Signaling Pathways Critical for Tooth Root Formation

Vascular Anomalies and Congenital Infiltrating Lipomatosis May Affect Dental Maturation and Development - a Case Control Study

OBJECTIVE

Vascular anomalies are often associated with hypertrophy and asymmetry of soft tissues and bony structures. The aim of this retrospective cross-sectional radiographic study was to evaluate dental maturation and development in patients with facial vascular anomalies and congenital infiltrating lipomatosis.

DESIGN

A sample of 342 patients with different vascular anomalies or congenital infiltrating lipomatosis involving the head and neck area was narrowed down to 31 patients with dental panoramic radiographs taken in the mixed dentition. A control group of 172 age-matched healthy subjects was used. Individual permanent teeth were given a maturation score from 1 to 12 and alveolar eruption stage according to Haavikko et al. 1970. The laterality of the anomaly was noted if applicable. Differences in dental development between affected and unaffected sides were recorded.

RESULTS

The study data included both syndromic and non-syndromic vascular anomalies as well as congenital infiltrating lipomatosis and segmental odontomaxillary dysplasia. Teeth on the side of the anomaly were more developed and the eruption of teeth was accelerated with canines, premolars and second molars being most affected. Interestingly all the patients with Sturge-Weber syndrome (n = 4) and infiltrating lipomatosis (n = 2) showed accelerated dental maturation of multiple permanent teeth on the side of the anomaly. Hypodontia, dental root resorption and macrodontia were also found.

CONCLUSIONS

Accelerated development and eruption of permanent teeth unilaterally in patients with vascular anomalies and congenital infiltrating lipomatosis may have a significant impact on the developing occlusion and should be thus followed by an orthodontist.

Prognostic risk factors for apical root resorption in orthodontic patients - Are the Kjær's morphologic characteristics of clinical relevance?

BACKGROUND

Patients undergoing orthodontic treatment (OT) face an increased risk of developing external apical root resorption (EARR). A prognostic risk assessment prior to OT can potentially be conducted through anatomical features in panoramic radiography. This retrospective study aimed to assess the significance of Kjær's morphological characteristics in analyzing the risk of EARR.

METHODS

Panoramic radiographs of 1,156 patients (624 females, 532 males) were retrospectively analyzed. Anamnestic and treatment-related data were extracted from patient records. The mean age at the start of OT was 12.8 ± 2.2 years (min. 6.4 years, max. 22.3 years) and at the end of OT 15.9 years (min. 8.5 years, max. 24.1 years). The mean treatment duration was 3.1 ± 1.6 years. Panoramic radiographs with a minimum of two per patient were examined for the presence of Kjær's characteristics. The degree of EARR was registered defining resorption in four degrees of severity. Bivariate analysis and multivariate Poisson regression were performed to assess the association between Kjær's characteristics and EARR patient- and tooth- related (α = 0.05).

RESULTS

In total, 72.8% of the patients showed EARR at the end of OT with lateral maxillary incisors most frequently affected. Short roots (p < 0.001) were significantly associated with EARR in patients. Tooth-related microdontia (#12, #22, lower second premolars), narrow crowns (#11, #21, lower incisors), short roots (upper incisors, lower first molars) and ectopia (#11, #21, #13), such as shorter distal roots of the mandibular first molar showed a significant association with EARR depending on severity degree. The type of orthodontic appliance (fixed: p < 0.001, fixed and removeable: p = 0.008), as well as treatment duration (p < 0.001) were also identified as risk factors for EARR.

CONCLUSIONS

Although the risk assessment for EARR development through panoramic radiography analysis is limited, predisposition appears to be present in specific dental characteristics and treatment-related factors.

Bone or Tooth dentin: The TGF-β signaling is the key

To investigate the cell linkage between tooth dentin and bones, we studied TGF-β roles during postnatal dentin development using TGF-β receptor 2 (Tgfβr2) cKO models and cell lineage tracing approaches. Micro-CT showed that the early Tgfβr2 cKO exhibit short roots and thin root dentin (n = 4; p<0.01), a switch from multilayer pre-odontoblasts/odontoblasts to a single-layer of bone-like cells with a significant loss of ~85% of dentinal tubules (n = 4; p<0.01), and a matrix shift from dentin to bone. Mechanistic studies revealed a statistically significant decrease in odontogenic markers, and a sharp increase in bone markers. The late Tgfβr2 cKO teeth displayed losses of odontoblast polarity, a significant reduction in crown dentin volume, and the onset of massive bone-like structures in the crown pulp with high expression levels of bone markers and low levels of dentin markers. We thus concluded that bones and tooth dentin are in the same evolutionary linkage in which TGF-β signaling defines the odontogenic fate of dental mesenchymal cells and odontoblasts. This finding also raises the possibility of switching the pulp odontogenic to the osteogenic feature of pulp cells via a local manipulation of gene programs in future treatment of tooth fractures.

Fibroblast growth factor signalling regulates the development of tooth root

Fibroblast growth factor (FGF) signalling plays a crucial role in the morphogenesis of multiple tissues including teeth. While the role of the signal has been studied in tooth crown development, little is known about root development. Of several FGF ligands involved in hard tissue formation, we suggest that FGF18 regulates the development of murine tooth roots. We implanted FGF18-soaked heparin beads into the lower first molar tooth buds at postnatal day 6 (P6), followed by transplantation under the kidney capsule. After 3 weeks, FGF18 significantly facilitated root elongation and periodontal tissue formation compared to the control. In situ hybridisation showed that Fgf18 transcripts were initially localised in the dental pulp along Hertwig's epithelial root sheath at P6 and P10 and subsequently in the dental follicle cells at P14. Fgf receptors were expressed in various dental tissues during these stages. In vitro analysis using the dental pulp stem cells revealed that FGF18 inhibited cell proliferation and decreased expression levels of osteogenic markers, Runx2, Alpl and Sp7. Consistently, after 1 week of kidney capsule transplantation, FGF18 application did not induce the expression of Sp7 and Bsp, but upregulated Periostin in the apical region of dental mesenchyme in the grafted molar. These findings suggest that FGF18 facilitates molar root development by regulating the calcification of periodontal tissues.

Genetic Variants in KCTD1 Are Associated with Isolated Dental Anomalies

KCTD1 plays crucial roles in regulating both the SHH and WNT/β-catenin signaling pathways, which are essential for tooth development. The objective of this study was to investigate if genetic variants in KCTD1 might also be associated with isolated dental anomalies. We clinically and radiographically investigated 362 patients affected with isolated dental anomalies. Whole exome sequencing identified two unrelated families with rare (p.Arg241Gln) or novel (p.Pro243Ser) variants in KCTD1. The variants segregated with the dental anomalies in all nine patients from the two families. Clinical findings of the patients included taurodontism, unseparated roots, long roots, tooth agenesis, a supernumerary tooth, torus palatinus, and torus mandibularis. The role of Kctd1 in root development is supported by our immunohistochemical study showing high expression of Kctd1 in Hertwig epithelial root sheath. The KCTD1 variants in our patients are the first variants found to be located in the C-terminal domain, which might disrupt protein-protein interactions and/or SUMOylation and subsequently result in aberrant WNT-SHH-BMP signaling and isolated dental anomalies. Functional studies on the p.Arg241Gln variant are consistent with an impact on β-catenin levels and canonical WNT signaling. This is the first report of the association of KCTD1 variants and isolated dental anomalies.

Morphogenesis of fungiform papillae in developing miniature pigs

Objective

Fungiform papillae contain taste buds and play a critical role in mastication and the gustatory system. In this study, we report a series of sequential observations of organogenesis of fungiform papillae in miniature pigs, as well as changes in the expression of BMP2, BMP4, Wnt5a, Sox2, and Notch1 signaling pathway components.

Design

In this study, we investigated the spatiotemporal expression patterns of BMP, Wnt, Sox2 and Notch in the fungiform papillae of miniature pigs at the bud stage (E40), cap stage (E50) and bell stage (E60). Pregnant miniature pigs were obtained, and the samples were processed for histological staining. Immunohistochemistry and real-time PCR were used to detect the mRNA and protein expression levels of BMP2, BMP4, Wnt5a, Sox2, and Notch1.

Results

At E40, fungiform papillae were present on the anterior two-thirds of the tongue in a specific array and pattern. The fungiform papillae were enlarged and basically developed at E50 and were largest at the earlier stage (E60). Most of the BMP2 was concentrated in the epithelial layer and the connective tissue core of the fungal papilloma and gradually accumulated from E40-E60. BMP-4 was weakly expressed in the fungiform papillae epithelia, but BMP-4-positive cells were also observed in the developing tongue muscle at E50 and E60. Wnt5a-positive cells were observed in the fungiform papillae epithelia and developing tongue muscle at all three time points. Sox2-positive cells were observed only in fungiform papillae epithelial cells, and Notch1-positive cells could not be detected.

Conclusions

This study provides primary data regarding the morphogenesis and expression of developmental signals in the fungiform papillae of miniature pigs, establishing a foundation for further research in both this model and humans.

The Biological Significance of AFF4: Promoting Transcription Elongation, Osteogenic Differentiation and Tumor Progression

As a member of the AF4/FMR2 (AFF) family, AFF4 is a scaffold protein in the superelongation complex (SEC). In this mini-view, we discuss the role of AFF4 as a transcription elongation factor that mediates HIV activation and replication and stem cell osteogenic differentiation. AFF4 also promotes the progression of head and neck squamous cell carcinoma, leukemia, breast cancer, bladder cancer and other malignant tumors. The biological function of AFF4 is largely achieved through SEC assembly, regulates SRY-box transcription factor 2 (SOX2), MYC, estrogen receptor alpha (ESR1), inhibitor of differentiation 1 (ID1), c-Jun and noncanonical nuclear factor-κB (NF-κB) transcription and combines with fusion in sarcoma (FUS), unique regulatory cyclins (CycT1), or mixed lineage leukemia (MLL). We explore the prospects of using AFF4 as a therapeutic in Acquired immunodeficiency syndrome (AIDS) and malignant tumors and its potential as a stemness regulator.

CDC42-mediated Wnt signaling facilitates odontogenic differentiation of DPCs during tooth root elongation

BACKGROUND

CDC42 is a member of Rho GTPase family, acting as a molecular switch to regulate cytoskeleton organization and junction maturation of epithelium in organ development. Tooth root pattern is a highly complicated and dynamic process that dependens on interaction of epithelium and mesenchyme. However, there is a lack of understanding of the role of CDC42 during tooth root elongation.

METHODS

The dynamic expression of CDC42 was traced during tooth development through immunofluorescence staining. Then we constructed a model of lentivirus or inhibitor mediated Cdc42 knockdown in Herwig's epithelial root sheath (HERS) cells and dental papilla cells (DPCs), respectively. Long-term influence of CDC42 abnormality was assessed via renal capsule transplantation and in situ injection of alveolar socket.

RESULTS

CDC42 displayed a dynamic spatiotemporal pattern, with abundant expression in HERS cells and apical DPCs in developing root. Lentivirus-mediated Cdc42 knockdown in HERS cells didn't disrupt cell junctions as well as epithelium-mesenchyme transition. However, inhibition of CDC42 in DPCs undermined cell proliferation, migration and odontogenic differentiation. Wnt/β-catenin signaling as the downstream target of CDC42 modulated DPCs' odontogenic differentiation. The transplantation and in situ injection experiments verified that loss of CDC42 impeded root extension via inhibiting the proliferation and differentiation of DPCs.

CONCLUSIONS

We innovatively revealed that CDC42 was responsible for guiding root elongation in a mesenchyme-specific manner. Furthermore, CDC42-mediated canonical Wnt signaling regulated odontogenic differentiation of DPCs during root formation.

Hertwig's epithelial root sheath cells show potential for periodontal complex regeneration

BACKGROUND

Although researchers have been exploring therapeutic strategies of treating serious periodontal tissue loss, including the application of stem cells, tissue regeneration of the periodontal complex involving cementum, periodontium, and alveolar bone has hardly been achieved. Aiming at tackling the problem of severely damaged periodontal complex, it is worth trying to make advantages of Hertwig's epithelial root sheath (HERS) cells to tissue regeneration mimicking the physiological developmental process with their ability of cementum, bone, and periodontium formation.

METHODS

HERS cells and dental follicle cells (DFCs) were acquired from Sprague Dawley rats' molar germs and identified by immunofluorescence. Alizarin red assay, ALP staining, AKP test, real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot were conducted to confirm the osteogenic potential, epithelial-mesenchymal transition (EMT) character of harvested HERS cells and epithelial-mesenchymal interaction (EMI) with DFCs. An animal model of periodontal defect was constructed to testify the tissue regeneration ability in vivo. Micro-CT and histological examinations were interpreted to unveil the tissue repair outcomes.

RESULTS

HERS cells expressed strong epithelial cell markers CK14 and E-cadherin. The in vitro experiments overall showed the concretely enhanced osteogenic differentiation ability in either HERS group or HERS+DFC group. Meanwhile, the in vivo conduction of rat mandibular periodontal repair experiment showed regenerative effectiveness of periodontal complex structure in both HERS and HERS+DFC group in situ, testified by Micro-CT and histological analysis.

CONCLUSIONS

HERS cells show potential for periodontal tissue regeneration which suggests the future possibilities of being considered as one of the cell choices for severely damaged periodontal tissue repair.

Effects of short-term orthodontic force application on the root at different developmental stages in rat maxillary molars

INTRODUCTION

The suitable timing and duration of orthodontic force to be applied to teeth with developing roots are unclear. We investigated the effects of short-term orthodontic force application on the roots at different root developmental stages in rats to predict the optimal timing for orthodontic treatment of teeth with developing roots.

METHODS

Light orthodontic force was applied on the maxillary first molars of rats from postnatal day (PN) 21 or PN28 for 3 days. After that, the force was released, and the roots were evaluated on PN35 to determine the root length, apical morphology, and cell proliferation of the maxillary first mesial roots using microcomputed tomography and histologic evaluation.

RESULTS

When a light orthodontic force was applied from PN21, the root length did not differ from that in age-matched controls. In addition, after the force was released, the roots attained the normal root-completing length and had a well-formed root apical morphology at PN35. Conversely, when the force was applied from PN28, the roots showed apical abnormalities characterized by deformed dentin and disorganized arrangement of odontoblasts, reduced apical cell proliferation, and significantly shorter length than those in the age-matched controls at PN31. The shortened root and disturbed apical integrity could not be rescued by releasing the orthodontic force at PN35.

CONCLUSIONS

Short-term orthodontic force at the late and slow root developmental stage results in a shortened root and a defect in the root apex with reduced cell proliferation. Our findings support that orthodontic force for a limited duration during the active and rapid root developmental stage is more favorable than during the late and slow stage.

Primary failure of tooth eruption: Etiology and management

Primary failure of eruption (PFE) is a rare disorder defined as incomplete tooth eruption despite the presence of a clear eruption pathway. PFE is known to be caused by rare variants in the parathyroid hormone 1 receptor gene (PTH1R). Although several PTH1R variants have been reported, the etiology of PFE remains unclear. However, important studies that help elucidate the pathology of PFE have recently been published. The purpose of this review is to summarize current treatment options, clinical symptoms or phenotypes for diagnosis, genetic information including solid evidence in mouse disease models and disease-specific induced pluripotent stem cells, thus approaching the etiology of PFE from the perspective of the latest research.

Diverse stem cells for periodontal tissue formation and regeneration

The periodontium is comprised of multiple units of mineralized and nonmineralized tissues including the cementum on the root surface, the alveolar bone, periodontal ligament (PDL), and the gingiva. PDL contains a variety of cell populations including mesenchymal stem/progenitor cells (MSCs) termed PDLSCs, which contribute to periodontal regeneration. Recent studies utilizing mouse genetic models shed light on the identities of these mesenchymal progenitors in their native environment, particularly regarding how they contribute to homeostasis and repair of the periodontium. The current concept is that mesenchymal progenitors in the PDL are localized to the perivascular niche. Single-cell RNA sequencing (scRNA-seq) analyses reveal heterogeneity and cell-type specific markers of cells in the periodontium, as well as their developmental relationship with precursor cells in the dental follicle. The characteristics of PDLSCs and their diversity in vivo are now beginning to be unraveled thanks to insights from mouse genetic models and scRNA-seq analyses, which aid to uncover the fundamental properties of stem cells in the human PDL. The new knowledge will be highly important for developing more effective stem cell-based regenerative therapies to repair periodontal tissues in the future.

Assessing the prevalence of S-shaped root canal and associated genes in humans

BACKGROUND

Multiple signaling molecules have been shown to play crucial roles in dental root development. Therefore, we aimed to investigate the prevalence of S-shaped roots and also to investigate, if single nucleotide polymorphisms (SNPs) in BMP2, BMP4 and SMAD6 are associated with this phenotype in humans.

METHODS

This is a cross-sectional phenotype-genotype association study that used radiographs to determine the phenotypes and DNA to investigate SNPs in candidate genes. During the radiographic exam, teeth presenting root canal(s) doubly curved were considered S-shaped roots. SNPs in BMP2 (rs1005464 and rs235768), BMP4 (rs17563) and SMAD6 (rs2119261 and rs3934908) were blindly genotyped by real-time PCR using TaqMan assay. The relative and absolute frequency of S-shaped roots were calculated. Chi-square test was used to compare the genotype distributions between control and S-shaped groups.

RESULTS

Among the 578 subjects, 61 (10.6%) presented at least one tooth with an S-shaped root. The most commonly affected type of tooth was the premolar. rs1005464 in BMP2 was statistically associated with an S-shaped root (p=0.036). rs235768 in BMP2 was associated with an S-shaped root also in mandibular teeth (p=0.017). A statistical significance was observed for the rs3934908 in SMAD6 (p=0.049) for S-shaped root in the mandible. In the analysis stratified according to the type of tooth, rs235768 in BMP2 was associated with S-shaped roots in premolars (p=0.029).

CONCLUSION

The prevalence of S-shaped roots is 10.6% in permanent teeth. SNPs in BMP2 and SMAD6 could be involved in a higher chance to present S-shaped roots.

Novel Dental Anomaly-associated Mutations in WNT10A Protein Binding Sites

OBJECTIVE

WNT/β-catenin signaling is initiated by binding of a WNT protein to a Frizzled (FZD) receptor and a co-receptor, low-density lipoprotein (LDL) receptor-related protein 5 or 6 (LRP5/6). The objective of this study was to find the genetic variants responsible for dental anomalies found in 4 families.

METHODS

Clinical and radiographic examination and whole exome sequencing were performed on 5 patients affected with dental anomalies and the mutant proteins modeled.

RESULTS

Five patients were heterozygous for the WNT10A variants, including c.877C>T; p.Arg293Cys, c.874A>G; p.Ser292Gly, c.1042C>T; p.Arg348Cys, and c.1039G>T; p.347GluX. The p.Arg293Cys and p.Ser292Gly mutations are located in the WNT10A N-terminal domain region with binding sites for FZD receptor, porcupine, WNTLESS, and extracellular binding proteins, so they are likely to have adverse effects on binding these proteins. The p.Arg348Cys mutation, which is located in the binding site of LRP5/6 co-receptors, is postulated to result in impaired binding to these co-receptors. The nonsense mutation p.347GluX is predicted to result in the truncation of most of the C-terminal domain, which is likely to disrupt the binding of WNT10A to WNTLESS, the membrane protein that binds lipid-acylated WNT proteins to carry them from the endoplasmic reticulum to the cell surface and FZD.

CONCLUSIONS

Four novel mutations in WNT10A were identified in patients with isolated tooth agenesis. The mutations in the N-terminal domain and the interface between the N- and C-terminal domains of WNT10A in our patients are likely to disrupt its binding with FZD, LRP5/6, and various other proteins involved in WNT10A processing and transport, impair WNT and SHH signaling, and subsequently result in tooth agenesis, microdontia, and root maldevelopment.

Expanding genotypic and phenotypic spectrums of LTBP3 variants in dental anomalies and short stature syndrome

Mutations in LTBP3 are associated with Dental Anomalies and Short Stature syndrome (DASS; MIM 601216), which is characterized by hypoplastic type amelogenesis imperfecta, hypodontia, underdeveloped maxilla, short stature, brachyolmia, aneurysm and dissection of the thoracic aorta. Here we report a novel (p.Arg545ProfsTer22) and a recurrent (c.3107-2A > G) LTBP3 variants, in a Turkish family affected with DASS. The proband, who carried compound heterozygous variant c.3107-2A > G, p.Arg545ProfsTer22, was most severely affected with DASS. The proband's father, who carried the heterozygous variant c.3107-2A > G had short stature and prognathic mandible. The mother and brother of the proband carried the heterozygous variant p.Arg545ProfsTer22, but only the mother showed any DASS characteristics. The c.3107-2A > G and the p.Arg545ProfsTer22 variants are expected to result in abnormal LTPB3 protein, failure of TGFβ-LAP-LTBP3 complex formation, and subsequent disruption of TGFβ secretion and activation. This is the first report of heterozygous carriers of LTBP3 variants showing phenotypes. The new findings of DASS found in this family include taurodontism, single-rooted molars, abnormal dentin, calcified dental pulp blood vessels, prognathic mandible, failure of mandibular tooth eruption, interatrial septal aneurysm, secundum atrial septal defect, tricuspid valve prolapse, and a recurrent glenohumeral joint dislocation.

Extracellular vesicles delivering nuclear factor I/C for hard tissue engineering: Treatment of apical periodontitis and dentin regeneration

Apical periodontitis (AP) causes arrest of tooth root development, which is associated with impaired odontoblastic differentiation of stem cells from apical papilla (SCAPs), but the underlying mechanism remains unclear. Here, we investigated roles of extracellular vesicle (EV) in AP and odontoblastic differentiation of SCAPs, moreover, a novel nuclear factor I/C (NFIC)-encapsulated EV was developed to promote dentin regeneration. We detected a higher expression of EV marker CD63 in inflamed apical papilla, and found that EVs from LPS-stimulated dental pulp cells suppressed odontoblastic differentiation of SCAPs through downregulating NFIC. Furthermore, we successfully constructed the NFIC-encapsulated EV by overexpressing NFIC in HEK293FT cells, which could upregulate cellular NFIC level in SCAPs, promoting the proliferation and migration of SCAPs, as well as dentinogenesis both in vitro and in vivo. Collectively, based on pathological roles of EV in AP, our study provides a novel strategy for dentin regeneration by exploiting EV to deliver NFIC.

A Review of In Vivo and Clinical Studies Applying Scaffolds and Cell Sheet Technology for Periodontal Ligament Regeneration

Different approaches to develop engineered scaffolds for periodontal tissues regeneration have been proposed. In this review, innovations in stem cell technology and scaffolds engineering focused primarily on Periodontal Ligament (PDL) regeneration are discussed and analyzed based on results from pre-clinical in vivo studies and clinical trials. Most of those developments include the use of polymeric materials with different patterning and surface nanotopography and printing of complex and sophisticated multiphasic composite scaffolds with different compartments to accomodate for the different periodontal tissues' architecture. Despite the increased effort in producing these scaffolds and their undoubtable efficiency to guide and support tissue regeneration, appropriate source of cells is also needed to provide new tissue formation and various biological and mechanochemical cues from the Extraccellular Matrix (ECM) to provide biophysical stimuli for cell growth and differentiation. Cell sheet engineering is a novel promising technique that allows obtaining cells in a sheet format while preserving ECM components. The right combination of those factors has not been discovered yet and efforts are still needed to ameliorate regenerative outcomes towards the functional organisation of the developed tissues.

Nuclear factor I-C disrupts cellular homeostasis between autophagy and apoptosis via miR-200b-Ambra1 in neural tube defects

Impaired autophagy and excessive apoptosis disrupt cellular homeostasis and contribute to neural tube defects (NTDs), which are a group of fatal and disabling birth defects caused by the failure of neural tube closure during early embryonic development. However, the regulatory mechanisms underlying NTDs and outcomes remain elusive. Here, we report the role of the transcription factor nuclear factor I-C (NFIC) in maintaining cellular homeostasis in NTDs. We demonstrated that abnormally elevated levels of NFIC in a mouse model of NTDs can interact with the miR-200b promoter, leading to the activation of the transcription of miR-200b, which plays a critical role in NTD formation, as reported in our previous study. Furthermore, miR-200b represses autophagy and triggers apoptosis by directly targeting the autophagy-related gene Ambra1 (Autophagy/Beclin1 regulator 1). Notably, miR-200b inhibitors mitigate the unexpected effects of NFIC on autophagy and apoptosis. Collectively, these results indicate that the NFIC-miR-200b-Ambra1 axis, which integrates transcription- and epigenome-regulated miRNAs and an autophagy regulator, disrupts cellular homeostasis during the closure of the neural tube, and may provide new insight into NTD pathogenesis.

Monitoring of canonical BMP and Wnt activities during postnatal stages of mouse first molar root formation

Objective

This study aimed to explore the precise temporospatial distributions of bone morphogenetic protein (BMP) and Wnt signaling pathways during postnatal development of mammalian tooth roots after the termination of crown morphogenesis.

Methodology

A total of two transgenic mouse lines, BRE-LacZ mice and BAT-gal mice, were undertaken. The mice were sacrificed on every postnatal (PN) day from PN 3d up to PN 21d. Then, the first lower molars were extracted, and the dissected mandibles were stained with 5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside (X-gal) and fixed. Serial sections at 10 µm were prepared after decalcification, dehydration, and embedding in paraffin.

Results

We observed BMP/Smads and Wnt/β-catenin signaling activities in the dental sac, dental pulp, and apical papilla with a certain degree of variation. The position of activation of the BMP/Smad signaling pathway was located more coronally in the early stage, which then gradually expanded as root elongation proceeded and was associated with blood vessels in the pulp and developing complex apical tissues in the later stage. However, Wnt/β-catenin signaling was highly concentrated in the mesenchyme below the cusps in the early stage, gradually expanded to regions around the root in the transition/root stage, and then disappeared entirely in the later stage.

Conclusions

These results further confirmed the participation of both BMP and Wnt canonical signaling pathways in tooth root development, as well as formed the basis for future studies on how precisely integrated signaling pathways regulate root morphogenesis and regeneration.

The Role of Wnt Signaling in Postnatal Tooth Root Development

Appropriate tooth root formation and tooth eruption are critical for achieving and maintaining good oral health and quality of life. Tooth eruption is the process through which teeth emerge from their intraosseous position to their functional position in the oral cavity. This temporospatial process occurs simultaneously with tooth root formation through a cascade of interactions between the epithelial and adjoining mesenchymal cells. Here, we will review the role of the Wnt system in postnatal tooth root development. This signaling pathway orchestrates the process of tooth root formation and tooth eruption in conjunction with several other major signaling pathways. The Wnt signaling pathway is comprised of the canonical, or Wnt/β-catenin, and the non-Canonical signaling pathway. The expression of multiple Wnt ligands and their downstream transcription factors including β-catenin is found in the cells in the epithelia and mesenchyme starting from the initiation stage of tooth development. The inhibition of canonical Wnt signaling in an early stage arrests odontogenesis. Wnt transcription factors continue to be present in dental follicle cells, the progenitor cells responsible for differentiation into cells constituting the tooth root and the periodontal tissue apparatus. This expression occurs concurrently with osteogenesis and cementogenesis. The conditional ablation of β-catenin in osteoblast and odontoblast causes the malformation of the root dentin and cementum. On the contrary, the overexpression of β-catenin led to shorter molar roots with thin and hypo-mineralized dentin, along with the failure of tooth eruption. Therefore, the proper expression of Wnt signaling during dental development is crucial for regulating the proliferation, differentiation, as well as epithelial-mesenchymal interaction essential for tooth root formation and tooth eruption.

Supernumerary roots in maxillary deciduous canines: A rare anomaly with a long history

OBJECTIVE

To describe two maxillary deciduous bi-rooted canines, one archeological and one modern, and examine the possible etiology of this condition.

DESIGN

Two cases of bi-rooted canines were described and compared to published examples. Both specimens were radiographed and measured and compared to one-rooted samples. The archeological specimen was scanned using CBCT to facilitate detailed examination of the deciduous teeth. The extracted modern tooth was embedded in epoxy resin and two coronal sections were cut, one through the crown and one through the roots and examined with a light microscope.

RESULTS

The bi-rooted canines were larger than the control samples. They showed none of the features commonly associated with gemination. The radiographs and scans showed that the canine roots in the archeological case diverged mesio-distally like the buccal roots in the adjacent first deciduous molar. In the clinical case, the root trunk was elongated mesio-distally and the furcation was located very close to the apex with a C-shaped root canal.

CONCLUSIONS

Both variants of the condition described above are rare in deciduous canines. They do not seem to be associated with fusion or gemination. However, as the teeth are relatively flattened bucco-lingually and we tentatively propose that this form results from spatial constraints during the early stages of crown development that have contributed to the development of additional roots. The megadont dimension of the recent bi-rooted deciduous canine may affect root development and the necessity of two mesio-distally located roots for anchorage in the maxilla.

The critical role of nuclear factor I-C in tooth development

OBJECTIVES

Nuclear factor I-C (NFIC) plays a critical role in regulating epithelial-mesenchymal crosstalk during tooth development. However, it remains largely unknown about how NFIC functions in dentin and enamel formation. In the present review, we aim to summarize the most recent discoveries in the field and gain a better understanding of the roles NFIC performs during tooth formation.

SUBJECTS AND METHODS

Nfic^-/- mice exhibit human dentin dysplasia type I (DDI)-like phenotypes signified by enlarged pulp chambers, the presence of short-root anomaly, and failure of odontoblast differentiation. Although loss of NFIC has little effect on molar crown morphology, researchers have detected aberrant microstructures of enamel in the incisors. Recently, accumulating evidence has further uncovered the novel function of NFIC in the process of enamel and dentin formation.

RESULTS

During epithelial-mesenchyme crosstalk, the expression of NFIC is under the control of SHH-PTCH-SMO-GLI1 pathway. NFIC is closely involved in odontoblast lineage cells proliferation and differentiation, and the maintenance of NFIC protein level in cytoplasm is negatively regulated by TGF-β signaling pathway. In addition, NFIC has mild effect on ameloblast differentiation, enamel mineralization and cementum formation.

CONCLUSIONS

NFIC plays an important role in tooth development and is required for the formation of dentin, enamel as well as cementum.

Signaling Modulation by miRNA-221-3p During Tooth Morphogenesis in Mice

miRNAs are conserved short non-coding RNAs that play a role in the modulation of various biological pathways during tissue and organ morphogenesis. In this study, the function of miRNA-221-3p in tooth development, through its loss or gain in function was evaluated. A variety of techniques were utilized to evaluate detailed functional roles of miRNA-221-3p during odontogenesis, including in vitro tooth cultivation, renal capsule transplantation, in situ hybridization, real-time PCR, and immunohistochemistry. Two-day in vitro tooth cultivation at E13 identified altered cellular events, including cellular proliferation, apoptosis, adhesion, and cytoskeletal arrangement, with the loss and gain of miRNA-221-3p. qPCR analysis revealed alterations in gene expression of tooth-related signaling molecules, including β-catenin, Bmp2, Bmp4, Fgf4, Ptch1, and Shh, when inhibited with miRNA-221-3p and mimic. Also, the inhibition of miRNA-221-3p demonstrated increased mesenchymal localizations of pSMAD1/5/8, alongside decreased expression patterns of Shh and Fgf4 within inner enamel epithelium (IEE) in E13 + 2 days in vitro cultivated teeth. Moreover, 1-week renal transplantation of in vitro cultivated teeth had smaller tooth size with reduced enamel and dentin matrices, along with increased cellular proliferation and Shh expression along the Hertwig epithelial root sheath (HERS), within the inhibitor group. Similarly, in 3-week renal calcified teeth, the overexpression of miRNA-221-3p did not affect tooth phenotype, while the loss of function resulted in long and slender teeth with short mesiodistal length. This study provides evidence that a suitable level of miRNA-221-3p is required for the modulation of major signaling pathways, including Wnt, Bmp, and Shh, during tooth morphogenesis.

Tooth Repair and Regeneration: Potential of Dental Stem Cells

Tooth defects are an extremely common health condition that affects millions of individuals. Currently used dental repair treatments include fillings for caries, endodontic treatment for pulp necrosis, and dental implants to replace missing teeth, all of which rely on the use of synthetic materials. By contrast, the fields of tissue engineering and regenerative medicine and dentistry (TERMD) use biologically based therapeutic strategies for vital tissue regeneration, and thus have the potential to regenerate living tissues. Methods to create bioengineered replacement teeth benefit from a detailed understanding of the molecular signaling networks regulating natural tooth development. We discuss how key signaling pathways regulating natural tooth development are being exploited for applications in TERMD approaches for vital tooth regeneration.

A Biphasic Feature of Gli1+-Mesenchymal Progenitors during Cementogenesis That Is Positively Controlled by Wnt/β-Catenin Signaling

Cementum, a specialized bony layer covering an entire molar root surface, anchors teeth into alveolar bone. Gli1, a key transcriptional activator in Hedgehog signaling, has been identified as a mesenchymal progenitor cell marker in various tissues, including the periodontal ligament (PDL). To address the mechanisms by which Gli1⁺ progenitor cells contribute to cementogenesis, we used the Gli1^lacZ/+ knock-in line to mark Gli1⁺ progenitors and the Gli1^CreERT2/+; R26R^tdTomato/+ line (named Gli1^Lin) to trace Gli1 progeny cells during cementogenesis. Our data unexpectedly displayed a biphasic feature of Gli1⁺ PDL progenitor cells and cementum growth: a negative relationship between Gli1⁺ progenitor cell number and cementogenesis but a positive correlation between Gli1-derived acellular and cellular cementoblast cell number and cementum growth. DTA-ablation of Gli1^Lin cells led to a cementum hypoplasia, including a significant reduction of both acellular and cellular cementoblast cells. Gain-of-function studies (by constitutive stabilization of β-catenin in Gli1^Lin cells) revealed a cementum hyperplasia. A loss of function (by conditional deletion of β-catenin in Gli1⁺ cells) resulted in a reduction of postnatal cementum growth. Together, our studies support a vital role of Gli1⁺ progenitor cells in contribution to both types of cementum, in which canonical Wnt/β-catenin signaling positively regulates the differentiation of Gli1⁺ progenitors to cementoblasts during cementogenesis.

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.

USP34 regulates tooth root morphogenesis by stabilizing NFIC

Tooth root morphogenesis involves two biological processes, root elongation and dentinogenesis, which are guaranteed by downgrowth of Hertwig's epithelial root sheath (HERS) and normal odontoblast differentiation. Ubiquitin-dependent protein degradation has been reported to precisely regulate various physiological processes, while its role in tooth development is still elusive. Here we show ubiquitin-specific protease 34 (USP34) plays a pivotal role in root formation. Deletion of Usp34 in dental mesenchymal cells leads to short root anomaly, characterized by truncated roots and thin root dentin. The USP34-deficient dental pulp cells (DPCs) exhibit decreased odontogenic differentiation with downregulation of nuclear factor I/C (NFIC). Overexpression of NFIC partially restores the impaired odontogenic potential of DPCs. These findings indicate that USP34-dependent deubiquitination is critical for root morphogenesis by stabilizing NFIC.

The human EDAR 370V/A polymorphism affects tooth root morphology potentially through the modification of a reaction-diffusion system

Morphological variations in human teeth have long been recognized and, in particular, the spatial and temporal distribution of two patterns of dental features in Asia, i.e., Sinodonty and Sundadonty, have contributed to our understanding of the human migration history. However, the molecular mechanisms underlying such dental variations have not yet been completely elucidated. Recent studies have clarified that a nonsynonymous variant in the ectodysplasin A receptor gene (EDAR 370V/A; rs3827760) contributes to crown traits related to Sinodonty. In this study, we examined the association between the EDAR polymorphism and tooth root traits by using computed tomography images and identified that the effects of the EDAR variant on the number and shape of roots differed depending on the tooth type. In addition, to better understand tooth root morphogenesis, a computational analysis for patterns of tooth roots was performed, assuming a reaction-diffusion system. The computational study suggested that the complicated effects of the EDAR polymorphism could be explained when it is considered that EDAR modifies the syntheses of multiple related molecules working in the reaction-diffusion dynamics. In this study, we shed light on the molecular mechanisms of tooth root morphogenesis, which are less understood in comparison to those of tooth crown morphogenesis.

METTL3-Mediated m6 A mRNA Methylation Modulates Tooth Root Formation by Affecting NFIC Translation

N6-methyladenosine (m⁶ A), as a eukaryotic mRNA modification catalyzed by methyltransferase METTL3, is involved in various processes of development or diseases via regulating RNA metabolism. However, the effect of METTL3-mediated m⁶ A modification in tooth development has remained elusive. Here we show that METTL3 is prevalently expressed in odontoblasts, dental pulp cells, dental follicle cells, and epithelial cells in Hertwig's epithelial root sheath during tooth root formation. Depletion of METTL3 in human dental pulp cells (hDPCs) impairs proliferation, migration, and odontogenic differentiation. Furthermore, conditional knockout of Mettl3 in Osterix-expressing cells leads to short molar roots and thinner root dentin featured by decreased secretion of pre-dentin matrix and formation of the odontoblast process. Mechanistically, loss of METTL3 cripples the translational efficiency of the key root-forming regulator nuclear factor I-C (NFIC). The odontogenic capacity of METTL3-silenced hDPCs is partially rescued via overexpressing NFIC. Our findings suggest that m⁶ A methyltransferase METTL3 is crucial for tooth root development, uncovering a novel epigenetic mechanism in tooth root formation. © 2020 American Society for Bone and Mineral Research (ASBMR).

The identification of critical time windows of postnatal root elongation in response to Wnt/β-catenin signaling

OBJECTIVES

In this study, we attempted to define the precise window of time for molar root elongation using a gain-of-function mutation of β-catenin model.

MATERIALS AND METHODS

Both the control and constitutively activated β-catenin (CA-β-cat) mice received a one-time tamoxifen administration (for activation of β-catenin at newborn, postnatal day 3, or 5, or 7, or 9) and were harvested at the same stage of P21. Multiple approaches were used to define the window of time of postnatal tooth root formation.

RESULTS

In the early activation groups (tamoxifen induction at newborn, or P3 or P5), there was a lack of molar root elongation in the CA-β-cat mice. When induced at P7, the root length was slightly reduced at P21. However, the root length was essentially the same as that in the control when β-cat activated at P9. This study indicates that root elongation occurs in a narrow time of window, which is highly sensitive to a change of β-catenin levels. Molecular studies showed a drastic decrease in the levels of nuclear factor I-C (NFIC) and osterix (OSX), plus sharp reductions of odontoblast differentiation markers, including Nestin, dentin sialoprotein (DSP), and dentin matrix protein 1 (DMP1) at both mRNA and protein levels.

CONCLUSIONS

Murine molar root elongation is precisely regulated by the Wnt/β-catenin signaling within a narrow window of time (newborn to day 5).

In vitro tooth-shaped scaffold construction by mimicking late bell stage

Neogenesis of osseous and ligamentous interfacial structures is essential for the regeneration of large oral or craniofacial defects. However, current treatment strategies are inadequate in renewing supporting tissues of teeth after trauma, chronic infections or surgical resection. Combined use of 3D scaffolds with stem cells became a promising treatment option for these injuries. Matching different scaffolding materials with different tissues can induce the correct cytokines and the differentiation of cells corresponding to that particular tissue. In this study, a hydroxyapatite (HA) based scaffold was used together with human adipose stem cells (hASCs), human bone marrow stem cells (hBMSCs) and gingival epithelial cells to mimic human tooth dentin-pulp-enamel tissue complexes and model an immature tooth at the late bell stage in vitro. Characteristics of the scaffold were determined via SEM, FTIR, pore size and density measurements. Changes in gene expression, protein secretions and tissue histology resulting from cross-interactions of different dental tissues grown in the system were shown. Classical tooth tissues such as cementum, pulp and bone like tissues were formed within the scaffold. Our study suggests that a HA-based scaffold with different cell lineages can successfully mimic early stages of tooth development and can be a valuable tool for hard tissue engineering.

[Role of bone morphogenetic protein 1/tolloid proteinase family in the development of teeth and bone]

The bone morphogenetic protein (BMP) 1/tolloid (TLD) proteinase family is a group of important metalloproteinases, which play key roles in the growth and development of tissues and organs via regulating the biosynthetic processing of the extracellular matrix. Clinical reports have revealed that mutations in the genes encoding BMP1/TLD proteinases lead to dentinogenesis imperfecta type Ⅰ, accompanied with osteogenesis imperfecta. Therefore, this proteinase family is essential for the development of hard tissues. In this study, we review the research progress in the function and mechanism of the BMP1/TLD proteinase family in the development of teeth and bone.

Berberine mediates root remodeling in an immature tooth with apical periodontitis by regulating stem cells from apical papilla differentiation

Once pulp necrosis or apical periodontitis occurs on immature teeth, the weak root and open root apex are challenging to clinicians. Berberine (BBR) is a potential medicine for bone disorders, therefore, we proposed to apply BBR in root canals to enhance root repair in immature teeth. An in vivo model of immature teeth with apical periodontitis was established in rats, and root canals were filled with BBR, calcium hydroxide or sterilized saline for 3 weeks. The shape of the roots was analyzed by micro-computed tomography and histological staining. In vitro, BBR was introduced into stem cells from apical papilla (SCAPs). Osteogenic differentiation of stem cells from apical papilla was investigated by alkaline phosphatase activity, mineralization ability, and gene expression of osteogenic makers. The signaling pathway, which regulated the osteogenesis of SCAPs was evaluated by quantitative real time PCR, Western blot analysis, and immunofluorescence. In rats treated with BBR, more tissue was formed, with longer roots, thicker root walls, and smaller apex diameters. In addition, we found that BBR promoted SCAPs osteogenesis in a time-dependent and concentration-dependent manner. BBR induced the expression of β-catenin and enhanced β-catenin entering into the nucleus, to up-regulate more runt-related nuclear factor 2 downstream. BBR enhanced root repair in immature teeth with apical periodontitis by activating the canonical Wnt/β-catenin pathway in SCAPs.

Combined in silico analysis identified a putative tooth root formation-related gene, Chd3, which regulates DNA synthesis in HERS01a cells

There exists a close connection between changes occurring in the teeth and those occurring in the jaw during the evolutionary process. In mammals, the roots of teeth are supported, along with periodontal ligaments and alveolar bones by a unique structure termed the gomphosis. In the present study, we performed combined in silico analysis using the information obtained from various DNA microarrays and identified 19 putative tooth root formation-related genes. Furthermore, quantitative PCR was performed on the candidate genes, Chd3 was confirmed as having sufficient expression levels in the early stage of tooth root formation and increased gene expression toward the middle stage. A high degree of Chd3 gene expression was observed in secretory ameloblasts and Hertwig's epithelial root sheath (HERS), but low expression was observed in developing odontoblasts and stellate reticulum. The CHD3 foci were observed in the nucleus of the HERS01a cells. In addition, knockdown experiments using SiChd3 suggested the involvement of Chd3 in the suppression of DNA synthesis. These results suggested that Chd3 plays a role in DNA synthesis in HERS cells for promoting tooth root development.

Maxillary incisor root morphology in patients with nonsyndromic tooth agenesis: A controlled cross-sectional pilot study

INTRODUCTION

This study aimed to investigate the association between root morphology of maxillary incisors and nonsyndromic tooth agenesis in patients compared with a control group without agenesis.

METHODS

This controlled cross-sectional pilot study (1:4) was performed with a random sample of 335 records from Brazilian applicants for orthodontic treatment, paired by sex and age. Panoramic and periapical radiographs were analyzed to diagnose tooth agenesis and to assess root morphology. The agenesis group (n = 67) included patients with nonsyndromic tooth agenesis, and the control group (n = 268) included patients without tooth agenesis. The statistical analysis included the Student t test and z test, conditional logistic regression, and odds ratio estimates.

RESULTS

Occurrence of root morphological changes was significantly higher among patients with agenesis (P <0.05). Significant morphological changes (short, blunt, apically bent, and pipette-shaped roots) were found in the roots of remaining teeth when comparing agenesis and control groups (P <0.05). Patients with agenesis were more likely to show root morphological changes (odds ratio, 74.23; 95% confidence interval, 16.93-325.46; P <0.001).

CONCLUSION

Patients with agenesis are more likely to present root morphological changes, which should be considered to minimize problems during orthodontic treatments.

The Role of Discoidin Domain Receptor 2 in Tooth Development

Collagen signaling is critical for proper bone and tooth formation. Discoidin domain receptor 2 (DDR2) is a collagen-activated tyrosine kinase receptor shown to be essential for skeletal development. Patients with loss of function mutations in DDR2 develop spondylo-meta-epiphyseal dysplasia (SMED), a rare, autosomal recessive disorder characterized by short stature, short limbs, and craniofacial anomalies. A similar phenotype was observed in Ddr2-deficient mice, which exhibit dwarfism and defective bone formation in the axial, appendicular, and cranial skeletons. However, it is not known if Ddr2 has a role in tooth formation. We first defined the expression pattern of Ddr2 during tooth formation using Ddr2-LacZ knock-in mice. Ddr2 expression was detected in the dental follicle/sac and dental papilla mesenchyme of developing teeth and in odontoblasts and the periodontal ligament (PDL) of adults. No LacZ staining was detected in wild-type littermates. This Ddr2 expression pattern suggests a potential role in the tooth and surrounding periodontium. To uncover the function of Ddr2, we used Ddr2^slie/slie mice, which contain a spontaneous 150-kb deletion in the Ddr2 locus to produce an effective null. In comparison with wild-type littermates, Ddr2^slie/slie mice displayed disproportional tooth size (decreased root/crown ratio), delayed tooth root development, widened PDL space, and interradicular alveolar bone defects. Ddr2^slie/slie mice also had abnormal collagen content associated with upregulation of periostin levels within the PDL. The delayed root formation and periodontal abnormalities may be related to defects in RUNX2-dependent differentiation of odontoblasts and osteoblasts; RUNX2-S319-P was reduced in PDLs from Ddr2^slie/slie mice, and deletion of Ddr2 in primary cell cultures from dental pulp and PDL inhibited differentiation of cells to odontoblasts or osteoblasts, respectively. Together, our studies demonstrate odontoblast- and PDL-specific expression of Ddr2 in mature and immature teeth, as well as indicate that DDR2 signaling is important for normal tooth formation and maintenance of the surrounding periodontium.

Mesenchymal Progenitor Regulation of Tooth Eruption: A View from PTHrP

Tooth eruption is a unique biological process by which highly mineralized tissues emerge into the outer world, and it occurs concomitantly with tooth root formation. These 2 processes have been considered independent phenomena; however, recent studies support the theory that they are indeed intertwined. Dental mesenchymal progenitor cells in the dental follicle lie at the heart of the coupling of these 2 processes, providing a source for diverse mesenchymal cells that support formation of the highly functional tooth root and the periodontal attachment apparatus, while facilitating formation of osteoclasts. These cells are regulated by autocrine signaling by parathyroid hormone-related protein (PTHrP) and its parathyroid hormone/PTHrP receptor PPR. This PTHrP-PPR signaling appears to crosstalk with other signaling pathways and regulates proper cell fates of mesenchymal progenitor cell populations. Disruption of this autocrine PTHrP-PPR signaling in these cells leads to defective formation of the periodontal attachment apparatus, tooth root malformation, and failure of tooth eruption in molars, which essentially recapitulate primary failure of eruption in humans, a rare genetic disorder exclusively affecting tooth eruption. Diversity and distinct functionality of these mesenchymal progenitor cell populations that regulate tooth eruption and tooth root formation are beginning to be unraveled.

Axin2+-Mesenchymal PDL Cells, Instead of K14+ Epithelial Cells, Play a Key Role in Rapid Cementum Growth

To date, attempts to regenerate functional periodontal tissues (including cementum) are largely unsuccessful due to a lack of full understanding about the cellular origin (epithelial or mesenchymal cells) essential for root cementum growth. To address this issue, we first identified a rapid cementum growth window from the ages of postnatal day 28 (P28) to P56. Next, we showed that expression patterns of Axin2 and β-catenin within cementum-forming periodontal ligament (PDL) cells are negatively associated with rapid cementum growth. Furthermore, cell lineage tracing studies revealed that the Axin2+-mesenchymal PDL cells and their progeny rapidly expand and directly contribute to postnatal acellular and cellular cementum growth. In contrast, the number of K14+ epithelial cells, which were initially active at early stages of development, was reduced during rapid cementum formation from P28 to P56. The in vivo cell ablation of these Axin2+ cells using Axin2CreERT2/+; R26RDTA/+ mice led to severe cementum hypoplasia, whereas constitutive activation of β-catenin in the Axin2+ cells resulted in an acceleration in cellular cementogenesis plus a transition from acellular cementum to cellular cementum. Thus, we conclude that Axin2+-mesenchymal PDL cells, instead of K14+ epithelial cells, significantly contribute to rapid cementum growth.

Isolation and characterization of a human cementocyte-like cell line, HCY-23

Cementum is the mineralized tissue covering the tooth root that functions in tooth attachment and post-eruptive adjustment of tooth position. It has been reported to be highly similar to bone in several respects but remains poorly understood in terms of development and regeneration. Here, we investigate whether cementocytes, the residing cells in cellular cementum, have the potential to be protagonist in cementum homeostasis, responding to endocrine signals and directing local cementum metabolism. Cells from healthy erupted human teeth were isolated using sequential collagenase/EDTA digestions, and maintained in standard cell culture conditions. A cementocyte-like cell line was cloned (HCY-23, for human cementocyte clone 23), which presented a cementocyte compatible gene expression signature, including the expression of dentin matrix protein 1 ( DMP1 ), sclerostin ( SOST ), and E11/gp38/podoplanin ( E11 ). In contrast, these cells did not express the odontoblast/dentin marker dentin sialoprotein ( DSPP ). HCY-23 cells produced mineral-like nodules in vitro under differentiation conditions, and were highly responsive to inorganic phosphate (Pi). Within the limits of the present study, it can be concluded that cementocytes are phosphate-responsive cells, and have the potential do play a key role in periodontal homeostasis and regeneration.

Distribution of glutamate receptor, ionotropic, kainate 1 and neuropeptide calcitonin gene-related peptide mRNAs during formation of the embryonic and postnatal mouse molar in the maxilla

The neuropeptide calcitonin gene-related peptide (CGRP) is a well-characterized neurotransmitter. Glutamate receptor, ionotropic, kainate 1 (Grik1) has also been demonstrated to generate high-affinity kainate receptors. However, little is known about the roles of CGRP and Grik1 during the developmental formation of teeth. In this study, we endeavoured to analyse the expression and localization of CGRP and Grik1 mRNAs using in situ hybridization on the mouse maxilla during development from the embryonic stage (E18.5) to after birth (P10, P15 and P20). We found that hybridization with an anti-sense probe for CGRP clearly localized in the maxilla at E18.5 in contrast to that of P15 and P20. Hybridization with an anti-sense probe for CGRP was not detected in the dental pulp of molars in the maxilla at P10, which is in contrast to Grik1 mRNA at the same developmental stage. Hybridization with an anti-sense probe for Grik1 mRNA was detected in the basal region of the dental pulp of molars at P10 and P15. Finally, these markers were not detected in molars in the mouse maxilla at P20. The ratio of positive cells for the hybridization signals of Grik1and CGRP in the dental pulp decreased from E18.5 (p<0.001). These features in CGRP and Grik1r mRNAs may indicate roles of function during tooth development between embryonic and postnatal stages with root formation and erupted movements.

Protective Variants in Alzheimer's Disease

PURPOSE OF REVIEW

Over the last decade over 40 loci have been associated with risk of Alzheimer's disease (AD). However, most studies have either focused on identifying risk loci or performing unbiased screens without a focus on protective variation in AD. Here, we provide a review of known protective variants in AD and their putative mechanisms of action. Additionally, we recommend strategies for finding new protective variants.

RECENT FINDINGS

Recent Genome-Wide Association Studies have identified both common and rare protective variants associated with AD. These include variants in or near APP, APOE, PLCG2, MS4A, MAPT-KANSL1, RAB10, ABCA1, CCL11, SORL1, NOCT, SCL24A4-RIN3, CASS4, EPHA1, SPPL2A, and NFIC.

SUMMARY

There are very few protective variants with functional evidence and a derived allele with a frequency below 20%. Additional fine mapping and multi-omic studies are needed to further validate and characterize known variants as well as specialized genome-wide scans to identify novel variants.

PTH1R signalling regulates the mechanotransduction process of cementoblasts under cyclic tensile stress

Objective

To investigate the regulatory role of type I parathyroid hormone receptor (PTH1R) signalling in the mechanotransduction process of cementoblasts under cyclic tensile stress (CTS).

Materials and methods

Immortalized cementoblast cell line OCCM-30 were employed and subjected to cyclic tensile strain applied by a four-point bending system. The expression of PTHrP and PTH1R, as well as cementoblastic transcription factor Runx-2, Osterix, and extracellular matrix protein COL-1 and OPN were assessed by quantitative real-time polymerase chain reaction and western blot analysis. PTH1R expression was knocked down by siPTH1R transfection, and the alteration of cementoblastic biomarkers expression was examined to evaluate the function of PTH1R. Furthermore, to investigate possible downstream molecules, expression of signal molecule ERK1/2 with or without siPTH1R transfection, and the effect of ERK inhibitor PD98059 on the expression of cementoblastic biomarkers was also examined.

Results

Cyclic tensile strain elevated the expression of PTHrP and PTH1R, as well as cementoblastic biomarkers Runx-2, Osterix, COL-1, and OPN in a time-dependent manner, which was inhibited by siPTH1R transfection. The expression of phosphorylated ERK1/2 was upregulated time-dependently under cyclic stretch, which was also inhibited by siPTH1R transfection, and pretreatment of p-ERK1/2 inhibitor PD98059 undermined the increase of Runx-2, Osterix, COL-1, and OPN prominently.

Conclusion

The findings of the present study indicate that PTH1R signalling plays a regulatory role in the CTS induced cementoblastic differentiation in mature cementoblasts, and ERK1/2 is essentially involved as a downstream intracellular signal molecule in this mechanotransduction process.

Nuclear import of transcriptional corepressor BCOR occurs through interaction with karyopherin α expressed in human periodontal ligament

Mutations in the gene encoding BCL-6 corepressor (BCOR) are responsible for oculofaciocardiodental (OFCD) syndrome, which is a rare X-linked dominant disorder characterized by radiculomegaly of permanent teeth as the most typical symptom. To function as a transcriptional corepressor, BCOR needs to enter the nucleus; however, the molecular pathway for its nuclear translocation during dental root formation remains unclear. The purpose of this study was to determine the mechanism underlying BCOR transport into the nucleus. Our results showed that human periodontal ligament (PDL) cells expressed karyopherin α (KPNA)2, KPNA4, and KPNA6 belonging to a family of nuclear import proteins, which interacted with BCOR in the immunoprecipitation assay. Site-directed mutagenesis targeting the two nuclear localization signals (NLSs) within BCOR reduced its nuclear translocation; however, co-expression of KPNA2, KPNA4, or KPNA6 with BCOR carrying a previously described mutation which eliminated one of the two NLSs significantly increased nuclear accumulation of the mutant BCOR, indicating participation of KPNA in BCOR nuclear translocation. Comparative expression profiling of PDL cells isolated from normal and OFCD patients revealed significant downregulation of SMAD4, GLI1, and nuclear factor 1-C (NFIC) mRNA expression, suggesting that BCOR mutations cause hyperactive root formation in OFCD syndrome by inhibiting SMAD4-Hedgehog-NFIC signaling implicated in dental root development. Our study contributes to understanding of the mechanisms providing nuclear import of BCOR during root formation.

Identification of the Novel Tooth-Specific Transcription Factor AmeloD

Basic-helix-loop-helix (bHLH) transcription factors play an important role in various organs' development; however, a tooth-specific bHLH factor has not been reported. In this study, we identified a novel tooth-specific bHLH transcription factor, which we named AmeloD, by screening a tooth germ complementary DNA (cDNA) library using a yeast 2-hybrid system. AmeloD was mapped onto the mouse chromosome 1q32. Phylogenetic analysis showed that AmeloD belongs to the achaete-scute complex-like ( ASCL) gene family and is a homologue of ASCL5. AmeloD was uniquely expressed in the inner enamel epithelium (IEE), but its expression was suppressed after IEE cell differentiation into ameloblasts. Furthermore, AmeloD expression showed an inverse expression pattern with the epithelial cell-specific cell-cell adhesion molecule E-cadherin in the dental epithelium. Overexpression of AmeloD in dental epithelial cell line CLDE cells resulted in E-cadherin suppression. We found that AmeloD bound to E-box cis-regulatory elements in the proximal promoter region of the E-cadherin gene. These results reveal that AmeloD functions as a suppressor of E-cadherin transcription in IEE cells. Our study demonstrated that AmeloD is a novel tooth-specific bHLH transcription factor that may regulate tooth development through the suppression of E-cadherin in IEE cells.

Pathogenesis of primordial odontogenic tumour based on tumourigenesis and odontogenesis

OBJECTIVE

Primordial odontogenic tumour (POT) is a rare benign mixed epithelial and mesenchymal odontogenic tumour. POT is composed of dental papilla-like tissue covered with cuboidal to columnar epithelium that resembles to inner and outer enamel epithelium of the enamel organ without dental hard tissue formation. The aim of this study was to examine pathogenesis of POT based on tumourigenesis and odontogenesis.

SUBJECTS AND METHODS

Six cases of POT were submitted for study. DNA analysis and transcriptome analysis were performed by next-generation sequencing. Expression of amelogenin, ameloblastin and dentin sialophosphoprotein (DSPP) was examined by immunohistochemistry.

RESULTS

There were no gene mutations detected in any of analysed 151 cancer- and 42 odontogenesis-associated genes. Enamel protein-coding genes of Amelx, Ambn and Enam, and dentin protein-coding genes of Col1a1, Dspp, Nes and Dmp1 were expressed, whereas expression of dentinogenesis-associated genes of Bglap, Ibsp and Nfic was negative or very weak suggesting inhibition of dentin formation in POT after odontoblast differentiation. Immunoreactivity of amelogenin, ameloblastin and DSPP was detected in POT.

CONCLUSIONS

Pathogenesis of POT is considered to be genetically different from other odontogenic tumours. It is suggested that inhibition of enamel and dentin formation in POT is due to defects in dentin formation process.

Genetic Evidence Supporting the Role of the Calcium Channel, CACNA1S, in Tooth Cusp and Root Patterning

In this study, we report a unique dominantly inherited disorganized supernumerary cusp and single root phenotype presented by 11 affected individuals belonging to 5 north-eastern Thai families. Using whole exome sequencing (WES) we identified a common single missense mutation that segregates with the phenotype in exon 6 of CACNA1S (Ca_v1.1) (NM_000069.2: c.[865A > G];[=] p.[Ile289Val];[=]), the Calcium Channel, Voltage-Dependent, L Type, Alpha-1s Subunit, OMIM ^∗ 114208), affecting a highly conserved amino-acid isoleucine residue within the pore forming subdomain of CACNA1S protein. This is a strong genetic evidence that a voltage-dependent calcium ion channel is likely to play a role in influencing tooth morphogenesis and patterning.

Essential Role of IFT140 in Promoting Dentinogenesis

Primary cilia, with highly regulated cellular sensory functions, play key roles in tissue development and function maintenance. Intraflagellar transport 140 (IFT140) is a subunit of IFT complex A, which is specialized for retrograde transportation in cilia. Mutations of Ift140 are usually associated with syndromic ciliopathy and may cause isolated diseases such as retinal dystrophy, short ribs, and polycystic kidney. However, the role of IFT140 in tooth development has not been well investigated. In this study, a close relationship between IFT140 and dentin formation is disclosed. During tooth development, IFT140 was highly expressed in odontoblasts. To further understand the role of IFT140 in dentinogenesis, Ift140^flox/flox/Osx-Cre mouse was generated. The dentin thickness of Ift140^flox/flox/Osx-Cre mouse is thinner and the dentin formation is slower than that in control. In vitro, deletion of IFT140 in odontoblasts led to poor odontogenic differentiation, abnormal primary cilia, and decreased Sonic hedgehog signaling molecules. More important, due to loss of primary cilia in odontoblasts by IFT140 deletion, reparative dentin formation was impaired in a tooth-drilling model. These results suggest that cilia gene IFT140 is essential in promoting dentin formation and reparation.