In SituHybridization Shows Dmp1 (AG1) to Be a Developmentally Regulated Dentin-Specific Protein Produced by Mature Odontoblasts

Abstract

Acidic phosphorylated proteins are prominent constituents of the extracellular matrix of bone and dentin. It has been postulated that they may have important structural and regulatory roles in the process of tissue mineralization. Studies of a cDNA library, prepared from cells of the rat incisor odontoblast-pulp complex of 3 week old Sprague-Dawley rats, led to the identification of a serine-rich acidic protein, designated AG1, which appeared to be a dentin matrix component. In order to determine which cells of the odontoblast-pulp complex were responsible for the making of AG1, in situ hybridization was carried out using digoxigenin-labeled probes. The full length AG1 cDNA was subcloned into the pBluescript vector, which contains two strong promoters, T3 and T7. The sense and antisense complementary RNA (cRNA) hybridization probes were prepared by in vitro transcription using T3 and T7 polymerases in the presence of 11-dUTP. Incisor sections were obtained from rat embryos at days 16, and 20, and newborns at days 2 and 5. No AG1 mRNA was detected in the embryonic sections, but digoxigenin labeling was evident in odontoblasts secreting mineralizing dentin at postnatal days 2 and 5. Sense probes showed no hybridization. Pulp cells, Meckel's cartilage, and alveolar bone were free of hybridization with the antisense probe. Unexpectedly, a low level of digoxigenin staining was seen in the cytoplasm of secretory ameloblasts, but not in the preameloblasts, stratum intermedium or stellate reticulum of the enamel organ. These data show that AG1 expression is regulated developmentally and is restricted to secretory stage mature odontoblasts.

Specific Amelogenin Gene Splice Products Have Signaling Effects on Cells in Culture and in Implants in Vivo

“…If that is the case, it is also likely that the amelogenin peptides in dentin are probably the specific gene splice products, rather than degradation peptides. An alternative scenario to the diffusion of the peptides into the mantle dentin comparable to the transient, very early expression of dentin matrix proteins in preameloblasts (21,22) is the transient expression of [Aϩ4]/[AϪ4] in the preodontoblasts. A study of that possibility is underway.…”

“…Thus, the cell signaling activities of the amelogenin peptides relate to the formation of mineralized tissues. The second point to be made, based on the demonstration of their mRNAs in the odontoblast pulp complex cells, is that the messages for the amelogenins may be transiently expressed within the odontoblasts during tooth morphogenesis, just as the messages for several supposedly dentin specific proteins are transiently expressed by ameloblasts (21)(22)(23).…”

“…DMP2, and DMP3 (dentin sialophosphoprotein, DSPP). Third, the mRNAs for these three dentin proteins are transiently expressed in mouse molar enamel organs during fetal and immediately post-natal tooth development (21)(22)(23), suggesting that there might be a reciprocal transient expression of particular splice products of the amelogenin gene in developing odontoblasts.…”

The NH2-terminal and COOH-terminal Fragments of Dentin Matrix Protein 1 (DMP1) Localize Differently in the Compartments of Dentin and Growth Plate of Bone

“…Dentin matrix protein 1 (DMP1), a member of the SIBLING family, was discovered by cDNA cloning using a rat odontoblast mRNA library (George et al 1993). DMP1 was originally thought to be found only in dentin, but later it was also detected in bone, cartilage, and non-mineralized tissues such as the brain, pancreas, kidney, and salivary glands (George et al 1995;Begue-Kirn et al 1998;Feng et al 2003;Ogbureke and Fisher 2004.…”

Spatially and Temporally Controlled Biomineralization Is Facilitated by Interaction between Self-Assembled Dentin Matrix Protein 1 and Calcium Phosphate Nuclei in Solution

“…Dentin matrix protein 1 (DMP1) is an acidic noncollagenous phosphoprotein now known to be present in the mineralized matrix of both dentin and bone (10)(11)(12)(13). Recent studies have established DMP1 as a multifunctional protein which plays a crucial role in osteoblast/ ondotoblast differentiation and mineral nucleation events (7,14 and 15).…”