Conserved features and evolutionary shifts of the EDA signaling pathway involved in vertebrate skin appendage development

Molecular basis and genetics of hypohidrotic ectodermal dysplasias

Ectodermal dysplasia (ED) is a heterogeneous group of hereditary diseases of the skin and its appendages, which are characterized by impaired development and/or homeostasis of two or more ectoderm derivatives, including: hair, teeth, nails, sweat glands and their modifications (mammary glands, for instance). The overall prevalence of ectodermal dysplasia remains precisely unknown not only in Russia, but also in the world, nor is known the contribution of individual genes to its structure. This complicates the DNA diagnosis establishment of this disease due to the lack of an accurate diagnostic algorithm and a universal cost-effective method of analysis. To date, the most highly-researched genes involved in the development of anhydrous or hypohidrotic forms of ED are EDA, EDAR, EDARADD and WNT10A. The ectodysplasin A (EDA) gene is the cause of the most common X-linked form of ED, a gene from the Wnt family (WNT10A) is responsible for the autosomal recessive form of the disease, and two other genes (EDAR and EDARADD) can cause both autosomal recessive and autosomal dominant forms. This review provides the characteristics of the genes involved in ED, their mutation spectra, the level of their expression in human tissues, as well as the interrelation of the aforementioned genes. The domain structures of the corresponding proteins are considered, as well as the molecular genetic pathways in which they are involved. Animal models for studying this disorder are also taken into consideration. Due to the cross-species genes conservation, their mutations cause the disruption of the development of ectoderm derivatives not only in humans, but also in mice, cows, dogs, and even fish. It can be exploited for a better understanding of the etiopathogenesis of ectodermal dysplasias. Moreover, this article brings up the possibility of recurrent mutations in the EDA and WNT10A genes. The review also presents data on promising approaches for intrauterine ED treatment.

Ancient lineages of the keratin-associated protein (KRTAP) genes and their co-option in the evolution of the hair follicle

BLAST searches against the human genome showed that of the 93 keratin-associated proteins (KRTAPs) of Homo sapiens, 53 can be linked by sequence similarity to an H. sapiens metallothionein and 16 others can be linked similarly to occludin, while the remaining KRTAPs can themselves be linked to one or other of those 69 directly-linked proteins. The metallothionein-linked KRTAPs comprise the high-sulphur and ultrahigh-sulphur KRTAPs and are larger than the occludin-linked set, which includes the tyrosine- and glycine-containing KRTAPs. KRTAPs linked to metallothionein appeared in increasing numbers as evolution advanced from the deuterostomia, where KRTAP-like proteins with strong sequence similarity to their mammalian congeners were found in a sea anemone and a starfish. Those linked to occludins arose only with the later-evolved mollusca, where a KRTAP homologous with its mammalian congener was found in snails. The presence of antecedents of the mammalian KRTAPs in a starfish, a sea anemone, snails, fish, amphibia, reptiles and birds, all of them animals that lack hair, suggests that some KRTAPs may have a physiological role beyond that of determining the characteristics of hair fibres. We suggest that homologues of these KRTAPs found in non-hairy animals were co-opted by placodes, formed by the ectodysplasin pathway, to produce the first hair-producing cells, the trichocytes of the hair follicles.

Divergent tooth development mechanisms of Mexican tetra fish (Astyanax mexicanus) of Pachón cave origin

The Mexican tetra (Astyanax mexicanus) is one of the fresh water teleost fish models in evolutionary developmental biology. The existence of two morphs: eyed, pigmented surface fish and blind depigmented cavefish from multiple cave populations, provides a unique system to study adaptive radiation. Compared to the adult surface fish, cavefish have large oral jaws with an increased number of structurally-complex teeth. Early tooth development has not been studied in detail in cavefish populations. In this study, bone-stained growth series and vital dye staining was used to trace the development and replacement of dentitions in Pachón cavefish. Our results show that first tooth eruption was delayed in cavefish compared to the surface fish. In particular, the first tooth eruption cycle persisted until 35 days post fertilization (dpf). Unlike surface fish, there are multicuspid teeth in cavefish first generation dentition. In addition to the teeth in the marginal oral jaw bones, Pachón cavefish have teeth in the ectopterygoid bone of the palatine roof. Next, we characterised the expression of ectodysplasin signalling pathway genes in tooth-forming regions of surface and cavefish. Interestingly, higher expression of Eda and Edar was found in cavefish compared to the surface fish. The altered ectodysplasin expression needs further investigation to confirm the different molecular mechanisms for tooth development in the oral and pharyngeal regions of surface fish and cavefish.

Structural insights into pathogenic mechanism of hypohidrotic ectodermal dysplasia caused by ectodysplasin A variants

EDA is a tumor necrosis factor (TNF) family member, which functions together with its cognate receptor EDAR during ectodermal organ development. Mutations of EDA have long been known to cause X-linked hypohidrotic dysplasia in humans characterized by primary defects in teeth, hair and sweat glands. However, the structural information of EDA interaction with EDAR is lacking and the pathogenic mechanism of EDA variants is poorly understood. Here, we report the crystal structure of EDA C-terminal TNF homology domain bound to the N-terminal cysteine-rich domains of EDAR. Together with biochemical, cellular and mouse genetic studies, we show that different EDA mutations lead to varying degrees of ectodermal developmental defects in mice, which is consistent with the clinical observations on human patients. Our work extends the understanding of the EDA signaling mechanism, and provides important insights into the molecular pathogenesis of disease-causing EDA variants.

Developmental and evolutionary comparative analysis of a regulatory landscape in mouse and chicken

Modifications in gene regulation are driving forces in the evolution of organisms. Part of these changes involve cis-regulatory elements (CREs), which contact their target genes through higher-order chromatin structures. However, how such architectures and variations in CREs contribute to transcriptional evolvability remains elusive. We use Hoxd genes as a paradigm for the emergence of regulatory innovations, as many relevant enhancers are located in a regulatory landscape highly conserved in amniotes. Here, we analysed their regulation in murine vibrissae and chicken feather primordia, two skin appendages expressing different Hoxd gene subsets, and compared the regulation of these genes in these appendages with that in the elongation of the posterior trunk. In the two former structures, distinct subsets of Hoxd genes are contacted by different lineage-specific enhancers, probably as a result of using an ancestral chromatin topology as an evolutionary playground, whereas the gene regulation that occurs in the mouse and chicken embryonic trunk partially relies on conserved CREs. A high proportion of these non-coding sequences active in the trunk have functionally diverged between species, suggesting that transcriptional robustness is maintained, despite considerable divergence in enhancer sequences.

Summary: Analyses of the relationships between chromatin architecture and regulatory activities at the HoxD locus show that ancestral transcription patterns can be maintained while new regulations evolve.

Evidence of selection in the ectodysplasin pathway among endangered aquatic mammals

Synopsis

The ectodysplasin pathway has been a target of evolution repeatedly. Genetic variation in the key genes of this pathway (EDA, EDAR, and EDARADD) results in a rich source of pleiotropic effects across ectodermally-derived structures, including teeth, hair, sweat glands, and mammary glands. In addition, a non-canonical Wnt pathway has a very similar functional role, making variation in the WNT10A gene also of evolutionary significance. The adaptation of mammals to aquatic environments has occurred independently in at least 4 orders, whose species occupy a wide geographic range (from equatorial to polar regions) and exhibit great phenotypic variation in ectodermally-derived structures, including the presence or absence of fur and extreme lactational strategies. The role of the ectodysplasin pathway in the adaptation to aquatic environments has been never explored in mammalian species. In the present study, we analyze the genetic variation in orthologous coding sequences from EDA, EDAR, EDARADD, and WNT10A genes together with ectodermally-derived phenotypic variation from 34 aquatic and non-aquatic mammalian species to assess signals of positive selection, gene-trait coevolution, and genetic convergence. Our study reveals strong evidence of positive selection in a proportion of coding sites in EDA and EDAR genes in 3 endangered aquatic mammals (the Hawaiian monk seal, the Yangtze finless porpoise, and the sea otter). We hypothesize functional implications potentially related to the adaptation to the low-latitude aquatic environment in the Hawaiian monk seal and the freshwater in the Yangtze finless porpoise. The signal in the sea otter is likely the result of an increased genetic drift after an intense bottleneck and reduction of genetic diversity. Besides positive selection, we have not detected robust signals of gene-trait coevolution or convergent amino acid shifts in the ectodysplasin pathway associated with shared phenotypic traits among aquatic mammals. This study provides new evidence of the evolutionary role of the ectodysplasin pathway and encourages further investigation, including functional studies, to fully resolve its relationship with mammalian aquatic adaptation.

Spanish

La vía de la ectodisplasina ha sido objeto de la evolución repetidamente. La variación genética en los principales genes de esta vía (EDA, EDAR y EDARADD) da como resultado una gran diversidad de efectos pleiotrópicos en las estructuras derivadas del ectodermo, incluidos los dientes, el cabello, las glándulas sudoríparas y las glándulas mamarias. Además, una vía wnt no canónica tiene un papel funcional muy similar, por lo que la variación en el gen WNT10A también tiene importancia evolutiva. La adaptación de los mamíferos a los entornes acuáticos se ha producido de forma independiente en al menos cuatro órdenes, cuyas especies ocupan un amplio rango geográfico (desde regiones ecuatoriales a polares) y presentan una gran variación fenotípica en las estructuras derivadas del ectodermo, incluyendo la presencia o ausencia de pelaje y estrategias de lactancia muy diferentes. El papel de la vía de la ectodisplasina en la adaptación a entornos acuáticos no se ha explorado nunca en especies de mamíferos. En este estudio, analizamos la variación genética en las secuencias codificantes ortólogas de los genes EDA, EDAR, EDARADD y WNT10A junto con la variación fenotípica derivada del ectodermo de 34 especies de mamíferos acuáticos y no acuáticos para evaluar señales de selección positiva, coevolución gen-rasgo y convergencia genética. Nuestro estudio revela señales de selección positiva en regiones de las secuencias codificantes de los genes EDA y EDAR en tres mamíferos acuáticos en peligro de extinción (la foca monje de Hawái, la marsopa lisa y la nutria marina). Estas señales podrían tener implicaciones funcionales potencialmente relacionadas con la adaptación al entorno acuático de baja latitud en la foca monje de Hawái y el agua dulce en la marsopa lisa. La señal en la nutria marina es probablemente el resultado de una mayor deriva genética tras un intenso un cuello de botella y una reducción de la diversidad genética. A parte de selección positiva, no hemos detectado señales sólidas de coevolución gen-rasgo o cambios convergentes de aminoácidos en la vía de la ectodisplasina asociados a rasgos fenotípicos compartidos entre mamíferos acuáticos. Este estudio proporciona nuevas evidencias del papel evolutivo de la vía de la ectodisplasina y quiere promover futuras investigaciones con estudios funcionales para acabar de resolver la relación de esta vía con la adaptación acuática de los mamíferos.

Correction of Vertebral Bone Development in Ectodysplasin A1-Deficient Mice by Prenatal Treatment With a Replacement Protein

X-linked hypohidrotic ectodermal dysplasia with the cardinal symptoms hypodontia, hypotrichosis and hypohidrosis is caused by a genetic deficiency of ectodysplasin A1 (EDA1). Prenatal EDA1 replacement can rescue the development of skin appendages and teeth. Tabby mice, a natural animal model of EDA1 deficiency, additionally feature a striking kink of the tail, the cause of which has remained unclear. We studied the origin of this phenomenon and its response to prenatal therapy. Alterations in the distal spine could be noticed soon after birth, and kinks were present in all Tabby mice by the age of 4 months. Although their vertebral bones frequently had a disorganized epiphyseal zone possibly predisposing to fractures, cortical bone density was only reduced in vertebrae of older Tabby mice and even increased in their tibiae. Different availability of osteoclasts in the spine, which may affect bone density, was ruled out by osteoclast staining. The absence of hair follicles, a well-known niche of epidermal stem cells, and much lower bromodeoxyuridine uptake in the tail skin of 9-day-old Tabby mice rather suggest the kink being due to a skin proliferation defect that prevents the skin from growing as fast as the skeleton, so that caudal vertebrae may be squeezed and bent by a lack of skin. Early postnatal treatment with EDA1 leading to delayed hair follicle formation attenuated the kink, but did not prevent it. Tabby mice born after prenatal administration of EDA1, however, showed normal tail skin proliferation, no signs of kinking and, interestingly, a normalized vertebral bone density. Thus, our data prove the causal relationship between EDA1 deficiency and kinky tails and indicate that hair follicles are required for murine tail skin to grow fast enough. Disturbed bone development appears to be partially pre-determined in utero and can be counteracted by timely EDA1 replacement, pointing to a role of EDA1 also in osteogenesis.

Tumor Necrosis Factor Superfamily: Ancestral Functions and Remodeling in Early Vertebrate Evolution

The evolution of the tumor necrosis factor superfamily (TNFSF) in early vertebrates is inferred by comparing the TNFSF genes found in humans and nine fishes: three agnathans, two chondrichthyans, three actinopterygians, and the sarcopterygian Latimeria chalumnae. By combining phylogenetic and synteny analyses, the TNFSF sequences detected are classified into five clusters of genes and 24 orthology groups. A model for their evolution since the origin of vertebrates is proposed. Fifteen TNFSF genes emerged from just three progenitors due to the whole-genome duplications (WGDs) that occurred before the agnathan/gnathostome split. Later, gnathostomes not only kept most of the genes emerged in the WGDs but soon added several tandem duplicates. More recently, complex, lineage-specific patterns of duplications and losses occurred in different gnathostome lineages. In agnathan species only seven to eight TNFSF genes are detected, because this lineage soon lost six of the genes emerged in the ancestral WGDs and additional losses in both hagfishes and lampreys later occurred. The orthologs of many of these lost genes are, in mammals, ligands of death-domain-containing TNFSF receptors, indicating that the extrinsic apoptotic pathway became simplified in the agnathan lineage. From the patterns of emergence of these genes, it is deduced that both the regulation of apoptosis and the control of the NF-κB pathway that depends in modern mammals on TNFSF members emerged before the ancestral vertebrate WGDs.

Sweat gland regeneration: Current strategies and future opportunities

For patients with extensive skin defects, loss of sweat glands (SwGs) greatly decreases their quality of life. Indeed, difficulties in thermoregulation, ion reabsorption, and maintaining fluid balance might render them susceptible to hyperthermia, heatstroke, or even death. Despite extensive studies on the stem cell biology of the skin in recent years, in-situ regeneration of SwGs with both structural and functional fidelity is still challenging because of the limited regenerative capacity and cell fate control of resident progenitors. To overcome these challenges, one must consider both the intrinsic factors relevant to genetic and epigenetic regulation and cues from the cellular microenvironment. Here, we describe recent progress in molecular biology, developmental pathways, and cellular evolution associated with SwGdevelopment and maturation. This is followed by a summary of the current strategies used for cell-fate modulation, transmembrane drug delivery, and scaffold design associated with SwGregeneration. Finally, we offer perspectives for creating more sophisticated systems to accelerate patients' innate healing capacity and developing engineered skin constructs to treat or replace damaged tissues structurally and functionally.

Whole genome sequence analysis reveals genetic structure and X-chromosome haplotype structure in indigenous Chinese pigs

Chinese indigenous pigs exhibit considerable phenotypic diversity, but their population structure and the genetic basis of agriculturally important traits need further exploration. Here, we sequenced the whole genomes of 24 individual pigs representing 22 breeds distributed throughout China. For comparison with European and commercial breeds (one pig per breed), we included seven published pig genomes with our new genomes for analyses. Our results showed that breeds grouped together based on morphological classifications are not necessarily more genetically similar to each other than to breeds from other groups. We found that genetic material from European pigs likely introgressed into five Chinese breeds. We have identified two new subpopulations of domestic pigs that encompass morphology-based criteria in China. The Southern Chinese subpopulation comprises the classical South Chinese Type and part of the Central China Type. In contrast, the Northern Chinese subpopulation comprises the North China Type, the Lower Yangtze River Basin Type, the Southwest Type, the Plateau Type, and the remainder of the Central China Type. Eight haplotypes and two recombination sites were identified within a conserved 40.09 Mb linkage-disequilibrium (LD) block on the X chromosome. Potential candidate genes (LEPR, FANCC, COL1A1, and PCCA) influencing body size were identified. Our findings provide insights into the phylogeny of Chinese indigenous pig breeds and benefit gene mining efforts to improve major economic traits.

Prenatal Treatment of X-Linked Hypohidrotic Ectodermal Dysplasia using Recombinant Ectodysplasin in a Canine Model

X-linked hypohidrotic ectodermal dysplasia (XLHED) is caused by defects in the EDA gene that inactivate the function of ectodysplasin A1 (EDA1). This leads to abnormal development of eccrine glands, hair follicles, and teeth, and to frequent respiratory infections. Previous studies in the naturally occurring dog model demonstrated partial prevention of the XLHED phenotype by postnatal administration of recombinant EDA1. The results suggested that a single or two temporally spaced injections of EDI200 prenatally might improve the clinical outcome in the dog model. Fetuses received ultrasound-guided EDI200 intra-amniotically at gestational days 32 and 45, or 45 or 55 alone (of a 65-day pregnancy). Growth rates, lacrimation, hair growth, meibomian glands, sweating, dentition, and mucociliary clearance were compared in treated and untreated XLHED-affected dogs, and in heterozygous and wild-type control dogs. Improved phenotypic outcomes were noted in the earlier and more frequently treated animals. All animals treated prenatally showed positive responses compared with untreated dogs with XLHED, most notably in the transfer of moisture through paw pads, suggesting improved onset of sweating ability and restored meibomian gland development. These results exemplify the feasibility of ultrasound-guided intra-amniotic injections for the treatment of developmental disorders, with improved formation of specific EDA1-dependent structures in dogs with XLHED.

Divergent genetic mechanism leads to spiny hair in rodents

Spines, or modified hairs, have evolved multiple times in mammals, particularly in rodents. In this study, we investigated the evolution of spines in six rodent families. We first measured and compared the morphology and physical properties of hairs between paired spiny and non-spiny sister lineages. We found two distinct hair morphologies had evolved repeatedly in spiny rodents: hairs with a grooved cross-section and a second near cylindrical form. Compared to the ancestral elliptical-shaped hairs, spiny hairs had higher tension and stiffness, and overall, hairs with similar morphology had similar functional properties. To examine the genetic basis of this convergent evolution, we tested whether a single amino acid change (V370A) in the Ectodysplasin A receptor (Edar) gene is associated with spiny hair, as this substitution causes thicker and straighter hair in East Asian human populations. We found that most mammals have the common amino acid valine at position 370, but two species, the kangaroo rat (non-spiny) and spiny pocket mouse (spiny), have an isoleucine. Importantly, none of the variants we identified are associated with differences in rodent hair morphology. Thus, the specific Edar mutation associated with variation in human hair does not seem to play a role in modifying hairs in wild rodents, suggesting that different mutations in Edar and/or other genes are responsible for variation in the spiny hair phenotypes we observed within rodents.

Human adipose tissue-derived stem cells inhibit the activity of keloid fibroblasts and fibrosis in a keloid model by paracrine signaling

BACKGROUND

Human adipose tissue-derived mesenchymal stem cells (ASCs) have potential utility as modulators of the regeneration of tissue that is inflamed or scarred secondary to injuries such as burns or trauma. However, the effect of ASCs on one particular type of scarring, keloidal disease, remains unknown. The absence of an optimal model for investigation has hindered the development of an effective therapy using ASCs for keloids.

OBJECTIVE

To investigate the influence of ASCs on angiogenesis, extracellular matrix deposition, and inflammatory cell influx in keloids.

METHODS

We analyzed the proliferation, migration, and apoptosis of human keloid-derived fibroblasts treated with a starvation-induced, conditioned medium from ASCs (ASCs-CM). This was achieved by Brdu proliferation assay, a validated co-culture migration assay, and flow cytometry, respectively. To assess the change in phenotype to a pro-fibrotic state, fibroblasts were analyzed by real-time PCR and contraction assay. A keloid implantation animal model was used to assess the paracrine effect of ASCs histochemically and immunohistochemically on scar morphology, collagen deposition, inflammatory cell composition, and blood vessel density. In tandem, an antibody-based array was used to identify protein concentration in the presence of ASCs-CM at time point 0, 24, and 48h.

RESULTS

ASCs-CM inhibited the proliferation and collagen synthesis of human keloid-derived fibroblasts. ASCs-CM was associated with reduced inflammation and fibrosis in the keloid implantation model. Thirty-four cytokines were differentially regulated by ASCs-CM at 24h. These included molecules associated with apoptosis, matrix metalloproteases, and their inhibitors. The same molecules were present at relatively higher concentrations at the 48h timepoint.

CONCLUSION

These results suggest that ASCs are associated with the inhibition of fibrosis in keloids by a paracrine effect. This phenomenon may have utility as a therapeutic approach in the clinical environment.

Hypohidrotic Ectodermal Dysplasia: Breastfeeding Complications Due to Impaired Breast Development

Background X-linked hypohidrotic ectodermal dysplasia (XLHED), the most common form of ectodermal dysplasia, is caused by mutations in the gene EDA. While only affected men develop the full-blown clinical picture, females who are heterozygous for an EDA mutation often also show symptoms such as hypodontia, hypotrichosis and hypohidrosis. These women may also suffer from malformations of the mammary gland which represent not just a cosmetic problem but can limit their breastfeeding capability. This paper summarizes the findings of the first systematic study on the impact of hypohidrotic ectodermal dysplasia on breastfeeding. Patients Thirty-eight adult female members of the German-Swiss-Austrian ectodermal dysplasia patient support group participated in a structured interview; most of them also agreed to a photodocumentation of their mammary region. Thirty-one women carried mutations in EDA (Group A) and seven were affected by other forms of hypohidrotic ectodermal dysplasia (Group B). Results 39 % of the women of Group A reported that their breasts were of different size or entirely absent on one side. In Group B, 86 % of the women reported differently sized or even absent breasts; two of these women lacked both breasts entirely. Most women described their nipples as exceptionally flat. 10 % of the women of Group A had more than two nipples. The high percentage of deviations from the norm was confirmed in the photodocumentation. Both groups had few or no sebaceous glands of Montgomery in the areolar region. Around 80 % of interviewed women had children and had attempted to breastfeed their first child. 67 % of the mothers in Group A had had difficulty in breastfeeding their infants and generally attributed this difficulty to their flat nipples. All of the mothers in Group B reported difficulties in breastfeeding; 60 % had not been able to breastfeed their first child. Conclusion Mothers with hypohidrotic ectodermal dysplasia very often have difficulty in breastfeeding because of their impaired breast development. This causal relationship needs to be taken into account in lactation counseling.

Ectodysplasin signalling genes and phenotypic evolution in sculpins (Cottus)

Despite their deeply conserved function among vertebrates, ectodysplasin (Eda) signalling genes are involved in microevolutionary change in humans and sticklebacks. If such a dual role is common, Eda signalling genes constitute hotspots for morphological evolution. Variation in sculpin (Cottus) skin prickling and body shape resembles patterns caused by variation in Eda signalling in sticklebacks. We mapped Eda signalling genes and performed quantitative trait locus mapping in crosses between Cottus rhenanus and Cottus perifretum. A genomic region containing the Eda receptor (Edar) was strongly associated with prickling and contributed to shape. The expression of Edar in developing prickles and skeletal elements in Cottus was confirmed by in situ hybridization. Coding sequence changes between Edar alleles in C. rhenanus and C. perifretum exceeded sequence differentiation in other vertebrates. However, it is likely that additional genetic elements besides coding changes affect the phenotypic variation. Although the phenotype in a natural hybrid lineage between C. rhenanus and C. perifretum resembles C. perifretum, the respective coding Edar alleles are not fully fixed (88.6%). Hence, our results support an involvement of Eda signalling in microevolutionary changes, but imply that the Edar gene is affected by multiple evolutionary processes that vary among freshwater sculpins.

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.

Ectodysplasin A Pathway Contributes to Human and Murine Skin Repair

The highly conserved ectodysplasin A (EDA)/EDA receptor signaling pathway is critical during development for the formation of skin appendages. Mutations in genes encoding components of the EDA pathway disrupt normal appendage development, leading to the human disorder hypohidrotic ectodermal dysplasia. Spontaneous mutations in the murine Eda (Tabby) phenocopy human X-linked hypohidrotic ectodermal dysplasia. Little is known about the role of EDA signaling in adult skin homeostasis or repair. Because wound healing largely mimics the morphogenic events that occur during development, we propose a role for EDA signaling in adult wound repair. Here we report a pronounced delay in healing in Tabby mice, demonstrating a functional role for EDA signaling in adult skin. Moreover, pharmacological activation of the EDA pathway in both Tabby and wild-type mice significantly accelerates healing, influencing multiple processes including re-epithelialization and granulation tissue matrix deposition. Finally, we show that the healing promoting effects of EDA receptor activation are conserved in human skin repair. Thus, targeted manipulation of the EDA/EDA receptor pathway has clear therapeutic potential for the future treatment of human pathological wound healing.

Tinkering signaling pathways by gain and loss of protein isoforms: the case of the EDA pathway regulator EDARADD

Background

Only a handful of signaling pathways are major actors of development and responsible for both the conservation and the diversification of animal morphologies. To explain this twofold nature, gene duplication and enhancer evolution were predominantly put forth as tinkering mechanisms whereas the evolution of alternative isoforms has been, so far, overlooked. We investigate here the role of gain and loss of isoforms using Edaradd, a gene of the Ecodysplasin pathway, implicated in morphological evolution. A previous study had suggested a scenario of isoform gain and loss with an alternative isoform (A) newly gained in mammals but secondarily lost in mouse lineage.

Results

For a comprehensive view of A and B Edaradd isoforms history during mammal evolution, we obtained sequences for both isoforms in representative mammals and performed in vitro translations to support functional predictions. We showed that the ancestral B isoform is well conserved, whereas the mammal-specific A isoform was lost at least 7 times independently in terminal lineages throughout mammal phylogeny. Then, to gain insights into the functional relevance of this evolutionary pattern, we compared the biological function of these isoforms: i) In cellulo promoter assays showed that they are transcribed from two alternative promoters, only B exhibiting feedback regulation. ii) RT-PCR in various tissues and ENCODE data suggested that B isoform is systematically expressed whereas A isoform showed a more tissue-specific expression. iii) Both isoforms activated the NF-κB pathway in an in cellulo reporter assay, albeit at different levels and with different dynamics since A isoform exhibited feedback regulation at the protein level. Finally, only B isoform could rescue a zebrafish edaradd knockdown.

Conclusions

These results suggest that the newly evolved A isoform enables modulating EDA signaling in specific conditions and with different dynamics. We speculate that during mammal diversification, A isoform regulation may have evolved rapidly, accompanying and possibly supporting the diversity of ectodermal appendages, while B isoform may have ensured essential roles. This study makes the case to pay greater attention to mosaic loss of evolutionarily speaking “young” isoforms as an important mechanism underlying phenotypic diversity and not simply as a manifestation of neutral evolution.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0395-0) contains supplementary material, which is available to authorized users.

Generation and characterization of function-blocking anti-ectodysplasin A (EDA) monoclonal antibodies that induce ectodermal dysplasia

Development of ectodermal appendages, such as hair, teeth, sweat glands, sebaceous glands, and mammary glands, requires the action of the TNF family ligand ectodysplasin A (EDA). Mutations of the X-linked EDA gene cause reduction or absence of many ectodermal appendages and have been identified as a cause of ectodermal dysplasia in humans, mice, dogs, and cattle. We have generated blocking antibodies, raised in Eda-deficient mice, against the conserved, receptor-binding domain of EDA. These antibodies recognize epitopes overlapping the receptor-binding site and prevent EDA from binding and activating EDAR at close to stoichiometric ratios in in vitro binding and activity assays. The antibodies block EDA1 and EDA2 of both mammalian and avian origin and, in vivo, suppress the ability of recombinant Fc-EDA1 to rescue ectodermal dysplasia in Eda-deficient Tabby mice. Moreover, administration of EDA blocking antibodies to pregnant wild type mice induced in developing wild type fetuses a marked and permanent ectodermal dysplasia. These function-blocking anti-EDA antibodies with wide cross-species reactivity will enable study of the developmental and postdevelopmental roles of EDA in a variety of organisms and open the route to therapeutic intervention in conditions in which EDA may be implicated.

The effects of cytokines in adipose stem cell-conditioned medium on the migration and proliferation of skin fibroblasts in vitro

Although adipose stem cell-conditioned medium (ASC-CM) has demonstrated the effect of promoting the cutaneous wound healing, the mechanism for this response on the effector cells (e.g., dermal fibroblasts) during the process remains to be determined. In this study, we aim to investigate the types and contents of cytokines in ASC-CM and the effects of some kinds of common cytokines in ASC-CM, such as EGF, PDGF-AA, VEGF, and bFGF, on dermal fibroblasts proliferation and migration in wound healing process. Results showed that these four cytokines had high concentrations in ASC-CM. The migration of skin fibroblasts could be significantly stimulated by VEGF, bFGF, and PDGF-AA, and the proliferation could be significantly stimulated by bFGF and EGF in ASC-CM. Additionally, ASC-CM had more obvious promoting effect on fibroblasts proliferation and migration than single cytokine. These observations suggested that ASC-CM played an important role in the cutaneous injury partly by the synergistic actions of several cytokines in promoting dermal fibroblasts proliferation and migration, and ASC-CM was more adaptive than each single cytokine to be applied in promoting the wound healing.

The ectodysplasin pathway: from diseases to adaptations

The ectodysplasin (EDA) pathway, which is active during the development of ectodermal organs, including teeth, hairs, feathers, and mammary glands, and which is crucial for fine-tuning the developmental network controlling the number, size, and density of these structures, was discovered by studying human patients affected by anhidrotic/hypohidrotic ectodermal dysplasia. It comprises three main gene products: EDA, a ligand that belongs to the tumor necrosis factor (TNF)-α family, EDAR, a receptor related to the TNFα receptors, and EDARADD, a specific adaptor. This core pathway relies on downstream NF-κB pathway activation to regulate target genes. The pathway has recently been found to be associated with specific adaptations in natural populations: the magnitude of armor plates in sticklebacks and the hair structure in Asian human populations. Thus, despite its role in human disease, the EDA pathway is a 'hopeful pathway' that could allow adaptive changes in ectodermal appendages which, as specialized interfaces with the environment, are considered hot-spots of morphological evolution.

Origin and evolution of TNF and TNF receptor superfamilies

The tumor necrosis factor superfamily (TNFSF) and the TNF receptor superfamily (TNFRSF) have an ancient evolutionary origin that can be traced back to single copy genes within Arthropods. In humans, 18 TNFSF and 29 TNFRSF genes have been identified. Evolutionary models account for the increase in gene number primarily through multiple whole genome duplication events as well as by lineage and/or species-specific tandem duplication and translocation. The identification and functional analyses of teleost ligands and receptors provide insight into the critical transition between invertebrates and higher vertebrates. Bioinformatic analyses of fish genomes and EST datasets identify 14 distinct ligand groups, some of which are novel to teleosts, while to date, only limited numbers of receptors have been characterized in fish. The most studied ligand is TNF of which teleost species possess between 1 and 3 copies as well as a receptor similar to TNFR1. Functional studies using zebrafish indicate a conserved role of this ligand-receptor system in the regulation of cell survival and resistance to infectious disease. The increasing interest and use of TNFSF and TNFRSF modulators in human and animal medicine underscores the need to understand the evolutionary origins as well as conserved and novel functions of these biologically important molecules.

Molecular aspects of hypohidrotic ectodermal dysplasia

Hypohidrotic (anhidrotic) ectodermal dysplasia (HED) is a congenital syndrome characterized by sparse hair, oligodontia, and reduced sweating. It is caused by mutations in any of the three Eda pathway genes: ectodysplasin (Eda), Edar, and Edaradd which encode a ligand, a receptor, and an intracellular signal mediator of a single linear pathway, respectively. In rare cases, HED is associated with immune deficiency caused by mutations in further downstream components of the Eda pathway that are necessary for the activation of the transcription factor NF-kappaB. Here I present a brief research update on the molecular aspects of this evolutionarily conserved pathway. The developmental role of Eda will be discussed in light of loss- and gain-of-function mouse models with emphasis on the past few years.

Enhanced Edar signalling has pleiotropic effects on craniofacial and cutaneous glands

The skin carries a number of appendages, including hair follicles and a range of glands, which develop under the influence of EDAR signalling. A gain of function allele of EDAR is found at high frequency in human populations of East Asia, with genetic evidence suggesting recent positive selection at this locus. The derived EDAR allele, estimated to have reached fixation more than 10,000 years ago, causes thickening of hair fibres, but the full spectrum of phenotypic changes induced by this allele is unknown. We have examined the changes in glandular structure caused by elevation of Edar signalling in a transgenic mouse model. We find that sebaceous and Meibomian glands are enlarged and that salivary and mammary glands are more elaborately branched with increased Edar activity, while the morphology of eccrine sweat and tracheal submucosal glands appears to be unaffected. Similar changes to gland sizes and structures may occur in human populations carrying the derived East Asian EDAR allele. As this allele attained high frequency in an environment that was notably cold and dry, increased glandular secretions could represent a trait that was positively selected to achieve increased lubrication and reduced evaporation from exposed facial structures and upper airways.

Distinct impacts of Eda and Edar loss of function on the mouse dentition

Background

The Eda-A1-Edar signaling pathway is involved in the development of organs with an ectodermal origin, including teeth. In mouse, mutants are known for both the ligand, Eda-A1 (Tabby), and the receptor, Edar (Downless). The adult dentitions of these two mutants have classically been considered to be similar. However, previous studies mentioned differences in embryonic dental development between Eda^Ta and Edar^dl-J mutants. A detailed study of tooth morphology in mutants bearing losses of functions of these two genes thus appears necessary to test the pattern variability induced by the developmental modifications.

Methodology/Principal Findings

3D-reconstructions of the cheek teeth have been performed at the ESRF (Grenoble, France) by X-ray synchrotron microtomography to assess dental morphology. The morphological variability observed in Eda^Ta and Edar^dl-J mutants have then been compared in detail. Despite patchy similarities, our detailed work on cheek teeth in Eda^Ta and Edar^dl-J mice show that all dental morphotypes defined in Edar^dl-J mice resolutely differ from those of Eda^Ta mice. This study reveals that losses of function of Eda and Edar have distinct impacts on the tooth size and morphology, contrary to what has previously been thought.

Conclusion/Signifiance

The results indicate that unknown mechanisms of the Eda pathway are implicated in tooth morphogenesis. Three hypotheses could explain our results; an unexpected role of the Xedar pathway (which is influenced by the Eda gene product but not that of Edar), a more complex connection than has been appreciated between Edar and another protein, or a ligand-independent activity for Edar. Further work is necessary to test these hypotheses and improve our understanding of the mechanisms of development.

Analysis of the temporal requirement for eda in hair and sweat gland development

EDA signaling is important in skin appendage initiation. Its possible involvement in appendage subtype determination and postinduction stage appendage development, however, has not been studied systematically. To address these issues we manipulated Eda-A1 transgene expression in a tetracycline-regulated conditional mouse model, where the transgene is the only source of active ectodysplasin (Eda). We find that Eda-A1 restores sweat glands and all hair subtypes in Tabby, but each requires its action at an idiosyncratic time of development: by E17 for guard, by E19 for awl, and starting at E18 for zigzag/auchen hair. Guard and awl hairs were indistinguishable from their wild-type counterparts; but restored zigzag and auchen hairs, although recognizable, were somewhat smaller and lacked characteristic bends. Notably, secondary hair follicle formation of awl, auchen, and zigzag hairs required higher Eda-A1 expression level than did guard hair or sweat glands. Furthermore, Eda-A1 expression is required until the early dermal papilla stage for guard hair germs to make follicles, but is dispensable for their maturation. Similarly, sweat gland pegs require Eda-A1 at an early stage to form mature glands. Thus we infer that EDA signaling is needed for the determination and development of various skin appendages at spatiotemporally restricted intervals.

The evolution of the ligand/receptor couple: a long road from comparative endocrinology to comparative genomics

Comparative endocrinology considers the evolution of bioregulatory systems and the anatomical structures and molecules that constitute the neuroendocrine and endocrine systems. One aim of comparative endocrinology is to trace the origins of the main endocrine systems. The understanding of the evolution of the ligand/receptor couple is central to this objective. One classical approach to tackle this question is the characterization of receptors and ligands in various types of non-model organisms using as a starting point the knowledge accumulated on classical models such as mammals (mainly human and mouse) and arthropods (with Drosophila among other insects). In this review we discuss the potential caveats associated to this two-by-two comparison between a classical model and non-model organisms. We suggest that the use of an evolutionary approach involving comparisons of several organisms in a coherent framework permits reconstruction of the most probable scenarios. The use of the vast amount of genomic data now available, coupled to functional experiments, offers unprecedented possibilities to trace back the origins of the main ligand/receptor couples.

A replication study confirmed the EDAR gene to be a major contributor to population differentiation regarding head hair thickness in Asia

Hair morphology is a highly divergent phenotype among human populations. We recently reported that a nonsynonymous SNP in the ectodysplasin A receptor (EDAR 1540T/C) is associated with head hair fiber thickness in an ethnic group in Thailand (Thai-Mai) and an Indonesian population. However, these Southeast Asian populations are genetically and geographically close, and thus the genetic contribution of EDAR to hair morphological variation in the other Asian populations has remained unclear. In this study, we examined the association of 1540T/C with hair morphology in a Japanese population (Northeast Asian). As observed in our previous study, 1540T/C showed a significant association with hair cross-sectional area (P = 2.7 x 10(-6)) in Japanese. When all populations (Thai-Mai, Indonesian, and Japanese) were combined, the association of 1540T/C was stronger (P = 3.8 x 10(-10)) than those of age, sex, and population. These results indicate that EDAR is the genetic determinant of hair thickness as well as a strong contributor to hair fiber thickness variation among Asian populations.