PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Cell Cycle. Author manuscript; available in PMC Apr 27, 2010.
Published in final edited form as:
Published online Sep 14, 2006.
PMCID: PMC2860309
NIHMSID: NIHMS191392
EDA Signaling and Skin Appendage Development
Chang-Yi Cui and David Schlessinger*
Laboratory of Genetics; National Institute on Aging; National Institutes of Health; Baltimore, Maryland USA
* Correspondence to: David Schlessinger; Laboratory of Genetics; National Institute on Aging; National Institutes of Health; 333 Cassell Dr.; Suite 3000; Baltimore, Maryland 21224 USA; Tel.: 410.558.8337; Fax: 410.558.8331; SchlessingerD/at/grc.nia.nih.gov
The same morphogenetic signals are often involved in the development of different organs. For developing skin appendages, a model for tissue-specific regulation of signaling is provided by the EDA pathway, which accesses the otherwise ubiquitous NFκB transcription factors. EDA signaling is mediated by ectodysplasin, EDAR and EDARADD, which form a new TNF ligand-receptor-adaptor family that is restricted to skin appendages in vertebrates from fish to human. The critical function of the pathway was demonstrated in the hereditary genetic disorder Anhidrotic Ectodermal Dysplasia (EDA), which is characterized by defective formation of hair follicles, sweat glands and teeth. The pathway does not appear to initiate the development of the appendages, but is regulated by and regulates the course of further morphogenesis. In mice, transgenic and knockout strains have increasingly revealed features of the mechanism, and suggest possible non-invasive interventions to alleviate EDA deficiency, especially in sweat glands and eyes.
Keywords: Ectodysplasin, EDAR, hair follicles, sweat glands, NFκBs, lymphotoxin, Troy
Skin appendages include hair follicles, nails, teeth and exocrine glands in mammals, feathers in birds, and scales in fish. Their exquisite adaptations for diverse physiological functions have attracted scientists to investigate the differential morphogenetic mechanisms. Follicle transplantation experiments, gene engineering, and genome-wide transcription profiling of skin and skin appendages have progressively discerned molecular mechanisms involved in skin appendage development.1,2 General signaling pathways such as Wnt, Shh, BMP and Notch all participate; the EDA signaling pathway rather modulates more general signals to promote the formation of specific nascent appendages.35
Anhidrotic/hypohidrotic ectodermal dysplasia (EDA) is the most frequent of a group of ectodermal dysplasias (EDs) that affect morphogenesis of two or more skin appendages (OMIM 34500). EDA affects development of hair, teeth and several exocrine glands, including sweat, meibomian and preputial glands.6
As a hereditary genetic disorder, EDA occurs in X-linked recessive, autosomal dominant, and autosomal recessive forms.79 Notably, the X-linked form was first described by Charles Darwin in 1875 in his book, “The variations of animals and plants under domestication”, in which he recorded precisely the skin appendage phenotypes and male-specific inheritance pattern of an affected Indian family.10 More than 100 years later, three genes mutated in various cases have been identified from patients. The X-linked EDA gene is mutated in more than 90% of cases, and EDAR and EDARADD genes account for most of the rarer instances of autosomal inheritances.711 Unanticipated were the findings that the EDA, EDAR and EDARADD genes encode a new TNF ligand-receptor-adaptor family - the first to be involved in skin appendage development (Fig. 1 and see below).8,9,12
Figure 1
Figure 1
Schematic representation of EDA signaling. EDA is expressed in interfollicular cells; its receptor EDAR in follicular cells. Wnt/Lef1 and other putative signals (GATA, Nkx2 and ???) regulate transcription. The protein product ectodysplasin, is cleaved (more ...)
It has turned out that mouse models for EDA have been available since early in the last century. Isolated as spontaneous mutant strains, Tabby, Downless/Sleek and Crinkled have been demonstrated to be mutated in the corresponding Eda, Edar, and Edaradd genes.8,9,13 Confirming their positioning in the same signaling pathway, the mutant strains show identical “all or none” skin appendage phenotypes. Sweat glands and two of the three types of mouse hair, “Guard” and “Zigzag”, are lacking; but a normal number of hair follicles is still formed, all of them producing an abnormal variant of the “Medium”, third type of hair.14,15 In addition, aberrant features of EDA in patients and a mouse model were reported recently in the ectodermally-derived cornea and conjunctiva.16,17 Thus patients and animal models have revealed the first actors in an EDA pathway, providing a novel system to study the development of ectoderm-derived tissues.
As comparative genomics and genetics has progressed, the EDA, EDAR and EDARADD genes initially discovered from patients and mouse models have been found to be highly conserved in other vertebrates, including fish, xenopus, chicken, dogs, cattle, and chimpanzee (e.g., EDAR in Fig. 2). Corresponding spontaneous mutant animal models for EDA pathway genes have thus far been identified in four species: Edar mutant medaka fish; Eda mutant dogs and cattle; and the Tabby, Downless/Sleek and Crinkled mouse mutants.8,9,13,1820 The skin appendages are often species-specific, so that in contrast to the effects on hair and sweat glands in mammals, fish show a loss of scales.18 In a recent study, the EDA gene was shown to be involved in adaptive evolution of armor plate patterning in three-spine stickleback fishes during the transition from marine to freshwater environment.21 A mouse Eda-A1 isoform restored marine-like armor plates to freshwater sticklebacks, a further indication of the adaptability of the gene to parallel evolution of skin appendages.21,22
Figure 2
Figure 2
Conservation of the EDAR protein during evolution. Complete (red) or partial (blue) homology of EDAR sequence tracts conserved between species. TNFR, transmembrane, and cytoplasmic death-domains (DD) are shown in thin, thick, and dotted underlines, respectively. (more ...)
Understanding EDA function in skin appendage development requires information about how EDA is regulated and how it regulates downstream targets.
We have shown that a 1.6kB genomic fragment upstream of EDA transcription start site includes most of the promoter and enhancer binding sites.23 By an extension of the approach, we extended the fragment to 5 kB and 15 kB upstream to study candidate promoter fragments, but transcription activity was unchanged, suggesting promoter and enhancer sites are concentrated in the small region (data not shown). EDA lacks basic TATA box, but has two active SP1 sites. Unlike other TATA-free, SP1-positive genes, however, EDA has a single transcription initiation site.23
A binding site for the Wnt pathway transcription factor Lef1 was detected in the 1.6 kB fragment.7,23 We demonstrated that the site is responsible for full activation of EDA transcription in cell transfection experiments (Fig. 1).24 Consistent with these results, Eda was not expressed in Lef1-null mouse skin, and Wnt6 induced Eda expression in a skin culture system.25 Though Wnt/Lef1 is probably not the sole regulator of EDA expression, because unlike Lef1, which shows a patterned focal expression in hair follicles, EDA is broadly transcribed in skin and hair follicles.25
Wnt signaling is thought to initiate hair follicle formation.26 EDA signaling would then occur directly downstream of the induction signal. Unlike Wnt pathway genes, over expression of Eda-A1 did not increase the number of hair follicles in mice, and the loss of Eda left the total number of hair follicles the same.15,26 Rather, its major effect was to change the types of hair produced from the nascent follicles (see below).
Two active candidate enhancer-binding sites, for GATA and Nkx2, were noted in the 1.6kB putative promoter fragment of the EDA gene (ref. 23 and our unpublished data). GATA and Nkx2 family members are known to interact with SP1 to effect tissue-specific and developmentally restricted expression of target genes, however, their role in EDA expression is still conjectural (Fig. 1). In fact, there is no explanation of the paradox that in spite of strong promoter and enhancer activity in vitro, EDA mRNA expression level in vivo is quite low.7,13,21 The full spectrum of regulatory sequences and protein factors affecting EDA transcription thus remain to be elucidated.
Ectodysplasin, encoded by the X-linked EDA gene, is a type II transmembrane protein.12 Ectodysplasin has a short collagen segment and a TNF domain in its extracellular region.12 A furin cleavage site near the collagen domain releases soluble EDA (TNF) ligands that then form active ligand-trimers comparable to those seen for other TNF ligand family members (Fig. 1).27,28 Missense or in-frame deletion mutations that cause the EDA syndrome are found in TNF, collagen, furin cleavage, and transmembrane sites.29,30
The TNF domain is the functional moiety of ectodysplasin, but mutations in patients indicate that the collagen domain also has an important though unknown function. The domain comprises 19 G-X-Y repeats in two neighboring stretches.13 In-frame deletion of 2 or 4 G-X-Y repeats has no effect on the functional TNF domain but causes EDA syndrome.29,30 One might expect that the domain could contribute to formation or stabilization of a ligand-trimer or multimer, as seen for complement protein C1q, which has 27 N-terminal G-X-Y repeats.27,31 However, the collagen domain in ectodysplasin lacks lysine, a critical cross-linking residue in standard collagen triple helices, including those in C1q-like proteins.32 Furthermore, the crystal structure of ectodysplasin suggests that the collagen domain is dispensable for ligand-trimer formation.33 Therefore the function of this domain remains an interesting puzzle.
That soluble EDA trimers initiate EDA signaling by binding to the receptor EDAR is well established.34 EDA-A1 was demonstrated to bind specifically to EDAR, and no affinity was detected for other TNF family members.34 EDAR has extracellular TNFR domains and an intracellular death domain (DD) region.8 The other DD-containing TNFR members, TNFR1, NGFR, DR3, 4, 5, 6 and Fas are all able to induce cell death, but there are contradictory reports about the ability of EDAR to promote cell death.3538
Its DD region is responsible for EDAR binding to its cytoplasmic signaling adaptor EDARADD.9 EDARADD is one of three DD-containing adaptor proteins identified in the TNF superfamily, and has high homology to the DD of Myd88, a cytoplasmic adaptor protein in the Toll/IL-1 signaling pathway.9 Like Myd88, EDARADD binds to the TRAF6/TAK1/TAB2 complex to activate the IKK complex (Fig. 1 and see below).39 Indeed, Traf6-deficient mice showed characteristic Tabby phenotypes along with immunodeficiency, suggesting that it is a critical mediator of EDA signaling.40
The EDA gene produces many splicing variants.41 Recently we recovered a total of 9 Eda-A isoforms from mouse keratinocytes.42 As predicted, A1 and A2 isoforms predominate, comprising about 80% of the total.42 The A2 isoform is only 2 amino acids shorter than A1, but binds to a different receptor, XEDAR, which also can activate NFκB mediated transcription in vitro.34,43 We also found two new isoforms, A5 and A5′, which bind to EDAR and XEDAR, respectively, and activate NFκBs in vitro.42
Especially because the Eda-A1 isoform does not fully rescue Tabby phenotypes (see below), involvement of alternative EDA signaling in the process might be anticipated, perhaps employing different isoforms and variant signaling cascades.15,44 However, signaling mediated by XEDAR seems dispensable for skin appendage development: Xedar knockout mice showed no skin appendage phenotypes and Eda-A2 transgenic mice showed no correction of Tabby phenotypes; and in contrast to the reported activity in vitro, a recent study suggests that EDA-A2/XEDAR pathway does not activate NFκBs in vivo.15,45,46
Another EDAR family member, Troy, is also highly expressed in skin appendages.46,47 To understand Troy function, we generated a mutant mouse strain by ENU mutagenesis (unpublished results).48 In the mice, in a C3H background, a missense mutation in the Troy coding region replaces a threonine with proline in TNFR domain 2 (at amino acid 109). We confirmed in cell transfection experiments that this mutation abolishes Troy function in NF-kB activation; but in the homozygous mutant mice hair follicles, hair shafts, hair type composition and sweat glands were all normal (work in progress).
Unlike EDAR, XEDAR and Troy both lack a death domain and are 55% homologous in their TNFR domain (and 100% homologous in cysteine residue content and placement). That is remarkably high for TNFR family members, and hints at a possible close functional relation between the two receptors.34,47 For example, the two might represent a redundant function, and it might then be informative to generate a mouse deficient in both.
As described above, the ectodysplasin-EDAR-EDARADD complex interacts with TRAF6 and thereby activates the IKK complex. The IKK complex contains two catalytic subunits, IKK1 and IKK2, and a regulatory subunit, NEMO (Fig. 1). The complex phosphorylates the downstream IkB complex, resulting in NFκB movement into the nucleus to activate transcription of responsive genes.49 Null mutations of the X-linked gene NEMO cause Incontinentia Pigmenti (IP2), a disorder in which males die in utero and heterozygous females show inflammatory and skin pigment changes in human patients and a mouse model.50,51 By contrast, less severe mutations in NEMO retain some NFκB activity and show characteristic EDA phenotypes along with immunodeficiency (EDA-ID).52,53 Thus, though the mechanism of pathological changes in these skin diseases remains largely unknown, NEMO is the mediator of EDA signaling to downstream targets (Fig. 1).50
EDA signaling is also likely mediated in part by IkBα (Fig. 1).54 EDA phenotypes along with immunodeficiency were observed in one patient with a mutant in the gene and in a mouse strain in which IkBα truncated at its N-terminus was inserted into a β-catenin gene.54,55 The mutant forms acted as a ‘super-repressor’ of NFκBs: they were no longer phosphorylatable by the IKK complex, thereby escaping subsequent degradation and maintaining NFκBs in the cytoplasm.54,55
NFκBs include 5 structurally related, evolutionarily conserved members—RelA (p65), p50, c-Rel, RelB and p52. Each can form either homo- or heterodimers, but with somewhat different properties.56 For example, RelA, c-Rel and RelB have a transcription regulatory domain, but p50 and p52 do not.56 Also, RelA, p50, c-Rel and RelB have been shown to regulate keratinocyte growth and differentiation, and to be involved in the pathogenesis of skin disorders including psoriasis, skin cancer, and inflammatory skin diseases.57 Mice deficient in RelA, c-Rel and TNFα lack Guard hair, a primary characteristic of Tabby animals.58 And in cell lines, EDA signaling up-regulates the expression of RelA/p50 but not RelB.46,52,59
Thus, genetic studies demonstrate the primacy of the ectodysplasin-EDAR-EDARADD-TRAF6-NEMO-IkBα-NFκB (RelA) signaling pathway in skin appendage development (Fig. 1), apparently working through the NEMO/IkBα-dependent canonical NFκB cascade.60 Any factors that affect NEMO or RelA activity in skin may result in Tabby-like phenotypes, as shown recently in mice transgenic for a glucocorticoid receptor (GR) under keratin 5 (K5) promoter control.61
The immediate downstream effectors TRAF6, NEMO, IkBα and NFκBs have the general roles usually associated with TNF-NFκB family members in immune or inflammatory processes.62 It is therefore not surprising that mutation in any of them causes severe immunodeficiency along with EDA phenotypes in mice and in human patients.40,5255 Although EDA is widely expressed in skin, its signaling becomes specific for skin appendage development because EDAR and EDARADD are only expressed in skin appendages.8,9 Thus, EDA can co-opt the function of immune pathway genes through EDARADD-TRAF6 interaction only in skin and at the time of appendage formation, and can thus act without accompanying immunodeficiency.39
General morphogenetic signaling pathways such as Wnt, BMP and Shh also play indispensable roles in skin appendage development.35 Their roles are, however, “double-edged”, because failure of fine regulation of the signals often results in skin tumorigenesis or “extreme phenotypes” such as embryonic lethality or excessive formation of skin appendages.26,6365 In contrast, EDA signaling is specific for skin appendage development, and overexpression or null mutations of the pathway genes only seem to modulate morphogenetic signals that have been otherwise turned on during development of the appendages.15,44,59
Our group and others have reported that Wnt, Shh, BMP and lymphotoxin-β (LTβ) pathways are located downstream of EDA signaling during Guard hair development (Fig. 1).8,25,59,66 EDA signaling was shown to positively activate Shh and LTβ pathways, but exerts a negative feedback regulation on Wnt and BMP pathways through pathway-specific antagonists.59 In particular, Wnt up-regulates EDA expression, but in turn, EDA signaling activates transcription of Wnt antagonists Dkk4 and Dkk1.24,25,59,67 The possible feedback regulatory action of EDA may provide a balance, helping to ensure proper function of the general morphogenetic signals while avoiding their potential “extreme effects” (Fig. 1).
Several groups have reported that expression of Shh pathway genes is most strikingly affected in Eda-null Tabby mice at various developmental stages, suggesting that this pathway is a proximal target of EDA signaling.8,25,46,59 However, Shh-null mice (and mice ablated for the downstream Shh effector Gli2) arrest hair follicle development only at E15.5, well after Guard hair peg formation; this is a phenotype strikingly different from mice deficient in other EDA pathway genes; and overexpression of Shh causes basal cell carcinoma-like skin tumors rather than augmented hair follicle formation.63,68,69 Therefore, although Shh expression was affected from very early embryonic stages in Tabby mice, its role in EDA signaling is still unclear.59
Lymphotoxin-β is a newly identified EDA target. It had previously been implicated only in immune system development, where LTβ initiates the noncanonical NF-kB pathway for lymphoid organogenesis in cooperation with LTα and LTβR.60,70 For hair follicle formation, however, mice defective in LTβ indicated that it primarily regulated hair shaft formation (again without effect on hair follicle induction); and unexpectedly, LTα and LTβR deficient mice showed normal hair follicles and hair shafts.59 Based on these findings, LTβ may have an unknown receptor active in hair follicle development.
An adhesion molecule, Madcam1 (mucosal addressin cell adhesion molecule 1) has also been suggested to be regulated by EDA signaling (Fig. 1).71 Madcam1 was transiently expressed in Guard hair germs but not in secondary hair follicles, and no expression was seen in Tabby, Downless or Traf6-null mice. Madcam1 has also been inferred as a target of lymphotoxin signaling in the immune system, raising the intriguing possibility that they cooperate in hair follicle development under EDA regulation.72,73
Overall, EDA signaling pathway is thus regulated by general morphogenetic signaling, but in turn regulates these pathways spatio-temporally for skin appendage formation, participating in later stages of specific organ development. A recent study found some premature Guard hair germs in the EDAR-deficient Downless mice at E14.5, again consistent with a role for EDA signaling only after the primary initiation signal.46
Though the EDA molecular pathway is increasingly characterized, its mechanism of action in skin appendage development is only partially known. As one approach to study the role of the gene in further detail, six Tabby mouse derivatives have been studied that are transgenic for EDA ligands under various promoters: CMV, conditional Tet (MMTV), K14 and Involucrin promoters for full length Eda-A1 or A2 transgenes; and K5 and myosin light-chain 2 (MLCH) promoters for the soluble part of EDA-A1 or A2.15,22,45,65,74 The results of studies with various models are concordant. In Tabby mice an A1 transgene restored Guard hair and sweat glands, but not Zigzag hair; whereas in wild-type mice the transgene suppressed Zigzag hair formation.15,22,65 The number of total back hairs was the same in Tabby mice and the transgenic strain, but hair development shifted.15 Guard hair number was restored to wild-type levels in transgenic mice, but some of the abnormal Tabby Awl hairs became structurally normal. This suggests that EDA-A1 is responsible for Guard hair formation and also participates in the patterning of nascent Awl hair.
In addition, the Eda-A1 transgene induced hypertrophic sebaceous glands, with both increased sebocyte numbers and size (but no indication of tumorigenesis).15,45,65 Because the Eda deficient Tabby mice still have sebaceous glands, this effect of EDA is inferred to be trophic rather than morphogenetic.15 This is the first indication that EDA can also act in selected targeted proliferative processes.
Notably, a recombinant EDA-A1 ligand on the IgG1 Fc tail showed restoration of skin appendages identical to the transgene when injected into pregnant Tabby mice intravenously—or for sweat glands, in the perinatal period.44 These results suggest a potential for therapeutic use (see below).
Three strains of Edar transgenic mice have also been studied, containing genomic Edar driven by the Edar promoter or a full-length or intracellular segment of Edar formed under K14 promoter control.7577 A genomic clone containing the gene fully restored Downless phenotypes, whereas the K14-driven full-length Edar unexpectedly suppressed Guard hair formation and the intracellular part of Edar led to disoriented hair follicles in slightly increased numbers.7577 Apparently, EDAR expression must be finely regulated for normal hair follicle formation.
Fundamental studies must (1) further analyze the initiation of the EDA pathway; (2) determine the downstream mechanism of action; and (3) assess possible therapeutic applications.
The initial regulatory steps in the EDA signaling pathway are still not fully understood. EDAR and EDARADD provide specificity for EDA signaling by restricting its expression to skin appendages. It was reported that recombinant activin A upregulates Edar expression in a skin culture system, but the factors that render EDAR expression tissue-specific have not been studied in detail.25 Furthermore, especially because Eda-A1 transgenes do not rescue all of the EDA phenotype, it remains possible that other EDA isoforms and receptors (including the large amounts of the EDA-A2 isoform and its specific receptor XEDAR, and perhaps the XEDAR-like Troy receptor) participate as well. Although knockout mouse models show dispensability of each of them for skin appendage formation, one can imagine, for example, that Troy and XEDAR have redundant actions in skin appendage formation and must both be disabled.
Downstream of the initiation of the pathway, the fundamental result remains that Eda-deficient mice still can form Medium-type hair. Only the first clues have been found to understand how EDA then participates in the generation of other hair types, and is dispensable for the formation of Medium hair. One extreme possibility is that different types of hair are generated by fundamentally different mechanisms, with EDA required only for Guard and Zigzag hair.8 Based on current data, Medium hair might, for example, be dependent only on Wnt/Lef1 and BMP/noggin.8,7881 However, direct studies of Guard hair formation show EDA signaling cooperating with Wnt, Shh and BMP pathways from the earliest stages.24,25,59 Furthermore, in humans all hair seems to be dependent on EDA; and in both mouse and man, sweat glands are completely EDA-dependent. In wild-type mice bearing an Eda-A1 transgene and to some extent in LTβ-null mice, Zigzag hairs lost their kinks and became Awl-like.15,59 This suggests that further work will detail a single molecular mechanism for EDA, and that Medium hairs are formed by an unusual default mechanism—possibly based on a downstream feature of the EDA pathway (such as increased endogenous activation of EDAR or an NFκB target). Consistent with this notion, NF-kB is active in Medium hair germs in Tabby and Downless mice.46 EDA pathway has also been suggested to have a comparable role in hair follicle cycling, which recapitulates the morphogenetic process.82
Finally, what are the prospects for eventual effective intervention in the EDA syndrome (or other ectodermal dysplasias)? The Tabby mouse should continue to provide critical tests of principle. Neither EDA transgenes nor injected ligands lead to any findings of lethality or tumorigenesis, providing minimum qualifications for their possible utility in treating the syndrome.15,22,44 One can speculate that the principle of the treatment would be to activate NFκBs at a restricted location and timing. Restoration of Guard hair pegs in cultured Tabby skin by TNFα treatment suggests that a noninvasive or local treatment like topical application of EDA ligands or NFκB activating reagents may be feasible.46 Further encouraging evidence comes from the successful restoration of hair and sweat glands by injection of recombinant EDA-A1 ligands.44 Notably, sweat glands were restored even after birth.44 Sweat gland remediation thus becomes a likely first target for experimental treatment studies. Similarly, the eye is open to topical treatments, and tests can be envisaged of a preventive regimen to prevent ocular surface disease.17
Acknowledgments
This work was supported by the Intramural Research Program of the NIH, National Institute on Aging. Authors thank Drs. T. Hashimoto, M.C. Durmowicz and R. Nagaraja for their helpful discussions and contributions to the inferences reviewed here.
ABBREVIATIONS
EDAanhidrotic/hypohidrotic ecto dermal dysplasia
EDARectodysplasin receptor
EDARADDEDAR associated death domain
XEDARX-linked ectodysplasin receptor
Troytumor necrosis factor receptor superfamily expressed on the mouse embryo
TRAFTNF receptor associated factor
TAK1TGFb activated kinase1
TAB2TAK1 binding protein2
NEMONF-κB essential modulator
IKKIkB kinase
IkBinhibitor of NF-κB
LTlymphotoxin

Footnotes
Previously published online as a Cell Cycle E-publication:http://www.landesbioscience.com/journals/cc/abstract.php?id=3403
1. Oliver RF. The induction of hair follicle formation in the adult hooded rat by vibrissa dermal papillae. J Embryol Exp Morphol. 1970;23:219–36. [PubMed]
2. Nakamura M, Sundberg JP, Paus R. Mutant laboratory mice with abnormalities in hair follicle morphogenesis, cycling, and/or structure: Annotated tables. Exp Dermatol. 2001;10:369–90. [PubMed]
3. Fuchs E, Merrill BJ, Jamora C, DasGupta R. At the roots of a never-ending cycle. Dev Cell. 2001;1:13–25. [PubMed]
4. Millar SE. Molecular mechanisms regulating hair follicle development. J Invest Dermatol. 2002;118:216–25. [PubMed]
5. Botchkarev VA, Sharov AA. BMP signaling in the control of skin development and hair follicle growth. Differentiation. 2004;72:512–26. [PubMed]
6. Pinheiro M, Freire-Maia N. Ectodermal dysplasias: A clinical classification and a causal review. Am J Med Genet. 1994;53:153–62. [PubMed]
7. Kere J, Srivastava AK, Montonen O, Zonana J, Thomas N, Ferguson B, Munoz F, Morgan D, Clarke A, Baybayan P, Chen EY, Ezer S, Saarialho-Kere U, de la Chapelle A, Schlessinger D. X-linked anhidrotic (hypohidrotic) ectodermal dysplasia is caused by mutation in a novel transmembrane protein. Nat Genet. 1996;13:409–16. [PubMed]
8. Headon DJ, Overbeek PA. Involvement of a novel Tnf receptor homologue in hair follicle induction. Nat Genet. 1999;22:370–74. [PubMed]
9. Headon DJ, Emmal SA, Ferguson BM, Tucker AS, Justice MJ, Sharpe PT, Zonana J, Overbeek PA. Gene defect in ectodermal dysplasia implicates a death domain adapter in development. Nature. 2001;414:913–16. [PubMed]
10. Darwin C. In: The variation of animals and plants under domestigation. 2. Murray John., editor. II. London: 1875. p. 319.
11. Chassaing N, Bourthoumieu S, Cossee M, Calvas P, Vincent MC. Mutations in EDAR account for one-quarter of non-ED1-related hypohidrotic ectodermal dysplasia. Hum Mutat. 2006;27:255–9. [PubMed]
12. Ezer S, Bayes M, Elomaa O, Schlessinger D, Kere J. Ectodysplasin is a collagenous trimeric type II membrane protein with a tumor necrosis factor-like domain and colocalizes with cytoskeletal structures at lateral and apical surfaces of cells. Hum Mol Genet. 1999;8:2079–86. [PubMed]
13. Srivastava AK, Pispa J, Hartung AJ, Du Y, Ezer S, Jenks T, Shimada T, Pekkanen M, Mikkola ML, Ko MS, Thesleff I, Kere J, Schlessinger D. The Tabby phenotype is caused by mutation in a mouse homologue of the EDA gene that reveals novel mouse and human exons and encodes a protein (ectodysplasin-A) with collagenous domains. Proc Natl Acad Sci USA. 1997;94:13069–74. [PubMed]
14. Vielkind U, Hardy MH. Changing patterns of cell adhesion molecules during mouse pelage hair follicle development. 2. Follicle morphogenesis in the hair mutants, Tabby and downy. Acta Anat (Basel) 1996;157:183–94. [PubMed]
15. Cui CY, Durmowicz M, Ottolenghi C, Hashimoto T, Griggs B, Srivastava AK, Schlessinger D. Inducible mEDA-A1 transgene mediates sebaceous gland hyperplasia and differential formation of two types of mouse hair follicles. Hum Mol Genet. 2003;12:2931–40. [PubMed]
16. Kaercher T. Ocular symptoms and signs in patients with ectodermal dysplasia syndromes. Graefes Arch Clin Exp Ophthalmol. 2004;242:495–00. [PubMed]
17. Cui CY, Smith JA, Schlessinger D, Chan CC. X-linked anhidrotic ectodermal dysplasia disruption yields a mouse model for ocular surface disease and resultant blindness. Am J Pathol. 2005;167:89–95. [PubMed]
18. Kondo S, Kuwahara Y, Kondo M, Naruse K, Mitani H, Wakamatsu Y, Ozato K, Asakawa S, Shimizu N, Shima A. The medaka rs-3 locus required for scale development encodes ectodysplasin-A receptor. Curr Biol. 2001;11:1202–6. [PubMed]
19. Casal ML, Scheidt JL, Rhodes JL, Henthorn PS, Werner P. Mutation identification in a canine model of X-linked ectodermal dysplasia. Mamm Genome. 2005;16:524–31. [PMC free article] [PubMed]
20. Drogemuller C, Distl O, Leeb T. Partial deletion of the bovine ED1 gene causes anhidrotic ectodermal dysplasia in cattle. Genome Res. 2001;11:1699–05. [PubMed]
21. Colosimo PF, Hosemann KE, Balabhadra S, Villarreal G, Jr, Dickson M, Grimwood J, Schmutz J, Myers RM, Schluter D, Kingsley DM. Widespread parallel evolution in sticklebacks by repeated fixation of Ectodysplasin alleles. Science. 2005;307:1928–33. [PubMed]
22. Srivastava AK, Durmowicz MC, Hartung AJ, Hudson J, Ouzts LV, Donovan DM, Cui CY, Schlessinger D. Ectodysplasin-A1 is sufficient to rescue both hair growth and sweat glands in Tabby mice. Hum Mol Genet. 2001;10:2973–81. [PubMed]
23. Pengue G, Srivastava AK, Kere J, Schlessinger D, Durmowicz MC. Functional characterization of the promoter of the X-linked ectodermal dysplasia gene. J Biol Chem. 1999;274:26477–84. [PubMed]
24. Durmowicz MC, Cui CY, Schlessinger D. The EDA gene is a target of, but does not regulate Wnt signaling. Gene. 2002;285:203–11. [PubMed]
25. Laurikkala J, Pispa J, Jung HS, Nieminen P, Mikkola M, Wang X, Saarialho-Kere U, Galceran J, Grosschedl R, Thesleff I. Regulation of hair follicle development by the TNF signal ectodysplasin and its receptor Edar. Development. 2002;129:2541–53. [PubMed]
26. Gat U, DasGupta R, Degenstein L, Fuchs E. De Novo hair follicle morphogenesis and hair tumors in mice expressing a truncated beta-catenin in skin. Cell. 1998;95:605–14. [PubMed]
27. Elomaa O, Pulkkinen K, Hannelius U, Mikkola M, Saarialho-Kere U, Kere J. Ectodysplasin is released by proteolytic shedding and binds to the EDAR protein. Hum Mol Genet. 2001;10:953–62. [PubMed]
28. Chen Y, Molloy SS, Thomas L, Gambee J, Bachinger HP, Ferguson B, Zonana J, Thomas G, Morris NP. Mutations within a furin consensus sequence block proteolytic release of ectodysplasin-A and cause X-linked hypohidrotic ectodermal dysplasia. Proc Natl Acad Sci USA. 2001;98:7218–23. [PubMed]
29. Schneider P, Street SL, Gaide O, Hertig S, Tardivel A, Tschopp J, Runkel L, Alevizopoulos K, Ferguson BM, Zonana J. Mutations leading to X-linked hypohidrotic ectodermal dysplasia affect three major functional domains in the tumor necrosis factor family member ectodysplasin-A. J Biol Chem. 2001;276:18819–27. [PubMed]
30. Paakkonen K, Cambiaghi S, Novelli G, Ouzts LV, Penttinen M, Kere J, Srivastava AK. The mutation spectrum of the EDA gene in X-linked anhidrotic ectodermal dysplasia. Hum Mutat. 2001;17:349. [PubMed]
31. Kishore U, Gaboriaud C, Waters P, Shrive AK, Greenhough TJ, Reid KB, Sim RB, Arlaud GJ. C1q and tumor necrosis factor superfamily: Modularity and versatility. Trends Immunol. 2004;25:551–61. [PubMed]
32. Reiser K, McCormick RJ, Rucker RB. Enzymatic and nonenzymatic cross-linking of collagen and elastin. Faseb J. 1992;6:2439–49. [PubMed]
33. Hymowitz SG, Compaan DM, Yan M, Wallweber HJ, Dixit VM, Starovasnik MA, de Vos AM. The crystal structures of EDA-A1 and EDA-A2: Splice variants with distinct receptor specificity. Structure. 2003;11:1513–20. [PubMed]
34. Yan M, Wang LC, Hymowitz SG, Schilbach S, Lee J, Goddard A, de Vos AM, Gao WQ, Dixit VM. Two-amino acid molecular switch in an epithelial morphogen that regulates binding to two distinct receptors. Science. 2000;290:523–7. [PubMed]
35. Locksley RM, Killeen N, Lenardo MJ. The TNF and TNF receptor superfamilies: Integrating mammalian biology. Cell. 2001;104:487–501. [PubMed]
36. Screaton G, Xu XN. T cell life and death signalling via TNF-receptor family members. Curr Opin Immunol. 2000;12:316–22. [PubMed]
37. Kumar A, Eby MT, Sinha S, Jasmin A, Chaudhary PM. The ectodermal dysplasia receptor activates the nuclear factor-kappaB, JNK, and cell death pathways and binds to ectodysplasin A. J Biol Chem. 2001;276:2668–77. [PubMed]
38. Koppinen P, Pispa J, Laurikkala J, Thesleff I, Mikkola ML. Signaling and subcellular localization of the TNF receptor Edar. Exp Cell Res. 2001;269:180–92. [PubMed]
39. Morlon A, Munnich A, Smahi A. TAB2, TRAF6 and TAK1 are involved in NF-kappaB activation induced by the TNF-receptor, Edar and its adaptator Edaradd. Hum Mol Genet. 2005;14:3751–57. [PubMed]
40. Naito A, Yoshida H, Nishioka E, Satoh M, Azuma S, Yamamoto T, Nishikawa S, Inoue J. TRAF6-deficient mice display hypohidrotic ectodermal dysplasia. Proc Natl Acad Sci USA. 2002;99:8766–71. [PubMed]
41. Bayes M, Hartung AJ, Ezer S, Pispa J, Thesleff I, Srivastava AK, Kere J. The anhidrotic ectodermal dysplasia gene (EDA) undergoes alternative splicing and encodes ectodysplasin-A with deletion mutations in collagenous repeats. Hum Mol Genet. 1998;7:1661–9. [PubMed]
42. Hashimoto T, Cui CY, Schlessinger D. Repertoire of mouse ectodysplasin-A (EDA-A) isoforms. Gene. 2006;371:42–51. [PubMed]
43. Sinha SK, Zachariah S, Quinones HI, Shindo M, Chaudhary PM. Role of TRAF3 and -6 in the activation of the NF-kappa B and JNK pathways by X-linked ectodermal dysplasia receptor. J Biol Chem. 2002;277:44953–61. [PubMed]
44. Gaide O, Schneider P. Permanent correction of an inherited ectodermal dysplasia with recombinant EDA. Nat Med. 2003;9:614–8. [PubMed]
45. Newton K, French DM, Yan M, Frantz GD, Dixit VM. Myodegeneration in EDA-A2 transgenic mice is prevented by XEDAR deficiency. Mol Cell Biol. 2004;24:1608–13. [PMC free article] [PubMed]
46. Schmidt-Ullrich R, Tobin DJ, Lenhard D, Schneider P, Paus R, Scheidereit C. NF-{kappa}B transmits Eda A1/EdaR signalling to activate Shh and cyclin D1 expression, and controls post-initiation hair placode down growth. Development. 2006;133:1045–57. [PubMed]
47. Kojima T, Morikawa Y, Copeland NG, Gilbert DJ, Jenkins NA, Senba E, Kitamura T. TROY, a newly identified member of the tumor necrosis factor receptor superfamily, exhibits a homology with Edar and is expressed in embryonic skin and hair follicles. J Biol Chem. 2000;275:20742–7. [PubMed]
48. Justice MJ, Noveroske JK, Weber JS, Zheng B, Bradley A. Mouse ENU mutagenesis. Hum Mol Genet. 1999;8:1955–63. [PubMed]
49. Courtois G, Israel A. NF-kappa B defects in humans: The NEMO/incontinentia pigmenti connection. Sci STKE 2000. 2000:PE1. [PubMed]
50. Smahi A, Courtois G, Rabia SH, Doffinger R, Bodemer C, Munnich A, Casanova JL, Israel A. The NF-kappaB signalling pathway in human diseases: From incontinentia pigmenti to ectodermal dysplasias and immune-deficiency syndromes. Hum Mol Genet. 2002;11:2371–5. [PubMed]
51. Schmidt-Supprian M, Bloch W, Courtois G, Addicks K, Israel A, Rajewsky K, Pasparakis M. NEMO/IKK gamma-deficient mice model incontinentia pigmenti. Mol Cell. 2000;5:981–92. [PubMed]
52. Doffinger R, Smahi A, Bessia C, Geissmann F, Feinberg J, Durandy A, Bodemer C, Kenwrick S, Dupuis-Girod S, Blanche S, Wood P, Rabia SH, Headon DJ, Overbeek PA, Le Deist F, Holland SM, Belani K, Kumararatne DS, Fischer A, Shapiro R, Conley ME, Reimund E, Kalhoff H, Abinun M, Munnich A, Israel A, Courtois G, Casanova JL. X-linked anhidrotic ectodermal dysplasia with immunodeficiency is caused by impaired NF-kappaB signaling. Nat Genet. 2001;27:277–85. [PubMed]
53. Courtois G, Smahi A, Israel A. NEMO/IKK gamma: Linking NF-kappa B to human disease. Trends Mol Med. 2001;7:427–30. [PubMed]
54. Courtois G, Smahi A, Reichenbach J, Doffinger R, Cancrini C, Bonnet M, Puel A, Chable-Bessia C, Yamaoka S, Feinberg J, Dupuis-Girod S, Bodemer C, Livadiotti S, Novelli F, Rossi P, Fischer A, Israel A, Munnich A, Le Deist F, Casanova JL. A hypermorphic IkappaBalpha mutation is associated with autosomal dominant anhidrotic ectodermal dysplasia and T cell immunodeficiency. J Clin Invest. 2003;112:1108–15. [PMC free article] [PubMed]
55. Schmidt-Ullrich R, Aebischer T, Hulsken J, Birchmeier W, Klemm U, Scheidereit C. Requirement of NF-kappaB/Rel for the development of hair follicles and other epidermal appendices. Development. 2001;128:3843–53. [PubMed]
56. Hayden MS, Ghosh S. Signaling to NF-kappaB. Genes Dev. 2004;18:2195–224. [PubMed]
57. Bell S, Degitz K, Quirling M, Jilg N, Page S, Brand K. Involvement of NF-kappaB signalling in skin physiology and disease. Cell Signal. 2003;15:1–7. [PubMed]
58. Gugasyan R, Voss A, Varigos G, Thomas T, Grumont RJ, Kaur P, Grigoriadis G, Gerondakis S. The transcription factors c-rel and RelA control epidermal development and homeostasis in embryonic and adult skin via distinct mechanisms. Mol Cell Biol. 2004;24:5733–45. [PMC free article] [PubMed]
59. Cui CY, Hashimoto T, Grivennikov SI, Piao Y, Nedospasov SA, Schlessinger D. Ectodysplasin regulates the lymphotoxin-beta pathway for hair differentiation. Proc Natl Acad Sci USA. 2006;103:9142–7. [PubMed]
60. Weih F, Caamano J. Regulation of secondary lymphoid organ development by the nuclear factor-kappaB signal transduction pathway. Immunol Rev. 2003;195:91–05. [PubMed]
61. Cascallana JL, Bravo A, Donet E, Leis H, Lara MF, Paramio JM, Jorcano JL, Perez P. Ectoderm-targeted overexpression of the glucocorticoid receptor induces hypohidrotic ectodermal dysplasia. Endocrinology. 2005;146:2629–38. [PubMed]
62. Aggarwal BB. Signalling pathways of the TNF superfamily: A double-edged sword. Nat Rev Immunol. 2003;3:745–56. [PubMed]
63. Oro AE, Higgins KM, Hu Z, Bonifas JM, Epstein EH, Jr, Scott MP. Basal cell carcinomas in mice overexpressing sonic hedgehog. Science. 1997;276:817–21. [PubMed]
64. Botchkarev VA. Bone morphogenetic proteins and their antagonists in skin and hair follicle biology. J Invest Dermatol. 2003;120:36–47. [PubMed]
65. Mustonen T, Pispa J, Mikkola ML, Pummila M, Kangas AT, Pakkasjarvi L, Jaatinen R, Thesleff I. Stimulation of ectodermal organ development by Ectodysplasin-A1. Dev Biol. 2003;259:123–36. [PubMed]
66. Cui CY, Durmowicz M, Tanaka TS, Hartung AJ, Tezuka T, Hashimoto K, Ko MS, Srivastava AK, Schlessinger D. EDA targets revealed by skin gene expression profiles of wild-type, Tabby and Tabby EDA-A1 transgenic mice. Hum Mol Genet. 2002;11:1763–73. [PubMed]
67. Andl T, Reddy ST, Gaddapara T, Millar SE. WNT signals are required for the initiation of hair follicle development. Dev Cell. 2002;2:643–53. [PubMed]
68. St-Jacques B, Dassule HR, Karavanova I, Botchkarev VA, Li J, Danielian PS, McMahon JA, Lewis PM, Paus R, McMahon AP. Sonic hedgehog signaling is essential for hair development. Curr Biol. 1998;8:1058–68. [PubMed]
69. Mill P, Mo R, Fu H, Grachtchouk M, Kim PC, Dlugosz AA, Hui CC. Sonic hedgehog-dependent activation of Gli2 is essential for embryonic hair follicle development. Genes Dev. 2003;17:282–94. [PubMed]
70. Tumanov AV, Kuprash DV, Nedospasov SA. The role of lymphotoxin in development and maintenance of secondary lymphoid tissues. Cytokine Growth Factor Rev. 2003;14:275–88. [PubMed]
71. Nishioka E, Tanaka T, Yoshida H, Matsumura K, Nishikawa S, Naito A, Inoue J, Funasaka Y, Ichihashi M, Miyasaka M. Mucosal addressin cell adhesion molecule 1 plays an unexpected role in the development of mouse Guard hair. J Invest Dermatol. 2002;119:632–8. [PubMed]
72. Stopfer P, Obermeier F, Dunger N, Falk W, Farkas S, Janotta M, Moller A, Mannel DN, Hehlgans T. Blocking lymphotoxin-beta receptor activation diminishes inflammation via reduced mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expression and leucocyte margination in chronic DSS-induced colitis. Clin Exp Immunol. 2004;136:21–9. [PubMed]
73. Cuff CA, Schwartz J, Bergman CM, Russell KS, Bender JR, Ruddle NH. Lymphotoxin alpha3 induces chemokines and adhesion molecules: Insight into the role of LT alpha in inflammation and lymphoid organ development. J Immunol. 1998;161:6853–60. [PubMed]
74. Zhang M, Brancaccio A, Weiner L, Missero C, Brissette JL. Ectodysplasin regulates pattern formation in the mammalian hair coat. Genesis. 2003;37:30–7. [PubMed]
75. Majumder K, ShAwlot W, Schuster G, Harrison W, Elder FF, Overbeek PA. YAC rescue of downless locus mutations in mice. Mamm Genome. 1998;9:863–8. [PubMed]
76. Mikkola ML, Thesleff I. Ectodysplasin signaling in development. Cytokine Growth Factor Rev. 2003;14:211–24. [PubMed]
77. Mou C, Jackson B, Schneider P, Overbeek PA, Headon DJ. Generation of the primary hair follicle pattern. Proc Natl Acad Sci USA. 2006;103:9075–80. [PubMed]
78. van Genderen C, Okamura RM, Farinas I, Quo RG, Parslow TG, Bruhn L, Grosschedl R. Development of several organs that require inductive epithelial-mesenchymal interactions is impaired in LEF-1-deficient mice. Genes Dev. 1994;8:2691–03. [PubMed]
79. Botchkarev VA, Botchkareva NV, Roth W, Nakamura M, Chen LH, Herzog W, Lindner G, McMahon JA, Peters C, Lauster R, McMahon AP, Paus R. Noggin is a mesenchymally derived stimulator of hair-follicle induction. Nat Cell Biol. 1999;1:158–64. [PubMed]
80. Plikus M, Wang WP, Liu J, Wang X, Jiang TX, Chuong CM. Morpho-regulation of ectodermal organs: Integument pathology and phenotypic variations in K14-Noggin engineered mice through modulation of bone morphogenic protein pathway. Am J Pathol. 2004;164:1099–14. [PubMed]
81. Jamora C, DasGupta R, Kocieniewski P, Fuchs E. Links between signal transduction, transcription and adhesion in epithelial bud development. Nature. 2003;422:317–22. [PMC free article] [PubMed]
82. Botchkarev VA, Fessing MY. Edar signaling in the control of hair follicle development. J Investig Dermatol Symp Proc. 2005;10:247–51. [PubMed]