Skin Appendage Formation Research Articles

Angiogenic Heparin-Mimetic Peptide Nanofiber Gel Improves Regenerative Healing of Acute Wounds.

Wound repair in adult mammals typically ends with the formation of a scar, which prevents full restoration of the function of the healthy tissue, although most of the wounded skin heals. Rapid and functional recovery of major wound injuries requires therapeutic approaches that can enhance the healing process via overcoming mechanical and biochemical problems. In this study, we showed that self-assembled heparin-mimetic peptide nanofiber gel was an effective bioactive wound dressing for the rapid and functional repair of full-thickness excisional wounds in the rat model. The bioactive gel-treated wounds exhibited increased angiogenesis (p < 0.05), re-epithelization (p < 0.05), skin appendage formation, and granulation tissue organization (p < 0.05) compared to sucrose-treated samples. Increased blood vessel numbers in the gel-treated wounds on day 7 suggest that angiogenesis played a key role in improvement of tissue healing in bioactive gel-treated wounds. Overall, the angiogenic heparin-mimetic peptide nanofiber gel is a promising platform for enhancing the scar-free recovery of acute wounds.

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.

Notch1 Signaling Regulates Wound Healing via Changing the Characteristics of Epidermal Stem Cells

During wound healing and reconstruction, epidermal stem cells (ESCs) migrate to the wound site and activate to repair the damaged epithelium. Moreover, there exist complicate signaling pathways to regulate wound regeneration including Notch signaling. The Notch signaling pathway is a regulator of epidermal differentiation, which may be an important mediator of wound regeneration that participates in various processes, from the development of the dermis to the formation of skin appendages. Here, we show that Notch signaling pathways are upregulated by Jagged1 in ESCs and stem cell characteristics of ESCs change when Notch1 signaling varies. By administration of siRNAJagged1 knockdown ESCs in wounds, we observe that the suppression of Jagged1 down regulate expression of Notch signaling and resulted in poor-quality wound healing. Connecting Notch1 pathways activity to ESCs response to wound repairing may develop a new therapeutic strategy for delayed healing.

Wnt11 is required for oriented migration of dermogenic progenitor cells from the dorsomedial lip of the avian dermomyotome.

The embryonic origin of the dermis in vertebrates can be traced back to the dermomyotome of the somites, the lateral plate mesoderm and the neural crest. The dermal precursors directly overlying the neural tube display a unique dense arrangement and are the first to induce skin appendage formation in vertebrate embryos. These dermal precursor cells have been shown to derive from the dorsomedial lip of the dermomyotome (DML). Based on its expression pattern in the DML, Wnt11 is a candidate regulator of dorsal dermis formation. Using EGFP-based cell labelling and time-lapse imaging, we show that the Wnt11 expressing DML is the source of the dense dorsal dermis. Loss-of-function studies in chicken embryos show that Wnt11 is indeed essential for the formation of dense dermis competent to support cutaneous appendage formation. Our findings show that dermogenic progenitors cannot leave the DML to form dense dorsal dermis following Wnt11 silencing. No alterations were noticeable in the patterning or in the epithelial state of the dermomyotome including the DML. Furthermore, we show that Wnt11 expression is regulated in a manner similar to the previously described early dermal marker cDermo-1. The analysis of Wnt11 mutant mice exhibits an underdeveloped dorsal dermis and strongly supports our gene silencing data in chicken embryos. We conclude that Wnt11 is required for dense dermis and subsequent cutaneous appendage formation, by influencing the cell fate decision of the cells in the DML.

&lt;b&gt; Comparative study of Low-level laser therapy and microcurrent on the healing of skin burns in rats&lt;/b&gt;

This study investigated and compared the effects of low-level laser therapy (LLLT) and microcurrent in the burn healing process in Wistar rats. We conducted a randomized controlled study with 30 rats divided into 3 groups (n = 10); control group (CG), laser group (LG) and microcurrent group (MG). After thermal damage, 10 applications of 660 nm diode laser were performed in GL and 10 applications of 60 Hz microcurrent (160 μA) in MG. The semi-quantitative histological analysis was done using scores (0-3), in sections stained by hematoxylin and eosin and Masson's trichrome. The results indicated a significant improvement in the fibroblasts proliferation, collagen fibers deposition, neoangiogenesis, and cutaneous appendages regeneration in MG and LG. When microcurrent and LLLT were compared, no difference was detected, except the regeneration and formation of new cutaneous appendages, observed in MG. Despite the similar effects, GM showed faster tissue repair with the formation of skin appendages.

Knocking out Smad3 favors allogeneic mouse fetal skin development in adult wounds

Fetal skin development represents a process of the interaction between skin progenitor cells and their unique extracellular matrix niche, which is also important for the mechanism study of skin progenitor cell differentiation and fetal scarless wound healing. Thus, a change in the niche environment, such as altered expression levels of growth factors or cytokines, may also change the outcome of fetal skin development. This study tested the hypothesis that deletion of mouse Smad3 creates a favorable environment for fetal skin development in adult wounds. Fetal skin of green fluorescent protein mouse (C57BL/B6) of gestational day 16.5 was respectively transplanted to the wound beds of wild-type (WT), heterozygous (HT), and homologous (KO) Smad3 deletion mice (C57BL/B6 × 129SV). The results showed that green fluorescent protein fetal mouse skin after its transplantation developed much better into hair follicle containing skin in KO or HT wound beds than in WT wound beds with significant differences in the number of follicles per mm(2) among the three groups at 1, 2, and 3 weeks posttransplantation (p < 0.05). In addition, less fibrosis was observed in KO wounds than in HT and WT wounds with significant difference in the wound bed thickness among the three groups at 3 weeks posttransplantation (p < 0.05). Interestingly, there was a delayed graft rejection in the KO group when compared with the HT and WT groups. In conclusion, deletion of Smad3 in a wound bed creates a better environment for skin progenitor cell differentiation and fetal skin development. Translation of such a concept to the creation of a wound environment that is favorable for adult stem cell differentiation and skin appendage formation may become an important strategy for the regeneration of wounded skin.

Plakoglobin as a Regulator of Desmocollin Gene Expression

Desmosomes are cell adhesion junctions required for the normal development and maintenance of mammalian tissues and organs such as the skin, skin appendages and the heart. The goal of the present study was to investigate how desmocollins (DSC), transmembrane components of desmosomes, are regulated at the transcriptional level. We hypothesized that differential expression of the Dsc2 and Dsc3 genes is a prerequisite for normal development of skin appendages. We demonstrate that plakoglobin (Pg) in conjunction with Lef-1 differentially regulates the proximal promoters of these two genes. Specifically, we found that Lef-1 acts as a switch activating Dsc2 and repressing Dsc3 in the presence of Pg. Interestingly, we also determined that NFκB pathway components, down-stream effectors of the Eda/EDAR signaling cascade, can activate Dsc2 expression. We hypothesize that Lef-1 and Eda/EDAR/NFκB signaling contribute to a shift in Dsc isoform expression from Dsc3 to Dsc2 in placode keratinocytes. It is tempting to speculate that this shift is required for invasive growth of placode keratinocytes into the dermis, a crucial step in skin appendage formation.

Keratocystoma of the parotid gland: a clinicopathological study and literature review

The authors investigated the clinicopathological characteristics of keratocystoma of the parotid gland. Two cases of parotid gland keratocystoma in the files of Nanjing Stomatological Hospital were analysed. These slowly growing parotid gland tumours occurred in two women aged 29 and 49 years. The cut surface showed multilocular cystic lesions filled with keratin materials. Histologically, there were multi-cystic spaces and solid epithelium islands, containing keratinized lamellae. Without cytological atypia, the lining stratified squamous epithelium showed apparent keratinization through an orthokeratotic or parakeratotic pathway. No skin appendage formation was observed. Both cases immunoreactively stained positively for AE1/AE3 and CK5/6 but negatively for CK8/18, S-100 and Calponin. There was no evidence of recurrence 3 or 4 years after superficial parotidectomy. The data from these two cases and cases previously published suggest that keratocystoma of the parotid gland is a benign cystic neoplasm. Surgical resection is apparently sufficient for cure.

Electrospun Fibers with Plasmid bFGF Polyplex Loadings Promote Skin Wound Healing in Diabetic Rats

Deep or chronic skin wounds are difficult to heal spontaneously due to the lack of scaffold to guide cell growth and reduced levels and activities of endogenous growth factors. Emulsion electrospinning process integrated with DNA condensation techniques indicated potentials to gradually release DNA, but no attempt has been made to clarify the advantages in promoting tissue regeneration and wound recovery. In this study, polyplexes of basic fibroblast growth factor-encoding plasmid (pbFGF) with poly(ethylene imine) were incorporated into electrospun fibers with a core-sheath structure, and poly(ethylene glycol) was included into the fiber sheath to allow a sustained release of pbFGF for 4 weeks. In vitro tests on mouse embryo fibroblasts indicated that pbFGF-loaded fibrous mats enhanced cell proliferation by the autocrine bFGF, and an effective cell transfection proceeded for over 28 days. Skin wounds were created in the dorsal area of diabetic rats for in vivo evaluation of skin regeneration after being covered with pbFGF-loaded fibrous mats. The gradual pbFGF release revealed significantly higher wound recovery rate with improved vascularization, enhanced collagen deposition and maturation, complete re-epithelialization and formation of skin appendages. The above results demonstrate the potential use of pbFGF-loaded electrospun fibrous mats to accelerate the healing of skin ulcers for patients with diabetic mellitus.

Human Umbilical Cord Blood (HUCB) Derived Pluripotent Stem Cells Enhances Wound Healing

Abstract 4824 Background:Recessive dystrophic epidermolysis bullosa (RDEB) is a severe inherited skin blistering disease caused by mutations in the type VII collagen (COL7A1) gene that encodes a major component in anchoring fibrils (Christiano et.al. Nat Gen 1993). Recently, iPSCs have been generated from RDEB patients, which provides promises on gene correction and future autologous Stem Cell Transplantation (SCT) (Itoh/Cairo/Christiano PNAS 2011). Currently, Allogeneic (Allo) SCT remains to be the best treatment for numerous malignant and non-malignant diseases in pediatric patients (Cairo et al BBMT 2008). This has also been supported by the first report on Allo-SCT in seven children with RDEB (Wagner et.al. N Engl J Med 2010). However no distinct anchoring fibrils were observed in the recipient skin. Moreover the functional cell populations are to be characterized. Stem cell populations with pluripotent properties, including unrestricted somatic stem cells (USSCs) have been isolated from HUCB, and may represent novel stem cells for the regenerative therapy for RDEB either by themselves, or by co-administration with BM or HUCB (Liao/Cairo et al, Exp. Hem, 2011). Goal:Determine the potential of USSCs in promoting wound healing and treating RDEB. Method:USSCs were isolated from HUCB in the presence of 30% FBS and 10−7M dexamethasone, and characterized by RT-PCR, bisulfate sequencing and immunocytochemistry. A 1cm2 full-thickness excisional wound was created at the dorsal of NSG mice, followed by intradermal injection of 1 million USSCs or PBS at a 1cm- distance from the margin of the created wound. The wound areas were photographed and quantitated using ImageJ. Skin biopsies were taken at selected days and characterized by H&E staining and immunohistochemistry. Results:USSCs transcribe a low level of Nanog, Oct4 and Sox2, as compared to ES cells. Their Nanog and Oct4 expression is about 20- and 400- fold higher than that in human fibroblasts, and could be further activated at least 10 fold by treatment of DNA methylation inhibitor, 5-azacytidine. Their level of DNA methylation at the regulatory regions of Oct4 and Nanog genes is also intermediate between ES and fibroblasts. This suggests that USSCs represent a cell type that is developmentally an intermediate between ES cells and somatic cells. In addition, flow cytometry analysis indicated that USSCs also express stem cell surface antigen SSEA4. USSCs express Col7a1, the protein that is missing in the RDEB patients, at a level that is comparable to human keratinocytes and fibroblasts (fig A). This implies a potential ability of USSCs to rescue the RDEB defect by secreting COL7a1. In the mouse wounding model, USSC-treated wounds closed at a faster rate and Bonferroni post-test showed a significant difference between USSC and PBS treatment on days 6– 10 (Fig B). Immunological staining of tissue sections for endothelial protein CD31 showed increased vasculature in USSC-treated wounds at as early as three days post wounding, compared with PBS-treated wounds. Using immunostaining against human specific α5 and/or β1 integrin that is expressed specifically in USSCs, we have detected the presence of human cells within the wounded, but not unwounded basal layer of the skin, up to 1 month post wounding (Fig C). This indicates specific migration of USSCs to the wounded area and such a directed migration is likely to be mediated by the chemotactic interaction between stroma-derived factor 1(SDF-1) and CXCR4 that is expressed at the surface of USSCs. H&E staining on the skin biopsies taken at different time points indicated that USSCs promoted epithelialization and facilitated the formation and remodeling of epidermis. The resultant USSC-treated skin was less fibrotic, and more importantly, demonstrated formation of normal skin appendages in the center of the wounded area (Fig D). However, human cells were not detected in the skin appendages by immunological analysis, suggesting that accelerated epithelialization in the wound following USSC treatment has created an optimal environment for the migration of follicle progenitor cells from the unwounded skin to the center of the wound. Conclusion:This study demonstrated the beneficial effect of HUCB derived USSCs in cutaneous regeneration and wound healing in a mouse wounding model. The ability of USSCs in secreting Col7A1 and promoting wound healing suggests their potential therapeutic application in treating RDEB. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

WNT/β-Catenin Signalling and Epithelial Patterning in the Homoscleromorph Sponge Oscarella

Sponges branch basally in the metazoan phylogenetic tree and are thus well positioned to provide insights into the evolution of mechanisms controlling animal development, likely to remain active in adult sponges. Of the four sponge clades, the Homoscleromorpha are of particular interest as they alone show the “true” epithelial organization seen in other metazoan phyla (the Eumetazoa). We have examined the deployment in sponges of Wnt signalling pathway components, since this pathway is an important regulator of many developmental patterning processes. We identified a reduced repertoire of three divergent Wnt ligand genes in the recently-sequenced Amphimedon queenslandica (demosponge) genome and two Wnts from our EST collection from the homoscleromorph Oscarella lobularis, along with well-conserved genes for intracellular pathway components (β-catenin, GSK3β). Remarkably, the two O. lobularis Wnt genes showed complementary expression patterns in relation to the evenly spaced ostia (canal openings) of the exopinacoderm (ectoderm), highly reminiscent of Wnt expression during skin appendage formation in vertebrates. Furthermore, experimental activation of the Wnt/β-catenin pathway using GSK3β inhibitors provoked formation of ectopic ostia, as has been shown for epithelial appendages in Eumetazoa. We thus suggest that deployment of Wnt signalling is a common and perhaps ancient feature of metazoan epithelial patterning and morphogenesis.

Role of FGFR2-signaling in the pathogenesis of acne.

It is the purpose of this review to extend our understanding of the fibroblast growth factor (FGF) receptor-2b-signaling network in the pathogenesis of acne. A new concept of the role of FGFR2b-signaling in dermal-epithelial interaction for skin appendage formation, pilosebaceous follicle homeostasis, comedogenesis, sebaceous gland proliferation and lipogenesis is presented. The FGFR2-gain-of-function mutations in Apert syndrome and unilateral acneiform nevus are most helpful model diseases pointing the way to androgen-dependent dermalepithelial FGFR2-signaling in acne. Androgen-mediated upregulation of FGFR2b-signaling in acne-prone skin appears to be involved in the pathogenesis of acne vulgaris. In organotypic skin cultures, keratinocyte-derived interleukin-1alpha stimulated fibroblasts to secrete FGF7 which stimulated FGFR2b-mediated keratinocyte proliferation. Postnatal deletion of FGFR2b in mice resulted in severe sebaceous gland atrophy. The importance of FGFR2b in sebaceous gland physiology is further supported by the mode of action of anti-acne agents which have been proposed to attenuate FGFR2b-signaling. Downregulation of FGFR2b-signaling by isotretinoin explains its therapeutic effect in acne. Downregulation of FGFR2b-signaling during the first trimester of pregnancy disturbs branched morphogenesis and explains retinoid embryotoxicity. Insulin-like growth factor-1 (IGF-1), the mediator of growth hormone during puberty, intracts with androgen-dependent FGFR2b-signaling and links androgen- and FGF-mediated signal transduction important in sebaceous gland homeostasis. The search for a follicular defect in the dermalepithelial regulation of growth factor-signaling in acne-prone skin appears to be a most promising approach to clarify the pathogenesis of acne.

FGFR2 signaling and the pathogenesis of acne

Acne in Apert syndrome and unilateral segmental acneiform nevus are associated with mutations of fibroblast growth factor receptor 2 (FGFR2), which are likely to be involved in the pathogenesis of acne. Translational animal and cellular models, developmental biology studies and clinical observations have contributed to our understanding of FGF-FGFR2 signaling in the pilosebaceous follicle. The importance of FGF-FGFR2 signaling in mesenchymal-epithelial interaction for skin appendage formation, pilosebaceous follicle homeostasis, comedogenesis and sebaceous gland proliferation is explored. Overstimulation of FGFR2 signaling with increased expression of interleukin-1alpha explains acne in Apert syndrome und nevus comedonicus. Androgen-mediated up-regulation of FGFR2 signaling could be the initiating signal in the pathogenesis of acne. The gain of function FGFR2 mutations in Apert syndrome and unilateral acneiform nevus are most helpful model diseases for uncovering the fundamental process of androgen-dependent mesenchymal-epithelial FGF-FGFR2 signaling in acne in Apert syndrome, nevus comedonicus and acne vulgaris.

BMP2 and BMP7 play antagonistic roles in feather induction

Feathers, like hairs, first appear as primordia consisting of an epidermal placode associated with a dermal condensation that is necessary for the continuation of their differentiation. Previously, the BMPs have been proposed to inhibit skin appendage formation. We show that the function of specific BMPs during feather development is more complex. BMP2 and BMP7, which are expressed in both the epidermis and the dermis, are involved in an antagonistic fashion in regulating the formation of dermal condensations, and thus are both necessary for subsequent feather morphogenesis. BMP7 is expressed earlier and functions as a chemoattractant that recruits cells into the condensation, whereas BMP2 is expressed later, and leads to an arrest of cell migration, likely via its modulation of the EIIIA fibronectin domain and alpha4 integrin expression. Based on the observed cell proliferation, chemotaxis and the timing of BMP2 and BMP7 expression, we propose a mathematical model, a reaction-diffusion system, which not only simulates feather patterning, but which also can account for the negative effects of excess BMP2 or BMP7 on feather formation.

Ectodysplasin regulates the lymphotoxin-β pathway for hair differentiation

Mutations in the EDA gene cause anhidrotic/hypohidrotic ectodermal dysplasia, a disorder characterized by defective formation of hair, sweat glands, and teeth in humans and in a mouse model, "Tabby" (Ta). The gene encodes ectodysplasin, a TNF ligand family member that activates the NF-kappaB-signaling pathway, but downstream targets and the mechanism of skin appendage formation have been only partially analyzed. Comparative transcription profiling of embryonic skin during hair follicle development in WT and Ta mice identified critical anhidrotic/hypohidrotic ectodermal dysplasia (EDA) effectors in four pathways, three already implicated in follicle formation. They included Shh and its effectors, as well as antagonists for the Wnt (Dkk4) and BMP (Sostdc1) pathways. The fourth pathway was unexpected, a variant NF-kappaB-signaling cascade based on lymphotoxin-beta (LTbeta)/RelB. Previously known to participate only in lymphoid organogenesis, LTbeta was enriched in developing hair follicles of WT but not in Ta mice. Furthermore, in mice lacking LTbeta, all three types of mouse hair were still formed, but all were structurally abnormal. Guard hairs became wavy and irregular, zigzag/auchen hairs lost their kinks, and in a phenocopy of features of Ta animals, the awl hairs doubled in number and were characteristically distorted and pinched. LTbeta-null mice that received WT bone marrow transplants maintained mutant hair phenotypes, consistent with autonomous LTbeta action in skin independent of its expression in lymphoid cells. Thus, as an EDA target, LTbeta regulates the form of hair in developing hair follicles; and when EDA is defective, failure of LTbeta activation can account for part of the Ta phenotype.

CDermo-1 misexpression induces dense dermis, feathers, and scales

Reciprocal epithelio-mesenchymal interactions between the prospective epidermis and the underlying dermis are the major driving forces in the development of skin appendages. Feather development is initiated by a still unknown signal from the dermis in feather-forming skin. The morphological response of the ectoderm to this signal is the formation of an epidermal placode, which signals back to the mesenchyme to induce dermal condensations. Together, epidermal and dermal components constitute the outgrowing feather bud. The bHLH transcription factor cDermo-1 is expressed in developing dermis and is the earliest known marker of prospective feather tracts. To test its function during feather development, we forced cDermo-1 expression in embryonic chicken dermis using a retroviral expression vector. In featherless (apteric) regions, cDermo-1 misexpression induced dense, thickened dermis normally observed in feathered skin (pterylae), and leads to the development of regularly spaced and normally shaped ectopic feather buds. In pterylae, cDermo-1 misexpression enhanced feather growth. In hindlimb skin, according to the local skin identity, misexpression of cDermo-1 induced ectopic scale formation. Thus, we show that forced cDermo-1 expression in developing dermis is sufficient to launch the developmental program leading to skin appendage formation. We propose a role of cDermo-1 at the initial stages of feather induction upstream of FGF10.

Gene expression in sheep skin and wool (hair)

We sequenced 2939 ESTs from fetal and adult sheep skin. Stages of gestation were picked to coincide with the major events in skin appendage (wool follicle) formation. Clustering analysis generated a nonredundant set of ESTs 2435 strong (83% nonredundant). Approximately 24% of these gave no hit to NCBI build 29 of the human genome, while 35% were tentatively classified by putative function based on BLASTX hits with a p( N) of <10 −4. In addition to bioinformatics analysis of our ESTs and gene mapping, we have generated a large EST spatial expression data set using in situ hybridization. One thousand one hundred forty-two ESTs have been used for in situ localization; about 31% are from adult sheep skin, 39% from late gestation fetal sheep skin, and 30% from midgestation fetal sheep skin. These probes have been used in over 3000 hybridization experiments. In this report, we summarize the results of in situs on adult sheep skin.

Synergistic effect of bismuth subgallate and borneol, the major components of Sulbogin ®, on the healing of skin wound

Most skin lesions heal delay and even heal efficiently within 1–2 weeks, the healed tissue is neither aesthetically nor functionally perfect. Therefore, facilitating skin healing rate and controlling healed skin quality are major aims of drug treatment for a ®wound event. Bismuth subgallate (BS) and Borneol (BO) are the two components of Sulbogin ®, a new Vaseline-based wound healing ointment , one for treating skin wounds. Although BO has antibiotic function, while BS is widely used clinically, neither has been used specifically for wound healing. The experiment described here aimed to study the effect of BS and BO on the healing of skin wounds. This study also compared the effects of BS and BO with Flamazine ® cream, which is currently the most popular drug for wound healing in hospitals. Full-thickness wounds (3 cm×3 cm×0.2 cm) were created on the back of adult male Sprague–Dawley rats. BS, BO, BS+BO, and Flamazine ® were then evenly applied to cheesecloth and placed over the lesion areas. The drug patches were replaced every 2–3 days until the wound areas were completely covered by epidermis in any kinds of drug treatment. The combined BS and BO treatment had the best effect on healing by decreasing lesion area, while increasing granulation tissue formation, re-epithelialization, eating behavior and reconstitution of skin appendages. This investigation showed that BS and BO have a synergistic effect on the skin wound restoration.

Permanent correction of an inherited ectodermal dysplasia with recombinant EDA.

X-linked hypohidrotic ectodermal dysplasia (XLHED; OMIM 305100) is a genetic disorder characterized by absence or deficient function of hair, teeth and sweat glands. Affected children may experience life-threatening high fever resulting from reduced ability to sweat. Mice with the Tabby phenotype share many symptoms with human XLHED patients because both phenotypes are caused by mutations of the syntenic ectodysplasin A gene (Eda) on the X chromosome. Two main splice variants of Eda, encoding EDA1 and EDA2, engage the tumor necrosis factor (TNF) family receptors EDAR and XEDAR, respectively. The EDA1 protein, acting through EDAR, is essential for proper formation of skin appendages; the functions of EDA2 and XEDAR are not known. EDA1 must be proteolytically processed to a soluble form to be active. Here, we show that treatment of pregnant Tabby mice with a recombinant form of EDA1, engineered to cross the placental barrier, permanently rescues the Tabby phenotype in the offspring. Notably, sweat glands can also be induced by EDA1 after birth. This is the first example of a developmental genetic defect that can be permanently corrected by short-term treatment with a recombinant protein.

Shift of localized growth zones contributes to skin appendage morphogenesis: role of the Wnt/beta-catenin pathway.

Skin appendage formation represents a process of regulated new growth. Bromodeoxyuridine labeling of developing chicken skin demonstrated the presence of localized growth zones, which first promote appendage formation and then move within each appendage to produce specific shapes. Initially, cells proliferate all over the presumptive skin. During the placode stage they are organized to form periodic rings. At the short feather bud stage, the localized growth zones shifted to the posterior and then the distal bud. During the long bud stage, the localized growth zones descended through the flank region toward the feather collar (equivalent to the hair matrix). During feather branch formation, the localized growth zones were positioned periodically in the basilar layer to enhance branching of barb ridges. Wnts were expressed in a dynamic fashion during feather morphogenesis that coincided with the shifting localized growth zones positions. The expression pattern of Wnt 6 was examined and compared with other members of the Wnt pathway. Early in feather development Wnt 6 expression overlapped with the location of the localized growth zones. Its function was tested through misexpression studies. Ectopic Wnt 6 expression produced abnormal localized outgrowths from the skin appendages at either the base, the shaft, or the tip of the developing feathers. Later in feather filament morphogenesis, several Wnt markers were expressed in regions undergoing rearrangements and differentiation of barb ridge keratinocytes. These data suggest that skin appendages are built to specific shapes by adding new cells from well-positioned and controlled localized growth zones and that Wnt activity is involved in regulating such localized growth zone activity.