2011 Group 4 Project

From CellBiology

Desmosomes

Introduction

Cell junctions occur at points of contact between cells and between cells and the matrix. These junctions are important in the integrity of tissues, cell communication and transport. Cell junctions can be grouped into three main classifications:

  • Occluding junctions that hold epithelial cells together to prevent the leaking of small molecules from one side to the other.
  • Anchoring junctions attach cells to adjacent cells as well as the extracellular matrix.
  • Communicating junctions allow for the transmission of chemical and electrical signals between cells [1]

Desmosomes are classified as anchoring junctions, reasons for which will be explained below.

Structure of a desmosome

Desmosome originates from the greek terms desmo meaning bond and soma meaning body. [2] This etymology reveals the main function of desmosomes which is to bind cells to one another. [3] Desmosomes, also known as macula adhaerens, have a number of other roles including strengthening the internal structure of a cell, sensing environmental cues, regulating tissue homeostasis and assisting in tissue morphogenesis. By indirectly connecting intermediate filaments of adjoining cells, they produce a strong adhesive force which can resist great shear forces. Hence, they are found in such tissues as the myocardium, the bladder, the gastrointestinal mucosa and many epithelia. [4]


This webpage will look into a number of areas to help in the understanding of what desmosomes are, how they work, and what can go wrong when these desmosomes don't work properly. These areas include:

History

Early 19th Century : Light microscopes allowed for the detection of desmosomes within cells.

1864 : Giulio Bizzozero gives the first description of the desmosome. He commented on the small, dense areas that were seen between cells and suggested that these were points of adhesion between adjacent cells. [5]

Guilio Bizzozero

1920 : Josef Schaffer names the structure being seen under the microscope, 'desmosome.' From a greek origin, the name comes from two words meaning 'bond' and 'body.' [6]

1956 : After biological sciences were revived after the world wars, Porter viewed cells using electron microscopy to note that between adjacent cells there were electron dense areas that branched off into cells with fibrous strands. [7] [8]

1974 : By developing new techniques, Skerrow and Matoltsky isolated desmosomes from other cellular components. [9] After running biochemical tests to identify their molecular characteristics, the pair found that the structures had a high glycoprotein content, and that it was these glycoproteins that were responsible for the cell-cell interactions. In doing this, they were able to confirm the hypothesis from 30 years earlier, that desmosomes were in fact junctions between cells. [10]

1981 : Franke and Steinberg characterized and purified the components of desmosomes. [11]

1983 : Using specific antibodies, Cowin and Garrod identify the localisation of desmosomes and note that desmosome distribution is similar between all vertebrates. [12] [13]

1985 : Steinberg, along with his colleagues, begin to isolate plaque proteins. [14]

1988 : Green isolated and analyzed the desmoplakin coding sequence. [15]

1990 : Blaschuk identifies that cadherins contain a tripeptide motif that is crucial in cell adhesion. [16]

1990 Green analyses the amino acid sequence of desmoplakin protein. It was predicted that desmoplakin would have a central alpha-helical, coiled-coil region. [17]

1990 : Koch isolated and characterised the cDNA encoding desmoglein. When screened with cDNA libraries, it was found that they had a high level of homology with cadherins, and as such identified it as a part of the cadherin superfamily. [18]

1991 : Desmocollin, another transmembrane protein in desmosome is isolated and characterised by Collins. Desmocollin has an a form and b form within the cytoplasm, which are produced by alternative splicing of mRNA. [19]

1991 : Amagai explained the pathogenesis of S. aureus bullous impetigo which is caused by toxin-mediated damage to desmosomes. This was achieved by using antibody immunotherapy. [20] [21]

1992 : Stappenbeck and Green define the functional domains of desmoplakin. [22]

1994 : Kouklis demonstrates that the interactions between desmoplakins and intermediate filaments are direct. [23]

1997 : McGrath describes that mutations in Plakophilin-1 leads to ectodermal dysplasia. [24]

1998 : Desmosomal cadherin attachments can be inhibited by peptides that correspond to desmocollin and desmoglein receptor sites (Tselepis). [25]

1999 : Structural studies of the demoplakin gene confirm that the carboxyl terminus acts as an intermediate filament binding site (Kowalczyk). [26]

2001 : Vasioukhin saw that epithelial cells rely on desmoplakin for integrity. [27] [28]

2002 : Windoffer suggests that desmosome structure is dynamic, using fluorescence recovery. [29] [30]

Dynamic Structure of Desmosomes - Video

2003 : Kljuic identifies the genes for desmogleins and desmocollins on the q arm of chromosome 18 in humans. [31] [32]

3D structure of a desmosome.jpg

2003 : He generates a three-dimensional image of a desmosome. [33][34]

2004 : Grossman confirmed the necessity for plakophilin in desmosomal plaques. [35] [36]

2005 : Kimura discovers that desmosomes can be switched from an adhesive and hyper-adhesive state by activation and suppression of Protein Kinase C [37]

2007 : Chidgey and Dawson investigate the role of desmosomes in cancers transforming from tumours to invasive malignancies [38]

2007 : Schmidt suggests that abnormalities that occur within the body may be influenced by changes in signalling properties of desmosomes. [39]

2011 : Al-AMoudi and others show the 3-dimensional structure of a demosomal plaque. [40]

Structure

Structure on a Cellular Level

Structure of a Desmosome and Desmosomal Plaque
Desmosome Electron Micrograph: Bovine Nasal Epidermis

The desmosome, ~300nm in diameter, consists of two distinct domains - the extracellular core domain, ~30-35nm in diameter, and the dense cytoplasmic plaque, ~30-40nm in diameter. [41]

The extracellular core domain, also known as the desmoglea, is made up of the transmembrane proteins - cadherins. [1] There are two types of desmosomal cadherins: desmogleins (DSGs) and desmocollins (DSCs). They extend from the plaque to the extracellular core where they connect to the adjacent cell's cadherins.

The disc shaped plaque, situated parallel to the inner leaflet of the cell membrane, is composed of an outer dense plaque and an inner dense plaque separated by a space of ~8nm. [41] The outer dense plaque is located closer to the plasma membrane than the inner dense plaque and links cadherin tails to desmosomal anchor proteins. [41]

The linker proteins involved are plakoglobin (PG), plakophilin (PKP) and desmoplakin (DP). Extending out from the outer dense plaque are the desmosomal anchor proteins desmoplakins. These form the majority of the inner dense plaque. On the other side of the inner dense plaque is where the intermediate filament network of the cytoskeleton attaches. [42]

Structure on a Molecular Level

Desmosome Diagram

Extracellular Domain

As outlined above, the extracellular domain consists of desmosomal cadherins: desmogleins (DSGs) and desmocollins (DSCs). Cadherins are arranged along the mid-line in ~7nm intervals, with alternating cis (interaction between same cell surface) and trans (interaction between different cell surfaces) dimers causing a tightly packed zipper formation. They are each made up of four extracellular immunoglobulin domains (EC1-4), an immunoglobin extracellular anchor (EA), a transmembrane domain (TM), an intracellular anchor (IA) and additional cytoplasmic domains, which distinguish the cadherin isoforms. [41] Each immunoglobin domain is connected end to end by three calcium ions, forming a curved structure of about 100 degrees. Along the domains are disulfide bonds, O-linked sugars and N-linked sugars. [43]


The cadherin isoforms are composed of different additional cytoplasmic domains as follows [41]:

Desmosomal Cadherins Diagram
Detailed Cadherin Diagram - Image (g) Shows Cis And Trans Interactions


Cytoplasmic Domains
Cadherin Isoform IA ICS IPL RUD DTD
DSCa Present Present - - -
DSCb Present - - - -
DSG1 Present Present Present 5 subunits Present
DSG2 Present Present Present 6 subunits Present
DSG3 Present Present Present 2 subunits Present
DSG4 Present Present Present 3 subunits Present

Note:

There are three isoforms of DSC (1-3), however they splice alternatively into two transcript variants named DSCa and DSCb.

ICS is an intracellular cadherin-like sequence, which binds to plakoglobin.

IPL is an intracellular proline-rich linker.

RUD is repeat unit domains.

DTD is a desmoglein terminal domain


Modulation

Tyrosinase-related protein 2 (Trp2) mediates the cis and trans interactions and is most likely responsible for the binding of cadherins to the plaque. [43] However it is currently unknown whether heterophilic cis and trans or homophobic cis and trans interactions are the main cause of cell adhesion. [44]

The extracellular domain mediates adhesion and whilst the mechanical structure is extremely strong, it is still dynamic since the attachment of both types of cadherins are reliant on Ca2+ levels. During embryonic development of the desmosome, the link between the two cells remains weak. Eventually the link strengths and the cell becomes hyperadhesive. This latter stage is calcium independent, as once protein kinase C is activated by Ca2+ it is able to remain activated in the long-term. Hence this hyperadhesive state will not be affected by changes in Ca2+ concentration. However, the desmosome is able to revert to the earlier state when responding to certain environmental signals to allow for such things as cell migration if regeneration of the epithelia is necessary. [43] [1] The primary morphological attribute which indicates calcium independence is a distinct electron-dense midline that bisects adjoining cell's extracellular core domains. [45] Whereas when desmosomes are calcium dependent the midline is lost and the diameter of the intercellular space decreases by 10%. Potentially this is caused by Ca2+ ions becoming trapped to the cadherins and securing their position into an ordered structure. [45]


Outer Dense Plaque

The dense plaque is made up of two electron-dense zones: an outer dense plaque and an inner dense plaque. The outer dense plaque being lower in density that the inner dense plaque. They are separated by an electron-lucent zone, ~8nm in diameter. The outer dense plaque is located in the cytoplasm, parallel to the plasma membrane. [45] It is ~15-20nm in diameter and characterised by two zones: a ~4nm zone located ~10nm from the plasma membrane and a ~8nm zone located ~20nm from the plasma membrane. The major plaque proteins are plakoglobin (PG), plakophilin (PKP) and desmoplakin (DP).21464301(Please note permission was sought and granted for citing of PNAS Article: The three-dimensional molecular structure of the desmosomal plaque)

Plakoglobin and plakophilin, from the armadillo family of proteins, help to mediate: the attachment of desmoplakin to the intermediate filaments, the arrangement of the plaque components and the signalling in some transduction pathways.


The structure of the major plaque proteins is as follows [41]:

Plakoglobin And Plakophilin Diagram
Desmoplakin Diagram
Major Plaque Proteins
Plaque Proteins Head Arm Repeats Insert Arm Repeats Rod Tail GSR
PG Present 12 - - - Present -
PKPa Present 5 Present 4 - Present -
PKPb Present 5 Present 4 - Present -
DP1 Present - - - Present Present (C-tail) Present
DP2 Present - - - Present Present (C-tail) Present

Note:

Head is an amino-globular head domain with a N terminus.

Tail is a caboxy-terminal tail with a C terminus. In desmoplakin, the tail constits of three plakin repeat domains.

GSR is a glycerine-serine-arginine rich domain.

Insert is a rigid structure producing the bent angle.

The two isoforms of plakophilin, PKP1 and PKP2, both splice into PKPa and PKPb. PKPa is shorter in length than PKPb. For PKPb in comparison to PKPa: in arm repeat three PKP1 version has an additional 21 amino acids, and in arm repeat four PKP2 version has an additional 44 amino acids.

The isoforms of desmoplakin, DP1 and DP2, are characterised by the length of their rod domain - the DP1 rod being ~2/3 longer than the DP2 rod.


Plakoglobin and desmoplakin complexes form an alternating arrangement which acts as a base for the desmosomal cadherins to attach. The cadherin tails bind to the N terminus of desmoplakin before they connecting to the adjoining cell's desmosomal cadherins. Formation of this initial structure is mediated by plakoglobin and plakophilin. For reinforcement the remaining space between the plaque and the plasma membrane is filled by plakophilins. 21464301

Inner Dense Plaque

The inner dense plaque, alike the outer dense plaque, is ~15-20nm in diameter. It is primarily comprised of the junctional complexes, desmoplakins, which tether to the intermediate filaments.[45] The molecular structure of desmoplakin is outlined in the above 'Outer Dense Plaque' section, as the protein spans through both parts of plaque. The leading theory is that the glycine-serine-arginine domain, adjacent to the carboxy-tail terminus of desmoplakin, regulates the attachment of the keratin intermediate filaments. The molecular structure of the plaque with its components having both medial and lateral connections, is thought to be one of the main reasons for the desmosome's adhesive strength.21464301

Function

The desmosome as a cellular adhesion junction

  • Establishes confluence or a continuous sheet of bonded cells
  • Stabilises cellular positioning
  • Strenghthens epithelium
  • Desmosome component proteins function in cellular regulatory pathways


Desmosomes are important components of many epithelia, occuring with greater or lesser prevalence in them. In a normal state, desmosomes establish continuity or confluence of epithelial sheets. [46] Desmosomes contribute to the barrier function of epithelia, a function that is largely brought about by the Zonula Adherens. [47] Desmosomes are normally permanent and prevent leaking of small molecules through the surface as well as resisting shearing forces. [48] Shearing forces encountered, for example particularly in the stratified, squamous, keratinised epithelium of the palmar or plantar epidermis as well as in muscular layers of the heart (myocardium).

Confocal microscopy of keratin intermediate filaments inside cultured embryonal carcinoma cells


  • Multiple desmosome adhesion complexes located on the plasma membrane bond cells to each other and in this way a confluent epithelial sheet is formed.

Importantly, once cells are bonded to each other their position in the sheet of epithelium becomes stabilised.

  • A sound epithelial structure is thus created.

There are many aspects of the structure of demosomes that are still not completely understood.

However, it is known that cytoplasmic surface molecular interactions, link a) extracellular transmembrane cadherins (desmoglein and desmocolin) with, b) intermediate keratin filaments located inside cells as part of the their cytostructure.[49] An attachment plaque is the go-between or bondage site that mediates the adhesion of the keratin filaments with the cadherin proteins that insert their tails into the plasma membrane. [50]


Electron microscopy (EM) and specialised staining techinques makes it possible to view these structures. It has become possible to hypothesise how desmoglein and desmocollin bond in a zipper-like fashion at the midline between the cells. Then as stated, the tails of these calcium mediated and dependent cadherins bind through the plasma membrane into the cytoplasm of the adjacent cells, forming a connection with the plaque located therein thus anchoring two cells together.[51]

Desmoplakin, plakoglobin and plakophilin are the proteins that form this dense plaque (each cell in question has one and one for every desmosome complex formed) that functions as the bondage site for the intermediate keratin filaments and the cadherins. [52]

The desmosome has linked the cytostructure of two separate individual cells together as one.

By having numerous desmosomes the cells in effect are riveted together in many ways like two bean bags side by side. Numerous desmosomes, above and below an imaginary midline plane running laterally through the epithelial sheet, means forces such as encountered in a mild sliding abrasion can be effectively countered.

  • In this way different physical stresses slightly above and below and along a lateral plane encountered by the organic material as whole can be withstood. Such stresses such as chafing of the epidermis, or the continuous muscular beating of rounded heart myocardium.

Desmosome protein composition can differ in the presence of the isoforms of core and other accessory proteins, and to their relative amount present. [53]

  • It is in this way that desmosomes can influence the specific way cells bind to the cytoskeleton of another, thus influencing tissue supracellular architecture.[54] [55]

[56] [57]

For instance meningothelia of the meninges differs from myocardium in terms of desmosome protein composition and amount contained. Desmosome adhesive qualities in these contrasted tissues differs significantly, in that one is much more robust than the other, enabling differing functions in the body. [58]


Changes in adhesive state influence function of epithelia

Epidermis epithelial cell wound healing involves changes in desmosome function



The adhesive state of the desmosome can change in accordance with the state of the epithelia in which they are found[59]


During embryogenisis, epithelial differentiation and wound healing the adhesives qualties of the proteins were found to change.[60] The desmosome allowed cellular movement. For example in wound healing the dissolving of desmosomes allowed keratinocytes to migrate into areas of epithelial injury. [61]

Hemidesmosomes

Diagram of Hemidesmosome

Hemidesmosomes like the name suggests are extremely similar to the desmosomes in the fact that they are specialized junctional complexes. However unlike desmosomes which specialises in cell to cell adhesion hemidesosomes contribute to the attachment of epithelial cells to the underlying basement membrane in stratified and other complex epithelia, such as the skin, the cornea and both parts of the respiratory and gastrointestinal tract.[62] Hemidesomosomes are multiprotein complexes and it is these proteins that help determine the cell – stromal coherence of the hemidesomoses. The proteins also provide the cells with cues critical for the polarization, the spatial organization and for tissue architecture. The functional activity can be modulated however the regulation of the adhesive interaction between the hemidesmosomes and the basement membrane below is essential in various normal biologic processes, such as wound healing and tissue morphogenesis.[63] The importance of these complexes is attested by the fact that an altered expression of hemidesmosomal constituents results in several types of blistering disorder of the skin and is thus likely to be involved in the development and progression of certain cancers. The function of hemidesmosomes may be regulated via many different factors for example extracellular matrix (ECM) proteins and growth factors. To add to this the α6β4 integrins in the hemidesmososme also act as regulatory components and this done by transducing signals that profoundly affect the cellular function. Thus hemidesmosomes are not only structural adhesion complexes but also serve as signalling devices via the α6β4 integrin which affecting cell phenotype.[64][65]


Morphology and Molecular Organisation of Hemidesmosomes

Ultrastructure of tracheal hemidesmosomes.


Hemidesmosomes in electron microscopic images appear as small electron dense domains approximately 0.5 m in size located on the plasma membrane of the ventral surface of basal keratinocytes in human skin. The most noticeable feature on the hemidesmosome is the tripartite cytoplasmic plaque, to which the bundles of intermediate filaments are attached. Hemidesmosomes are actually associated with sub-basal dense plates in the lamina lucida and are connecter via what looks like a fine thread-like anchoring filament to the lamina densa. The laminar densa is then anchored to the papillary dermis which underlies the laminar densa by cross banded anchoring fibrils. The morphological structures listed above which include the Intermediate Filaments, Hemidesomal Plaques, Anchoring Filaments and Anchoring Fibrils constitute the so called Hemidesmosmal adhesion complex which stably adheres the keratinocytes to the underlying epidermal basement membrane.[66]

The so called molecular organisation of Hemidesmosomes is actually based on three main classes of protein and these include the cytoplasmic plaque protein which acts as the linker for elements of the cytoskeleton at the cytoplasmic surface of the plasma membrane, the transmembrane proteins which serve as cell receptors connecting the cell interior to the to the Extracellular matrix and last but not least the basement membrane – associated proteins of the extra cellular membrane.[67]



Similarities and Differences Between Desmosomes and Hemidesmosomes

Desmosomes Hemidesmosomes
Similarities
  • Both are composed of a tripartite electron-dense plaques structure which is specialised for Intermediate Filament anchorage.
  • Both Found in Epithelia where they associate with keratin containing intermediate filaments.
  • Both are composed of a tripartite electron-dense plaques structure which is specialised for Intermediate Filament anchorage.
  • Both Found in Epithelia where they associate with keratin containing intermediate filaments.
Differences
  • Mirror image plaques sandwich a membrane core region
  • Extracellularly, they are separated by a 30 nm space filled with material that represents in large part the extracellular domains of the single span transmembrane desmosomal cadherin molecules.
  • Are thought to exhibit a more widespread tissue distribution
  • A single plaque located at the basement membrane serves this function in the hemidesmosome
  • Attached through an integrin-based mechanism to the underlying basement membrane and stroma
  • Less widespread tissue distribution
[68]

Regulation

Calcium

Calcium ion levels are integral in junction assembly. In vitro, extracellular calcium levels have been found to trigger the formation of the junctions. [69] After cells that have been incubated in low calcium medium, were switched into a medium containing standard calcium concentrations, the formation of desmosomes was seen as soon as 5 minutes. [70] The deregulation of calcium levels within cells have been associated with junctional defects. Hailey-Hailey disease and Darier's disease are caused by defects in Golgi and ER calcium pumps. [71] These both lead to a loss of integrity in skin epithelium, due to a lack of cell-cell attachment via desmosomes. [72] [73]

Calcium regulation


Desmoplakin

Desmoplakin

It has been suggested that regulation of desmosome assembly is closely associated with the assembly of adherens junctions. [74] Desmoplakin is the only protein, so far identified, that is common to both junctions. In vitro, cells that did not express desmoplakin were unable to localise the proteins specific for the adherens junctions and the desmosomes. [75] Thus, it has been suggested that it plays a role in segregating the proteins relative to each junction and so affecting assembly.


Phosphorylation

Phosphorylation has been found to be largely involved in activating and deactivating desmosome assembly. It has been suggested that protein kinase C (PKC) is involved in the regulation of this action. [76] PKC inhibition is required for desmosome assembly to occur, that is, dephosphorylation encourages formation. Phosphorylation onto serine of desmoplakin by protein kinase C can lead to the disassembly of the cytoskeleton, junctions, and a loss of cell-cell contact. An increase in level of serine phosphorylation has also been linked with an increase in junction solubility of the desmoplakin. This suggests that phosphorylation may play an integral role in the dissociation of the desmosomal plaque from the keratin filaments. [77] The outcome of plakoglobin (an important desmosomal protein) is also largely dependent on its phosphorylation. [78]

Desmosomes and Disease

Investigations into function through knock out gene models

Changes in desmosomes in transgenic mice

Knock out gene animal model investigations into the absence of desmosome protein isoforms in various epithelia have shown how they may be involved in associated disease states of the epithelia in which they are located, thus giving a window into their non pathological function. It has been suggested that the distribution of one or other desmosome protein isoforms in various epithelia is due to the degree of adhesion necessary according to any stresses encountered at that location. [79]

Studies into the function of these protein isoforms has also suggested they may act as influencing the function of the associated epithelia itself outside of the mere adhesive function.

An example of this is desmoplakin 1 which is found in all desmosomes including the endothelial cells of of capillaries. [80]

During tumourous cancer growth, in such cancers as oropharyngeal and breast cancer, desmoplakin type 1 function becomes down regulated and aids tumour growth by stimulating angiogenesis or the growth of new blood vessels from existing vascular structures [81]

This down regulation means that now the desmosomes may function in tumour cell proliferation.

It is the abnormal over or under functioning of desmosome proteins that highlights its specialised adhesion function.

Related Diseases

Disease Description Image
Bullous Impetigo Impetigo is a skin condition common in school children, especially those who play close contact sports. This skin condition is also known as school sores and is caused by a bacterial infection. Bullous Impetigo causes fluid-filled blisters in the skin, primarily on the trunk, arms and legs. These blisters are painless and scab over before they heal. [82]

Staphylococcous aureas is the bacteria responsible for inducing bullous impetigo through its release of exfoliative toxins. When mice are injected with exfoliative toxin from S. aureas blistering of the skin is noticed and under an electron microscope it is possible to see that the desmosomes within the epithelia have been torn apart. [83] Exfoliative toxin A has been proven to cause the blistering through its serine protease activity. The blisters of Bullous Impetigo are localised to the superficial epidermis, and as such it is possible to confirm that the exfoliative toxin A is specific to Desmoglein-1. Desmoglein -1 is present not only in the superficial layers of epithelium but also in the deeper layers. Desmoglein-3 however is not present in the superficial layer. Given that blistering does not occur in the deeper layers it is possible to assume that Desmoglein-3 compensates for the destruction of Desmoglein-1. Experimental results have shown that on injection of exfoliative toxin A, Desmoglein-1 was damaged while Desmoglein-3 remained unaltered. This was done by addition of antibodies for Desmoglein-1 and Desmoglein-3 followed by immunoflurorescence. [84]

Bullous Impetigo has similar symptoms to many drug reaction symptoms. The differentiation between these is possible through a skin biopsy. Bullous impetigo will only have blistering on the superficial layers while a drug reaction will see blistering in the lower layers of the epithelium as well as necrotic keratinocytes. Treatment usually consists of a course of antibiotics but it is important to consider that antibiotic-resistant strains of S.aureas are quite common. [85]

Bullous Impetigo

Pathophysiology of Bullous Diseases - video

Palmoplantar Keratoderma Desmoplakin is the most abundant protein in desmosomal plaques, therefore having an important role in linking the intermediate filaments to the plasma membrane of cells in the epidermis and heart. Palmoplantar Keratoderma is skin condition that results from a mutation on the gene that encodes desmoplankin. Mutations can either lead to a loss of the gene completely, or cause haploinsufficiency. This genetic disorder was noted in patients who were affected by this skin condition. [86]

Palmoplantar Keratoderma is a rare condition. It is characterised by hyperkeratosison the palms of the hands and soles of the feet. This leads to a distinctive thickening of the skin, often in a striated pattern. When viewed under a light microscope, affected areas showed an increase in space between the keratinocytes. Moreover, the desmosomes appeared to be smaller and less were found when compared to a normal section of skin from the same patient. [87]

Keratoderma
Arrhythmogenic Right Ventricular Cardiomyopathy Arrhythmogenic Right Ventricular Cardiomyopathy is a cardiomyopathy is related to the functioning of desmosomes. When cell adhesions are compromised, the cardiac tissue loses its integrity. As a result of this, the body attempts to repair the damage by replacing the tissue with fibrofatty tissues. This presents a number of problems for the cardiovascular system and results in some fatal complications. [88] This condition is more common in individuals under the age of 30. Clinical symptoms present with misarrhythmias or in some cases, sudden death. Most prominent symptoms are seen during or after intense physical activity when the heart is put under stress.
Arrythmogenic Right Ventricular Cardiomyopathy

Current Associated Research

Human Epidermal Desmosome-Enriched Tissue Fractions for Analytical and Prospective Studies (2011)

This report written by Sandjeu et al. describes a method that has now been adapted to the human epidermis which allows for the isolation of desmosomes in small tissue fractions as the previous methods which were developed for animal epidermis did not work as efficiently on human tissue. In the process, the desmosomes are initially enriched by the association of a two incubation step in acidic solution which consisted of the detergent NP-40 at 2 different concentrations. This was then followed by sonication. The suspension was then centrifuged twice: the first time was to remove heavy cell fragments. It was the centrifuged again at 16000g on a discontinuous sucrose gradient. A desmosome enriched fraction was then collected at approximate 30-50% sucrose gradient levels. Both immunoelectron microscopy and western blotting technique was then used on the desmosome enriched fraction to show that the central part of the desmosomes are preserved as well as retaining their antigenicity. This method can be used to both immunise animals as well as creating new antibodies that are directed toward the desmosomal components. The hope of this study is that it allows for new studies to be done on a not well understood topic: The incorporation of molecules into the desmosome core which could as a result be targeted more easily.[89]


Lack Of Plakoglobin Leads To Lethal Congenital Epidermolysis Bullosa: A Novel Clinico-Genetic Entity (2011)

Epidermolisis Bullosa

As stated above epidermal integrity is essential for skin functions. This integrity is actually maintained by adhesive structures between keratinocytes, mainly the desmosomes and adherens junctions. These adhesive structures provide resistance against mechanical stress and regulate the formation of the skin barrier. Plakoglobin is one of the constituents in both types of intracellular junctions and thus has a numerous number of interaction partners. Studies into genetic mutations associated with plakoglobin has associated this with mild cutaneous disease, keratoderma and arrthythmogenic heart disease for example.

In this article, Pigros et al. report a so called novel lethal phenotype cause by a nonsense mutation in the gene that codes for plakoglobin [Junction Plakoglobin (JUP)] however this mutation and its effects have never been described before in either human or murine. The patient in this article suffered from a severe congenital skin fragility, with generalised epidermolysis and substantial transcutaneous fluid loss. Yet the patient did not ever present to health care professionals with cardiac dysfunction. It was noticed when immunofluroescence and immunoblot analysis was done that unlike JUP mutations before where truncated plakoglobin was present, here there was a complete loss of plakoglobin in the skin. Thus only a few abnormal desmosomes were formed and no adhesion structures between keratinocytes were recognisable. The role of distribution of desmosomal components was extremely affected which suggest that plakoglobin plays an essential role for plakoglobin in demosomal assembly. This current research reinforces the fundamental role of plakoglobin in epidermal cohesion. [90]


Wide Spectrum of Desmosomal Mutations in Danish Patients with Arrhythmogenic Right Ventricular Cardiomyopathy (2010)

Heart with Cardiomyopathy

In the study performed by Christensen et al. , 65 unrelated patients with Arrhythmogenic right ventricular cardiomyopathy (ARVC), a lethal disease which is characterised by Ventricular tachyarrhythmias with right and/or left ventricular involvement and fibro fatty infiltrations in the myocardium were screened for mutations in the number of genes that code for desmosomes which include desmocollin-2 (DSC2), desmoglein-2 (DSG2), desmoplakin (DSP), plakoglobin (JUP) and plakophilin-2 (PKP2) and TGFb3. The results of the study were the identification of 19 different mutations with all genes that code for desmosomes being affected apart from TGFb3 which showed no genomic rearrangements or mutations. The conclusion of the study was that 33% of patients in this Danish cohort with ARVC carried desmosomal mutations with a surprisingly wide mutation spectrum. A substantial proportion of patients carried more than one mutation. The results achieved in this study supports comprehensive desmosomal mutation screening beyond the first encountered mutation, whereas routine screening for genomic rearrangements does not seem indicated.[91]

3D molecular structure of the desmosomal plaque


Desmosomes: new perpetrators in tumour suppression (2011)

Adherens Junctions, which are intercellular adhesive complexes that are crucial for maintaining epithelial homeostasis, are down regulated in many cancers to promote tumour progression. However the role of desmosomes - adhesion complexes that are related to adherens junctions – in carcinogenesis has remained elusive. This study conducted by Dusek et al. has using a mouse genetic approach uncovered a role for desmosomes in tumour suppression which demonstrates that the down regulation of desmosomes occur before adherens junctions drive tumour development and early invasion. Thus also suggesting that there is a two – step model of adhesion dysfunction in cancer progression. [92]


The three-dimensional molecular structure of the desmosomal plaque (2011)

Until now, the exact structure of desmosomal plaques has remained a mystery. Although the proteins involved in the structure have previously been identified, the architechture was unknown. Al-Amoudi et al, used cyroelectron tomography of epithelial desmosomes to acheive this goal. The main advantage of this technique, was that no heavy metal staining was used, and so a higher resolution image could be produced. However, due to the cutting of cyrosections to observe the structure, artifacts such as knife marks, were prominent. These artifacts and challenges were eventually overcome, and 3D imaging was used to produce a detailed image, never seen before. [93]




Glossary

A

Alpha Helix a secondary structural motif of proteins. The amino acids are arranged in a right-handed helix. The backbone it made up of N-H, contributing hydrogen bonds to strengthen the structure.

Anchoring Junctions a type of cell junction that attache cells to adjacent cells as well as to the extracellular matrix.

Antibody a protein produced by B cells that are used to identify and neutralize foreign material in the body

C

Cadherin a group of proteins that cross the membrane. They are heavily involved in cell adhesions. As the name suggests, they are dependant on calcium for their regulation

Carboxy Terminus the end of an amino acid chain with a free carboxyl group.

cDNA also known as complementary DNA. It is produced from mature mRNA by reverse transcriptase and DNA polymerase.

Communicating Junctions allow for the transmission of chemical and electrical signals between cells.

D

Desmocollin a cadherin specific for desmosomes. Refers to the human genes DSC1, DC2 and DSC3

Desmoglein a member of the cadherin family. They are involved in the formation of desmosomes and expressed by genes DSG1, DSG2, DSG3 and DSG4

Desmoplakin a protein associated with desmosomes, anchoring the intermediate filaments to the desmosomal plaques.

Desmosomes are a type of cell junction that indirectly connect the intermediate filaments of adjoining cells. Their main function is to bind cells to one another.

Dysplasia ’’Dysplasia’’’ refers to abnormal development. It is usually associated with a neoplastic process

E

Electron Microscopy the use of an electron microscope. An electron microscope uses a beam of electrons to illuminate a specimen.

Epithelium a basic type of tissue that lines the cavities of the body as well as glands.

F

Fluorescence Recovery a useful mechanism to investigate the motion and diffusion of macromolecules. A specimen is exposed to an intense burst of laser light and then the recovery of the area is observed.

G

Glycoprotein a protein that has a carbohydrate attached to it

H

Hemidesmosomes are a type of cell junction that attaches epithelial cells to the underlying basement membrane in stratified and other complex epithelia.

Homology describes how different animals have the same organs but may vary in form and function

Hyper-adhesion very strong adhesion adopted by desmosomes

I

Immunotherapy treating a disease by influencing the immune response. This may be by inducing, enhancing or supressing the response

Intermediate Filaments a family of proteins that make up part of the cytoskeleton. They are around 10nm in diameter and found in the cytoskeleton and nucleus.

M

Malignancy describes how some diseases are likely to lead to death, often by invasion and metastasis.

mRNA Splicing a modification of mRNA after transcription that results in the removal of introns and the connection of adjacent exons.

O

Occluding Junctions hold epithelial cells together to prevent the leaking of small molecules from one side to the other.

P

Pathogenesis The chain of events involved in a disease from origin to death/recovery

Plakophilin proteins of the cytoskeleton. Expressed on genes PKP1 and PKP2

T

Transmembrane Proteins are proteins that cross the cellular membrane. In desmosomes the transmembrane proteins are the cadherins, desmoglein and desmocollin, and make up the extracellular core domain.

Tripeptide is a peptide. It consists of three amino acids attached by peptide bonds.

Images and Videos

[http://www.pnas.org/content/early/2011/03/30/1019469108.full.pdf The three-dimensional molecular structure of the desmosomal plaque]

Reference List

  1. 1.0 1.1 1.2 [1]| Cell Junctions- Molecular Biology of the cell
  2. 20672011</pubmed>
  3. Molecular Biology of the Cell Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002|Gethin R Owen, David L Stokes Exploring the Nature of Desmosomal Cadherin Associations in 3D. Dermatol Res Pract: 2010, 2010(1);930401
  4. Emmanuella Delva, Dana K Tucker, Andrew P Kowalczyk The desmosome. Cold Spring Harb Perspect Biol: 2009, 1(2);a002543 PubMed 20066089
  5. [2]|Culkins CC, Setzer S (2007) Spotting Desmosomes: The First 100 Years. Journal of Investigative Dermatology Jan 30;127(E1):E2-E3.
  6. [3]|Culkins CC, Setzer S (2007) Spotting Desmosomes: The First 100 Years. Journal of Investigative Dermatology Jan 30;127(E1):E2-E3.
  7. Porter KR (1956) Observations on the fine structure of animal epidermis. Proceedings of the International Congress on Electron Microscopy, London, July 1954. Royal Microscopical Society, London, p 539
  8. [4]|Culkins CC, Setzer S (2007) Spotting Desmosomes: The First 100 Years. Journal of Investigative Dermatology Jan 30;127(E1):E2-E3.
  9. [5]|Skerrow CJ, Matoltsy AG. (1974) Chemical characterization of isolated epidermal desmosomes. Journal of Cell Biology 63(2 Pt 1):524-30.
  10. [6]|Skerrow CJ, Matoltsy AG.(1974) Journal of cell biology(2 Pt 1):524-30.
  11. [7]|Gorbsky G, Steinberg MS. (1981) Isolation of the intercellular glycoproteins of desmosomes. Journal of Cell Biology 90(1):243-8.
  12. [8]
  13. [9]| Cowin P, Garrod DR. (1983) Antibodies to epithelial desmosomes show wide tissue and species cross-reactivity. Nature;302(5904):148-50.
  14. [10]|Gorbsky G, Cohen SM, Shida H, Giudice GJ, Steinberg MS. (1985) Isolation of the non-glycosylated proteins of desmosomes and immunolocalization of a third plaque protein: desmoplakin III. Proceedings National Academy of Science USA.82(3):810-4.
  15. [11]|Green KJ, Goldman RD, Chisholm RL. (1988)Isolation of cDNAs encoding desmosomal plaque proteins: evidence that bovine desmoplakins I and II are derived from two mRNAs and a single gene. Proceedings National Academy of Science U.S.A. 85(8):2613-7.
  16. [12]|Blaschuk OW, Sullivan R, David S, Pouliot Y. (1990) Identification of a cadherin cell adhesion recognition sequence. Developmental Biology 139(1):227-9.
  17. [13]|Green KJ, Parry DA, Steinert PM, Virata ML, Wagner RM, Angst BD, Nilles LA. (1990) Structure of the human desmoplakins. Implications for function in the desmosomal plaque. Journal of Biological Chemistry15;265(5):2603-12.
  18. [14]|Koch PJ, Walsh MJ, Schmelz M, Goldschmidt MD, Zimbelmann R, Franke WW.Identification of desmoglein, a constitutive desmosomal glycoprotein, as a member of the cadherin family of cell adhesion molecules. European Version of Cell Biology 53(1):1-12.
  19. [15]|Collins JE, Legan PK, Kenny TP, MacGarvie J, Holton JL, Garrod DR. (1991) Cloning and sequence analysis of desmosomal glycoproteins 2 and 3 (desmocollins): cadherin-like desmosomal adhesion molecules with heterogeneous cytoplasmic domains. Journal of Cell Biology 113(2):381-91.
  20. [16]| Amagai M, Klaus-Kovtun V, Stanley JR. (1991) Autoantibodies against a novel epithelial cadherin in pemphigus vulgaris, a disease of cell adhesion. Cell 67(5):869-77.Simpson CL, Green KJ. Identification of Desmogleins as Disease Targets. Journal of Investigative Dermatology 127(E1):E15-E16.
  21. [17]
  22. [18]|Stappenbeck TS, Green KJ. (1992) The desmoplakin carboxyl terminus coaligns with and specifically disrupts intermediate filament networks when expressed in cultured cells. Journal of Cell Biology 116(5):1197-209.
  23. [19]|Kouklis PD, Hutton E, Fuchs E. Making a connection: direct binding between keratin intermediate filaments and desmosomal proteins.Jounral of Cell Biology 127(4):1049-60.
  24. [20]|McGrath JA, McMillan JR, Shemanko CS, Runswick SK, Leigh IM, Lane EB, Garrod DR, Eady RA. Mutations in the plakophilin 1 gene result in ectodermal dysplasia/skin fragility syndrome. Nature Genetics 17(2):240-4.
  25. [21]|Tselepis C, Chidgey M, North A, Garrod D.Desmosomal adhesion inhibits invasive behavior. Proceedings National Academy U.S.A. 95(14):8064-9.
  26. [22]
  27. [23]Vasioukhin V, Bowers E, Bauer C, Degenstein L, Fuchs E. (2001) Desmoplakin is essential in epidermal sheet formation. Nature Cell Biology 3(12):1076-85.
  28. [24]|Hopkins G, Kimura TE, Garrod DR. Desmoplakin Is Essential for Epidermal Sheet Formation. Journal for investigative dermatology 127(E1):E12.
  29. Reinhard Windoffer, Monika Borchert-Stuhlträger, Rudolf E Leube Desmosomes: interconnected calcium-dependent structures of remarkable stability with significant integral membrane protein turnover. J. Cell. Sci.: 2002, 115(Pt 8);1717-32 PubMed 11950889
  30. R Cusmai, P Curatolo, S Mangano, R Cheminal, B Echenne Hemimegalencephaly and neurofibromatosis. Neuropediatrics: 1990, 21(4);179-82 PubMed 2127080 ]
  31. [25]
  32. [26]
  33. [27]
  34. [28]
  35. [29]
  36. [30]
  37. [31]
  38. [32]
  39. [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2633677/}
  40. [33]
  41. 41.0 41.1 41.2 41.3 41.4 41.5 http://www.ncbi.nlm.nih.gov/pubmed?term=20066089
  42. David Garrod Desmosomes in vivo. Dermatol Res Pract: 2010, 2010;212439 PubMed 20671997
  43. 43.0 43.1 43.2 [34]
  44. Zhuxiang Nie, Anita Merritt, Mansour Rouhi-Parkouhi, Lydia Tabernero, David Garrod Membrane-impermeable cross-linking provides evidence for homophilic, isoform-specific binding of desmosomal cadherins in epithelial cells. J. Biol. Chem.: 2011, 286(3);2143-54 PubMed 21098030
  45. 45.0 45.1 45.2 45.3 Helen A Thomason, Anthea Scothern, Selina McHarg, David R Garrod Desmosomes: adhesive strength and signalling in health and disease. Biochem. J.: 2010, 429(3);419-33 PubMed 20626351
  46. [35]
  47. [36]
  48. [37]
  49. [38]
  50. [39]
  51. [40]
  52. [41]
  53. [42]
  54. [43]
  55. [44]
  56. [45]
  57. [46]
  58. [47]
  59. [48]
  60. [49]
  61. [50]
  62. [51]>
  63. [52]
  64. [53]
  65. [54]
  66. [55]
  67. [56]
  68. [57]
  69. F M Watt, D L Mattey, D R Garrod Calcium-induced reorganization of desmosomal components in cultured human keratinocytes. J. Cell Biol.: 1984, 99(6);2211-5 PubMed 6209289
  70. [58]
  71. [59]
  72. [60]
  73. [61]
  74. [62]
  75. [63]
  76. [64]
  77. [65]
  78. [66]
  79. [67]
  80. [68]
  81. [69]
  82. http://www.nhs.uk/conditions/Impetigo/Pages/Introduction.aspx
  83. http://www.ncbi.nlm.nih.gov/pubmed/15363804
  84. http://www.nature.com/nm/journal/v6/n11/abs/nm1100_1275.html
  85. John R. Stanley, M.D., and Masayuki Amagai, M.D., Ph.D. Pemphigus, Bullous Impetigo, and the Staphylococcal Scalded-Skin Syndrome. N Engl J Med 2006; 355:1800-1810October 26, 2006
  86. D. Keith B. Armstrong*, Kevin E. McKenna1, Patricia E. Purkis2, Kathleen J. Green3, Robin A. J. Eady4, Irene M. Leigh2 and Anne E. Hughes. Haploinsufficiency of Desmoplakin Causes a Striate Subtype of Palmoplantar Keratoderma. Human Molecular Genetics. (1999) 8 (1): 143-148.
  87. Neil V Whittock, Gabrielle H S Ashton, Patricia J C Dopping-Hepenstal, Matthew J Gratian, Fiona M Keane, Robin A J Eady and John A McGrath. Striate Palmoplantar Keratoderma Resulting from Desmoplakin Haploinsufficiency. Nature. (1999) 113: 940-946.
  88. http://content.onlinejacc.org/cgi/reprint/38/7/1773.pdf
  89. [70]
  90. [71]
  91. A H Christensen, M Benn, H Bundgaard, A Tybjaerg-Hansen, S Haunso, J H Svendsen Wide spectrum of desmosomal mutations in Danish patients with arrhythmogenic right ventricular cardiomyopathy. J. Med. Genet.: 2010, 47(11);736-44 PubMed 20864495
  92. [72]
  93. [73]


Coordinator Comment to all Groups

I will add a general comment that will be the same to all groups under this heading.

Referencing Extension Problem

--Mark Hill 13:16, 3 May 2011 (EST) As mentioned in the lecture, I am aware of the referencing extension problem on your project pages. I have the following temporary solution, of removing the extension, so that groups can continue to add content to their project pages. I am also giving everyone a 1 week extension before the peer assessment.

This should only be done if your project page is not allowing you to save changes!

A. The Easy Way....

The following 4 steps can be done on the webpage or select all content in edit mode, copy and paste into a text editor. All steps must be completed before you attempt to save.

  1. In page edit mode, find all <pubmed> reference tags.
  2. Replace this tag with [http://www.ncbi.nlm.nih.gov/pubmed/ Note, there should be no spaces between the internet address and the pmid number.
  3. Now find all </pubmed> reference tags.
  4. Replace this second tag with ]

This will generate a numbered reference list that we can later fix up.


B. The Better Looking Result....

Whatever is between the <ref> </ref></pubmed> tags is what will appear in your reference list, so you can format the reference and link to appear in your reference list.

2011 Projects: Synaptic Junctions | Gap Junctions | Tight Junctions | Desmosomes | Adherens Junctions | Neuromuscular Junction