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Enamel is formed by the repetitive secretion of a tooth-specific extracellular matrix and its decomposition. Calcification of the enamel matrix via hydroxyapatite (HAP) maturation requires pH cycling to be tightly regulated through the neutralization of protons released during HAP synthesis. We found that Gpr115, which responds to changes in extracellular pH, plays an important role in enamel formation. Gpr115-deficient mice show partial enamel hypomineralization, suggesting that other pH-responsive molecules may be involved. In this study, we focused on the role of Gpr111/Adgrf2, a duplicate gene of Gpr115, in tooth development. Gpr111 was highly expressed in mature ameloblasts. Gpr111-KO mice showed enamel hypomineralization. Dysplasia of enamel rods and high carbon content seen in Gpr111-deficient mice suggested the presence of residual enamel matrices in enamel. Depletion of Gpr111 in dental epithelial cells induced the expression of ameloblast-specific protease, kallikrein-related peptidase 4 (Klk4), suggesting that Gpr111 may act as a suppressor of Klk4 expression. Moreover, reduction of extracellular pH to 6.8 suppressed the expression of Gpr111, while the converse increased Klk4 expression. Such induction of Klk4 was synergistically enhanced by Gpr111 knockdown, suggesting that proper enamel mineralization may be linked to the modulation of Klk4 expression by Gpr111. Furthermore, our in vitro suppression of Gpr111 and Gpr115 expression indicated that their suppressive effect on calcification was additive. These results suggest that both Gpr111 and Gpr115 respond to extracellular pH, contribute to the expression of proteolytic enzymes, and regulate the pH cycle, thereby playing important roles in enamel formation.

DOI： 10.1096/fj.202202053R

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OBJECTIVES: Epithelial-mesenchymal interactions are extremely important in tooth development and essential for ameloblast differentiation, especially during tooth formation. We aimed to identify the type of mesenchymal cells important in ameloblast differentiation. METHODS: We used two types of cell culture systems with chambers and found that a subset of dental mesenchymal cells is important for the differentiation of dental epithelial cells into ameloblasts. Among odontogenic mesenchymal cells, dental pulp stem cell-like cells induced the expression of ameloblast differentiation markers. Therefore, we induced dental pulp stem cell-like cells from dental pulp stem cells using the small molecule compound BIO (a GSK-3 inhibitor IX) to clarify the mechanism involved in inducing ameloblast differentiation of dental pulp stem cells. RESULTS: The BIO-induced dental pulp cells promoted the expression of mesenchymal stem cell markers Oct3/4 and Bcrp1. Furthermore, we used artificial dental pulp stem cells induced by BIO to identify the molecules expressed in dental pulp stem cells required for ameloblast differentiation. Panx3 expression was induced in the dental pulp stem cell through interaction with the dental epithelial cells. In addition, ATP release from cells increased in Panx3-expressing cells. We also confirmed that ATP stimulation is accepted in dental epithelial cells. CONCLUSIONS: These results showed that the Panx3 expressed in dental pulp stem cells is important for ameloblast differentiation and that ATP release by Panx3 may play a role in epithelial-mesenchymal interaction.

DOI： 10.1016/j.job.2022.10.002

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DOI： 10.3390/ma15155172

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SAGE Publications  

Organ development is dictated by the regulation of genes preferentially expressed in tissues or cell types. Gene expression profiling and identification of specific genes in organs can provide insights into organogenesis. Therefore, genome-wide analysis is a powerful tool for clarifying the mechanisms of development during organogenesis as well as tooth development. Single-cell RNA sequencing (scRNA-seq) is a suitable tool for unraveling the gene expression profile of dental cells. Using scRNA-seq, we can obtain a large pool of information on gene expression; however, identification of functional genes, which are key molecules for tooth development, via this approach remains challenging. In the present study, we performed cap analysis of gene expression sequence (CAGE-seq) using mouse tooth germ to identify the genes preferentially expressed in teeth. The CAGE-seq counts short reads at the 5′-end of transcripts; therefore, this method can quantify the amount of transcripts without bias related to the transcript length. We hypothesized that this CAGE data set would be of great help for further understanding a gene expression profile through scRNA-seq. We aimed to identify the important genes involved in tooth development via bioinformatics analyses, using a combination of scRNA-seq and CAGE-seq. We obtained the scRNA-seq data set of 12,212 cells from postnatal day 1 mouse molars and the CAGE-seq data set from postnatal day 1 molars. scRNA-seq analysis revealed the spatiotemporal expression of cell type–specific genes, and CAGE-seq helped determine whether these genes are preferentially expressed in tooth or ubiquitously. Furthermore, we identified candidate genes as novel tooth-enriched and dental cell type–specific markers. Our results show that the integration of scRNA-seq and CAGE-seq highlights the genes important for tooth development among numerous gene expression profiles. These findings should contribute to resolving the mechanism of tooth development and establishing the basis for tooth regeneration in the future.

DOI： 10.1177/00220345211049785

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Other Link： http://journals.sagepub.com/doi/full-xml/10.1177/00220345211049785

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/jcp.30667

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/jcp.30667

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Development of chemotherapy has led to a high survival rate of cancer patients; however, the severe side effects of anticancer drugs, including organ hypoplasia, persist. To assume the side effect of anticancer drugs, we established a new ex vivo screening model and described a method for suppressing side effects. Cyclophosphamide (CPA) is a commonly used anticancer drug and causes severe side effects in developing organs with intensive proliferation, including the teeth and hair. Using the organ culture model, we found that treatment with CPA disturbed the growth of tooth germs by inducing DNA damage, apoptosis and suppressing cellular proliferation and differentiation. Furthermore, low temperature suppressed CPA-mediated inhibition of organ development. Our ex vivo and in vitro analysis revealed that low temperature impeded Rb phosphorylation and caused cell cycle arrest at the G1 phase during CPA treatment. This can prevent the CPA-mediated cell damage of DNA replication caused by the cross-linking reaction of CPA. Our findings suggest that the side effects of anticancer drugs on organ development can be avoided by maintaining the internal environment under low temperature.

DOI： 10.1038/s41598-022-06945-7

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Tissue-specific basic helix-loop-helix (bHLH) transcription factors play an important role in cellular differentiation. We recently identified AmeloD as a tooth-specific bHLH transcription factor. However, the role of AmeloD in cellular differentiation has not been investigated. The aim of this study was to elucidate the role of AmeloD in dental epithelial cell differentiation. We found that AmeloD-knockout (AmeloD-KO) mice developed an abnormal structure and altered ion composition of enamel in molars, suggesting that AmeloD-KO mice developed enamel hypoplasia. In molars of AmeloD-KO mice, the transcription factor Sox21 encoding SRY-Box transcription factor 21 and ameloblast differentiation marker genes were significantly downregulated. Furthermore, overexpression of AmeloD in the dental epithelial cell line M3H1 upregulated Sox21 and ameloblast differentiation marker genes, indicating that AmeloD is critical for ameloblast differentiation. Our study demonstrated that AmeloD is an important transcription factor in amelogenesis for promoting ameloblast differentiation. This study provides new insights into the mechanisms of amelogenesis.

DOI： 10.1002/jcp.30639

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DOI： 10.3390/children8121189

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Connexin 43 (Cx43) is an integral membrane protein that forms gap junction channels. These channels mediate intercellular transport and intracellular signaling to regulate organogenesis. The human disease oculodentodigital dysplasia (ODDD) is caused by mutations in Cx43 and is characterized by skeletal, ocular, and dental abnormalities including amelogenesis imperfecta. To clarify the role of Cx43 in amelogenesis, we examined the expression and function of Cx43 in tooth development. Single-cell RNA-seq analysis and immunostaining showed that Cx43 is highly expressed in pre-secretory ameloblasts, differentiated ameloblasts, and odontoblasts. Further, we investigated the pathogenic mechanisms of ODDD by analyzing Cx43-null mice. These mice developed abnormal teeth with multiple dental epithelium layers. The expression of enamel matrix proteins such as ameloblastin (Ambn), which is critical for enamel formation, was significantly reduced in Cx43-null mice. TGF-β1 induces Ambn transcription in dental epithelial cells. The induction of Ambn expression by TGF-β1 depends on the density of the cultured cells. Cell culture at low densities reduces cell-cell contact and reduces the effect of TGF-β1 on Ambn induction. When cell density was high, Ambn expression by TGF-β1 was enhanced. This induction was inhibited by the gap junction inhibitors, oleamide, and 18α-grycyrrhizic acid and was also inhibited in cells expressing Cx43 mutations (R76S and R202H). TGF-β1-mediated phosphorylation and nuclear translocation of ERK1/2, but not Smad2/3, were suppressed by gap junction inhibitors. Cx43 gap junction activity is required for TGF-β1-mediated Runx2 phosphorylation through ERK1/2, which forms complexes with Smad2/3. In addition to its gap junction activity, Cx43 may also function as a Ca2+ channel that regulates slow Ca2+ influx and ERK1/2 phosphorylation. TGF-β1 transiently increases intracellular calcium levels, and the increase in intracellular calcium over a short period was not related to the expression level of Cx43. However, long-term intracellular calcium elevation was enhanced in cells overexpressing Cx43. Our results suggest that Cx43 regulates intercellular communication through gap junction activity by modulating TGF-β1-mediated ERK signaling and enamel formation.

DOI： 10.3389/fphys.2021.748574

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The epithelial-mesenchymal interactions are essential for the initiation and regulation of the development of teeth. Following the initiation of tooth development, numerous growth factors are secreted by the dental epithelium and mesenchyme that play critical roles in cellular differentiation. During tooth morphogenesis, the dental epithelial stem cells differentiate into several cell types, including inner enamel epithelial cells, which then differentiate into enamel matrix-secreting ameloblasts. Recently, we reported that the novel basic-helix-loop-helix transcription factor, AmeloD, is actively engaged in the development of teeth as a regulator of dental epithelial cell motility. However, the gene regulation mechanism of AmeloD is still unknown. In this study, we aimed to uncover the mechanisms regulating AmeloD expression during tooth development. By screening growth factors that are important in the early stages of tooth formation, we found that TGF-β1 induced AmeloD expression and ameloblast differentiation in the dental epithelial cell line, SF2. TGF-β1 phosphorylated ERK1/2 and Smad2/3 to induce AmeloD expression, whereas treatment with the MEK inhibitor, U0126, inhibited AmeloD induction. Promoter analysis of AmeloD revealed that the proximal promoter of AmeloD showed high activity in dental epithelial cell lines, which was enhanced following TGF-β1 stimulation. These results suggested that TGF-β1 activates AmeloD transcription via ERK1/2 phosphorylation. Our findings provide new insights into the mechanisms that govern tooth development.

DOI： 10.1002/jcp.30389

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A subpopulation of mesenchymal stem cells, developmentally derived from multipotent neural crest cells that form multiple facial tissues, resides within the dental pulp of human teeth. These stem cells show high proliferative capacity in vitro and are multipotent, including adipogenic, myogenic, osteogenic, chondrogenic, and neurogenic potential. Teeth containing viable cells are harvested via minimally invasive procedures, based on various clinical diagnoses, but then usually discarded as medical waste, indicating the relatively low ethical considerations to reuse these cells for medical applications. Previous studies have demonstrated that stem cells derived from healthy subjects are an excellent source for cell-based medicine, tissue regeneration, and bioengineering. Furthermore, stem cells donated by patients affected by genetic disorders can serve as in vitro models of disease-specific genetic variants, indicating additional applications of these stem cells with high plasticity. This review discusses the benefits, limitations, and perspectives of patient-derived dental pulp stem cells as alternatives that may complement other excellent, yet incomplete stem cell models, such as induced pluripotent stem cells, together with our recent data.

DOI： 10.3390/ijms22052269

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DOI： 10.1016/j.pdj.2020.08.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Society for Biochemistry & Molecular Biology (ASBMB)  

Dental enamel, the hardest tissue in the human body, is derived from dental epithelial cell ameloblast-secreted enamel matrices. Enamel mineralization occurs in a strictly synchronized manner along with ameloblast maturation in association with ion transport and pH balance, and any disruption of these processes results in enamel hypomineralization. G-protein coupled receptors (GPCRs) function as transducers of external signals by activating associated G-proteins and regulate cellular physiology. Tissue-specific GPCRs play important roles in organ development, though their activities in tooth development remains poorly understood. The present results show that the adhesion-GPCR <italic>Gpr115</italic> (<italic>Adgrf4</italic>) is highly and preferentially expressed in mature ameloblasts and plays a crucial role during enamel mineralization. To investigate the in vivo function of <italic>Gpr115</italic>, knockout (<italic>Gpr115</italic>-KO) mice were created and found to develop hypo-mineralized enamel, with a larger acidic area due to the dysregulation of ion composition. Transcriptomic analysis also revealed that deletion of <italic>Gpr115</italic> disrupted pH homeostasis and ion transport processes in enamel formation. In addition, in vitroanalyses using the dental epithelial cell line Cervical Loop-Derived Dental Epithelial (CLDE) cell demonstrated that <italic>Gpr115</italic> is indispensable for the expression of carbonic anhydrase 6 (<italic>Car6</italic>), which has a critical role in enamel mineralization. Furthermore, an acidic condition induced Car6 expression under the regulation of <italic>Gpr115</italic> in CLDE cells. Thus, we concluded that <italic>Gpr115</italic> plays an important role in enamel mineralization via regulation of Car6 expression in ameloblasts. The present findings indicate a novel function of <italic>Gpr115</italic> in ectodermal organ development and clarify the molecular mechanism of enamel formation.

DOI： 10.1074/jbc.ra120.014281

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.isci.2020.101329

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© Copyright © 2020 Nakamura, Iwamoto, Nakamura, Shindo, Saito, Yamada, Yamada, Fukumoto and Nakamura. Many genes encoding growth factors, receptors, and transcription factors are induced by the epithelial-mesenchymal interaction during tooth development. Recently, numerous functions of microRNAs (miRNAs) are reportedly involved in organogenesis and disease. miRNAs regulate gene expression by inhibiting translation and destabilizing mRNAs. However, the expression and function of miRNAs in tooth development remain poorly understood. This study aimed to analyze the expression of miRNAs produced during tooth development using a microarray system to clarify the role of miRNAs in dental development. miR-1 showed a unique expression pattern in the developing tooth. miR-1 expression in the tooth germ peaked on embryonic day 16.5, decreasing gradually on postnatal days 1 and 3. An in situ hybridization assay revealed that miR-1 is expressed at the cervical loop of the dental epithelium. The expression of miR-1 and connexin (Cx) 43, a target of miR-1, were inversely correlated both in vitro and in vivo. Knockdown of miR-1 induced the expression of Cx43 in dental epithelial cells. Interestingly, cells with miR-1 downregulation proliferated slower than the control cells. Immunocytochemistry revealed that Cx43 in cells with miR-1 knockdown formed both cell-cell gap junctions and hemichannels at the plasma membrane. Furthermore, the rate of ATP release was higher in cells with miR-1 knockdown than in control cells. Furthermore, Cx43 downregulation in developing molars was observed in Epiprofin-knockout mice, along with the induction of miR-1 expression. These results suggest that the expression pattern of Cx43 is modulated by miR-1 to control cell proliferation activity during dental epithelial cell differentiation.

DOI： 10.3389/fcell.2020.00156

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>Epithelial-mesenchymal interaction has critical roles for organ development including teeth, during which epithelial thickening and mesenchymal condensation are initiated by precise regulation of the signaling pathway. In teeth, neural crest-derived mesenchymal cells expressed PDGF receptors migrate and become condensed toward invaginated epithelium. To identify the molecular mechanism of this interaction, we explored the specific transcriptional start sites (TSSs) of tooth organs using cap analysis of gene expression (CAGE). We identified a tooth specific TSS detected in the chromosome 15qD1 region, which codes microRNA-875 (mir875). MiR875-5p is specifically expressed in dental mesenchyme during the early stage of tooth development. Furthermore, PRRX1/2 binds to the mir875 promoter region and enhances the expression of mir875. To assess the role of miR875-5p in dental mesenchyme, we transfected mimic miR875-5p into mouse dental pulp (mDP) cells, which showed that cell migration toward dental epithelial cells was significantly induced by miR875-5p via the PDGF signaling pathway. Those results also demonstrated that miR875-5p induces cell migration by inhibiting PTEN and STAT1, which are regulated by miR875-5p as part of post-transcriptional regulation. Together, our findings indicate that tooth specific miR875-5p has important roles in cell condensation of mesenchymal cells around invaginated dental epithelium and induction of epithelial-mesenchymal interaction.

DOI： 10.1038/s41598-020-61693-w

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Other Link： http://www.nature.com/articles/s41598-020-61693-w

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There is growing evidence showing that tight junctions play an important role in developing enamel. Claudins are one of the main components of tight junctions and may have pivotal functions in modulating various cellular events, such as regulating cell differentiation and proliferation. Mutations in CLDN10 of humans are associated with HELIX syndrome and cause enamel defects. However, current knowledge regarding the expression patterns of claudins and the function of Cldn10 during tooth development remains fragmented. In this study, we aimed to analyze the expression patterns of claudin family members during tooth development and to investigate the role of Cldn10 in amelogenesis. Using cap analysis gene expression of developing mouse tooth germs compared with that of the whole body, we found that Cldn1 and Cldn10 were highly expressed in the tooth. Furthermore, single-cell RNA-sequence analysis using 7-day postnatal Krt14-RFP mouse incisors revealed Cldn1 and Cldn10 exhibited distinct expression patterns. Cldn10 has two isoforms, Cldn10a and Cldn10b, but only Cldn10b was expressed in the tooth. Immunostaining of developing tooth germs revealed claudin-10 was highly expressed in the inner enamel epithelium and stratum intermedium. We also found that overexpression of Cldn10 in the dental epithelial cell line, SF2, induced alkaline phosphatase (Alpl) expression, a marker of maturated stratum intermedium. Our findings suggest that Cldn10 may be a novel stratum intermedium marker and might play a role in cytodifferentiation of stratum intermedium.

DOI： 10.3389/fcell.2020.595593

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Authorship：Last author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：(一社)日本障害者歯科学会  

一般社団法人日本障害者歯科学会は、平成20年に日本障害者歯科学会指導歯科衛生士(以下:指導DH)、日本歯科衛生士会認定衛生士(認定分野B:障害者歯科、以下:認定DH)制度を導入した。本制度の下、障害者歯科診療のための歯科衛生士養成の認定DH研修ガイドライン(以下:研修ガイドライン)が作成され、指導DHは本研修ガイドラインに沿って認定DH等の育成を行うことが望ましいとされている。しかし、歯科衛生士(以下:DH)の障害者歯科研修あるいは指導等において、本ガイドラインに提示されている項目の達成状況を検討した報告はない。そこで本研究は、研修ガイドラインに準じたアンケート調査を行うことで、障害者歯科に携わるDHのガイドライン項目の達成状況を把握することを目的とした。調査は、指導DH、認定DH、および認定資格を有していないDH(以下:一般DH)を対象とした。本調査において、指導DH、認定DH、一般DHの各研修ガイドラインの項目の達成状況の評価に特徴が認められた。研修ガイドラインの項目によっては、臨床経験だけでなく、時代背景や教育課程の違いが関与していることが示唆された。これらの結果より、DH育成において研修ガイドラインの項目ごとにその達成状況を調査分析することは、今後のDH教育に必要とされる項目の検討や、臨床現場で働くそれぞれの立場に応じたDHに対する研修項目の拡充を検討する際に活用できると考えられた。(著者抄録)

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Other Link： https://search.jamas.or.jp/index.php?module=Default&action=Link&pub_year=2020&ichushi_jid=J02489&link_issn=&doc_id=20201110230001&doc_link_id=10.14958%2Fjjsdh.41.277&url=https%3A%2F%2Fdoi.org%2F10.14958%2Fjjsdh.41.277&type=J-STAGE&icon=https%3A%2F%2Fjk04.jamas.or.jp%2Ficon%2F00007_3.gif

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

DOI： 10.3389/fcell.2020.00841

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Event date： 2021.2

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Authorship：Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

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Language：Japanese   Publisher：医歯薬出版(株)  

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Authorship：Lead author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

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Language：Japanese   Publisher：(公社)日本小児歯科学会  

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Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：(公社)日本小児歯科学会  

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