Project description:Single-cell transcriptomics has revolutionized tooth biology by uncovering previously unexplored areas. The mouse is a widely used model for studying human tissues and diseases, including dental pulp tissues. While human and mouse molars share many similarities, mouse incisors differ significantly from human teeth due to their continuous growth throughout their lifespan. The extent to which studies on mouse teeth can be applied to human disease translation remains underexplored. By leveraging multiple single-cell datasets, we constructed a comprehensive dental pulp cell landscape to clarify tissue similarities and species-specific differences between humans and mice. Notably, we identified a distinct cell population, Sfrp2hi fibroblast progenitors, found exclusively in mouse incisors and the developing tooth root of human molars. These cells are uniquely present to sustain continuous tissue growth. Mechanistically, we found that the transcription factor Twist1, regulated by MAPK phosphorylation, binds to the Sfrp2 promoter and modulates Wnt signaling activation to maintain stem cell identities. Our research reveals a previously unrecognized subset of dental mesenchymal stem cells instrumental in tooth growth. This distinct subset is evolutionarily conserved in both humans and mice, offering valuable translational insights.
Project description:Evolutionary changes in vertebrates are linked to genetic alterations that often affect tooth-crown shape, which is a criterion of speciation events, especially in mammals. The Notch pathway is highly conserved between species and controls morphogenetic processes in most developing organs, including teeth. Epithelial loss of the Notch-ligand Jagged1 in developing mouse molars affects the location, size and interconnections of their cusps that lead to minor tooth-crown shape modifications convergent to those observed along Muridae evolution. RNA sequencing analysis revealed that these alterations are due to the modulation of more than 2000 genes and that Notch signaling is a hub for significant morphogenetic networks, such as Wnts and Fibroblast Growth Factors. The modeling of these tooth-crown changes in mutant mice, via a three-dimensional metamorphosis approach, allowed prediction of how Jagged1-associated mutations in humans could affect the morphology of their teeth. These results shed new light on Notch/Jagged1-mediated signaling as one of the crucial components for dental variations in evolution.
Project description:Mutations in MSX1 cause craniofacial developmental defects, including tooth agenesis, in humans and mice. Previous studies suggest that Msx1 activates Bmp4 expression in the developing tooth mesenchyme to drive early tooth organogenesis. Whereas Msx1−/− mice exhibit developmental arrest of all tooth germs at the bud stage, however, mice with neural crest-specific inactivation of Bmp4 (Bmp4ncko/ncko), which lack Bmp4 expression in the developing tooth mesenchyme, showed developmental arrest of only mandibular molars. We recently demonstrated that deletion of Osr2, which encodes a zinc finger transcription factor expressed in a lingual-to-buccal gradient in the developing tooth bud mesenchyme, rescued molar tooth morphogenesis in both Msx1−/− and Bmp4ncko/ncko mice. In this study, through RNA-seq analyses of the developing tooth mesenchyme in mutant and wildtype embryos, we found that Msx1 and Osr2 have opposite effects on expression of several secreted Wnt antagonists in the tooth bud mesenchyme. Remarkably, both Dkk2 and Sfrp2 exhibit Osr2-dependent preferential expression on the lingual side of the tooth bud mesenchyme and expression of both genes was up-regulated and expanded into the tooth bud mesenchyme in Msx1−/− and Bmp4ncko/ncko mutant embryos. We show that pharmacological activation of canonical Wnt signaling by either lithium chloride (LiCl) treatment or by inhibition of Dkk in utero was sufficient to rescue mandibular molar tooth morphogenesis in Bmp4ncko/ncko mice. Furthermore, whereas inhibition of Dkk alone was insufficient to rescue tooth morphogenesis in Msx1−/− mice, pharmacological inhibition of Dkk in combination with genetic inactivation of Sfrp2 and Sfrp3 rescued maxillary molar morphogenesis in Msx1−/− mice. Together, these data reveal a novel mechanism that the Bmp4-Msx1 pathway drives tooth organogenesis by activating Wnt signaling via regulation of the secreted Wnt antagonists.
Project description:Mutations in MSX1 cause craniofacial developmental defects, including tooth agenesis, in humans and mice. Previous studies suggest that Msx1 activates Bmp4 expression in the developing tooth mesenchyme to drive early tooth organogenesis. Whereas Msx1−/− mice exhibit developmental arrest of all tooth germs at the bud stage, however, mice with neural crest-specific inactivation of Bmp4 (Bmp4ncko/ncko), which lack Bmp4 expression in the developing tooth mesenchyme, showed developmental arrest of only mandibular molars. We recently demonstrated that deletion of Osr2, which encodes a zinc finger transcription factor expressed in a lingual-to-buccal gradient in the developing tooth bud mesenchyme, rescued molar tooth morphogenesis in both Msx1−/− and Bmp4ncko/ncko mice. In this study, through RNA-seq analyses of the developing tooth mesenchyme in mutant and wildtype embryos, we found that Msx1 and Osr2 have opposite effects on expression of several secreted Wnt antagonists in the tooth bud mesenchyme. Remarkably, both Dkk2 and Sfrp2 exhibit Osr2-dependent preferential expression on the lingual side of the tooth bud mesenchyme and expression of both genes was up-regulated and expanded into the tooth bud mesenchyme in Msx1−/− and Bmp4ncko/ncko mutant embryos. We show that pharmacological activation of canonical Wnt signaling by either lithium chloride (LiCl) treatment or by inhibition of Dkk in utero was sufficient to rescue mandibular molar tooth morphogenesis in Bmp4ncko/ncko mice. Furthermore, whereas inhibition of Dkk alone was insufficient to rescue tooth morphogenesis in Msx1−/− mice, pharmacological inhibition of Dkk in combination with genetic inactivation of Sfrp2 and Sfrp3 rescued maxillary molar morphogenesis in Msx1−/− mice. Together, these data reveal a novel mechanism that the Bmp4-Msx1 pathway drives tooth organogenesis by activating Wnt signaling via regulation of the secreted Wnt antagonists.
Project description:To identify genes heretofore undiscovered as critical players in the biogenesis of teeth, we have used microarray gene expression analysis of the developing mouse molar tooth (DMT) between 1 and 10 days postnatal to identify genes differentially expressed when compared to 16 control tissues (GEO accession # GSE1986). Of the top 100 genes exhibiting increased expression in the DMT, 29 were found to have been previously associated with tooth development. Differential expression of the remaining 71 genes not previously associated with tooth development was confirmed by qRT-PCR analysis. Further analysis of seven of the latter genes by mRNA in situ hybridization found that five were specific to the developing tooth in the craniofacial region (Rspo4, Papln, Amtn, Gja1, Maf). Of the remaining two, one was found to be more widely expressed (Sp7) and the other was found to be specific to the nasal serous gland, which is close to, but distinct from, the developing tooth (Vrm). Experiment Overall Design: mRNA from molar teeth extracted from Swiss Webster mouse pups between 1 and 10 days post-natal was pooled, labeled, and hybridized in quadruplicate to Affymetrix Mouse Genome Expression 430 2.0 microarrays. This data was compared to that of 16 control tissues (GEO accession # GSE1986) to identify genes differentially expressed in the DMT mRNA.
Project description:Throughout the various stages of tooth development, reciprocal epithelial-mesenchymal interactions are the driving force, for instance crucially involved in the differentiation of mature enamel-forming ameloblasts and dentin-producing odontoblasts. Here we established mouse tooth ‘assembloids’, comprised of tooth organoid-derived dental epithelial cells (from mouse molars and incisors) cultured together with molar dental pulp stem cells (DPSCs), to mimic these developmental interactions. Assembloids from both tooth types were grown both in basal- and differentiation-inducing conditions. Single cell transcriptomics analysis was applied to in detail characterize and validate the newly developed mouse tooth assembloid model and evaluate the induced differentiation processes.
Project description:Numerous genes that play important regulative roles during tooth development in mice have been identified. However, very little is known about gene expression and function in human odontogenesis. We used microarrays to detail the global programme of gene expression underlying tooth development and identified distinct classes of up-regulated genes during in the tooth germs. Tooth germs of molar, incisor, and canine at the cap stage were dissected, respectively, from 12-week-old human embryonic oral cavity for RNA extraction and hybridization on Affymetrix microarrays. We sought to screen for the genes that are strongly expressed in the dental tissues and analysis if these genes related to mammalian tooth development and tooth abnormalities.