Homeobox genes and growth factors in regulation of craniofacial and tooth morphogenesis

MSX1 involved selective tooth agenesis and abnormal labial frenum, pedigree, and retrospective study

OBJECTIVE

Muscle segment homeobox gene 1 (MSX1) is widely expressed in craniofacial development and tooth formation. The aim of this study was to report a novel MSX1 mutation in a Chinese family with selective tooth agenesis and abnormal median maxillary labial frenum (MMLF).

MATERIALS AND METHODS

Mutation analysis was carried out by whole exome sequencing. The pMD18-T vector was used to verify the mutations. PubMed and Human Gene Mutation Database were searched to analyze the relationship between the mutations in MSX1 and related phenotypes.

RESULTS

A novel heterozygous mutation (c.75delG) in MSX1 was detected in the proband and her mother. They presented as oligodontia and lower attached hypertrophy median maxillary labial frenum. 60 MSX1 mutations from 39 reports did not declare malformed MMLF except our cases. Meanwhile, we found that the types and sites of MSX1 mutations may affect the selectivity of tooth agenesis and orofacial cleft.

CONCLUSION

This study suggests malformed MMLF as a new phenotype of MSX1 mutation and a specific relationship between MSX1 genotype and phenotype.

Hematopoietic-Mesenchymal Signals Regulate the Properties of Mesenchymal Stem Cells

It is well known that the properties of hematopoietic stem/progenitor cells (HSCs), such as their self-renewal ability and multipotency, are maintained through interactions with mesenchymal stem/stromal cells (MSCs). MSCs are rare cells that are present in the bone marrow and are useful for clinical applications due to their functional ability. To obtain the necessary number of cells, MSCs must be cultured to expand, but this causes a remarkable decrease in stem cell properties, such as multipotency and proliferation ability. In this study, we show that the c-Mpl signal, which is related to the maintenance of hematopoietic stem cells, has an important effect on the proliferation and differentiation ability of MSCs. Utilizing a co-culture system comprising MSCs and HSCs, it is suggested that signaling from hematopoietic cells to MSCs supports cell proliferation. Interestingly, the enhanced proliferation ability of the HSCs was decreased in c-Mpl knock-out HSCs (c-Mpl-KO). In addition, the MSCs co-cultured with c-Mpl-KO HSCs had reduced MSC marker expression (PDGFRa and Sca-1) compared to the MSCs co-cultured with c-Mpl-wild-type HSCs. These results suggest that a hematopoietic–mesenchymal signal exists, and that the state of the HSCs is important for the stability of MSC properties.

The Human Genetics of Dental Anomalies

The development of tooth is a highly complex procedure and mastered by specific genetic programs. Genetic alterations, environmental factors, and developmental timing can disturb the execution of these programs, and result in various dental anomalies like hypodontia/oligodontia, and supernumerary teeth, which are commonly seen in our clinical practice. Advances in molecular research enabled the identification of various genes involved in the pathogenesis of dental anomalies. In the near future, it will help provide a more accurate diagnosis and biological-based treatment for these anomalies. In this article, we present the molecular phenomenon of tooth development and the genetics of various dental anomalies.

Association of Polymorphic and Haplotype Variants of the MSX1 Gene and the Impacted Teeth Phenomenon

It is known that genetic factors determine odontogenesis; furthermore, studies have revealed that various genes in humans can regulate the development of different types and generations of teeth. In this study it has been assumed that tooth impaction—at least to some extent—also depends on the presence of specific genetic markers, especially allelic variants of the MSX1 gene. The primary objective of the study was to evaluate the suitability of selected molecular markers located within the MSX1 gene for the determination of the risk of tooth impaction in particular patients. The study participants were divided into two groups: (1) the study group—at least one secondary tooth was impacted in the jaws; (2) the control group—no impacted tooth in the jaws. Real-Time PCR and TaqMan probes were used to detect selected polymorphisms in the analyzed genes. Two single nucleotide polymorphisms of MSX1 were analyzed. After the two subgroups of patients were distinguished in the study group based on the number of impacted teeth, statistically significant differences in the frequency of genotypes described for rs12532 in the MSX1 gene were found.

Odontogenic and Developmental Oral Lesions in Pediatric Patients

This article reviews odontogenic and developmental oral lesions encountered in the gnathic region of pediatric patients. The process of odontogenesis is discussed as it is essential to understanding the pathogenesis of odontogenic tumors. The clinical presentation, microscopic features, and prognosis are addressed for odontogenic lesions in the neonate (dental lamina cysts/gingival cysts of the newborn, congenital (granular cell) epulis of the newborn, melanotic neuroectodermal tumor, choristoma/heterotopia, cysts of foregut origin), lesions associated with unerupted/erupting teeth (hyperplastic dental follicle, eruption cyst, dentigerous cyst, odontogenic keratocyst/keratocystic odonogenic tumor, buccal bifurcation cyst/inflammatory collateral cyst) and pediatric odontogenic hamartomas and tumors (odontoma, ameloblastic fibroma, ameloblastoma, adenomatoid odontogenic tumor, primordial odontogenic tumor). Pediatric odontogenic and developmental oral lesions range from common to rare, but familiarity with these entities is essential due to the varying management implications of these diagnoses.

Biomineralization process in hard tissues: The interaction complexity within protein and inorganic counterparts

Biomineralization can be considered as nature's strategy to produce and sustain biominerals, primarily via creation of hard tissues for protection and support. This review examines the biomineralization process within the hard tissues of the human body with special emphasis on the mechanisms and principles of bone and teeth mineralization. We describe the detailed role of proteins and inorganic ions in mediating the mineralization process. Furthermore, we highlight the various available models for studying bone physiology and mineralization starting from the historical static cell line-based methods to the most advanced 3D culture systems, elucidating the pros and cons of each one of these methods. With respect to the mineralization process in teeth, enamel and dentin mineralization is discussed in detail. The key role of intrinsically disordered proteins in modulating the process of mineralization in enamel and dentine is given attention. Finally, nanotechnological interventions in the area of bone and teeth mineralization, diseases and tissue regeneration is also discussed. STATEMENT OF SIGNIFICANCE: This article provides an overview of the biomineralization process within hard tissues of the human body, which encompasses the detailed mechanism innvolved in the formation of structures like teeth and bone. Moreover, we have discussed various available models used for studying biomineralization and also explored the nanotechnological applications in the field of bone regeneration and dentistry.

Overexpression of Dlx2 enhances osteogenic differentiation of BMSCs and MC3T3-E1 cells via direct upregulation of Osteocalcin and Alp

Genetic studies have revealed a critical role of Distal-homeobox (Dlx) genes in bone formation, and our previous study showed that Dlx2 overexpressing in neural crest cells leads to profound abnormalities of the craniofacial tissues. The aim of this study was to investigate the role and the underlying molecular mechanisms of Dlx2 in osteogenic differentiation of mouse bone marrow stromal cells (BMSCs) and pre-osteoblast MC3T3-E1 cells. Initially, we observed upregulation of Dlx2 during the early osteogenesis in BMSCs and MC3T3-E1 cells. Moreover, Dlx2 overexpression enhanced alkaline phosphatase (ALP) activity and extracellular matrix mineralization in BMSCs and MC3T3-E1 cell line. In addition, micro-CT of implanted tissues in nude mice confirmed that Dlx2 overexpression in BMSCs promoted bone formation in vivo. Unexpectedly, Dlx2 overexpression had little impact on the expression level of the pivotal osteogenic transcription factors Runx2, Dlx5, Msx2, and Osterix, but led to upregulation of Alp and Osteocalcin (OCN), both of which play critical roles in promoting osteoblast maturation. Importantly, luciferase analysis showed that Dlx2 overexpression stimulated both OCN and Alp promoter activity. Through chromatin-immunoprecipitation assay and site-directed mutagenesis analysis, we provide molecular evidence that Dlx2 transactivates OCN and Alp expression by directly binding to the Dlx2-response cis-acting elements in the promoter of the two genes. Based on these findings, we demonstrate that Dlx2 overexpression enhances osteogenic differentiation in vitro and accelerates bone formation in vivo via direct upregulation of the OCN and Alp gene, suggesting that Dlx2 plays a crucial role in osteogenic differentiation and bone formation.

The distal-less homeobox (Dlx) gene family is related to various features of bone development, and the Dlx2 member of that family has been found to play a crucial role in bone formation. A team headed by Steve Guofang Shen at the Shanghai Jiao Tong University School of Medicine in China investigated the function of Dlx2 in osteogenic (bone development) differentiation of mouse bone marrow stromal cells (BMSCs) and MC3T3-E1 cells (precursors of osteoblasts, the major cellular component of bone). The team found that overexpression of Dlx2 promotes osteogenic differentiation in vitro and accelerates bone formation in vivo by enhancing Osteocalcin and Alp genes (both of which play critical roles in promoting osteoblast maturation). The authors conclude that their results suggest a promising future strategy for treating bone defects where BMSCs overexpress Dlx2.

Clinicopathologic and Molecular Characteristics of Familial Cherubism with Associated Odontogenic Tumorous Proliferations

Cherubism is a rare autosomal dominant condition affecting the jaws and caused by mutations in the gene encoding for the adapter protein SH3BP2 that maps to chromosome 4p16.3. Cherubism is characterized by symmetrically developing bone lesions in the maxilla and mandible. The lesions have been radiographically and histopathologically well-described. Here, we present a family with cherubism with two of its members featuring odontogenic tumorous proliferations in association with persistent central giant cell lesions (CGCL). Specifically, the proband, a 25-year-old male, developed a radiolucent lesion characterized histologically by central odontogenic fibroma-like proliferation in association with a CGCL component, while his mother, at age 57, was diagnosed with primary intraosseous odontogenic carcinoma with areas of benign fibro-osseous lesions. In both patients the lesions occurred in the anterior mandible and presented with clinical enlargement. The son underwent incisional biopsy and did not have additional treatment. His mother underwent extensive mandibulectomy due to widespread tumor. The son has two affected children with classic cherubism while a third child at age 5, had not shown any features of the disease. Mutation analysis of three affected members resulted in the identification of a heterozygous mutation in SH3BP2 (c.1244G>C; p.Arg415Pro). To the best of our knowledge, association of cherubism with odontogenic neoplastic lesions has hitherto not been reported in the literature, thus suggesting a relationship between cherubism with disturbed odontogenesis.

Evolving concepts of heredity and genetics in orthodontics

The field of genetics emerged from the study of heredity early in the 20th century. Since that time, genetics has progressed through a series of defined eras based on a number of major conceptual and technical advances. Orthodontics also progressed through a series of conceptual stages over the past 100 years based in part on the ongoing and often circular debate about the relative importance of heredity (nature) and the local environment (nurture) in the etiology and treatment of malocclusion and dentofacial deformities. During the past 20 years, significant advancements in understanding the genomic basis of craniofacial development and the gene variants associated with dentofacial deformities have resulted in a convergence of the principles and concepts in genetics and in orthodontics that will lead to significant advancement of orthodontic treatments. Fundamental concepts from genetics and applied translational research in orthodontics provide a foundation for a new emphasis on precision orthodontics, which will establish a modern genomic basis for major improvements in the treatment of malocclusion and dentofacial deformities as well as many other areas of concern to orthodontists through the assessment of gene variants on a patient-by-patient basis.

The dental development in patients with Aperts syndrome

OBJECTIVES

The aim of this retrospective study was to quantify the level of dental developmental delay in a group of patients with Aperts syndrome when compared to matched controls.

METHODS

Twenty-six Dental Panoramic Tomographic (DPT) radiographs of patients with Apert syndrome attending Great Ormond Street Hospital were compared to controls (n = 29) from the Eastman Dental Hospital, UK. Dental development was assessed using the staging systems of Demirjian and Haavikko, and dental age (DA) was estimated using the weighted averages method.

RESULTS

Dental age, as estimated using the 12 stages of Haavikko and eight stages of Demirjian, suggested no statistical evidence of developmental delay between the Aperts and control group.

CONCLUSIONS

The hypothesis 'that there is no difference in the dental development of subjects with Apert syndrome, when compared to a group of matched controls', was accepted.

Role of homeobox genes in tooth morphogenesis: a review

In oral cavity, disturbances due to genetic alterations may range from lack of tooth development to morphological defects. Due to technical advances in genetic engineering and molecular biology, valuable information regarding dentofacial growth could be studied in detailed manner. This helped us to explain the aetiology and pathogenesis of many dentofacial disorders. The success in treatment lies first in determining the aetiology of tooth anomalies and finally differentiating the effect of genes and environment on the orofacial diseases of that particular individual. Several genes belonging to class II homeobox families are expressed during odontogenesis however homeobox genes are not directly imvolved in tooth formation as they are not directly expressed in the first branchial arch derivatives.

Mutations in the MSX1 gene in Turkish children with non-syndromic tooth agenesis and other dental anomalies

Aim:

To search for mutations on the MSX1 gene and to present a genetic basis for non-syndromic tooth agenesis in conjunction with dental anomalies in a Turkish population.

Materials and Methods:

The patients included in this study were otherwise healthy, with ages ranging from seven to eighteen years. Eighty-two of them had one to six teeth missing (Group I) and 26 had more than six teeth missing (Group II), except for the third molars,. The missing teeth and dental anomalies were examined clinically and radiographically. The MSX1 gene was sequenced from the blood samples of patients who consented to the study.

Results:

Mutations or polymorphisms on the MSX1 gene were identified in six patients. Taurodontism was seen in patients from both groups I and II. The nucleotide changes were identified by mutation screening.

Conclusions:

Performing family studies, screening other candidate genes, and investigation of interactions between genes will provide a basis for better analysis of tooth agenesis models and their association with other dental anomalies.

A theoretical model of dentinogenesis: dentin and dentinal tubule formation

INTRODUCTION

Dentinogenesis, odontoblast dentin formation, includes dentinal growth, mineralization and dentinal tubule formation. Odontoblasts synthesize collagen resulting in collagen apposition contributing to dentinogenesis. Furthermore, within the tubule, they express non-collagenous proteins, such as dentin phosphoprotein (DPP), associated with hydroxyapatite crystal formation and growth. The aim of this work was to determine patterns of growth and dentin formation and quantification of its mineralization. Findings from our work are relevant to endodontics for future regenerative treatment.

METHODS

We formulated a 3D domain mathematical model, which recreates the events that lead to dentinal tubule mineralization. As reference we used collagen apposition and DPP activity.

RESULTS

We obtained a model depicting predentin's mineralization distribution during dentin development. Furthermore, we verified different DPP diffusion coefficients to test the model's sensitivity.

CONCLUSIONS

We present a model to shed light on the process of dentin and dentinal tubule formation, and its relation to diffusion and mineralization processes.

Protein-mediated enamel mineralization

Enamel is a hard nanocomposite bioceramic with significant resilience that protects the mammalian tooth from external physical and chemical damages. The remarkable mechanical properties of enamel are associated with its hierarchical structural organization and its thorough connection with underlying dentin. This dynamic mineralizing system offers scientists a wealth of information that allows the study of basic principels of organic matrix-mediated biomineralization and can potentially be utilized in the fields of material science and engineering for development and design of biomimetic materials. This chapter will provide a brief overview of enamel hierarchical structure and properties and the process and stages of amelogenesis. Particular emphasis is given to current knowledge of extracellular matrix protein and proteinases, and the structural chemistry of the matrix components and their putative functions. The chapter will conclude by discussing the potential of enamel for regrowth.

Differential Shh, Bmp and Wnt gene expressions during craniofacial development in mice

In this study, Bmp-4, Wnt-5a and Shh gene expressions were compared during early craniofacial development in mice by comparative non-isotopic in situ hybridization. Wild-type C57BL/6J mice were studied at various stages of embryonic development (from 8.5- to 13.5-day-old embryos--E8.5-13.5). During early odontogenesis, transcripts for Bmp-4, Shh and Wnt-5a were co-localised at the tooth initiation stage. At E8.5, Shh mRNA expression was restricted to diencephalon and pharyngeal endoderm. Before maxillae and mandible ossification, Bmp-4 and Wnt-5a signals were detected in the mesenchymal cells and around Meckel's cartilage. During palatogenesis, Shh was expressed only in the epithelium and Wnt-5a only in the mesenchyme of the elevating palatal shelves. During tongue development, Shh expression was found in mesenchyme, probably contributing to tongue miogenesis, while Wnt-5a signal was in the epithelium, possibly during placode development and papillae formation. Taken together, these findings suggest that Bmp-4, Shh and Wnt-5a gene expressions may act together on the epithelial-mesenchymal interactions occurring in several aspects of the early mouse craniofacial development, such as odontogenesis, neuronal development, maxillae and mandible ossification, palatogenesis and tongue formation.

Differential effects of growth differentiation factor-5 on porcine dental papilla- and follicle-derived cells

In this study, the effect of growth differentiation factor-5 (GDF-5) on the growth and differentiation of porcine dental papilla- and follicle-derived cells was investigated. Furthermore, the effect was compared with that of BMP-2. Recombinant mouse GDF-5 (rmGDF-5) enhanced alkaline phosphatase (ALP) activity in dental papilla-derived cells in a dose-dependent manner, while ALP activity in dental follicle-derived cells was reduced. In rmGDF-5 stimulated dental papilla-derived cells, the expressions of odontoblast-marker genes were up-regulated. Conversely, recombinant human BMP-2 (rhBMP-2) enhanced ALP activity dose-dependently in both dental papilla- and follicle-derived cells. When combined, GDF-5 did not further enhance BMP-2-induced ALP activities. Rather, GDF-5 reduced BMP-2-induced ALP activities in both dental papilla- and follicle-derived cells. This suggests that affinity of GDF-5 to the shared receptors may be higher than that of BMP-2 in both cell types. These observations indicate that GDF-5 regulates differentiation of both dental papilla and follicle during odontogenesis, co-operatively with other growth factors such as BMP-2.

Radiographic features of mandibular trabecular bone structure in hypodontia

PURPOSE

Radiographic parameters of mandibular trabecular bone structure between 67 subjects having hypodontia and those without were studied on digital panoramic radiographs.

MATERIALS AND METHODS

Three regions of interest (ROI) were defined: the ascending ramus, apical of the mandibular molar and mesial of the first mandibular molar. The effects of the presence of hypodontia and the ROI on the mandibular trabecular bone structure were tested for statistical significance by means of multivariate analysis.

RESULTS

Radiographic parameters of trabecular bone architecture were found to differ between various regions of the mandible (p = 0.000), but not between the group of hypodontia subjects and their controls (p = 0.23). There was no interaction effect between the ROIs and the two groups (p = 0.79). For people having hypodontia, some directional parameters of trabecular bone have a reverse correlation with the number of missing teeth. The fractal dimension and the number and perimeter of white segments in the binarized image correlate positively with the number of congenitally missing teeth.

CONCLUSIONS

A limited number of parameters of radiographic mandibular trabecular bone structure correlate with the number of missing teeth. However, a markable difference in radiographic parameters of mandibular trabecular bone structure between hypodontia and non-hypodontia subjects could not be demonstrated.

Dentofacial characteristics of patients with hypodontia

This study aims to identify distinctive dentofacial characteristics of hypodontia patients. For this purpose, 189 young hypodontia patients (cases) were divided into subgroups, based on criteria from literature. Normalised differences between cases and controls were calculated for various parameters of dentofacial form. Subsequently, cluster analysis was applied to disclose subsets of hypodontia patients with distinctive dentofacial features. The ANB angle, interincisal angle and lower anterior face height were consistently significantly different amongst the subsets. Four clusters of patients with an increasing number of missing teeth and distinctive dentofacial characteristics could be identified. Patients in cluster 1 display a high-angle facial pattern. Patients in clusters 2 and 3 exhibit markable dentoalveolar characteristics (a relatively small and a large interincisal angle, respectively). Patients in cluster 4 exhibited notable sagittal-skeletal discriminative features predominantly because of a retrognathic maxilla. The smallest nasolabial angle and lower anterior face height were seen in this cluster. It is concluded that the anterior-posterior relationship between the jaws, the interincisal angle and the lower anterior face height are discriminative parameters of dentofacial form in hypodontia patients. Patients with hypodontia can be clustered in four groups, each with distinctive vertical-skeletal, dentoalveolar and sagittal-skeletal characteristics. This categorisation of patients with hypodontia into meaningful groups may be useful for treatment planning, interdisciplinary communication and as a means of identifying groups of patients that qualify for reimbursement of costs. Other dental factors should be appreciated as well during restorative clinical decision making in patients with hypodontia.

Localization of Bmp-4, Shh and Wnt-5a transcripts during early mice tooth development by in situ hybridization

A comparative nonisotopic in situ hybridization (ISH) analysis was carried out for the detection of Bmp-4, Shh and Wnt-5a transcripts during mice odontogenesis from initiation to cap stage. Bmp-4 was expressed early in the epithelium and then in the underlying mesenchyme. Shh expression was seen in the odontogenic epithelial lining thickening, being stronger in the enamel knot area, during the cap stage. Wnt-5a transcripts were expressed only in the mesenchyme during the initiation, bud and cap stages, with strong expression in the dental mesenchyme during the bud stage. The present results showed that Bmp-4, Shh and Wnt-5a are expressed since the very early stages of tooth development, and they suggest that the Wnt-5a gene is expressed in different cell populations than Bmp-4 and Shh.

Hypodontia as a risk marker for epithelial ovarian cancer: a case-controlled study

BACKGROUND

Genetic mutations that result in hypodontia also may be associated with abnormalities in other parts of the body. The authors conducted a study to establish the prevalence rates of hypodontia among subjects with epithelial ovarian cancer (EOC) and control subjects to explore possible genetic associations between these two phenotypes.

METHODS

The authors recruited 50 subjects with EOC and 100 control subjects who did not have EOC. The authors performed a dental examination on each subject to detect hypodontia, and they reviewed pertinent radiographs and dental histories. They also recorded any family history of cancer and hypodontia.

RESULTS

The prevalence of hypodontia was 20 percent for EOC subjects and 3 percent for control subjects. The difference between these two hypodontia rates was significant. This difference implied that women with EOC are 8.1 times more likely to have hypodontia than are women without EOC. The severity of hypodontia was similar between the two groups, with one to two teeth being affected. Maxillary lateral incisors followed by second premolars were the most frequently affected teeth.

CONCLUSION

The preliminary data suggest a statistical association between hypodontia of the permanent dentition and EOC.

CLINICAL IMPLICATIONS

Genetic analysis of the genes of interest is necessary to explore similarities between hypodontia and EOC further. An association could allow hypodontia to serve as a potential risk marker for EOC.

Characterization of excess hard tissue occurring in the mesio-buccal surface of the mandibular first molar in microphthalmic mouse

OBJECTIVE

The aim of the present study was to characterize the excess hard tissue on the mandible of the microphthalmic mouse having a mutation at the mitf locus.

DESIGN

Homozygous mutant (mi/mi) and wild-type (+/+) mice were obtained by mating a breeding pair (strain name, B6C3Fe a/a-Mitf(mi)/J). We used mi/mi and +/+ mice at ages 6, 7, 8, 9, 28, and 49 days for micro-computed tomographic and histologic analyses.

RESULTS

Excess hard tissue was found on the mesio-buccal surface of the mandibular first molar in all 11mi/mi mice, but none was found in the 8mi/+ or 14 +/+ mice. The excess hard tissue was located in the mental foramen connected to the mandibular canal. The mandibular canal passed near the basal part of the incisor and the root of the mandibular first molar due to aberrant development of the teeth and mandible. The excess hard tissue contained predentine immunostained for dentine sialoprotein, a marker for early stages of dentinogenesis, which was first observed at about 7 days of age. Dentine, predentine, pulp, and root-like structures were observed in the excess hard tissue, but neither enamel nor enamel organ was observed.

CONCLUSION

Odontogenic cells in the basal part of the incisor and/or the mandibular first molar with the ability to develop into odontoblasts and pulp cells appeared to migrate through the mandibular canal to the mental foramen, where they developed into odontoblasts and pulp-like cells, and then formed dentine and predentine-like structures.

Elevated TGF-beta2 signaling in dentin results in sex related enamel defects

Initiation of enamel formation requires reciprocal signaling between epithelially and mesenchymally derived cells.

OBJECTIVE

In this study, we used a transgenic mouse model which drives overexpression of an activated form of TGF-beta2 under control of the osteocalcin promoter, to investigate the role of TGF-beta2 in the dental mesenchyme, on enamel formation.

DESIGN

Dentin and enamel were imaged by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Dentin mechanical properties were characterized for hardness and elasticity, following nanoindentation with a modified AFM. Pores found in enamel were quantified and compared using image analysis software (Scion Imagetrade mark).

RESULTS

The elastic modulus of dentin was significantly reduced in the male TGF-beta2 overexpressor mice as compared to male wildtype mice, with no significant differences between female mice. Similarly, there were significantly more pores in enamel of the male transgenic mice as compared to male wildtype mice, with no significant differences between female mice. In situ hybridization of the continuously erupting incisor confirmed that osteocalcin expression was limited to the odontoblast cell layer at all stages of tooth formation.

CONCLUSION

TGF-beta2 overexpression in the dentin matrix, results in sex-linked differences in dentin and enamel formation.

Molecular fingerprinting of BMP2- and BMP4-treated embryonic maxillary mesenchymal cells

OBJECTIVE

To determine the differences in gene expression between control-, bone morphogenetic protein (BMP)2- and BMP4-treated murine embryonic maxillary mesenchymal (MEMM) cells.

DESIGN

Transcript profiles of BMP2-, BMP4- and vehicle-treated MEMM cells were compared utilizing the murine high-density GeneChip arrays from Affymetrix. The raw chip data (probe intensities) were pre-processed using robust multichip averaging with GC-content background correction and further normalized with GeneSpring v7.2 software. Cluster analysis of the microarray data was performed with the GeneSpring software. Changes in the gene expression were verified by TaqMan quantitative real-time PCR.

RESULTS

Expression of approximately 50% of the 45 101 genes and expressed sequence tags examined in this study were detected in BMP2-, BMP4- and vehicle-treated MEMM cells and that of several hundred genes was significantly altered (up or downregulated) in these cells in response to BMP2 and BMP4. Expression profiles of each of the 26 mRNAs tested by TaqMan quantitative real-time PCR were found to be consistent with the microarray data. Genes whose expression was modulated following BMP2 or BMP4 treatment, could be broadly classified based on the functions of the encoded proteins such as the growth factors and signaling molecules, transcription factors, and proteins involved in epithelial-mesenchymal interactions, extracellular matrix synthesis, cell adhesion, proliferation, differentiation, and apoptosis.

CONCLUSION

Utilization of the Affymetrix GeneChip microarray technology has enabled us to delineate a detailed transcriptional map of BMP2 and BMP4 responsiveness in embryonic maxillary mesenchymal cells and offers revealing insights into crucial molecular regulatory mechanisms employed by these two growth factors in orchestrating embryonic orofacial cellular responses.

Vitamin D and tissue non-specific alkaline phosphatase in dental cells

Dental epithelium comprises different cell populations, including ameloblasts and stratum intermedium cells. Ameloblasts are vitamin D targets, and at least five proteins undergo specific modulation of their expression following the addition of 1alpha,25(OH)2 vitamin D3[1alpha,25(OH)2D3]. Stratum intermedium cells have not been studied in any great detail regarding vitamin D impact. Interestingly, in these cells, the tissue non-specific alkaline phosphatase (TNAP) is overexpressed. On the other hand, TNAP is a reliable bone marker of vitamin D action, similar to calbindins in kidney and intestine, previously used for studies of vitamin D activity in ameloblasts. Here, TNAP expression and activity were investigated in vivo in the microdissected epithelium and mesenchyme of mandible incisors. Physiological doses of 1alpha,25(OH)2D3 injected in control rats failed to modify TNAP activity in both dental epithelium and mesenchyme. No significant differences were observed in the steady-state levels of TNAP mRNAs of dental tissues from wild-type and vitamin D nuclear receptor (VDRnuc)-deficient mice of the same litters. These data suggest that, in contrast to ameloblasts, stratum intermedium cells are not sensitive to 1alpha,25(OH)2D3. An explanation for such a responsiveness of stratum intermedium cells to 1alpha,25(OH)2D3 is proposed based on the respective expressions of both vitamin D receptors (VDRnuc and 1,25D3-[MARRS]) and the Dlx2 homeobox gene.

Genetic determinants of upper airway structures that predispose to obstructive sleep apnea

Genetic factors are thought to play an important role in human development. Recent data indicate that obstructive sleep apnea may have a genetic basis. Sleep apnea is a very common disorder with significant cardiovascular and neurophysiologic morbidity. The pathogenesis of sleep apnea is related to a reduction in the size of the upper airway. The reduction in airway size is secondary to increased adipose tissue (enlargement of the parapharyngeal fat pads), alterations in craniofacial structure (reduction in mandibular size) and enlargement of the surrounding soft tissue structures (tongue, lateral pharyngeal walls). Genetic factors are one of the factors that have been proposed to mediate the size of each of these anatomic risk factors for sleep apnea. Recent evidence is accumulating about the genetic loci for these structural risk factors that predispose to the development of obstructive sleep apnea.

Gene expression in the developing rat mandible: a gene array study

To analyse the molecular events that occur in the developing mandible, gene arrays containing probes for 1176 known genes were used. Total RNA was extracted from the mandibles of 1- and 6-day-old rats. Radiolabeled probes were then synthesised and used to probe the DNA arrays. Of the 1176 genes examined, 306 were detectable, and the latter were analyzed by bioinformatics algorithms. K-means clustering grouped 72 genes into Up, 56 genes into Down and 178 genes into NO change. A large number of genes related to cell receptors (by ligands) were grouped into the Down cluster. Gene array technology appears to be a useful tool for studying the complex process of mandibular development.

Precursor Tissue Analogs as a Tissue-Engineering Strategy

Natural tissues are composed of functionally diverse cell types that are organized in spatially complex arrangements. Organogenesis of complex tissues requires a coordinated sequential transformation process, with individual stages involving time-dependent expression of cell-cell, cell-matrix, and cell-signal interactions in three dimensions. The common theme of temporal-spatial patterning of these cellular interactions is also observed in other physiological processes, such as growth and development, wound healing, and tumor migration. The "precursor tissue analog" (PTA) applies the temporal-spatial patterning theme to tissue engineering. The goal of PTA in tissue engineering is not to fabricate the final transplantable tissue but rather to guide the dynamic organization, maturation, and remodeling leading to the formation of normal and functional tissues. We describe the critical design principles of PTA. First, structural, mechanical, and physiological requirements of the PTA as a temporary scaffold must be met by a fabrication method with flexibility. The fabrication potential incorporating biological materials such as living cells and plasmid DNA has been addressed. Second, the PTA concept is considered suitable for future tissue engineering in light of the use of undifferentiated stem cells, and may possess a capability to guide stem cells toward diverse differentiation characteristics in situ. To this end, the behavior of the engineered cell and tissue must be monitored in detail. The development of a practical phenotype monitoring system such as a DNA microarray may be integral to the fabrication strategies of PTA. Third, the microtopographical and microenvironmental control on the liquid-solid interaction may lead to a critical design for PTA to provide soluble factors, nutrients, and gases to the cells embedded within the scaffold. We suggest that the level set numerical simulation method may be utilized to engineer the consistent circulation of bioactive liquid throughout the PTA microenvironment.

Gene expression of growth differentiation factors in the developing periodontium of rat molars

Growth and differentiation factors (GDF) 5, 6, and 7 are known to play roles in tendon and ligament formation, and are therefore probably involved in the formation of periodontal ligament. In this study, we sought to determine temporal and spatial expression of GDF-5, -6, and -7 mRNA in developing periodontal tissue of rat molars using in situ hybridization. GDF gene expression in the periodontal ligament was first detected in cells associated with the initial process of periodontal ligament fiber bundle formation. Gene signals were also detected in cells located along the alveolar bone and cementum surfaces, the insertion sites of periodontal ligaments, during the course of root formation. GDF expression in these cells were down-regulated after completion of root formation. Our results appeared to suggest the involvement of GDF-5, -6, and -7 in the formation of the dental attachment apparatus.

Expression of bone morphogenetic proteins and Msx genes during root formation

Like crown development, root formation is also regulated by interactions between epithelial and mesenchymml tissues. Bone morphogenetic proteins (BMPs), together with the transcription factors Msx1 and Msx2, play important roles in these interactions during early tooth morphogenesis. To investigate the involvement of this signaling pathway in root development, we analyzed the expression patterns of Bmp2, Bmp3, Bmp4, and Bmp7 as well as Msx1 and Msx2 in the roots of mouse molars. Bmp4 was expressed in the apical mesenchyme and Msx2 in the root sheath. However, Bmps were not detected in the root sheath epithelium, and Msx transcripts were absent from the underlying mesenchyme. These findings indicate that this Bmp signaling pathway, required for tooth initiation, does not regulate root development, but we suggest that root shape may be regulated by a mechanism similar to that regulating crown shape in cap-stage tooth germs. Msx2 expression continued in the epithelial cell rests of Malassez, and the nearby cementoblasts intensely expressed Bmp3, which may regulate some functions of the fragmented epithelium.

Molecular dissection of craniofacial development using zebrafish

The zebrafish, Danio rerio, is a small, freshwater teleost that only began to be used as a vertebrate genetic model by the late George Streisinger in the early 1980s. The strengths of the zebrafish complement genetic studies in mice and embryological studies in avians. Its advantages include high fecundity, externally fertilized eggs and transparent embryos that can be easily manipulated, inexpensive maintenance, and the fact that large-scale mutagenesis screens can be performed. Here we review studies that have used the zebrafish as a model for craniofacial development. Lineage studies in zebrafish have defined the origins of the cranial skeleton at the single-cell level and followed the morphogenetic behaviors of these cells in skeletal condensations. Furthermore, genes identified by random mutational screening have now revealed genetic pathways controlling patterning of the jaw and other pharyngeal arches, as well as the midline of the skull, that are conserved between fish and humans. We discuss the potential impact of specialized mutagenesis screens and the future applications of this versatile, vertebrate developmental model system in the molecular dissection of craniofacial development.

BMPs induce dermal markers and ectopic feather tracts

Bone morphogenetic protein (BMP) signaling is known to be involved in multiple inductive events during embryogenesis including the development of amniote skin. Here, we demonstrate that early application of BMP-2 to the lateral trunk of chick embryos induces the formation of dense dermis, which is competent to participate in feather development. We show that BMPs induce the dermis markers Msx-1 and cDermo-1 and lead to dermal proliferation, to expression of beta-catenin, and eventually to the formation of ectopic feather tracts in originally featherless regions of chick skin. Moreover, we present a detailed analysis of cDermo-1 expression during early feather development. The data implicate that cDermo-1 is located downstream of BMP in a signaling pathway that leads to condensation of dermal cells. The roles of BMP and cDermo-1 during development of dermis and feather primordia are discussed.

Pure ectodermal dysplasia: retrospective study of 16 cases and literature review

OBJECTIVE

To review the possible craniomaxillofacial deformative consequences associated with ectodermal dysplasias and embryonic malformations, which include dental ageneses.

SETTING

Oral and Maxillofacial Surgery Department, University Hospital, Lille, France.

PATIENTS

Sixteen patients (seven boys and nine girls, aged 4 to 34 years) with pure ectodermal dysplasia (no ectodermal dysplasia syndromes).

INTERVENTIONS

All patients had a clinical examination. Seven (two boys and five girls, aged 4 to 25 years) had undergone plaster casts and radiographic and Delaire's cephalometric studies before being treated.

MAIN OUTCOME MEASURES

All patients had tooth ageneses (from hypodontia to anodontia), associated with cutaneous dyshidrosis and hair and nail dystrophy. Most of them had a short face, with an unusual facial concavity, a maxillary retrusion, and a relative mandibular protrusion. MANAGEMENT RESULTS AND DISCUSSION: Depending on their ages and their orthopedic abnormalities, patients underwent either dental or prosthodontic, orthodontic, orthopedic, orthognathic, or implant treatment. So as not to interfere with the growth pattern, we preferred to reserve implant and orthognathic surgery for full-grown cases.

CONCLUSIONS

Oral and maxillofacial surgeons must undertake a comprehensive approach to these patients to improve their dental, masticatory, growing, and orthognathic conditions.

Enamel structure and composition in the tricho-dento-osseous syndrome

Tricho-dento-osseous syndrome (TDO) is an autosomal dominant disorder characterized by curly hair, hypoplastic enamel, taurodontism, and dense bone. The purpose of this investigation was to characterize the enamel defects in a TDO population in North Carolina. Twelve TDO teeth and 12 normal teeth were examined. The enamel thickness was decreased in all TDO teeth ranging from having no enamel to about 60% the thickness of normal teeth. Half of the TDO teeth had primarily prismless enamel while the remainder had at least occasional areas of prismatic enamel. TDO enamel crystallites appeared similar to normal crystallites with TEM. The mineral per volume of TDO enamel (n = 9) (68.5%) was significantly less, on average, compared with normal enamel (n = 8) (84.5). The genetic mutation responsible for the TDO phenotype results in alteration of a developmental pathway(s) common to hair, teeth and bone. This further illustrates that these embryologically diverse tissues share common developmental controls at the molecular level.

Normal formation and development defects of the human dentition

Oral health and systemic health are intimately related, and a thorough evaluation of the oral health of children is critical in providing appropriate health care. By understanding the normal sequence and patterns of tooth development, clinicians can readily identify children who deviate from normal dental development and provide appropriate interventions or make appropriate referrals. Developmental defects of the human dentition are not uncommon and can severely adversely affect the physical and psychological health of children. Despite the severity of some developmental defects of the dentition, the ability to diagnose and manage these conditions, in most cases, allows children the benefit of optimal oral health.

Highly regulated expression of subtilisin-like proprotein convertase PACE4 (SPC4) during dentinogenesis

Expressions of mRNAs for four subtilisin-like proprotein convertases (SPCs: furin, PACE4, PC6, and PC8) and bone morphogenetic protein 4 (BMP4) in the rat molar tooth during development were analyzed by Northern blotting, reverse transcriptase-polymerase chain reaction (RT-PCR), and in situ hybridization to explore the possible involvement of SPCs in the processing of proBMPs. We found a temporospacial expression of PACE4, but not one of the other SPCs, in this tissue; i.e., RT-PCR analysis revealed that the level of PACE4 mRNA, but not that of the other SPC mRNAs became high around the second postnatal day. This increase was in good accordance with the increase in BMP4 mRNA, indicating an apparent association of these molecules with the differentiation and establishment of functional ameloblasts and odontoblasts. During dentinogenesis, PACE4 mRNA was localized in the ameloblasts and odontoblasts. These observations suggest that PACE4 plays a crucial role in dentinogenesis, especially via the activation of BMPs.

Increased tooth crown size in females with twin brothers: Evidence for hormonal diffusion between human twins in utero

In rodents, the position of a fetus in utero is associated with the expression of sexually dimorphic traits. This phenomenon has been explained by prenatal diffusion of sex hormones among litter mates. To test for such effects in humans, female-male twin pairs provide a natural experiment. The size of dental crowns is a sexually dimorphic trait which can be measured with a high degree of reliability. Thus, two crown diameters of 28 permanent teeth were recorded for 56 opposite-sexed (OS) and 242 same-sexed (SS) twin pairs, and 150 singletons. Comparisons of OS twins with SS twins and singletons within each sex reveal that OS females have consistently larger teeth (on average) than other females, while there is no consistent difference between OS and SS twin males. It is proposed that diffusion of sex hormones from male to female co-twins in utero may account for the increased tooth size in OS females. This study is one of the first to report such an effect on a morphological variable in humans. The finding that the maxillary canine, one of the most sexually dimorphic teeth, exhibits the least effect in OS female twins, suggests that prenatal sex hormone levels may have less impact on sexual dimorphism in the maxillary canines than in other permanent teeth. Am. J. Hum. Biol. 11:577-586, 1999. Copyright 1999 Wiley-Liss, Inc.

Normal and increased functional asymmetries in the craniofacial area

Normal asymmetry in the area of the craniofacial skeleton can be directional or fluctuating in nature. Directionality can in principle be found in three dimensions: anteroposterior, cranio-caudal, and asymmetries in the left-right dimension. When it comes to directional left right differences, an explanation has been difficult to find, although expressions of this type are obvious. Recent findings made in molecular genetics strongly support the genetic inheritance pattern of laterality. When functionally increased asymmetries of facial structures are concerned, it is often difficult to determine the exact contribution of each factor involved. In the light of recent experimental data, however, it seems that the influence of occlusion on the development of balanced facial structures is highly important during the early periods of life. A review of these factors is given in this article.

Dental abnormalities and ectopic eruption in patients with isolated cleft palate

The aim of this study was to evaluate the influence of cleft size and surgical treatment on the development of permanent teeth in patients with isolated cleft palate. The series comprised 109 children with isolated cleft palate, 70 girls and 39 boys, including 14 patients with Robin sequence. The patients were grouped according to the sagittal extent of the palatal cleft, measured on dental casts obtained before the primary palate surgery. Forty-six children were treated by one-stage palatoplasty, and 63 in two stages. The dentition was studied on orthopantomograms taken at 5, 8, 11, and 14 years of age. Congenitally missing permanent teeth (third molars excluded) were found in 33 subjects (30%). Children with large clefts had significantly more missing teeth than children with small clefts. The tooth most usually missing was the mandibular second premolar, followed by the maxillary lateral incisor, and the upper second premolar. The incidence of dental malformation was 23%, mostly mild forms. Ectopic eruption of the upper first permanent molars was seen in 23 (45%) of the subjects with large clefts, and in 18 (31%) of those with small clefts. The surgical method did not significantly affect the direction of the eruption. There is a correlation between cleft size and hypodontia, dental deformity, and ectopic eruption. Children with Robin sequence had almost the same incidence of hypodontia, malformed teeth, and ectopic eruption as children with large clefts. There was no correlation between surgical method and ectopic eruption of the maxillary first permanent molars.