Antagonistic interaction between Ezh2 and Arid1a coordinates root patterning and development via Cdkn2a in mouse molars

Role and mechanisms of histone methylation in osteogenic/odontogenic differentiation of dental mesenchymal stem cells

Dental mesenchymal stem cells (DMSCs) are pivotal for tooth development and periodontal tissue health and play an important role in tissue engineering and regenerative medicine because of their multidirectional differentiation potential and self-renewal ability. The cellular microenvironment regulates the fate of stem cells and can be modified using various optimization techniques. These methods can influence the cellular microenvironment, activate disparate signaling pathways, and induce different biological effects. "Epigenetic regulation" refers to the process of influencing gene expression and regulating cell fate without altering DNA sequences, such as histone methylation. Histone methylation modifications regulate pivotal transcription factors governing DMSCs differentiation into osteo-/odontogenic lineages. The most important sites of histone methylation in tooth organization were found to be H3K4, H3K9, and H3K27. Histone methylation affects gene expression and regulates stem cell differentiation by maintaining a delicate balance between major trimethylation sites, generating distinct chromatin structures associated with specific downstream transcriptional states. Several crucial signaling pathways associated with osteogenic differentiation are susceptible to modulation via histone methylation modifications. A deeper understanding of the regulatory mechanisms governing histone methylation modifications in osteo-/odontogenic differentiation and immune-inflammatory responses of DMSCs will facilitate further investigation of the epigenetic regulation of histone methylation in DMSC-mediated tissue regeneration and inflammation. Here is a concise overview of the pivotal functions of epigenetic histone methylation at H3K4, H3K9, and H3K27 in the regulation of osteo-/odontogenic differentiation and renewal of DMSCs in both non-inflammatory and inflammatory microenvironments. This review summarizes the current research on these processes in the context of tissue regeneration and therapeutic interventions.

A single-cell transcriptomic atlas of human stem cells from apical papilla during the committed differentiation

AIM

Human stem cells derived from the apical papilla (SCAPs) are recognized for their multilineage differentiation potential and their capacity for functional tooth root regeneration. However, the molecular mechanisms underlying odonto/osteogenic differentiation remain largely unexplored. In this study, we utilized single-cell RNA sequencing (scRNA-seq) to conduct an in-depth analysis of the transcriptional changes associated with chemically induced osteogenesis in SCAPs.

METHODOLOGY

scRNA-seq identified SCAPs as distinct subpopulations. Differentially expressed genes (DEGs) and Gene Ontology (GO) analyses were conducted to evaluate the potential function of each cluster. Pseudotime trajectory analysis was employed to elucidate the potential differentiation processes of the identified SCAP populations. To investigate the osteo/odontogenic potential of Deiodinase Iodothyronine Type 2 (DIO2) on SCAPs, we performed alkaline phosphatase staining, western blot analysis, Alizarin Red S staining and immunofluorescence staining. Additionally, SCAP components were transplanted into mouse calvarial defects to evaluate osteogenesis in vivo.

RESULTS

The analysis of cell clusters derived from our scRNA-seq data revealed a significant shift in cellular composition when cells were cultured in a mineralization induction medium compared to those cultured in a complete medium. Both groups exhibited heterogeneity, with some cells intrinsically predisposed to osteogenesis and others appearing to be primed for proliferative functions. Notably, we identified a subpopulation characterized by high expression of DIO2, which exhibited pronounced osteogenic activity during differentiation.

CONCLUSIONS

Our study is the first to reveal a shift in the cellular composition of SCAPs when cultured in a mineralization induction medium compared to a complete medium. Following both in vitro and in vivo validation, the DIO2+ subpopulation exhibited the highest transcriptional similarity to osteogenic function, suggesting its potential utility in tissue regeneration applications.

Histone-modifying enzymes: Roles in odontogenesis and beyond

OBJECTIVES

Odontogenesis, an intricate process initiated by epithelium-mesenchyme interaction, is meticulously regulated by a cascade of regulatory mechanisms. Epigenetic modifications, especially histone modification, have been found to exhibit spatiotemporal specificity during tooth development. However, the expression patterns and roles of enzymes associated with histone modifications have yet to be systematically explored in odontogenesis. This review aims to summarize the histone-modifying enzymes in odontogenesis and their regulation mechanism during tooth development and provide the potential theoretical basis for the clinical management and intervention of dental developmental diseases.

SUBJECTS AND METHODS

This study conducted a systematic search across PubMed and Web of Science databases, utilizing the keywords "odontogenesis," "histone modification," and "enzyme" for pertinent articles.

RESULTS

No doubt histone modification contributes extensively to odontogenesis regulation, and the disturbances in histone modifications can derange the odontogenesis process.

CONCLUSION

Further studies are warranted to elucidate these roles and their potential downstream effects, positioning histone modifications as a pivotal focal point for unraveling the intricacies of tooth development and regeneration.

FGF signaling modulates mechanotransduction/WNT signaling in progenitors during tooth root development

Stem/progenitor cells differentiate into different cell lineages during organ development and morphogenesis. Signaling pathway networks and mechanotransduction are important factors to guide the lineage commitment of stem/progenitor cells during craniofacial tissue morphogenesis. Here, we used tooth root development as a model to explore the roles of FGF signaling and mechanotransduction as well as their interaction in regulating the progenitor cell fate decision. We show that Fgfr1 is expressed in the mesenchymal progenitor cells and their progeny during tooth root development. Loss of Fgfr1 in Gli1+ progenitors leads to hyperproliferation and differentiation, which causes narrowed periodontal ligament (PDL) space with abnormal cementum/bone formation leading to ankylosis. We further show that aberrant activation of WNT signaling and mechanosensitive channel Piezo2 occurs after loss of FGF signaling in Gli1-CreER;Fgfr1fl/fl mice. Overexpression of Piezo2 leads to increased osteoblastic differentiation and decreased Piezo2 leads to downregulation of WNT signaling. Mechanistically, an FGF/PIEZO2/WNT signaling cascade plays a crucial role in modulating the fate of progenitors during root morphogenesis. Downregulation of WNT signaling rescues tooth ankylosis in Fgfr1 mutant mice. Collectively, our findings uncover the mechanism by which FGF signaling regulates the fate decisions of stem/progenitor cells, and the interactions among signaling pathways and mechanotransduction during tooth root development, providing insights for future tooth root regeneration.

Fundamentals and Translational Applications of Stem Cells and Biomaterials in Dental, Oral and Craniofacial Regenerative Medicine

Regenerative dental medicine continuously expands to improve treatments for prevalent clinical problems in dental and oral medicine. Stem cell based translational opportunities include regenerative therapies for tooth restoration, root canal therapy, and inflammatory processes (e.g., periodontitis). The potential of regenerative approaches relies on the biological properties of dental stem cells. These and other multipotent somatic mesenchymal stem cell (MSC) types can in principle be applied as either autologous or allogeneic sources in dental procedures. Dental stem cells have distinct developmental origins and biological markers that determine their translational utility. Dental regenerative medicine is supported by mechanistic knowledge of the molecular pathways that regulate dental stem cell growth and differentiation. Cell fate determination and lineage progression of dental stem cells is regulated by multiple cell signaling pathways (e.g., WNTs, BMPs) and epigenetic mechanisms, including DNA modifications, histone modifications, and non-coding RNAs (e.g., miRNAs and lncRNAs). This review also considers a broad range of novel approaches in which stem cells are applied in combination with biopolymers, ceramics, and composite materials, as well as small molecules (agonistic or anti-agonistic ligands) and natural compounds. Materials that mimic the microenvironment of the stem cell niche are also presented. Promising concepts in bone and dental tissue engineering continue to drive innovation in dental and non-dental restorative procedures.

Spatiotemporal cellular dynamics and molecular regulation of tooth root ontogeny

Tooth root development involves intricate spatiotemporal cellular dynamics and molecular regulation. The initiation of Hertwig's epithelial root sheath (HERS) induces odontoblast differentiation and the subsequent radicular dentin deposition. Precisely controlled signaling pathways modulate the behaviors of HERS and the fates of dental mesenchymal stem cells (DMSCs). Disruptions in these pathways lead to defects in root development, such as shortened roots and furcation abnormalities. Advances in dental stem cells, biomaterials, and bioprinting show immense promise for bioengineered tooth root regeneration. However, replicating the developmental intricacies of odontogenesis has not been resolved in clinical treatment and remains a major challenge in this field. Ongoing research focusing on the mechanisms of root development, advanced biomaterials, and manufacturing techniques will enable next-generation biological root regeneration that restores the physiological structure and function of the tooth root. This review summarizes recent discoveries in the underlying mechanisms governing root ontogeny and discusses some recent key findings in developing of new biologically based dental therapies.

Ezh2-dependent methylation in oral epithelia promotes secondary palatogenesis

BACKGROUND

In addition to genomic risk variants and environmental influences, increasing evidence suggests epigenetic modifications are important for orofacial development and their alterations can contribute to orofacial clefts. Ezh2 encodes a core catalytic component of the Polycomb repressive complex responsible for addition of methyl marks to Histone H3 as a mechanism of repressing target genes. The role of Ezh2 in orofacial clefts remains unknown.

AIMS

To investigate the epithelial role of Ezh2-dependent methylation in secondary palatogenesis.

METHODS

We used conditional gene-targeting methods to ablate Ezh2 in the surface ectoderm-derived oral epithelium of mouse embryos. We then performed single-cell RNA sequencing combined with immunofluorescence and RT-qPCR to investigate gene expression in conditional mutant palate. We also employed double knockout analyses of Ezh1 and Ezh2 to address if they have synergistic roles in palatogenesis.

RESULTS

We found that conditional inactivation of Ezh2 in oral epithelia results in partially penetrant cleft palate. Double knockout analyses revealed that another family member Ezh1 is dispensable in orofacial development, and it does not have synergistic roles with Ezh2 in palatogenesis. Histochemistry and single-cell RNA-seq analyses revealed dysregulation of cell cycle regulators in the palatal epithelia of Ezh2 mutant mouse embryos disrupts palatogenesis.

CONCLUSION

Ezh2-dependent histone H3K27 methylation represses expression of cell cycle regulator Cdkn1a and promotes proliferation in the epithelium of the developing palatal shelves. Loss of this regulation may perturb movement of the palatal shelves, causing a delay in palate elevation which may result in failure of the secondary palate to close altogether.

An Unusual Gingival (Peripheral) Tumor with Features of Keratoameloblastoma with Cytologic Atypia or Possible Malignant Transformation Exhibiting ARID1A Mutation

BACKGROUND

Keratoameloblastoma is a poorly characterized and rarely reported odontogenic neoplasm that can exhibit overlapping histopathologic features with conventional ameloblastoma and keratocystic odontogenic tumor (KCOT), with an ambiguous relationship to the so-called solid KCOT.

METHODS

A peripheral maxillary tumor causing bone saucerization in a 54-year-old male is described and investigated with immunohistochemistry and Next-Generation Sequencing (NGS).

RESULTS

Microscopically, the tumor comprised of a predominantly plexiform proliferation of odontogenic epithelium with central keratinization and evidence of surface origin. Peripheral cells exhibited nuclear palisading with variable reverse polarization, while stellate reticulum-like areas were observed internally. A few follicles and a few foci in the lining of cystic spaces revealed increased cellularity with cells exhibiting small but conspicuous nucleoli, focal nuclear hyperchromatism, and a few mitoses mostly seen in the peripheral outer cell layer. Nuclear staining for ki-67 was increased in those areas when compared with the other cystic, follicular, and plexiform areas. These features were interpreted as cytologic atypia suggesting also the possibility of a malignant process. Immunohistochemically, the tumor was positive for CK19 and negative for BRAF VE1, calretinin, and CD56. Ber-Ep4 was only focally positive. By sequencing, an ARID1A c.6527_6538delAG frameshift mutation (VAF: 5.8%), classified as likely oncogenic, and an FBXW7 c.1627 A > G missense mutation (VAF: 8.0%), classified as a variant of uncertain significance, were detected. Two mutations, probably germline (VAF ~ 50%), were recorded for RNF43 and FBXW7. No pathogenic variants were identified in PTCH1, BRAF, NRAS, HRAS, KRAS, FGFR2, or SMO genes.

CONCLUSION

The significance of an ARID1A variant in keratoameloblastoma is uncertain since this variant has not been reported in ameloblastoma or KCOT, to date. Alternatively, it may characterize malignant transformation in the present case since ARID1A mutations have been encountered in various cancers. Sequencing of additional cases is necessary to determine whether this may represent a recurrent genomic event.

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.

Current Understanding of the Regulatory Mechanism of Tooth Root Development and Future Perspectives

Background

The purpose of this review article is to understand tooth root development and its regulation through evolution and epigenetics as well as future implications involving root regeneration and tissue engineering.

Types of Studies Reviewed

we performed a comprehensive PubMed search to review all published studies related to the molecular regulation of tooth root development and regeneration until August 2022. Articles selected include original research studies and reviews.

Results

Epigenetic regulation strongly influences dental tooth root patterning and development. One study highlights how genes such as Ezh2 and Arid1a are crucial components in the development of tooth root furcation patterning. Another study shows that loss of Arid1a ultimately leads to shortened root morphology. Furthermore, researchers are utilizing information about root development and stem cells to find alternative treatments in replacing missing teeth through a stem cell-mediated bioengineered tooth root (bio-root).

Practical Implications

Dentistry values preserving natural tooth morphology. Presently, implants are the best treatment for replacing missing teeth, but alternative future treatments might include tissue engineering/bio-root regeneration to restore our dentition.

Rodent incisor as a model to study mesenchymal stem cells in tissue homeostasis and repair

The homeostasis of adult tissues, such as skin, hair, blood, and bone, requires continuous generation of differentiated progeny of stem cells. The rodent incisor undergoes constant renewal and can provide an extraordinary model for studying stem cells and their progeny in adult tissue homeostasis, cell differentiation and injury-induced regeneration. Meanwhile, cellular heterogeneity in the mouse incisor also provides an opportunity to study cell-cell communication between different cell types, including interactions between stem cells and their niche environment. More importantly, the molecular and cellular regulatory mechanisms revealed by the mouse incisor have broad implications for other organs. Here we review recent findings and advances using the mouse incisor as a model, including perspectives on the heterogeneity of cells in the mesenchyme, the niche environment, and signaling networks that regulate stem cell behavior. The progress from this field will not only expand the knowledge of stem cells and organogenesis, but also bridge a gap between animal models and tissue regeneration.

Epigenetic Regulation of Methylation in Determining the Fate of Dental Mesenchymal Stem Cells

Dental mesenchymal stem cells (DMSCs) are crucial in tooth development and periodontal health, and their multipotential differentiation and self-renewal ability play a critical role in tissue engineering and regenerative medicine. Methylation modifications could promote the appropriate biological behavior by postsynthetic modification of DNA or protein and make the organism adapt to developmental and environmental prompts by regulating gene expression without changing the DNA sequence. Methylation modifications involved in DMSC fate include DNA methylation, RNA methylation, and histone modifications, which have been proven to exert a significant effect on the regulation of the fate of DMSCs, such as proliferation, self-renewal, and differentiation potential. Understanding the regulation of methylation modifications on the behavior and the immunoinflammatory responses involved in DMSCs contributes to further study of the mechanism of methylation on tissue regeneration and inflammation. In this review, we briefly summarize the key functions of histone methylation, RNA methylation, and DNA methylation in the differentiation potential and self-renewal of DMSCs as well as the opportunities and challenges for their application in tissue regeneration and disease therapy.

Spatiotemporal single-cell regulatory atlas reveals neural crest lineage diversification and cellular function during tooth morphogenesis

Cranial neural crest cells are an evolutionary innovation of vertebrates for craniofacial development and function, yet the mechanisms that govern the cell fate decisions of postmigratory cranial neural crest cells remain largely unknown. Using the mouse molar as a model, we perform single-cell transcriptome profiling to interrogate the cell fate diversification of postmigratory cranial neural crest cells. We reveal the landscape of transcriptional heterogeneity and define the specific cellular domains during the progression of cranial neural crest cell-derived dental lineage diversification, and find that each domain makes a specific contribution to distinct molar mesenchymal tissues. Furthermore, IGF signaling-mediated cell-cell interaction between the cellular domains highlights the pivotal role of autonomous regulation of the dental mesenchyme. Importantly, we reveal cell-type-specific gene regulatory networks in the dental mesenchyme and show that Foxp4 is indispensable for the differentiation of periodontal ligament. Our single-cell atlas provides comprehensive mechanistic insight into the cell fate diversification process of the cranial neural crest cell-derived odontogenic populations.

Cell Differentiation and Replication during Postnatal Development of the Murine First Molar

Simple Summary

Teeth are necessary to prepare food for swallowing. The process of teeth development before and after birth may be studied in normal mice and also by reproducing diseases or genetic conditions. However, mice teeth are different from human teeth, since mice have only permanent teeth. Moreover, their incisors continue to grow for the whole lifespan. Hence, it is important to know how the mouse teeth develop. We studied the development of the first molar in mice from birth to weaning and showed that dividing cells are located in a different part of the developing tooth according to age.

Abstract

Various signaling molecular pathways are involved in odontogenesis to promote cellular replication and differentiation. Tooth formation is controlled mainly by epithelial–mesenchymal interactions. The aim of this work was to investigate how cellular replication and differentiation ensue during the formation of the murine first molar in postnatal ages until eruption, focusing on morphogenesis, odontoblast differentiation and cellular replication. Wild-type CD1 mice were examined from birth to weaning. Morphogenesis and interaction between developing epithelial and mesenchymal tissues were evaluated in hematoxylin–eosin and Gomori trichome stained sections. Immunohistochemistry for nestin, which mediates the differentiation of odontoblasts, especially their polarization and elongation, showed that this intermediate filament was apparent already at postnatal day P1 in the apical region of odontoblasts and progressed apically from cusp tips, while it was not present in epithelial tissues. The expression of nuclear antigen Ki-67 highlighted dividing cells in both epithelial and mesenchymal tissues at P1, while one week later they were restricted to the cementoenamel junction, guiding root elongation. The link between odontoblast maturation and cellular replication in the different tooth tissues is essential to understand the development of tooth shape and dimension, to outline mechanisms of tooth morphogenesis and possibly eruption.

Ezh2 knockout in mesenchymal cells causes enamel hyper-mineralization

Enhancer of zeste homolog 2 (EZH2) is the catalytic core of polycomb repressive complex 2 (PRC2), which primarily methylates lysine 27 on histone H3 (H2K27me3), generating transcriptionally suppressed heterochromatin. Since EZH2 suppresses expression of genes involved in dentin formation, we examined the role of EZH2 in tooth development. Intriguingly, microCT analysis of teeth from mice with conditional Ezh2 knockout in uncommitted mesenchymal cells showed hyper-mineralization of enamel, which is produced by the epithelial-lineage cells, ameloblasts. Scanning electron microscopy analysis and nano-indentation of the incisor enamel from knockout mice revealed smaller inter-rod spaces and higher hardness compared to wild type enamel, respectively. Interestingly, expression of the calcium channel subunit gene, Orai2, was decreased compared to its competitor, Orai1, both in knockout mouse incisors and the ex vivo culture of ameloblasts with the surrounding tissues under EZH2 inhibition. Moreover, histological analysis of incisor from knockout mice showed decreased ameloblastin and expedited KLK4 expression in the ameloblasts. These observations suggest that EZH2 depletion in dental mesenchymal cells reduces enamel matrix formation and increases enamel protease activity from ameloblasts, resulting in enamel hyper-mineralization. This study demonstrates the significant role of the suppressive H3K27me3 mark for heterochromatin on enamel formation.

Role of enhancer of zeste homolog 2 in osteoclast formation and periodontitis development by downregulating microRNA-101-regulated VCAM-1

The enhancer of zeste homolog 2 (EZH2) represents a potential target for periodontitis treatment; however, its role in the development of periodontitis remains unclear. The current study aimed to elucidate the role of EZH2 in osteoclasts (OCs) growth as well as the mechanism underpinning the related process. The potential interaction among EZH2, microRNA-101 (miR-101), and vascular cell adhesion molecule 1 (VCAM-1) was evaluated using chromatin immunoprecipitation and dual-luciferase reporter gene assay. The expressions of EZH2 and miR-101 in OCs were examined by Western blot analysis and reverse transcription squantitative polymerase chain reaction. Loss- and gain-function assays were then performed to determine the role of EZH2/miR-101/VCAM-1 in periodontitis and OCs proliferation, followed by OC growth and proliferation detected using tartrate resistant acid phosphatase (TRAP) and 5-ethynyl-2'-deoxyuridine staining. Enzyme-linked immunoassay was conducted to determine the expression of interleukin 1β (IL-1β) and tumor necrosis factor-α (TNF-α). A periodontitis rat model was established to investigate the effect of EZH2 and VCAM-1 in vivo. EZH2 was overexpressed, while miR-101 was downregulated in the OCs of periodontitis. Silencing of EZH2, VCAM-1 repression, or miR-101 elevation suppressed the growth and proliferation of OC while acting to encumber the release of IL-1β and TNF-α. EZH2 negatively targeted miR-101, while miR-101 negatively targeted VCAM-1. Moreover, silencing of EZH2 or VCAM-1 was observed to attenuate periodontitis which was evidenced by an increase in BMD, BV/TV, and BS/BV as well as reduction in TRAP and cathepsin K in vivo. Taken together, the key findings of the current study demonstrate that EZH2 knockdown inhibited OC formation by elevating the expression of miR-101 via suppression of VCAM-1, ultimately attenuating periodontitis.

Fork-shaped mandibular incisors as a novel phenotype of LRP5-associated disorder

The LRP5 gene encodes a Wnt signaling receptor to which Wnt binds directly. In humans, pathogenic monoallelic variants in LRP5 have been associated with increased bone density and exudative vitreoretinopathy. In mice, LRP5 plays a role in tooth development, including periodontal tissue stability and cementum formation. Here, we report a 14-year-old patient with a de novo non-synonymous variant, p.(Val1245Met), in LRP5 who exhibited mildly reduced bone density and mild exudative vitreoretinopathy together with a previously unreported phenotype consisting of dental abnormalities that included fork-like small incisors with short roots and an anterior open bite, molars with a single root, and severe taurodontism. In that exudative vitreoretinopathy has been reported to be associated with heterozygous loss-of-function variants of LRP5 and that our patient reported here with the p.(Val1245Met) variant had mild exudative vitreoretinopathy, the variant can be considered as an incomplete loss-of-function variant. Alternatively, the p.(Val1245Met) variant can be considered as exerting a dominant-negative effect, as no patients with truncating LRP5 variants and exudative vitreoretinopathy have been reported to exhibit dental anomalies. The documentation of dental anomalies in the presently reported patient strongly supports the notion that LRP5 plays a critical role in odontogenesis in humans, similar to its role in mice.

Lhx6 regulates canonical Wnt signaling to control the fate of mesenchymal progenitor cells during mouse molar root patterning

Mammalian tooth crown formation has long served as a model for investigating how patterning and morphogenesis are orchestrated during development. However, the mechanism underlying root patterning and morphogenesis remains poorly understood. In this study, we find that Lhx6 labels a subpopulation of root progenitor cells in the apical dental mesenchyme, which is closely associated with furcation development. Loss of Lhx6 leads to furcation and root number defects, indicating that Lhx6 is a key root patterning regulator. Among the multiple cellular events regulated by Lhx6 is the odontoblast fate commitment of progenitor cells, which it controls in a cell-autonomous manner. Specifically, Lhx6 loss leads to elevated expression of the Wnt antagonist Sfrp2 and down-regulation of Wnt signaling in the furcation region, while overactivation of Wnt signaling in Lhx6+ progenitor cells partially restore the furcation defects in Lhx6-/- mice. Collectively, our findings have important implications for understanding organ morphogenesis and future strategies for tooth root regeneration.

Epithelial Wnt10a Is Essential for Tooth Root Furcation Morphogenesis

WNT10A (Wingless-type MMTV integration site family, member 10A) plays a crucial role in tooth development, and patients with biallelic WNT10A mutation and mice lacking Wnt10a show taurodontism. However, whether epithelial or mesenchymal WNT10A controls the initiation of the root furcation formation remains unclear, and the functional significance of WNT10A in regulating root morphogenesis has not been clarified. Here, we investigated how Wnt10a affects tooth root development by generating different tissue-specific Wnt10a conditional knockout mice. Wnt10a knockout in the whole tissue (EIIa-Cre;Wnt10a^flox/flox) and in dental epithelium (K14-Cre;Wnt10a^flox/flox) led to an absence of or apically located root furcation in molars of mice, a phenotype that resembled taurodontism. An RNAscope analysis showed that the dynamic epithelial and mesenchymal Wnt10a expression pattern occurred during root development. Immunofluorescent staining of E-cadherin and EdU revealed decreased epithelial cell proliferation at the cervical region of the molar in K14-Cre;Wnt10a^flox/flox mice at postnatal day 0 (PN0), just before the initiation of root morphogenesis. Interestingly, we found increased pulpal mesenchymal cell proliferation in the presumptive root furcating region of the molar in K14-Cre;Wnt10a^flox/flox mice at PN4 and PN7. RNA-seq indicated that among the Wnt ligands with high endogenous expression levels in molars, Wnt4 was increased after epithelial knockout of Wnt10a. The RNAscope assay confirmed that the expression of Wnt4 and Axin2 in the dental papilla of the presumptive root furcating region, where dental pulp overgrowth occurred, was increased in K14-Cre;Wnt10a^flox/flox molars. Furthermore, after suppression of the elevated Wnt4 level in K14-Cre;Wnt10a^flox/flox molars by Wnt4 shRNA adenovirus and kidney capsule grafts, the root furcation defect was partially rescued. Taken together, our study provides the first in vivo evidence that epithelial Wnt10a guides root furcation formation and plays a crucial role in controlling the organized proliferation of adjacent mesenchymal cells by regulating proper Wnt4 expression during root furcation morphogenesis.

Antagonistic interaction between Ezh2 and Arid1a coordinates root patterning and development via Cdkn2a in mouse molars

Patterning is a critical step during organogenesis and is closely associated with the physiological function of organs. Tooth root shapes are finely tuned to provide precise occlusal support to facilitate the function of each tooth type. However, the mechanism regulating tooth root patterning and development is largely unknown. In this study, we provide the first in vivo evidence demonstrating that Ezh2 in the dental mesenchyme determines patterning and furcation formation during dental root development in mouse molars. Mechanistically, an antagonistic interaction between epigenetic regulators Ezh2 and Arid1a controls Cdkn2a expression in the dental mesenchyme to regulate dental root patterning and development. These findings indicate the importance of balanced epigenetic regulation in determining the tooth root pattern and the integration of roots with the jaw bones to achieve physiological function. Collectively, our study provides important clues about the regulation of organogenesis and has general implications for tooth regeneration in the future.