assay demonstrated that recombinant DMP1 (rDMP1) possesses calcium-binding ability under physiological conditions. The in vitro nucleation experiments when conducted with rDMP1-coated glass plates demonstrated hydroxyapatite nucleation, while amorphous mineral was deposited on blank or BSA-coated surface. This mineral deposition was found to be 10-fold higher on rDMP1-coated glass surface when compared with the control glass plates. These findings suggest that DMP1 could be considered as a nucleator for apatite deposition in vitro. [ABSTRACT FROM AUTHOR]

Collagens are modular triple-helical proteins that constitute the major structural components of the extracellular matrix of all animals. They occur as diverse superstructures such as fibrils, and networks that play functional roles in cell adhesion, cell differentiation, and structural integrity of organs. The suprastructures are assembled from a family of 43 distinct gene-products called a-chains that are classified as 28 types of collagens. A key self organizing step, common to all collagen types, is trimerization that selects, binds and registers cognate a-chains for assembly of triple-helical protomers that subsequently oligomerize into suprastructures. How a-chains recognize each other is a fundamental question in matrix biology that remains largely unanswered. In this presentation, we review recent findings on the chain-selection mechanism. We infer that terminal noncollagenous domains function as recognition modules in trimerization, and are therefore key determinants of specificity in the assembly of suprastructures. [ABSTRACT FROM AUTHOR]

Abstract: Amelogenin proteins comprise up to 90% of the organic matrix of developing enamel in the vertebrate tooth. Alternative splicing of mouse amelogenin pre-mRNA leads to the production of more than 14 protein isoforms, the functions of which are not totally understood. The smaller splice products, [A + 4] or M73 and [A − 4] or M59, have been shown to act differently as signaling molecules affecting odontogenic and other cell types. The mechanisms of these signaling processes, beginning with receptor identification, are not well understood. Utilizing radiolabeled [A − 4], we show here that 3H[A − 4] binds in a saturable fashion to the cell surface of C2C12 mouse fetal myoblasts at 4°C, and not only binds at the surface but is internalized at 37°C. “Far Western” immunohistochemistry performed on sections of E18 mouse incisors and molars with biotin-labeled [A − 4] as the primary ligand demonstrates [A − 4]-biotin binding to polarizing ameloblasts and odontoblasts, cells of the dental follicle, and along the stratum intermedium. Using [A − 4] affinity column chromatography and [A − 4]-biotin label transfer reaction, we have identified a 95 kDa C2C12 cell surface protein which bound [A − 4]. Utilizing Tandem MS (MS/MS) sequencing, we report the novel finding of the 95 kDa murine transmembrane protein, LAMP-1, originally identified as a lysosomal membrane protein that is also found at the cell surface, as an [A − 4] cell binding protein. [Copyright &y& Elsevier]