Hereditary Dentin Defects

Mineral and matrix changes in Brtl/+ teeth provide insights into mineralization mechanisms

The Brtl/+ mouse is a knock-in model for osteogenesis imperfecta type IV in which a Gly349Cys substitution was introduced into one COL1A1 allele. To gain insight into the changes in dentin structure and mineral composition in these transgenic mice, the objective of this study was to use microcomputed tomography (micro-CT), scanning electron microscopy (SEM), and Fourier transform infrared imaging (FTIRI) to analyze these structures at 2 and 6 months of age. Results, consistent with the dental phenotype in humans with type IV OI, showed decreased molar volume and reduced mineralized tissue volume in the teeth without changes in enamel properties. Increased acid phosphate content was noted at 2 and 6 months by FTIRI, and a trend towards altered collagen structure was noted at 2 but not 6 months in the Brtl/+ teeth. The increase in acid phosphate content suggests a delay in the mineralization process, most likely associated with the defect in the collagen structure. It appears that in the Brtl/+ teeth slow maturation of the mineralized structures allows correction of altered mineral content and acid phosphate distribution.

Inhabitual autosomal recessive form of dentin dysplasia type I in a large consanguineous Moroccan family

Dentin dysplasia is a rare autosomal dominant genetic disease characterized by defect of dentin development and the causal gene is DSPP (Dentin Sialophosphoprotein gene). We report in the present study a large Moroccan family in which dentin dysplasia is clearly transmitted as an autosomal recessive trait. Four males and females family members born from healthy consanguineous parents are carriers of the typical features of the dentin dysplasia type I. Polymorphic markers that span the DSPP gene, allowed us to show that this locus is not linked to dentin dysplasia in our family. We also excluded in our family the SMOC2 gene (Sparc Related Modular Calcium Binding Protein 2) which was recently identified as a causal gene in dentin dysplasia type I with microdontia and misshapen teeth. This family represents, a new description of autosomal recessive pattern of inheritance of dentin dysplasia type I. Moreover, this form of dentin dysplasia is not allelic to the autosomal dominant dentin dysplasia and the genetic cause is to be discovered.

Orthodontic treatment of a patient with dentin dysplasia type I

Dentin dysplasia is a genetic disorder of the teeth that affects the dentin and the pulp. Type I is sometimes called "rootless teeth," because of the loss of organization of the root dentin, which often leads to a shortened root length. The purpose of this article was to present a rare clinical case of a girl who was diagnosed with dentin dysplasia type I when she was referred for an orthodontic evaluation. Panoramic and periapical radiographs showed defective root formation and areas with periapical radiolucencies in several teeth. Her Angle Class I malocclusion was successfully treated, providing esthetic and functional results, without clinical symptoms or signs of periodontitis or odontogenic infections.

miR-145 and miR-143 regulate odontoblast differentiation through targeting Klf4 and Osx genes in a feedback loop

Dentin tissue is derived from mesenchymal cells induced into the odontoblast lineage. The differentiation of odontoblasts is a complex process regulated by several transcriptional factor signaling transduction pathways. However, post-translational regulation of these factors during dentinogenesis remains unclear. To further explore the mechanisms, we investigated the role of microRNA (miRNA) during odontoblast differentiation. We profiled the miRNA expression pattern during mouse odontoblast differentiation using a microarray assay and identified that miR-145 and miR-143 were down-regulated during this process. In situ hybridization verified that the two miRNAs were gradually decreased during mouse odontoblast differentiation. Loss-of-function and gain-of-function experiments revealed that down-regulation of miR-145 and miR-143 could promote odontoblast differentiation and increased Dspp and Dmp1 expression in mouse primary dental pulp cells and vice versa. We found that miR-145 and miR-143 controlled odontoblast differentiation through several mechanisms. First, KLF4 and OSX bind to their motifs in Dspp and Dmp1 gene promoters and up-regulate their transcription thereby inducing odontoblast differentiation. The miR-145 binds to the 3'-UTRs of Klf4 and Osx genes, inhibiting their expression. Second, KLF4 repressed miR-143 transcription by binding to its motifs in miR-143 regulatory regions as detected by ChIP assay and dual luciferase reporter assay. Third, miR-143 regulates odontoblast differentiation in part through miR-145 pathway. Taken together, we for the first time showed that the miR-143 and miR-145 controlled odontoblast differentiation and dentin formation through KLF4 and OSX transcriptional factor signaling pathways.

The rescue of dentin matrix protein 1 (DMP1)-deficient tooth defects by the transgenic expression of dentin sialophosphoprotein (DSPP) indicates that DSPP is a downstream effector molecule of DMP1 in dentinogenesis

Dentin matrix protein 1 (DMP1) and dentin sialophosphoprotein (DSPP) are essential for the formation of dentin. Previous in vitro studies have indicated that DMP1 might regulate the expression of DSPP during dentinogenesis. To examine whether DMP1 controls dentinogenesis through the regulation of DSPP in vivo, we cross-bred transgenic mice expressing normal DSPP driven by a 3.6-kb rat Col1a1 promoter with Dmp1 KO mice to generate mice expressing the DSPP transgene in the Dmp1 KO genetic background (referred to as "Dmp1 KO/DSPP Tg mice"). We used morphological, histological, and biochemical techniques to characterize the dentin and alveolar bone of Dmp1 KO/DSPP Tg mice compared with Dmp1 KO and wild-type mice. Our analyses showed that the expression of endogenous DSPP was remarkably reduced in the Dmp1 KO mice. Furthermore, the transgenic expression of DSPP rescued the tooth and alveolar bone defects of the Dmp1 KO mice. In addition, our in vitro analyses showed that DMP1 and its 57-kDa C-terminal fragment significantly up-regulated the Dspp promoter activities in a mesenchymal cell line. In contrast, the expression of DMP1 was not altered in the Dspp KO mice. These results provide strong evidence that DSPP is a downstream effector molecule that mediates the roles of DMP1 in dentinogenesis.

Gene evolution and functions of extracellular matrix proteins in teeth

The extracellular matrix (ECM) not only provides physical support for tissues, but it is also critical for tissue development, homeostasis and disease. Over 300 ECM molecules have been defined as comprising the "core matrisome" in mammals through the analysis of whole genome sequences. During tooth development, the structure and functions of the ECM dynamically change. In the early stages, basement membranes (BMs) separate two cell layers of the dental epithelium and the mesenchyme. Later in the differentiation stages, the BM layer is replaced with the enamel matrix and the dentin matrix, which are secreted by ameloblasts and odontoblasts, respectively. The enamel matrix genes and the dentin matrix genes are each clustered in two closed regions located on human chromosome 4 (mouse chromosome 5), except for the gene coded for amelogenin, the major enamel matrix protein, which is located on the sex chromosomes. These genes for enamel and dentin matrix proteins are derived from a common ancestral gene, but as a result of evolution, they diverged in terms of their specific functions. These matrix proteins play important roles in cell adhesion, polarity, and differentiation and mineralization of enamel and dentin matrices. Mutations of these genes cause diseases such as odontogenesis imperfect (OI) and amelogenesis imperfect (AI). In this review, we discuss the recently defined terms matrisome and matrixome for ECMs, as well as focus on genes and functions of enamel and dentin matrix proteins.

Disruption of Wnt/β-catenin signaling in odontoblasts and cementoblasts arrests tooth root development in postnatal mouse teeth

Tooth development undergoes a series of complex reciprocal interactions between dental epithelium and the underlying mesenchymal cells. Compared with the study in tooth crown formation, little is known about the molecular mechanism underlying the development of tooth roots. In the present study, we conditionally knock out β-catenin gene (Ctnnb1) within developing odontoblasts and cementoblasts during the development of tooth roots, and observed rootless molars as well as incomplete incisors. Histological analyses revealed intact structure of molar crown and labial side of incisor, however, as for the molar roots and the lingual portion of incisor, the formation of dentin and periodontal tissues were greatly hampered. In situ hybridization experiments using probes of odontoblastic marker genes collagen type I, alpha 1 (Col1a1), osteocalcin (OC) and dentin sialophosphoprotein (Dspp) manifested striking undifferentiation of root odontoblasts in which Ctnnb1 was eliminated. Bromodeoxyuridine (BrdU) labeling and proliferating cell nuclear antigen (PCNA) immunohistochemical experiments also showed retarded proliferation of pre-odontoblasts in mutant mice. However, cell apoptosis was not affected. Additionally, a disrupted formation of cementoblasts, suggested by the absence of transcripts of bone sialoprotein (Bsp) in follicle mesenchyme, was also evident in mutant mice. Our study provides strong in vivo evidence to confirm that Wnt/β-catenin signaling is functionally significant to root odontogenesis and cementogenesis during the tooth root development.

Full-mouth rehabilitation for a patient with dentinogenesis imperfecta: a clinical report

Dentinogenesis imperfecta (DI) is a genetic disorder affecting the structural integrity of the dentin that can result in weakened dentin. The affected teeth, especially posterior teeth, often need to be extracted due to severe wear or fracture. This frequently yields a loss of posterior occlusion and occlusal vertical dimension. Besides wear and fracture, anterior teeth often have an unesthetic appearance because of discoloration. Current treatments of choice, including composite bonding restorations and, more recently, all-ceramic restorations, are typically suggested to preserve the remaining teeth and tooth structure. However, there are a limited number of studies on dental implants in patients with DI. The effectiveness of dentin bonding and dental implants in patients with DI is not known. This clinical report describes a 32-year-old Asian woman with DI who underwent full-mouth rehabilitation. The posterior occlusion, mostly in the molar areas, was restored with dental implants and ceramometal restorations. The anterior teeth and premolars were restored with bonded lithium disilicate glass-ceramic pressed veneers and crowns made with computer-aided design/computer-aided manufacturing. This case demonstrates that restoring functional occlusion and esthetics for a patient with DI can be completed successfully using contemporary implant therapy and adhesive dentistry.

A DSPP mutation causing dentinogenesis imperfecta and characterization of the mutational effect

Mutations in the DSPP gene have been identified in nonsyndromic hereditary dentin defects, but the genotype-phenotype correlations are not fully understood. Recently, it has been demonstrated that the mutations of DSPP affecting the IPV leader sequence result in mutant DSPP retention in rough endoplasmic reticulum (ER). In this study, we identified a Korean family with dentinogenesis imperfecta type III. To identify the disease causing mutation in this family, we performed mutational analysis based on candidate gene sequencing. Exons and exon-intron boundaries of DSPP gene were sequenced, and the effects of the identified mutation on the pre-mRNA splicing and protein secretion were investigated. Candidate gene sequencing revealed a mutation (c.50C > T, p.P17L) in exon 2 of the DSPP gene. The splicing assay showed that the mutation did not influence pre-mRNA splicing. However, the mutation interfered with protein secretion and resulted in the mutant protein remaining largely in the ER. These results suggest that the mutation affects ER-to-Golgi apparatus export and results in the reduction of secreted DSPP and ER overload. This may induce cell stress and damage processing and/or transport of dentin matrix proteins or other critical proteins.

Transcriptional repression of the Dspp gene leads to dentinogenesis imperfecta phenotype in Col1a1-Trps1 transgenic mice

Dentinogenesis imperfecta (DGI) is a hereditary defect of dentin, a calcified tissue that is the most abundant component of teeth. Most commonly, DGI is manifested as a part of osteogenesis imperfecta (OI) or the phenotype is restricted to dental findings only. In the latter case, DGI is caused by mutations in the DSPP gene, which codes for dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). Although these two proteins together constitute the majority of noncollagenous proteins of the dentin, little is known about their transcriptional regulation. Here we demonstrate that mice overexpressing the Trps1 transcription factor (Col1a1-Trps1 mice) in dentin-producing cells, odontoblasts, present with severe defects of dentin formation that resemble DGI. Combined micro-computed tomography (µCT) and histological analyses revealed tooth fragility due to severe hypomineralization of dentin and a diminished dentin layer with irregular mineralization in Col1a1-Trps1 mice. Biochemical analyses of noncollagenous dentin matrix proteins demonstrated decreased levels of both DSP and DPP proteins in Col1a1-Trps1 mice. On the molecular level, we demonstrated that sustained high levels of Trps1 in odontoblasts lead to dramatic decrease of Dspp expression as a result of direct inhibition of the Dspp promoter by Trps1. During tooth development Trps1 is highly expressed in preodontoblasts, but in mature odontoblasts secreting matrix its expression significantly decreases, which suggests a Trps1 role in odontoblast development. In these studies we identified Trps1 as a potent inhibitor of Dspp expression and the subsequent mineralization of dentin. Thus, we provide novel insights into mechanisms of transcriptional dysregulation that leads to DGI.

Proteolytic processing of dentin sialophosphoprotein (DSPP) is essential to dentinogenesis

DSPP, which plays a crucial role in dentin formation, is processed into the NH(2)-terminal and COOH-terminal fragments. We believe that the proteolytic processing of DSPP is an essential activation step for its biological function in biomineralization. We tested this hypothesis by analyzing transgenic mice expressing the mutant D452A-DSPP in the Dspp-knock-out (Dspp-KO) background (referred to as "Dspp-KO/D452A-Tg" mice). We employed multipronged approaches to characterize the dentin of the Dspp-KO/D452A-Tg mice, in comparison with Dspp-KO mice and mice expressing the normal DSPP transgene in the Dspp-KO background (named Dspp-KO/normal-Tg mice). Our analyses showed that 90% of the D452A-DSPP in the dentin of Dspp-KO/D452A-Tg mice was not cleaved, indicating that D452A substitution effectively blocked the proteolytic processing of DSPP in vivo. While the expression of the normal DSPP fully rescued the dentin defects of the Dspp-KO mice, expressing the D452A-DSPP failed to do so. These results indicate that the proteolytic processing of DSPP is an activation step essential to its biological function in dentinogenesis.

Hypophosphatasia-associated deficiencies in mineralization and gene expression in cultured dental pulp cells obtained from human teeth

INTRODUCTION

Mutations in the gene ALPL in hypophosphatasia (HPP) reduce the function of tissue nonspecific alkaline phosphatase, and the resulting increase in pyrophosphate (PP(i)) contributes to bone and tooth mineralization defects by inhibiting physiologic calcium-phosphate (P(i)) precipitation. Although periodontal phenotypes are well documented, pulp/dentin abnormalities have been suggested in the clinical literature although reports are variable and underlying mechanisms remains unclear. In vitro analyses were used to identify mechanisms involved in HPP-associated pulp/dentin phenotypes.

METHODS

Primary pulp cells cultured from HPP subjects were established to assay alkaline phosphatase (ALP) activity, mineralization, and gene expression compared with cells from healthy controls. Exogenous P(i) was provided to the correct P(i)/PP(i) ratio in cell culture.

RESULTS

HPP cells exhibited significantly reduced ALP activity (by 50%) and mineral nodule formation (by 60%) compared with the controls. The expression of PP(i) regulatory genes was altered in HPP pulp cells, including reduction in the progressive ankylosis gene (ANKH) and increased ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). Odontoblast marker gene expression was disrupted in HPP cells, including reduced osteopontin (OPN), dentin matrix protein 1 (DMP1), dentin sialophosphoprotein (DSPP), and matrix extracellular phosphoprotein (MEPE). The addition of P(i) provided a corrective measure for mineralization and partially rescued the expression of some genes although cells retained altered messenger RNA levels for PP(i)-associated genes.

CONCLUSIONS

These studies suggest that under HPP conditions pulp cells have the compromised ability to mineralize and feature a disrupted odontoblast profile, providing a first step toward understanding the molecular mechanisms for dentin phenotypes observed in HPP.

Immunohistochemical localization of the NH(2)-terminal and COOH-terminal fragments of dentin sialoprotein in mouse teeth

Dentin sialoprotein (DSP) is a major non-collagenous protein in dentin. Mutation studies in human, along with gene knockout and transgenic experiments in mice, have confirmed the critical role of DSP for dentin formation. Our previous study reported that DSP is processed into fragments in mouse odontoblast-like cells. In order to gain insights into the function of DSP fragments, we further evaluated the expression pattern of DSP in the mouse odontoblast-like cells using immunohistochemistry and western blot assay with antibodies against the NH(2)-terminal and COOH-terminal regions of DSP. Then, the distribution profiles of the DSP NH(2)-terminal and COOH-terminal fragments and osteopontin (OPN) were investigated in mouse teeth at different ages by immunohistochemistry. In the odontoblast-like cells, multiple low molecular weight DSP fragments were detected, suggesting that part of the DSP protein was processed in the odontoblast-like cells. In mouse first lower molars, immunoreactions for anti-DSP-NH(2) antibody were intense in the predentin matrix but weak in mineralized dentin; in contrast, for anti-DSP-COOH antibody, strong immunoreactions were found in mineralized dentin, in particular dentinal tubules but weak in predentin. Therefore, DSP NH(2)-terminal and COOH-terminal fragments from odontoblasts were secreted to different parts of teeth, suggesting that they may play distinct roles in dentinogenesis. Meanwhile, both DSP antibodies showed weak staining in reactionary dentin (RD), whereas osteopontin (OPN) was clearly positive in RD. Therefore, DSP may be less crucial for RD formation than OPN.

Dentin sialophosphoprotein and dentin matrix protein-1: Two highly phosphorylated proteins in mineralized tissues

Dentin sialophosphoprotein (DSPP) and dentin matrix protein-1 (DMP-1) are highly phosphorylated proteins that belong to the family of small integrin-binding ligand N-linked glycoproteins (SIBLINGs), and are essential for proper development of hard tissues such as teeth and bones. In order to understand how they contribute to tissue organization, DSPP and DMP-1 have been analyzed for over a decade using both in vivo and in vitro techniques. Among the five SIBLINGs, the DSPP and DMP-1 genes are located next to each other and their gene and protein structures are most similar. In this review we examine the phenotypes of the genetically engineered mouse models of DSPP and DMP-1 and also introduce complementary in vitro studies into the molecular mechanisms underlying these phenotypes. DSPP affects the mineralization of dentin more profoundly than DMP-1. In contrast, DMP-1 significantly affects bone mineralization and importantly controls serum phosphate levels by regulating serum FGF-23 levels, whereas DSPP does not show any systemic effects. DMP-1 activates integrin signalling and is endocytosed into the cytoplasm whereupon it is translocated to the nucleus. In contrast, DSPP only activates integrin-dependent signalling. Thus it is now clear that both DSPP and DMP-1 contribute to hard tissue mineralization and the tissues affected by each are different presumably as a result of their different expression levels. In fact, in comparison with DMP-1, the functional analysis of cell signalling by DSPP remains relatively unexplored.

Hereditary dentine diseases resulting from mutations in DSPP gene

OBJECTIVES

This review groups the newest results of molecular analyses of DSPP gene for patients diagnosed either with dentinogenesis imperfecta type II/III or dentine dysplasia and tries to link the phenotypes with specific mutations in the DSPP gene.

DATA

The review includes biochemical data introducing a specificity of DSPP protein which justifies it as a critical factor for dentine mineralization and maturation. The majority of the review analyzes mutations in the DSPP gene which result in phenotypes of dentinogenesis imperfecta types II or/and III or dentine dysplasia.

SOURCES

An electronic search was conducted in the databases of Pub Med and supplemented by manual study of relevant references.

STUDY SELECTION

52 out of 108 references were finally selected for the review based on the novelty and/or originality of data.

CONCLUSION

Hereditary dentine disorders dentinogenesis imperfecta type II/III and dentine dysplasia are currently proposed to be one disease with distinct clinical manifestations reflecting various mutations in the same DSPP gene. For years both disorders were linked exclusively to mutations in the DSP code but a growing number of papers describe mutations which manifest a similar phenotype but are localized in the strongly repetitive sequence of the 3' terminus of the DSPP which codes DPP protein. Our search suggests that the localization of mutation in the sequence of the DSPP gene might result in a different phenotype due to the diverse cellular fate of the mutated protein. Thus comprehensive research on the cellular fate and processing of both normal and mutated DSPP is still required.

Mutation identification of the DSPP in a Chinese family with DGI-II and an up-to-date bioinformatic analysis

In this study, through linkage analysis of a four-generation Chinese family with multiple members afflicted with DGI (type II), we identified a novel missense mutation in DSPP. The mutation was located in exon 2 at the second nucleotide position of the last codon and resulted in a substitution of a proline with a leucine residue (c.50C>T, p.P17L, g.50C>T). To assess the potential effects of this novel mutation, we utilized various bioinformatics analysis programs. The results indicate that the mutation likely affects protein cleavage/trafficking. We also analyzed previously reported mutations of DSPP. In summary, our finding supports that the genomic sequence that corresponds to the P17 residue of DSPP is a mutational hotspot and P17 may be critical for the function of DSPP.

Enamel malformations associated with a defined dentin sialophosphoprotein mutation in two families

Dentin sialophosphoprotein (DSPP) mutations cause dentin dysplasia type II (DD-II) and dentinogenesis imperfecta types II and III (DGI-II and DGI-III, respectively). We identified two kindreds with DGI-II who exhibited vertical bands of hypoplastic enamel. Both families had a previously reported DSPP mutation that segregated with the disease phenotype. Oral photographs and dental radiographs of four affected and one unaffected participant in one family and of the proband in the second family were used to document the dental phenotypes. We aligned the 33 unique allelic DSPP sequences showing variable patterns of insertions and deletions (indels), generated a merged dentin phosphoprotein (DPP) sequence that includes sequences from all DSPP length haplotypes, and mapped the known DSPP mutations in this context. Analyses of the DSPP sequence changes and their probable effects on protein expression, as well as published findings of the dental phenotype in Dspp null mice, support the hypothesis that all DSPP mutations cause pathology through dominant-negative effects. Noting that Dspp is transiently expressed by mouse pre-ameloblasts during formation of the dentino-enamel junction, we hypothesize that DSPP dominant-negative effects potentially cause cellular pathology in pre-ameloblasts that, in turn, causes enamel defects. We conclude that enamel defects can be part of the dental phenotype caused by DSPP mutations, although DSPP is not critical for dental enamel formation.

Expression of dentine sialophosphoprotein in mouse nasal cartilage

OBJECTIVE

Dentine sialophosphoprotein (DSPP) was initially thought to be unique for dentine formation during tooth development, whilst recent reports have shown a much broader expression pattern such as in bone, periodontium and inner ear. Our goal was to explore its expression and potential impact during early nasal cartilage formation in comparison with tooth development.

STUDY DESIGN

We investigated DSPP expression in the nasal cartilage by immunohistochemistry and in situ hybridisation. We also cloned a 719bp partial DSPP cDNA from nasal cartilage and analysed its homology to the published mouse DSPP cDNA sequence. In addition, quantitative RT-PCR was undertaken to compare the expression pattern of DSPP in nasal cartilage and tooth germs during embryonic development.

RESULTS

The expression of DSPP in mouse nasal chondrocytes was detected using in situ hybridisation and immunohistochemical staining. The quantitative RT-PCR data showed that expression levels of DSPP in nasal cartilage are similar to that of tooth: low at E18, and increased during development with the peak level at P3. Furthermore, DSPP levels in nasal cartilage are lower than tooth but higher than bone.

CONCLUSION

DSPP is expressed in nasal cartilage, and a similar temporal expression pattern in cartilage and tooth indicates the potential importance of DSPP during development.

Novel dentin phosphoprotein frameshift mutations in dentinogenesis imperfecta type II

The dentin sialophosphoprotein (DSPP) gene encodes the most abundant non-collagenous protein in tooth dentin and DSPP protein is cleaved into several segments including the highly phosphorylated dentin phosphoprotein (DPP). Mutations in the DSPP gene have been solely related to non-syndromic form of hereditary dentin defects. We recruited three Korean families with dentinogenesis imperfecta (DGI) type II and sequenced the exons and exon-intron boundaries of the DSPP gene based on the candidate gene approach. Direct sequencing of PCR products and allele-specific cloning of the highly repetitive exon 5 revealed novel single base pair (bp) deletional mutations (c.2688delT and c.3560delG) introducing hydrophobic amino acids in the hydrophilic repeat domain of the DPP coding region. All affected members of the three families showed exceptionally rapid pulp chambers obliteration, even before tooth eruption. Individuals with the c.3560delG mutation showed only mild, yellowish tooth discoloration, in contrast to the affected individuals from two families with c.2688delT mutation. We believe that these results will help us to understand the molecular pathogenesis of DGI type II as well as the normal process of dentin biomineralization.

Frameshift mutations in dentin phosphoprotein and dependence of dentin disease phenotype on mutation location

We describe results from a mutational analysis of the region of the dentin sialophosphoprotein (DSPP) gene encoding dentin phosphoprotein (DPP) in 12 families with dominantly inherited dentin diseases. In eight families (five mutations in the N-terminal third of DPP), the clinical and radiologic features were uniform and compatible with dentin dysplasia type II (DD-II) with major clinical signs in the deciduous dentition. In the other families (four mutations in the more C-terminal part), the permanent teeth also were affected, and the diseases could be classified as variants of dentinogenesis imperfecta. Attrition was not prominent, but periapical infections were common. Discoloring with varying intensity was evident, and pulps and root canals were obliterated in the permanent dentition. All mutations caused a frameshift that replaced the Ser-Ser-Asx repeat by a code for a hydrophobic downstream sequence of approximately original length. We conclude that frameshift mutations in DSPP explain a significant part of dentin diseases. Furthermore, we propose that the location of the mutation is reflected in the phenotypic features as a gradient from DD-II to more severe disease that does not conform to the classic definitions of DI-II.

Porcine dentin sialoprotein glycosylation and glycosaminoglycan attachments

Background

Dentin sialophosphoprotein (Dspp) is a multidomain, secreted protein that is critical for the formation of tooth dentin. Mutations in DSPP cause inherited dentin defects categorized as dentin dysplasia type II and dentinogenesis imperfecta type II and type III. Dentin sialoprotein (Dsp), the N-terminal domain of dentin sialophosphoprotein (Dspp), is a highly glycosylated proteoglycan, but little is known about the number, character, and attachment sites of its carbohydrate moieties.

Results

To identify its carbohydrate attachment sites we isolated Dsp from developing porcine molars and digested it with endoproteinase Glu-C or pronase, fractionated the digestion products, identified fractions containing glycosylated peptides using a phenol sulfuric acid assay, and characterized the glycopeptides by N-terminal sequencing, amino acid analyses, or LC/MSMS. To determine the average number of sialic acid attachments per N-glycosylation, we digested Dsp with glycopeptidase A, labeled the released N-glycosylations with 2-aminobenzoic acid, and quantified the moles of released glycosylations by comparison to labeled standards of known concentration. Sialic acid was released by sialidase digestion and quantified by measuring β-NADH reduction of pyruvic acid, which was generated stoichiometrically from sialic acid by aldolase. To determine its forms, sialic acid released by sialidase digestion was labeled with 1,2-diamino-4,5-methyleneoxybenzene (DMB) and compared to a DMB-labeled sialic acid reference panel by RP-HPLC. To determine the composition of Dsp glycosaminoglycan (GAG) attachments, we digested Dsp with chondroitinase ABC and compared the chromotagraphic profiles of the released disaccharides to commercial standards. N-glycosylations were identified at Asn³⁷, Asn⁷⁷, Asn¹³⁶, Asn¹⁵⁵, Asn¹⁶¹, and Asn¹⁷⁶. Dsp averages one sialic acid per N-glycosylation, which is always in the form of N-acetylneuraminic acid. O-glycosylations were tentatively assigned at Thr²⁰⁰, Thr²¹⁶ and Thr³¹⁶. Porcine Dsp GAG attachments were found at Ser²³⁸ and Ser²⁵⁰ and were comprised of chondroitin 6-sulfate and chondroitin 4-sulfate in a ratio of 7 to 3, respectively.

Conclusions

The distribution of porcine Dsp posttranslational modifications indicate that porcine Dsp has an N-terminal domain with at least six N-glycosylations and a C-terminal domain with two GAG attachments and at least two O-glycosylations.

Comparative analysis of in vitro osteo/odontogenic differentiation potential of human dental pulp stem cells (DPSCs) and stem cells from the apical papilla (SCAP)

OBJECTIVE

The aim of this study was to compare the in vitro osteo/odontogenic differentiation potential of mesenchymal stem cells (MSCs) derived from the dental pulp (dental pulp stem cells - DPSCs) or the apical papilla (stem cells from the apical papilla - SCAP) of permanent developing teeth.

DESIGN

DPSCs and SCAP cultures were established from impacted third molars of young healthy donors at the stage of root development. Cultures were analysed for stem cell markers, including STRO-1, CD146, CD34 and CD45 using flow cytometry. Cells were then induced for osteo/odontogenic differentiation by media containing dexamethasone, KH(2)PO(4) and β-glycerophosphate. Cultures were analysed for morphology, growth characteristics, mineralization potential (Alizarin Red method) and differentiation markers (dentine sialophosphoprotein-DSPP, bone sialoprotein-BSP, osteocalcin-OCN, alkaline phosphatase-ALP), using immunocytochemistry and reverse transcriptase-polymerase chain reaction.

RESULTS

All DPSCs and SCAP cultures were positive for STRO-1, CD146 and CD34, in percentages varying according to cell type and donor, but negative for CD45. Both types of MSCs displayed an active potential for cellular migration, organization and mineralization, producing 3D mineralized structures. These structures progressively expressed differentiation markers, including DSPP, BSP, OCN, ALP, having the characteristics of osteodentin. SCAP, however, showed a significantly higher proliferation rate and mineralization potential, which might be of significance for their use in bone/dental tissue engineering.

CONCLUSIONS

This study provides evidence that different types of dental MSCs can be used in tissue engineering/regeneration protocols as an approachable stem cell source for osteo/odontogenic differentiation and biomineralization that could be further applied for stem cell-based clinical therapies.

Astacin proteases cleave dentin sialophosphoprotein (Dspp) to generate dentin phosphoprotein (Dpp)

Dentin sialophosphoprotein (Dspp) is critical for proper dentin biomineralization because genetic defects in DSPP cause dentin dysplasia type II and dentinogenesis imperfecta types II and III. Dspp is processed by proteases into smaller subunits; the initial cleavage releases dentin phosphoprotein (Dpp). We incubated fluorescence resonance energy transfer (FRET) peptides containing the amino acid context of the Dpp cleavage site (YEFDGKSMQGDDPN, designated Dspp-FRET) or a mutant version of that context (YEFDGKSIEGDDPN, designated mutDspp-FRET) with BMP-1, MEP1A, MEP1B, MMP-2, MMP-8, MMP-9, MT1-MMP, MT3-MMP, Klk4, MMP-20, plasmin, or porcine Dpp and characterized the peptide cleavage products. Only BMP-1, MEP1A, and MEP1B cleaved Dspp-FRET at the G-D peptide bond that releases Dpp from Dspp in vivo. We isolated Dspp proteoglycan from dentin power and incubated it with the three enzymes that cleaved Dspp-FRET at the G-D bond. In each case, the released Dpp domain was isolated, and its N-terminus was characterized by Edman degradation. BMP-1 and MEP1A both cleaved native Dspp at the correct site to generate Dpp, making both these enzymes prime candidates for the protease that cleaves Dspp in vivo. MEP1B was able to degrade Dpp when the Dpp was at sufficiently high concentration to deplete free calcium ion concentration. Immunohistochemistry of developing porcine molars demonstrated that astacins are expressed by odontoblasts, a result that is consistent with RT-PCR analyses. We conclude that during odontogenesis, astacins in the predentin matrix cleave Dspp before the DDPN sequence at the N-terminus of Dpp to release Dpp from the parent Dspp protein.

Case report: Clinical, histological and ultrastructural characterization of type II dentinogenesis imperfecta

BACKGROUND

Type II dentinogenesis imperfecta (DGIII) is an autosomal dominant dental development anomaly that affects both the primary and permanent dentition.

CASE REPORT

This case report describes the clinical, radiographic and morphological characteristics of the teeth of a seven-year-old child with DGI-II determined by optical microscopy and scanning electron microscopy.

TREATMENT

This consisted of extraction of the primary teeth with periapical lesions due to the advanced state of tooth resorption. Aesthetic restorations were performed on the mandibular anterior teeth and occlusal fissure sealants were applied to erupting teeth. A removable partial upper denture was made in order to return anterior aesthetic function and to aid mastication and speech.

FOLLOW UP

The child was examined at 3 month intervals. Over the following 3 years the prosthesis was replaced due to facial growth and fluoride was applied at each follow-up visit to all teeth. The patient remains in follow up and management.

CONCLUSION

Individuals with DGI-II must not neglect their dental health. Early diagnosis, professional advice and treatment with periodic follow-up can help improve the quality of life of such patients.

Molecular determinants of extracellular matrix mineralization in bone and blood vessels

PURPOSE OF REVIEW

Mineralization imparts important biomechanical and other functional properties to bones and teeth. Ectopic pathologic mineralization, however, occurring in soft tissues such as blood vessels, kidneys, articular cartilage and also in body fluids, including urine and synovial fluid, is generally debilitating, often painful and typically is destructive of compromised tissue. Here we review new findings on direct molecular determinants of mineralization operating locally at the level of the extracellular matrix, with a focus on bone and blood vessels.

RECENT FINDINGS

Accumulating evidence indicates important key roles for secreted noncollagenous proteins in regulating mineralization, wherein they also contribute structurally to the scaffolding properties of the extracellular matrix. Mineral-binding proteins contain conserved acidic peptide domains (often highly phosphorylated), which bind strongly to calcium within the apatitic mineral phase of bone and calcified blood vessels to regulate crystal growth. Other recent work has underscored the importance of the small-molecule mineralization inhibitor pyrophosphate in inhibiting tissue mineralization - an inhibition released through its enzymatic cleavage by tissue-nonspecific alkaline phosphatase. Recent findings on mechanisms involved in matrix vesicle-mediated mineralization are also discussed.

SUMMARY

Mechanistic details are emerging that describe a scenario wherein the combined actions of mineral-binding noncollagenous matrix peptides/proteins within a scaffolding of collagen (and also elastin in blood vessels), phosphatases and matrix vesicles all contribute importantly to promoting or limiting mineralization.

Case report: Rehabilitation of a child with dentinogenesis imperfecta and congenitally missing lateral incisors

BACKGROUND

Dentinogenesis imperfecta is one of the most common hereditary disorders of dentine formation. Opalescent teeth composed of irregularly formed and undemineralised dentine that obliterates pulp chambers and root canals characterize it. Complete-coverage crowns are usually the preferred restoration for patients with this condition.

CASE REPORT

A 9 year-old girl presented with dentinogenesis imperfecta, congenitally missing maxillary lateral incisors and maxillary right permanent second molar retention.

TREATMENT

The treatment comprised an initial approach to allow the correct eruption of the retained second molar. The use of low-fusion metal ceramic restorations comprised a second stage to improve the aesthetic appearance and decrease the risk of overload on teeth with limited value.

FOLLOW-UP

The patient has been recalled regularly and at the last visit, 10 years after initial prosthetic treatment, no problems or signs of complications have occurred. The patient is now aged 25 years and is still satisfied with the prosthetic rehabilitation.

CONCLUSION

This case illustrates the need for appropriate and timely restorative treatment to prevent deterioration of the dentition. This case will also demonstrate that low-fusion metal ceramic restoration is a viable esthetic treatment option for today's patients.

Immortalized mouse floxed Bmp2 dental papilla mesenchymal cell lines preserve odontoblastic phenotype and respond to BMP2

Bone morphogenetic protein 2 (Bmp2) is essential for odontogensis and dentin mineralization. Generation of floxed Bmp2 dental mesenchymal cell lines is a valuable application for studying the effects of Bmp2 on dental mesenchymal cell differentiation and its signaling pathways during dentinogenesis. Limitation of the primary culture of dental mesenchymal cells has led to the development of cell lines that serve as good surrogate models for the study of dental mesenchymal cell differentiation into odontoblasts and mineralization. In this study, we established and characterized immortalized mouse floxed Bmp2 dental papilla mesenchymal cell lines, which were isolated from 1st mouse mandibular molars at postnatal day 1 and immortalized with pSV40 and clonally selected. These transfected cell lines were characterized by RT-PCR, immunohistochemistry, and analyzed for alkaline phosphatase activity and mineralization nodule formation. One of these immortalized cell lines, iBmp2-dp, displayed a higher proliferation rate, but retained the genotypic and phenotypic characteristics similar to primary cells as determined by expression of tooth-specific markers as well as demonstrated the ability to differentiate and form mineralized nodules. In addition, iBmp2-dp cells were inducible and responded to BMP2 stimulation. Thus, we for the first time described the establishment of an immortalized mouse floxed Bmp2 dental papilla mesenchyma cell line that might be used for studying the mechanisms of dental cell differentiation and dentin mineralization mediated by Bmp2 and other growth factor signaling pathways.

Effect of HIP/ribosomal protein L29 deficiency on mineral properties of murine bones and teeth

Mice lacking HIP/RPL29, a component of the ribosomal machinery, display increased bone fragility. To understand the effect of sub-efficient protein synthetic rates on mineralized tissue quality, we performed dynamic and static histomorphometry and examined the mineral properties of both bones and teeth in HIP/RPL29 knock-out mice using Fourier transform infrared imaging (FTIRI). While loss of HIP/RPL29 consistently reduced total bone size, decreased mineral apposition rates were not significant, indicating that short stature is not primarily due to impaired osteoblast function. Interestingly, our microspectroscopic studies showed that a significant decrease in collagen crosslinking during maturation of HIP/RPL29-null bone precedes an overall enhancement in the relative extent of mineralization of both trabecular and cortical adult bones. This report provides strong genetic evidence that ribosomal insufficiency induces subtle organic matrix deficiencies which elevates calcification. Consistent with the HIP/RPL29-null bone phenotype, HIP/RPL29-deficient teeth also showed reduced geometric properties accompanied with relative increased mineral densities of both dentin and enamel. Increased mineralization associated with enhanced tissue fragility related to imperfection in organic phase microstructure evokes defects seen in matrix protein-related bone and tooth diseases. Thus, HIP/RPL29 mice constitute a new genetic model for studying the contribution of global protein synthesis in the establishment of organic and inorganic phases in mineral tissues.

De novo mutation in the DSPP gene associated with dentinogenesis imperfecta type II in a Japanese family

Dentinogenesis imperfecta (DGI) type II is one of the most common dominantly inherited dentin defects, in which both the primary and permanent teeth are affected. Here, we report a Japanese family with autosomal-dominant DGI type II, including both molecular genetic defects and pathogenesis with histological analysis. Mutation analysis revealed a mutation (c.53T>A, p.V18D, g.1192T>A) involving the second nucleotide of the first codon within exon 3 of the dentin sialophosphoprotein (DSPP) gene. This mutation has previously been reported in a Korean family. Thus far, 24 allelic DSPP mutations have been reported, and this is the seventh mutation involving the DSPP V18 residue. Among those, only one other was shown to be caused by a de novo mutation, and that mutation also affected the V18 amino acid residue. The DSPP V18 residue is highly conserved among other mammalian species. These findings thus suggest that the V18 amino acid might be a sensitive mutational hot spot, playing a critical role in the pathogenesis of DGI.

Dentinogenesis imperfecta in children with osteogenesis imperfecta: a clinical and ultrastructural study

AIM

The aim of this study was to assess the correlation between osteogenesis imperfecta (OI) and dentinogenesis imperfecta (DI) from both a clinical and histological point of view, particularly clarifying the structural and ultrastructural dentine changes.

DESIGN

Sixteen children (6-12 years aged) with diagnosis of OI were examined for dental alterations referable to DI. For each patient, the OI type (I, III, or IV) was recorded. Extracted or normally exfoliated primary teeth were subjected to a histological examination (to both optical microscopy and confocal laser-scanning microscopy).

RESULTS

A total of ten patients had abnormal discolourations referable to DI: four patients were affected by OI type I, three patients by OI type III, and three patients by OI type IV. The discolourations, yellow/brown or opalescent grey, could not be related to the different types of OI. Histological exam of primary teeth showed severe pathological change in the dentin, structured into four different layers. A collagen defect due to odontoblast dysfunction was theorized to be on the base of the histological changes.

CONCLUSIONS

There is no correlation between the type of OI and the type of discolouration. The underlying dentinal defect seems to be related to an odontoblast dysfunction.

A novel DSPP mutation causes dentinogenesis imperfecta type II in a large Mongolian family

BACKGROUND

Several studies have shown that the clinical phenotypes of dentinogenesis imperfecta type II (DGI-II) may be caused by mutations in dentin sialophosphoprotein (DSPP). However, no previous studies have documented the clinical phenotype and genetic basis of DGI-II in a Mongolian family from China.

METHODS

We identified a large five-generation Mongolian family from China with DGI-II, comprising 64 living family members of whom 22 were affected. Linkage analysis of five polymorphic markers flanking DSPP gene was used to genotype the families and to construct the haplotypes of these families. All five DSPP exons including the intron-exon boundaries were PCR-amplified and sequenced in 48 members of this large family.

RESULTS

All affected individuals showed discoloration and severe attrition of their teeth, with obliterated pulp chambers and without progressive high frequency hearing loss or skeletal abnormalities. No recombination was found at five polymorphic markers flanking DSPP in the family. Direct DNA sequencing identified a novel A-->G transition mutation adjacent to the donor splicing site within intron 3 in all affected individuals but not in the unaffected family members and 50 unrelated Mongolian individuals.

CONCLUSION

This study identified a novel mutation (IVS3+3A-->G) in DSPP, which caused DGI-II in a large Mongolian family. This expands the spectrum of mutations leading to DGI-II.

Identification of a novel dentin matrix protein-1 (DMP-1) mutation and dental anomalies in a kindred with autosomal recessive hypophosphatemia

An autosomal recessive form of hypophosphatemia (ARHP) was recently shown to be caused by homozygous mutations in DMP1, the gene encoding dentin matrix protein-1 (DMP-1), a non-collagenous bone matrix protein with an important role in the development and mineralization of bone and teeth. Here, we describe a previously not reported consanguineous ARHP kindred in which the three affected individuals carry a novel homozygous DMP-1 mutation. The index case presented at the age of 3 years with bowing of his legs and showed hypophosphatemia due to insufficient renal phosphate retention. Serum alkaline phosphatase activity was elevated, with initially normal PTH. FGF23 was inappropriately normal at an older age while being treated with oral phosphate and 1,25(OH)(2)D. Similar clinical and biochemical findings, except for elevated FGF23 levels, were present in his 16-month-old brother and his 12.5-year-old female cousin; the parents of the three affected children are first-degree cousins. Nucleotide sequence analysis was performed on PCR-amplified exons encoding DMP-1 and flanking intronic regions. A novel homozygous frame-shift mutation (c.485Tdel; p.Glu163ArgfsX53) in exon 6 resulting in a premature stop codon was identified in all effected individuals. The parents and available unaffected siblings were heterozygous for c.485Tdel. Tooth growth and shape were normal for the index case, his affected brother and cousin, but their permanent and deciduous teeth displayed enlarged pulp chambers. The identified genetic mutation underscores the importance of DMP-1 mutations in the pathogenesis of ARHP. Furthermore, DMP-1 mutations appear to contribute, through yet unknown mechanisms, to tooth development.

Dentin dysplasia type I: a case report and review of the literature

Introduction

Dentin dysplasia is a rare hereditary disturbance of dentin formation characterized by defective dentin development with clinically normal appearing crowns, severe hypermobility of teeth and spontaneous dental abscesses or cysts. Radiographic analysis shows obliteration of all pulp chambers, short, blunted and malformed or absent roots and peri-apical radiolucencies of non carious teeth.

Case presentation

We present a case of dentin dysplasia type I in a 12-year-old Iranian boy, and the clinical, radiographic and histopathologic findings of this condition and treatment are described.

Conclusions

There are still many inconclusive issues in the diagnosis and management of patients with dentin dysplasia. The diagnostic features of this rare disturbance will remain incompletely defined until additional cases have been described. Early diagnosis of the condition and initiation of effective regular dental treatments may help these patients to prevent or delay loss of dentition.

Potential Role of Dentin Sialoprotein by Inducing Dental Pulp Mesenchymal Stem Cell Differentiation and Mineralization for Dental Tissue Repair

INTRODUCTION: Dentin sialoprotein (DSP) is a dentin extracellular matrix protein, a unique marker of dentinogenesis and plays a vital role in odontoblast differentiation and dentin mineralization. Recently, studies have shown that DSP induces differentiation and mineralization of periodontal ligament stem cells and dental papilla mesenchymal cells in vitro and rescues dentin deficiency and increases enamel mineralization in animal models. THE HYPOTHESIS: DSP as a nature therapeutic agent stimulates dental tissue repair by inducing endogenous dental pulp mesenchymal stem/progenitor cells into odontoblast-like cells to synthesize and to secrete dentin extracellular matrix forming new tertiary dentin as well as to regenerate a functional dentin-pulp complex. As DSP is a nature protein, and clinical procedure for DSP therapy is easy and simple, application of DSP may provide a new avenue for dentists with additional option for the treatment of substantially damaged vital teeth. EVALUATION OF THE HYPOTHESIS: Dental caries is the most common dental disease. Deep caries and pulp exposure have been treated by various restorative materials with limited success. One promising approach is dental pulp stem/progenitor-based therapies to regenerate dentin-pulp complex and restore its functions by DSP induction in vivo.

Expression of Axin2 indicates a role for canonical Wnt signaling in development of the crown and root during pre- and postnatal tooth development

Previously two reporter mice, TOPgal and BATgal, have been used to uncover the spatial patterns of canonical Wnt activity up to the bell stage of tooth development. To further understand the function of this pathway, not only at the early developmental stages of odontogenesis but also in postnatal teeth, we have used Axin2-lacZ mice a direct reporter of canonical Wnt activity. As tooth development progresses, Axin2 expression becomes localized to the primary and secondary enamel knots, and the underlying mesenchyme. In postnatal teeth, Axin2 expression is observed in developing odontoblasts, in the dental pulp and concentrated around the developing roots. Expression is excluded from the ameloblasts and associated with the enamel-free zones at the tip of the molar cusps. This expression identifies new roles for Wnt signaling in defining the regions where enamel will form, and controlling root development at late stages of tooth development.

Runx2, osx, and dspp in tooth development

The transcription factors Runx2 and Osx are necessary for osteoblast and odontoblast differentiation, while Dspp is important for odontoblast differentiation. The relationship among Runx2, Osx, and Dspp during tooth and craniofacial bone development remains unknown. In this study, we hypothesized that the roles of Runx2 and Osx in the regulation of osteoblast and odontoblast lineages may be independent of one another. The results showed that Runx2 expression overlapped with Osx in dental and osteogenic mesenchyme from E12 to E16. At the later stages, from E18 to PN14, Runx2 and Osx expressions remained intense in alveolar bone osteoblasts. However, Runx2 expression was down-regulated, whereas Osx expression was clearly seen in odontoblasts. At later stages, Dspp transcription was weakly present in osteoblasts, but strong in odontoblasts where Osx was highly expressed. In mouse odontoblast-like cells, Osx overexpression increased Dspp transcription. Analysis of these data suggests differential biological functions of Runx2, Osx, and Dspp during odontogenesis and osteogenesis.

Molecular characterization of young and mature odontoblasts

The odontoblast is the secretory cell responsible for primary, secondary and tertiary reactionary dentinogenesis. We provide evidence that the changes in secretory activity of odontoblasts reflect differential transcriptional control and that common regulatory processes may exist between dentine and bone.

INTRODUCTION

Based on the hypothesis that differential dentine secretion (primary and secondary dentinogenesis) is associated with changes in the transcriptional control within the cell, we have investigated the transcriptome of odontoblasts at young and mature stages and subsequently used this information to identify key regulatory intracellular pathways involved in this process.

MATERIALS AND METHODS

We used microarray analysis to compare the transcriptome of early stage (primary dentinogenesis) and late stage (secondary dentinogenesis) odontoblasts from 30 month old bovine teeth. Secondarily, we used post-array sqRT-PCR to confirm the differential expression of 23 genes in both populations of odontoblasts. Finally, immunohistochemistry was performed on bovine and murine tissues with antibodies to DMP1 and anti-phospho p38 proteins.

RESULTS

DMP-1 and osteocalcin gene expression were up-regulated in the mature odontoblasts, whereas collagen I, DSPP, TGF-beta1 and TGF-beta1R gene expression were down-regulated. Microarray analysis highlighted 574 differentially regulated genes (fold change>2 - p<0.05). This study supports further existing similarities between pulp cells and bone cells. Using post-array Sq-RT-PCR we characterized transcript levels of genes involved in the p38 MAP kinase pathway (PTPRR, NTRKK2, MAPK13, MAP2K6, MKK3). Differential p38 gene activation was confirmed by immunohistochemistry for p38 protein in murine teeth. Finally, immunohistochemistry for DMP1 indicated that odontoblasts involved in primary and secondary dentinogenesis may coexist in the same tooth.

CONCLUSION

As established in bone cells, the transcriptome of the odontoblast was shown here to evolve with their stage and functional maturity. Identification of the involved signalling pathways, as highlighted for p38, will enable the deciphering of physiology and pathology of mineralised tissue formation.

BCOR regulates mesenchymal stem cell function by epigenetic mechanisms

The BCL-6 co-repressor (BCOR) represses gene transcription by interacting with BCL-6 (Refs 1, 2). BCOR mutation is responsible for oculo-facio-cardio-dental (OFCD) syndrome, which is characterized by canine teeth with extremely long roots, congenital cataracts, craniofacial defects and congenital heart disease. Here we show that BCOR mutation increased the osteo-dentinogenic potential of mesenchymal stem cells (MSCs) isolated from a patient with OFCD, providing a molecular explanation for abnormal root growth. AP-2alpha was identified as a repressive target of BCOR, and BCOR mutation resulted in abnormal activation of AP-2alpha. Gain- and loss-of-function assays suggest that AP-2alpha is a key factor that mediates the increased osteo-dentinogenic capacity of MSCs. Moreover, we found that BCOR maintained tissue homeostasis and gene silencing through epigenetic mechanisms. BCOR mutation increased histone H3K4 and H3K36 methylation in MSCs, thereby reactivating transcription of silenced target genes. By studying a rare human genetic disease, we have unravelled an epigenetic mechanism for control of human adult stem cell function.

Tissue-specific expression of dentin sialophosphoprotein (DSPP) and its polymorphisms in mouse tissues

Dentin sialophosphoprotein (DSPP) consists of dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). DSPP is highly expressed in mineralized tissues. However, recent studies have shown that DSPP is also expressed in several active metabolic ductal epithelial tissues and exists in a variety of sequences. We have investigated DSPP expression in various mouse tissues using RT-PCR, in situ hybridization and immunohistochemical analyses. To identify DSPP gene polymorphisms, we screened a mouse tooth cDNA library as well as isolated and characterized DSPP variations. Our results show that DSPP is predominantly expressed in teeth and moderately in bone tissues. We also have characterized a full-length DSPP cDNA clone with an open-reading frame of 940 codons and this polyadenylation signal. Compared to previously reported mouse DSPP cDNAs, 13 sequence variations were identified, including 8 non-synonymous single nucleotide polymorphisms and an in-frame indel (8 amino acids) at DPP domain of the mouse DSPP. These 8 amino acids are rich in aspartic acid and serine residues. Northern blot assay showed a prominent band at 4.4kb. RT-PCR demonstrated that this mouse DSPP gene was dominantly expressed in teeth. The predicted secondary structure of DPP domain of this DSPP showed differences from the previously published mouse DPPs, implying that they play different roles during tooth development and formation.

Dentin sialoprotein and dentin phosphoprotein have distinct roles in dentin mineralization

Dentin sialophosphoprotein (DSPP), a major non-collagenous matrix protein of odontoblasts, is proteolytically cleaved into dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). Our previous studies revealed that DSPP null mice display a phenotype similar to human autosomal dominant dentinogenesis imperfecta, in which teeth have widened predentin and irregular dentin mineralization resulting in sporadic unmineralized areas in dentin and frequent pulp exposure. Earlier in vitro studies suggested that DPP, but not DSP, plays a significant role in initiation and maturation of dentin mineralization. However, the precise in vivo roles of DSP and DPP are far from clear. Here we report the generation of DPPcKO mice, in which only DSP is expressed in a DSPP null background, resulting in a conditional DPP knockout. DPPcKO teeth show a partial rescue of the DSPP null phenotype with the restored predentin width, an absence of irregular unmineralized areas in dentin, and less frequent pulp exposure. Micro-computed tomography (micro-CT) analysis of DPPcKO molars further confirmed this partial rescue with a significant recovery in the dentin volume, but not in the dentin mineral density. These results indicate distinct roles of DSP and DPP in dentin mineralization, with DSP regulating initiation of dentin mineralization, and DPP being involved in the maturation of mineralized dentin.

A novel splice site mutation in the dentin sialophosphoprotein gene in a Chinese family with dentinogenesis imperfecta type II

Twenty-four individuals were investigated that spanned six generations in a Chinese family affected with an apparently autosomal dominant form of dentinogenesis imperfecta type II (DGI-II, OMIM #125490). All affected individuals presented with typical, clinical and radiographic features of DGI-II, but without bilateral progressive high-frequency sensorineural hearing loss. To investigate the mutated molecule, a positional candidate approach was used to determine the mutated gene in this family. Genomic DNA was obtained from 24 affected individuals, 18 unaffected relatives of the family and 50 controls. Haplotype analysis was performed using leukocyte DNA for 6 short tandem repeat (STR) markers present in chromosome 4 (D4S1534, GATA62A11, DSPP, DMP1, SPP1 and D4S1563). In the critical region between D4S1534 and DMP1, the dentin sialophosphoprotein (DSPP) gene (OMIM *125485) was considered as the strongest candidate gene. The first four exons and exon/intron boundaries of the gene were analyzed using DNA from 24 affected individuals and 18 unaffected relatives of the same family. DNA sequencing revealed a heterozygous deletion mutation in intron 2 (at positions -3 to -25), which resulted in a frameshift mutation, that changed the acceptor site sequence from CAG to AAG (IVS2-3C-->A) and may also have disrupted the branch point consensus sequence in intron 2. The mutation was found in the 24 affected individuals, but not in the 18 unaffected relatives and 50 controls. The deletion was identified by allele-specific sequencing and denaturing high-performance liquid chromatography (DHPLC) analysis. We conclude that the heterozygous deletion mutation contributed to the pathogenesis of DGI-II.