Aspects of the structure and assembly of desmosomes

Triptonide is a reversible non-hormonal male contraceptive agent in mice and non-human primates

There are no non-hormonal male contraceptives currently on the market despite decades of efforts toward the development of "male pills". Here, we report that triptonide, a natural compound purified from the Chinese herb Tripterygium Wilfordii Hook F displays reversible male contraceptive effects in both mice and monkeys. Single daily oral doses of triptonide induces deformed sperm with minimal or no forward motility (close to 100% penetrance) and consequently male infertility in 3-4 and 5-6 weeks in mice and cynomolgus monkeys, respectively. Male fertility is regained in ~4-6 weeks after cessation of triptonide intake in both species. Either short- or long-term triptonide treatment causes no discernable systematic toxic side effects based on histological examination of vital organs in mice and hematological and serum biochemical analyses in monkeys. Triptonide appears to target junction plakoglobin and disrupts its interactions with SPEM1 during spermiogenesis. Our data further prove that targeting late spermiogenesis represents an effective strategy for developing non-hormonal male contraceptives.

AMPK in regulation of apical junctions and barrier function of intestinal epithelium

Gut epithelium covers the inner layer of the gastrointestinal tract and provides a physical barrier to separate the host from its external environment, and its barrier function is critical for maintaining host health. AMP-activated protein kinase (AMPK) as a master regulator of energy metabolism plays a critical role in epithelial barrier function. AMPK activation promotes epithelial differentiation and facilitates cell polarity establishment, both of which strengthen epithelial barrier. In addition, AMPK promotes the assembly of tight junctions and adherens junctions by direct phosphorylation of proteins composing apical junctions, junctional anchors, and cytoskeletons. Pharmacological and nutraceutical compounds, as well as physiological states triggering AMPK activation strengthen epithelial barrier function. This review summarized recent progress in delineating the regulatory roles of AMPK in apical junction formation and barrier function of intestinal epithelium.

Development of Hair Fibres

The growth of hairs occurs during the anagen phase of the follicle cycle. Hair growth begins with basement membrane-bound stem cells (mother cells) around the dermal papilla neck which continuously bud off daughter cells which further divide as a transient amplifying population. Division ceases as cell line differentiation begins, which entails changes in cell junctions, cell shape and position, and cell-line specific cytoplasmic expression of keratin and trichohyalin. As the differentiating cells migrate up the bulb, nuclear function ceases in cortex, cuticle and inner root sheath (IRS) layers. Past the top of the bulb, cell shape/position changes cease, and there is a period of keratin and keratin-associated protein (KAP) synthesis in fibre cell lines, with increases, in particular of KAP species. A gradual keratinization process begins in the cortex at this point and then non-keratin cell components are increasingly broken down. Terminal cornification, or hardening, is associated with water loss and precipitation of keratin. In the upper follicle, the hair, now in its mature form, detaches from the IRS, which is then extracted of material and becomes fragmented to release the fibre. Finally, the sebaceous and sudoriferous (if present) glands coat the fibre in lipid-rich material and the fibre emerges from the skin. This chapter follows the origin of the hair growth in the lower bulb and traces the development of the various cell lines.

Efficacy of magnesium chloride in the treatment of Hailey-Hailey disease: from serendipity to evidence of its effect on intracellular Ca(2+) homeostasis

BACKGROUND

Hailey-Hailey disease (HHD), also known as familial benign chronic pemphigus, is a rare autosomal dominant inherited intraepidermal blistering genodermatosis. Mutations in the ATP2C1 gene encoding for the Golgi secretory pathway Ca(2+) /Mn(2+) -ATPasi protein 1 (SPCA1) affect the processing of desmosomal components and the epidermal suprabasal cell-cell adhesion by deregulating the keratinocyte cytosolic Ca(2+) concentration. We report the unexpected, dramatic, and persistent clinical improvement of the skin lesions of a patient affected with longstanding HHD with daily intake of a solution containing magnesium chloride hexahydrate (MgCl2 ).

MATERIALS AND METHODS

We investigated the effect of MgCl2 on the intracellular Ca(2+) homeostasis and on the activity of particular Ca(2+) -effectors in HeLa cells transfected with chimeric aequorins (cytAEQ, mtAEQ, erAEQ and GoAEQ) targeted to different subcellular compartments (cytosol, mitochondria, endoplasmic reticulum, and Golgi, respectively).

RESULTS

Experimental investigations on HeLa cells showed the effect of MgCl2 on the function of Ca(2+) -extrusor systems, resulting in increased cytosolic and mitochondrial Ca(2+) levels, without altering the mechanisms of intraluminal Ca(2+) -filling and Ca(2+) -release of stores.

CONCLUSIONS

Based on our clinical observation and experimental results, it can be hypothesized that MgCl2 could act as an inhibitor of the Ca(2+) -extruding activity in keratinocytes favoring intracellular Ca(2+) -disponibility and Ca(2+) -dependent mechanisms in desmosome assembly. This may represent the molecular basis of the good response of the HHD clinical features with MgCl2 solution in the patient described.

The molecular composition and function of desmosomes

Desmosomes are intercellular adhesive junctions that are particularly prominent in tissues experiencing mechanical stress, such as the heart and epidermis. Whereas the related adherens junction links actin to calcium-dependent adhesion molecules known as classical cadherins, desmosomes link intermediate filaments (IF) to the related subfamily of desmosomal cadherins. By tethering these stress-bearing cytoskeletal filaments to the plasma membrane, desmosomes serve as integrators of the IF cytoskeleton throughout a tissue. Recent evidence suggests that IF attachment in turn strengthens desmosomal adhesion. This collaborative arrangement results in formation of a supracellular network, which is critical for imparting mechanical integrity to tissues. Diseases and animal models targeting desmosomal components highlight the importance of desmosomes in development and tissue integrity, while the downregulation of individual protein components in cancer metastasis and wound healing suggests their importance in cell homeostasis. This chapter will provide an update on desmosome composition, function, and regulation, and will also discuss recent work which raises the possibility that desmosome proteins do more than play a structural role in tissues where they reside.

Intercellular junction assembly, dynamics, and homeostasis

Intercellular anchoring junctions are highly specialized regions of the plasma membrane where members of the cadherin family of transmembrane adhesion molecules on opposing cells interact through their extracellular domains, and through their cytoplasmic domains serve as a platform for organizing cytoskeletal anchors and remodelers. Here we focus on assembly of so-called "anchoring" or "adhering" junctions-adherens junctions (AJs) and desmosomes (DSMs), which associate with actin and intermediate filaments, respectively. We will examine how the assembly and function of AJs and DSMs are intimately connected during embryogenesis and in adult cells and tissues, and in some cases even form specialized "mixed" junctions. We will explore signaling and trafficking machineries that drive assembly and remodeling and how these mechanisms are co-opted in human disease.

Desmosomes in the uterine epithelium of noninvasive skink placentae

Australian species of viviparous skinks have noninvasive epitheliochorial placentation where there is no breeching or interruption of the uterine epithelial cell barrier. This is contrary to some African and South American species of skinks which exhibit invading chorionic cells and a localized endotheliochorial placenta. The desmosomes, which maintain the adhesive properties of the junctional complex between uterine epithelial cells, were found to decrease as gestation progressed in the uterus of two highly placentotrophic Australian skinks, but no changes in desmosomal numbers were present in the uterus of two Australian oviparous skinks or viviparous skinks with a simple placenta. In mammals, desmosomes decrease in the uterine epithelium of species with invasive hemochorial placentation, where less chemical and mechanical adhesion between cells assists the invading trophoblast at the time of implantation. However, Australian viviparous skinks do not have an invasive trophoblast; yet, similarities in decreasing lateral cellular adhesion exist in the uterus of both invasive and noninvasive placental types. This similarity in cellular mechanisms suggests a conservation of plasma membrane changes across placentation irrespective of reptilian or mammalian origin.

The impact of tissue fixatives on morphology and antibody-based protein profiling in tissues and cells

Pathology archives harbor large amounts of formalin-fixed, paraffin-embedded tissue samples, used mainly in clinical diagnostics but also for research purposes. Introduction of heat-induced antigen retrieval has enabled the use of tissue samples for extensive immunohistochemical analysis, despite the fact that antigen retrieval may not recover all epitopes, owing to alterations of the native protein structure induced by formalin. The aim of this study was to investigate how different fixatives influence protein recognition by immunodetection methods in tissues, cell preparations, and protein lysates, as compared with formalin. Seventy-two affinity-purified polyclonal antibodies were used to evaluate seven different fixatives. The aldehyde-based fixative Glyo-fixx proved to be excellent for preservation of proteins in tissue detected by immunohistochemistry (IHC), similar to formalin. A non-aldehyde-based fixative, NEO-FIX was superior for fixation of cultured cells, in regard to morphology, and thereby also advantageous for IHC. Large variability in the amount of protein extracted from the differently fixed tissues was observed, and the HOPE fixative provided the overall highest yield of protein. In conclusion, morphological resolution and immunoreactivity were superior in tissues fixed with aldehyde-based fixatives, whereas the use of non-aldehyde-based fixatives can be advantageous in obtaining high protein yield for Western blot analysis. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Structure and function of desmosomes

Desmosomes are prominent adhesion sites that are tightly associated with the cytoplasmic intermediate filament cytoskeleton providing mechanical stability in epithelia and also in several nonepithelial tissues such as cardiac muscle and meninges. They are unique in terms of ultrastructural appearance and molecular composition with cell type-specific variations. The dynamic assembly properties of desmosomes are important prerequisites for the acquisition and maintenance of tissue homeostasis. Disturbance of this equilibrium therefore not only compromises mechanical resilience but also affects many other tissue functions as becomes evident in various experimental scenarios and multiple diseases.

Inhibition of e-cadherin-mediated homotypic adhesion of Caco-2 cells: a novel evaluation assay for peptide activities in modulating cell-cell adhesion

Transient modulation of E-cadherin-mediated cell-cell adhesion may improve paracellular drug delivery through biological barriers. Therefore, there is a need to develop an efficient method to evaluate cadherin peptides that can modulate the intercellular junctions. The objective of this study was to establish a novel assay to evaluate peptide activity in modulating E-cadherin-mediated homophilic interactions, based on the homotypic adhesion of Caco-2 cells. Fluorescence-labeled Caco-2 single cells were incubated with Caco-2 monolayers that were treated beforehand with Ca(2+)-free medium. The homotypic adhesion in the presence or absence of peptide and antibody was determined fluorometrically. The Ca(2+)-deficient pretreatment dramatically increased the number of single cells bound to the monolayers. Immunofluorescence staining showed that some of E-cadherins became accessible without surfactant-induced permeabilization of Caco-2 cell monolayers after the Ca(2+)-deficient pretreatment. The homotypic adhesion was largely dependent on extracellular Ca(2+) concentrations and significantly inhibited by the presence of anti-E-cadherin monoclonal antibody DECMA-1. In contrast, DECMA-1 did not inhibit E-cadherin-independent adhesion, such as the homotypic adhesion of Caco-2 cells in the absence of Ca(2+) or the heterotypic adhesion of Molt-3 T cells to Caco-2 monolayers. These results indicate the predominant involvement of E-cadherin-mediated cell-cell adhesion in this assay. E-cadherin-derived peptides, which had been shown in our previous studies to inhibit E-cadherin-mediated cell-cell adhesion, significantly inhibited homotypic adhesion in a dose-dependent manner. These results, taken together, suggest that the present assay can be used for evaluation of peptide, protein, or antibody activity in modulating the E-cadherin-mediated homophilic interactions in the context of whole live cells.

A genetic strategy to overcome the senescence of primary meningioma cell cultures

Even though meningiomas are the second most common brain tumor in adults, little is known about the molecular basis of their growth and development. The lack of suitable cell culture model systems is an impediment to this understanding. Most studies on meningiomas rely on primary, early passage cell lines that eventually senesce or a few established cell lines that have been derived from aggressive variants of meningiomas. We have isolated three primary meningioma cell lines that are negative for telomerase activity. We can overcome the senescence of a Grade III derived meningioma cell line by expressing the telomerase catalytic subunit (hTERT), whereas Grade I meningioma cell lines require the expression of the human papillomavirus E6 and E7 oncogenes in conjunction with hTERT. Meningioma cell lines, immortalized in this manner, maintain their pre-transfection morphology and form colonies in vitro. We have confirmed the meningothelial origin of these cell lines by assessing expression of vimentin and desmoplakin, characteristic markers for meningiomas. Additionally, we have karyotyped these cell lines using array CGH and shown that they represent a spectrum of the genetic diversity seen in primary meningiomas. Thus, these cell lines represent novel cellular reagents for investigating the molecular oncogenesis of meningiomas.

Changes in myofibrils and cytoskeleton of neonatal hamster myocardial cells in culture: an immunofluorescence study

Myocardial cells in culture offer many possibilities for studying cellular and molecular biology of cardiac muscles. However, it is important to know how long these cells can be maintained in vitro without significant structural and biochemical changes. In this study, we have investigated the morphological changes of myofibril proteins and cytoskeletons by using immunofluorescent techniques in cultured neonatal hamster myocardial cells at different culture durations. Our results have demonstrated that these cultured cells still contain intact myofibrils and cytoskeletal proteins after 6 days in vitro incubation, however, the organization of some of these proteins is altered. The proteins most sensitive to these in vitro conditions are: myosin heavy chain, actin and desmin. The data indicate that the duration of the culture and the contractile activity of the myocardial cells in culture can influence organization of their contractile apparatus and cytoskeleton.

Ultrastructure of bronchial biopsies from patients with allergic and non-allergic asthma

Epithelial damage is commonly found in airways of asthma patients. The aim of this study was to investigate epithelial damage in allergic and non-allergic asthma at the ultrastructural level. Bronchial biopsies obtained from patients with allergic asthma (n=11), non-allergic asthma (n=7), and healthy controls (n=5) were studied by transmission electron microscopy. Epithelial damage was found to be extensive in both asthma groups. Both in basal and in columnar cells, relative desmosome length was reduced by 30-40%. In columnar cells, half-desmosomes (i.e., desmosomes of which only one side was present) were frequently noticed. Eosinophils showing piece-meal degranulation were commonly observed in allergic asthma. Degranulating mast cells were more often observed in allergic asthma. Goblet cell hyperplasia was only found in allergic asthma. Lymphocytes were increased in both groups. In both groups, the lamina densa of the basal lamina was thicker than the control by about 40-50%. In allergic asthma the lamina densa was irregular with focal thickening. While there was always a tendency for changes (epithelial damage, desmosomes, degranulating mast cells, basal lamina) to be more extensive in allergic asthma compared to non-allergic asthma, there was no significant difference between the two groups in this respect. Reduced desmosomal contact may be an important factor in the epithelial shedding observed in patients with asthma.

Nanostructure of the Epidermal Extracellular Space as Observed by Cryo-Electron Microscopy of Vitreous Sections of Human Skin

The newly developed method, cryo-electron microscopy of vitreous sections, was used to observe the nanostructure of the epidermal extracellular space. The data were obtained from vitreous sections of freshly taken, fully hydrated, non-cryo-protected human skin. The extracellular space of viable epidermis contains desmosomes, expressing a characteristic extracellular transverse approximately 5 nm periodicity, interconnected by a relatively electron lucent inter-desmosomal space. The extracellular space between viable and cornified epidermis contains transition desmosomes at different stages of reorganization interconnected by widened areas expressing a rich variety of complex membrane-like structures. The extracellular space of cornified epidermis contains approximately 9, approximately 14, approximately 25, approximately 33, approximately 39, approximately 44, and approximately 48 nm thick regions in turn containing one, two, four, six, eight, eight, and ten parallel electron-dense lines, respectively, between adjacent corneocyte lipid envelopes. The eight-line approximately 44 nm thick regions are most prevalent.

Upregulation of the expression of tight and adherens junction-associated proteins during maturation of neonatal pancreatic islets in vitro

Cell-cell contacts mediated by intercellular junctions are crucial for proper insulin secretion in the endocrine pancreas. The biochemical composition of the intercellular junctions in this organ and the role of junctional proteins in endocrine pancreatic dysfunctions are still unclear. In this study, we investigated the expression and cellular location of junctional and cytoskeletal proteins in cultured neonatal rat pancreatic islets. Neonatal B-cells had an impaired insulin secretion compared to adult cells. Cultured neonatal islets showed a time-dependent increase in the glucose-induced secretory response. The maturation of B-cells in vitro was accompanied by upregulation of the expression of some junctional proteins in islet cells. Neonatal islets cultured for only 24 h showed a low expression and a diffuse cytoplasmic location of the tight junctional proteins occludin and ZO-1 and of the adherens junctional proteins alpha- and beta-catenins, as demonstrated by immunoblotting and immunocytochemistry. Culturing islets for up to 8 days significantly increased the cell expression of these junctional proteins but not of the cytoskeletal proteins vinculin and alpha-actinin. A translocation of ZO-1 and catenins to the cell-cell contact region, as well as a higher association of F-actin with the intercellular junction, were also observed in neonatal islets following prolonged culturing. ZO-1 and beta-catenin were immunolocated in the endocrine pancreas of adult rats indicating that these junctional proteins are also expressed in this organ in situ. In conclusion, endocrine pancreatic cells express several junctional proteins that are upregulated following differentiation of the endocrine pancreas in vitro.

Progesterone treatment and the progress of early pregnancy reduce desmoglein 1&2 staining along the lateral plasma membrane in rat uterine epithelial cells

Uterine epithelium undergoes dramatic changes during early pregnancy in preparation for implantation. We have studied distribution patterns of the desmosomal marker, desmoglein 1&2, in rat uterine epithelial cells during early pregnancy as well as in hormonally stimulated ovariectomised animals. On day 1 of pregnancy as well as in oestradiol treated rats, desmoglein 1&2 staining was localized along the entire length of the lateral plasma membrane. By day 3 and on subsequent days of pregnancy as well as in ovariectomised animals treated with progesterone alone or in combination with oestradiol, desmoglein 1&2 staining was concentrated at the apical portion of the lateral plasma membrane. We suggest that the reorganisation of these desmosomal cadherins is an important component of uterine epithelial receptivity and this relocation is under the control of the ovarian hormone progesterone.

Desmosomes in uterine epithelial cells decrease at the time of implantation: An ultrastructural and morphometric study

Displacement of uterine epithelial cells is an important aspect of implantation in the rat and other species, allowing invasion of the blastocyst into the endometrial stroma. Desmosomes, which are part of the lateral junctional complex, function in cell-to-cell adhesion, and are therefore likely to be involved in displacement of uterine epithelial cells at the time of implantation. This study used transmission electron microscopy to study rat uterine epithelial cells during the peri-implantation period to investigate the change in the number of structural desmosomes along the lateral plasma membrane of uterine epithelial cells. We found a significant decrease in the number of desmosomes along the entire lateral plasma membrane as pregnancy progressed. Furthermore, there were also significant decreases in the number of desmosomes on the apical portion of the lateral plasma membrane between all days of pregnancy examined. In addition, on day 6 of pregnancy, the time of attachment, desmosomes were larger and seen as "giant desmosomes." For the first time, this study has shown that there is a significant reduction in cell height and actual number of ultrastructurally observable desmosomes at the time of implantation in the rat. It is proposed that this reduction in desmosome number leads to a decrease in lateral adhesion between uterine epithelial cells at the time of implantation, and hence is involved in the loss of uterine epithelial cells to facilitate blastocyst invasion.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

The cadherin-catenin complex as a focal point of cell adhesion and signalling: new insights from three-dimensional structures

Cadherins are a large family of single-pass transmembrane proteins principally involved in Ca2+-dependent homotypic cell adhesion. The cadherin molecules comprise three domains, the intracellular domain, the transmembrane domain and the extracellular domain, and form large complexes with a vast array of binding partners (including cadherin molecules of the same type in homophilic interactions and cellular protein catenins), orchestrating biologically essential extracellular and intracellular signalling processes. While current, contrasting models for classic cadherin homophilic interaction involve varying numbers of specific repeats found in the extracellular domain, the structure of the domain itself clearly remains the main determinant of cell stability and binding specificity. Through intracellular interactions, cadherin enhances its adhesive properties binding the cytoskeleton via cytoplasmic associated factors alpha- catenin, beta-catenin and p120ctn. Recent structural studies on classic cadherins and these catenin molecules have provided new insight into the essential mechanisms underlying cadherin-mediated cell interaction and catenin-mediated cellular signalling. Remarkable structural diversity has been observed in beta-catenin recognition of other cellular factors including APC, Tcf and ICAT, proteins that contribute to or compete with cadherin/catenin functioning.

Striate palmoplantar keratoderma arising from desmoplakin and desmoglein 1 mutations is associated with contrasting perturbations of desmosomes and the keratin filament network

BACKGROUND

Several hereditary human diseases are now known to be caused by distinct mutations in genes encoding various desmosome components. Although the effects of some of these mutant genes have been analysed by targeted disruption experiments in mouse models, little is known about the cell and tissue changes in affected human patients.

OBJECTIVES

To investigate the effects of heterozygous nonsense mutations in desmoplakin (Dp) and desmoglein (Dsg) 1 which cause the autosomal dominant disorder striate palmoplantar keratoderma (SPPK), focusing on changes in desmosome structure and composition and the associated keratin intermediate filament (KIF) network in palm skin, and in cultured keratinocytes generated from the same site.

METHODS

We analysed palm and nonpalm skin sections from four SPPK patients with Dp mutations and one patient with a Dsg1 mutation with respect to tissue and subcellular morphologies, and correlated the in vivo and in vitro findings.

RESULTS

Using electron microscopy, we found abnormalities of desmosomes and cell-cell adhesion in the suprabasal layers in the epidermis from patients with both Dsg1- and Dp-associated SPPK. These changes were more advanced in skin from patients with Dp mutations. Both Dp and Dsg1 mutations were accompanied by significantly reduced numbers of desmosomes in the suprabasal layers, while decreased desmosome size was evident only in Dsg1-associated SPPK. Confocal microscopy analysis showed marked differences in the expression of keratins and of desmosome components, both between the two types of SPPK, and between SPPK and normal skin. The expression of keratins K5, K14 and K10 was reduced in Dsg1-associated SPPK skin, whereas perinuclear aggregation of keratin filaments was more evident in Dp-associated SPPK. In both types of SPPK upregulation of K16 was pronounced and involucrin labelling was abnormal.

CONCLUSIONS

Mutations in Dp and Dsg1 genes causing SPPK may be associated with perturbations in epidermal differentiation accompanied by a marked disruption of several components of the epidermal scaffold including desmosomes and the KIF network.

Homo-oligomerization of human corneodesmosin is mediated by its N-terminal glycine loop domain

Corneodesmosin (CDSN), a glycoprotein expressed during the late stages of epidermal differentiation, localizes in the extracellular core of upper desmosomes and of corneodesmosomes. Since it displays homophilic adhesive properties, CDSN is thought to reinforce cell-cell cohesion within the upper layers of the epidermis. CDSN presents two serine- and glycine-rich domains in its N- and C-terminus that may fold into highly flexible and adhesive secondary structures called glycine loops. We analyzed the importance of these domains in CDSN homophilic adhesion by producing full-length and truncated recombinant forms of the protein deleted of the N- and/or the C-terminal domain. The adhesive properties of the various proteins were then tested in vitro by overlay binding assays and surface plasmon resonance quantitative analysis. Experiments evidenced the homophilic adhesive properties of the N-terminal glycine loop domain, confirming its involvement in CDSN-CDSN interactions. They further indicated that most of the C-terminal domain is not necessary for the adhesive properties of the protein. The dissociation constant (K(D)) was calculated to be 1.3x10(-5) M. This interaction strength might allow dynamic regulation of the CDSN-CDSN association to occur in vivo. Moreover, molecular filtration analyses demonstrated for the first time that non-glycosylated CDSN is able to spontaneously form large homo-oligomers in vitro and that the N-terminal glycine loop domain is necessary for the formation of these macromolecular complexes.

Calcium pumps and keratinocytes: lessons from Darier's disease and Hailey-Hailey disease

Darier's disease and Hailey-Hailey disease are autosomal dominantly inherited skin disorders in which desmosomal adhesion between keratinocytes is abnormal. ATP2A2 and ATP2C1 have been identified as the causative genes for Darier's disease and Hailey-Hailey disease, respectively. ATP2A2 encodes the sarco(endo)plasmic reticulum Ca(2+)-ATPase isoform 2 (SERCA2) pump, while ATP2C1 encodes a secretory pathway Ca(2+)/Mn(2+)-ATPase (SPCA1) found in the Golgi apparatus. We review recent work into the function of these pumps in human keratinocytes and discuss how mutations in these genes might cause these diseases by altering the formation or stability of desmosomes.

The flagella connector of Trypanosoma brucei: an unusual mobile transmembrane junction

Throughout its elongation, the new flagellum of the procyclic form of the African trypanosome Trypanosoma brucei is tethered at its tip to the lateral aspect of the old flagellum. This phenomenon provides a cytotactic mechanism for influencing inheritance of cellular pattern. Here, we show that this tethering is produced via a discrete, mobile transmembrane junction - the flagella connector. Light and electron microscopy reveal that the flagella connector links the extending microtubules at the tip of the new flagellum to the lateral aspect of three of the doublet microtubules in the old flagellar axoneme. Two sets of filaments connect the microtubules to three plates on the inner faces of the old and new flagellar membranes. Three differentiated areas of old and new flagellar membranes are then juxtaposed and connected by a central interstitial core of electron-dense material. The flagella connector is formed early in flagellum extension and is removed at the end of cytokinesis, but the exact timing of the latter event is slightly variable. The flagella connector represents a novel form of cellular junction that is both dynamic and mobile.

Desmosomes exhibit site-specific features in human palm skin

Hereditary skin disorders resulting from desmosome gene pathology may preferentially involve the palms and soles. Why this is so is not clear. Moreover, even in normal control skin it is unknown whether there are differences in desmosome number, size or structural organization in palmoplantar sites compared with skin from other body regions. Therefore, we sought evidence for such differences by examining desmosome expression in relation to epidermal differentiation in both epidermis and cultured keratinocytes from normal human palm and breast skin samples. Confocal microscopy of skin biopsy material showed relative differences in the expression profiles of several desmosomal proteins (desmogleins, desmocollins, desmoplakin, plakoglobin and plakophilin 1) between the two sites. Western blotting revealed a higher expression level of all five proteins in palm compared with breastcultured keratinocytes. Staining for the differentiation-associated component, involucrin, suggested an earlier onset of synthesis of this protein in palm epidermis, and a suspension-induced differentiation assay showed that involucrin synthesis began earlier in palm keratinocytes than in breast cells. At 4-8 h, the number of involucrin-positive cells in palm keratinocytes was almost twice that in breast. Morphometric analysis showed that, overall, desmosomes were larger but of similar population density in the palm compared with breast skin. These findings demonstrate differences in desmosome structure and protein expression between the two sites, possibly reflecting the needs of palms and soles to withstand constant mechanical stress. They may also help to explain the preferential involvement of this region in certain hereditary disorders (palmoplantar keratodermas), associated with mutations in desmoplakin or desmoglein 1.

Demonstration of a tissue factor pathway inhibitor 2 messenger RNA synthesis by pure villous cytotrophoblast cells isolated from term human placentas

Tissue factor pathway inhibitor 2 (TFPI-2), a Kunitz-type proteinase inhibitor, might play an important role during placenta growth by regulating trophoblast invasion and differentiation. Many TFPI-2 transcripts have been detected in syncytiotrophoblast cells, but conflicting results have been reported concerning TFPI-2 synthesis by the cytotrophoblast. To address this issue, we developed a method to isolate pure preparations of human villous cytotrophoblast cells from normal term placentas, and the synthesis of tissue factor, TFPI-1, and TFPI-2 mRNAs was then evaluated. Cells were isolated by trypsin-DNase-EDTA digestion, followed by Percoll gradient separation and immunodepletion of human leukocyte antigen-positive cells. The quality of villous cytotrophoblast cells was verified by electron microscopy. Purity of cell preparations was assessed by labeling cells with GB25, a monoclonal antibody specific to villous trophoblast cells, and by checking the absence of contaminating cells using anti-CD9 antibody. The lack of hCG, CD32 mRNA, and tissue factor mRNA also indicated the absence of contaminating cells. Using competitive reverse transcription polymerase chain reaction, we showed that freshly isolated villous cytotrophoblast cells synthesized significant levels of TFPI-1 mRNA and larger amounts of TFPI-2 mRNA. TFPI-1 and TFPI-2 mRNA synthesis remained unchanged when cytotrophoblast cells were cultured in complete medium and evolved as a multinucleated syncytiotrophoblast. These results indicate that the villous cytotrophoblast and syncytiotrophoblast are both important sites of TFPI-2 synthesis in the human placenta. This study also indicates that tissue factor detection should be used systematically to check the purity of cytotrophoblast cell preparations because it allows detection of contamination by monocytes/macrophages and by syncytial fragments.

A novel mouse desmosomal cadherin family member, desmoglein 1 gamma

The mouse desmogleins are members of the desmosomal cadherin superfamily, and are critical structural components of the desmosome. The genes encoding mouse desmogleins are tightly clustered within 600 kb of chromosome 18, within a desmosomal cadherin gene family also containing the three desmocollin genes. In this study, we have characterized a novel mouse desmoglein gene, highly homologous to both mouse and human Dsg1, designated desmoglein 1 gamma (Dsg1c). Dsg1 gamma shares 83% amino acid identity to the previously described mouse Dsg1, now designated as Dsg1 alpha, and 32% and 40% identity to mouse Dsg2 and 3, respectively. The Dsg1 gamma gene maps within the desmosomal gene cluster, between Dsc1 and Dsg1 alpha. Comparison of its exon-intron structure revealed a high level of evolutionary conservation with related family members. In contrast to Dsg1 alpha and Dsg3 whose expression is largely restricted to the skin, Dsg1 gamma is also expressed in the brain, skeletal muscle, and liver, among other tissues, and is thus more similar to Dsg2 in its tissue distribution. Interestingly, an orthologous Dsg1 gamma was not found in the human genome, suggesting that the desmosomal cadherin gene cluster contracted during mammalian evolution.

Intermediate filament-membrane attachments function synergistically with actin-dependent contacts to regulate intercellular adhesive strength

By tethering intermediate filaments (IFs) to sites of intercellular adhesion, desmosomes facilitate formation of a supercellular scaffold that imparts mechanical strength to a tissue. However, the role IF-membrane attachments play in strengthening adhesion has not been directly examined. To address this question, we generated Tet-On A431 cells inducibly expressing a desmoplakin (DP) mutant lacking the rod and IF-binding domains (DPNTP). DPNTP localized to the plasma membrane and led to dissociation of IFs from the junctional plaque, without altering total or cell surface distribution of adherens junction or desmosomal proteins. However, a specific decrease in the detergent-insoluble pool of desmoglein suggested a reduced association with the IF cytoskeleton. DPNTP-expressing cell aggregates in suspension or substrate-released cell sheets readily dissociated when subjected to mechanical stress whereas controls remained largely intact. Dissociation occurred without lactate dehydrogenase release, suggesting that loss of tissue integrity was due to reduced adhesion rather than increased cytolysis. JD-1 cells from a patient with a DP COOH-terminal truncation were also more weakly adherent compared with normal keratinocytes. When used in combination with DPNTP, latrunculin A, which disassembles actin filaments and disrupts adherens junctions, led to dissociation up to an order of magnitude greater than either treatment alone. These data provide direct in vitro evidence that IF-membrane attachments regulate adhesive strength and suggest furthermore that actin- and IF-based junctions act synergistically to strengthen adhesion.

Expression of sarco/endo-plasmic reticulum Ca2+-ATPase type 2 isoforms (SERCA2) in normal human skin and mucosa, and Darier's disease skin

BACKGROUND

The recent report that mutations in ATP2A2, which encodes the Ca2+ transporting sarco/endo-plasmic reticulum pump type 2 isoforms (SERCA2), cause Darier's disease (DD) suggests that SERCA2 plays an important role in epidermal cell adhesion and differentiation. However, no data exist regarding SERCA2 expression in normal human skin, mucosa and DD.

OBJECTIVES

We have therefore investigated SERCA2 expression in normal human skin (40 samples), oral and vaginal mucosa (13 samples) and DD lesional skin (six samples).

MATERIALS AND METHODS

These investigations were performed with a mouse monoclonal antibody specific for human SERCA2, using a standard ABC immunoperoxidase technique.

RESULTS

SERCA2 was expressed in all specimens. SERCA2 expression was pronounced in the subnuclear aspect of basal epidermal keratinocytes, with variable suprabasal expression. SERCA2 expression was also observed in the infundibulum and outer root sheath of hair follicles; germinative and mature cells of sebaceous glands; secretory coil and duct of eccrine glands; apocrine gland cells, and arrector pili muscle. Fibroblasts and blood vessels (endothelium and muscle) expressed SERCA2, whereas nerves did not. SERCA2 expression was observed throughout oral and vaginal mucosa. In DD skin, strong SERCA2 positivity was detected in the basal, suprabasal and acantholytic lesional cells. Perilesional DD skin was comparable to normal skin.

CONCLUSIONS

These findings support the hypothesis that SERCA2 is an important player in cutaneous biology, and provide baseline data that will facilitate the design and interpretation of functional studies of cutaneous SERCA2.

Effects of Brefeldin A on disassembly of the Golgi body in MDCK cells subjected to a Ca2+ shift at low temperature

When Madin-Darby canine kidney (MDCK) cells were grown in low-Ca2+ medium (LCM) the trans-Golgi cisternae, like those of cells maintained in high-Ca2+ medium (HCM), showed discrete localization of reaction product after thiamine pyrophosphatase (TPPase) staining. After exposure to Brefeldin A (BFA, 5 microg/ml) in LCM at 19 degrees C, the Golgi body dispersed and reaction product was distributed to the nuclear envelope and endoplasmic reticulum. The Golgi body reassembled in cells shifted back to HCM at 37 degrees C, with or without BFA, suggesting that low temperature and LCM exert synergistic effects in aiding dispersal of the Golgi apparatus in the presence of BFA. However, these results appear to be more directly correlated with the lack of defined cell polarity. Cells in LCM are unpolarized and both the centrosomes and the Golgi body are sub-nuclear in position, in contrast to their location in HCM where both organelles lie above the nucleus. The effects of BFA on the disassembly of the Golgi body therefore suggest that MDCK cells grown in LCM at low temperature cells are comparable to those non-polarized cell lines that are sensitive to BFA.

Desmosome assembly in MDCK cells: transport of precursors to the cell surface occurs by two phases of vesicular traffic and involves major changes in centrosome and Golgi location during a Ca(2+) shift

Desmosome formation in MDCK cells was investigated using a Ca(2+) shift. Following preliminary treatment with cycloheximide at 37 degrees C, continued surface transport and subsequent endocytosis were minimized by incubating cells at 19 degrees C to trap nascent glycoproteins within the Golgi body. Release into high Ca(2+) medium (HCM) at 37 degrees C resulted in junction formation as well as relocation of the Golgi body and centrosomes to a subapical location. Desmosome formation occurred in two stages over 2 h, the first occurring within 30 min of the shift to HCM, in 60-nm vesicles containing chiefly Dsc2 and lower concentrations of Dsg and E-cadherin distributed to the entire cell surface. Much of this material was subsequently endocytosed. The second stage involved transport of Dsg, E-cadherin, plakoglobin, and beta-catenin, in more complex vesicles some 200 nm in size, directed to possible nucleation sites on the developing basolateral surface. Plaque proteins such as desmoplakin I/II were added subsequently. Stage-two vesicles, but possibly not those of stage one, were accessible to endocytic markers via retrograde transport from multivesicular bodies prelabeled at 19 degrees C.

Mutation analysis of the ATP2A2 gene in Taiwanese patients with Darier's disease

BACKGROUND

Darier's disease (DD) is an autosomal dominant skin disorder characterized by abnormal keratinization and acantholysis. Pathogenic mutations in the ATP2A2 gene encoding SERCA2, a calcium pump of the sarco/endoplasmic reticulum, have recently been identified.

OBJECTIVES

To identify mutations of the ATP2A2 gene in Taiwanese patients with DD.

METHODS

Mutation analysis of genomic DNA was performed on five families with DD and two sporadic cases. All 21 exons and the flanking intron boundaries were amplified and followed by direct sequencing. Restriction fragment analysis or direct sequencing in each family and in normal controls further verified the mutations.

RESULTS

Mutations in the functional domains of the ATP2A2 gene were identified and verified in all seven pedigrees. They consisted of four mis-sense mutations (R131Q, P680L, G703S, G807R), one altered splice-site mutation (2980 + 5insA) and one frameshift deletion mutation (1457-1458delAG). Of these, R131Q, which was reported twice previously, was detected in two unrelated families. The remaining five were novel mutations.

CONCLUSIONS

Six pathogenic mutations in the ATP2A2 gene were identified in seven Taiwanese DD pedigrees. The results confirmed that most mutations in the ATP2A2 gene are private and of the mis-sense type.

Desmosomes: interconnected calcium-dependent structures of remarkable stability with significant integral membrane protein turnover

Desmosomes are prominent cell adhesion structures that are major stabilizing elements, together with the attached cytoskeletal intermediate filament network, of the cytokeratin type in epithelial tissues. To examine desmosome dynamics in tightly coupled cells and in situations of decreased adhesion, fluorescent desmosomal cadherin desmocollin 2a (Dsc2a) chimeras were stably expressed in human hepatocellular carcinoma-derived PLC cells (clone PDc-13) and in Madin-Darby canine kidney cells (clone MDc-2) for the continuous monitoring of desmosomes in living cells. The hybrid polypeptides integrated specifically and without disturbance into normal-appearing desmosomes that occurred in association with typical cytokeratin filament bundles. Tracking of labeled adhesion sites throughout the cell cycle by time-lapse fluorescence microscopy revealed that they were immobile and that they maintained their structural integrity for long periods of time. Time-space diagrams further showed that desmosomal positioning was tightly controlled, even during pronounced cell shape changes, although the desmosomal arrays extended and contracted, suggesting that they were interconnected by a flexible system with intrinsic elasticity. Double-fluorescence microscopy detecting Dsc2a chimeras together with fluorescent cytokeratin 18 chimeras revealed the association and synchronous movement of labeled desmosomes and fluorescent cytokeratin filaments. Only a minor destabilization of desmosomes was observed during mitosis, demonstrated by increased diffuse plasma membrane fluorescence and the fusion of desmosomes into larger structures. Desmosomes did not disappear completely at any time in any cell, and residual cytokeratin filaments remained in association with adhesion sites throughout cell division. On the other hand, a rapid loss of desmosomes was observed upon calcium depletion, with irreversible uptake of some desmosomal particles. Simultaneously, diffusely distributed desmosomal cadherins were detected in the plasma membrane that retained the competence to nucleate the reformation of desmosomes after the cells were returned to a standard calcium-containing medium. To examine the molecular stability of desmosomes, exchange rates of fluorescent chimeras were determined by fluorescence recovery after photobleaching, thereby identifying considerable Dsc2a turnover with different rates of fluorescence recovery for PDc-13 cells (36±17% recovery after 30 minutes) and MDc-2 cells (60±20% recovery after 30 minutes). Taken together, our observations suggest that desmosomes are pliable structures capable of fine adjustment to functional demands despite their overall structural stability and relative immobility.

Compound heterozygosity for non-sense and mis-sense mutations in desmoplakin underlies skin fragility/woolly hair syndrome

The constitutive desmosomal plaque protein desmoplakin plays a vital part in keratinocyte adhesion in linking the transmembranous desmosomal cadherins to the cytoplasmic keratin filament network. Recently, mutations in desmoplakin have been shown to underlie some cases of the autosomal dominant disorder, striate palmoplantar keratoderma, as well as an autosomal recessive condition characterized by dilated cardiomyopathy, woolly hair, and keratoderma. Here, we describe two unrelated individuals with a new autosomal recessive genodermatosis characterized by focal and diffuse palmoplantar keratoderma, hyperkeratotic plaques on the trunk and limbs, varying degrees of alopecia, but no apparent cardiac anomalies. Mutation screening of desmoplakin demonstrated compound heterozygosity for a non-sense/mis-sense combination of mutations in both cases, C809X/N287K and Q664X/R2366C, respectively. Heterozygous carriers of any of these mutations displayed no phenotypic abnormalities. Immunohistochemistry of skin biopsies from both affected individuals revealed that desmoplakin was not just located at the cell periphery but there was also cytoplasmic staining. In addition, electron microscopy demonstrated acantholysis throughout all layers of the skin, focal detachment of desmosomes into the intercellular spaces, and perinuclear condensation of the suprabasal keratin intermediate filament network. Clinicopathologic and mutational analyses therefore demonstrate that desmoplakin haploinsufficiency can be tolerated in some cases, but that in combination with a mis-sense mutation on the other allele, the consequences are a severe genodermatosis with specific clinical manifestations.

Asymmetrical morphogenesis and medio-lateral positioning of molars during mouse development

The functionality of the dentition depends on occlusal relationships between opposing crown surfaces. To investigate the relative changes in positioning of upper and lower molar germs during mouse development, we used serial histological sections of late day 13 (embryonic day (ED)13.5) to early day 18 (ED18) foetus heads and performed computer-aided 3D reconstructions. From ED13.5 to ED15.5. the first lower molar (M1) got a less medial position relative to its upper counterpart (M1); superimposition progressed postero-anteriorly. From ED14.5, the apparent medial displacement of M(1) vs. M1 was partly due to the asymmetrical growth of the M(1) to give rise to the lingual row of cusps, conspicuous at ED17. The superimposition of M(2)/M2 along the medio-lateral axis was observed from their bud stage (ED14.5), and the one of M(1)/M1 was almost complete at ED15.5. However, this was not the final position. as at ED 18, M1 and M2 had a more lateral location than their upper counterparts. Immunostaining showed that differential expression of antigens associated to desmosomes but not to adherens junctions might be involved in the asymmetrical development of M(1) thus contributing to the relative medio-lateral positioning of the first molars at early stages.

Desmosomes: structure and function in normal and diseased epidermis

Desmosomes are important epidermal adhesion complexes that are characterized by a cell-specific expression of transmembrane cadherins and plaque-associated molecules. Desmosomes have so far, been implicated in three main disease types: autoimmune diseases that involve desmosome components (such as pemphigus vulgaris and pemphigus foliaceus), congenital diseases that affect intracellular calcium channels (such as Hailey-Hailey disease and Darier disease) and congenital diseases that directly affect desmosomal structural components. The identification of the first congenital defect affecting a desmosome component was in the gene for plakophilin I which caused an autosomal recessive skin fragility-ectodermal dysplasia syndrome with skin, hair and nail defects. Subsequently, either a haploinsufficiency of desmoplakin or a defect in desmoglein 1 was found to underlie the autosomal dominant condition Striate Palmoplantar Keratoderma. In addition, plakoglobin has been shown to be defective in Naxos disease, which results in a cardiomyopathy and growth of abnormal hair. These findings pave the way for the discovery of further cell cohesion-related diseases and will help to greatly increase our understanding of the specific function of desmosome and other epithelial junction components.

Characterization of the desmosomal cadherin gene family: genomic organization of two desmoglein genes on human chromosome 18q12

The human desmoglein genes, desmogleins 1--3, are members of the desmosomal cadherin superfamily, and encode critical components of the desmosome. These genes are tightly clustered within 150--200 kb of chromosome 18q12.1 and represent excellent candidate genes for genetic disorders of the epidermis linked to this region of the genome. Mutations in desmoglein 1 have already been implicated in the genetic disorder striate palmoplantar keratoderma. Similarly, a mutation in desmoglein 3 underlies the balding mouse phenotype, although no human mutations in desmoglein 3 have been identified to date. In this study, we have characterized the genomic organization of two of the three desmoglein genes mapped to chromosome 18q12. Comparison of their exon-intron structure reveals the high level of evolutionary conservation expected from these related genes. The identification of the genomic structure of the desmoglein genes will facilitate mutation detection in genodermatoses with desmosomal abnormalities resulting from underlying defects in these genes.

Cadherins and catenins, Wnts and SOXs: embryonic patterning in Xenopus

Wnt signaling plays a critical role in a wide range of developmental and oncogenic processes. Altered gene regulation by the canonical Wnt signaling pathway involves the cytoplasmic stabilization of beta-catenin, a protein critical to the assembly of cadherin-based cell-cell adherence junctions. In addition to binding to cadherins, beta-catenin also interacts with transcription factors of the TCF-subfamily of HMG box proteins and regulates their activity. The Xenopus embryo has proven to be a particularly powerful experimental system in which to study the role of Wnt signaling components in development and differentiation. We review this literature, focusing on the role of Wnt signaling and interacting components in establishing patterns within the early embryo.

Spectrum of dominant mutations in the desmosomal cadherin desmoglein 1, causing the skin disease striate palmoplantar keratoderma

The adhesive proteins of the desmosome type of cell junction consist of two types of cadherin found exclusively in that structure, the desmogleins and desmocollins, coded by two closely linked loci on human chromosome 18q12.1. Recently we have identified a mutation in the DSG1 gene coding for desmoglein 1 as the cause of the autosomal dominant skin disease striate palmoplantar keratoderma (SPPK) in which affected individuals have marked hyperkeratotic bands on the palms and soles. In the present study we present the complete exon-intron structure of the DSG1 gene, which occupies approximately 43 kb, and intron primers sufficient to amplify all the exons. Using these we have analysed the mutational changes in this gene in five further cases of SPPK. All were heterozygotic mutations in the extracellular domain leading to a truncated protein, due either to an addition or deletion of a single base, or a base change resulting in a stop codon. Three mutations were in exon 9 and one in exon 11, both of which code for part of the third and fourth extracellular domains, and one was in exon 2 coding for part of the prosequence of this processed protein. This latter mutation thus results in the mutant allele synthesising only 25 amino acid residues of the prosequence of the protein so that this is effectively a null mutation implying that dominance in the case of this mutation was caused by haploinsufficiency. The most severe consequences of SPPK mutations are in regions of the body where pressure and abrasion are greatest and where desmosome function is most necessary. SPPK therefore provides a very sensitive measure of desmosomal function.

The regulatory region of the human desmocollin 3 promoter forms a DNA four-way junction

Adhesion between desmosomal junctions is mediated by structural proteins of the cadherin family, viz. three desmocollins (DSC) and three desmogleins (DSG). Promoter and primer extension analysis of human DSC3 showed a TATA-less sequence initiating transcription via a cluster of sites upstream of the coding region. Deletion analysis of 1 kb of the promoter showed that expression is regulated between --303 and --203 bp upstream of the start-site of translation. Tertiary structure analysis of this cis-active region (cis 1) revealed a potential DNA 4-way junction which is notably G/C-rich in sequence. PAGE analysis of this region identified four differently migrating forms of the DNA. Structure-specific cleavage of the DNA with bacteriophage T7 endonuclease I showed the slowest migrating form to be either an extended/cruciform or stacked-X 4-way junction. DNA-binding, gel retardation assays of the cis 1 region showed distinct DNA-protein complexes and by competition experiments and using purified junction DNA we show that one of these complexes bound with both sequence and structure specificity to the 4-way junction DNA.

Desmosomes are reduced in the mouse uterine luminal epithelium during the preimplantation period of pregnancy: a mechanism for facilitation of implantation

Dynamic regulation of intercellular junctions is an essential aspect of many developmental, reproductive, and physiological processes. We have shown that expression of the desmosomal protein desmoplakin decreases in the luminal uterine epithelium during the preimplantation period of pregnancy in mice. By the time of implantation (between Days 4.5 and 5 of pregnancy), desmoplakin protein can barely be detected by SDS-PAGE and Western blotting, and by immunocytochemistry, it is restricted to well-spaced, punctate dots at the apicolateral junction. Using confocal XZ series and electron microscope quantitation, both the density and distribution of desmosomes along the lateral cell surfaces of luminal epithelial cells were observed to change during early pregnancy. On Day 1 of pregnancy, desmosomes were found at high density in the apicolateral junctional complex, being present here in 79% of ultrathin sections examined, whereas on Day 5, the density was much reduced (present in only 18% of ultrathin sections examined). Desmosomes were found along the lateral surfaces, at or below the level of the nucleus, in 15% of ultrathin sections examined on Day 1 of pregnancy but in only 1% on Day 5. Desmoplakin mRNA declined during the first 4-5 days of pregnancy, along with the protein, suggesting that these changes are controlled at the level of mRNA. This study shows that desmosomes are regulated during early pregnancy, and we propose that a reduction in desmosome adhesion facilitates penetration of the luminal epithelium by trophoblast cells at implantation.

Autoantibodies to BP180 associated with bullous pemphigoid release interleukin-6 and interleukin-8 from cultured human keratinocytes

Bullous pemphigoid is an inflammatory subepidermal blistering disease that is associated with auto- antibodies to the keratinocyte surface protein, BP180. In addition to the binding of autoantibodies, the infiltration of inflammatory cells is necessary for blister formation. Cytokines, including interleukin-6 and interleukin-8, have been implicated in the disease process of both human and experimental murine bullous pemphigoid. This study was aimed at testing the hypothesis that the binding of anti-BP180 antibodies to their target antigen triggers a signal transduction event that results in the secretion of these pro-inflammatory cytokines. Consistent with this hypothesis, treatment of cultured normal human epidermal keratinocytes with bullous pemphigoid IgG, but not control IgG, led to increased levels of interleukin-6 and interleukin-8, but not interleukin-1alpha, interleukin-1beta, tumor necrosis factor-alpha, interleukin-10, or monocyte chemoattractant protein-1, in the culture medium. This effect was concentration- and time-dependent and was abolished by depleting the bullous pemphigoid IgG of reactivity to two distinct epitopes on the BP180 NC16A domain. Upregulation of interleukin-6 and interleukin-8 was found at both protein and mRNA levels. In addition, bullous pemphigoid IgG did not induce the release of interleukin-6 and interleukin-8 from BP180-deficient keratinocytes obtained from a patient with generalized atrophic benign epidermolysis bullosa. These data indicate that bullous pemphigoid-associated autoantibodies to the human BP180 ectodomain trigger a signal transducing event that leads to expression and secretion of interleukin-6 and interleukin-8 from human keratinocytes.

Genomic organization and amplification of the human desmosomal cadherin genes DSC1 and DSC3, encoding desmocollin types 1 and 3

The desmosomal cadherins comprise the desmocollins and desmogleins and are involved in epithelial cell-cell adhesion. There are three desmocollins (DSC 1-3) and three desmogleins (DSG 1-3) that are expressed in a tissue- and development-specific manner. Desmosomal proteins have been implicated in a number of disorders characterized by loss of cell-cell adhesion and trauma-induced skin fragility. Therefore, the desmocollins are potential candidates for genodermatoses involving epithelial tissues. In order to screen the entire DSC1 and DSC3 genes, we have characterized their intron-exon organization. The DSC1 gene comprises 17 exons spanning approximately 33 kb on 18q12.1, and the DSC3 gene comprises 17 exons spanning approximately 49 kb on 18q12.1. We have also developed a comprehensive PCR-based mutation detection strategy for desmocollins 1, 2, and 3 using primers placed on flanking introns followed by direct sequencing of the PCR products.

Extracellularly truncated desmoglein 1 compromises desmosomes in MDCK cells

The formation and stability of epithelial tissue involves cell adhesion and the connection of the intermediate filaments of contiguous cells, mediated by desmosomes. The cadherin family members Desmocollins (Dsc) and Desmogleins (Dsg) mediate desmosome extracellular adhesion. The main intracellular molecules identified linking Dscs and Dsgs with the intermediate filament network are Plakoglobin (PG), Plakophilins (PPs) and Desmoplakin (DP). Previous studies on desmosome-mediated adhesion have focused on the intracellular domains of Dsc and Dsg because of their capacity to interact with PG, PPs and DP. This study examines the role of the extracellular domain of Dsg1 upon desmosome stability in MDCK cells. Dsg1 was constructed containing an extracellular deletion (Dsg delta 1EC) and was expressed in MDCK cells. A high expressor Dsg delta 1EC/MDCK clone was obtained and analysed for its capacity to form desmosomes in cell monolayers and when growing under mechanical stress in three-dimensional collagen cultures. Phenotypic changes associated with the ectopic expression of Dsg1 delta EC in MDCK cells were: disturbance of the cytokeratin network, a change in the quality and number of desmosomes and impairment of the formation of cysts in suspension cultures. Interestingly, Dsg1 delta EC was not localized in desmosomes, but was still able to maintain its intracytoplasmic interaction with PG, suggesting that the disruptive effects were largely due to PG and/or PP sequestration.

Clustered cadherin genes: a sequence-ready contig for the desmosomal cadherin locus on human chromosome 18

We describe the assembly of a cosmid and PAC contig of approximately 700 kb on human chromosome 18q12 spanning the DSC and DSG genes coding for the desmocollins and desmogleins. These are members of the cadherin superfamily of calcium-dependent cell adhesion proteins present in the desmosome type of cell junction found especially in epithelial cells. They provide the strong cell-cell adhesion generated by this type of cell junction for which expression of both a desmocollin and a desmoglein is required. In the autoimmune skin diseases pemphigus foliaceous and pemphigus vulgaris (PV), where the autoantigens are, respectively, encoded by the DSG1 and DSG3 genes, severe areas of acantholysis (cell separation), potentially life-threatening in the case of PV, are evident. Dominant mutations in the DSG1 gene causing striate palmoplantar keratoderma result in hyperkeratosis of the skin on the parts of the body where pressure and abrasion are greatest, viz., on the palms and soles. These genes are also candidate tumor suppressor genes in squamous cell carcinomas and other epithelial cancers. We have screened two chromosome 18-specific cosmid libraries by hybridization with previously isolated YAC clones and DSC and DSG cDNAs, and a whole genome PAC library, both by hybridization with the YACs and by screening by PCR using cDNA sequences and YAC end sequence. The contigs were extended by further PCR screens using STSs generated by vectorette walking from the ends of the cosmids and PACs, together with sequence from PAC ends. Despite screening of two libraries, the cosmid contig still had four gaps. The PAC contig filled these gaps and in fact covered the whole locus. The positions of 45 STSs covering the whole of this region are presented. The desmocollin and desmoglein genes, which are about 30-35 kb in size, are quite well separated at approximately 20-30 kb apart and are arranged in two clusters, one DSC cluster and one DSG cluster, which are transcribed outward from the interlocus region. The order of the genes is correlated with the spatial order of gene expression in the developing mouse embryo, and this, and previous transgenic experiments, suggests that long-range genetic elements that coordinate expression of these genes may be present. The complete bacterial clone contig described in this paper is thus a resource not only for future sequencing but also for investigations into the control of expression of these clustered genes.