Background:The role of dental epithelium in stem cell differentiation has not been clearly elucidated. Results: SP cells differentiated into odontoblasts by epithelial BMP4, whereas iPS cells differentiated into ameloblasts when cultured with dental epithelium. Conclusion: Stem cells can be induced to odontogenic cell fates when co-cultured with dental epithelium. Significance: This is the first report to show induction of ameloblasts from iPS cells.

Similar to embryonic stem cells, induced pluripotent stem (iPS) cells can differentiate into various cell types upon appropriate induction, and thus, may be valuable cell sources for regenerative medicine. However, iPS cells have not been reported to differentiate into odontogenic cells for tooth regeneration. Here we demonstrated that neural crest-like cells (NCLC) derived from mouse iPS cells have the potential to differentiate into odontogenic mesenchymal cells. We developed an efficient culture protocol to induce the differentiation of mouse iPS cells into NCLC. We confirmed that the cells exhibited neural crest (NC) cell markers as evidenced by immunocytochemistry, flow cytometry, and real-time reverse transcription-polymerase chain reaction. Further, in recombination cultures of NCLC and mouse dental epithelium, NCLC exhibited a gene expression pattern involving dental mesenchymal cells. Some NCLC also expressed dentin sialoprotein. Conditioned medium of mouse dental epithelium cultures further enhanced the differentiation of NCLC into odontoblasts. These results suggest that iPS cells are useful cell sources for tooth regeneration and tooth development studies.

During tooth development, dental epithelial cells interact with extracellular matrix components, such as the basement membrane and enamel matrix. Ameloblastin, an enamel matrix protein, plays a crucial role in maintaining the ameloblast differentiation state and is essential for enamel formation. Ameloblastin-null mice developed severe enamel hypoplasia. In mutant mice, dental epithelial cells started to differentiate into ameloblasts, but ameloblasts soon lost cell polarity, proliferated, and formed multiple cell layers, indicative of some aspects of preameloblast phenotypes. In addition, the expression of amelogenin, another component of the enamel matrix, was specifically reduced in mutant ameloblasts. More than 20% of amelobastin-null mice developed odontogenic tumors. We also found that recombinant ameloblastin specifically bound to ameloblasts and inhibited proliferation of dental epithelial cells. These results suggest that ameloblastin is an important regulator to maintain the differentiation state of ameloblasts.

Dental epithelial stem cells give rise to four types of dental epithelial cells: inner enamel epithelium (IEE), outer enamel epithelium (OEE), stratum intermedium (SI), and stellate reticulum (SR). IEE cells further differentiate into enamel-forming ameloblasts, which play distinct roles, and are essential for enamel formation. These are conventionally classified by their shape, although their transcriptome and biological roles are yet to be fully understood. Here, we aimed to use single-cell RNA sequencing to clarify the heterogeneity of dental epithelial cell types. Unbiased clustering of 6,260 single cells from incisors of postnatal day 7 mice classified them into two clusters of ameloblast, IEE/OEE, SI/SR, and two mesenchymal populations. Secretory-stage ameloblasts expressed Amel and Enam were divided into Dspp + and Ambn + ameloblasts. Pseudo-time analysis indicated Dspp + ameloblasts differentiate into Ambn + ameloblasts. Further, Dspp and Ambn could be stage-specific markers of ameloblasts. Gene ontology analysis of each cluster indicated potent roles of cell types: OEE in the regulation of tooth size and SR in the transport of nutrients. Subsequently, we identified novel dental epithelial cell marker genes, namely Pttg1 , Atf3 , Cldn10 , and Krt15 . The results not only provided a resource of transcriptome data in dental cells but also contributed to the molecular analyses of enamel formation.

AMBN (ameloblastin)is an enamel matrix protein that regulates cell adhesion, proliferation, and differentiation of ameloblasts. In AMBN-deficient mice, ameloblasts are detached from the enamel matrix, continue to proliferate, and form a multiple cell layer; often, odontogenic tumors develop in the maxilla with age. However, the mechanism of AMBN functions in these biological processes remains unclear. By using recombinant AMBN proteins, we found that AMBN had heparin binding domains at the C-terminal half and that these domains were critical for AMBN binding to dental epithelial cells. Overexpression of fulllength AMBN protein inhibited proliferation of human ameloblastoma AM-1 cells, but overexpression of heparin binding domain-deficient AMBN protein had no inhibitory effect. In full-length AMBN-overexpressing AM-1 cells, the expression of Msx2, which is involved in the dental epithelial progenitor phenotype, was decreased, whereas the expression of cell proliferation inhibitors p21 and p27 was increased. We also found that the expression of enamelin, a marker of differentiated ameloblasts, was induced, suggesting that AMBN promotes odontogenic tumor differentiation. Thus, our results suggest that AMBN promotes cell binding through the heparin binding sites and plays an important role in preventing odontogenic tumor development by suppressing cell proliferation and maintaining differentiation phenotype through Msx2, p21, and p27.The extracellular matrix provides structural support for cells and regulates cell proliferation, migration, differentiation, and apoptosis for tissue development and homeostasis (1). The extracellular matrix also plays a crucial role in pathological processes and diseases, such as wound healing, tumorigenesis, and cancer development (2, 3). AMBN (ameloblastin), also known as amelin and sheathlin, is a tooth-specific extracellular matrix and the most abundant non-amelogenin enamel matrix protein (4 -6). AMBN is expressed primarily by ameloblasts, which are differentiated from the oral ectoderm and form a polarized single cell layer underlying the enamel matrix. In a previous study, we created Ambn-null mice and demonstrated that AMBN is required for cell attachment and polarization and for maintaining the differentiation state of ameloblasts and is essential for enamel formation (3). Overexpression of Ambn in transgenic mice causes abnormal enamel crystallite formation and enamel rod morphology (7). These results suggest that enamel formation and rod morphology are influenced by temporal and spatial expressions of AMBN and imply that the AMBN gene locus may be involved in the etiology of a number of cases of undiagnosed hereditary amelogenesis imperfecta (8). Further, it was reported that recombinant AMBN enhances pulpal wound healing and reparative dentine formation following pulpotomy procedures, suggesting that it functions as a signal molecule in epithelial-mesenchymal interactions (9).We previously reported that about 20% of Ambn-null mice developed an odontogenic tumor of dental ep...

A coordinated reciprocal interaction between epithelium and mesenchyme is involved in salivary gland morphogenesis. The submandibular glands (SMGs) of Wnt1-Cre/R26R mice have been shown positive for mesenchyme, whereas the epithelium is ␤-galactosidase-negative, indicating that most mesenchymal cells are derived from cranial neural crest cells. Platelet-derived growth factor (PDGF) receptor ␣ is one of the markers of neural crest-derived cells. In this study, we analyzed the roles of PDGFs and their receptors in the morphogenesis of mouse SMGs. PDGF-A was shown to be expressed in SMG epithelium, whereas PDGF-B, PDGFR␣, and PDGFR␤ were expressed in mesenchyme. Exogenous PDGF-AA and -BB in SMG organ cultures demonstrated increased levels of branching and epithelial proliferation, although their receptors were found to be expressed in mesenchyme. In contrast, short interfering RNA for Pdgfa and -b as well as neutralizing antibodies for PDGF-AB and -BB showed decreased branching. PDGF-AA induced the expression of the fibroblast growth factor genes Fgf3 and -7, and PDGF-BB induced the expression of Fgf1, -3, -7, and -10, whereas short interfering RNA for Pdgfa and Pdgfb inhibited the expression of Fgf3, -7, and -10, indicating that PDGFs regulate Fgf gene expression in SMG mesenchyme. The PDGF receptor inhibitor AG-17 inhibited PDGF-induced branching, whereas exogenous FGF7 and -10 fully recovered. Together, these results indicate that fibroblast growth factors function downstream of PDGF signaling, which regulates Fgf expression in neural crest-derived mesenchymal cells and SMG branching morphogenesis. Thus, PDGF signaling is a possible mechanism involved in the interaction between epithelial and neural crest-derived mesenchyme.

Background Esketamine nasal spray (Spravato) in conjunction with oral antidepressants (ADs) is approved in the European Union, United States, and other markets for treatment-resistant depression (TRD). Efficacy, safety, and tolerability of esketamine nasal spray in Japanese patients with TRD needs to be assessed. Methods This Phase 2b, randomized, double-blind (DB), placebo-controlled study was conducted in adult Japanese patients with TRD meeting the Diagnostic and Statistical Manual of Mental Disorders (fifth edition) criteria of major depressive disorder with nonresponse to ≥ 1 but < 5 different ADs in the current episode at screening. Patients were treated with a new oral AD for 6 weeks (prospective lead-in phase); nonresponders were randomized (2:1:1:1) to placebo or esketamine (28-, 56-, or 84-mg) nasal spray along with the continued use of AD for 4 weeks (DB induction phase). Responders (≥50% reduction from baseline in the Montgomery-Asberg Depression Rating Scale [MADRS] total score) from the DB induction phase continued into the 24-week posttreatment phase and patients who relapsed could participate in a 4-week open-label (OL) second induction (flexibly-dosed esketamine). The primary efficacy endpoint, change from baseline in the MADRS total score at Day 28 in the DB induction phase, was based on mixed-effects model using repeated measures pairwise comparisons using a Dunnett adjustment. Results Of the 202 patients randomized in the DB induction phase (esketamine [n = 122] or placebo [n = 80]), the MADRS total scores decreased from baseline to Day 28 of the DB induction phase (− 15.2, − 14.5, − 15.1, and − 15.3 for esketamine 28 mg, 56 mg, 84 mg, and placebo groups, respectively), indicating an improvement in depressive symptoms; however, the difference between the esketamine and placebo groups was not statistically significant. The most common treatment-emergent adverse events during the DB induction phase in the combined esketamine group (incidences ranging from 12.3 to 41.0%) were blood pressure increased, dissociation, dizziness, somnolence, nausea, hypoaesthesia, vertigo, and headache; the incidence of each of these events was > 2-fold higher than the corresponding incidence in the placebo group. Conclusions Efficacy of esketamine plus oral AD in Japanese TRD patients was not established; further investigation is warranted. All esketamine doses were safe and tolerated. Trial registration ClinicalTrials.gov Identifier: NCT02918318. Registered: 28 September 2016.

Neurotrophic factors play an important role in the development and maintenance of not only neural but also nonneural tissues. Several neurotrophic factors are expressed in dental tissues, but their role in tooth development is not clear. Here, we report that neurotrophic factor neurotrophin (NT)-4 promotes differentiation of dental epithelial cells and enhances the expression of enamel matrix genes. Dental epithelial cells from 3-day-old mice expressed NT-4 and three variants of TrkB receptors for neurotrophins (full-length TrkB-FL and truncated TrkB-T1 and -T2). Dental epithelial cell line HAT-7 expressed these genes, similar to those in dental epithelial cells. We found that NT-4 reduced HAT-7 cell proliferation and induced the expression of enamel matrix genes, such as ameloblastin (Ambn). Transfection of HAT-7 cells with the TrkB-FL expression construct enhanced the NT-4-mediated induction of Ambn expression. This enhancement was blocked by K252a, an inhibitor for Trk tyrosine kinases. Phosphorylation of ERK1/2, a downstream molecule of TrkB, was induced in HAT-7 cells upon NT-4 treatment. TrkB-FL but not TrkB-T1 transfection increased the phosphorylation level of ERK1/2 in NT-4-treated HAT-7 cells. These results suggest that NT-4 induced Ambn expression via the TrkB-MAPK pathway. The p75 inhibitor TAT-pep5 decreased NT-4-mediated induction of the expression of Ambn, TrkB-FL, and TrkB-T1, suggesting that both high affinity and low affinity neurotrophin receptors were required for NT-4 activity. We found that NT-4-null mice developed a thin enamel layer and had a decrease in Ambn expression. Our results suggest that NT-4 regulates proliferation and differentiation of the dental epithelium and promotes production of the enamel matrix.Mammalian development is a complex and highly orchestrated process that involves intricate cross-talk between growth factors and other regulatory molecules. The interaction between the epithelium and mesenchyme induces specific molecular and cellular changes that lead to organogenesis. These interactions are particularly crucial during the initiation of the development of ectodermal organs, such as teeth, skin, hair, and mammary and prostate glands (1). The oral epithelium provides the initial signaling for neuronal crest-derived ectomesenchyme development, and then both tissues interact during tooth formation. Various transcription factors, growth factors, and extracellular matrices are expressed by enamel matrix-producing ameloblasts during tooth development (2-4). The principal components of the enamel matrix that are synthesized by secretory ameloblasts can be classified into two major categories, amelogenin (Amel) 2 and non-Amel, which includes ameloblastin (Ambn) and enamelin (Enam) (5). Ambn, also known as amelin or sheathlin, is a tooth-specific glycoprotein that represents the most abundant non-Amel enamel matrix protein. We previously created Ambn-null mice, which develop severe enamel hypoplasia in which ameloblasts detached from the matrix, lost cell polarity, resumed ...