Mutations in AEC syndrome skin reveal a role for p63 in basement membrane adhesion, skin barrier integrity and hair follicle biology

Effects of TP63 mutations on keratinocyte adhesion and migration

The goal of this study was to investigate the molecular mechanisms responsible for the formation of skin erosions in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC). This ectodermal dysplasia is caused by mutations in the TP63 gene, which encodes several transcription factors that control epidermal development and homeostasis. We generated induced pluripotent stem cells (iPSC) from AEC patients and corrected the TP63 mutations using genome editing tools. Three pairs of the resulting conisogenic iPSC lines were differentiated into keratinocytes (iPSC-K). We identified a significant downregulation of key components of hemidesmosomes and focal adhesions in AEC iPSC-K compared to their gene-corrected counterparts. Further, we demonstrated reduced AEC iPSC-K migration, suggesting the possibility that a process critical for cutaneous wound healing might be impaired in AEC patients. Next, we generated chimeric mice expressing a TP63-AEC transgene and confirmed a downregulation of these genes in transgene-expressing cells in vivo. Finally, we also observed these abnormalities in AEC patient skin. Our findings suggest that integrin defects in AEC patients might weaken the adhesion of keratinocytes to the basement membrane. We propose that reduced expression of extracellular matrix adhesion receptors, potentially in conjunction with previously identified desmosomal protein defects, contribute to skin erosions in AEC.

Effects of TP63 Mutations on Keratinocyte Adhesion and Migration

The goal of this study was to investigate the molecular mechanisms responsible for the formation of skin erosions in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC). This ectodermal dysplasia is caused by mutations in the TP63 gene, which encodes several transcription factors that control epidermal development and homeostasis. We generated induced pluripotent stem cells (iPSC) from AEC patients and corrected the TP63 mutations using genome editing tools. Three pairs of the resulting conisogenic iPSC lines were differentiated into keratinocytes (iPSC-K). We identified a significant downregulation of key components of hemidesmosomes and focal adhesions in AEC iPSC-K compared to their gene-corrected counterparts. Further, we demonstrated reduced iPSC-K migration, suggesting the possibility that a process critical for cutaneous wound healing might be impaired in AEC patients. Next, we generated chimeric mice expressing a TP63-AEC transgene and confirmed a downregulation of these genes in transgene-expressing cells in vivo. Finally, we also observed these abnormalities in AEC patient skin. Our findings suggest that integrin defects in AEC patients might weaken the adhesion of keratinocytes to the basement membrane. We propose that reduced expression of extracellular matrix adhesion receptors, potentially in conjunction with previously identified desmosomal protein defects, contribute to skin erosions in AEC.

Correlation between novel compound heterozygous ADAMTSL4 variants and primary phenotypes of ectopia lentis et pupillae

PURPOSE

To investigate molecular pathogenesis of congenital ectopia lentis accompanied by various ophthalmic manifestations in a pedigree.

METHODS

Three female siblings, their spouse and offspring underwent ophthalmic and general medical examinations. Genetic variants were screened with the whole exome sequencing and analyzed in either a dominant or recessive inheritance manner. Gene mutations were ascertained with the Sanger sequencing after the polymerase chain reaction.

RESULTS

All three female siblings were diagnosed as the Ectopia lentis et pupillae (ELeP) through combination of clinical examination and genetic analysis. No characteristic pathological changes of skeletal, metabolic and cardiac abnormalities were observed. Thirteen genetic variants were selected out through analyzing in the dominant or recessive inheritance manner, but they were not associated with EL. Among them, ALOX15B variant may explain the skin disease in this pedigree. After inspection the known genes related to EL, novel compound heterozygous mutations (p.Ser264LeufsX37/p.Gly757ValfsX62) in ADAMTSL4 were discreetly identified in this ELeP pedigree.

CONCLUSIONS

Novel compound heterozygous ADAMTSL4 variants are responsible for ELeP in the current pedigree. Correlation between ADAMTSL4 variants and ELeP was firstly established based on our 12 years follow-up studies and previous reports of ELeP and of ADAMTSL4-related eye disorders. The primary phenotypes caused by ADAMTSL4 variants include EL, EP, poor pupillary dilation, and axial elongation. Highly varying phenotypes including glaucoma, high myopia retinapathy, and poor vision and so on may be the secondary impairments. All these secondary impairments may be improved if proper clinical interventions are implemented in time.

P63 targeted deletion under the FOXN1 promoter disrupts pre-and post-natal thymus development, function and maintenance as well as induces severe hair loss

Progressive immune deficiency of aging is characterized by severe thymic atrophy, contracted T cell repertoire, and poor immune function. p63 is critical for the proliferative potential of embryonic and adult stem cells, as well as thymic epithelial cells (TECs). Because p63 null mice experience rapid post-natal lethality due to epidermal and limb morphogenesis defects, studies to define a role for p63 expression in TEC biology focused on embryonic thymus development and in vitro experiments. Since post-natal thymic stromal development and function differs from that of the embryo, we assessed the impact of lineage-restricted p63 loss on pre- and post-natal murine TEC function by generating mice with a loss of p63 function targeted to TEC, termed p63TECko mice. In adult p63TECko mice, severe thymic hypoplasia was observed with a lack in a discernable segregation into medullary and cortical compartments and peripheral T cell lymphopenia. This profound thymic defect was seen in both neonatal as well as embryonic p63TECko mice. In addition to TECs, p63 also plays in important role in the development of stratified epithelium of the skin; lack of p63 results in defects in skin epidermal stratification and differentiation. Interestingly, all adult p63TECko mice lacked hair follicles despite having normal p63 expression in the skin. Together our results show a critical role of TEC p63 in thymic development and maintenance and show that p63 expression is critical for hair follicle formation.

Genomic Regions Associated with the Position and Number of Hair Whorls in Horses

Simple Summary

Whorls have been used to indicate the temperaments of domestic animals; however, little is known about the biological events that drive this association. The present study is the first that aims to find the main genomic regions that influence the whorl traits in livestock, with horses as a model. Genes related to hair follicle growth were found. Interestingly, some of these genes also influence psychiatric diseases and neurological disorders, thus evidencing a consistent biological explanation for the association.

Abstract

The position and number of hair whorls have been associated with the behavior, temperament, and laterality of horses. The easy observation of whorls assists in the prediction of reactivity, and thus permits the development of better measures of handling, training, mounting, and riding horses. However, little is known about the genetics involved in the formation of hair whorls. Therefore, the aim of this study was to perform a genome-wide association analysis to identify chromosome regions and candidate genes associated with hair whorl traits. Data from 342 Quarter Horses genotyped for approximately 53,000 SNPs were used in an association study using a single-step procedure. The following traits were analyzed: vertical position of hair whorl on the head, number of whorls on the head, and number of whorls on the left and right sides of the neck. The traits had between one and three genomic windows associated. Each of them explained at least 4% of the additive variance. The windows accounted for 20–80% of additive variance for each trait analyzed. Many of the prospected genes are related to hair follicle growth. Some of these genes exert a pleiotropic effect on neurological and behavioral traits. This is the first indication of biological and physiological activity that might explain the association of hair whorls and temperament.

Rare Genetic Disorders: Novel Treatment Strategies and Insights Into Human Biology

The last decade has seen a dramatic increase in innovative ideas for the treatment of genetic disorders for which no curative therapies exist. Gene and protein replacement therapies stand out as novel approaches to treat a select group of these diseases, such as certain tissue fragility disorders. Further, the advent of stem cell approaches, such as induced pluripotent stem cells (iPSC) technology, has led to the development of new methods of creating replacement tissues for regenerative medicine. This coincided with the discovery of genome editing techniques, which allow for the correction of disease-causing mutations. The culmination of these discoveries suggests that new and innovative therapies for monogenetic disorders affecting single organs or tissues are on the horizon. Challenges remain, however, especially with diseases that simultaneously affect several tissues and organs during development. Examples of this group of diseases include ectodermal dysplasias, genetic disorders affecting the development of tissues and organs such as the skin, cornea, and epithelial appendages. Gene or protein replacement strategies are unlikely to be successful in addressing the multiorgan phenotype of these diseases. Instead, we believe that a more effective approach will be to focus on correcting phenotypes in the most severely affected tissues. This could include the generation of replacement tissues or the identification of pharmaceutical compounds that correct disease pathways in specific tissues.

Analysis of histology and long noncoding RNAs involved in the rabbit hair follicle density using RNA sequencing

BACKGROUND

Hair follicle density influences wool fibre production, which is one of the most important traits of the Wan Strain Angora rabbit. However, molecular mechanisms regulating hair follicle density have remained elusive.

RESULTS

In this study, hair follicle density at different body sites of Wan Strain Angora rabbits with high and low wool production (HWP and LWP) was investigated by histological analysis. Haematoxylin-eosin staining showed a higher hair follicle density in the skin of the HWP rabbits. The long noncoding RNA (lncRNA) profile was investigated by RNA sequencing, and 50 and 38 differentially expressed (DE) lncRNAs and genes, respectively, were screened between the HWP and LWP groups. A gene ontology analysis revealed that phospholipid, lipid metabolic, apoptotic, lipid biosynthetic, and lipid and fatty acid transport processes were significantly enriched. Potential functional lncRNAs that regulate lipid metabolism, amino acid synthesis, as well as the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) and hedgehog signalling pathways, were identified. Consequently, five lncRNAs (LNC_002171, LNC_000797, LNC_005567, LNC_013595, and LNC_020367) were considered to be potential regulators of hair follicle density and development. Three DE lncRNAs and genes were validated by quantitative real-time polymerase chain reaction (q-PCR).

CONCLUSIONS

LncRNA profiles provide information on lncRNA expression to improve the understanding of molecular mechanisms involved in the regulation of hair follicle density.

Severe bilateral ankyloblepharon filiforme adnatum

We present a case of bilateral ankyloblepharon filiforme adnatum in 1-day-old girl and describe our surgical approach. The bands connecting the upper and lower eyelids of both eyes were severed using blunt scissors. Point bleeding at the cut bands stopped in 1-2 minutes, without the need for cauterization or compression. The patient was able to open her eyes shortly after the procedure, as she woke up from anesthesia. Examination under general anesthesia showed normal eye examination appropriate for age. Postoperatively, the patient maintained open palpebral fissures. Visual development over 3 years' follow-up was normal.

Downregulation of C-Terminal Tensin-Like Protein (CTEN) Suppresses Prostate Cell Proliferation and Contributes to Acinar Morphogenesis

C-terminal tensin-like protein (CTEN) is a member of tensin family, which is crucial for the assembly of cell-matrix adhesome. Unlike other tensins, CTEN is selectively expressed only in a few tissues such as the prostate. However, the biological relevance of CTEN in normal prostate is poorly understood. In this study, we revealed that CTEN is selectively expressed in the prostate epithelial cells and enriched in the basal compartment. Knockdown of CTEN in RWPE-1 cells suppresses cell proliferation and results in G1/S cell cycle arrest as well as the accumulation of cyclin-dependent kinase (CDK) inhibitors, p21 and p27. Moreover, the expression of CTEN is decreased during acinar morphogenesis using Matrigel-based three-dimensional (3D) culture. In the course of acinar formation, induction of CTEN reactivates focal adhesion kinase (FAK) Y³⁹⁷ phosphorylation and disrupts the acini structure. This study, to our knowledge, is the first report demonstrating that downregulation of CTEN is required for luminal differentiation and acinar formation.

A rare form of ankyloblepharon filiforme adnatum associated with the Hay-Wells syndrome and a c.1709T>C mutation on the TP63 gene

INTRODUCTION

Ankyloblepharon filiforme adnatum associated with Hay-Wells syndrome is a rare congenital disease caused by mutations in TP63 gene on the 3q27 chromosome. Here, we report a case of a new-born suffering from this syndrome in whom we detected a mutation c.1709T>C not previously included in the Ensemble database.

CASE DESCRIPTION

A girl delivered in the 34th week of gestation from a physiological pregnancy was born with extensive burn-like skin defects, ankyloblepharon filiforme adnatum, palate cleft, onychodystrophy of all limbs and syndactyly of toes. Hay-Wells syndrome was suspected and confirmed by genetic examination. A heterozygous missense change c.1709T>C was found in the TP63 gene. This variant leads to a 570th codon exchange of leucine for proline (p.Leu570Pro) on the protein level. The eyelid separation was performed surgically, burns were treated locally and cosmetic surgeries correcting other defects are planned for the near future. The girl is still monitored by a multidisciplinary team.

CONCLUSIONS

The mutation was not previously described in the literature or databases and should be included into these as probably pathogenic. A multidisciplinary approach is necessary to care for a patient with Hay-Wells syndrome, such care however can provide good results.

Multiple-trait QTL mapping and genomic prediction for wool traits in sheep

BACKGROUND

The application of genomic selection to sheep breeding could lead to substantial increases in profitability of wool production due to the availability of accurate breeding values from single nucleotide polymorphism (SNP) data. Several key traits determine the value of wool and influence a sheep's susceptibility to fleece rot and fly strike. Our aim was to predict genomic estimated breeding values (GEBV) and to compare three methods of combining information across traits to map polymorphisms that affect these traits.

METHODS

GEBV for 5726 Merino and Merino crossbred sheep were calculated using BayesR and genomic best linear unbiased prediction (GBLUP) with real and imputed 510,174 SNPs for 22 traits (at yearling and adult ages) including wool production and quality, and breech conformation traits that are associated with susceptibility to fly strike. Accuracies of these GEBV were assessed using fivefold cross-validation. We also devised and compared three approximate multi-trait analyses to map pleiotropic quantitative trait loci (QTL): a multi-trait genome-wide association study and two multi-trait methods that use the output from BayesR analyses. One BayesR method used local GEBV for each trait, while the other used the posterior probabilities that a SNP had an effect on each trait.

RESULTS

BayesR and GBLUP resulted in similar average GEBV accuracies across traits (~0.22). BayesR accuracies were highest for wool yield and fibre diameter (>0.40) and lowest for skin quality and dag score (<0.10). Generally, accuracy was higher for traits with larger reference populations and higher heritability. In total, the three multi-trait analyses identified 206 putative QTL, of which 20 were common to the three analyses. The two BayesR multi-trait approaches mapped QTL in a more defined manner than the multi-trait GWAS. We identified genes with known effects on hair growth (i.e. FGF5, STAT3, KRT86, and ALX4) near SNPs with pleiotropic effects on wool traits.

CONCLUSIONS

The mean accuracy of genomic prediction across wool traits was around 0.22. The three multi-trait analyses identified 206 putative QTL across the ovine genome. Detailed phenotypic information helped to identify likely candidate genes.

Tooth agenesis and orofacial clefting: genetic brothers in arms?

Tooth agenesis and orofacial clefts represent the most common developmental anomalies and their co-occurrence is often reported in patients as well in animal models. The aim of the present systematic review is to thoroughly investigate the current literature (PubMed, EMBASE) to identify the genes and genomic loci contributing to syndromic or non-syndromic co-occurrence of tooth agenesis and orofacial clefts, to gain insight into the molecular mechanisms underlying their dual involvement in the development of teeth and facial primordia. Altogether, 84 articles including phenotype and genotype description provided 9 genomic loci and 26 gene candidates underlying the co-occurrence of the two congenital defects: MSX1, PAX9, IRF6, TP63, KMT2D, KDM6A, SATB2, TBX22, TGFα, TGFβ3, TGFβR1, TGFβR2, FGF8, FGFR1, KISS1R, WNT3, WNT5A, CDH1, CHD7, AXIN2, TWIST1, BCOR, OFD1, PTCH1, PITX2, and PVRL1. The molecular pathways, cellular functions, tissue-specific expression and disease association were investigated using publicly accessible databases (EntrezGene, UniProt, OMIM). The Gene Ontology terms of the biological processes mediated by the candidate genes were used to cluster them using the GOTermMapper (Lewis-Sigler Institute, Princeton University), speculating on six super-clusters: (a) anatomical development, (b) cell division, growth and motility, (c) cell metabolism and catabolism, (d) cell transport, (e) cell structure organization and (f) organ/system-specific processes. This review aims to increase the knowledge on the mechanisms underlying the co-occurrence of tooth agenesis and orofacial clefts, to pave the way for improving targeted (prenatal) molecular diagnosis and finally to reflect on therapeutic or ultimately preventive strategies for these disabling conditions in the future.

High-Potency Topical Steroids: An Effective Therapy for Chronic Scalp Inflammation in Rapp-Hodgkin Ectodermal Dysplasia

Chronic erosive pustular dermatitis with a predilection for the scalp is a hallmark of ectodermal dysplasias (EDs) caused by mutations in TP63, including Rapp-Hodgkin and Hay-Wells EDs. It is among the most troublesome and symptomatic complications and is typically refractory to classic wound care approaches. We report two cases of Rapp-Hodgkin ED with refractory scalp erosions that markedly improved with the use of potent topical steroids. We also note marked similarities between this scalp inflammation and "erosive pustular dermatosis of the scalp," a condition more typically found in elderly individuals with severe scalp sun damage, and speculate about possible shared pathogenetic mechanisms.

Gene regulatory mechanisms orchestrated by p63 in epithelial development and related disorders

The transcription factor p63 belongs to the p53 family and is a key regulator in epithelial commitment and development. Mutations in p63 give rise to several epithelial related disorders with defects in skin, limb and orofacial structures. Since the discovery of p63, efforts have been made to identify its target genes using individual gene approaches and to understand p63 function in normal epithelial development and related diseases. Recent genome-wide approaches have identified tens of thousands of potential p63-regulated target genes and regulatory elements, and reshaped the concept of gene regulation orchestrated by p63. These data also provide insights into p63-related disease mechanisms. In this review, we discuss the regulatory role of p63 in normal and diseased epithelial development in light of these novel findings. We also propose future perspectives for dissecting the molecular mechanism of p63-mediated epithelial development and related disorders as well as for potential therapeutic strategies.

Epidermal cell junctions and their regulation by p63 in health and disease

As the outermost tissue of the body, the epidermis is the first physical barrier for any pressure, stress or trauma. Several specialized cell-matrix and cell-cell adhesion structures, together with an intracellular network of dedicated intermediate filaments, are required to confer critical resilience to mechanical stress. The transcription factor p63 is a master regulator of gene expression in the epidermis and in other stratified epithelia. It has been extensively demonstrated that p63 positively controls a large number of tissue-specific genes, including those encoding a large fraction of tissue-restricted cell adhesion molecules. Consistent with p63 functions in cell adhesion and in epidermal differentiation, heterozygous mutations clustered mainly in the p63 C-terminus are causative of AEC syndrome, an autosomal dominant disorder characterized by cleft palate, ankyloblepharon and ectodermal dysplasia associated with severe skin erosions, bleeding and infections. The molecular basis of skin erosions in AEC patients is not fully understood, although defects in desmosomes and in other cell junctions are likely to be involved. Here, we provide an extensive review of the different epidermal cell junctions that cooperate to withstand mechanical stress and on the mechanisms by which p63 regulates gene expression of their components in healthy skin and in AEC syndrome. Collectively, advancement in understanding the molecular mechanisms by which epidermal cell junctions precisely exert their functions and how p63 orchestrates their coordinated expression, will ultimately lead to insight into developing future strategies for the treatment of AEC syndrome and more in generally for diseases that share an overlapping phenotype.

p63-dependent and independent mechanisms of nectin-1 and nectin-4 regulation in the epidermis

Nectins are immunoglobulin-like cell adhesion molecules mainly localized in adherens junctions. The transcription factor p63 is a master regulator of gene expression in stratified epithelia and controls several molecular processes. As mutations in the Pvrl1 and Pvrl4 genes encoding for nectins cause genetic disorders with phenotypes similar to p63-related syndromes, we investigated whether these proteins might be under p63 transcriptional control. Here, we show that in p63-null skin, Pvrl1 gene expression is strongly reduced, whereas Pvrl4 expression is unaffected. In human and mouse primary keratinocytes p63 depletion leads to a specific downregulation of the Pvrl1 gene. Consistent with a direct regulation, chromatin immunoprecipitation experiments (ChIP) indicate that p63 binds to two conserved intronic Pvrl1 enhancer regions. Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare autosomal dominant disorder, caused by mutations in p63 gene, mainly characterized by skin fragility. To test whether nectins may be affected in AEC syndrome, their expression was measured in keratinocytes obtained from patients with AEC or from a conditional mouse model for AEC syndrome. Pvrl1 expression was reduced in AEC keratinocytes, consistent with impaired p63 function. Surprisingly, Pvrl4 expression was similarly affected, in parallel with decreased expression of the transcription factor Irf6. Consistent with the well-characterized role of Irf6 in keratinocyte differentiation and its strong downregulation in AEC syndrome, Irf6 depletion caused reduced expression of Pvrl4 in wild-type keratinocytes. Taken together, our results indicate that Pvrl1 is a bona fide target gene of the transcription factor p63, whereas Pvrl4 regulation is linked to epidermal differentiation and is under Irf6 control.

Syndrome in question. Hay-Wells syndrome

Hay-Wells syndrome or AEC (Ankyloblepharon, Ectodermal dysplasia and Cleft lip and palate syndrome) is a rare ectodermal disorder. The treatment is aimed to prevent clinical complications. We describe the case of a four-month old male patient with erosions on the scalp, trunk and arms, trachyonychia, deformity of the ears, micropenis, cleft palate, decreased eyebrow and eyelash hairs, in addition to antecedents of surgical correction of ankyloblepharon. The importance of the correct diagnosis is emphasized, besides the investigation of the associated diseases, treatment of complications and genetic counseling of the parents.

Integrating animal models and in vitro tissue models to elucidate the role of desmosomal proteins in diseases

Desmosomes are intercellular junctions that provide tissues with structural stability. These junctions might also act as signaling centers that transmit environmental clues to the cell, thereby affecting cell differentiation, migration, and proliferation. The importance of desmosomes is underscored by devastating skin and heart diseases caused by mutations in desmosomal genes. Recent observations suggest that abnormal desmosomal protein expression might indirectly contribute to skin disorders previously not linked to these proteins. For example, it has been postulated that reduced desmosomal protein expression occurs in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC), a skin fragility disorder caused by mutations in the transcription factor TP63. Currently, it is not clear how these changes in desmosomal gene expression contribute to AEC. We will discuss new approaches that combine in vitro and in vivo models to elucidate the role of desmosomal gene deregulation in human skin diseases such as AEC.

Modeling AEC-New approaches to study rare genetic disorders

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare monogenetic disorder that is characterized by severe abnormalities in ectoderm-derived tissues, such as skin and its appendages. A major cause of morbidity among affected infants is severe and chronic skin erosions. Currently, supportive care is the only available treatment option for AEC patients. Mutations in TP63, a gene that encodes key regulators of epidermal development, are the genetic cause of AEC. However, it is currently not clear how mutations in TP63 lead to the various defects seen in the patients' skin. In this review, we will discuss current knowledge of the AEC disease mechanism obtained by studying patient tissue and genetically engineered mouse models designed to mimic aspects of the disorder. We will then focus on new approaches to model AEC, including the use of patient cells and stem cell technology to replicate the disease in a human tissue culture model. The latter approach will advance our understanding of the disease and will allow for the development of new in vitro systems to identify drugs for the treatment of skin erosions in AEC patients. Further, the use of stem cell technology, in particular induced pluripotent stem cells (iPSC), will enable researchers to develop new therapeutic approaches to treat the disease using the patient's own cells (autologous keratinocyte transplantation) after correction of the disease-causing mutations.

Delineating Molecular Mechanisms of Squamous Tissue Homeostasis and Neoplasia: Focus on p63

Mouse models have informed us that p63 is critical for normal epidermal development and homeostasis. The p53/p63/p73 family is expressed as multiple protein isoforms due to a combination of alternative promoter usage and C-terminal alternative splicing. These isoforms can mimic or interfere with one another, and their balance ultimately determines biological outcome in a context-dependent manner. While not frequently mutated, p63, and in particular the ΔNp63 subclass, is commonly overexpressed in human squamous cell cancers. In vitro keratinocytes and murine transgenic and transplantation models have been invaluable in elucidating the contribution of altered p63 levels to cancer development, and studies have identified the roles for ΔNp63 isoforms in keratinocyte survival and malignant progression, likely due in part to their transcriptional regulatory function. These findings can be extended to human cancers; for example, the novel recognition of NFκB/c-Rel as a downstream effector of p63 has identified a role for NFκB/c-Rel in human squamous cell cancers. These models will be critical in enhancing the understanding of the specific molecular mechanisms of cancer development and progression.

Genetic pathways in disorders of epidermal differentiation

More than 100 human genetic skin diseases, impacting over 20% of the population, are characterized by disrupted epidermal differentiation. A significant proportion of the 90 genes identified in these disorders to date are concentrated within several functional pathways, suggesting the emergence of organizing themes in epidermal differentiation. Among these are the Notch, transforming growth factor β (TGFβ), IκB kinase (IKK), Ras/mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K), p63, and Wnt signaling pathways, as well as core biological processes mediating calcium homeostasis, tissue integrity, cornification, and lipid biogenesis. Here, we review recent results supporting the central role of these pathways in epidermal differentiation, highlighting the integration of genetic information with functional studies to illuminate the biological actions of these pathways in humans as well as to guide development of future therapeutics to correct their dysfunction.

p63 control of desmosome gene expression and adhesion is compromised in AEC syndrome

Ankyloblepharon, ectodermal defects, cleft lip/palate (AEC) syndrome is a rare autosomal dominant disorder caused by mutations in the p63 gene, essential for embryonic development of stratified epithelia. The most severe cutaneous manifestation of this disorder is the long-lasting skin fragility associated with severe skin erosions after birth. Using a knock-in mouse model for AEC syndrome, we found that skin fragility was associated with microscopic blistering between the basal and suprabasal compartments of the epidermis and reduced desmosomal contacts. Expression of desmosomal cadherins and desmoplakin was strongly reduced in AEC mutant keratinocytes and in newborn epidermis. A similar impairment in desmosome gene expression was observed in human keratinocytes isolated from AEC patients, in p63-depleted keratinocytes and in p63 null embryonic skin, indicating that p63 mutations causative of AEC syndrome have a dominant-negative effect on the wild-type p63 protein. Among the desmosomal components, desmocollin 3, desmoplakin and desmoglein 1 were the most significantly reduced by mutant p63 both at the RNA and protein levels. Chromatin immunoprecipitation experiments and transactivation assays revealed that p63 controls these genes at the transcriptional level. Consistent with reduced desmosome function, AEC mutant and p63-deficient keratinocytes had an impaired ability to withstand mechanical stress, which was alleviated by epidermal growth factor receptor inhibitors known to stabilize desmosomes. Our study reveals that p63 is a crucial regulator of a subset of desmosomal genes and that this function is impaired in AEC syndrome. Reduced mechanical strength resulting from p63 mutations can be alleviated pharmacologically by increasing desmosome adhesion with possible therapeutic implications.