TNF signaling via the ligand-receptor pair ectodysplasin and edar controls the function of epithelial signaling centers and is regulated by Wnt and activin during tooth organogenesis

Postnatal Effects of Prenatal Exposure to Periodontitis in Wistar Rat Pups

BACKGROUND

Periodontitis during pregnancy is associated with preterm births and low birth weight. This study evaluated how experimental periodontitis induced in female rats impacts the physical development, motor skills, and dental and maxillary development of their pups.

METHOD

Pregnant Wistar rats were divided into the control group (C, n = 12) and the induced periodontal disease group (P, n = 12). Periodontitis was induced in the first maxillary molars 14 days before mating. Delivery occurred on the 21st day of gestation, and four offspring from each litter were evaluated (n = 48) for 30 days to verify physical and reflexological development. The first molars and alveolar bone were evaluated in 30-day-old animals using X-ray microtomography and histopathological analysis. Differences between groups were considered significant if p < 0.05.

RESULTS

The P group had a lower number of live offspring (9.4 ± 1.9 pups) than the C group (11.4 ± 2.1, p = 0.03). The P offspring group showed lower weight (F = 1.17; p < 0.0001) and length (F = 3.47; p < 0.0001), as well as delayed hair growth (p = 0.01) and eruption of incisors (p = 0.001). The P offspring presented a delay in the motor development of postural straightening (p = 0.01), adult gait (p = 0.01), and negative geotaxis (p = 0.01). No developmental anomalies were observed in the maxillary first molars; however, the P group showed a decreased number (p = 0.02) and increased distance (p = 0.007) between the maxillary bone trabeculae.

CONCLUSIONS

Periodontitis delayed physical and reflexological development and impaired maxillary bone quality in offspring.

Ectodermal dysplasia: a narrative review of the clinical and biological aspects relevant to oral health

Ectodermal dysplasias (ED) are disorders that affect ectodermal-derived tissues during embryonic development. These disorders occur when the ectoderm, the outermost layer of embryonic tissue does not develop normally. Patients present abnormalities of two or more ectoderm-derived structures and the clinical presentation can vary greatly depending on the type a patient has. The authors compiled and provided their perspective on articles describing the classification, molecular signaling pathways, systemic and dental implications, genetic diagnosis and dental treatment considerations for patients with ED. Emphasis was placed on the main signaling pathways affecting tooth development and the relevant signs that ED patients can present including dental anomalies. Sources included original or review articles written in English that had an ED focus from PubMed and also information available in National Foundation of Ectodermal Dysplasias website. A broad and flexible narrative review is provided regarding ED which represents a diverse array of systemic symptoms that are often present with dental-related issues. The genetic diagnosis of this condition has evolved significantly during the last decade but is still an adjunct to clinical presentation. The treatment of ED involves a multidisciplinary team encompassing primary care physicians, pediatricians, nutritionists, speech therapists, dental professionals, and geneticists. Evidence from the last decade has significantly expanded our understanding of the classification and molecular signaling pathways involved in the etiology of ED. The dental professional is a critical, essential part of the team of healthcare professionals and often the first step involved in providing personalized and humanistic care and better quality of life to the patients affected by this condition.

A Chemically Defined Culture for Tooth Reconstitution

It is known for decades that dental epithelium and mesenchyme can reconstitute and regenerate a functional tooth. However, the mechanism of tooth reconstitution remains largely unknown due to the lack of an efficient in vitro model. Here, a chemically defined culture system is established that supports tooth reconstitution, further development with normal anatomy, and prompt response to chemical interference in key developmental signaling pathways, termed as toothoids. By using such a system, it is discovered that, during reconstitution, instead of resetting the developmental clock, dental cells reorganized and restarted from the respective developmental stage where they are originally isolated. Moreover, co-stimulation of Activin A and Hedgehog/Smoothened agonist (SAG) sustained the initial induction of tooth fate from the first branchial arch, which would be otherwise quickly lost in culture. Furthermore, activation of Bone Morphogenetic Protein (BMP) signaling triggered efficient enamel formation in the late-stage toothoids, without affecting the normal development of ameloblasts. Together, these data highlight the toothoid culture as a powerful tool to dissect the molecular mechanisms of tooth reconstitution and regeneration.

A Missense Mutation in the Collagen Triple Helix of EDA Is Associated with X-Linked Recessive Hypohidrotic Ectodermal Dysplasia in Fleckvieh Cattle

Mutations within the ectodysplasin A (EDA) gene have been associated with congenital hypotrichosis and anodontia (HAD/XHED) in humans, mice, dogs and cattle. We identified a three-generation family of Fleckvieh cattle with male calves exhibiting clinical and histopathological signs consistent with an X-linked recessive HAD (XHED). Whole genome and Sanger sequencing of cDNA showed a perfect association of the missense mutation g.85716041G>A (ss2019497443, rs1114816375) within the EDA gene with all three cases following an X-linked recessive inheritance, but normal EDAR and EDARADD. This mutation causes an exchange of glycine (G) with arginine (R) at amino acid position 227 (p.227G>R) in the second collagen triple helix repeat domain of EDA. The EDA variant was associated with a significant reduction and underdevelopment of hair follicles along with a reduced outgrowth of hairs, a complete loss of seromucous nasolabial and mucous tracheal and bronchial glands and a malformation of and reduction in number of teeth. Thermostability of EDA G227R was reduced, consistent with a relatively mild hair and tooth phenotype. However, incisors and canines were more severely affected in one of the calves, which correlated with the presence of a homozygous missense mutation of RNF111 (g.51306765T>G), a putative candidate gene possibly associated with tooth number in EDA-deficient Fleckvieh calves.

The EDA/EDAR/NF-κB pathway in non-syndromic tooth agenesis: A genetic perspective

Non-syndromic tooth agenesis (NSTA) is one of the most common dental developmental malformations affected by genetic factors predominantly. Among all 36 candidate genes reported in NSTA individuals, EDA, EDAR, and EDARADD play essential roles in ectodermal organ development. As members of the EDA/EDAR/NF-κB signaling pathway, mutations in these genes have been implicated in the pathogenesis of NSTA, as well as hypohidrotic ectodermal dysplasia (HED), a rare genetic disorder that affects multiple ectodermal structures, including teeth. This review provides an overview of the current knowledge on the genetic basis of NSTA, with a focus on the pathogenic effects of the EDA/EDAR/NF-κB signaling pathway and the role of EDA, EDAR, and EDARADD mutations in developmental tooth defects. We also discuss the phenotypic overlap and genetic differences between NSTA and HED. Ultimately, this review highlights the importance of genetic analysis in diagnosing and managing NSTA and related ectodermal disorders, and the need for ongoing research to improve our understanding of these conditions.

Eda controls the size of the enamel knot during incisor development

Ectodysplasin (Eda) plays important roles in both shaping the developing tooth and establishing the number of teeth within the tooth row. Sonic hedgehog (Shh) has been shown to act downstream of Eda and is involved in the initiation of tooth development. Eda-/- mice possess hypoplastic and hypomineralized incisors and show changes in tooth number in the molar region. In the present study we used 3D reconstruction combined with expression analysis, cell lineage tracing experiments, and western blot analysis in order to investigate the formation of the incisor germs in Eda-/- mice. We show that a lack of functional Eda protein during early stages of incisor tooth germ development had minimal impact on development of the early expression of Shh in the incisor, a region proposed to mark formation of a rudimental incisor placode and act as an initiating signalling centre. In contrast, deficiency of Eda protein had a later impact on expression of Shh in the primary enamel knot of the functional tooth. Eda-/- mice had a smaller region where Shh was expressed, and a reduced contribution from Shh descendant cells. The reduction in the enamel knot led to the formation of an abnormal enamel organ creating a hypoplastic functional incisor. Eda therefore appears to influence the spatial formation of the successional signalling centres during odontogenesis.

Tooth number abnormality: from bench to bedside

Tooth number abnormality is one of the most common dental developmental diseases, which includes both tooth agenesis and supernumerary teeth. Tooth development is regulated by numerous developmental signals, such as the well-known Wnt, BMP, FGF, Shh and Eda pathways, which mediate the ongoing complex interactions between epithelium and mesenchyme. Abnormal expression of these crutial signalling during this process may eventually lead to the development of anomalies in tooth number; however, the underlying mechanisms remain elusive. In this review, we summarized the major process of tooth development, the latest progress of mechanism studies and newly reported clinical investigations of tooth number abnormality. In addition, potential treatment approaches for tooth number abnormality based on developmental biology are also discussed. This review not only provides a reference for the diagnosis and treatment of tooth number abnormality in clinical practice but also facilitates the translation of basic research to the clinical application.

The Role of Ectodysplasin A on the Ocular Surface Homeostasis

Ectodysplasin A (EDA), a ligand of the TNF family, plays an important role in maintaining the homeostasis of the ocular surface. EDA is necessary for the development of the meibomian gland, the lacrimal gland, as well as the proliferation and barrier function of the corneal epithelium. The mutation of EDA can induce the destruction of the ocular surface resulting in keratopathy, abnormality of the meibomian gland and maturation of the lacrimal gland. Experimental animal studies showed that a prenatal ultrasound-guided intra-amniotic injection or postnatal intravenous administration of soluble recombinant EDA protein can efficiently prevent the development of ocular surface abnormalities in EDA mutant animals. Furthermore, local application of EDA could restore the damaged ocular surface to some extent. Hence, a recombinant EDA-based therapy may serve as a novel paradigm to treat ocular surface disorders, such as meibomian gland dysfunction and corneal epithelium abnormalities.

Parallels in signaling between development and regeneration in ectodermal organs

Ectodermal organs originate from the outermost germ layer of the developing embryo and include the skin, hair, tooth, nails, and exocrine glands. These organs develop through tightly regulated, sequential and reciprocal epithelial-mesenchymal crosstalk, and they eventually assume various morphologies and functions while retaining the ability to regenerate. As with many other tissues in the body, the development and morphogenesis of these organs are regulated by a set of common signaling pathways, such as Shh, Wnt, Bmp, Notch, Tgf-β, and Eda. However, subtle differences in the temporal activation, the multiple possible combinations of ligand-receptor activation, the various cofactors, as well as the underlying epigenetic modulation determine how each organ develops into its adult form. Although each organ has been studied separately in considerable detail, the mechanisms underlying the parallels and differences in signaling that regulate their development have rarely been investigated. First, we will use the tooth, the hair follicle, and the mammary gland as representative ectodermal organs to explore how the development of signaling centers and establishment of stem cell populations influence overall growth and morphogenesis. Then we will compare how some of the major signaling pathways (Shh, Wnt, Notch and Yap/Taz) differentially regulate developmental events. Finally, we will discuss how signaling regulates regenerative processes in all three.

The developmental origins of heterodonty and acrodonty as revealed by reptile dentitions

Despite the exceptional diversity and central role of dentitions in vertebrate evolution, many aspects of tooth characters remain unknown. Here, we exploit the large array of dental phenotypes in acrodontan lizards, including EDA mutants showing the first vertebrate example of positional transformation in tooth identity, to assess the developmental origins and evolutionary patterning of tooth types and heterodonty. We reveal that pleurodont versus acrodont dentition can be determined by a simple mechanism, where modulation of tooth size through EDA signaling has major consequences on dental formula, thereby providing a new flexible tooth patterning model. Furthermore, such implication of morphoregulation in tooth evolution allows predicting the dental patterns characterizing extant and fossil lepidosaurian taxa at large scale. Together, the origins and diversification of tooth types, long a focus of multiple research fields, can now be approached through evo-devo approaches, highlighting the importance of underexplored dental features for illuminating major evolutionary patterns.

Understanding the impact of missense mutations on the structure and function of the EDA gene in X-linked hypohidrotic ectodermal dysplasia: A bioinformatics approach

X-linked hypohidrotic dysplasia (XLHED), caused by mutations in the EDA gene, is a rare genetic disease that affects the development and function of the teeth, hair, nails, and sweat glands. The structural and functional consequences of caused by an ectodysplasin-A (EDA) mutations on protein phenotype, stability, and posttranslational modifications (PTMs) have not been well investigated. The present investigation involves five missense mutations that cause XLHED (L56P, R155C, P220L, V251M, and V322A) in different domains of EDA (TM, furin, collagen, and tumor necrosis factor [TNF]) from previously published papers. The deleterious nature of EDA mutant variants was identified using several computational algorithm tools. The point mutations induce major drifts in the structural flexibility of EDA mutant variants and have a negative impact on their stability, according to the 3D protein modeling tool assay. Using the molecular docking technique, EDA/EDA variants were docked to 10 EDA interacting partners, retrieved from the STRING database. We found a novel biomarker CD68 by molecular docking analysis, suggesting all five EDA variants had lower affinity for EDAR, EDA2R, and CD68, implying that they would affect embryonic signaling between the ectodermal and mesodermal cell layers. In silico research such as gene ontology, subcellular localization, protein-protein interaction, and PTMs investigations indicates major functional alterations would occur in EDA variants. According to molecular simulations, EDA variants influence the structural conformation, compactness, stiffness, and function of the EDA protein. Further studies on cell line and animal models might be useful in determining their specific roles in functional annotations.

Novel truncating mutations in CTNND1 cause a dominant craniofacial and cardiac syndrome

CTNND1 encodes the p120-catenin (p120) protein, which has a wide range of functions, including the maintenance of cell–cell junctions, regulation of the epithelial-mesenchymal transition and transcriptional signalling. Due to advances in next-generation sequencing, CTNND1 has been implicated in human diseases including cleft palate and blepharocheilodontic (BCD) syndrome albeit only recently. In this study, we identify eight novel protein-truncating variants, six de novo, in 13 participants from nine families presenting with craniofacial dysmorphisms including cleft palate and hypodontia, as well as congenital cardiac anomalies, limb dysmorphologies and neurodevelopmental disorders. Using conditional deletions in mice as well as CRISPR/Cas9 approaches to target CTNND1 in Xenopus, we identified a subset of phenotypes that can be linked to p120-catenin in epithelial integrity and turnover, and additional phenotypes that suggest mesenchymal roles of CTNND1. We propose that CTNND1 variants have a wider developmental role than previously described and that variations in this gene underlie not only cleft palate and BCD but may be expanded to a broader velocardiofacial-like syndrome.

Tumor Necrosis Factor Alpha Signaling and Organogenesis

Tumor necrosis factor alpha (TNF-α) plays important roles in processes such as immunomodulation, fever, inflammatory response, inhibition of tumor formation, and inhibition of viral replication. TNF-α and its receptors are ubiquitously expressed in developing organs and they regulate the survival, proliferation, and apoptosis of embryonic stem cells (ESCs) and progenitor cells. TNF-α is an important inflammatory factor that also regulates the inflammatory response during organogenesis, and its cytotoxic effects can interfere with normal developmental processes, even leading to the onset of diseases. This review summarizes the various roles of TNF-α in organogenesis in terms of its secreting pattern, concentration-dependent activities, and interactions with other signaling pathways. We also explored new potential functions of TNF-α.

Evolutionary developmental genetics of teeth and odontodes in jawed vertebrates: a perspective from the study of elasmobranchs

Most extant vertebrates display a high variety of tooth and tooth-like organs (odontodes) that vary in shape, position over the body and nature of composing tissues. The development of these structures is known to involve similar genetic cascades and teeth and odontodes are believed to share a common evolutionary history. Gene expression patterns have previously been compared between mammalian and teleost tooth development but we highlight how the comparative framework was not always properly defined to deal with different tooth types or tooth developmental stages. Larger-scale comparative analyses also included cartilaginous fishes: sharks display oral teeth and dermal scales for which the gene expression during development started to be investigated in the small-spotted catshark Scyliorhinus canicula during the past decade. We report several descriptive approaches to analyse the embryonic tooth and caudal scale gene expressions in S. canicula. We compare these expressions wih the ones reported in mouse molars and teleost oral and pharyngeal teeth and highlight contributions and biases that arise from these interspecific comparisons. We finally discuss the evolutionary processes that can explain the observed intra and interspecific similarities and divergences in the genetic cascades involved in tooth and odontode development in jawed vertebrates.

The human EDAR 370V/A polymorphism affects tooth root morphology potentially through the modification of a reaction-diffusion system

Morphological variations in human teeth have long been recognized and, in particular, the spatial and temporal distribution of two patterns of dental features in Asia, i.e., Sinodonty and Sundadonty, have contributed to our understanding of the human migration history. However, the molecular mechanisms underlying such dental variations have not yet been completely elucidated. Recent studies have clarified that a nonsynonymous variant in the ectodysplasin A receptor gene (EDAR 370V/A; rs3827760) contributes to crown traits related to Sinodonty. In this study, we examined the association between the EDAR polymorphism and tooth root traits by using computed tomography images and identified that the effects of the EDAR variant on the number and shape of roots differed depending on the tooth type. In addition, to better understand tooth root morphogenesis, a computational analysis for patterns of tooth roots was performed, assuming a reaction-diffusion system. The computational study suggested that the complicated effects of the EDAR polymorphism could be explained when it is considered that EDAR modifies the syntheses of multiple related molecules working in the reaction-diffusion dynamics. In this study, we shed light on the molecular mechanisms of tooth root morphogenesis, which are less understood in comparison to those of tooth crown morphogenesis.

Pax9's Interaction With the Ectodysplasin Signaling Pathway During the Patterning of Dentition

In these studies, we explored for the first time the molecular relationship between the paired-domain-containing transcription factor, Pax9, and the ectodysplasin (Eda) signaling pathway during mouse incisor formation. Mice that were deficient in both Pax9 and Eda were generated, and the status of dentition analyzed in all progeny using gross evaluation and histomorphometric means. When compared to wildtype controls, Pax9^+/–Eda^–/– mice lack mandibular incisors. Interestingly, Fgf and Shh signaling are down-regulated while Bmp4 and Lef1 appear unaffected. These findings suggest that Pax9-dependent signaling involves the Eda pathway and that this genetic relationship is important for mandibular incisor development. Studies of records of humans affected by mutations in PAX9 lead to the congenital absence of posterior dentition but interestingly involve agenesis of mandibular central incisors. The latter phenotype is exhibited by individuals with EDA or EDAR mutations. Thus, it is likely that PAX9, in addition to playing a role in the formation of more complex dentition, is also involved with EDA signaling in the initiation of odontogenesis within the incisal domain.

Ectodysplasin A receptor (EDAR) promotes colorectal cancer cell proliferation via regulation of the Wnt/β-catenin signaling pathway

Colorectal cancer is the second leading cause of cancer mortality worldwide with poor prognosis and high recurrence. Aberrant Wnt/β-catenin signaling promotes oncogenesis by transcriptional activation of c-Myc and its downstream signals. EDAR is characterized as an important effector of canonical Wnt signaling in developing skin appendages, but the interplay between EDAR and Wnt signaling in tumorigenesis and progression remains to be elucidated. In this study, we revealed that EDAR expression is prevalently elevated in colorectal cancer tissues compared with normal tissues. Further analysis suggests there is a strict correlation between EDAR expression and colorectal cancer progression. EDAR silencing by shRNA in colorectal cancer cells showed proliferative suppression via retarding cell cycle at G1 phase. Xenograft mice transplanted with shEDAR-transduced tumor cells significantly alleviated tumor burden in comparison with control mice. Furthermore, downregulation of EDAR was accompanied by reduction of β-catenin, c-Myc and other G1 cell cycle regulators, while β-catenin agonist restored the expression of these proteins and overrode the proliferative block induced by EDAR knockdown. These findings indicate that EDAR functions as a component of Wnt/β-catenin signaling pathway, and is a potential modulator in colorectal carcinogenesis.

A novel EDA1 missense mutation in X-linked hypohidrotic ectodermal dysplasia

A mutation in the epithelial morphogen gene ectodysplasin-A1 (EDA1) is responsible for the disorder X-linked hypohidrotic ectodermal dysplasia (XLHED), the most common form of ectodermal dysplasia. XLHED is characterized by impaired development of hair, eccrine sweat glands, and teeth. This study aimed to identify potentially pathogenic mutations in four Chinese XLHED families.Genomic DNA was extracted from the peripheral blood and sequenced. Sanger sequencing was used to carry out mutational analysis of the EDA1 gene, and the three-dimensional structure of the novel mutant residues in the EDA trimer was determined. Transcriptional activity of NF-κB was tested by Dual luciferin assay.We identified a novel EDA1 mutation (c.1046C>T) and detected 3 other previously-reported mutations (c.146T>A; c.457C>T; c.467G>A). Our findings demonstrated that novel mutation c.1046C>T (p.A349 V) resulted in XLHED. The novel mutation could cause volume repulsion in the protein due to enlargement of the amino acid side chain. Dual luciferase assay revealed that transcriptional NF-κB activation induced by XLHED EDA1 protein was significantly reduced compared with wild-type EDA1.These results extend the spectrum of EDA1 mutations in XLHED patients and suggest a functional role of the novel mutation in XLHED.

Tooth Regeneration: Insights from Tooth Development and Spatial-Temporal Control of Bioactive Drug Release

Tooth defect and tooth loss are common clinical diseases in stomatology. Compared with the traditional oral restoration treatment, tooth regeneration has unique advantages and is currently the focus of oral biomedical research. It is known that dozens of cytokines/growth factors and other bioactive factors are expressed in a spatial-temporal pattern during tooth development. On the other hand, the technology for spatial-temporal control of drug release has been intensively studied and well developed recently, making control release of these bioactive factors mimicking spatial-temporal pattern more feasible than ever for the purpose of tooth regeneration. This article reviews the research progress on the tooth development and discusses the future of tooth regeneration in the context of spatial-temporal release of developmental factors.

High-fat diet increases labial groove formation in maxillary incisors and is related to aging in C57BL/6 mice

OBJECTIVES

The aim of this study was to explore the relationship between the consumption of a high-fat diet and aging-dependent formation of maxillary incisor grooves in C57BL/6 mice, and to identify putative maxillary incisor groove-related genes.

METHODS

We fed 2-month-old and 16-month-old C57BL/6 mice on either a chow diet or a high-fat diet for three months and observed changes in maxillary incisor grooves. We examined tissue sections of the maxillary incisors with grooves and carried out transcriptome analysis of the apical tissue fragments of maxillary incisors with/without grooves.

RESULTS

Consumption of a high-fat diet for three months resulted in significant increases in both body weight and the number of incisor grooves. Both the number and frequency of incisor grooves increased in an age-dependent manner from 26 to 28 months, during which time an additional groove appeared. There was abnormal differentiation and apoptosis of ameloblasts on the labial surface at the grooves of the maxillary incisors. Transcriptome analysis identified 23 genes as being specific to 24-month-old mice; these included several genes related to apoptosis and cell differentiation.

CONCLUSIONS

The study findings indicate that, in C57BL/6 mice, consumption of a high-fat diet increases labial groove formation in maxillary incisors, which is related to aging of the tissue stem cells in the apical root end of the teeth.

[Expression patterns of ectodysplasin and ectodysplasin receptor during early dental development in zebrafish]

OBJECTIVE

This study aims to study the expression patterns of ectodysplasin (EDA) and ectodysplasin receptor (EDAR) during the early development of zebrafish and provide a foundation for further research of the Eda signaling pathway in tooth development.

METHODS

Total RNA was extracted from zebrafish embryos at 48 hours postfertilization (hpf) and then reverse transcribed for cDNA library generation. The corresponding RNA polymerase was selected for the synthesis of the digoxin-labeled antisense mRNA probe of zebrafish pharyngeal tooth specific marker dlx2b and Eda signaling-associated genes eda and edar in vitro. The three sequences were ligated into a pGEMT vector with a TA cloning kit, and polymerase chain reaction (PCR) was applied to linearize the plasmid. The resultant PCR sequences were used as templates for synthesizing Dig-labeled mRNA probe dlx2b, eda, and edar. Zebrafish embryos were collected at 36, 48, 56, 60, 72, and 84 hpf, then whole mount in situ hybridization was performed for the detection of eda and edar expression patterns. Then, their expression patterns at 72 hpf were compared with the expression pattern of dlx2b.

RESULTS

The mRNA antisense probes of dlx2b, eda, and edar were successfully obtained. The positive signals of eda and edar were observed in zebrafish pharyngeal tooth region at 48-72 hpf and thus conform to the signals of dlx2b in the positive regions.

CONCLUSIONS

The ligand eda and edar, which are associated with the Eda signaling pathway, are strongly expressed only at the pharyngeal tooth region in zebrafish from tooth initiation to the morphogenesis stage. Thus, the Eda signaling pathway may be involved in the regulation of the early development of zebrafish pharyngeal teeth.

Ectodysplasin-A signaling is a key integrator in the lacrimal gland-cornea feedback loop

A lack of ectodysplasin-A (Eda) signaling leads to dry eye symptoms, which have so far only been associated with altered Meibomian glands. Here, we used loss-of-function (Eda ^-/-) mutant mice to unravel the impact of Eda signaling on lacrimal gland formation, maturation and subsequent physiological function. Our study demonstrates that Eda activity is dispensable during lacrimal gland embryonic development. However, using a transcriptomic approach, we show that the Eda pathway is necessary for proper cell terminal differentiation in lacrimal gland epithelium and correlated with modified expression of secreted factors commonly found in the tear film. Finally, we discovered that lacrimal glands present a bilateral reduction of Eda signaling activity in response to unilateral corneal injury. This observation hints towards a role for the Eda pathway in controlling the switch from basal to reflex tears, to support corneal wound healing. Collectively, our data suggest a crucial implication of Eda signaling in the cornea-lacrimal gland feedback loop, both in physiological and pathophysiological conditions. Our findings demonstrate that Eda downstream targets could help alleviate dry eye symptoms.

Novel and Private EDA Mutations and Clinical Phenotypes of Korean Patients with X-Linked Hypohidrotic Ectodermal Dysplasia

X-linked hypohidrotic ectodermal dysplasia (XLHED; OMIM 305100) is the most common form of ectodermal dysplasia, presenting with the triad of hypotrichosis, hypodontia, and hypohidrosis. This disorder is caused by mutations in EDA, which encodes ectodysplasin A, a member of the tumor necrosis factor superfamily. In this study, we describe clinical and genetic characteristics of 10 Korean XLHED patients (9 males, 1 female) from 9 families. Nine out of the 10 patients manifested the cardinal triad of symptoms. Six patients had a positive family history, while 2 patients were brothers. The most common initial presentation was hypotrichosis or hypodontia, while 1 patient presented with recurrent high fever in early infancy. Sanger sequencing of the EDA gene was performed and revealed 9 different mutations. Three had been reported previously, and 6 were novel mutations. One female patient, carrying a previously reported missense mutation, might be affected by skewed X-inactivation. This is the first observational study investigating genetically confirmed XLHED patients in Korea. To provide appropriate supportive care and genetic counseling, clinicians should consider the possibility of XLHED in the differential diagnosis of recurrent fever in infants, as well as recognize the typical triad of symptoms.

Effect of canonical NF-κB signaling pathway on the differentiation of rat dental epithelial stem cells

BACKGROUND

Nuclear factor-κB (NF-κB), an important transcription factor, participates in many physiological and pathological processes such as growth, differentiation, organogenesis, apoptosis, inflammation, and immune response, including tooth development. However, it is still unknown whether NF-κB participates in the regulation of dental epithelial stem cells (DESCs) in postnatal rat incisors. Here, we investigated the specific differentiation regulatory mechanisms of the canonical NF-κB signaling pathway in DESCs and provided the mechanism of cross-talk involved in DESC differentiation.

METHODS

After adding the activator or inhibitor of the NF-κB signaling pathway, Western blot and quantitative real-time PCR were used to analyze the expressions of amelogenesis-related genes and proteins and canonical transforming growth factor-β (TGF-β) signaling. In addition, we used amelogenesis induction in vitro by adding the activator or inhibitor of the NF-κB signaling pathway to the amelogenesis-induction medium, respectively. Recombinant TGF-β was used to activate the TGF-β pathway, and SMAD7 siRNA was used to downregulate the expression of SMAD7 in DESCs.

RESULTS

We found that the expression of amelogenesis-related genes and proteins as well as TGF-β signaling were downregulated, while SMAD7 expression was increased in NF-κB-activated DESCs. In addition, NF-κB-inhibited DESCs exhibited opposite results compared with NF-κB-activated DESCs. Furthermore, the canonical NF-κB signaling pathway suppressed the canonical TGF-β-SMAD signaling by inducing SMAD7 expression involved in the regulation of DESC differentiation.

CONCLUSIONS

These results indicate that the canonical NF-κB signaling pathway participated in the regulation of DESC differentiation, which was through upregulating SMAD7 expression and further suppressing the canonical TGF-β-SMAD signaling pathway.

X-Linked Hypohidrotic Ectodermal Dysplasia-General Features and Dental Abnormalities in Affected Dogs Compared With Human Dental Abnormalities

X-linked hypohidrotic ectodermal dysplasia (XLHED) is a genetic disorder characterized by abnormalities in ectodermal derivatives such as sweat glands, hair, and teeth. In animals, the highest number of cases has been reported in dogs, which show characteristic congenital alopecia and develop abnormalities in the shape and number of teeth. Although the clinical phenotype of the affected individuals is typical, this disorder remains almost unknown in veterinary clinical practice. With the aim of making it better known, we gathered in this review the main clinical and genetic aspects of XLHED, placing emphasis on dental abnormalities.

Modeling Edar expression reveals the hidden dynamics of tooth signaling center patterning

When patterns are set during embryogenesis, it is expected that they are straightly established rather than subsequently modified. The patterning of the three mouse molars is, however, far from straight, likely as a result of mouse evolutionary history. The first-formed tooth signaling centers, called MS and R2, disappear before driving tooth formation and are thought to be vestiges of the premolars found in mouse ancestors. Moreover, the mature signaling center of the first molar (M1) is formed from the fusion of two signaling centers (R2 and early M1). Here, we report that broad activation of Edar expression precedes its spatial restriction to tooth signaling centers. This reveals a hidden two-step patterning process for tooth signaling centers, which was modeled with a single activator-inhibitor pair subject to reaction-diffusion (RD). The study of Edar expression also unveiled successive phases of signaling center formation, erasing, recovering, and fusion. Our model, in which R2 signaling center is not intrinsically defective but erased by the broad activation preceding M1 signaling center formation, predicted the surprising rescue of R2 in Edar mutant mice, where activation is reduced. The importance of this R2-M1 interaction was confirmed by ex vivo cultures showing that R2 is capable of forming a tooth. Finally, by introducing chemotaxis as a secondary process to RD, we recapitulated in silico different conditions in which R2 and M1 centers fuse or not. In conclusion, pattern formation in the mouse molar field relies on basic mechanisms whose dynamics produce embryonic patterns that are plastic objects rather than fixed end points.

The Function and Regulatory Network of Pax9 Gene in Palate Development

Cleft palate, a common congenital deformity, can arise from disruptions in any stage of palatogenesis, including palatal shelf growth, elevation, adhesion, and fusion. Paired box gene 9 (Pax9) is recognized as a vital regulator of palatogenesis with great relevance to cleft palate in humans and mice. Pax9-deficient murine palatal shelves displayed deficient elongation, postponed elevation, failed contact, and fusion. Pax9 is expressed in epithelium and mesenchyme, exhibiting a dynamic expression pattern that changes according to the proceeding of palatogenesis. Recent studies highlighted the Pax9-related genetic interactions and their critical roles during palatogenesis. During palate growth, PAX9 interacts with numerous molecules and members of pathways (e.g., OSR2, FGF10, SHOS2, MSX1, BARX1, TGFβ3, LDB1, BMP, WNT β-catenin dependent, and EDA) in the mesenchyme and functions as a key mediator in epithelial-mesenchymal communications with FGF8, TBX1, and the SHH pathway. During palate elevation, PAX9 is hypothesized to mediate the time point of the elevation event in the anterior and posterior parts of the palatal shelves. The delayed elevation of Pax9 mutant palatal shelves probably results from abnormal expressions of a series of genes ( Osr2 and Bmpr1a) leading to deficient palate growth, abnormal tongue morphology, and altered hyaluronic acid distribution. The interactions between PAX9 and genes encoding the OSR2, TGFβ3, and WNT β-catenin-dependent pathways provide evidence that PAX9 might participate in the regulation of palate fusion. This review summarizes the current understanding of PAX9’s functions and emphasizes the interactions between PAX9 and vital genes during palatogenesis. We hope to provide some clues for further exploration of the function and mechanism of PAX9, especially during palate elevation and fusion events.

Hair follicle dermal condensation forms via Fgf20 primed cell cycle exit, cell motility, and aggregation

Mesenchymal condensation is a critical step in organogenesis, yet the underlying molecular and cellular mechanisms remain poorly understood. The hair follicle dermal condensate is the precursor to the permanent mesenchymal unit of the hair follicle, the dermal papilla, which regulates hair cycling throughout life and bears hair inductive potential. Dermal condensate morphogenesis depends on epithelial Fibroblast Growth Factor 20 (Fgf20). Here, we combine mouse models with 3D and 4D microscopy to demonstrate that dermal condensates form de novo and via directional migration. We identify cell cycle exit and cell shape changes as early hallmarks of dermal condensate morphogenesis and find that Fgf20 primes these cellular behaviors and enhances cell motility and condensation. RNAseq profiling of immediate Fgf20 targets revealed induction of a subset of dermal condensate marker genes. Collectively, these data indicate that dermal condensation occurs via directed cell movement and that Fgf20 orchestrates the early cellular and molecular events.

All mammal hair springs from hair follicles under the skin. These follicles sit in the dermis, beneath the outermost skin layer, the epidermis. In the embryo, hair follicles develop from unspecialized cells in two tissues, the epithelium and the mesenchyme, which will later develop into the dermis and epidermis, respectively. As development progresses, the cells of these tissues begin to cluster, and signals passing back and forth between the epithelium and mesenchyme instruct the cells what to do. In the mesenchyme, cells called fibroblasts squeeze up against their neighbors, forming patches called dermal condensates. These mature into so-called dermal papillae, which supply specific molecules called growth factors that regulate hair formation throughout lifetime.

Fibroblasts in the developing skin respond to a signal from the epithelium called fibroblast growth factor 20 (Fgf20), but we do not yet understand its effects. It is possible that Fgf20 tells the cells to divide, forming clusters of daughter cells around their current location. Or, it could be that Fgf20 tells the cells to move, encouraging them to travel towards one another to form groups.

To address this question, Biggs, Mäkelä et al. examined developing mouse skin grown in the laboratory. They traced cells marked with fluorescent tags to analyze their behavior as the condensates formed. This revealed that the Fgf20 signal acts as a rallying call, triggering fibroblast movement. The cells changed shape and moved towards one another, rather than dividing to create their own clusters. In fact, they switched off their own cell cycle as the condensates formed, halting their ability to divide. A technique called RNA sequencing revealed that Fgf20 also promotes the use of genes known to be active in dermal condensates.

Dermal papillae control hair growth, and transplanting them under the skin can form new hair follicles. However, these cells lose this ability when grown in the laboratory. Understanding how they develop could be beneficial for future hair growth therapy. Further work could also address fundamental questions in embryology. Condensates of cells from the mesenchyme also precede the formation of limbs, bones, muscles and organs. Extending this work could help us to understand this critical developmental step.

Ectodysplasin A regulates epithelial barrier function through sonic hedgehog signalling pathway

Ectodysplasin A (Eda), a member of the tumour necrosis factor superfamily, plays an important role in ectodermal organ development. An EDA mutation underlies the most common of ectodermal dysplasias, that is X-linked hypohidrotic ectodermal dysplasia (XLHED) in humans. Even though it lacks a developmental function, the role of Eda during the postnatal stage remains elusive. In this study, we found tight junctional proteins ZO-1 and claudin-1 expression is largely reduced in epidermal, corneal and lung epithelia in Eda mutant Tabby mice at different postnatal ages. These declines are associated with tail ulceration, corneal pannus formation and lung infection. Furthermore, topical application of recombinant Eda protein markedly mitigated corneal barrier dysfunction. Using cultures of a human corneal epithelial cell line and Tabby mouse skin tissue explants, Eda up-regulated expression of ZO-1 and claudin-1 through activation of the sonic hedgehog signalling pathway. We conclude that EDA gene expression contributes to the maintenance of epithelial barrier function. Such insight may help efforts to identify novel strategies for improving management of XLHED disease manifestations in a clinical setting.

Anti-EDAR Agonist Antibody Therapy Resolves Palate Defects in Pax9-/- Mice

To date, surgical interventions are the only means by which craniofacial anomalies can be corrected so that function, esthetics, and the sense of well-being are restored in affected individuals. Unfortunately, for patients with cleft palate-one of the most common of congenital birth defects-treatment following surgery is prolonged over a lifetime and often involves multidisciplinary regimens. Hence, there is a need to understand the molecular pathways that control palatogenesis and to translate such information for the development of noninvasive therapies that can either prevent or correct cleft palates in humans. Here, we use the well-characterized model of the Pax9^-/- mouse, which displays a consistent phenotype of a secondary cleft palate, to test a novel therapeutic. Specifically, we demonstrate that the controlled intravenous delivery of a novel mouse monoclonal antibody replacement therapy, which acts as an agonist for the ectodysplasin (Eda) pathway, can resolve cleft palate defects in Pax9^-/- embryos in utero. Such pharmacological interventions did not reverse the arrest in tooth, thymus, and parathyroid gland development, suggesting that the relationship of Pax9 to the Eda/Edar pathway is both unique and essential for palatogenesis. Expression analyses and unbiased gene expression profiling studies offer a molecular explanation for the resolution of palatal defects, showing that Eda and Edar-related genes are expressed in normal palatal tissues and that the Eda/Edar signaling pathway is downstream of Pax9 in palatogenesis. Taken together, our data uncover a unique relationship between Pax9 and the Eda/Edar signaling pathway that can be further exploited for the development of noninvasive, safe, and effective therapies for the treatment of cleft palate conditions and other single-gene disorders affecting the craniofacial complex.

The Impact of the Eda Pathway on Tooth Root Development

The Eda pathway ( Eda, Edar, Edaradd) plays an important role in tooth development, determining tooth number, crown shape, and enamel formation. Here we show that the Eda pathway also plays a key role in root development. Edar (the receptor) is expressed in Hertwig's epithelial root sheath (HERS) during root development, with mutant mice showing a high incidence of taurodontism: large pulp chambers lacking or showing delayed bifurcation or trifurcation of the roots. The mouse upper second molars in the Eda pathway mutants show the highest incidence of taurodontism, this enhanced susceptibility being matched in human patients with mutations in EDA-A1. These taurodont teeth form due to defects in the direction of extension of the HERS from the crown, associated with a more extensive area of proliferation of the neighboring root mesenchyme. In those teeth where the angle at which the HERS extends from the crown is very wide and therefore more vertical, the mutant HERSs fail to reach toward the center of the tooth in the normal furcation region, and taurodont teeth are created. The phenotype is variable, however, with milder changes in angle and proliferation leading to normal or delayed furcation. This is the first analysis of the role of Eda in the root, showing a direct role for this pathway during postnatal mouse development, and it suggests that changes in proliferation and angle of HERS may underlie taurodontism in a range of syndromes.

Early epithelial signaling center governs tooth budding morphogenesis

During organogenesis, cell fate specification and patterning are regulated by signaling centers, specialized clusters of morphogen-expressing cells. In many organs, initiation of development is marked by bud formation, but the cellular mechanisms involved are ill defined. Here, we use the mouse incisor tooth as a model to study budding morphogenesis. We show that a group of nonproliferative epithelial cells emerges in the early tooth primordium and identify these cells as a signaling center. Confocal live imaging of tissue explants revealed that although these cells reorganize dynamically, they do not reenter the cell cycle or contribute to the growing tooth bud. Instead, budding is driven by proliferation of the neighboring cells. We demonstrate that the activity of the ectodysplasin/Edar/nuclear factor κB pathway is restricted to the signaling center, and its inactivation leads to fewer quiescent cells and a smaller bud. These data functionally link the signaling center size to organ size and imply that the early signaling center is a prerequisite for budding morphogenesis.

Embryonic Explant Culture: Studying Effects of Regulatory Molecules on Gene Expression in Craniofacial Tissues

The ex vivo culture of embryonic tissue explants permits the continuous monitoring of growth and morphogenesis at specific embryonic stages. The functions of soluble regulatory molecules can be analyzed by introducing them into culture medium or locally with beads to the tissue. Gene expression in the manipulated tissue explants can be analyzed using in situ hybridization, quantitative PCR, and reporter constructs combined to organ culture to examine the functions of the signaling molecules.

The Wnt Blows: On the Functional Role of Wnt Signaling in Mycobacterium tuberculosis Infection and Beyond

In recent years, it has become apparent that the Wnt signaling pathway, known for its essential functions in embryonic development and tissue homeostasis, exerts immunomodulatory functions during inflammation and infection. Most functional studies indicate that Wnt5a exerts pro-inflammatory functions on its cellular targets, which include various types of immune and non-immune cells. Wnt5a expression has also been linked to the pathogenesis of chronic inflammatory diseases. Activation of beta-catenin-dependent Wnt signaling, e.g., by Wnt3a, has however been shown to limit inflammation by interfering with the nuclear factor kappa-light chain-enhancer of activated B-cells (NF-kappaB) pathway. This review focuses on the regulation of Wnt5a, Wnt3a, and the recently identified Wnt6 and their functional role in bacterial infections with a primary focus on pulmonary tuberculosis, a leading infectious cause of morbidity and mortality worldwide.

Opg, Rank, and Rankl in Tooth Development: Co-ordination of Odontogenesis and Osteogenesis

Osteoprotegerin (OPG), receptor activator of nuclear factor-κB (RANK), and RANK ligand (RANKL) are mediators of various cellular interactions, including bone metabolism. We analyzed expression of these three genes during murine odontogenesis from epithelial thickening to cytodifferentiation stages. Opg showed expression in the thickening and bud epithelium. Expression of Opg and Rank was observed in both the internal and the external enamel epithelium as well as in the dental papilla mesenchyme. Although Rankl expression was not detected in tooth epithelium or mesenchyme, it was expressed in pre-osteogenic mesenchymal cells close to developing tooth germs. All three genes were detected in developing dentary bone at P0. The addition of exogenous OPG to explant cultures of tooth primordia produced a delay in tooth development that resulted in reduced mineralization. We propose that the spatiotemporal expression of these molecules in early tooth and bone primordia cells has a role in co-ordinating bone and tooth development.

Looking Beyond the Genes: The Interplay Between Signaling Pathways and Mechanics in the Shaping and Diversification of Epithelial Tissues

The core of Evo-Devo lies in the intuition that the way tissues grow during embryonic development, the way they sustain their structure and function throughout lifetime, and the way they evolve are closely linked. Epithelial tissues are ubiquitous in metazoans, covering the gut and internal branched organs, as well as the skin and its derivatives (ie, teeth). Here, we discuss in vitro, in vivo, and in silico studies on epithelial tissues to illustrate the conserved, dynamical, and complex aspects of their development. We then explore the implications of the dynamical and nonlinear nature of development on the evolution of their size and shape at the phenotypic and genetic levels. In rare cases, when the interplay between signaling and mechanics is well understood at the cell level, it is becoming clear that the structure of development leads to covariation of characters, an integration which in turn provides some predictable structure to evolutionary changes. We suggest that such nonlinear systems are prone to genetic drift, cryptic genetic variation, and context-dependent mutational effects. We argue that experimental and theoretical studies at the cell level are critical to our understanding of the phenotypic and genetic evolution of epithelial tissues, including carcinomas.

De novo EDA mutations: Variable expression in two Egyptian families

OBJECTIVE

Mutations in the EDA gene, encoding the epithelial morphogen ectodysplasin-A, can result in different but overlapping phenotypes. Therefore the aim of the study was to search for etiological variations of EDA and other candidate genes in two unrelated Egyptian male children with sporadic non-syndromic tooth agenesis (NTA) and hypohidrotic ectodermal dysplasia (HED).

DESIGN

Direct sequencing of the coding regions including exon-intron boundaries of EDA, MSX1, PAX9, WNT10A and EDAR was performed in probands and their available family members.

RESULTS

Two etiological mutations were found in the EDA coding region. The patient with NTA in both deciduous and permanent dentition was a carrier of a novel in-frame deletion situated in the short collagenous domain (c.663-680delTCCTCCTGGTCCTCAAGG, p.222-227delPPGPQG). The second mutation, located outside the minimal furin consensus motif (c.463C>T, p.Arg155Cys, rs132630312), was identified in the patient exhibiting all typical features of HED. The identified EDA mutations were not detected in probands' family members as well as in 188 unrelated control individuals. No pathogenic variants were found in the MSX1, PAX9, WNT10A and EDAR genes.

CONCLUSION

Our results increase the knowledge of the spectrum of EDA mutations and confirm that this gene is an important candidate gene for two developmental diseases sharing the common feature of the congenital lack of teeth. In addition, these results can support the hypothesis that X-linked HED and EDA-related NTA are the same disease with different degrees of severity.

Embryonic attenuated Wnt/β-catenin signaling defines niche location and long-term stem cell fate in hair follicle

Long-term adult stem cells sustain tissue regeneration throughout the lifetime of an organism. They were hypothesized to originate from embryonic progenitor cells that acquire long-term self-renewal ability and multipotency at the end of organogenesis. The process through which this is achieved often remains unclear. Here, we discovered that long-term hair follicle stem cells arise from embryonic progenitor cells occupying a niche location that is defined by attenuated Wnt/β-catenin signaling. Hair follicle initiation is marked by placode formation, which depends on the activation of Wnt/β-catenin signaling. Soon afterwards, a region with attenuated Wnt/β-catenin signaling emerges in the upper follicle. Embryonic progenitor cells residing in this region gain expression of adult stem cell markers and become definitive long-term hair follicle stem cells at the end of organogenesis. Attenuation of Wnt/β-catenin signaling is a prerequisite for hair follicle stem cell specification because it suppresses Sox9, which is required for stem cell formation.

DOI:http://dx.doi.org/10.7554/eLife.10567.001

Many tissues and organs in an adult’s body – including bone marrow, skin and intestines – contain a small number of cells called adult stem cells. These cells usually stay dormant within these tissues (at a site called a ‘niche’) until they are required to repair damaged or lost cells. At this point, adult stem cells can specialize, or ‘differentiate’, into the many different cell types that make up the tissue or organ where they reside.

The cells that produce hairs are an example of adult stem cells. In mammals, hairs grow from structures called hair follicles that are found in the skin, and over the life of an animal, old hairs are shed and replaced. Previous research had suggested that certain embryonic cells are set to become hair follicle stem cells before the hair follicles emerge in the adult tissue. However it remained unclear how this decision is made, and which genes and molecules are involved in this process.

Xu et al. have now found that, in mice, the fate of hair follicle stem cells is decided at an early stage in development, when the hair follicle is a simpler structure called a ‘hair peg’. Cells near the upper part of the hair peg tend to become dormant and adopt an adult stem cell fate, while the ones in the lower part are more likely to differentiate straight away. This shows that the position, hence the niche environment, plays a key role in determining these different cells’ fates.

Xu et al. went on to discover that the decision for a cell to become a hair follicle stem cell relies on reduced signaling through the so-called Wnt signal pathway. Understanding how adult stem cells become established during development may help future efforts to grow tissues and organs in the laboratory for research purposes or organ transplantation.

DOI:http://dx.doi.org/10.7554/eLife.10567.002

Ectodysplasin/NF-κB Promotes Mammary Cell Fate via Wnt/β-catenin Pathway

Mammary gland development commences during embryogenesis with the establishment of a species typical number of mammary primordia on each flank of the embryo. It is thought that mammary cell fate can only be induced along the mammary line, a narrow region of the ventro-lateral skin running from the axilla to the groin. Ectodysplasin (Eda) is a tumor necrosis factor family ligand that regulates morphogenesis of several ectodermal appendages. We have previously shown that transgenic overexpression of Eda (K14-Eda mice) induces formation of supernumerary mammary placodes along the mammary line. Here, we investigate in more detail the role of Eda and its downstream mediator transcription factor NF-κB in mammary cell fate specification. We report that K14-Eda mice harbor accessory mammary glands also in the neck region indicating wider epidermal cell plasticity that previously appreciated. We show that even though NF-κB is not required for formation of endogenous mammary placodes, it is indispensable for the ability of Eda to induce supernumerary placodes. A genome-wide profiling of Eda-induced genes in mammary buds identified several Wnt pathway components as potential transcriptional targets of Eda. Using an ex vivo culture system, we show that suppression of canonical Wnt signalling leads to a dose-dependent inhibition of supernumerary placodes in K14-Eda tissue explants.

Mammary glands are the most characteristic feature of all mammals. The successful growth and function of the mammary glands is vital for the survival of offspring since the secreted milk is the main nutritional source of a new-born. Ectodysplasin (Eda) is a signaling molecule that regulates the formation of skin appendages such as hair, teeth, feathers, scales, and several glands in all vertebrates studied so far. In humans, mutations in the EDA gene cause a congenital disorder characterized by sparse hair, missing teeth, and defects in exocrine glands including the breast. We have previously shown that excess Eda induces formation of supernumerary mammary glands in mice. Here, we show that Eda leads to extra mammary gland formation also in the neck, a region previously not thought to harbor capacity to support mammary development. Using Eda loss- and gain-of-function mouse models and transcriptional profiling we identify the downstream mediators of Eda. The presence of extra nipples is a fairly common developmental abnormality in humans. We suggest that misregulation of Eda or its effectors might account for some of these malformations. Further, the number and location of the mammary glands vary widely between different species. Tinkering with the Eda pathway activity could provide an evolutionary means to modulate the number of mammary glands.

Suppression of epithelial differentiation by Foxi3 is essential for molar crown patterning

Epithelial morphogenesis generates the shape of the tooth crown. This is driven by patterned differentiation of cells into enamel knots, root-forming cervical loops and enamel-forming ameloblasts. Enamel knots are signaling centers that define the positions of cusp tips in a tooth by instructing the adjacent epithelium to fold and proliferate. Here, we show that the forkhead-box transcription factor Foxi3 inhibits formation of enamel knots and cervical loops and thus the differentiation of dental epithelium in mice. Conditional deletion of Foxi3 (Foxi3 cKO) led to fusion of molars with abnormally patterned shallow cusps. Foxi3 was expressed in the epithelium, and its expression was reduced in the enamel knots and cervical loops and in ameloblasts. Bmp4, a known inducer of enamel knots and dental epithelial differentiation, downregulated Foxi3 in wild-type teeth. Using genome-wide gene expression profiling, we showed that in Foxi3 cKO there was an early upregulation of differentiation markers, such as p21, Fgf15 and Sfrp5. Different signaling pathway components that are normally restricted to the enamel knots were expanded in the epithelium, and Sostdc1, a marker of the intercuspal epithelium, was missing. These findings indicated that the activator-inhibitor balance regulating cusp patterning was disrupted in Foxi3 cKO. In addition, early molar bud morphogenesis and, in particular, formation of the suprabasal epithelial cell layer were impaired. We identified keratin 10 as a marker of suprabasal epithelial cells in teeth. Our results suggest that Foxi3 maintains dental epithelial cells in an undifferentiated state and thereby regulates multiple stages of tooth morphogenesis.

A 190 base pair, TGF-β responsive tooth and fin enhancer is required for stickleback Bmp6 expression

The ligands of the Bone Morphogenetic Protein (BMP) family of developmental signaling molecules are often under the control of complex cis-regulatory modules and play diverse roles in vertebrate development and evolution. Here, we investigated the cis-regulatory control of stickleback Bmp6. We identified a 190bp enhancer ~2.5 kilobases 5' of the Bmp6 gene that recapitulates expression in developing teeth and fins, with a core 72bp sequence that is sufficient for both domains. By testing orthologous enhancers with varying degrees of sequence conservation from outgroup teleosts in transgenic reporter gene assays in sticklebacks and zebrafish, we found that the function of this regulatory element appears to have been conserved for over 250 million years of teleost evolution. We show that a predicted binding site for the TGFβ effector Smad3 in this enhancer is required for enhancer function and that pharmacological inhibition of TGFβ signaling abolishes enhancer activity and severely reduces endogenous Bmp6 expression. Finally, we used TALENs to disrupt the enhancer in vivo and find that Bmp6 expression is dramatically reduced in teeth and fins, suggesting this enhancer is necessary for expression of the Bmp6 locus. This work identifies a relatively short regulatory sequence that is required for expression in multiple tissues and, combined with previous work, suggests that shared regulatory networks control limb and tooth development.

Multidisciplinary management of hypohydrotic ectodermal dysplasia - a case report

Hypohydrotic ectodermal dysplasia is a hereditary disorder, which affects ectodermal derivatives. It manifests several abnormalities of the teeth, and is commonly inherited through female carriers. This case report presents a patient with compromised esthetics and function. A multidisciplinary approach was planned involving an oral pathologist, endodontist, orthodontist and a prosthodontist.

Involvement of Wnt, Eda and Shh at defined stages of sweat gland development

To maintain body temperature, sweat glands develop from embryonic ectoderm by a poorly defined mechanism. We demonstrate a temporal cascade of regulation during mouse sweat gland formation. Sweat gland induction failed completely when canonical Wnt signaling was blocked in skin epithelium, and was accompanied by sharp downregulation of downstream Wnt, Eda and Shh pathway genes. The Wnt antagonist Dkk4 appeared to inhibit this induction: Dkk4 was sharply downregulated in β-catenin-ablated mice, indicating that it is induced by Wnt/β-catenin; however, its overexpression repressed Wnt target genes and significantly reduced gland numbers. Eda signaling succeeded Wnt. Wnt signaling was still active and nascent sweat gland pre-germs were still seen in Eda-null mice, but the pre-germs failed to develop further and the downstream Shh pathway was not activated. When Wnt and Eda were intact but Shh was ablated, germ induction and subsequent duct formation occurred normally, but the final stage of secretory coil formation failed. Thus, sweat gland development shows a relay of regulatory steps initiated by Wnt/β-catenin - itself modulated by Dkk4 - with subsequent participation of Eda and Shh pathways.

The WNT10A gene in ectodermal dysplasias and selective tooth agenesis

Mutations in the WNT10A gene were first detected in the rare syndrome odonto-onycho-dermal dysplasia (OODD, OMIM257980) but have now also been found to cause about 35-50% of selective tooth agenesis (STHAG4, OMIM150400), a common disorder that mostly affects the permanent dentition. In our random sample of tooth agenesis patients, 40% had at least one mutation in the WNT10A gene. The WNT10A Phe228Ile variant alone reached an allele frequency of 0.21 in the tooth agenesis cohort, about 10 times higher than the allele frequency reported in large SNP databases for Caucasian populations. Patients with bi-allelic WNT10A mutations have severe tooth agenesis while heterozygous individuals are either unaffected or have a mild phenotype. Mutations in the coding areas of the WNT10B gene, which is co-expressed with WNT10A during odontogenesis, and the WNT6 gene which is located at the same chromosomal locus as WNT10A in humans, do not contribute to the tooth agenesis phenotype.

Malformation of Incisor Teeth in Grem2-/- Mice

GREMLIN 2 ( GREM2)—formerly, protein related to Dan and cerberus ( PRDC)—is a potent antagonist of the bone morphogenetic proteins 2 and 4, but little else in known about its functions. We found that Grem2-/- mice developed small deformed mandibular and maxillary incisors, indicating that GREMLIN2 is required for normal tooth morphogenesis. Although DEXA scans suggested that bone mineral density might be increased in Grem2-/- mice, histology did not reveal any evident bone phenotype. Grem2-/- mice did not display any other notable phenotypes evaluated in a high-throughput screening process that encompassed a range of immunologic, metabolic, ophthalmic, and behavioral parameters. Our findings indicate that Grem2 can be added to the growing list of genes that affect tooth development in mice.