3D reconstructions of dental epithelium during Oryctolagus cuniculus embryonic development related to the publication "Morphological features of tooth development and replacement in the rabbit Oryctolagus cuniculus"

In wild-type (WT) mice, epithelial apoptosis is involved in reducing the embryonic tooth number and the mesial delimitation of the first molar. We investigated whether apoptosis could also be involved in the reduction of tooth number and the determination of anomalous tooth boundaries in tabby (Ta)/EDA mice. Using serial histological sections and computer-aided 3D reconstructions, we investigated epithelial apoptosis in the lower cheek dentition at embryonic days 14.5–17.5. In comparison with WT mice, apoptosis was increased mainly mesially in Ta dental epithelium from day 15.5. This apoptosis showed a similar mesio-distal extent in all 5 morphotypes (Ia,b,c and IIa,b) of Ta dentition and eliminated the first cheek tooth in morphotypes IIa,b. Apoptosis did not appear to play any causal role in positioning inter-dental gaps. Analysis of the present data suggests that the increased apoptosis in Ta mice is a consequence of impaired tooth development caused by a defect in segmentation of dental epithelium.

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BMP Activity Is Required for Tooth Development from the Lamina to Bud Stage

Journal of Dental Research ◽

10.1177/0022034512448660 ◽

2012 ◽

Vol 91 (7) ◽

pp. 690-695 ◽

Cited By ~ 40

Author(s):

Y. Wang ◽

L. Li ◽

Y. Zheng ◽

G. Yuan ◽

G. Yang ◽

...

Keyword(s):

Cell Proliferation ◽

Molecular Marker ◽

Tooth Development ◽

Tooth Germ ◽

Bmp Signaling ◽

Expression Of Genes ◽

Dental Epithelium ◽

Initiation Stage ◽

Transgenic Embryos ◽

Bmp Antagonist

Several Bmp genes are expressed in the developing mouse tooth germ from the initiation to the late-differentiation stages, and play pivotal roles in multiple steps of tooth development. In this study, we investigated the requirement of BMP activity in early tooth development by transgenic overexpression of the extracellular BMP antagonist Noggin. We show that overexpression of Noggin in the dental epithelium at the tooth initiation stage arrests tooth development at the lamina/early-bud stage. This phenotype is coupled with a significantly reduced level of cell proliferation rate and a down-regulation of Cyclin-D1 expression, specifically in the dental epithelium. Despite unaltered expression of genes known to be implicated in early tooth development in the dental mesenchyme and dental epithelium of transgenic embryos, the expression of Pitx2, a molecular marker for the dental epithelium, became down-regulated, suggesting the loss of odontogenic fate in the transgenic dental epithelium. Our results reveal a novel role for BMP signaling in the progression of tooth development from the lamina stage to the bud stage by regulating cell proliferation and by maintaining odontogenic fate of the dental epithelium.

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Wnt Production in Dental Epithelium Is Crucial for Tooth Differentiation

Journal of Dental Research ◽

10.1177/0022034519835194 ◽

2019 ◽

Vol 98 (5) ◽

pp. 580-588 ◽

Cited By ~ 5

Author(s):

Y. Xiong ◽

Y. Fang ◽

Y. Qian ◽

Y. Liu ◽

X. Yang ◽

...

Keyword(s):

Wnt Signaling ◽

Signaling Pathway ◽

Tooth Development ◽

Wnt Signaling Pathway ◽

Conditional Knockout ◽

Canonical Wnt Signaling ◽

Odontoblast Differentiation ◽

Wnt Ligands ◽

Dental Epithelium ◽

Canonical Wnt

The Wnt ligands display varied spatiotemporal expression in the epithelium and mesenchyme in the developing tooth. Thus far, the actions of these differentially expressed Wnt ligands on tooth development are not clear. Shh expression specifies the odontogenic epithelium during initiation and is consistently restricted to the dental epithelium during tooth development. In this study, we inactivate Wntless ( Wls), the key regulator for Wnt trafficking, by Shh-Cre to investigate how the Wnt ligands produced in the dental epithelium lineage act on tooth development. We find that conditional knockout of Wls by Shh-Cre leads to defective ameloblast and odontoblast differentiation. WlsShh-Cre teeth display reduced canonical Wnt signaling activity in the inner enamel epithelium and the underlying mesenchyme at the early bell stage, as exhibited by target gene expression and BAT-gal staining. The expression of Wnt5a and Wnt10b is not changed in WlsShh-Cre teeth. By contrast, Wnt10a expression is significantly increased in response to epithelial Wls deficiency. In addition, the expression of Hedgehog signaling pathway components Shh, Gli1, and Patched1 was greatly decreased in WlsShh-Cre teeth. Epithelial Wls loss of function in Shh lineage also leads to aberrant cell proliferation in dental epithelium and mesenchyme at embryonic day 16.5; however, the cell apoptosis is unaffected. Moreover, we find that Decorin and Col1a1, the key markers for odontoblast differentiation that are downregulated in WlsShh-Cre teeth, act as direct downstream targets of the canonical Wnt signaling pathway by chromatin immunoprecipitation analysis. Additionally, Decorin and Col1a1 expression can be increased by lithium chloride (LiCl) treatment in the in vitro tooth explants. Taken together, our results suggest that the spatial expression of Wnt ligands within the dental epithelial lineage regulates the differentiation of tooth structures in later stages.

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Smad7 Regulates Dental Epithelial Proliferation during Tooth Development

Journal of Dental Research ◽

10.1177/0022034519872487 ◽

2019 ◽

Vol 98 (12) ◽

pp. 1376-1385 ◽

Cited By ~ 3

Author(s):

Z. Liu ◽

T. Chen ◽

D. Bai ◽

W. Tian ◽

Y. Chen

Keyword(s):

Cell Cycle ◽

Cell Proliferation ◽

Cyclin D1 ◽

Transforming Growth Factor ◽

Tooth Development ◽

Tooth Germ ◽

Transforming Growth Factor Β ◽

Tooth Size ◽

Dental Epithelium ◽

Tooth Morphogenesis

Tooth morphogenesis involves dynamic changes in shape and size as it proceeds through the bud, cap, and bell stages. This process requires exact regulation of cell proliferation and differentiation. Smad7, a general antagonist against transforming growth factor–β (TGF-β) signaling, is necessary for maintaining homeostasis and proper functionality in many organs. While TGF-β signaling is widely involved in tooth morphogenesis, the precise role of Smad7 in tooth development remains unknown. In this study, we showed that Smad7 is expressed in the developing mouse molars with a high level in the dental epithelium but a moderate to weak level in the dental mesenchyme. Smad7 deficiency led to a profound decrease in tooth size primarily due to a severely compromised cell proliferation capability in the dental epithelium. Consistent with the tooth shrinkage phenotype, RNA sequencing (RNA-seq) analysis revealed that Smad7 ablation downregulated genes referred to epithelial cell proliferation and cell cycle G1/S phase transition, whereas the upregulated genes were involved in responding to TGF-β signaling and cell cycle arrest. Among these genes, the expression of Cdkn1a (encoding p21), a negative cell proliferation regulator, was remarkably elevated in parallel with the diminution of Ccnd1 encoding the crucial cell cycle regulator cyclin D1 in the dental epithelium. Meanwhile, the expression level of p-Smad2/3 was ectopically elevated in the developing tooth germ of Smad7 null mice, indicating the hyperactivation of the canonical TGF-β signaling. These effects were reversed by addition of TGF-β signaling inhibitor in cell cultures of Smad7−/− molar tooth germs, with rescued expression of cyclin D1 and cell proliferation rate. In sum, our studies demonstrate that Smad7 functions primarily as a positive regulator of cell proliferation via inhibition of the canonical TGF-β signaling during dental epithelium development and highlight a crucial role for Smad7 in regulating tooth size.

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Expression of Uchl1 in the Dental Epithelium during Mouse Tooth Development

Korean Journal of Physical Anthropology ◽

10.11637/kjpa.2007.20.3.235 ◽

2007 ◽

Vol 20 (3) ◽

pp. 235

Author(s):

Hyang Seok Kim ◽

Dong Won Kim ◽

Jin Young Yang ◽

Eun Ha Jang ◽

Tak Heun Kim ◽

...

Keyword(s):

Tooth Development ◽

Dental Epithelium

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Activated Epithelial FGF8 Signaling Induces Fused Supernumerary Incisors

Journal of Dental Research ◽

10.1177/00220345211046590 ◽

2021 ◽

pp. 002203452110465

Author(s):

Y. Chen ◽

Z. Wang ◽

C. Lin ◽

Y. Chen ◽

X. Hu ◽

...

Keyword(s):

Cell Fate ◽

De Novo ◽

Tooth Development ◽

Epithelial Stem Cells ◽

Unique Type ◽

Enamel Epithelium ◽

Enamel Mineralization ◽

Dental Epithelium ◽

Fgf8 Signaling ◽

The Impact

FGF8, which is specifically expressed in the dental epithelium prior to the E12.5 bud stage, is a key player during odontogenesis, being responsible for the initiation of tooth development. Here, to investigate the impact of persistent FGF8 signaling on tooth development, we forcibly activated FGF8 signaling in the dental epithelium after the bud stage by generating K14-Cre;R26R-Fg8 mice. We found that a unique type of fused supernumerary incisors is formed, although morphologically resembling the features of type II dens invaginatus in humans. Further analysis revealed that ectopically activated epithelial FGF8 alters the cell fate of the incisor lingual outer enamel epithelium, endowing it with odontogenic potential by the activation of several key tooth genes, including Pitx2, Sox2, Lef-1, p38, and Erk1/2, and induces de novo formation of an extra incisor crown lingually in parallel to the original one, leading to the formation of an extra incisor crown and fused with the original incisor eventually. Meanwhile, the overdosed epithelial FGF8 signaling dramatically downregulates the expression of mesenchymal Bmp4, leading to severely impaired enamel mineralization. Based on the location of the extra incisors, we propose that they are likely to be rescued replacement teeth. Our results further demonstrate the essential role of FGF8 signaling for tooth initiation and the establishment of progenitor cells of dental epithelial stem cells during development.

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FGFs and BMP4 induce both Msx1-independent and Msx1-dependent signaling pathways in early tooth development

Development ◽

10.1242/dev.125.21.4325 ◽

1998 ◽

Vol 125 (21) ◽

pp. 4325-4333 ◽

Cited By ~ 13

Author(s):

M. Bei ◽

R. Maas

Keyword(s):

Signaling Pathways ◽

Tooth Development ◽

Signaling Molecules ◽

Dependent Manner ◽

Wild Type ◽

Independent Manner ◽

Dental Lamina ◽

Bmp4 Expression ◽

Dental Epithelium ◽

Tooth Germs

During early tooth development, multiple signaling molecules are expressed in the dental lamina epithelium and induce the dental mesenchyme. One signal, BMP4, has been shown to induce morphologic changes in dental mesenchyme and mesenchymal gene expression via Msx1, but BMP4 cannot substitute for all the inductive functions of the dental epithelium. To investigate the role of FGFs during early tooth development, we examined the expression of epithelial and mesenchymal Fgfs in wild-type and Msx1 mutant tooth germs and tested the ability of FGFs to induce Fgf3 and Bmp4 expression in wild-type and Msx1 mutant dental mesenchymal explants. Fgf8 expression is preserved in Msx1 mutant epithelium while that of Fgf3 is not detected in Msx1 mutant dental mesenchyme. Moreover, dental epithelium as well as beads soaked in FGF1, FGF2 or FGF8 induce Fgf3 expression in dental mesenchyme in an Msx1-dependent manner. These results indicate that, like BMP4, FGF8 constitutes an epithelial inductive signal capable of inducing the expression of downstream signaling molecules in dental mesenchyme via Msx1. However, the BMP4 and FGF8 signaling pathways are distinct. BMP4 cannot induce Fgf3 nor can FGFs induce Bmp4 expression in dental mesenchyme, even though both signaling molecules can induce Msx1 and Msx1 is necessary for Fgf3 and Bmp4 expression in dental mesenchyme. In addition, we have investigated the effects of FGFs and BMP4 on the distal-less homeobox genes Dlx1 and Dlx2 and we have clarified the relationship between Msx and Dlx gene function in the developing tooth. Dlx1,Dlx2 double mutants exhibit a lamina stage arrest in maxillary molar tooth development (Thomas B. L., Tucker A. S., Qiu M., Ferguson C. A., Hardcastle Z., Rubenstein J. L. R. and Sharpe P. T. (1997) Development 124, 4811–4818). Although the maintenance of molar mesenchymal Dlx2 expression at the bud stage is Msx1-dependent, both the maintenance of Dlx1 expression and the initial activation of mesenchymal Dlx1 and Dlx2 expression during the lamina stage are not. Moreover, in contrast to the tooth bud stage arrest observed in Msx1 mutants, Msx1,Msx2 double mutants exhibit an earlier phenotype closely resembling the lamina stage arrest observed in Dlx1,Dlx2 double mutants. These results are consistent with functional redundancy between Msx1 and Msx2 in dental mesenchyme and support a model whereby Msx and Dlx genes function in parallel within the dental mesenchyme during tooth initiation. Indeed, as predicted by such a model, BMP4 and FGF8, epithelial signals that induce differential Msx1 and Msx2 expression in dental mesenchyme, also differentially induce Dlx1 and Dlx2 expression, and do so in an Msx1-independent manner. These results integrate Dlx1, Dlx2 and Fgf3 and Fgf8 into the odontogenic regulatory hierarchy along with Msx1, Msx2 and Bmp4, and provide a basis for interpreting tooth induction in terms of transcription factors which, individually, are necessary but not sufficient for the expression of downstream signals and therefore must act in specific combinations.

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Cbfa1 is required for epithelial-mesenchymal interactions regulating tooth development in mice

Development ◽

10.1242/dev.126.13.2911 ◽

1999 ◽

Vol 126 (13) ◽

pp. 2911-2920 ◽

Cited By ~ 8

Author(s):

R.N. D'Souza ◽

T. Aberg ◽

J. Gaikwad ◽

A. Cavender ◽

M. Owen ◽

...

Keyword(s):

Bone Formation ◽

Osteoblast Differentiation ◽

Tooth Development ◽

Enamel Organ ◽

Molecular Characteristics ◽

Cleidocranial Dysplasia ◽

Autosomal Dominant Disorder ◽

Tooth Formation ◽

Dental Epithelium

Osteoblasts and odontoblasts, cells that are responsible for the formation of bone and dentin matrices respectively, share several molecular characteristics. Recently, Cbfa1 was shown to be a critical transcriptional regulator of osteoblast differentiation. Mutations in this gene cause cleidocranial dysplasia (CCD), an autosomal dominant disorder in humans and mice characterized by defective bone formation. CCD also results in dental defects that include supernumerary teeth and delayed eruption of permanent dentition. The dental abnormalities in CCD suggest an important role for this molecule in the formation of dentition. Here we describe results of studies aimed at understanding the functions of Cbfa1 in tooth formation. RT-PCR and in situ hybridization analyses show that Cbfa1 has a unique expression pattern in dental mesenchyme from the bud to early bell stages during active epithelial morphogenesis. Unlike that observed in osteoblast differentiation, Cbfa1 is downregulated in fully differentiated odontoblasts and is surprisingly expressed in ectodermally derived ameloblasts during the maturation phase of enamel formation. The role of Cbfa1 in tooth morphogenesis is further illustrated by the misshapen and severely hypoplastic tooth organs in Cbfa1−/− mice. These tooth organs lacked overt odontoblast and ameloblast differentiation and normal dentin and enamel matrices. Epithelial-mesenchymal recombinants demonstrate that dental epithelium regulates mesenchymal Cbfa1 expression during the bud and cap stages and that these effects are mimicked by the FGFs but not by the BMPs as shown by our bead implantation assays. We propose that Cbfa1 regulates the expression of molecules in mesenchyme that act reciprocally on dental epithelium to control its growth and differentiation. Taken together, our data indicate a non-redundant role for Cbfa1 in tooth development that may be distinct from that in bone formation. In odontogenesis, Cbfa1 is not involved in the early signaling networks regulating tooth initiation and early morphogenesis but regulates key epithelial-mesenchymal interactions that control advancing morphogenesis and histodifferentiation of the epithelial enamel organ.

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Epithelial-mesenchymal interactions are required for msx 1 and msx 2 gene expression in the developing murine molar tooth

Development ◽

10.1242/dev.117.2.461 ◽

1993 ◽

Vol 117 (2) ◽

pp. 461-470 ◽

Cited By ~ 11

Author(s):

A.K. Jowett ◽

S. Vainio ◽

M.W. Ferguson ◽

P.T. Sharpe ◽

I. Thesleff

Keyword(s):

Gene Expression ◽

Tooth Development ◽

Homeobox Gene ◽

Oral Epithelium ◽

Tooth Formation ◽

Dental Papilla ◽

Tissue Interactions ◽

Dental Epithelium

Duplication of the msh-like homeobox gene of Drosophila may be related to the evolution of the vertebrate head. The murine homologues of this gene, msx 1 and msx 2 are expressed in the developing craniofacial complex including the branchial arches, especially in regions of epithelial-mesenchymal organogenesis including the developing tooth. By performing in vitro recombination experiments using homochronic dental and non-dental epithelial and mesenchymal tissues from E10 to E18 mouse embryos, we have found that the maintenance of homeobox gene expression in the tooth is dependent upon tissue interactions. In homotypic recombinants, dental-type tissue interactions occur, leading to expression of both genes in a manner similar to that seen during in vivo development. msx 1 is expressed exclusively in mesenchyme, both in the dental papilla and follicle. msx 2 is expressed in the dental epithelium and only in the mesenchyme of the dental papilla. In heterotypic recombinants, the dental epithelium is able to induce msx 1 expression in non-dental mesenchyme, this potential being lost at the bell stage. In these recombinants msx 2 was induced by presumptive dental epithelium prior to the bud stage but not thereafter. The expression of msx 1 and msx 2 in dental mesenchyme requires the presence of epithelium until the early bell stage. However, whereas non-dental, oral epithelium is capable of maintaining expression of msx 1 in dental mesenchyme throughout tooth development, induction of msx 2 was temporally restricted suggesting regulation by a specific epithelial-mesenchymal interaction related to the inductive events of tooth formation. msx 1 and msx 2, as putative transcription factors, may play a role in regulating the expression of other genes during tooth formation. We conclude that expression of msx 1 in jaw mesenchyme requires a non-specific epithelial signal, whereas msx 2 expression in either epithelium or mesenchyme requires reciprocal interactions between specialized dental cell populations.

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