Impact of Periodontal Disease on the Quality of Life of Older People in Indonesia: A Qualitative Study

Introduction:

The impact of periodontal disease on oral health–related quality of life (OHRQoL) has often been investigated from a quantitative research perspective, which is based on clinical findings and an OHRQoL questionnaire. Very few studies have examined the issue from the view of qualitative research. To our knowledge, there have been no previous qualitative studies focusing the effect of periodontal disease on OHRQoL in Indonesian older people.

Objectives:

To explore and understand the impact of periodontal disease on the OHRQoL of older people as a subjective reflection in relation to periodontal disease experiences.

Methods:

Semi-structured interviews were conducted in a sample of 31 older people with generalized chronic periodontitis. Thematic analysis was used to identify the key issues in participants’ accounts. The analysis was undertaken by 2 independent coders to ensure reliability. To achieve thematic saturation, successive interviews were undertaken until 5 sequential interviews did not bring new themes.

Results:

Participants reported the negative effects likely related to periodontal disease. The impacts of periodontal disease were described by these older people as affecting more than pain, physical discomfort, and physical function restrictions. Periodontal disease also affected their psychological and social aspects of daily living. In addition, this study identified themes related to individual and environmental factors that may modify and personalize periodontal disease experiences. Furthermore, this study identified a misleading belief that problems related to periodontal disease were a normal part of aging, which might influence individuals’ expectations toward oral health. Relatedly, participants frequently reported that the progression of tooth mobility to tooth loss was an inevitable part of the aging process.

Conclusions:

Periodontal disease negatively affected participants’ OHRQoL. It is fundamental to understand older people’s perceptions toward their periodontal disease as well as individual and environmental factors that may have an influence on their periodontal disease experiences.

Knowledge Transfer Statement:

This study is a reflection of Indonesian older people’s subjective periodontal disease experiences. Therefore, the present study can be used to understand older people’s perceptions, attitudes, behaviors, and experiences toward periodontal disease and how this disease may affect their quality of life. This study also highlights a widespread and misleading belief that oral problems related to periodontal disease are an inevitable part of aging in this study population.

Periodontal Disease and Oral Health-Related Quality of Life in the Older Population in Indonesia

Introduction:

Despite being acknowledged as the second global burden of oral disease, periodontal disease has few epidemiologic studies in the literature, particularly for developing countries. Many previous studies have assessed the relationship between periodontal disease and oral health–related quality of life (OHRQoL), with patients attending dental clinic or hospitals rather than a general population. This study attempted to fill the knowledge gap in limited information about periodontal disease and OHRQoL, with reference to a general population in a developing country.

Objectives:

To investigate the relationship between OHRQoL and periodontal diseases in an older population in Indonesia.

Methods:

We invited 582 older people from community health centers. The 369 (63.4%) older people who agreed to participate consented to an oral health examination and a questionnaire capturing demographic, socioeconomic, behavioral, and Oral Health Impact Profile–14 (OHIP-14) data.

Results:

Almost 75% of the older people had generalized periodontitis; 3% had healthy periodontal status; and around 22% had localized periodontitis. There was a lack of statistical evidence for an association between periodontal disease status and OHRQoL. This result was based on the appraisal of the prevalence of the impact (Odds ratio [OR], 0.95 [95% CI, 0.54 to 1.59]; P = 0.77), difference in mean severities (0.07 [95% CI, –1.66 to 1.80]; P = 0.94), and extent of the impact (P = 0.996). However, we found evidence for a relationship between tooth mobility and OHRQoL for all of the OHIP assessments, including prevalence of the impact (OR, 1.87 [95% CI, 1.16 to 3.01]; P = 0.009), difference in mean severities (–2.98 [95% CI, –4.50 to –1.45]; P < 0.001), and extent of the impact (P = 0.001).

Conclusion:

There was a lack of statistical evidence for a relationship between periodontal disease status and OHRQoL in this society. However, we found evidence that tooth mobility, as a sign of periodontal disease progression, is related to OHRQoL.

Knowledge Transfer Statement:

The present study can be used by dentists, community health workers, and policy makers in Indonesia to understand the prevalence, severity, and extent of the negative impacts of periodontal disease on older people’s quality of life. In addition, this study provides information about factors that might considerably affect the oral health–related quality of life in this society, such as brushing habits, dental visit, family income, DMF-T status, and subjective appraisal toward dental health.

Dentine sialophosphoprotein signal in dentineogenesis and dentine regeneration

Dentineogenesis starts on odontoblasts, which synthesise and secrete non-collagenous proteins (NCPs) and collagen. When dentine is injured, dental pulp progenitors/mesenchymal stem cells (MSCs) can migrate to the injured area, differentiate into odontoblasts and facilitate formation of reactionary dentine. Dental pulp progenitor cell/MSC differentiation is controlled at given niches. Among dental NCPs, dentine sialophosphoprotein (DSPP) is a member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family, whose members share common biochemical characteristics such as an Arg-Gly-Asp (RGD) motif. DSPP expression is cell- and tissue-specific and highly seen in odontoblasts and dentine. DSPP mutations cause hereditary dentine diseases. DSPP is catalysed into dentine glycoprotein (DGP)/sialoprotein (DSP) and phosphoprotein (DPP) by proteolysis. DSP is further processed towards active molecules. DPP contains an RGD motif and abundant Ser-Asp/Asp-Ser repeat regions. DPP-RGD motif binds to integrin αVβ3 and activates intracellular signalling via mitogen-activated protein kinase (MAPK) and focal adhesion kinase (FAK)-ERK pathways. Unlike other SIBLING proteins, DPP lacks the RGD motif in some species. However, DPP Ser-Asp/Asp-Ser repeat regions bind to calcium-phosphate deposits and promote hydroxyapatite crystal growth and mineralisation via calmodulin-dependent protein kinase II (CaMKII) cascades. DSP lacks the RGD site but contains signal peptides. The tripeptides of the signal domains interact with cargo receptors within the endoplasmic reticulum that facilitate transport of DSPP from the endoplasmic reticulum to the extracellular matrix. Furthermore, the middle- and COOH-terminal regions of DSP bind to cellular membrane receptors, integrin β6 and occludin, inducing cell differentiation. The present review may shed light on DSPP roles during odontogenesis.

Third Dentition Is the Main Cause of Premolar Supernumerary Tooth Formation

While the prevalence of supernumerary teeth (ST) is high in permanent dentition, the etiology of ST in humans remains unclear. However, multiple murine models of ST have elaborated on dated mechanisms traditionally ascribed to ST etiology: one involves the rescue of rudimental teeth, and the second considers the contribution of odontogenic epithelial stem cells. It remains unclear whether these mechanisms of ST formation in mice are applicable to humans. The third dentition is usually regressed apoptotic-that is, the teeth do not completely form in humans. Recently, it was suggested that ST result from the rescue of regression of the third dentition in humans. The present investigation evaluates the proportion of collected general ST cases that evinced a third dentition based on the clinical definition of ST derived from the third dentition. We also investigated the contribution of SOX2-positive odontogenic epithelial stem cells to ST formation in humans. We collected 215 general ST cases from 15,008 patients. We confirmed that the general characteristics of the collected ST cases were similar to the results from previous reports. Of the 215 cases, we narrowed our analysis to the 78 patients who had received a computed tomography scan. The frequency of ST considered to have been derived from the third dentition was 26 out of 78 cases. Evidence of a third dentition was especially apparent in the premolar region, was more common in men, and was more likely among patients with ≥3 ST. SOX2-positive odontogenic epithelial stem cells within the surrounding epithelial cells of developing ST were observed in non-third dentition cases and not in third dentition cases. In conclusion, the third dentition is the main cause of ST in humans. The odontogenic epithelial stem cells may contribute to ST formation in cases not caused by a third dentition.

Pumps or Multiple Daily Injections in Pregnancy Involving Type 1 Diabetes: A Prespecified Analysis of the CONCEPTT Randomized Trial

OBJECTIVE

To compare glycemic control, quality of life, and pregnancy outcomes of women using insulin pumps and multiple daily injection therapy (MDI) during the Continuous Glucose Monitoring in Women With Type 1 Diabetes in Pregnancy Trial (CONCEPTT).

RESEARCH DESIGN AND METHODS

This was a prespecified analysis of CONCEPTT involving 248 pregnant women from 31 centers. Randomization was stratified for pump versus MDI and HbA_1c. The primary outcome was change in HbA_1c from randomization to 34 weeks' gestation. Key secondary outcomes were continuous glucose monitoring (CGM) measures, maternal-infant health, and patient-reported outcomes.

RESULTS

At baseline, pump users were more often in stable relationships (P = 0.003), more likely to take preconception vitamins (P = 0.03), and less likely to smoke (P = 0.02). Pump and MDI users had comparable first-trimester glycemia: HbA_1c 6.84 ± 0.71 vs. 6.95 ± 0.58% (51 ± 7.8 vs. 52 ± 6.3 mmol/mol) (P = 0.31) and CGM time in target (51 ± 14 vs. 50 ± 13%) (P = 0.40). At 34 weeks, MDI users had a greater decrease in HbA_1c (-0.55 ± 0.59 vs. -0.32 ± 0.65%, P = 0.001). At 24 and 34 weeks, MDI users were more likely to achieve target HbA_1c (P = 0.009 and P = 0.001, respectively). Pump users had more hypertensive disorders (P = 0.011), mainly driven by increased gestational hypertension (14.4 vs. 5.2%; P = 0.025), and more neonatal hypoglycemia (31.8 vs. 19.1%, P = 0.05) and neonatal intensive care unit (NICU) admissions >24 h (44.5 vs. 29.6%; P = 0.02). Pump users had a larger reduction in hypoglycemia-related anxiety (P = 0.05) but greater decline in health/well-being (P = 0.02).

CONCLUSIONS

In CONCEPTT, MDI users were more likely to have better glycemic outcomes and less likely to have gestational hypertension, neonatal hypoglycemia, and NICU admissions than pump users. These data suggest that implementation of insulin pump therapy is potentially suboptimal during pregnancy.

Mouse Amelogenin Exons 8 and 9: Sequence Analysis and Protein Distribution

Amelogenin is the major protein of the developing enamel. Two additional exons, termed 8 and 9, have been characterized in the rat. Our aim was: to identify the mouse amelogenin exons 8/9 sequences; to investigate the potential presence of the alternative spliced isoforms of amelogenin exons 8/9; and to immunolocalize proteins containing sequences encoded by exons 8/9 during odontogenesis. RT-PCR analysis with exon 9 anti-sense primer generated 2 major amplicons with the use of a mouse tooth cDNA library and dental cell lines. DNA sequence analysis showed 93% identify with the rat exons 8/9 sequence. Alternative splicing of exon 3 was also found, but only in cDNAs lacking exons 8 and 9. Immunohistochemistry localized exons 8/9-encoded proteins in ameloblasts, young odontoblasts, and stratum intermedium cells. Analysis of our data supports the hypothesis that: (1) AMELX contains 2 additional exons; (2) ameloblasts and odontoblasts synthesize amelogenin 8/9; and (3) amelogenin splice variants may have unique functions during tooth formation.

Factors associated with a clinician's offer of screening HIV-positive patients for sexually transmitted infections, including syphilis

This retrospective study assessed whether Quality Improvement Scotland national standards for the sexual health care offered to HIV-positive individuals are being met by the Edinburgh genitourinary (GU) medicine clinic; specifically whether HIV-positive patients are offered: (a) sexually transmitted infection (STI) screening annually and (b) syphilis testing six-monthly. The study also reviewed what factors were associated with a clinician's offer of STI screening and syphilis testing. Of the 509 patients seen within the study period, case notes documented that 64% were offered STI screens, and 69% were offered syphilis testing, results consistent with audits of services elsewhere. Sexual orientation (P < 0.0005), relationship status (P = 0.007) and receipt of antiretrovirals (P = 0.001) were independent predictors of clinician offer of STI screening, while gender (P < 0.0005) and receipt of antiretrovirals (P = 0.063) were independent predictors of offer of syphilis testing. Our results suggest that one explanation for clinicians failing to offer STI screens and syphilis serology testing is their (implicit) risk assessment that STI testing is not required in individual patients.

Competing roles of TGFbeta and Nma/BAMBI in odontoblasts

Nma/BAMBI is a novel pseudoreceptor with homology to a TGFbeta type I receptor that lacks a serine/threonine kinase domain. Nma/BAMBI functions as a dominant-negative protein that regulates reciprocal epithelial-mesenchymal interactions during organogenesis. Therefore, we hypothesized that Nma/BAMBI regulates TGFbeta signaling and downstream gene expression during dentinogenesis. To test this hypothesis, we examined the downstream gene expression profiles of major dentin extracellular matrix proteins in response to Nma/BAMBI, and we examined the roles of Nma/BAMBI and TGFbeta-1 during dentinogenesis. Overexpression of Nma/BAMBI in the mouse odontoblast-like cell line MD10-A2 down-regulated expression of DSPP by 66% and up-regulated expression of DMP1 four-fold. TGFbeta treatment reversed Nma/BAMBI's negative effect on DSPP expression. Furthermore, we demonstrated that TGFbeta negatively regulates Nma/BAMBI's expression levels in MD10-A2 odontoblast-like cells. Analysis of these data, together, indicates that TGFbeta and Nma/BAMBI are inversely regulated and that the sequence of expression determines the net effect on downstream gene expression.

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.

Phenotype characterization and DSPP mutational analysis of three Brazilian dentinogenesis imperfecta type II families

The aim of this study was to perform phenotype analysis and dentin sialophosphoprotein (DSPP) mutational analysis on 3 Brazilian families diagnosed with dentinogenesis imperfecta type II (DGI-II) attending the Dental Anomalies Clinic in Brasilia, Brazil. Physical and oral examinations, as well as radiographic and histopathological analyses, were performed on 28 affected and unaffected individuals. Clinical, radiographic and histopathological analyses confirmed the diagnosis of DGI-II in 19 individuals. Pulp stones were observed in ground sections of several teeth in 2 families, suggesting that obliteration of pulp chambers and root canals results from the growth of these nodular structures. Mutational DSPP gene analysis of representative affected family members revealed 7 various non-disease-causing alterations in exons 1-4 within the dentin sialoprotein domain. Further longitudinal studies are necessary to elucidate the progression of pulpal obliteration in the DGI-II patients studied as well as the molecular basis of their disease.

PDGF up-regulates CSF-1 gene transcription in ameloblast-like cells

Macrophage colony-stimulating factor (CSF-1) is a key regulatory cytokine for amelogenesis, and ameloblasts synthesize CSF-1. We hypothesized that PDGF stimulates DNA synthesis and regulates CSF-1 in these cells. We determined the effect of PDGF on CSF-1 expression using MEOE-3M ameloblasts as a model. By RT-PCR, MEOE-3M expressed PDGFRs and PDGF A- and B-chain mRNAs. PDGF-BB increased DNA synthesis and up-regulated CSF-1 mRNA and protein in MEOE-3M. Cells transfected with CSF-1 promoter deletion constructs were analyzed. A PDGF-responsive region between -1.7 and -0.795 kb, containing a consensus Pea3 binding motif, was identified. Electrophoretic mobility shift assay (EMSA) showed that PDGF-BB stimulated protein binding to this motif that was inhibited in the presence of anti-Pea3 antibody. Analysis of these data provides the first evidence that PDGF-BB is a mitogen for MEOE-3M and increases CSF-1 protein levels, predominantly by transcription. Elucidation of the cellular pathways that control CSF-1 expression may provide novel strategies for the regulation of enamel matrix formation.

Isolation and characterization of multipotent human periodontal ligament stem cells

BACKGROUND

Periodontal ligament (PDL) repair is thought to involve mesenchymal progenitor cells capable of forming fibroblasts, osteoblasts and cementoblasts. However, full characterization of PDL stem cell (SC) populations has not been achieved.

OBJECTIVE

To isolate and characterize PDLSC and assess their capability to differentiate into bone, cartilage and adipose tissue.

METHODS

Human PDL cells were stained for STRO-1, FACS sorted and expanded in culture. Human bone marrow SC (BMSC) served as a positive control. PDLSC and BMSC were cultured using standard conditions conducive for osteogenic, chondrogenic and adipogenic differentiation. Osteogenic induction was assayed using alizarine red S staining and expression of alkaline phosphatase (ALP) and bone sialoprotein (BSP). Adipogenic induction was assayed using Oil Red O staining and the expression of PPAR gamma 2 (early) and LPL (late) adipogenic markers. Chondrogenic induction was assayed by collagen type II expression and toluidine blue staining.

RESULTS

Human PDL tissue contains about 27% STRO-1 positive cells with 3% strongly positive. In osteogenic cultures ALP was observed by day-7 in BMSC and day-14 in PDLSC. BSP expression was detectable by day-7; with more intense staining in PDLSC cultures. In adipogenic cultures both cell populations showed positive Oil Red O staining by day-25 with PPAR gamma 2 and LPL expression. By day-21, both BMSC and PDLSC chondrogenic induced cultures expressed collagen type II and glycosaminoglycans.

CONCLUSIONS

The PDL contains SC that have the potential to differentiate into osteoblasts, chondrocytes and adipocytes, comparable with previously characterized BMSC. This adult PDLSC population can be utilized for potential therapeutic procedures related to PDL regeneration.

Factors influencing the expression of dental extracellular matrix biomineralization

The forming tooth organ provides a number of opportunities to investigate the cellular and molecular biology of cell-mediated extracellular matrix (ECM) biomineralization. Regulatory processes associated with tooth formation are being investigated by identifying when and where cell adhesion molecules (CAMs), substrate adhesion molecules (SAMs), dentine phosphoprotein and enamel gene products are expressed during sequential developmental stages. In vitro organotypic culture studies in serumless, chemically-defined medium, have shown that instructive and permissive signalling are required for both morphogenesis and cytodifferentiation. Intrinsic developmental instructions (autocrine and paracrine factors) act independently of long-range hormonal or exogenous growth factors and mediate morphogenesis from the initiation of the dental lamina to the crown stages of tooth development. This review summarizes the results of studies using experimental embryology, recombinant DNA technology and immunocytology to elucidate mechanisms responsive to instructive epithelial-mesenchymal interactions associated with ameloblast differentiation, odontoblast differentiation, and dentine and enamel ECM biomineralization.

Predicting survival in patients with hepatocellular carcinoma: A UK perspective

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is a cancer of rising incidence in the UK. The aim of this study was to compare the Okuda, Cancer of the Liver Italian Program (CLIP), and Barcelona Clinic Liver Cancer (BCLC) classifications as predictors of survival in UK patients with HCC.

METHODS

Data were analysed from a prospective database maintained in a specialist hepatobiliary unit from 1998 to 2003. Each system was assessed for its discriminatory power, monotonicity of gradient, and independent contribution to prediction of mortality status based on a multivariate model.

RESULTS

One hundred and two patients (77 males, 25 females) were identified with a median age of 65 (range, 14-87) years. The overall median survival time was 13 months and the one- and five-year survival rates were 52.9% (95% CI: 43.2%, 62.6%) and 35.3% (95% CI: 26.0%, 44.6%), respectively. All three classification systems had the capacity to differentiate between patient survival times across different stages. The Okuda system was superior in overall discriminatory power and in strength of monotonicity. The BCLC system, however, made the highest independent contribution of all three systems in predicting survival in the Cox regression model.

CONCLUSIONS

All three classification systems were effective in predicting survival for patients with HCC in a UK population.

MEPE expression in osteocytes during orthodontic tooth movement

MEPE and DMP1 may play a role in mineralisation and demineralisation within the osteocyte microenvironment. Our earlier studies showed that DMP1 is mechanically responsive [Gluhak-Heinrich J, Ye L, Bonewald LF, Feng JQ, MacDougall M, Harris SE, et al. Mechanical loading stimulates dentin matrix protein 1 (DMP1) in osteocytes in vivo. J Bone Min Res 2003;18(5):807-17].

OBJECTIVES

To examine the effect of mechanical loading on the expression of MEPE using mouse tooth movement model, and compare this effect to that on DMP1.

METHODS

In situ hybridisation and immunohistochemistry was performed on 38 treated and 38 control bone sites loaded 6-72 h. ImageJ was used for quantification of mRNA expression in osteocytes.

RESULTS

Alveolar osteocytes showed high basal level of MEPE that decreased during the first day of loading, followed by 2.8-fold stimulation at day 3, and returning to a control level by day 7.

CONCLUSION

The osteocyte specific mechanical stimulation of MEPE was delayed and different, compared to that of DMP1. This suggests a distinct role of MEPE and DMP1 in the response of osteocytes to mechanical loading in vivo.

Targeted expression of csCSF-1 in op/op mice ameliorates tooth defects

OBJECTIVE

The aim of this study was to characterize the tooth phenotype of CSF-1-deficient op/op mice and determine whether expression of csCSF-1 in these mice has a role in primary tooth matrix formation.

DESIGN

Ameloblasts and odontoblasts, isolated from wt/wt frozen sections using laser capture microdissection, were analysed for csCSF-1, sCSF-1 and CSF-1R mRNA by RT-PCR. Mandibles, excised from 8 days op/op and wt/wt littermates, were examined for tooth morphology as well as amelogenin and DMP1 expression using in situ hybridisation. op/opCS transgenic mice, expressing csCSF-1 in teeth and bone using the osteocalcin promoter, were generated. Skeletal X-rays and histomorphometry were performed; teeth were analysed for morphology and matrix proteins.

RESULTS

Normal dental cells in vivo express both CSF-1 isoforms and CSF-1R. Compared to wt/wt, op/op teeth prior to eruption showed altered dental cell morphology and dramatic reduction in DMP1 transcripts. op/opCS mice showed marked resolution of osteopetrosis, tooth eruption and teeth that resembled amelogenesis imperfecta-like phenotype. At 3 weeks, op/op teeth showed severe enamel and dentin defects and barely detectable amelogenin and DMP1. In op/opCS mice, DMP1 in odontoblasts increased to near normal and dentin morphology was restored; amelogenin also increased. Enamel integrity improved in op/opCS, although it was thinner than wt enamel.

CONCLUSIONS

Results demonstrate that ameloblasts and odontoblasts are a source and potential target of CSF-1 isoforms in vivo. Expression of csCSF-1 within the tooth microenvironment is essential for normal tooth morphogenesis and may provide a mechanism for coordinating the process of tooth eruption with endogenous matrix formation.

Ultrastructural and immunocytochemical characterization of immortalized odontoblast MO6-G3

AIM

To investigate an immortalized murine odontoblast cell line as a potential alternative for experimental studies on dentinogenesis.

METHODOLOGY

The MO6-G3 cell line was investigated morphologically over 3, 7, 11 and 42 days of culture, using histochemical localization of dentine sialoprotein (DSP), alkaline phosphatase (AP), type I collagen and actin filaments, histoenzymatic staining and biochemical investigation of AP and finally, transmission and scanning electron microscopy.

RESULTS

Scanning electron micrographs showed elongated cells. Accordingly, a polarized organization of odontoblasts was observed by transmission electron microscopy, identifying distinct subcellular compartments as described in vivo. The secretion apparatus, which includes cisternae of rough endoplasmic reticulum, Golgi apparatus saccules and secretion vesicles and granules, was longitudinally organized in the supranuclear compartment ending distally in the secretory pole. A cellular process was observed. The investigation of the cytoskeleton network revealed that actin microfilaments were organized in parallel stress fibre oriented depending on the longitudinal axis of the cytoplasm. Immunofluorescent labelling showed a continuous expression of type I collagen, DSP and AP. A unipolar distribution characterized intracellular DSP immunoreactivity. Histoenzymology revealed AP active sites increasing from 3 to 11 days albeit with a moderate level of activity comparatively to the in vivo situation in dental cells.

CONCLUSION

This cell line MO6-G3 not only showed the criteria of odontoblast phenotype as previously reported but also the characteristic morphodifferentiation pattern of polarized odontoblasts at the cellular level but with an apparent random distribution.

TGF beta-1 downregulates DMP-1 and DSPP in odontoblasts

Transforming growth factor beta-1 (TGF beta-1) is a multifunctional growth factor that is expressed in numerous cell types. It has been shown to induce secretion of dentin extracellular matrix components associated with primary dentinogenesis and to play a role in tertiary or reparative dentinogenesis. In this study, we investigated the potential transcriptional regulation by TGF beta-1 of two dentin matrix proteins: dentin matrix protein 1 (DMP-1), and dentin sialophosphoprotein (DSPP). In vitro promoter studies were performed using plasmid constructs containing mouse DMP-1 and DSPP promoter sequences fused to the luciferase reporter gene. Constructs were transiently transfected in the mouse odontoblast cell line M06-G3 and cultured in the presence or absence of TGF beta-1. The integrity of the TGF beta-1 signaling pathway was investigated in the M06-G3 cells by identifying known key effectors of TGF beta-1 signal transduction. Transient transfection studies demonstrate for the first time that TGF beta-1 downregulates both DMP-1 and DSPP genes. Our findings indicate that the TGF beta-1 type I receptor ALK5 is expressed by odontoblasts as well as the signal transduction proteins Smad2, Smad3, and Smad4. These results suggest that TGF beta-1 regulates two key dentin proteins involved in matrix mineralization most likely mediated through the type I ALK5 receptor and transduced by Smads 2, 3, and 4.

Cross-talk between Msx/Dlx homeobox genes and vitamin D during tooth mineralization

Rickets is associated with site-specific disorders of enamel and dentin formation, which may reflect the impact of vitamin D on a morphogenetic pathway. This study is devoted to potential cross-talk between vitamin D and Msx/Dlx transcription factors. We raised the question of a potential link between tooth defects seen in mice with rickets and Msx2 gene misexpression, using mutant mice lacking the nuclear vitamin D receptor as an animal model. Our data showed a modulation of Msx2 expression. In order to search for a functional impact of this Msx2 misexpression secondary to rickets, we focused our attention on osteocalcin as a target gene for both vitamin D and Msx2. Combining Msx2 overexpression and vitamin D addition in vitro, we showed an inhibitory effect on osteocalcin expression in immortalized MO6-G3 odontoblasts. Finally, in the same cells, such combinations appeared to modulate VDR expression outlining the existence of complex cross-regulations between vitamin D and Msx/Dix pathways.

Genomic organization and localization of mouse Nma/BAMBI: possible implications related to ameloblastoma formation

Our laboratory has determined the DNA sequence and transcriptional expression pattern of a mouse cDNA clone termed Nma/BAMBI. This clone encodes a highly conserved protein with 89% identity to the human homologue (termed Nma) and 78% similarity to the Xenopus homologue (termed BAMBI) at the predicted amino acid level. Nma/BAMBI encodes a 260-amino-acid transmembrane protein that has homology to the transforming growth factor (TGF) beta type I receptor family. This protein contains an extracellular ligand binding domain, a 24-amino-acid transmembrane domain, and a short intracellular domain that lacks a functional serine/threonine kinase domain. It is believed that Nma/BAMBI is important in the negative regulation of TGF beta signal transduction pathways during development and has implications in tumor progression. We have determined the genomic organization of the mouse Nma/BAMBI gene and confirmed the chromosomal mapping to human chromosome 10 and mouse chromosome 2. Furthermore, we report the production and utilization of an anti-peptide antibody in preliminary immunohistochemical analysis of an ameloblastoma.

Msx1 homeogene antisense mRNA in mouse dental and bone cells

Msx1 plays a key role in early dental and cranio-facial patterning. A systematic screening of Msx1 transcripts during late postnatal stages of development evidenced not only sense mRNA but also antisense mRNA in the skeleton. Natural antisenses are able to bind their corresponding sense RNAs and block protein expression. Specific reverse-transcription polymerase chain reaction (RT-PCR) Northern-blotting using riboprobes and primer extension analysis allowed to identify and sequence a mouse 2184-base Msx1 antisense transcript. The transcription start site was located in a region including a consensus TATA box. In situ hybridization evidenced an increase in antisense mRNA expression during dental and bone cell differentiation in prenatal (Theiler stages E15.5-18.5) and newborn mice. This upregulation was related to Msx1 protein downregulation in cells expressing Msx1 sense mRNA. In vitro, transient Msx1 sense and antisense mRNA overexpression was performed in MO6-G3 cells, which pertain to the odontoblast lineage (polarization and dentin sialoprotein and phosphoprotein synthesis). The balance between antisense and sense Msx1 mRNAs appeared to control Msx1 protein levels. These data suggest that a bidirectional transcription of Msx1 homeogene may control Msx1 protein levels, and therefore may be critical in cell communication and differentiation during dental and cranio-facial development and mineralization.

Differential epithelial and mesenchymal regulation of tooth-specific matrix proteins expression by 1,25-dihydroxyvitamin D3 in vivo

Enamel defects have been reported in rickets and related to disturbed expression of amelogenin in ameloblasts. The present study is devoted to amelogenin, enamelin, ameloblastin, and dentin sialophosphoprotein (DSPP) expression in both the epithelium and mesenchyme of vitamin D-deficient rat incisors. Quantitative Northern blotting analysis (relatively to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA steady-state levels) was performed on microdissected cells of rachitic (-D) and control (+D) 56 day old rats. Steady-state levels of amelogenin and enamelin mRNA were significantly reduced in the -D epithelium versus the +D epithelium ones. In contrast, ameloblastin expression was slightly increased in -D epithelium. In the same samples, DSPP mRNA levels remained unchanged in -D dental mesenchyme. Comparative electron microscopy studies between +D and -D animals showed a dramatic decrease of intraprismatic enamel (amelogenin and enamelin immunoreactive) consistent with our molecular results. In conclusion, tooth formation results from the coordinated expression of several matrix proteins that may be controlled by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3].

Expression of amelogenin in odontoblasts

Amelogenin is the major enamel protein produced by ameloblasts. Its expression has been shown to be down-regulated in ameloblasts of vitamin-D-deficient (-D) rats. The potential expression and localization of amelogenin in odontoblasts and its regulation by vitamin D were investigated in this study. RT-PCR and semi-quantitative Northern blot analyses were performed using the odontoblast cell line MO6-G3 and microdissected dental pulp mesenchyme. Both in vitro and in vivo odontoblasts expressed various alternatively spliced amelogenin transcripts. In situ hybridization studies showed that amelogenin expression was restricted to young odontoblasts during mantle dentin deposition. Electron microscopy studies localized the amelogenin protein in the odontoblast cell process cytoplasm and mantle dentin. Amelogenin immunolabeling was stronger in -D rats, suggesting an inverse regulation by vitamin D in odontoblasts. Furthermore, amelogenin mRNA steady-state levels were significantly increased in -D dental pulp mesenchyme. In addition, a temporal-spatial lengthening of the mantle dentin stage was observed in -D animals, suggesting that developmental perturbations occur in relation to the vitamin D status and/or amelogenin expression. These data show that amelogenin is expressed by odontoblasts selectively during mantle dentin deposition. This developmental regulated expression pattern is enhanced under vitamin-D-deficiency status and in a broader context may play an important role during ameloblast and odontoblast differentiation and function.

Cloning, characterization, and tissue expression pattern of mouse Nma/BAMBI during odontogenesis

Degenerate oligonucleotides to consensus serine kinase functional domains previously identified a novel, partial rabbit tooth cDNA (Zeichner-David et al., 1992) that was used in this study to identify a full-length mouse clone. A 1390-base-pair cDNA clone was isolated encoding a putative 260-amino-acid open reading frame containing a hydrophobic 25-amino-acid potential transmembrane domain. This clone shares some homology with the TGF-beta type I receptor family, but lacks the intracellular kinase domain. DNA database analysis revealed that this clone has 86% identity to a newly isolated human gene termed non-metastatic gene A and 80% identity to a Xenopus cDNA clone termed BMP and activin membrane bound inhibitor. Here we report the mouse Nma/BAMBI cDNA sequence, the tissue expression pattern, and confirmed expression in dental cell lines. This study demonstrates that Nma/BAMBI is a highly conserved protein across species and is expressed at high levels during odontogenesis.

Utilization of MO6-G3 immortalized odontoblast cells in studies regarding dentinogenesis

Tooth formation is the result of reciprocal instructive interactions between oral epithelium and cranial neural-crest-derived ectomesenchymal tissues. These interactions lead to the cytodifferentiation of highly specialized matrix-forming cell types, the ameloblast, odontoblast, and cementoblast, that produce the mineralized tissues enamel, dentin, and cementum, respectively. Our laboratory has been developing immortalized dental cell lines representative of these various cell types to facilitate studies on gene regulation, cell differentiation, matrix formation, and mineralization. Odontoblasts are solely responsible for the synthesis and secretion of the dentin extracellular matrix bilayer that consists of non-mineralized predentin and mineralized dentin. The mouse immortalized MO6-G3 cell line expresses the major matrix proteins associated with the odontoblast phenotype, producing a matrix that is capable of mineralization. This cell line serves as a useful tool in studies designed to explore the various processes of dentinogenesis. In this paper, we present studies using the mouse odontoblast cell line MO6-G3 as examples of the various research applications. Studies highlighted are: in vitro promoter studies investigating the tooth-specific gene regulation of the major non-collagenous dentin matrix protein, dentin sialophosphoprotein; regulation of tertiary dentin formation by cytokines, such as transforming growth factor-Beta 1; and the utilization of dentally relevant cells in dental material biocompatibility testing.

Murine enamelin: cDNA and derived protein sequences

Enamelin is the largest enamel protein. Recently we reported the characterization of a cDNA clone encoding porcine enamelin. The secreted protein has 1104 amino acids--over 6 times the length of amelogenin (173 amino acids) and almost 3 times the lengths of sheathlin (395 amino acids) and tuftelin (389 amino acids). Immunohistochemistry has shown that uncleaved porcine enamelin concentrates at the growing tips of the enamel crystallites while its cleavage products localize to rod and interrod enamel. Here we report the isolation and characterization of cDNA encoding murine amelogenin and demonstrate the tooth specificity of porcine enamelin. The murine clone is 4154 nucleotides in length and encodes a protein of 1274 amino acids. In the absence of post-translational modifications murine enamelin has an isotope averaged molecular mass of 137 kDa and an isoelectric point of 9.4. Multiple tissue Northern blot analyses detect porcine enamelin mRNA in developing teeth but not in liver, heart, brain, spleen, skeletal muscle and lung. Mouse and porcine enamelin share 61% amino acid identity and 75% DNA sequence identity. Mouse enamelin has 14 tandemly arranged copies of an 11 amino acid segment that is found only once in porcine enamelin.

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.

Identification and characterization of a cDNA for mouse ameloblastin

Ameloblastin was first identified as one of the most abundant novel transcripts from a random screening of a rat incisor cDNA library. In situ hybridization experiments have shown ameloblastin expression to be specific to ameloblasts, with highest levels in secretory and maturation stage ameloblasts and cells of the epithelial root sheath. Ameloblastin has been identified as a candidate gene for the local hypoplastic form of autosomal dominant amelogenesis imperfecta, by virtue of it's location within the critical disease locus. The purpose of this study was to isolate a full length mouse ameloblastin cDNA and determine its temporal expression pattern during odontogenesis. A newborn mouse molar cDNA library was screened using a rat ameloblastin cDNA probe. Positive clones were confirmed by PCR analysis with ameloblastin-specific primers, and their size determined with vector-specific primers. Phage clones were rescued to phagemid using Exassist helper phage and the nucleotide sequence determined. We report here the identification of two clones, exhibiting alternative splicing of the putative open reading frame, and use of multiple polyadenylation signals. Nucleotide sequence analysis indicated a high degree of similarity to rat ameloblastin, rat amelin 1 and 2 and porcine sheathlin. Reverse transcriptase-PCR analysis using mouse first and second mandibular molar mRNA indicated initial expression at E-14. This is one day after the initial expression of tuftelin (E-13) and one day prior to that of amelogenin (E-15).

Human ameloblastin gene: genomic organization and mutation analysis in amelogenesis imperfecta patients

A gene encoding the enamel protein ameloblastin (AMBN) was recently localized to a region on chromosome 4q21 containing a gene for the inherited enamel defect local hypoplastic amelogenesis imperfecta (AIH2). Ameloblastin protein is located at the Tomes processes of secretory ameloblasts and in the sheath space between rod-interrod enamel, and the AMBN gene therefore represents a viable candidate gene for local hypoplastic amelogenesis imperfecta (AI). In this study, the genomic organization of human AMBN was characterized. The gene was shown to consist of 13 exons and 12 introns. An alternatively spliced 45 bp sequence was shown not to represent a separate exon and is most likely spliced by the use of a cryptic splice site. The finding that there were no recombinations between an intragenic microsatellite and AIH2 encouraged us to evaluate this gene's potential role as a candidate gene for local hypoplastic AI. Mutation screening was performed on all 13 exons in 20 families and 8 sporadic cases with 6 different forms of AI. DNA variants were found but none that was associated exclusively with local hypoplastic AI or any of the other variants of AI in the identified Swedish families. This study excludes the coding regions and the splice sites of AMBN from a causative role in the pathogenesis of AIH2.

Enamelin maps to human chromosome 4q21 within the autosomal dominant amelogenesis imperfecta locus

Amelogenesis imperfecta is a group of hereditary enamel defects. Of the autosomal dominant forms, only the local hypoplastic type has been mapped to human chromosome 4q 13-4q21. Enamelin is a large enamel matrix protein secreted by ameloblasts. The purpose of this study was to determine the human chromosomal localization of enamelin to establish an association with various forms of amelogenesis imperfecta. Chromosomal mapping was performed by polymerase chain reaction (PCR) amplification using somatic hybrid and deletion/derivation cell line panels with an enamelin primer set based on 100% conserved regions between pig and mouse cDNAs. Sequence-tagged site content mapping using eight markers within the critical local hypoplastic amelogenesis imperfecta region was then performed using an isolated human enamelin genomic BAC clone. The human enamelin amplicon was confirmed by DNA sequence analysis, revealing 81% and 73% identity to pig and mouse cDNAs, respectively. PCR amplification using a somatic cell hybrid panel placed enamelin on chromosome 4 with analysis of a regional chromosome 4 mapping panel refining the localization to 4q 13.1-q21.23. An identified human enamelin BAC genomic clone was shown to contain markers D4S2604 and D4S2670, as well as the first exon of the human ameloblastin gene, placing enamelin in the critical amelogenesis imperfecta locus between markers HIS1 and D4S2604 at 4q21. Our results suggest that enamelin is a strong candidate gene for this disease. Furthermore, human 4q21 may contain a second cluster of enamel matrix genes located proximally to the identified cluster of dentin and bone genes.

Inositol hexasulphate, a casein kinase inhibitor, alters enamel formation in cultured embryonic mouse tooth germs

Post-translational modification of enamel proteins is regulated by casein kinases (CK) and results in binding sites for calcium ions that subsequently play a key role during the initial stages of mineralization. Phosphorylation may also influence the secretion and extracellular organization of enamel proteins. Previous studies indicated that inositol hexasulphate inhibited the activity of CK-I and/or CK-II in mouse tooth germs (Torres-Quintana et al., 1998). We hypothesized that inositol hexasulphate would also inhibit the activity of the specific casein kinase(s) identified in secretory ameloblasts, and would prove useful for determination of the extent to which phosphorylation might influence the organization of enamel proteins at early stages of enamel formation. To test this hypothesis, we dissected mandibular first molars from 18-day-old mouse embryos and cultured them for 11 days in the presence of 0-0.1 mM inositol hexasulphate. Ultastructural analysis revealed that the formation of enamel was largely impaired at an inhibitor concentration > or = 0.08 mM. Quantitative radioautographic analysis of [33P]phosphate incorporation indicated that radiolabeled phosphate normally secreted into forming enamel was retained within ameloblasts. In contrast, no significant difference was observed between control and inositol-hexasulphate-treated tooth germs when cultures were labeled with [3H]serine and [3H]proline. SDS-PAGE and Western blot analysis confirmed that while inositol hexasulphate inhibited CK-mediated phosphorylation, it did not significantly alter protein synthesis. We conclude that impairment of phosphorylation leads to intracellular accumulation of [3H]phosphate-containing material by ameloblasts. We also conclude that when non-phosphorylated enamel matrix proteins are secreted, they are either unable to form an enamel matrix that supports mineralization, or they diffuse throughout a poorly mineralized dentin.

Cloning, characterization and immunolocalization of human ameloblastin

Amelogenesis imperfecta is a broad classification of hereditary enamel defects, exhibiting both genetic and clinical diversity. Most amelogenesis imperfecta cases are autosomal dominant disorders, yet only the local hypoplastic form has been mapped to human chromosome 4q between D4S242 1 and the albumin gene. An enamel protein cDNA, termed ameloblastin (also known as amelin and sheathlin), has been isolated from rat, mouse and pig. Its human homolog has been mapped to chromosome 4q21 between markers D4S409 and D4S400, flanking the local hypoplastic amelogenesis imperfecta critical region. Therefore, ameloblastin is a strong candidate gene for this form of amelogenesis imperfecta. To facilitate genetic studies related to this dental disease, we isolated and characterized a human ameloblastin cDNA. A human third molar cDNA library was screened and two ameloblastin clones identified. Nucleotide sequencing of these cDNAs indicated alternative splicing of the putative open reading frame, use of different polyadenylation signals, and a high degree of similarity to reported rat, mouse and porcine cDNAs. Immunohistochemistry studies on embryonic human teeth using an antibody to recombinant ameloblastin indicated ameloblastin expression by ameloblasts with localization in the enamel matrix associated with the sheath structures.

Dental cells express factors that regulate bone resorption

Odontoblasts and osteoblasts produce similar highly mineralized extracellular matrices. In bone, osteoblasts/stromal cells regulate osteoclast (ocl) formation and bone resorption by producing factors like osteoprotegerin (OPG), osteoclast differentiating factor (ODF/RANKL), and macrophage colony-stimulating factor (M-CSF) that interact with hematopoietic ocl precursor cells. Using odontoblast and pulp cell lines, we detected a constitutive expression of OPG, RANKL, and M-CSF mRNA in both cell types. OPG and RANKL proteins were also detectable. In vivo, RANKL and OPG were localized to odontoblasts, ameloblasts, and pulp cells in developing mouse teeth by immunohistochemistry. In a coculture system, we found the dental cells to be inhibitory to ocl formation from spleen and bone marrow precursors, despite their production of osteoclast stimulatory factors. Our data indicate for the first time that dental cells express factors important in regulation of osteoclastogenesis and bone resorption. Since both stimulatory (RANKL, M-CSF) and inhibitory (OPG) factors are expressed, a balance between positive and negative factors may contribute to regulation of bone resorption.

Comparative study of MSX-2, DLX-5, and DLX-7 gene expression during early human tooth development

Msx and Dlx family transcription factors are key elements of craniofacial development and act in specific combinations with growth factors to control the position and shape of various skeletal structures in mice. In humans, the mutations of MSX and DLX genes are associated with specific syndromes, such as tooth agenesis, craniosynostosis, and tricho-dento-osseous syndrome. To establish some relationships between those reported human syndromes, previous experimental data in mice, and the expression patterns of MSX and DLX homeogenes in the human dentition, we investigated MSX-2, DLX-5, and DLX-7 expression patterns and compared them in orofacial tissues of 7.5- to 9-wk-old human embryos by using in situ hybridization. Our data showed that MSX-2 was strongly expressed in the progenitor cells of human orofacial skeletal structures, including mandible and maxilla bones, Meckel's cartilage, and tooth germs, as shown for DLX-5. DLX-7 expression was restricted to the vestibular lamina and, later on, to the vestibular part of dental epithelium. The comparison of MSX-2, DLX-5, and DLX-7 expression patterns during the early stages of development of different human tooth types showed the existence of spatially ordered sequences of homeogene expression along the vestibular/lingual axis of dental epithelium. The expression of MSX-2 in enamel knot, as well as the coincident expression of MSX-2, DLX-5, and DLX-7 in a restricted vestibular area of dental epithelium, suggests the existence of various organizing centers involved in the control of human tooth morphogenesis.

Spatial and temporal activity of the dentin sialophosphoprotein gene promoter: differential regulation in odontoblasts and ameloblasts

Dentin sialoprotein and dentin phosphoprotein are non-collagenous proteins that are cleavage products of dentin sialophosphoprotein (DSPP). Although these two protein products are believed to have a crucial role in the process of tooth mineralization, their precise biological functions and the molecular mechanisms of gene regulation are not clearly understood. To understand such functions, we have developed a transgenic mouse model expressing a reporter gene (lacZ) under the control of approximately 6 kb upstream sequences of Dspp. The transgenic fusion protein was designed to reside within the cells to facilitate the precise identification of cell type and developmental stages at which the Dspp-lacZ gene is expressed. The results presented in this report demonstrate: (a) the 6 kb upstream sequences of Dspp have the necessary regulatory elements to direct the tissue specific expression of the transgene similar to endogenous Dspp, (b) both odontoblasts and ameloblasts exhibit transgene expression in a differentiation dependent manner, and (c) a differential regulation of the transgene in odontoblasts and ameloblasts occurs during tooth development and mineralization.

Genetic linkage of the dentinogenesis imperfecta type III locus to chromosome 4q

Dentinogenesis imperfecta type III (DGI-III) is an autosomal-dominant disorder of dentin formation which appears in a tri-racial southern Maryland population known as the "Brandywine isolate". This disease has suggestive evidence of linkage to the long arm of human chromosome 4 (LOD score of 2.0) in a family presenting with both juvenile periodontitis and DGI-III. The purpose of this study was to screen a family presenting with only DGI-III to determine if this locus was indeed on chromosome 4q. Furthermore, we wanted to determine if DGI-III co-localized with dentinogenesis imperfecta type II (DGI-II), which has been localized to 4q21-q23. Therefore, a large kindred from the Brandywine isolate was identified, oral examination performed, and blood samples collected from 21 family members. DNA from this family was genotyped with 6 highly polymorphic markers that span the DGI-II critical region of chromosome 4q. Analysis of the data yielded a maximum two-point LOD score of 4.87 with a marker for the dentin matrix protein 1 (DMP1) locus, a gene contained in the critical region for DGI-II. Our results demonstrated that the DGI-III locus is on human chromosome 4q21 within a 6.6 cM region that overlaps the DGI-II critical region. These results are consistent with the hypothesis that DGI-II is either an allelic variant of DGI-III or the result of mutations in two tightly linked genes.

Expression of DLX5 during human embryonic craniofacial development

Dlx (distal-less gene) homeogenes encode transcription factors that are involved in the patterning of orofacial skeleton derived from cephalic neural crest cells. In order to study the role of DLX genes during embryonic development in human, DLX5 expression pattern was investigated in 6- to 11-week-old human embryos. A DLX5 PCR fragment was amplified from a human dental cDNA library subcloned and used for in situ hybridization investigations. DLX5 gene expression was primarily detected in the mandible at 6 weeks and then, after in the maxilla. DLX5 gene expression became restricted to progenitor cells of developing tooth germs, bones and cartilages of mandible and maxilla. During odontogenesis from bud to late cap stages, DLX5 transcripts were present in both dental epithelium and mesenchyme tissues. DLX5 expression was restricted to few cells in the vestibular aspect of the dental epithelium, while DLX5 mRNA signal was more widely distributed in dental mesenchyme. The observed expression pattern of DLX5 homeogene extends the proposed site-specific combination of homeogene expression in neural crest derived cells to human specific dentition. Furthermore, during the bud and cap stages of tooth morphogenesis, the asymmetric expression of DLX5 in the dental epithelium and dental mesenchyme may contribute to the complex patterning of human tooth shape.

Cloning, characterization, and tissue expression pattern of mouse tuftelin cDNA

Tuftelin is a protein that has been suggested to function during enamel crystal nucleation. Published sequences for bovine tuftelin cDNA and genomic clones proposed different reading frames that radically affected the derived amino acid sequence of the tuftelin carboxyl-terminus. We have isolated and characterized a full-length mouse cDNA clone and a partial porcine cDNA clone that include the region of the proposed frame-shift. The mouse tuftelin clone is 2572 nucleotides in length, exclusive of the poly(A+) tail. Translation from the 5'-most ATG yields a protein of 390 amino acids with an isotope-averaged molecular mass of 44.6 kDa and an isoelectric point of 5.9. Comparison of the bovine, mouse, and porcine cDNAs supports the revised bovine tuftelin amino acid sequence and suggests that the bovine tuftelin translation initiation codon be re-assigned to a more 5' ATG. Re-assigning the translation initiation codon lengthens the tuftelin protein by 52 amino acids, 51 of which are identical between bovine and mouse. At the carboxyl-terminus, the revised bovine and the mouse sequences match at 39 of the final 42 amino acid positions, compared with 2 identities with the originally published bovine reading frame. Northern blot analysis reveals that tuftelin is not ameloblast-specific but is expressed in multiple tissues, including kidney, lung, liver, and testis. Two tuftelin RNA messages, of 2.6 and 3.2 kb, were detected. DNA sequence characterization of an RT-PCR amplification product confirmed expression of tuftelin in kidney, and identified an alternatively spliced mouse tuftelin mRNA lacking exon 2.

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.

Identification of a novel isoform of mouse dentin matrix protein 1: spatial expression in mineralized tissues

Dentin matrix protein 1 (Dmp1) is an acidic phosphoprotein first identified by cDNA cloning from a rat tooth library. Northern blot hybridization of a variety of tissues detected Dmp1 mRNAs only in odontoblasts, suggesting that this protein was odontoblast specific. In situ hybridization studies showed expression of Dmp1 in odontoblasts with transient expression in secretory ameloblasts. The purpose of this study was to isolate and characterize a mouse Dmp1 cDNA and determine its spatial expression pattern related to other mineralizing tissues. A mouse molar cDNA library was screened with a 32P-labeled Dmp1 polymerase chain reaction amplification product in order to isolate a full-length clone. DNA sequence analysis of the largest mouse Dmp1 cDNA (2802 base pairs [bp]) revealed an open reading frame of 1509 nucleotides encoding a 503 amino acid protein with a single polyadenylation signal. Comparison with rat and bovine Dmp1 sequence showed high homology and the identification of a 45 bp (15 amino acid) insert, representing an alternative spliced mRNA. This 45 bp segment was shown to represent a small exon by DNA analysis of a mouse genomic Dmp1 clone. In situ hybridization studies revealed a much broader Dmp1 tissue expression pattern than previously reported. Dmp1 transcripts were detected in the odontoblast and ameloblasts, osteoblasts, and cementoblasts. Our data indicate that Dmp1 is alternatively spliced, and the primary full-length transcript contains a 45 bp insert which is encoded by a small exon. Therefore, Dmp1 is not a tooth-specific protein but rather is expressed in a number of mineralizing tissues including enamel, bone, and cementum.

Refined mapping of the human dentin sialophosphoprotein (DSPP) gene within the critical dentinogenesis imperfecta type II and dentin dysplasia type II loci

Dentinogenesis imperfecta type II and dentin dysplasia type II are diseases resulting in abnormal dentin formation, which have been mapped to overlapping regions of human chromosome 4q defined by markers D4S2691 and D4S2692 (6.6 cM) and D4S3291 and SPP1 (14.1 cM), respectively. Recently, two of the major non-collagenous proteins of dentin, dentin sialoprotein (DSP) and dentin phosphoprotein (DPP, phosphophoryn) have been shown to be encoded by a single gene, termed dentin sialophosphoprotein (DSPP), which has been mapped to human chromosome 4. The purpose of this study was to perform refined mapping of DSPP related to these disease loci by gene content mapping, as well as to place the DSPP gene on the physical map of human chromosome 4 by sequence tagged site (STS) content mapping. Human genomic DSPP clones were isolated, and gene content mapping performed with specific primers for dentin matrix protein 1 (DMP1), bone sialoprotein (BSP) and osteopontin (secreted phosphoprotein 1, SPP1). STS content mapping was then performed with flanking STS markers to these dentin/bone gene loci. Our results demonstrate that the DSPP and DMP1 genes are within a maximum distance of 110 kb. Both DSPP and DMP-1 have been placed on the physical map of human chromosome 4 within the interval defined by markers D4S564 and D4S1292. DSPP is thereby strengthened as a candidate gene for both DGI-II and DD-II.

Immortalized mouse odontoblast cell line MO6-G3 application for in vitro biocompatibility testing

PURPOSE

This study was designed to determine the usefulness of an established stable immortalized mouse odontoblast cell line (MO6-G3) for dental material biocompatibility testing. Using a standard toxicity assay based on cell respiratory activity, the response to MO6-G3 cells was compared to the mouse fibroblastic cell line, L929, presently used for dental materials testing. The dental resin monomer TEGDMA was used as the dental material for the assay.

MATERIALS AND METHODS

Cell lines (1 x 10(3)/well) were plated in 96 well culture plates and grown in DMEM supplemented with 10% FCS, 100 units/ml each of penicillin and streptomycin, and 50 micrograms/ml ascorbic acid in an atmosphere of 95% air and 5% CO2. Cells were exposed to TEGDMA resin monomer covering a dose range of 1 x 10(-6) to 0.5 x 10(-3) M. Unexposed control cells, as well as cells exposed to the DMSO vehicle in which the TEGDMA was dissolved, were included in all assays. Cytotoxicity was evaluated by determining cell respiratory activity spectrophotometrically using the tetrazolium compound WST-1.

RESULTS

Statistical analysis by ANOVA using Tukey's method for pair wise comparisons as the post hoc test indicated toxic effects of TEGDMA at 1 x 10(-5) M in the odontoblast cell line MO6-G3. By contrast, the monomer produced no toxic effects on the L929 fibroblast cell line after 24 hours of exposure, over the entire concentration range tested. Furthermore, MO6-G3 cells exposed to a concentration of 0.5 x 10(-3) M were unable to recover from the effects of the exposure 48 hours after removal of the resin. MO6-G3 cells exposed to 1 x 10(-4) and 0.5 x 10(-4) TEGDMA recovered 40-50% and 75-80% of control respiratory activity respectively, 48 hours after removal of the resin. Respiratory activity by L929 cells exposed to all TEGDMA concentrations tested was not different from the vehicle control 48 hours after removal of the resin.

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.

Role of the glucagon receptor COOH-terminal domain in glucagon-mediated signaling and receptor internalization

The binding of glucagon to its hepatic receptor is known to result in a number of effects, including the intracellular accumulation of cAMP, the mobilization of intracellular Ca2+, and the endocytosis of glucagon and its receptor into intracellular vesicles. In this study, we begin to define the functional role of the COOH-terminal tail of the human glucagon receptor in glucagon-stimulated signal transduction and receptor internalization. We have created and expressed in Chinese hamster ovary (CHO) cells five truncation mutants in which the COOH-terminal 24, 56, 62, 67, and 73 amino acids have been removed. Cells expressing relevant truncated receptors were assayed for cell surface expression by immunofluorescence, for ligand-binding properties, for cAMP and Ca2+-mediated signal transduction properties, and for receptor endocytosis. In addition, a mutant receptor containing seven serine-to-alanine mutations in the COOH-terminal tail was studied. Our results reveal the following: 1) a region of the COOH-terminal tail that is required for proper cell surface expression, 2) the COOH-terminal 62 amino acids, which comprise the majority of the tail, are not required for ligand binding, cAMP accumulation, or Ca2+ mobilization, and 3) phosphorylation of the COOH-terminal tail is crucial for glucagon-stimulated receptor endocytosis.