Epithelial-mesenchymal interactions are required for msx 1 and msx 2 gene expression in the developing murine molar tooth

Anatomy, development and regeneration of zebrafish elasmoid scales

Vertebrate skin appendages - particularly avian feathers and mammalian hairs, glands and teeth - are perennially useful systems for investigating fundamental mechanisms of development. The most common type of skin appendage in teleost fishes is the elasmoid scale, yet this structure has received much less attention than the skin appendages of tetrapods. Elasmoid scales are thin, overlapping plates of partially mineralized extracellular matrices, deposited in the skin in a hexagonal pattern by a specialized population of dermal cells in cooperation with the overlying epidermis. Recent years have seen rapid progress in our understanding of elasmoid scale development and regeneration, driven by the deployment of developmental genetics, live imaging and transcriptomics in larval and adult zebrafish. These findings are reviewed together with histological and ultrastructural approaches to understanding scale development and regeneration.

Thoughts on the Etiology of Cherubism

Cherubism is nowadays classified as an autoimmune disease and was first described in 1933. Although suspected at that time to be the result of defective tooth development, it was primarily classified as a bone disease caused by a mutation in the SH3BP2 gene. Despite a knock-in mouse model, phenotypic signs in the jaw area were not reproducible in this model. The features of classical cherubism can be attributed to a disturbed formation of the dental placode of the second molar. Since 2019, it has become clear that inhibition of the WNT pathway leads to the accumulation of SH3BP2 via tankyrase inhibition. As the dental placode is triggered via WNT (in epithelia) and MSX1 (in mesenchyme), aplasia of the second and third molars occurs due to a block in the WNT pathway. The mesenchymal part, which occurs prior to the body plan regulation of the WNT/MSX1 pathway, remains unaffected and provides the substrate for the giant cell granuloma. Considering macrophage polarization and the role of the extracellular matrix in general, cherubism is situated in the field of tension between autoimmune diseases and cancer. In this sense, we see the cause of cherubism in a WNT-related dysregulation, which can be proven postnatally in the neural crest-related tooth development of the replacement tooth ridge, both genotypically and phenotypically.

Mesenchymal condensation in tooth development and regeneration: a focus on translational aspects of organogenesis

The teeth are vertebrate-specific, highly specialized organs performing fundamental functions of mastication and speech, the maintenance of which is crucial for orofacial homeostasis and is further linked to systemic health and human psychosocial well-being. However, with limited ability for self-repair, the teeth can often be impaired by traumatic, inflammatory, and progressive insults, leading to high prevalence of tooth loss and defects worldwide. Regenerative medicine holds the promise to achieve physiological restoration of lost or damaged organs, and in particular an evolving framework of developmental engineering has pioneered functional tooth regeneration by harnessing the odontogenic program. As a key event of tooth morphogenesis, mesenchymal condensation dictates dental tissue formation and patterning through cellular self-organization and signaling interaction with the epithelium, which provides a representative to decipher organogenetic mechanisms and can be leveraged for regenerative purposes. In this review, we summarize how mesenchymal condensation spatiotemporally assembles from dental stem cells (DSCs) and sequentially mediates tooth development. We highlight condensation-mimetic engineering efforts and mechanisms based on ex vivo aggregation of DSCs, which have achieved functionally robust and physiologically relevant tooth regeneration after implantation in animals and in humans. The discussion of this aspect will add to the knowledge of development-inspired tissue engineering strategies and will offer benefits to propel clinical organ regeneration.

Chitosan Hydrogel-Delivered ABE8e Corrects PAX9 Mutant in Dental Pulp Stem Cells

Hypodontia (dental agenesis) is a genetic disorder, and it has been identified that the mutation C175T in PAX9 could lead to hypodontia. Cas9 nickase (nCas9)-mediated homology-directed repair (HDR) and base editing were used for the correction of this mutated point. This study aimed to investigate the effect of HDR and the base editor ABE8e in editing PAX9 mutant. It was found that the chitosan hydrogel was efficient in delivering naked DNA into dental pulp stem cells (DPSCs). To explore the influence of the C175T mutation in PAX9 on the proliferation of DPSCs, hydrogel was employed to deliver PAX9 mutant vector into DPSCs, finding that the PAX9-containing C175T mutation failed to promote the proliferation of DPSCs. Firstly, DPSCs stably carrying PAX9 mutant were constructed. Either an HDR or ABE8e system was delivered into the above-mentioned stable DPSCs, and then the correction efficiency using Sanger sequencing and Western blotting was determined. Meanwhile, the ABE8e presented significantly higher efficiency in correcting C175T compared with HDR. Furthermore, the corrected PAX9 presented enhanced viability and differentiation capacity for osteogenic and neurogenic lineages; the corrected PAX9 even possessed extremely enhanced transcriptional activation ability. In summary, this study has powerful implications for studies into base editors, chitosan hydrogel, and DPSCs in treating hypodontia.

Homeobox Genes in Odontogenic Lesions: A Scoping Review

BACKGROUND

Homeobox genes play crucial roles in tooth morphogenesis and development and thus mutations in homeobox genes cause developmental disorders such as odontogenic lesions. The aim of this scoping review is to identify and compile available data from the literatures on the topic of homeobox gene expression in odontogenic lesions.

METHOD

An electronic search to collate all the information on studies on homeobox gene expression in odontogenic lesions was carried out in four databases (PubMed, EBSCO host, Web of Science and Cochrane Library) with selected keywords. All papers which reported expression of homeobox genes in odontogenic lesions were considered.

RESULTS

A total of eleven (11) papers describing expression of homeobox genes in odontogenic lesions were identified. Methods of studies included next generation sequencing, microarray analysis, RT-PCR, Western blotting, in situ hybridization, and immunohistochemistry. The homeobox reported in odontogenic lesions includes LHX8 and DLX3 in odontoma; PITX2, MSX1, MSX2, DLX, DLX2, DLX3, DLX4, DLX5, DLX6, ISL1, OCT4 and HOX C in ameloblastoma; OCT4 in adenomatoid odontogenic tumour; PITX2 and MSX2 in primordial odontogenic tumour; PAX9 and BARX1 in odontogenic keratocyst; PITX2, ZEB1 and MEIS2 in ameloblastic carcinoma while there is absence of DLX2, DLX3 and MSX2 in clear cell odontogenic carcinoma.

CONCLUSIONS

This paper summarized and reviews the possible link between homeobox gene expression in odontogenic lesions. Based on the current available data, there are insufficient evidence to support any definite role of homeobox gene in odontogenic lesions.

Domestic cat embryos reveal unique transcriptomes of developing incisor, canine, and premolar teeth

Division of the dentition into morphologically distinct classes of teeth (incisors, canines, premolars, and molars) and the acquisition of tribosphenic molars facilitated precise occlusion between the teeth early in mammal evolution. Despite the evolutionary and ecological importance of distinct classes of teeth with unique cusp, crest, and basin morphologies, relatively little is known about the genetic basis for the development of different tooth classes within the embryo. Here we investigated genetic differences between developing deciduous incisor, canine, and premolar teeth in the domestic cat (Felis catus), which we propose to be a new model for tooth development. We examined differences in both developmental timing and crown morphology between the three tooth classes. Using RNA sequencing of early bell stage tooth germs, we showed that each of the three deciduous tooth classes possess a unique transcriptional profile. Three notable groups of genes emerged from our differential expression analysis; genes involved in the extracellular matrix (ECM), Wnt pathway signaling, and members of multiple homeobox gene families (Lhx, Dlx, Alx, and Nkx). Our results suggest that ECM genes may play a previously under-appreciated role in shaping the surface of the tooth crown during development. Differential regulation of these genes likely underlies differences in tooth crown shape and size, although subtle temporal differences in development between the tooth germs could also be responsible. This study provides foundational data for future experiments to examine the function of these candidate genes in tooth development to directly test their potential effects on crown morphology.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

Evaluation of the effects of hypodontia on the morphology of craniofacial structures

OBJECTIVE

The study aimed to investigate the effects of hypodontia on the sagittal and vertical dimensions of the jaws, dentition and the related soft tissue.

MATERIALS AND METHODS

The hypodontia group included 111 patients whose growth was completed with one or more congenitally missing teeth (CMT). Sixty additional patients with skeletal and dental class I relationship, without CMT, and who completed growth, were included as the control group. The hypodontia group was divided into three subgroups according to the intermaxillary (maxillary or mandibular) location, intramaxillary (anterior or posterior) location and the severity of hypodontia (mild: 1-2 CMT or moderate: 3-6 CMT). Twenty-three measurements were performed on lateral cephalograms of the patients. The one-way and Kruskal-Wallis Analysis of Variance tests were used for the statistical analysis. The false discovery-rate analysis was applied for the multiple comparison adjustment.

RESULTS

No significant difference was found in the skeletal measurements between all hypodontia subgroups and the control (P > .05). Upper incisors were found to be retroclined in the anterior hypodontia group. The upper lip was found to be protruded in the mandibulary hypodontia group compared to the control (P < .05).

CONCLUSION

The mild-to-moderate hypodontia did not produce a significant skeletal effect. However, hypodontia can affect the incisors, especially when CMT is in the anterior region. Besides, the effects of severe hypodontia could not be evaluated due to the insufficient number of oligodontia patients.

MACRODONTIA: A brief overview and a case report of KBG syndrome

Macrodontia is a dental condition where a tooth or group of teeth are abnormally larger than average. Functional and aesthetic discrepancies may arise in affected individuals resulting in lowering the quality of life. It has been noted that macrodontia is associated with several genetic and endocrine abnormalities. Among which, KBG syndrome is a rare genetic disorder characterized by developmental and dental abnormalities. This case report provides a brief overview of the significance of macrodontia, along with presenting a case of KBG syndrome with atypical features in a South African, 16-year-old female. The dental manifestations are often overshadowed by other more conspicuous and complex syndromic features. Recognition of both the clinical and oral changes that occur in KBG syndrome facilitates accurate diagnosis and appropriate management of this condition. The authors highlight the importance for clinicians to be cognizant of the clinical implications of macrodontia.

In the absence of a basal lamina, ameloblasts absorb enamel in a serumless and chemically defined organ culture system

OBJECTIVES

Tooth organ development was examined in a serumless, chemically defined organ culture system to determine whether morphological and functional development was identical to that in in vivo and serum-supplemented organ cultures.

METHODS

Mouse mandibular first molar tooth organs at 16 days of gestation were cultured for up to 28 days in a Tronwell culture system using a serum-supplemented or serumless, chemically defined medium. After culture, specimens were processed for assessing tooth development using ultrastructural, immunohistochemical, and mRNA expression analyses.

RESULTS

In serum-supplemented conditions, inner enamel epithelial cells differentiated into secretory-stage ameloblasts, which formed enamel and reached the maturation stage after 14 and 21 days of culture, respectively. Ameloblasts deposited a basal lamina on immature enamel. Conversely, in serumless conditions, ameloblasts formed enamel on mineralized dentin after 21 days. Moreover, maturation-stage ameloblasts did not form basal lamina and directly absorbed mineralized enamel after 28 days of culture. RT-PCR analysis indicated that tooth organs, cultured in serumless conditions for 28 days, had significantly reduced expression levels of ODAM, amelotin, and laminin-322.

CONCLUSIONS

These results indicate that several differences were detected compared to the development in serum-supplemented conditions, such as delayed enamel and dentin formation and the failure of maturation-stage ameloblasts to form basal laminae. Therefore, our results suggest that some factors might be required for the steady formation of mineralized dentin, enamel, and a basal lamina. Additionally, our results indicate that a basal lamina is necessary for enamel maturation.

A novel mutation of MSX1 in oligodontia inhibits odontogenesis of dental pulp stem cells via the ERK pathway

Background

Tooth agenesis, one of the most common developmental anomalies, can affect the function and esthetics of patients. The aim of the present study was to identify genetic clues for familial tooth agenesis and explore the underlying mechanisms, focusing on the role of human dental pulp stem cells (hDPSCs).

Methods

We applied Sanger sequencing to identify the cause of oligodontia in a Chinese family. DNA transfection and functional analysis in DPSCs was also performed to explore the impact of the identified mutation on this phenotype.

Results

In this study, a novel frameshift mutation, the twenty-nucleotide deletion (c.128_147del20, p.Met43Serfsx125), in exon1 of MSX1 was detected in a Chinese family causing autosomal dominant nonsyndromic oligodontia. The mutation cosegregated with the tooth agenesis phenotype in this family. DPSCs transfected with mutant MSX1 plasmid showed decreased capacity of osteo/odontogenic differentiation with a lower expression level of dentin sialophosphoprotein (DSPP) and bone sialoprotein (BSP) compared with those transfected with control MSX1 plasmid. Mechanically, control MSX1 showed nuclear localization while the mutant MSX1 inhibited its nuclear translocation and localized on the cytoplasm to inhibit ERK phosphorylation. Furthermore, we inhibited the ERK pathway using ERK inhibitor (U0126) treatment in control MSX1-transfected DPSCs which could downregulate mineralized nodule formation and the expression of odontogenic genes.

Conclusion

We demonstrated a novel MSX1 mutation causing familial nonsyndromic oligodontia and mechanically MSX1 regulates odontogenesis through the ERK signaling pathway in human dental pulp stem cells.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0965-3) contains supplementary material, which is available to authorized users.

Radiographic Study of the Prevalence and Distribution of Hypodontia Associated with Unilateral and Bilateral Clef Lip and Palate in a Hungarian Population

Background

Cleft defects are one of the most frequent birth-deformities of the orofacial region and they are commonly associated with anomalies of the tooth structure, size, shape, formation, eruption, and tooth number. The aim of our study was to evaluate the prevalence, distribution, and potential association of combined hypodontia in cleft-affected patients with regard to all types of teeth in both jaws in the permanent dentition.

Material/Methods

This retrospective radiographic analysis included patients with various types of clefts treated orthodontically in the Department of Orofacial Orthopedics and Orthodontics at Heim Pàl Children’s Hospital, Budapest. There were 150 patients (84 males, 66 females) with non-syndromic unilateral (UCLP; n=120 patients) or bilateral (BCLP; n=30 patients) cleft formation (lip, alveolus and palate) who met the inclusion criteria. Statistical analysis was performed using the chi-square test and Fisher’s exact test (significance level p<0.05).

Results

Hypodontia was significantly more frequent in patients with cleft-sided lateral incisor (104 patients, 69%), with a total of 235 missing teeth, followed by the second premolars of the upper and lower jaw. A significant correlation of congenital missing teeth was observed in left-sided clefts between the upper and lower second premolar in the cleft area.

Conclusions

Hypodontia inside and outside the cleft area was frequently observed. This should affect the therapy plans, especially if the cleft-sided premolar is also absent. Further comprehensive research including numerous random samples is necessary for better estimating other possible associations.

MSX1 mutations and associated disease phenotypes: genotype-phenotype relations

The Msx1 transcription factor is involved in multiple epithelial-mesenchymal interactions during vertebrate embryogenesis. It has pleiotropic effects in several tissues. In humans, MSX1 variants have been related to tooth agenesis, orofacial clefting, and nail dysplasia. We correlate all MSX1 disease causing variants to phenotypic features to shed light on this hitherto unclear association. MSX1 truncations cause more severe phenotypes than in-frame variants. Mutations in the homeodomain always cause tooth agenesis with or without other phenotypes while mutations outside the homeodomain are mostly associated with non-syndromic orofacial clefts. Downstream effects can be further explored by the edgetic perturbation model. This information provides new insights for genetic diagnosis and for further functional analysis of MSX1 variants.

Chondrogenic Potential of Mouse Calvarial Mesenchyme

Facial and calvarial bones form intramembranously without a cartilagenous model; however, cultured chick calvarial mesenchyme cells may differentiate into both osteoblasts and chondroblasts and, in rodents, small cartilages occasionally form at the sutures in vivo. Therefore, we wanted to investigate what factors regulate normal differentiation of calvarial mesenchymal cells directly into osteoblasts. In embryonic mouse heads and in cultured tissue explants, we analyzed the expression of selected transcription factors and extracellular matrix molecules associated with bone and cartilage development. Cartilage markers Sox9 and type II collagen were expressed in all craniofacial cartilages. In addition, Msx2 and type I collagen were expressed in sense capsule cartilages. We also observed that the undifferentiated calvarial mesenchyme and the osteogenic fronts in the jaw expressed Co∗∗∗l2A1. Moreover, we found that cultured mouse calvarial mesenchyme could develop into cartilage. Of the 49 explants that contained mesenchyme, intramembranous ossification occurred in 35%. Only cartilage formed in 4%, and both cartilage and bone formed in 4%. Our study confirms that calvarial mesenchyme, which normally gives rise to intramembranous bone, also has chondrogenic potential.

MSX2 Induces Trophoblast Invasion in Human Placenta

Normal implantation depends on appropriate trophoblast growth and invasion. Inadequate trophoblast invasion results in pregnancy-related disorders, such as early miscarriage and pre-eclampsia, which are dangerous to both the mother and fetus. Msh Homeobox 2 (MSX2), a member of the MSX family of homeobox proteins, plays a significant role in the proliferation and differentiation of various cells and tissues, including ectodermal organs, teeth, and chondrocytes. Recently, MSX2 was found to play important roles in the invasion of cancer cells into adjacent tissues via the epithelial-mesenchymal transition (EMT). However, the role of MSX2 in trophoblastic invasion during placental development has yet to be explored. In the present study, we detected MSX2 expression in cytotrophoblast, syncytiotrophoblast, and extravillous cytotrophoblast cells of first or third trimester human placentas via immunohistochemistry analysis. Furthermore, we found that the in vitro invasive ability of HTR8/SVneo cells was enhanced by exogenous overexpression of MSX2, and that this effect was accompanied by increased protein expression of matrix metalloproteinase-2 (MMP-2), vimentin, and β-catenin. Conversely, treatment of HTR8/SVneo cells with MSX2-specific siRNAs resulted in decreased protein expression of MMP-2, vimentin, and β-catenin, and reduced invasion levels in a Matrigel invasion test. Notably, however, treatment with the MSX2 overexpression plasmid and the MSX2 siRNAs had no effect on the mRNA expression levels of β-catenin. Meanwhile, overexpression of MSX2 and treatment with the MSX2-specific siRNA resulted in decreased and increased E-cadherin expression, respectively, in JEG-3 cells. Lastly, the protein expression levels of MSX2 were significantly lower in human pre-eclamptic placental villi than in the matched control placentas. Collectively, our results suggest that MSX2 may induce human trophoblast cell invasion, and dysregulation of MSX2 expression may be associated with pre-eclampsia.

A Longitudinal Study of the Presence of Dental Anomalies in the Primary and Permanent Dentitions of Cleft Lip and/or Palate Patients

OBJECTIVE

The aim is to survey primary and permanent dental anomalies: hypodontia, microdontia, a supernumerary tooth, and fused teeth in patients with cleft lip and/or palate.

DESIGN

Retrospective longitudinal study Subjects :  The subjects were selected from all 1724 patients with cleft lip and/or palate who were registered at the orthodontic clinic of Kyushu University Hospital, Fukuoka, Japan, from 1970 to 2009. Finally, 994 subjects were evaluated for primary dentition, 1352 for permanent dentition, and 871 for the longitudinal changes from primary to permanent dentition.

METHODS

The prevalence of dental anomalies was compared for each tooth type, among various cleft types, between males and females, and between the alveolar cleft area and the noncleft area.

RESULTS

The prevalence of hypodontia was 16.2% for primary dentition and 52.7% for permanent dentition in the subjects with cleft lip and/or palate. Hypodontia increased with the severity of the cleft type. Multiple hypodontia was found more frequently in the subjects with bilateral cleft lip and palate and the subjects with unilateral cleft lip and palate. Microformed lateral incisors were found in 22.7% of permanent lateral incisors but not in primary dentition. Supernumerary teeth were found in 17.7% of the subjects with cleft lip and/or palate for primary maxillary dentition and in 5.7% for permanent maxillary dentition.

CONCLUSION

The prevalence of hypodontia was greater in permanent dentition than in primary dentition; although, it was not much different between males and females or between the right and left sides. The prevalence of dental anomalies was significantly different among four groups by cleft type: cleft lip, cleft lip and alveolus, cleft lip and palate, and cleft palate.

Tooth and scale morphogenesis in shark: an alternative process to the mammalian enamel knot system

BACKGROUND

The gene regulatory network involved in tooth morphogenesis has been extremely well described in mammals and its modeling has allowed predictions of variations in regulatory pathway that may have led to evolution of tooth shapes. However, very little is known outside of mammals to understand how this regulatory framework may also account for tooth shape evolution at the level of gnathostomes. In this work, we describe expression patterns and proliferation/apoptosis assays to uncover homologous regulatory pathways in the catshark Scyliorhinus canicula.

RESULTS

Because of their similar structural and developmental features, gene expression patterns were described over the four developmental stages of both tooth and scale buds in the catshark. These gene expression patterns differ from mouse tooth development, and discrepancies are also observed between tooth and scale development within the catshark. However, a similar nested expression of Shh and Fgf suggests similar signaling involved in morphogenesis of all structures, although apoptosis assays do not support a strictly equivalent enamel knot system in sharks. Similarities in the topology of gene expression pattern, including Bmp signaling pathway, suggest that mouse molar development is more similar to scale bud development in the catshark.

CONCLUSIONS

These results support the fact that no enamel knot, as described in mammalian teeth, can be described in the morphogenesis of shark teeth or scales. However, homologous signaling pathways are involved in growth and morphogenesis with variations in their respective expression patterns. We speculate that variations in this topology of expression are also a substrate for tooth shape evolution, notably in regulating the growth axis and symmetry of the developing structure.

Suppression of epithelial differentiation by Foxi3 is essential for molar crown patterning

Epithelial morphogenesis generates the shape of the tooth crown. This is driven by patterned differentiation of cells into enamel knots, root-forming cervical loops and enamel-forming ameloblasts. Enamel knots are signaling centers that define the positions of cusp tips in a tooth by instructing the adjacent epithelium to fold and proliferate. Here, we show that the forkhead-box transcription factor Foxi3 inhibits formation of enamel knots and cervical loops and thus the differentiation of dental epithelium in mice. Conditional deletion of Foxi3 (Foxi3 cKO) led to fusion of molars with abnormally patterned shallow cusps. Foxi3 was expressed in the epithelium, and its expression was reduced in the enamel knots and cervical loops and in ameloblasts. Bmp4, a known inducer of enamel knots and dental epithelial differentiation, downregulated Foxi3 in wild-type teeth. Using genome-wide gene expression profiling, we showed that in Foxi3 cKO there was an early upregulation of differentiation markers, such as p21, Fgf15 and Sfrp5. Different signaling pathway components that are normally restricted to the enamel knots were expanded in the epithelium, and Sostdc1, a marker of the intercuspal epithelium, was missing. These findings indicated that the activator-inhibitor balance regulating cusp patterning was disrupted in Foxi3 cKO. In addition, early molar bud morphogenesis and, in particular, formation of the suprabasal epithelial cell layer were impaired. We identified keratin 10 as a marker of suprabasal epithelial cells in teeth. Our results suggest that Foxi3 maintains dental epithelial cells in an undifferentiated state and thereby regulates multiple stages of tooth morphogenesis.

BMP4 promotes EMT and mesodermal commitment in human embryonic stem cells via SLUG and MSX2

Bone morphogenetic proteins (BMPs) initiate differentiation in human embryonic stem cells (hESCs) but the exact mechanisms have not been fully elucidated. We demonstrate here that SLUG and MSX2, transcription factors involved in epithelial-mesenchymal transitions, essential features of gastrulation in development and tumor progression, are important mediators of BMP4-induced differentiation in hESCs. Phosphorylated Smad1/5/8 colocalized with the SLUG protein at the edges of hESC colonies where differentiation takes place. The upregulation of the BMP target SLUG was direct as shown by the binding of phosphorylated Smad1/5/8 to its promoter, which interrupted the formation of adhesion proteins, resulting in migration. Knockdown of SLUG by short hairpin RNA blocked these changes, confirming an important role for SLUG in BMP-mediated mesodermal differentiation. Furthermore, BMP4-induced MSX2 expression leads to mesoderm formation and then preferential differentiation toward the cardiovascular lineage.

A novel non-stop mutation in MSX1 causing autosomal dominant non-syndromic oligodontia

Oligodontia, which is the congenital absence of six or more permanent teeth, excluding the third molars, may contribute to masticatory dysfunction, speech alteration, aesthetic problems and malocclusion. Msh homeobox 1 (MSX1) was the first gene identified as causing non-syndromic oligodontia. In this study, we identified a novel heterozygous non-stop mutation (c.910_911dupTA, p.*304Tyrext*48) in MSX1 in a Chinese family with autosomal dominant non-syndromic oligodontia. This novel mutation substitutes the stop codon with a tyrosine residue, potentially adding 48 amino acids to the C-terminus of MSX1. Further in vitro study found that mutant MSX1 could be expressed but had lost its ability to enter the nucleus. This is the first report indicating that a non-stop mutation in MSX1 is responsible for oligodontia. This study broadens the mutation spectrum for MSX1 and provides a new way to clarify the mechanism of MSX1 in tooth agenesis.

A comparison of skeletal maturation in patients with tooth agenesis and unaffected controls assessed by the cervical vertebral maturation (CVM) index

OBJECTIVE

The aims of this study were to (1) investigate if there is a difference in skeletal maturation between tooth agenesis and control patients and (2) whether skeletal maturation is affected by the severity of tooth agenesis. The cervical vertebral maturation (CVM) index can be used to assess skeletal maturation.

DESIGN

A retrospective cross-sectional study.

SETTING

Eastman Dental Hospital, London, UK.

METHODS AND MATERIALS

A total of 360 cephalograms of patients aged 9-17 years (164 males and 196 females) allocated to four subgroups (mild, moderate and severe tooth agenesis patients, and controls) were assessed retrospectively. There were 90 patients in each of the four subgroups. The skeletal maturation of each subject was assessed both quantitatively and qualitatively using the CVM index. All patients in the study were either currently receiving treatment or had been discharged from the hospital.

RESULTS

There was no statistically significant relationship between skeletal maturation and the presence of tooth agenesis. Furthermore, there was no statistically significant relationship between the skeletal maturity of patients and different severities of tooth agenesis.

CONCLUSIONS

The data obtained from this group of patients and using this measurement tool alone does not supply sufficient reason to reject the null hypothesis. However, it suggests that it is possible that no difference exists between the groups.

Developmental basis of toothlessness in turtles: insight into convergent evolution of vertebrate morphology

The tooth is a major component of the vertebrate feeding apparatus and plays a crucial role in species survival, thus subjecting tooth developmental programs to strong selective constraints. However, irrespective of their functional importance, teeth have been lost in multiple lineages of tetrapod vertebrates independently. To understand both the generality and the diversity of developmental mechanisms that cause tooth agenesis in tetrapods, we investigated expression patterns of a series of tooth developmental genes in the lower jaw of toothless turtles and compared them to that of toothed crocodiles and the chicken as a representative of toothless modern birds. In turtle embryos, we found impairment of Shh signaling in the oral epithelium and early-stage arrest of odontoblast development caused by termination of Msx2 expression in the dental mesenchyme. Our data indicate that such changes underlie tooth agenesis in turtles and suggest that the mechanism that leads to early-stage odontogenic arrest differs between birds and turtles. Our results demonstrate that the cellular and molecular mechanisms that regulate early-stage arrest of tooth development are diverse in tetrapod lineages, and odontogenic developmental programs may respond to changes in upstream molecules similarly thereby evolving convergently with feeding morphology.

Geminin is required for epithelial to mesenchymal transition at gastrulation

Geminin is a multifunctional protein previously suggested to both maintain the bone morphogenetic protein inhibition required for neural induction and to control cell-cycle progression and cell fate in the early embryo. Since Geminin is required in the blastocyst on E3.5, we employed shRNA to examine its role during postimplantation development. Geminin knockdown inhibited the epithelial to mesenchymal transition (EMT) required at gastrulation and neural crest delamination, resulting in anterior-posterior axis and patterning defects, while overexpression promoted EMT at both locations. Geminin was negatively correlated with expression of E-cadherin, which is critically involved in controlling epithelial architecture. In addition, Geminin expression level was correlated with Wnt signaling and expression of the Wnt target gene Axin2 and with Msx2, and negatively correlated with the expression of Bmp4 and Neurog1 in quantitative reverse transcriptase-polymerase chain reaction analysis of RNAs from individual embryos. These results suggest that in addition to patterning the early embryo, Geminin plays a previously unrecognized role in EMT via its ability to affect Wnt signaling and E-cadherin expression.

Wnt signaling in the murine diastema

The correct number and shape of teeth are critical factors for an aesthetic and functional dentition. Understanding the molecular mechanisms regulating tooth number and shape are therefore important in orthodontics. Mice have only one incisor and three molars in each jaw quadrant that are divided by a tooth-less region, the diastema. Although mice lost teeth in the diastema during evolution, the remnants of the evolutionary lost teeth are observed as transient epithelial buds in the wild-type diastema during early stages of development. Shh and Fgf signaling pathways that are essential for tooth development have been shown to be repressed in the diastema. It remains unclear however how Wnt signaling, that is also required for tooth development, is regulated in the diastema. In this study we found that in the embryonic diastema, Wnt5a expression was observed in mesenchyme, whereas Wnt4 and Wnt10b were expressed in epithelium. The expression of Wnt6 and Wnt11 was found in both tissues. The Wnt co-receptor, Lrp6, was weakly expressed in the diastema overlapping with weak Lrp4 expression, a co-receptor that inhibits Wnt signaling. Secreted Wnt inihibitors Dkk1, Dkk2, and Dkk3 were also expressed in the diastema. Lrp4 mutant mice develop supernumerary teeth in the diastema that is accompanied by upregulation of Wnt signaling and Lrp6 expression. Wnt signaling is thus usually attenuated in the diastema by these secreted and membrane bound Wnt inhibitors.

Lymphocyte enhancer-binding factor 1: an essential factor in odontoblastic differentiation of dental pulp cells enzymatically isolated from rat incisors

Lymphocyte enhancer-binding factor 1 (Lef1), a HMG-domain protein, is thought to play important roles in inductive tissue interaction during tooth development. Lef1 knockdown in mice causes arrest at the bud stage in tooth development. As this gene participates in the regulation of a large and diverse set of peptide growth factors in ectomesenchymal cell differentiation of dental papilla, Lef1 appears to be a key factor in odontoblast differentiation. However, the relationship between Lef1 and odontoblast differentiation is still unclear. To analyze the biological roles of Lef1 in regulating odontoblast differentiation, we transiently overexpressed or suppressed Lef1 in cultured dental pulp cells. Lef1-overexpressing cells expressed higher levels of dentin sialoprotein (DSPP), osteocalcin and alkaline phosphatase (ALP) mRNA and formed larger numbers of mineralized nodules compared to control cells. However, Msx-1 expression or cell proliferation was unaffected by overexpression of Lef1. To further examine the role of Lef1 in dental pulp cells, we knocked down Lef1 expression in dental pulp cells using short interfering RNA (siRNA). Transient expression of siRNA against Lef1 markedly reduced Lef1 mRNA levels, and Lef1-suppressed cells expressed lower levels of DSPP, osteocalcin and ALP mRNA compared to control cells. Furthermore, the formation of mineralized nodules was inhibited by siRNA against Lef1; however, neither Msx-1 expression or cell proliferation was inhibited by siRNA against Lef1. These results outline the role of Lef1 in accelerating odontoblast differentiation by regulating DSP and osteocalcin mRNA expression in dental pulp cells, confirming that Lef1 is a key factor for odontoblast differentiation.

Biological synthesis of tooth enamel instructed by an artificial matrix

The regenerative capability of enamel, the hardest tissue in the vertebrate body, is fundamentally limited due to cell apoptosis following maturation of the tissue. Synthetic strategies to promote enamel formation have the potential to repair damage, increase the longevity of teeth and improve the understanding of the events leading to tissue formation. Using a self-assembling bioactive matrix, we demonstrate the ability to induce ectopic formation of enamel at chosen sites adjacent to a mouse incisor cultured in vivo under the kidney capsule. The resulting material reveals the highly organized, hierarchical structure of hydroxyapatite crystallites similar to native enamel. This artificially triggered formation of organized mineral demonstrates a pathway for developing cell fabricated materials for treatment of dental caries, the most ubiquitous disease in man. Additionally, the artificial matrix provides a unique tool to probe cellular mechanisms involved in tissue formation further enabling the development of tooth organ replacements.

A novel g.-1258G>A mutation in a conserved putative regulatory element of PAX9 is associated with autosomal dominant molar hypodontia

Mutations in the transcription factor PAX9 which plays a critical role in the switching of odontogenic potential from the epithelium to the mesenchyme during tooth development cause autosomal dominant non-syndromic hypodontia primarily affecting molars. Linkage analysis on a family segregating autosomal dominant molar hypodontia with markers flanking and within PAX9 yielded a maximum multipoint LOD score of 3.6. No sequence variants were detected in the coding or 5'- and 3'-untranslated regions (UTRs) of PAX9. However, we identified a novel g.-1258G>A sequence variant in all affected individuals of the family but not in the unaffected family members or in 3088 control chromosomes. This mutation is within a putative 5'-regulatory sequence upstream of PAX9 highly conserved in primates, somewhat conserved in ungulates and carnivores but not conserved in rodents. Bioinformatics analysis of the sequence determined that there was no abolition or creation of a putative binding site for known transcription factors. Based on our previous findings that haploinsufficiency for PAX9 leads to hypodontia, we postulate that the g.-1258G>A variant reduces the expression of PAX9 which underlies the hypodontia phenotype in this family.

Expression of MSX2 predicts malignancy of branch duct intraductal papillary mucinous neoplasm of the pancreas

BACKGROUND

To distinguish malignant from benign branch duct (BD)-intraductal papillary mucinous neoplasm (IPMN) still remains difficult. Recently, we revealed that MSX2 was frequently expressed in pancreatic cancer and its expression was correlated with aggressive behavior of the cancer. The aim of this study was to assess the involvement of MSX2 in IPMN development and whether its expression would differentiate malignant from benign IPMN.

METHODS

Seventeen microdissected lesions and 45 IPMN tissues were used for quantitative real-time reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. The role of MSX2 in the pancreatic duct cell was assessed by the induced expression of MSX2 in a normal human pancreatic duct epithelial cell line (HPDE).

RESULTS

Malignant IPMN expressed significantly higher levels of MSX2 mRNA than benign IPMN lesions. MSX2 protein expression was frequently found in borderline and malignant lesions (20/29, 68.9%), while its expression was seen in only one of 16 benign IPMN tissues. Univariate analysis showed that nodules of 6 mm or more and MSX2 expression were significantly correlated with the malignancy of BD-IPMN (P = 0.022 and 0.0026, respectively), and multivariate analysis revealed that only MSX2 expression was identified as an independent factor to predict malignant BD-IPMN. HPDE cells expressing MSX2 showed increased cellular proliferation compared to control cells.

CONCLUSIONS

Based on our results, MSX2 plays a pivotal role in the development of IPMN through growth stimulation of tumor cells, and its expression was identified as an independent predictive factor for malignancy of BD-IPMN.

A regulatory feedback loop involving p63 and IRF6 links the pathogenesis of 2 genetically different human ectodermal dysplasias

The human congenital syndromes ectrodactyly ectodermal dysplasia-cleft lip/palate syndrome, ankyloblepharon ectodermal dysplasia clefting, and split-hand/foot malformation are all characterized by ectodermal dysplasia, limb malformations, and cleft lip/palate. These phenotypic features are a result of an imbalance between the proliferation and differentiation of precursor cells during development of ectoderm-derived structures. Mutations in the p63 and interferon regulatory factor 6 (IRF6) genes have been found in human patients with these syndromes, consistent with phenotypes. Here, we used human and mouse primary keratinocytes and mouse models to investigate the role of p63 and IRF6 in proliferation and differentiation. We report that the DeltaNp63 isoform of p63 activated transcription of IRF6, and this, in turn, induced proteasome-mediated DeltaNp63 degradation. This feedback regulatory loop allowed keratinocytes to exit the cell cycle, thereby limiting their ability to proliferate. Importantly, mutations in either p63 or IRF6 resulted in disruption of this regulatory loop: p63 mutations causing ectodermal dysplasias were unable to activate IRF6 transcription, and mice with mutated or null p63 showed reduced Irf6 expression in their palate and ectoderm. These results identify what we believe to be a novel mechanism that regulates the proliferation-differentiation balance of keratinocytes essential for palate fusion and skin differentiation and links the pathogenesis of 2 genetically different groups of ectodermal dysplasia syndromes into a common molecular pathway.

Accelerated closure of skin wounds in mice deficient in the homeobox gene Msx2

Differences in cellular competence offer an explanation for the differences in the healing capacity of tissues of various ages and conditions. The homeobox family of genes plays key roles in governing cellular competence. Of these, we hypothesize that Msx2 is a strong candidate regulator of competence in skin wound healing because it is expressed in the skin during fetal development in the stage of scarless healing, affects postnatal digit regeneration, and is reexpressed transiently during postnatal skin wound repair. To address whether Msx2 affects cellular competence in injury repair, 3 mm full-thickness excisional wounds were created on the back of C.Cg-Msx2(tm1Rilm)/Mmcd (Msx2 null) mice and the healing pattern was compared with that of the wild type mice. The results show that Msx2 null mice exhibited faster wound closure with accelerated reepithelialization plus earlier appearance of keratin markers for differentiation and an increased level of smooth muscle actin and tenascin in the granulation tissue. In vitro, keratinocytes of Msx2 null mice exhibit increased cell migration and the fibroblasts show stronger collagen gel contraction. Thus, our results suggest that Msx2 regulates the cellular competence of keratinocytes and fibroblasts in skin injury repair.

Regulation of Msx2 Gene Expression by Steroid Hormones in Human Nonmalignant and Malignant Breast Cancer Explants Cultured in Vitro

Muscle segment homeobox genes, which regulate developmental programs and are expressed in embryonic and adult tissue, play a role in development of some malignancies. There are no reports on the expression of these families of genes in breast cancer tissue. The aim of this study was to compare expression of Msx2 gene in breast cancer of different genotypes as well as in surrounding nonmalignant tissues. Explants obtained during surgery were divided according to their sex steroid receptor status determined by immunocytochemistry. Four explants obtained from malignant and nonmalignant tissue of each individual patient were incubated in a control medium or with the addition of progesterone (10(-7) M) alone, estradiol 17 beta (10(-5) M) or both. The relative level of Msx2 transcripts was evaluated by a semiquantitative RT-PCR and cell proliferation by Alamar Blue test. Results of RT-PCR analysis showed that the relative expression of Msx2 gene depended on the presence of ER/PR receptors both in nonmalignant and malignant tissues Relative amount of Msx2 mRNA was the highest in surrounding nonmalignant ER+/PR- and ER-/PR+ tissue, whereas in ER-/PR- and ER+/PR+ tissue it was 1.4-1.6-fold lower. Tumorigenesis led to about a twofold decrease in the relative amount of Msx2 mRNA except for ER+/PR+ immunophenotype, where no changes were observed. Addition of estradiol or progesterone to the culture of ER-/PR- type tissue explants did not change significantly the relative amount of Msx2 gene mRNA. An opposite effect was observed in ER+/PR- type of tissue. Addition of estradiol alone, or estradiol and progesterone together to tissue culture explants decreased two to three fold the relative amount of Msx2 gene mRNA in both, malignant and surrounding tissues. Progesterone alone had no effect on Msx2 gene expression in this type of tissue. The most complicated regulation was observed in ER+/PR+ type of tissue. Culture of tissue explants supplemented with estradiol significantly increased the relative amount of Msx2 gene mRNA in the surrounding tissue. Progesterone enhanced the stimulatory effect of estradiol in surrounding tissues but not in the malignant tissue. Increased expression of Msx2 correlated with an increased proliferation in ER-/PR- and ER+/PR+ types, but not in ER+/PR- type of tissues. In conclusion, obtained results provide evidence that estrogen affects Msx2 gene expression. Significant changes in the relative amount of Msx2 gene mRNA and lack of canonical ERE element in 5'-upstream sequence of this gene suggest that regulation takes place indirectly probably by protein-protein interaction. The decrease in the relative amount of Msx2 gene mRNA in ER+/PR- type tumor suggests that progesterone also affects Msx2 gene expression by an indirect mechanism(s).

Epigenetic gene regulation in stem cells and correlation to cancer

Through the classic study of genetics, much has been learned about the regulation and progression of human disease. Specifically, cancer has been defined as a disease driven by genetic alterations, including mutations in tumor-suppressor genes and oncogenes, as well as chromosomal abnormalities. However, the study of normal human development has identified that in addition to classical genetics, regulation of gene expression is also modified by 'epigenetic' alterations including chromatin remodeling and histone variants, DNA methylation, the regulation of polycomb group proteins, and the epigenetic function of non-coding RNA. These changes are modifications inherited during both meiosis and mitosis, yet they do not result in alterations of the actual DNA sequence. A number of biological questions are directly influenced by epigenetics, such as how does a cell know when to divide, differentiate or remain quiescent, and more importantly, what happens when these pathways become altered? Do these alterations lead to the development and/or progression of cancer? This review will focus on summarizing the limited current literature involving epigenetic alterations in the context of human cancer stems cells (CSCs). The extent to which epigenetic changes define cell fate, identity, and phenotype are still under intense investigation, and many questions remain largely unanswered. Before discussing epigenetic gene silencing in CSCs, the different classifications of stem cells and their properties will be introduced. This will be followed by an introduction to the different epigenetic mechanisms. Finally, there will be a discussion of the current knowledge of epigenetic modifications in stem cells, specifically what is known from rodent systems and established cancer cell lines, and how they are leading us to understand human stem cells.

Immunohistochemical localization of barx2 in the developing fetal mouse submandibular glands

The development of mouse submandibular gland (SMG) begins at embryonic day 11.5-12 (E11.5-12), during which successive rounds of epithelial clefting and branching create complex epithelial tree-like structures. Homeobox genes regulate place-dependent morphogenesis, including epithelial-mesenchymal interactions, and control the expression patterns of signaling molecules. The Barx2 containing Homeobox exerts several key roles in development. Some studies have shown that the Barx2 plays important roles in the epithelial-mesenchymal interactions of organogenesis. However, the mechanisms of Barx2 associated with the development of SMG are obscure. In this study, we demonstrated for the first time the exact spatial and temporal Barx2 expression pattern in SMG epithelial tissue during development using immunohistochemical staining and Real-Time quantitative PCR. Barx2 was expressed in the nucleus of the epithelial cells located in the proliferative and differentiative regions of the developing SMG during the early development stages (E11.5-E13.5). After the E14.5-time period, the expression gradually decreased, and at E16.5, expression mostly disappeared despite the fact that evidence of cytodifferentiation, such as the appearance of proacinar cells, distinct lumen formation, and secretory products, was beginning to be observed. Results of Real-Time PCR demonstrated that the amount of Barx2 mRNA expression in SMG was maximal on E14.5, and gradually decreased by E18.5. These results indicate that Barx2 is associated with early stage epithelial tissue development, and can be a useful epithelial marker of the SMG during early developmental stages.

Dento-craniofacial phenotypes and underlying molecular mechanisms in hypohidrotic ectodermal dysplasia (HED): a review

The hypohidrotic ectodermal dysplasias (HED) belong to a large and heterogeneous nosological group of polymalfomative syndromes characterized by dystrophy or agenesis of ectodermal derivatives. Molecular etiologies of HED consist of mutations of the genes involved in the Ectodysplasin (EDA)-NF-kappaB pathway. Besides the classic ectodermal signs, craniofacial and bone manifestations are associated with the phenotypic spectrum of HED. The dental phenotype of HED consists of various degrees of oligodontia with other dental abnormalities, and these are important in the early diagnosis and identification of persons with HED. Phenotypic dental markers of heterozygous females for EDA gene mutation-moderate oligodontia, conical incisors, and delayed dental eruption-are important for individuals giving reliable genetic counseling. Some dental ageneses observed in HED are also encountered in non-syndromic oligodontia. These clinical similarities may reflect possible interactions between homeobox genes implicated in early steps of odontogenesis and the Ectodysplasin (EDA)-NF-kappaB pathway. Craniofacial dysmorphologies and bone structural anomalies are also associated with the phenotypic spectrum of persons with HED patients. The corresponding molecular mechanisms involve altered interactions between the EDA-NF-kappaB pathway and signaling molecules essential in skeletogenic neural crest cell differentiation, migration, and osteoclastic differentiation. Regarding oral treatment of persons with HED, implant-supported prostheses are used with a relatively high implant survival rate. Recently, groundbreaking experimental approaches with recombinant EDA or transgenesis of EDA-A1 were developed from the perspective of systemic treatment and appear very promising. All these clinical observations and molecular data allow for the specification of the craniofacial phenotypic spectrum in HED and provide a better understanding of the mechanisms involved in the pathogenesis of this syndrome.

Dental agenesis: genetic and clinical perspectives

Dental agenesis is the most common developmental anomaly in humans and is frequently associated with several other oral abnormalities. Whereas the incidence of missing teeth may vary considerably depending on dentition, gender, and demographic or geographic profiles, distinct patterns of agenesis have been detected in the permanent dentition. These frequently involve the last teeth of a class to develop (I2, P2, M3) suggesting a possible link with evolutionary trends. Hypodontia can either occur as an isolated condition (non-syndromic hypodontia) involving one (80% of cases), a few (less than 10%) or many teeth (less than 1%), or can be associated with a systemic condition or syndrome (syndromic hypodontia), essentially reflecting the genetically and phenotypically heterogeneity of the condition. Based on our present knowledge of genes and transcription factors that are involved in tooth development, it is assumed that different phenotypic forms are caused by different genes involving different interacting molecular pathways, providing an explanation not only for the wide variety in agenesis patterns but also for associations of dental agenesis with other oral anomalies. At present, the list of genes involved in human non-syndromic hypodontia includes not only those encoding a signaling molecule (TGFA) and transcription factors (MSX1 and PAX9) that play critical roles during early craniofacial development, but also genes coding for a protein involved in canonical Wnt signaling (AXIN2), and a transmembrane receptor of fibroblast growth factors (FGFR1). Our objective was to review the current literature on the molecular mechanisms that are responsible for selective dental agenesis in humans and to present a detailed overview of syndromes with hypodontia and their causative genes. These new perspectives and future challenges in the field of identification of possible candidate genes involved in dental agenesis are discussed.

Up-regulation of MSX2 enhances the malignant phenotype and is associated with twist 1 expression in human pancreatic cancer cells

MSX2 is thought to be a regulator of organ development and a downstream target of the ras signaling pathway; however, little is known about the role of MSX2 in the development of pancreatic cancers, most of which harbor a K-ras gene mutation. Therefore, we examined whether the presence of MSX2 correlates with the malignant behavior of pancreatic cancer cells. BxPC3 pancreatic cancer cells that stably overexpress MSX2 showed a flattened and scattered morphology accompanied by a change in localization of E-cadherin and beta-catenin from membrane to cytoplasm. Cell proliferation rate, cell migration, and anchorage-independent cell growth were enhanced in MSX2-expressing cells. Injection of MSX2-expressing cells into the pancreas of nude mice resulted in a significant increase in liver metastases and peritoneal disseminations compared with injection of control cells. Microarray analysis revealed a significant induction of Twist 1 expression in cells that express MSX2. When MSX2 was inactivated in pancreatic cancer cells following transfection with an MSX2-specific small interfering RNA, Twist 1 was down-regulated. Immunohistochemistry of human pancreatic carcinoma tissue revealed that MSX2 was frequently expressed in cancer cells, and that increased expression of MSX2 significantly correlated with higher tumor grade, vascular invasion, and Twist 1 expression. These data indicate that MSX2 plays a crucial role in pancreatic cancer development by inducing changes consistent with epithelial to mesenchymal transition through enhanced expression of Twist 1.

A novel autosomal-recessive mutation, whitish chalk-like teeth, resembling amelogenesis imperfecta, maps to rat chromosome 14 corresponding to human 4q21

A rat mutant, whitish chalk-like teeth (wct), with white, chalk-like abnormal incisors, was discovered and morphologically and genetically characterized. The mutant rats showed tooth enamel defects that were similar to those of human amelogenesis imperfecta. The wct mutation was found to disturb the morphological transition of ameloblasts from secretory to maturation stages and to induce cyst formation. This mutation also disturbs the transfer of iron into the enamel, resulting in the whitish chalk-like incisors. A genetic linkage study indicated that the wct locus maps to a specific interval of rat chromosome 14 between D14Got13 and D14Wox2. Interestingly, the human chromosomal region orthologous to wct, a 5.5-Mb interval in human chromosome 4q21, is a critical region for the locus of human amelogenesis imperfecta AIH2. These results strongly suggest that this wct mutant is a useful model for the identification of genes responsible for amelogenesis imperfecta and molecular mechanisms of tooth development.

Cranial suture biology and dental development: genetic and clinical perspectives

Premature fusion of the calvarial bones at the sutures, or craniosynostosis (CS), is a relatively common birth defect (1:2000-3000) frequently associated with limb deformity. Patients with CS may present oral defects, such as cleft soft palate, hypodontia, hyperdontia, and delayed tooth eruption, but also unusual associations of major dental anomalies such as taurodontism, microdontia, multiple dens invaginatus, and dentin dysplasia. The list of genes that are involved in CS includes those coding for the different fibroblast growth factor receptors and a ligand of ephrin receptors, but also genes encoding transcription factors, such as MSX2 and TWIST. Most of these genes are equally involved in odontogenesis, providing a pausible explanation for clinical associations of CS with dental agenesis or tooth malformations. On the basis of the present knowledge on genes and transcription factors that are involved in craniofacial morphogenesis, and from dental clinics of CS syndromes, the molecular mechanisms that control suture formation and suture closure are expected to play key roles in patterning events and development of teeth. The purpose of this article is to review and merge the recent advances in the field of suture research at the genetic and cellular levels with those of tooth development, and to apply them to the dental clinics of CS syndromes. These new perspectives and future challenges in the field of both dental clinics and molecular genetics, more in particular the identification of possible candidate genes involved in both CS and dental defects, are discussed.

Wnt/beta-catenin signaling directs multiple stages of tooth morphogenesis

Wnt/beta-catenin signaling plays key roles in tooth development, but how this pathway intersects with the complex interplay of signaling factors regulating dental morphogenesis has been unclear. We demonstrate that Wnt/beta-catenin signaling is active at multiple stages of tooth development. Mutation of beta-catenin to a constitutively active form in oral epithelium causes formation of large, misshapen tooth buds and ectopic teeth, and expanded expression of signaling molecules important for tooth development. Conversely, expression of key morphogenetic regulators including Bmp4, Msx1, and Msx2 is downregulated in embryos expressing the secreted Wnt inhibitor Dkk1 which blocks signaling in epithelial and underlying mesenchymal cells. Similar phenotypes are observed in embryos lacking epithelial beta-catenin, demonstrating a requirement for Wnt signaling within the epithelium. Inducible Dkk1 expression after the bud stage causes formation of blunted molar cusps, downregulation of the enamel knot marker p21, and loss of restricted ectodin expression, revealing requirements for Wnt activity in maintaining secondary enamel knots. These data place Wnt/beta-catenin signaling upstream of key morphogenetic signaling pathways at multiple stages of tooth development and indicate that tight regulation of this pathway is essential both for patterning tooth development in the dental lamina, and for controlling the shape of individual teeth.

Regulating the Role of Bone Morphogenetic Protein 4 in Tooth Bioengineering

PURPOSE

Culture of the whole organ and regulation of its development using biologic and engineering principles can be used to produce structures and organs for reconstructing defects. The application of these bioengineering approaches in artificial tooth development may be the alternative way to replace missing dentition.

MATERIALS AND METHODS

For the artificial bioengineering of a mouse tooth, tooth buds were dissected and transplanted into the diastema of the developing mandible. The mandiblular primordia containing transplanted tooth buds were culture in vitro and in vivo using a bioengineering method. In addition, to regulate the development of tooth germs, bone morphogenetic protein 4 (BMP4) or its antagonist, Noggin was administered.

RESULTS

After the period of in vitro and in vivo culture, the transplanted tooth germ in the diastema showed tooth development with supportive structure formation. In the BMP-treated group, the bioengineered tooth was observed with increased maturation of cusp and enamel matrix. However, in the Noggin-treated tooth germs, the developing molar had a crater-like appearance with the immature development of the cusp and suppressed formation of the enamel matrix.

CONCLUSIONS

This study confirmed that tooth germ transplantation in the diastema and culture with administration of BMP4 could lead to the mature development of the dental structures. In addition, these results suggest the possibility of bioengineering the tooth in morphogenesis and differentiation even in the toothless area.

Fetal alcohol syndrome and developing craniofacial and dental structures--a review

OBJECTIVES

Fetal alcohol syndrome (FAS) is a collection of signs and symptoms seen in children exposed to alcohol in the prenatal period. It is characterized mainly by a distinct pattern of craniofacial malformations, physical and mental retardation. However, with the increased incidence of FAS, there is a great variation in the clinical features of FAS.

DESIGN

Narrative review.

RESULTS

This review describes data from clinical and experimental studies, and in vitro models. Experimental studies have shown that alcohol has a direct toxic effect on the ectodermal and mesodermal cells of the developing embryo, particularly in the cells destined to give rise to dentofacial structures (i.e. cranial neural crest cells). Other effects, such as, abnormal pattern of cranial and mandibular growth and altered odontogenesis are described in detail. The exact mechanism by which alcohol induces its teratogenic effects remains still unknown. The possible mechanisms are outlined here, with an emphasis on the developing face and tooth. Possible future research directions and treatment strategies are also discussed.

CONCLUSION

Early identification of children affected by prenatal alcohol exposure leads to interventions, services, and improved outcomes. FAS can be prevented with the elimination of alcohol consumption during pregnancy. We need to provide education, target high-risk groups, and make this issue a high priority in terms of public health.

Hypodontia Patterns and Variations in Craniofacial Morphology in Japanese Orthodontic Patients

Objective: The purpose of this study was to explore the association of hypodontia patterns and variations in craniofacial morphology in Japanese orthodontic patients.

Materials and Methods: A total of 50 girls with hypodontia (the total group) were selected and categorized into anterior, posterior, and anterior-posterior groups according to the location of the congenitally missing teeth. By using the lateral cephalograms of each subject, 28 angular and 37 linear measurements were made. The cephalometric data were statistically analyzed and compared among the groups and with the Japanese cephalometric standards from 36 age-matched female subjects without hypodontia or malocclusion (the control group).

Results: Every hypodontia group showed shorter anterior and overall cranial base lengths, shorter maxillary length, greater retroclination and elongation of mandibular incisors, and a larger interincisal angle than the control group. The total and anterior-posterior groups especially exhibited a significantly more prognathic mandible, larger retroclination of maxillary incisors, and a more counterclockwise-rotated occlusal plane. Furthermore, these skeletal and dental deviations were more remarkable in the anterior-posterior group than in either the anterior or the posterior group. Anterior hypodontia exerted as much influence on craniofacial morphology as posterior hypodontia.

Conclusions: When orthodontic treatment is performed on patients with hypodontia, not only the number but also the distribution of missing teeth should be taken into consideration, though there was no significant difference in craniofacial morphology between anterior hypodontia and posterior hypodontia.

Functional interactions between Dlx2 and lymphoid enhancer factor regulate Msx2

Dlx2, Lymphoid Enhancer Factor (Lef-1) and Msx2 transcription factors are required for several developmental processes. To understand the control of gene expression by these factors, chromatin immunoprecipitation (ChIP) assays identified Msx2 as a downstream target of Dlx2 and Lef-1. Dlx2 activates the Msx2 promoter in several cell lines and binds DNA as a monomer and dimer. A Lef-1 beta-catenin-dependent isoform minimally activates the Msx2 promoter and a Lef-1 beta-catenin-independent isoform is inactive, however co-expression of Dlx2 and both Lef-1 isoforms synergistically activate the Msx2 promoter. Co-immunoprecipitation and protein pull-down experiments demonstrate Lef-1 physically interacts with Dlx2. Deletion analyses of the Lef-1 protein reveal specific regions required for synergism with Dlx2. The Lef-1 beta-catenin binding domain (betaDB) is not required for its interaction with Dlx2. Msx2 can auto-regulate its promoter and repress Dlx2 activation. Msx2 repression of Dlx2 activation is dose-specific and both bind a common DNA-binding element. These transcriptional mechanisms correlate with the temporal and spatial expression of these factors and may provide a mechanism for the control of several developmental processes. We demonstrate new transcriptional activities for Dlx2, Msx2 and Lef-1 through protein interactions and identification of downstream targets.

A novel missense mutation in MSX1 underlies autosomal recessive oligodontia with associated dental anomalies in Pakistani families

Tooth agenesis constitutes the most common anomaly of dental development in humans. In the majority of familial cases of hypodontia alone or in association with other anomalies, the mode of inheritance is autosomal dominant. In the present study, we have identified two distantly related consanguineous Pakistani kindreds with an autosomal recessive form of oligodontia with associated dental anomalies. Locus in this case has been mapped on chromosome 4p16.1-p16.3. The maximum two-point LOD score of 2.85 (theta=0.0) was obtained at markers D4S2925 and D4S2285. A maximum multipoint LOD score exceeding 4 was obtained at the same markers. Recombination events observed in affected individuals localized the disease locus between markers D4S412 and D4S2935, spanning a 9.24-cM region on chromosome 4p16.1-p16.3. Sequence analysis of candidate gene MSX1 revealed a novel recessive missense mutation resulting in substitution of alanine to threonine amino acid (p. A219T), located in the MSX1 homeodomain, which is important for DNA binding and protein-protein interaction. The mutation, p. A219T, is the first recessive mutation identified in MSX1.