Desmoglein 4 mutations underlie localized autosomal recessive hypotrichosis in humans, mice, and rats.

A newly defined form of inherited hair loss, named localized autosomal recessive hypotrichosis (LAH, OMIM 607903), was recently described in the literature and shown to be linked to chromosome 18. A large, intragenic deletion in the desmoglein 4 gene (DSG4) as the underlying mutation in several unrelated families of Pakistani origin. LAH is an autosomal recessive form of hypotrichosis affecting the scalp, trunk, and extremities, and largely sparing the facial, pubic, and axillary hair. Typical hairs are fragile and break easily, leaving short sparse scalp hairs with a characteristic appearance. Using comparative genomics, we also demonstrated that human LAH is allelic with the lanceolate hair (lah) mouse, as well as the lanceolate hair (lah) rat phenotype. Together, these models provide new information about the role of desmosomal cadherins in disease, and serve as in vivo models for functional and mechanistic studies into the role of desmoglein 4 in the skin and hair follicle.

Differential structural properties and expression patterns suggest functional significance for multiple mouse desmoglein 1 isoforms.

The four isoforms of desmosomal cadherin desmogleins (Dsg1-4) are expressed in epithelial tissues in a differentiation-specific manner. Extensive sequencing of the human genome has revealed only one copy of the Dsg1 gene. However, we recently cloned two novel additional mouse Dsg1 genes, Dsg1-beta and -gamma, which flank the original Dsg1-alpha on chromosome 18. Sequence conservation between the Dsg1 isoforms diverged significantly at exon 11, particularly in the region that encodes for the extracellular anchoring (EA) domains. Computational analysis revealed very low hydrophilic potential of the Dsg1-gamma EA compared with the corresponding sequences of Dsg1-alpha and -beta, suggesting that the Dsg1-gamma EA domain may have a stronger affinity to the cell membrane. We generated antibodies using synthetic peptides or recombinant proteins localized within the EA domains. These antibodies were tested for their specificity and were then used to demonstrate expression of Dsg1 isoforms in various tissues. In the epidermis, all Dsg1 isoforms were differentially expressed in the differentiating cell layers. In the hair follicle, all Dsg1 isoforms were present throughout the entire process of its development and cycling but the expression of Dsg1 isoforms is subject to significant hair cycle-dependent changes. Dsg1-beta and -gamma, but not Dsg1-alpha, were detected in the sebaceous gland epithelium and the stratified epithelium of the stomach. Finally, Dsg1-alpha and Dsg1-beta, but not Dsg1-gamma, are proteolytically cleaved by exfoliative toxin A. These results suggest that the developmental complexity of mouse tissues, including skin and hair, may play a significant role in the evolutionary driving force to maintain multiple Dsg1 genes in mouse.

Intragenic deletion in the Desmoglein 4 gene underlies the skin phenotype in the Iffa Credo "hairless" rat.

The Iffa Credo (IC) "hairless" rat is an autosomal recessive hypotrichotic animal model actively used in pharmacological and dermatological studies. Although the molecular basis of the IC rat phenotype was never defined, the designation "hr/hr" (hairless) has been used for this rat mutation. Despite the observation that IC rats share many phenotypic similarities with Charles River (CR) 'hairless rats', crossbreeding between CR and IC rats indicated that these mutations are not allelic, and moreover, genetic analysis of both CR and IC hairless mutant rats showed no mutations in the hr gene. Here, we present a detailed analysis of the skin phenotype in the IC rat. While the initial stages of hair follicle (HF) morphogenesis reveal no significant abnormalities, the subsequent processes of inner root sheath and hair shaft formation are severely disturbed due to impaired proliferation in the hair matrix and abnormal differentiation in the precortex zone. This results in significant reduction of hair bulb volume, and the formation of dysmorphic "blebbed" hair shafts lacking medullar structure and resembling "lanceolate" hairs. Based on the presence of lance-head hairs typical of rodent lanceolate mutants, we performed molecular analysis of the desmoglein 4 gene and found a large intragenic deletion encompassing nine exons of the gene. This finding, together with specific morphological features of skin and hairs, confirms that the IC rat is allelic with the lanceolate hair (lah) mutations in mice and rats. Our results elucidate the genetic and morphological basis of the IC rat mutation, thus providing a new model to study molecular mechanisms of hair growth control.

Genomic organization of mouse desmocollin genes reveals evolutionary conservation.

Desmosomal cadherins are a family of calcium regulated proteins involved in the formation of desmosomes, a type of cell junction important in maintaining cell adhesion and tissue stability. The desmosomal plaque consists of members of the desmosomal cadherin, plakin and armadillo family of proteins. Desmosomal cadherins are transmembrane glycoproteins that interact with desmosomal cadherins of the adjacent cells via their extracellular repeat domains and are divided in two subfamilies, the desmogleins (Dsg) and the desmocollins (Dsc). On the cytoplasmic side, the cadherins connect to the intermediate filament (IF) network indirectly by interacting with plakin and armadillo proteins. Here, we report the elucidation of the genomic structure of two mouse desmocollin genes, Dsc2 and Dsc3. Interestingly, at the genomic level, desmocollins show a higher degree of similarity to the classical cadherins, such as E-cadherin, than to the desmogleins.

The lanceolate hair rat phenotype results from a missense mutation in a calcium coordinating site of the desmoglein 4 gene.

Desmosomal cadherins are essential cell adhesion molecules present throughout the epidermis and other organs, whose major function is to provide mechanical integrity and stability to epithelial cells in a wide variety of tissues. We recently identified a novel desmoglein family member, Desmoglein 4 (Dsg4), using a positional cloning approach in two families with localized autosomal recessive hypotrichosis (LAH) and in the lanceolate hair (lah) mouse. In this study, we report cloning and identification of the rat Dsg4 gene, in which we discovered a missense mutation in a naturally occurring lanceolate hair (lah) rat mutant. Phenotypic analysis of lah/lah mutant rats revealed a striking hair shaft defect with the appearance of a lance head within defective hair shafts. The mutation disrupts a critical calcium binding site bridging the second and third extracellular domains of Dsg4, likely disrupting extracellular interactions of the protein.

'Designer' tumors in mice.

We have developed and tested successfully a general method based on Cre-mediated recombination that can be used for ubiquitous or tissue-specific expression of protein products, including tumor-inducing oncoproteins. Depending on the specificity of a chosen promoter driving cre expression, tumors develop by design in bitransgenic mouse progeny derived by crossing Cre-producing mice with partners carrying a dormant oncogenic transgene (targeted into the 3' noncoding region of the cytoplasmic beta-actin locus) that becomes functional after excision of a 'floxed' DNA segment. To provide proof-of-principle, we have used as models transgenes encoding the polyomavirus middle T antigen (PVMT) and the T antigens of the SV40 early region (SVER). Cre-dependent activation of widespread SVER expression resulted in hyperplasias or invasive tumors affecting particular visceral smooth muscles, whereas Cre-dependent, mammary gland-specific expression of PVMT-induced adenocarcinomas, according to plan. Unexpectedly, we also encountered spontaneous (Cre-independent) oncogene expression occurring as a rare event, which simulates the initiation of sporadic tumors and leads to PVMT-induced hemangiomas and mammary carcinomas or SVER-induced disseminated sarcomas, thus, revealing particular tissue susceptibilities to the actions of these oncoproteins.

A mouse model of uterine leiomyosarcoma.

We are using an approach that is based on the cre/loxP recombination process and involves a binary system of Cre-producing and Cre-responding transgenic mice to achieve ubiquitous or tissue-specific expression of oncoproteins. To develop mouse models of tumorigenesis, Cre-producers are mated with responder animals carrying a dormant oncogene targeted into the 3' untranslated region of the locus encoding cytoplasmic beta-actin (actin cassette). Production of oncoprotein from a bicistronic message is accomplished in bitransgenic progeny by Cre-mediated excision of a segment flanked by loxP sites that is located upstream from the oncogenic sequence. Widespread Cre-dependent activation and expression of an actin-cassette transgene encoding the T antigens of the SV40 early region (SVER) commencing in embryos was compatible with normal development and did not impair viability. However, at approximately 3 months of age, all female animals developed massive uterine leiomyosarcomas, whereas practically all males exhibited enormously enlarged seminal vesicles because of pronounced hyperplasia of the smooth muscle layers. In addition, because of smooth muscle hyperproliferation, marked dilation of the gallbladder was observed in mice of both sexes. To begin exploring aberrant signaling events in the SVER-triggered tumorigenic pathways, we analyzed the expression profile of leiomyosarcomas by DNA microarray analysis.

A nonsense mutation in the desmoglein 1 gene underlies striate keratoderma.

Striate keratodermas (PPKS) (OMIM 148700) are a rare group of autosomal dominant genodermatoses characterized by palmoplantar keratoderma typified by streaking hyperkeratosis along each finger and extending onto the palm of the hand. We report a four-generation kindred originating from Iran-Syria in which three members were affected with PPKS. Clinically, these patients present with hyperkeratotic palms and plantar plaques. Direct DNA sequencing analysis revealed a heterozygous C-to-A transversion at nt 395 of the DSG1 gene. This mutation converted a serine residue (TCA) in exon 5 to a nonsense mutation (TAA) designated S132X. The mutation identified in this study is a novel mutation in the DSG1 gene and extends the body of evidence implicating the desmoglein gene family in the pathogenesis of human skin disorders.

Desmoglein 4 in hair follicle differentiation and epidermal adhesion: evidence from inherited hypotrichosis and acquired pemphigus vulgaris.

Cell adhesion and communication are interdependent aspects of cell behavior that are critical for morphogenesis and tissue architecture. In the skin, epidermal adhesion is mediated in part by specialized cell-cell junctions known as desmosomes, which are characterized by the presence of desmosomal cadherins, known as desmogleins and desmocollins. We identified a cadherin family member, desmoglein 4, which is expressed in the suprabasal epidermis and hair follicle. The essential role of desmoglein 4 in skin was established by identifying mutations in families with inherited hypotrichosis, as well as in the lanceolate hair mouse. We also show that DSG4 is an autoantigen in pemphigus vulgaris. Characterization of the phenotype of naturally occurring mutant mice revealed disruption of desmosomal adhesion and perturbations in keratinocyte behavior. We provide evidence that desmoglein 4 is a key mediator of keratinocyte cell adhesion in the hair follicle, where it coordinates the transition from proliferation to differentiation.