Molecular mechanism of abnormal dentin calcification in dentinogenesis imperfecta

点击翻译按钮获取中文摘要

The dental disorder "dentinogenesis imperfecta type II (DGI-typeII)" is an autosomal dominant condition that has a prevalence of 1 in 6,000-8,000 individuals. Linkage studies had previously mapped DGI to chromosome 4q13-21, where several candidate genes that encode tooth extracellular matrix proteins (ameloblastin, dentin matrix protein 1, have also been mapped. We focused two genes (ameloblastin and dentin matrix protein 1, Dentin sialophosphoprotein) of them and analyzed them by molecular level.Human ameloblastin (AMBN) gene had not sequenced so far. Therefore, we isolated the full-length human AMBN cDNA.Sequence analysis of the AMBN cDNA revealed an open reading frame of 1341 bp encoding a 447-amino acid protein. Comparison with pig, cattle, rat, and mouse AMBN sequences showed high amino acid sequence similarity and led to the identification of a novel 78 bp (26-amino acid) insert resulting from internal sequence duplication. By DNA analysis of a human genomic clones, the AMBN gene was shown to consist of 13 exons and a novel 78 bp segment which proved to comprise two small exons. There were little polymorphisms of human AMBN gene in Asian populations.Dentin matrix protein 1 (DMP1) is an acidic phosphoprotein expressed in tooth organ and bone. We demonstrated that in chicken, which is not capable of forming tooth, DMP1 mRNA is highly expressed in bone by Northern blot analysis. To clarify the significance of DMP1 expression in bone, the expression of DMP1 mRNA and its protein was examined in chicken and rat. In the chicken and rat, DMP1 mRNA was detected only in bone tissues and was localized in osteocytes but not in osteoblasts. Antiserum was raised against the peptide from rat DMP1, and the localization of DMP1 was examined by immunohistochemistry. These data demonstrate that DMP1 is a bone matrix protein specifically expressed in osteocytes.