Translating Science into Improved Health for All

Our world is at a turning point with biological and social pathogens wreaking havoc at the same time that science and technology are exploding with new discoveries. It is a pivotal time for the new report Oral Health in America: Advances and Challenges to be released and a pivotal time for our profession to take action and lead. The art, science, and practice of dentistry is very different from 20 y ago when the original Surgeon General's report was released. We are on the precipice of individualized health care where providers will collaborate to deliver diagnostics and therapeutics that are data driven and inclusive of the social determinants of health. To move forward with alacrity requires a strong scientific foundation, effective educational approaches, an understanding of the upstream determinants of health, and partnerships across the health professions and beyond. Oral health has never been more important, and now is the time for our profession to further develop, elevate, and translate the science into practice and policy to improve the nation's health.

Molecular Diagnostics and In Utero Therapeutics for Orofacial Clefts

Orofacial clefts and their management impose a substantial burden on patients, on their families, and on the health system. Under the current standard of care, affected patients are subjected to a lifelong journey of corrective surgeries and multidisciplinary management to replace bone and soft tissues, as well as restore esthetics and physiologic functions while restoring self-esteem and psychological health. Hence, a better understanding of the dynamic interplay of molecular signaling pathways at critical phases of palate development is necessary to pioneer novel prenatal interventions. Such pathways include transforming growth factor-β (Tgfβ), sonic hedgehog (Shh), wingless-integrated site (Wnt)/β-catenin, bone morphogenetic protein (Bmp), and fibroblast growth factor (Fgf) and its associated receptors, among others. Here, we summarize commonly used surgical methods used to correct cleft defects postnatally. We also review the advances made in prenatal diagnostics of clefts through imaging and genomics and the various in utero surgical corrections that have been attempted thus far. An overview of how key mediators of signaling that drive palatogenesis are emphasized in the context of the framework and rationale for the development and testing of therapeutics in animal model systems and in humans is provided. The pros and cons of in utero therapies that can potentially restore molecular homeostasis needed for the proper growth and fusion of palatal shelves are presented. The theme advanced throughout this review is the need to develop preclinical molecular therapies that could ultimately be translated into human trials that can correct orofacial clefts at earlier stages of development.

Gender Inequalities in the Dental Workforce: Global Perspectives

The aim of this review is to investigate the growth of diversity and inclusion in global academic dental research with a focus on gender equality. A diverse range of research methodologies were used to conduct this review, including an extensive review of the literature, engagement of key informants in dental academic leadership positions around the world, and review of current data from a variety of national and international organizations. Results provide evidence of gender inequalities that currently persist in dental academics and research. Although the gender gap among graduating dental students in North America and the two most populous countries in Europe (the United Kingdom and France) has been narrowed, women make up 30% to 40% of registered dentists in countries throughout Europe, Oceania, Asia, and Africa. In academic dentistry around the globe, greater gender inequality was found to correlate with higher ranking academic and leadership positions in the United States, United Kingdom, several countries in European Union, Japan, and Saudi Arabia. Further disparities are noted in the dental research sector, where women make up 33% of dental researchers in the European Union, 35% in North America, 55% in Brazil, and 25% in Japan. Family and societal pressures, limited access to research funding, and lack of mentoring and leadership training opportunities are reported as also contributing to gender inequalities. To continue advancing gender equality in dental academia and research, efforts should be geared toward the collection and public dissemination of data on gender-specific distributions. Such evidence-driven information will guide the selection of future strategies and best practices for promoting gender equity in the dental workforce, which provides a major pipeline of researchers and scholars for the dental profession.

Empowering Women Researchers in the New Century: IADR's Strategic Direction

Gender inequality in science, medicine, and dentistry remains a central concern for the biomedical research workforce today. Although progress in areas of inclusivity and gender diversity was reported, growth has been slow. Women still face multiple challenges in reaching higher ranks and leadership positions while maintaining holistic success in these fields. Within dental research and academia, we might observe trends toward a more balanced pipeline. However, women continue to face barriers in seeking leadership roles and achieving economic equity and scholarship recognition. In an effort to evaluate the status of women in dental research and academia, the authors examined the role of the International Association for Dental Research (IADR), a global research organization, which has improved awareness on gender inequality. The goal of this article is to review five crucial issues of gender inequality in oral health research and academics-workforce pipeline, economic inequality, workplace harassment, gender bias in scholarly productivity, and work-life balance-and to discuss proactive steps that the IADR has taken to promote gender equality. Providing networking and training opportunities through effective mentoring and coaching for women researchers, the IADR has developed a robust pipeline of women leaders while promoting gender equality for women in dental academia through a culture shift. As knowledge gaps remained on the levels of conscious and unconscious bias and sexist culture affecting women advancement in academics, as well as the intersectionality of gender with race, gender identity, ability status, sexual orientation, and cultural backgrounds, the IADR has recognized that further research is warranted.

Anti-EDAR Agonist Antibody Therapy Resolves Palate Defects in Pax9-/- Mice

To date, surgical interventions are the only means by which craniofacial anomalies can be corrected so that function, esthetics, and the sense of well-being are restored in affected individuals. Unfortunately, for patients with cleft palate-one of the most common of congenital birth defects-treatment following surgery is prolonged over a lifetime and often involves multidisciplinary regimens. Hence, there is a need to understand the molecular pathways that control palatogenesis and to translate such information for the development of noninvasive therapies that can either prevent or correct cleft palates in humans. Here, we use the well-characterized model of the Pax9^-/- mouse, which displays a consistent phenotype of a secondary cleft palate, to test a novel therapeutic. Specifically, we demonstrate that the controlled intravenous delivery of a novel mouse monoclonal antibody replacement therapy, which acts as an agonist for the ectodysplasin (Eda) pathway, can resolve cleft palate defects in Pax9^-/- embryos in utero. Such pharmacological interventions did not reverse the arrest in tooth, thymus, and parathyroid gland development, suggesting that the relationship of Pax9 to the Eda/Edar pathway is both unique and essential for palatogenesis. Expression analyses and unbiased gene expression profiling studies offer a molecular explanation for the resolution of palatal defects, showing that Eda and Edar-related genes are expressed in normal palatal tissues and that the Eda/Edar signaling pathway is downstream of Pax9 in palatogenesis. Taken together, our data uncover a unique relationship between Pax9 and the Eda/Edar signaling pathway that can be further exploited for the development of noninvasive, safe, and effective therapies for the treatment of cleft palate conditions and other single-gene disorders affecting the craniofacial complex.

Our Essential and Endangered Dentist-Scientist Workforce

Future advances in dental medicine rely on a robust and stable pipeline of dentist-scientists who are dedicated to research inspired by the patients' condition. The biomedical research community faces external and internal pressures that have been building over years. This is now threatening the current and future status of basic, translational and patient-oriented research by dentist-scientists who study dental, oral and craniofacial diseases, population sciences, and prevention. The dental academic, research and practicing communities can no longer ignore the warning signs of a system that is under considerable stress. Here, the authors report findings of the Physician-Scientist Workforce Working Group, charged by the National Institutes of Health (NIH) Director, to perform quantitative and qualitative analyses on dentist-scientists by addressing the size, composition and activities of the group, relative to other health professions. From 1999 to 2012, trends in the numbers of grant applications and awards to dentist-scientists point to an overall decline. Disturbing are the low numbers of new investigators who apply for Early Career NIH Programs. While more seasoned dentist researchers enjoy greater success, the average age of first-time funded dentists is 52.7 y for females and 54.6 y for males, with a relatively low number of applications submitted and funded. These new data led the panel to stress the need to expand the capacity of the dentist-scientist workforce to leverage technologies and research opportunities that benefit the profession at-large. Suggestions were made to invest in developing clinical research faculty, including those with foreign degrees, through new training mechanisms. The creation of new alliances between national organizations like the American Association for Dental Research, the American Dental Education Association and the American Dental Association will undoubtedly lead to bold and concerted actions that must be pursued with a sense of urgency. A more supportive culture within dental schools and universities for dentist-scientists is needed, as their success is critical to the future career choices of their mentees. Knowledge Transfer Statement: Advances in dental medicine rely on a pipeline of dentist-scientists who are dedicated to research inspired by the patients' condition. Despite the recent advancement in technology and innovation, the dental community can no longer ignore the various pressures that threaten the future of the dentist-scientist profession. Here, the authors report findings of the Physician-Scientist Workforce Working Group of NIH that were published in 2014, and draw attention to the key issues threatening the NIH-funded pool of dentist-scientists.

A Novel Role for Twist-1 in Pulp Homeostasis

The molecular mechanisms that maintain the equilibrium of odontoblast progenitor cells in dental pulp are unknown. Here we tested whether homeostasis in dental pulp is modulated by Twist-1, a nuclear protein that partners with Runx2 during osteoblast differentiation. Our analysis of Twist-1(+/−) mice revealed phenotypic changes that involved an earlier onset of dentin matrix formation, increased alkaline phosphatase activity, and pulp stones within the pulp. RT-PCR analyses revealed Twist-1 expression in several adult organs, including pulp. Decreased levels of Twist-1 led to higher levels of type I collagen and Dspp gene expression in perivascular cells associated with the pulp stones. In mice heterozygous for both Twist-1 and Runx2 inactivation, the phenotype of pulp stones appeared completely rescued. These findings suggest that Twist-1 plays a key role in restraining odontoblast differentiation, thus maintaining homeostasis in dental pulp. Furthermore, Twist-1 functions in dental pulp are dependent on its interaction with Runx2.

Ex Vivo Modeling of Multidomain Peptide Hydrogels with Intact Dental Pulp

Preservation of a vital dental pulp is a central goal of restorative dentistry. Currently, there is significant interest in the development of tissue engineering scaffolds that can serve as biocompatible and bioactive pulp-capping materials, driving dentin bridge formation without causing cytotoxic effects. Our earlier in vitro studies described the biocompatibility of multidomain peptide (MDP) hydrogel scaffolds with dental pulp-derived cells but were limited in their ability to model contact with intact 3-dimensional pulp tissues. Here, we utilize an established ex vivo mandible organ culture model to model these complex interactions. MDP hydrogel scaffolds were injected either at the interface of the odontoblasts and the dentin or into the pulp core of mandible slices and subsequently cultured for up to 10 d. Histology reveals minimal disruption of tissue architecture adjacent to MDP scaffolds injected into the pulp core or odontoblast space. Additionally, the odontoblast layer is structurally preserved in apposition to the MDP scaffold, despite being separated from the dentin. Alizarin red staining suggests mineralization at the periphery of MDP scaffolds injected into the odontoblast space. Immunohistochemistry reveals deposition of dentin sialophosphoprotein by odontoblasts into the adjacent MDP hydrogel, indicating continued functionality. In contrast, no mineralization or dentin sialophosphoprotein deposition is evident around MDP scaffolds injected into the pulp core. Collagen III expression is seen in apposition to gels at all experimental time points. Matrix metalloproteinase 2 expression is observed associated with centrally injected MDP scaffolds at early time points, indicating proteolytic digestion of scaffolds. Thus, MDP scaffolds delivered centrally and peripherally within whole dental pulp tissue are shown to be biocompatible, preserving local tissue architecture. Additionally, odontoblast function and pulp vitality are sustained when MDP scaffolds are intercalated between dentin and the odontoblast region, a finding that has significant implications when considering these materials as pulp-capping agents.

Loss of dentin sialophosphoprotein leads to periodontal diseases in mice

BACKGROUND AND OBJECTIVE

Dentin sialophosphoprotein (DSPP) and its cleaved products, dentin phosphoprotein (DPP) and dentin sialoprotein (DSP), play important roles in biomineralization. Recently, we observed that DSPP is highly expressed in the alveolar bone and cementum, indicating that this molecule may play an important role in the formation and maintenance of a healthy periodontium, and its deletion may cause increased susceptibility to periodontal diseases. The objective of this investigation was to study the effects of Dspp ablation on periodontal tissues by analyzing Dspp null mice.

MATERIAL AND METHODS

Newborn to 6-mo-old Dspp null mice were examined, and the 3- and 6-mo-old Dspp null mice were characterized in detail using X-ray radiography, histology and scanning electron microscopy (backscattered as well as resin-infiltrating). Wild-type mice of the same age groups served as the normal controls.

RESULTS

The Dspp null mice showed significant loss of alveolar bone and cementum, particularly in the furcation and interproximal regions of the molars. The alveolar bone appeared porous while the quantity of cementum was reduced in the apical region. The canalicular systems and osteocytes in the alveolar bone were abnormal, with reduced numbers of canaliculi and altered osteocyte morphology. The loss of alveolar bone and cementum along with the detachment of the periodontal ligaments (PDL) led to the apical migration of the epithelial attachment and formation of periodontal pockets.

CONCLUSION

Inactivation of DSPP leads to the loss of alveolar bone and cementum and increased susceptibility to bacterial infections in PDL of Dspp null mice. The fact that the loss of DSPP results in periodontal diseases indicates that this molecule plays a vital role in maintaining the health of the periodontium.

TWIST1 promotes the odontoblast-like differentiation of dental stem cells

Stem cells derived from the dental pulp of extracted human third molars (DPSCs) have the potential to differentiate into odontoblasts, osteoblasts, adipocytes, and neural cells when provided with the appropriate conditions. To advance the use of DPSCs for dentin regeneration, it is important to replicate the permissive signals that drive terminal events in odontoblast differentiation during tooth development. Such a strategy is likely to restore a dentin matrix that more resembles the tubular nature of primary dentin. Due to the limitations of culture conditions, the use of ex vivo gene therapy to drive the terminal differentiation of mineralizing cells holds considerable promise. In these studies, we asked whether the forced expression of TWIST1 in DPSCs could alter the potential of these cells to differentiate into odontoblast-like cells. Since the partnership between Runx2 and Twist1 proteins is known to control the onset of osteoblast terminal differentiation, we hypothesized that these genes act to control lineage determination of DPSCs. For the first time, our results showed that Twist1 overexpression in DPSCs enhanced the expression of DSPP, a gene that marks odontoblast terminal differentiation. Furthermore, co-transfection assays showed that Twist1 stimulates Dspp promoter activity by antagonizing Runx2 function in 293FT cells. Analysis of our in vitro data, taken together, suggests that lineage specification of DPSCs can be modulated through ex vivo gene modifications.

Scaffolds for dental pulp tissue engineering

For tissue engineering strategies, the choice of an appropriate scaffold is the first and certainly a crucial step. A vast variety of biomaterials is available: natural or synthetic polymers, extracellular matrix, self-assembling systems, hydrogels, or bioceramics. Each material offers a unique chemistry, composition and structure, degradation profile, and possibility for modification. The role of the scaffold has changed from passive carrier toward a bioactive matrix, which can induce a desired cellular behavior. Tailor-made materials for specific applications can be created. Recent approaches to generate dental pulp rely on established materials, such as collagen, polyester, chitosan, or hydroxyapatite. Results after transplantation show soft connective tissue formation and newly generated dentin. For dentin-pulp-complex engineering, aspects including vascularization, cell-matrix interactions, growth-factor incorporation, matrix degradation, mineralization, and contamination control should be considered. Self-assembling peptide hydrogels are an example of a smart material that can be modified to create customized matrices. Rational design of the peptide sequence allows for control of material stiffness, induction of mineral nucleation, or introduction of antibacterial activity. Cellular responses can be evoked by the incorporation of cell adhesion motifs, enzyme-cleavable sites, and suitable growth factors. The combination of inductive scaffold materials with stem cells might optimize the approaches for dentin-pulp complex regeneration.

TEGDMA reduces mineralization in dental pulp cells

Direct application of dentin bonding agents onto the exposed pulp has been advocated, but in vivo studies indicate a lack of reparative dentin formation. Our objective was to investigate the role of triethylene glycol dimethacrylate (TEGDMA), a commonly used compound in dentin bonding agents, as a potential inhibitor of mineralization. Human pulp cells were exposed to different concentrations of TEGDMA, and expression of the mineralization-related genes collagen I, alkaline phosphatase, bone sialoprotein, osteocalcin, Runx2, and dentin sialophosphoprotein was analyzed. Gene expression studies by real-time polymerase chain-reaction revealed a concentration- and time-dependent decrease of mineralization markers. A subtoxic TEGDMA concentration (0.3 mM) reduced expression levels by 5 to 20% after 4 hrs and by 50% after 12 hrs. Furthermore, alkaline phosphatase activity and calcium deposition were significantly lower in dental pulp cells treated with TEGDMA over 14 days. These findings indicate that even low TEGDMA concentrations might inhibit mineralization induced by dental pulp cells, thus impairing reparative dentin formation after pulp capping with dentin bonding agents.

Tooth eruption and cementum formation in the Runx2/Cbfa1 heterozygous mouse

Cleidocranial dysplasia (CCD) is an autosomal dominant human disorder that affects development of bones and teeth. The dental disorders in CCD patients include formation of supernumerary teeth, delayed tooth eruption, and lack of formation of cellular cementum in permanent teeth. This disorder involves a mutation in the osteoblast-specific transcription factor Runx2/Cbfa1, leading to haploinsufficiency of the Runx2/Cbfa1 protein. Here, we examined if Runx2/Cbfa1 heterozygous mice (with one functional allele for Runx2/Cbfa1) exhibit similar changes in tooth eruption, and dental cementum formation as in CCD patients. Heads of Runx2/Cbfa1 heterogeneous and wildtype mice aged days 16-35 postnatally were serially sectioned and stained with hematoxylin-eosin or for tartrate resistant acid phosphatase (TRAP) to identify osteoclasts. The results showed that the eruption pattern of the first and second molars in maxilla and mandible in Runx2/Cbfa1 +/- mice was the same as in wildtype animals. No clear difference in distribution or in the (estimated) number of osteoclasts was found. Cellular cement at the apical portions of the molar roots was present in both groups. The data suggests that in the mouse one allele for Runx2/Cbfa1 is sufficient for an undisturbed tooth eruption and an apparently normal formation of the periodontium.

Cellular, molecular, and genetic determinants of tooth eruption

Tooth eruption is a complex and tightly regulated process that involves cells of the tooth organ and the surrounding alveolus. Mononuclear cells (osteoclast precursors) must be recruited into the dental follicle prior to the onset of eruption. These cells, in turn, fuse to form osteoclasts that resorb alveolar bone, forming an eruption pathway for the tooth to exit its bony crypt. Some of the molecules possibly involved in the signaling cascades of eruption have been proposed in studies from null mice, osteopetrotic rodents, injections of putative eruption molecules, and cultured dental follicle cells. In particular, recruitment of the mononuclear cells to the follicle may require colony-stimulating factor-one (CSF-1) and/or monocyte chemotactic protein-1 (MCP-1). Osteoclastogenesis is needed for the bone resorption and may involve inhibition of osteoprotegerin transcription and synthesis in the follicle, as well as enhancement of receptor activator of NF kappa B ligand (RANKL), in the adjacent alveolar bone and/or in the follicle. Paracrine signaling by parathyroid-hormone-related protein and interleukin -1 alpha, produced in the stellate reticulum adjacent to the follicle, may also play a role in regulating eruption. Osteoblasts might also influence the process of eruption, the most important physiologic role likely being at the eruptive site, in the formation of osteoclasts through signaling via the RANKL/OPG pathway. Evidence thus far supports a role for an osteoblast-specific transcription factor, Cbfa1 (Runx2), in molecular events that regulate tooth eruption. Cbfa1 is also expressed at high levels by the dental follicle cells. This review concludes with a discussion of the several human conditions that result in a failure of or delay in tooth eruption.

A novel mutation in human PAX9 causes molar oligodontia

Experimental and animal studies, as well as genetic mutations in man, have indicated that the development of dentition is under the control of several genes. So far, mutations in MSX1 and PAX9 have been associated with dominantly inherited forms of human tooth agenesis that mainly involve posterior teeth. We identified a large kindred with several individuals affected with molar oligodontia that was transmitted as an isolated autosomal-dominant trait. Two-point linkage analysis using DNA from the family and polymorphic marker D14S288 in chromosome 14q12 produced a maximum lod score of 2.29 at theta = 0.1. Direct sequencing of exons 2 to 4 of PAX9 revealed a cytosine insertion mutation at nucleotide 793, leading to a premature termination of translation at aa 315. Our results support the conclusion that molar oligodontia is due to allelic heterogeneity in PAX9, and these data further corroborate the role of PAX9 as an important regulator of molar development.

Identification of tooth-specific downstream targets of Runx2

Odontogenesis or tooth development is a highly regulated process that involves complex epithelial-mesenchymal signaling interactions that lead to cuspal morphogenesis, cell differentiation and the subsequent formation of the specialized matrices of enamel, dentin, cementum and bone. Although studies on tooth epithelial-mesenchymal signaling interactions have greatly increased our understanding of molecules that regulate tooth initiation and early morphogenesis (review: Jernvall and Thesleff, Mech. Dev. 92 (2000) 19), the precise nature of the molecular events controlling late morphogenesis and terminal cytodifferentiation is not known. We have recently reported a unique phenotype involving dentition in mice lacking a functional Runx2 gene (D'Souza et al., Development 126 (1999) 2911). The markedly hypoplastic tooth organs as well as defects in the maturation of ameloblasts and odontoblasts point to an important and non-redundant role for Runx2 in tooth morphogenesis and cytodifferentiation. In order to identify genes that are affected by the absence of Runx2, a cDNA library was generated from Runx2(-/-) and Runx2(+/+) first molar organs. Thus far, our analysis has revealed several tooth-specific downstream target genes of Runx2 that include extracellular matrix proteins, kinases, receptors, growth factors, mitochondrial proteins and transcription molecules. Sequence analysis of 61 differentially expressed genes revealed that 96.03% of the clones matched previously described genes in the GenBank/EBML database and 3.96% did not match any entries in the database. Our preliminary expression analysis of one of the differentially expressed clones which encodes for a zinc finger transcription factor termed Zfp reveals that the gene is temporally regulated during tooth development. In conclusion, we have successfully generated a library enriched in genes expressed in Runx2(+/+) molar tooth organs and performed preliminary studies to assess the role of Zfp in tooth development.

Gene expression in a pure population of odontoblasts isolated by laser-capture microdissection

Studies of odontoblast differentiation and function have been limited due to difficulties in obtaining sufficient numbers of intact cells. We describe a novel approach of laser-capture microdissection to obtain homogenous populations of pre-odontoblasts and odontoblasts from tissue sections of mouse molar cusp tips. Fixation, processing, and staining conditions were assessed for the optimal retrieval of total RNA from microdissected odontoblasts. Fluorometric assays and RT-PCR analysis of alpha1(I) collagen, dentin sialophosphoprotein (Dspp), and osteocalcin (OC) confirmed that the total RNA from three-day-old captured odontoblasts was sufficient in quantity and quality. Odontoblast-specific gene expression was studied by RT-PCR analysis performed in a single streptavidin-coated tube. At E15.5, Days 0 and 3, gene expression in laser-captured odontoblasts resembled that seen in vivo by in situ hybridization. The use of LCM is thus a valuable means of retrieving quality RNA from discrete populations of odontoblasts at different stages of dentinogenesis.

Molecular insights into the lineage-specific determination of odontoblasts: the role of Cbfa1

The role of stable transcription complexes in initiating and consolidating programs of gene expression during lineage specification has been extensively studied. Despite the progress made in the identification of key molecules of tooth initiation and patterning, the mechanisms leading to cell differentiation during odontogenesis are unknown. Odontoblasts are exclusive dentin-producing cells that are phenotypically and functionally distinct from osteoblasts. However, not much is known about the precise determinants of odontoblast terminal differentiation--in particular, how the fate of these cells becomes delineated from that of osteogenic mesenchyme. Cbfa1(-/-) mice completely lack osteoblasts and bone, while tooth development arrests at the time of odontoblast differentiation. The purpose of this paper is to overview our studies on the role of Cbfa1 in odontoblast determination and differentiation using the Cbfa1(-/-) mouse model and various experimental approaches. Our expression analyses confirm the down-regulation of Cbfa1 expression in newly differentiated and functional odontoblasts. Second, we demonstrate that Cbfa1(-/-) incisor organs arrest at a later stage than molars, and that alpha 1 (I) collagen, a marker of odontoblast differentiation shared in common with osteoblasts, is not significantly affected by the absence of the transcription factor. Interestingly, Dspp expression in Cbfa1(-/-) appeared markedly down-regulated in putative odontoblasts. The overexpression of Cbfa1 in an odontoblast cell line (MDPC-23) results in the selective down-regulation of Dspp and not type I collagen. It is likely that, in addition to its influence on tooth epithelial morphogenesis, Cbfa1 plays a non-redundant and stage-specific role in the lineage determination and terminal differentiation of odontoblasts from dental papilla mesenchyme.

Cell-specific patterns of Cbfa1 mRNA and protein expression in postnatal murine dental tissues

Cbfa1 (core binding factor alpha 1) is a transcription factor that is a key determinant of the osteoblastic lineage. Recent data showed that Cbfa1 is also highly expressed in early stages of tooth development and is involved in crown morphogenesis and cytodifferentiation of odontoblasts. Here we report the mRNA expression and protein localization of Cbfa1 in the mouse dentition in (later) stages of crown and root development. In addition to osteoblasts, osteocytes, chondrocytes, odontoblasts, dental follicle cells, cementoblasts and periodontal ligament cells, we report also Cbfa1 expression in dental epithelial cells (secretory and maturation ameloblasts) and several non-mineralizing cell types (hair follicles, ducts of salivary glands, and junctional epithelium of the gingiva).

Developmental regulation of dentin sialophosphoprotein during ameloblast differentiation: a potential enamel matrix nucleator

The two major dentin matrix proteins, dentin sialoprotein and dentin phosphoprotein have been shown to be expressed as a single large transcript termed dentin sialophosphoprotein (DSPP). These non-collagenous matrix proteins, identified biochemically by their unique physical-chemical properties, are specific cleavage products of a large parent acidic phosphorylated protein (pI 4.0). Previous studies have shown expression of dentin sialoprotein at the protein level by ameloblasts. The purpose of this study was to determine the temporal-spatial pattern of DSPP expression during amelogenesis. In situ hybridization and immunohistochemistry were performed on sections of developing mouse molars. These data were correlated with RT-PCR analysis of in vitro enamel organ epithelium monolayer cell cultures enriched for ameloblasts. Our data indicates initial expression of the DSPP transcripts and protein during early ameloblast differentiation prior to the secretory phase when the majority of the enamel matrix is formed. Ameloblasts appear to tightly down-regulate DSPP transcription as enamel matrix formation is up-regulated. These data demonstrate DSPP expression during amelogenesis is under highly controlled developmental regulation. Therefore, DSPP may have a primary role in the initial mineralization events of both enamel and dentin, acting as a potential nucleator of hydroxyapatite crystal formation.

Clinical, radiographic, and genetic evaluation of a novel form of autosomal-dominant oligodontia

A frameshift mutation recently identified within the paired domain of the transcription factor, PAX9, has been linked to a unique form of oligodontia in a single, multigenerational family (Stockton et al., 2000). We now describe the phenotypic and segregation analyses of this remarkable kindred, the initial approach taken to identify a candidate gene involved in this form of oligodontia, and the power of this single-family pedigree to generate significant linkage in a genome search. Of the 43 family members enrolled in this study, 21 individuals were affected with several congenitally missing permanent teeth. The pattern of inheritance of the oligodontia trait suggested the involvement of a single gene bearing a dominant mutation. To various degrees, affected members lacked permanent first, second, and third molars in all four quadrants. Several individuals with missing molars also lacked second premolars- most commonly, maxillary second premolars and mandibular central incisors. To the best of our knowledge, this pattern of non-syndromic, familial tooth agenesis has not been previously described in the literature. Since a missense mutation in the homeobox gene, MSX1, was previously linked to tooth agenesis in a single family lacking second premolars and third molars, we performed a mutational analysis of MSX1 by PCR. The absence of a mutation in exons 1 and 2 of MSX1 suggested that allelic mutations in the coding region of MSX1 are not associated with this phenotypically distinct form of oligodontia. Computer simulation of linkage analysis further proved that this pedigree alone was sufficient to generate a significant result for a total genome scan.

Cbfa1 is required for epithelial-mesenchymal interactions regulating tooth development in mice

Osteoblasts and odontoblasts, cells that are responsible for the formation of bone and dentin matrices respectively, share several molecular characteristics. Recently, Cbfa1 was shown to be a critical transcriptional regulator of osteoblast differentiation. Mutations in this gene cause cleidocranial dysplasia (CCD), an autosomal dominant disorder in humans and mice characterized by defective bone formation. CCD also results in dental defects that include supernumerary teeth and delayed eruption of permanent dentition. The dental abnormalities in CCD suggest an important role for this molecule in the formation of dentition. Here we describe results of studies aimed at understanding the functions of Cbfa1 in tooth formation. RT-PCR and in situ hybridization analyses show that Cbfa1 has a unique expression pattern in dental mesenchyme from the bud to early bell stages during active epithelial morphogenesis. Unlike that observed in osteoblast differentiation, Cbfa1 is downregulated in fully differentiated odontoblasts and is surprisingly expressed in ectodermally derived ameloblasts during the maturation phase of enamel formation. The role of Cbfa1 in tooth morphogenesis is further illustrated by the misshapen and severely hypoplastic tooth organs in Cbfa1−/− mice. These tooth organs lacked overt odontoblast and ameloblast differentiation and normal dentin and enamel matrices. Epithelial-mesenchymal recombinants demonstrate that dental epithelium regulates mesenchymal Cbfa1 expression during the bud and cap stages and that these effects are mimicked by the FGFs but not by the BMPs as shown by our bead implantation assays. We propose that Cbfa1 regulates the expression of molecules in mesenchyme that act reciprocally on dental epithelium to control its growth and differentiation. Taken together, our data indicate a non-redundant role for Cbfa1 in tooth development that may be distinct from that in bone formation. In odontogenesis, Cbfa1 is not involved in the early signaling networks regulating tooth initiation and early morphogenesis but regulates key epithelial-mesenchymal interactions that control advancing morphogenesis and histodifferentiation of the epithelial enamel organ.

Characterization of immunocompetent cells in the diseased canine periodontium

The beagle dog with naturally occurring periodontal disease is one of the most widely used animal models in periodontal research for histological studies on disease pathogenesis and on the effect of potential therapeutic regimens. However, previous studies were restricted to morphological assessment of immunocompetent cells because of the lack of available cell-specific markers. In this study we systematically characterized the specificity and immunoreactivity of a panel of anti-human antibodies for identification (ABC method) of immunocompetent cells in formalin-fixed, EDTA-decalcified, paraffin-embedded inflamed periodontal tissues obtained from six beagle dogs. Canine lymph nodes and a panel of different human tissues served as positive controls. Polyclonal anti-CD3 immunolabeled canine T-lymphocytes specifically. Anti-CD79alpha (clone HM57) reacted with B-lymphocytes and plasma cells, and CD79alpha (clone JCP117) showed no staining in canine tissues. Neutrophils, monocytes, small macrophages, and keratinocytes reacted with an anti-myeloid/histiocyte antibody (clone MAC387). Anti-CD68 (clones PG-M1 and EBM11) immunolabeled large macrophages and plasma cells. Clone EBM11 also stained osteoclasts and cementoclasts. With the exception of JCB117, all antibodies revealed similarly favorable immunolabeling of canine and human immunocompetent cells. Long-term EDTA decalcification appeared to weaken immunostaining of plasma cells with HM57. MAC387 and CD68 can be used to distinguish macrophages in different differentiation stages in canine periodontal tissues. (J Histochem Cytochem 46:1443-1454, 1998)

Genomic organization, chromosomal mapping, and promoter analysis of the mouse dentin sialophosphoprotein (Dspp) gene, which codes for both dentin sialoprotein and dentin phosphoprotein

Our laboratory has reported that two major noncollagenous dentin proteins, dentin sialoprotein and dentin phosphoprotein, are specific cleavage products of a larger precursor protein termed dentin sialophosphoprotein (MacDougall, M., Simmons, D., Luan, X., Nydegger, J., Feng, J. Q., and Gu, T. T. (1997) J. Biol. Chem. 272:835-842). To confirm our single gene hypothesis and initiate in vitro promoter studies, we have characterized the structural organization of the mouse dentin sialophosphoprotein gene. This gene has a transcription unit of approximately 9.4 kilobase pairs and is organized into 5 exons and 4 introns. Exon 1 contains a noncoding 5' sequence, and exon 2 contains the transcriptional start site, signal peptide, and first two amino acids of the NH2 terminus. Exons 3 and 4 contain coding information for 29 and 314 amino acids, respectively. The remainder of the coding information and the untranslated 3' region are contained in exon 5. Chromosomal mapping localized the gene to mouse chromosome 5q21 in close proximity to other dentin/bone matrix genes. Computer analysis of the promoter proximal 1.6-kilobase pair sequence revealed a number of potentially important cis-regulatory sequences; these include the recognition elements of AP-1, AP-2, Msx-1, serum response elements, SP-1, and TCF-1. In vitro studies showed that the DSPP promoter is active in an odontoblast cell line, MO6-G3, with basal activity mapped to -95 bp. Two potential enhancer and suppresser elements were identified in the regions between -1447 and -791 bp and -791 and -95 bp, respectively. The structural organization of the dentin sialophosphoprotein gene confirms our finding that both dentin sialoprotein and dentin phosphoprotein are encoded by a single gene with a continuous open reading frame.

Bone morphogenetic protein-7 (osteogenic protein-1, OP-1) and tooth development

Bone morphogenetic proteins (BMPs) form a family of growth factors originally isolated from extracellular bone matrix that are capable of inducing bone formation ectopically. We studied the expression, tissue localization, and function of BMP-7 (OP-1) during tooth development in rodents. Patterns of BMP-7 gene expression and peptide distribution indicated that BMP-7 was present in dental epithelium during the dental lamina, bud, and cap stages. During the bell stage, BMP-7 mRNA expression and protein distribution shifted from dental epithelium toward the dental mesenchyme. With advancing differentiation of odontoblasts, BMP-7 protein staining in the dental papilla became restricted to the layer of fully functional odontoblasts in the process of depositing (pre)dentin. Secretory-stage ameloblasts exhibited weak immunostaining for BMP-7. A restricted pattern of staining in ameloblasts became apparent in post-secretory stages of amelogenesis. Also, cells of the forming periodontal ligament were immunopositive. Histological analysis of tooth development in neonatal BMP-7-deficient mice did not reveal obvious changes compared with wild-type mice. We conclude that, in developing dental tissues, BMP-7 has distribution and expression patterns similar to those of other BMP members but is not an essential growth factor for tooth development, possibly because of functional redundancy with other BMP members or related growth factors.

TGF-beta1 is essential for the homeostasis of the dentin-pulp complex

Among the complex network of cytokines that influence odontoblast function during development and repair, TGF-beta1 is unique in its dual abilities to function as a potent immunosuppressant and as an inducer of extracellular matrix production. These properties underscore the importance of this molecule in maintaining the homeostasis of the dentin-pulp complex after injury. The purpose of this paper is to describe new findings of our phenotypic analysis of dentition in mice in which the TGF-beta1 gene has been disrupted. The major phenotype of TGF-beta1(-/-) offspring is one of diffuse immune system activation with progressive inflammation, wasting and death. Our studies of adult TGF-beta1(-/-) dentition show widespread pulpal and periapical inflammation and necroses. In addition, the coronal surfaces of occluding molars show marked attrition. To determine whether the phenotypic changes in TGF-beta1(-/-) dentition are directly linked to the loss of TGF-beta1 rather than the inflammatory process itself, we studied adult dentition in TGF-beta1(-/-) mice backcrossed into immunodeficient backgrounds. Results of our histopathologic and radiographic analyses show that teeth of TGF-beta1(-/-) immunodeficient mice retain vitality in pulpal and periapical regions but show excessive wear of occlusal surfaces.

Gene expression patterns of murine dentin matrix protein 1 (Dmp1) and dentin sialophosphoprotein (DSPP) suggest distinct developmental functions in vivo

Although the precise mechanisms of the conversion of predentin to dentin are not well understood, several lines of evidence implicate the noncollagenous proteins (NCPs) as important regulators of dentin biomineralization. Here we compared the in vivo temporospatial expression patterns of two dentin NCP genes, dentin matrix protein 1 (Dmp1), and dentin sialophosphoprotein (DSPP) in developing molars. Reverse transcription-polymerase chain reaction was performed on embryonic day 13 to 1-day-old first molars using Dmp1- and DSPP-specific primer sets. Dmp1 transcripts appeared at the late bud stage, while DSPP mRNA was seen at the cap stage. Expression of both genes was sustained throughout odontogenesis. In situ hybridization analysis revealed interesting differences in the expression patterns of these genes. While Dmp1 and DSPP showed coexpression in young odontoblasts before the start of mineralization, the expression of these genes was notably distinct at later stages. Dmp1 expression decreased in secretory odontoblasts after the appearance of mineral, while high levels of DSPP were sustained in odontoblasts. In early secretory ameloblasts, DSPP expression was transient and down-regulated with the appearance ofdentin matrix. Interestingly, Dmp1 expression became evident in ameloblasts during the maturative phase of amelogenesis. In contrast to Dspp expression that was tooth-specific, Dmp1 was expressed by osteoblasts throughout ossification in the skeleton. Probes directed to the "DSP" and "DPP" regions of the DSPP gene showed identical patterns of mRNA expression. These data show that the developmental expression patterns of Dmp1 and DSPP are distinct, implying that these molecules serve different biological functions in vivo.

OP-1 (BMP-7) affects mRNA expression of type I, II, X collagen, and matrix Gla protein in ossifying long bones in vitro

In long bone development, a regulating role of OP-1 is suggested by the local correlated expression of both OP-1 ligand and OP-1 binding receptors in developing mouse hind limbs. OP-1 is expressed in the interdigital mesenchyme, whereas OP-1 binding receptors are found in the bordering perichondrium, and both OP-1 ligand and receptors are present in the zone of (pre)hypertrophic chondrocytes. We investigated the role of OP-1 in long bone development experimentally by treating organ cultures of embryonic mouse metatarsals with rhOP-1. The mRNA expression patterns of type I, II, X collagen, and matrix Gla protein (MGP) were studied using in situ hybridization and cell proliferation using [3H]thymidine and BrdU labeling. In the epiphyseal perichondrium, treatment with 40 ng/ml OP-1 enhanced cell proliferation after day 2, while 6-day treatment caused a shift in expression from type I collagen to type II collagen mRNA. This supports previous histochemical findings that OP-1 induced the transition of perichondrium into cartilage. In the center of the rudiment, OP-1 inhibited the expression of type X collagen mRNA, indicating inhibition of chondrocyte hypertrophy. An arrest of differentiation at the (pre)hypertrophic chondrocyte stage was also indicated by the large area of cells expressing MGP mRNA in the OP-1-treated rudiments. We conclude that OP-1 affected the expression of marker genes of chondrocyte differentiation by acting on two steps in endochondral ossification. First, cell proliferation was enhanced, particularly so in the perichondrium where cells started to express the chondrocyte phenotype. Second, the terminal differentiation of mature chondrocytes into hypertrophic chondrocytes was inhibited. These results, combined with the known pattern of OP-1 ligand and BMP receptor expression in the embryo, suggest that OP-1 plays a local role in the cascade of events during endochondral ossification.

DNA fragmentation during bone formation in neonatal rodents assessed by transferase-mediated end labeling

To study the fate of bone cells, we used the transferase-mediated, biotin-dUTP nick end-labeling (TUNEL) assay to detect DNA fragmentation during the formation of intramembranous and endochondral bone in newly born hamsters, mice, and rats. In alveolar bone forming around the developing tooth crowns, DNA fragmentation was found in three cell types: TRAP-negative mononuclear cells at the bone surface, osteocytes, and some but not all nuclei of TRAP-positive osteoclasts. Osteoblasts did not undergo DNA fragmentation. A strong positive correlation was found between contacts of TUNEL-positive osteocytes and osteoclasts. Extracellular bone matrix also stained occasionally for the presence of DNA fragments. During endochondral bone formation, TUNEL staining was detected in late hypertrophic chondrocytes of the epiphyseal growth plate. During rapid longitudinal growth of long bones, TUNEL-positive hypertrophic chondrocytes were found coincident with or slightly after invasion of blood vessels from the diaphysis. However, during slow longitudinal growth and in secondary ossification centers, DNA fragmentation was seen in hypertrophic chondrocytes still located within their lacunae. We conclude that some of the osteocytes in deeper layers of bone die within their lacuna and disperse nuclear fragments over the extracellular matrix, that a majority of the osteocytes are phagocytosed and degraded by osteoclasts at sites of intense bone resorption, and that during endochondral ossification, substantial numbers of late hypertrophic chondrocyte cells undergo cell death.

Nuclear DNA fragmentation during postnatal tooth development of mouse and hamster and during dentin repair in the rat

The TUNEL (transferase-mediated, dUTP-biotin nick end labeling) method for in situ labeling of DNA strands was utilized to localize DNA fragmentation in cells involved in tooth formation in the neonatal mouse and hamster. Positive reactions for the presence of DNA fragments were obtained in some epithelial cells of the cervical loop region of incisors, late secretory, transitional and early maturation stage ameloblasts, stratum intermedium cells and in shortened ameloblasts just before eruption. Also, cells of the periodontal ligament of the continuously erupting incisors stained positive shortly before eruption. Odontoblasts were negative but became strongly positive during the formation of physiological osteodentin at the tip of developing incisors. Osteodentin matrix and the surfaces of unerupted enamel and cementum just prior to eruption stained for DNA fragments as well. DNA fragmentation could be elicited in odontoblasts and underlying pulpal tissues of mature erupted molars after mechanical injury to the odontoblast processes during cavity preparation. We conclude that, in rodents, DNA fragmentation and cell death are biological processes which take place in a variety of cells involved in formation of teeth. The TUNEL staining technique is a simple but powerful tool to examine the fate of cells and tissues undergoing either programmed cell death (apoptosis) or fragmentation of nuclear DNA induced by external factors leading to pathological changes.

Characterization of cellular responses involved in reparative dentinogenesis in rat molars

During primary dentin formation, differentiating primary odontoblasts secrete an organic matrix, consisting principally of type I collagen and non-collagenous proteins, that is capable of mineralizing at its distal front. In contrast to ameloblasts that form enamel and undergo programmed cell death, primary odontoblasts remain metabolically active in a functional tooth. When dentin is exposed to caries or by operative procedures, and when exposed dentinal tubules are treated with therapeutic dental materials, the original population of odontoblasts is often injured and destroyed. The characteristics of the replacement pool of cells that form reparative dentin and the biologic mechanisms that modulate the formation of this matrix are poorly understood. Based on the hypothesis that events governing primary dentinogenesis are reiterated during dentin repair, the present study was designed to test whether cells that form reparative dentin are odontoblast-like. Cervical cavities were prepared in rat first molars to generate reparative dentin, and animals were killed at various time intervals. In situ hybridization with gene-specific riboprobes for collagen types I and III was used to study de novo synthesis by cells at the injured dentin-pulp interface. Polyclonal antibodies raised against dentin sialoprotein (DSP), a dentin-specific protein that marks the odontoblast phenotype, were used in immunohistochemical experiments. Data from our temporal and spatial analyses indicated that cells forming reparative dentin synthesize type I but not type III collagen and are immunopositive for DSP. Our results suggest that cells that form reparative dentin are odontoblast-like.

Analysis of tooth development in mice bearing a TGF-beta 1 null mutation

While transforming growth factor-beta 1 (TGF-beta 1) and its related mammalian isoforms TGF-beta 2 and TGF-beta 3 are coexpressed in developing tooth organs, the specific biological role of each isoform is unknown. To delineate the role of TGF-beta 1 in odontogenesis, we have studied tissues from mice that lack a functional TGF-beta 1 gene. Histologic analyses revealed that in TGF-beta 1 (-/-) mice, tooth morphogenesis, cytodifferentiation and histogenesis were unaffected. Using in situ hybridization we studied the patterns of distribution of TGFs-beta 1, beta 2 and beta 3 in the TGF-beta 1 (+/+, +/- and -/-) genotypes. Our results indicate no detectable TGF-beta 1 mRNA in null tissues while TGFs-beta 2 and beta 3 showed normal temporal-spatial patterns of distribution. Using antibodies against TGF-beta 1, we observed immunoreactive TGF-beta 1 in tissues from null mice suggesting that maternally-derived TGF-beta 1 may be involved in the rescue of several developmental events in TGF-beta 1 knockout mice.

Osteoblast-specific expression of the alpha 2(I) collagen promoter in transgenic mice: correlation with the distribution of TGF-beta 1

To begin to assess the transcriptional mechanisms that regulate type I collagen gene expression in differentiating osteoblasts, we have sought to determine the minimal promoter sequences that confer osteoblast-specific expression to the alpha 2(I) collagen gene during murine development. Transgenic mice were generated harboring DNA constructs in which the -2000, -500, and -350 to +54 regions located upstream of the start of transcription were linked to the Escherichia coli beta-galactosidase reporter gene (LacZ). Histochemical staining using X-gal indicated that the -2000 lacZ transgene was strongly expressed in newly differentiated and fully functional osteoblasts at intramembranous and endochondral sites of ossification. The promoter was also active in osteocytes in regions of bone remodeling within alveolar bone. The temporal and spatial activity of this region of the promoter closely resembled the developmental patterns of expression of the endogenous alpha 2(I) collagen gene as determined by in situ hybridization. The cis-acting elements within the 500 and 350 bp segments of the alpha 2(I) collagen promoter also drove reporter gene expression in forming osteoblasts, although levels of transgene expression were not as marked as that seen with the 2000 bp promoter. Furthermore, the synthesis and secretion of TGF-beta 1 in osteogenic zones coincided with areas where the alpha 2(I) collagen promoter constructs were transcriptionally active. Since a nuclear factor 1 binding site present at -300 has been shown to mediate the effects of TGF-beta 1 on the alpha 2(I) collagen promoter, these data support a role for TGF-beta 1 in the control of this gene during development.

Dentin sialoprotein: biosynthesis and developmental appearance in rat tooth germs in comparison with amelogenins, osteocalcin and collagen type-I

A non-collagenous protein, extracted from rat incisor dentin, is a dentin sialoprotein (DSP). We examined immunohistochemically the developmental appearance and tissue distribution of DSP in 1 to 3-day-old rat molar and incisor tooth germs. The earliest staining for DSP was observed in newly differentiated odontoblasts. In more advanced stages, immunostaining for DSP gradually increased in pre-dentin, odontoblasts and dentin, and appeared in many cells of the dental papilla. In early stages of development before the breakdown of the dental basement membrane, pre-ameloblasts were also positive for DSP. This staining disappeared from the ameloblast cell body soon after deposition of the first layer of mineralized dentin. Radiolabelling of tooth matrix proteins with 14C-serine in vitro followed by immunoprecipitation and fluorography confirmed that DSP was synthesized by tooth-forming cells. The immunolocalization for DSP was different from that of either collagen type-I, osteocalcin or the amelogenins. Whereas collagen type-I and osteocalcin were restricted to the mesenchymal dental tissues, the amelogenins were detectable in both epithelial and mesenchymal dental cells and tissues at the epithelio-mesenchymal interface at early stages of development, prior to the onset of dentin mineralization. We conclude that DSP is expressed in and secreted by odontoblasts and some dental papilla cells from early stages of dentinogenesis onwards, i.e. later than type-I collagen, but before deposition of the first layer of mineralized dentin. In pre-mineralizing stages, some of the matrix proteins may be endocytosed from the pre-dentin by both cell types involved in the epithelio-mesenchymal interaction.

Minimal DNA sequences that control the cell lineage-specific expression of the pro alpha 2(I) collagen promoter in transgenic mice

The pattern of expression of the pro alpha 2(I) collagen gene is highly tissue specific in adult mice and shows its strongest expression in bones, tendons, and skin. Transgenic mice were generated harboring promoter fragments of the mouse pro alpha 2(I) collagen gene linked to the Escherichia coli beta-galactosidase or firefly luciferase genes to examine the activity of these promoters during development. A region of the mouse pro alpha 2(I) collagen promoter between -2,000 and +54 exhibited a pattern of beta-galactosidase activity during embryonic development that corresponded to the expression pattern of the endogenous pro alpha 2(I) collagen gene as determined by in situ hybridization. A similar pattern of activity was also observed with much smaller promoter fragments containing either 500 or 350 bp of upstream sequence relative to the start of transcription. Embryonic regions expressing high levels of beta-galactosidase activity included the bulbus arteriosus, valves of the developing heart, sclerotomes, meninges, limb buds, connective tissue fascia between muscle fibers, osteoblasts in newly formed bones, fibroblasts in tendons, periosteum, dermis, and peritoneal membranes. The pattern of beta-galactosidase activity was similar and included within the extracellular immunohistochemical localization pattern of transforming growth factor-beta 1 (TGF-beta 1). The -315(-)-284 region of the pro alpha 2(I) collagen promoter was previously shown to mediate the stimulatory effects of TGF-beta 1 on the pro alpha 2(I) collagen promoter in DNA transfection experiments with cultured fibroblasts. A construct containing this sequence tandemly repeated 5' to a very short alpha 2(I) collagen promoter (-40(-)+54) showed preferential activity in tail and skin of 4-wk-old transgenic mice. Except for low expression of the transgene in bone, this pattern mimics the expression of the endogenous pro alpha 2(I) collagen gene. We propose the hypothesis that the tissue-specific expression of the pro alpha 2(I) collagen gene during embryogenesis is controlled by both TGF-beta 1 and cell-specific transcription factors; one of these could interact directly or indirectly with either the -315(-)-284 or the -40(-)+54 segment.

Isolation, characterization and immunolocalization of a 53-kDal dentin sialoprotein (DSP)

We isolated a sialic-rich protein from rat dentin extracts and have named it dentin sialoprotein, DSP (formerly called 95K glycoprotein). DSP is rich in aspartic acid, glutamic acid, glycine and serine, but contains no cysteine or phosphate. The 30% carbohydrate content includes about 9% sialic acid and indicates that several N-glycosides and O-glycosides are present. Sedimentation equilibrium analysis gave a M(r) of 52,570. Based on this molecular weight we calculated that DSP contains about 350-amino acids and 75 monosaccharides. With automated Edman degradation the sequence of the first 8-amino acids was shown to be: Ile-Pro-Val-Pro-Gln-Leu-Val-Pro. The initial 3 residues of this sequence are identical to the first 3 in human osteopontin (OPN) and are closely similar to the Leu-Pro-Val sequences of OPN from other species, as well as at the beginning of bone acidic glycoprotein-75 (BAG-75). On Western immunoblots, purified polyclonal antibodies reacted only with DSP in dentin extracts and with none of the proteins from bone. Similarly, immunolocalization experiments showed the presence of DSP in dentin but not in enamel or alveolar bone. Along with immunohistochemical localization data reported elsewhere, these observations suggest that DSP may be an important marker for cells in the odontoblast lineage.

Developmental expression of a 53 KD dentin sialoprotein in rat tooth organs

Rat dentin contains a major sialic acid-rich glycoprotein, DSP, with an overall composition similar to that of bone sialoproteins but whose biological role in dentinogenesis is unknown. Using polyclonal affinity-purified antibodies to rat DSP and four immunohistochemical methods of detection, we studied the cell and tissue localization of DSP and the time course of its appearance during odontoblast differentiation. DSP first appeared within young odontoblasts concomitant with early secretion of pre-dentin matrix and before the onset of mineralization but was absent in pre-odontoblasts. DSP immunostaining also localized within secretory odontoblasts and was intense in odontoblastic processes. Early pre-dentin stained positive for DSP, in contrast to more mature pre-dentin, where immunoreactivity was less intense and more restricted to odontoblastic processes. In the zone of mineralized dentin matrix, a moderate and uniform staining pattern was evident. Intense immunostaining was also seen within the cells and matrix of dental pulp during dentinogenesis. Other cells and tissues within the tooth organ and those surrounding it were non-reactive. These findings suggest that DSP is developmentally expressed in cells of the odontoblastic lineage and may be a biochemical marker of odontoblastic activity.

Histochemical localization of transforming growth factor-beta 1 in developing rat molars using antibodies to different epitopes

In this study transforming growth factor-beta 1 (TGF-beta 1) has been immunolocalized in developing rat molars using two well characterized polyclonal antibodies, Anti-CC and Anti-LC, that recognize extracellular and intracellular TGF-beta 1, respectively. With immunohistochemical methods and the ABC-peroxidase system of detection, the growth factor was immunolocalized within the ectodermally derived enamel organ and the neural crest-derived dental papilla at the early and advanced bell stages of development. With Anti-CC, widespread and abundant extracellular TGF-beta 1 was found associated with the stellate reticulum and within central and apical regions of dental papilla mesenchyme. In contrast, Anti-LC localized TGF-beta 1 intensely within the cells of the outer dental epithelium. Moderate immunostaining for TGF-beta 1 with Anti-LC was also evident within the apical cytoplasm of inner dental epithelial cells and odontoblasts. These findings support the hypothesis that TGF-beta 1 may play a paracrine role in tooth development by regulating the epithelial-mesenchymal interactions that influence growth and cytodifferentiation events.

Temporal and spatial patterns of transforming growth factor-beta 1 expression in developing rat molars

Regulatory peptides of the TGF-beta family affect various aspects of embryonic development. Recent immunolocalization and in situ hybridization studies have demonstrated a specific time- and tissue-dependent expression of TGF-beta 1 in the developing mouse embryo. The purpose of this study was to evaluate the distribution of TGF-beta 1 within rat molars at different stages of development, using a well-characterized antibody, highly specific for TGF-beta 1, and immunohistochemical methods of detection. TGF-beta 1 was immunolocalized intensely within the ectodermally derived stellate reticulum and the mesenchyme of the dental papilla at the bell stage of development. Marked immunostaining was also evident in the papillary layer and the reduced dental organ subjacent to ameloblasts in the differentiation and secretory phases of amelogenesis. During the formation of coronal tissues and in the pre-eruptive phase, immunoreactive TGF-beta 1 was localized conspicuously within the dental follicle overlying the tooth germ. This temporospatial pattern of expression of TGF-beta 1 appears to correlate with specific events in morphogenesis, histogenesis and cytodifferentiation during tooth development.