A Study On Dentin Phosphoprotein Expression And Its Regulatory Mechanism On Teeth Development

Collagen and non-collagenous proteins (NCPs) are required for proper biomineralization of dentin. Dentin phosphoprotein (DPP) and dentin sialoprotein (DSP) are two major NCPs, which are different proteins encoded by the same gene, dentin sialophosphoprotein (DSPP) gene. It is believed that DPP could combine specific sites of collagen molecule to promote nucleation and growth of hydroxyapatite crystals and help dentin mineralization. Recently DSPP gene is thought as the causative gene in the pathogenesis of DGI-II. Defects in the DSPP gene were found to be associated with dentinogenesis imperfecta (DGI). Previous studies clearly indicate the importance of DPP in both normal and diseased dentin formation. The gene and amino acid sequencesDepartment of Operative Dentistry and Endodontics FMMUof DPP are well acknowledged in recent years. People begin to investigate the possible role DPP plays and its regulatory mechanism on tooth development and pulp repair after injury.Some scientists have indicated that TGF- 1 could promote cell proliferation and differentiation and matrix secretion, and thus had a lot to do with tooth development, dentin formation and repair. It is suggested that TGF- 1 and BMP2 could induce odontoblasts to differentiate and express DPP and DSP. Another scientitsts also believe that overexpression of active TGF- 1 in odontoblasts of transgenic mouse could significantly down-regulate the expression of DPP, and the DPP expression regulated by TGF- 1 could play a crucial role in dentin development. However, the precise regulation pattern of TGF- 1 on DPP during dentin matrix formation is not known yet.The aim of the present study was to clarify the expression pattern of DPP during teeth development and dentin formation and regulation pattern of TGF- 1 on DPP, to get a better understanding on teeth development, dentin mineralization and dentin repair after injury, and to provide basis for the treatment of DGI and dental pulp injury. The main content and results of the study are presented as following. 1. Expression of DPP during tooth developmentFirst at all, we designed the DPP oligonucleotide probe according to human DPP cDNA sequence on GeneBank. By using in situ hybridization, we detected DPP mRNA expression in human germ and observed the expression pattern at the transcript level. Our results showed that DPP was detected in odontoblasts and preameloblasts at the initial bell stage, and it went on expressing in odontoblasts; the expression of DPP had a temporospacial characteristic; no DPP mRNA was detected in the secretory ameloblasts, neither was it detected at the stage before dentin matrix formation. But weDepartment of Operative Dentistry and Endodontics FMMUcould detect DPP expressionn in the thighbone at the same stages. It tended to suggest that DPP took part in tooth hard tissue formation, DPP was not a dentin-specific protein and shared expression in other tissues.Secondly, we designed the DPP oligonucleotide probe according to rat and mouse DPP cDNA sequence on GeneBank. By using in situ hybridization, we detected DPP mRNA expression in rat tooth germ and teeth in the period of tooth root formation. The results are as follows: DPP mRNA could be detected in the odontoblast at the later bell stage and continued at the stage of tooth formation. It could also be detected in preameloblasts, though weakly positive in ameloblasts, negative in periodontal ligament cells and pulp cells. The results indicated that DPP mRNA expression was present throughout the process of dentin formation, and it might play an important role in dentin formation and possibly regulated the enamel formation as the signaling molecule of ameloblasts differentiation to determine the limit of tooth root and coronal. DPP and DSP expressions were consistent with each other at the transcriptional level.Finally, we detected the dog permanent tooth germ, erupting per...