A desmosome (; "binding body"), also known as a macula adherens (plural: maculae adherentes) (

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for ''adhering spot''), is a cell structure specialized for cell-to-

cell adhesion Cell adhesion is the process by which cells interact and attach to neighbouring cells through specialised molecules of the cell surface. This process can occur either through direct contact between cell surfaces such as Cell_junction, cell junc ...

. A type of junctional complex, they are localized spot-like adhesions randomly arranged on the lateral sides of plasma membranes. Desmosomes are one of the stronger cell-to-cell adhesion types and are found in tissue that experience intense mechanical stress, such as

cardiac muscle Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall o ...

tissue,

bladder The bladder () is a hollow organ in humans and other vertebrates that stores urine from the kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the bladder is a distens ...

tissue,

gastrointestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. ...

mucosa, and epithelia.

Structure

Desmosomes are composed of desmosome-intermediate filament complexes (DIFCs), a network of

cadherin Cadherins (named for "calcium-dependent adhesion") are cell adhesion molecules important in forming adherens junctions that let cells adhere to each other. Cadherins are a class of type-1 transmembrane proteins, and they depend on calcium (Ca2+) ...

proteins, linker proteins and

intermediate filament Intermediate filaments (IFs) are cytoskeleton, cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate ''Branchiostoma' ...

s. The DIFCs can be broken into three regions: the extracellular core region ("desmoglea"), the outer dense plaque (ODP), and the inner dense plaque (IDP). The extracellular core region, approximately 34 nm in length, contains

desmoglein The desmogleins are a family of desmosomal cadherins consisting of proteins DSG1, DSG2, DSG3, and DSG4. They play a role in the formation of desmosomes that join cells to one another. Pathology Desmogleins are targeted in the autoimmune disease ...

and

desmocollin Desmocollins are a subfamily of desmosomal cadherins, the transmembrane constituents of desmosomes. They are co-expressed with desmogleins to link adjacent cells by extracellular adhesion. There are seven desmosomal cadherins in humans, three desm ...

, which are in the

family of cell adhesion proteins. Both have five extracellular domains, and have calcium-binding motifs. Extracellular calcium helps form the cadherin adhesion by allowing the cadherin extracellular domain on desmoglein and desmocollin to become rigid. They bind to each other via heterophilic interactions in the extracellular space near their N-termini, in contrast with the homophilic binding characteristic of other cadherins. Desmoglein and desmocollin have a single pass transmembrane region plus an intracellular anchor to secure its position in the cell membrane. Desmogleins and the desmocollin isoform "Dsc-a" contain an intracellular cadherin domain, which binds to

plakoglobin Plakoglobin, also known as junction plakoglobin or gamma-catenin, is a protein that in humans is encoded by the ''JUP'' gene. Plakoglobin is a member of the catenin protein family and homologous to β-catenin. Plakoglobin is a cytoplasmic compon ...

. The outer dense plaque, which is about 15–20 nm in length, contains the intracellular ends of desmocollin and desmoglein, the N-terminus side of

desmoplakin Desmoplakin is a protein in humans that is encoded by the ''DSP'' gene. Desmoplakin is a critical component of desmosome structures in cardiac muscle and epidermal cells, which function to maintain the structural integrity at adjacent cell co ...

, and the armadillo family of mediatory proteins

and plakophilin. Armadillo proteins are involved in mediating attachment to intracellular filaments and cell membrane proteins. Armadillo proteins consist of

β-catenin Catenin beta-1, also known as β-catenin (''beta''-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene. β-Catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcr ...

p120-catenin p120 catenin, or simply p120, also called catenin delta-1, is a protein that in humans is encoded by the ''CTNND1'' gene. Function This gene encodes a member of the Armadillo protein family, which function in adhesion between cells and signal ...

, plakoglobin (

γ-catenin Plakoglobin, also known as junction plakoglobin or gamma-catenin, is a protein that in humans is encoded by the ''JUP'' gene. Plakoglobin is a member of the catenin protein family and homologous to β-catenin. Plakoglobin is a cytoplasmic compon ...

), and plakophilins 1-3. In desmosomes, plakoglobin and plakophilin help to anchor desmoplakin and keratin filaments to the desmosome structure. Plakoglobin has 12-arm repeats with a head and tail structure. Plakophilins have 9-arm repeats, and exist in two isoforms: a shorter "a" form and longer "b" form. The inner dense plaque, also about 15–20 nm in length, contains the C-terminus end of desmoplakin and their attachment to keratin intermediate filaments. Desmoplakin is the most abundant part of the desmosome, as it operates as the mediator between the cadherin proteins in the plasma membrane and the keratin filaments. Desmoplakin has two isoforms that differ in the length of their middle rod domain. All desmoplakins have an N-terminal head, a C-tail consisting of three plakin repeats, and a glycine-serine-arginine rich domain (GSR) at the C-end.

Clinical significance

Arrhythmogenic cardiomyopathy

Mutations within the desmosome are the main cause of

arrhythmogenic cardiomyopathy Arrhythmogenic cardiomyopathy (ACM) is an inherited heart disease. ACM is caused by genetic defects of parts of the cardiac muscle known as desmosomes, areas on the surface of muscle cells which link them together. The desmosomes are composed ...

(ACM), a life-threatening disease caused by mutations usually in desmoglein 2, but sometimes in desmocollin 2. It often afflicts individuals between 20 and 50 years, and has been publicly known as a cause of death in young athletes, although the majority of sudden deaths do not occur in close connection to physical activity. The current incidence within the population is accepted as 1/10,000; however, it is thought that 1/200 may have a mutation that may predispose to ACM. Symptoms of ACM include fainting, shortness of breath, and heart palpitations and the condition is treated by implanting a small defibrillator device.

Blisters

Blistering diseases such as

pemphigus vulgaris Pemphigus vulgaris is a rare chronic blistering skin disease and the most common form of pemphigus. Pemphigus was derived from the Greek word ''pemphix'', meaning blister. It is classified as a type II hypersensitivity reaction in which antibody, ...

(PV) and pemphigus foliaceus (PF) are

autoimmune diseases An autoimmune disease is a condition that results from an anomalous response of the adaptive immune system, wherein it mistakenly targets and attacks healthy, functioning parts of the body as if they were foreign organisms. It is estimated that ...

in which auto-antibodies target desmogleins. PV is caused by circulating

autoantibodies An autoantibody is an antibody (a type of protein) produced by the immune system that is directed against one or more of the individual's own proteins. Many autoimmune diseases (notably lupus erythematosus) are associated with such antibodies. Pr ...

( IgG) that target

Dsg3 Desmoglein-3 is a protein that in humans is encoded by the ''DSG3'' gene. In the skin epidermis Desmoglein-3 is expressed in the basal lower layers of the epidermis, and dominates in terms of expression on mucosal surfaces compared to Desmoglein-1 ...

( Desmoglein 3) and sometimes Dsg1. PV is manifested by suprabasal acantholysis, or blisters in the mucous membrane and blisters in the epidermis. PF patients have autoantibodies that target Dsg1 with superficial blisters on the epidermis with no mucous membrane issues. Both disease result in a loss of keratinocyte adhesion. Pemphigus can also be caused by a bacterial infection: bullous impetigo is an infection caused by a

staphylococcus ''Staphylococcus'', from Ancient Greek σταφυλή (''staphulḗ''), meaning "bunch of grapes", and (''kókkos''), meaning "kernel" or " Kermes", is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillale ...

bacterium that releases a toxin that cleaves the Dsg1 extracellular domain. Similar symptoms occur with Hailey–Hailey disease, though the cause is not autoimmune but genetic. A

haploinsufficiency Haploinsufficiency in genetics describes a model of dominant gene action in diploid organisms, in which a single copy of the wild-type allele at a locus in heterozygous combination with a variant allele is insufficient to produce the wild-type ...

of the ATP2C1 gene located on chromosome 3, which encodes the protein hSPCA1, causes malformation of the desmosomes. Desmoglein 1 haploinsufficiency leads to striate palmoplantar keratoderma, a disease which causes extreme thickening of the epidermis. Loss of desmoglein 4 leads to defective hair-follicle differentiation.

Epidermolysis bullosa simplex Epidermolysis bullosa simplex (EBS) is a disorder resulting from mutations in the genes encoding keratin 5 or keratin 14.Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. . It is one of the major f ...

is an epidermal blistering disease caused by mutations in genes coding for keratin 5 and 14, which attach to desmoplakin. This disease manifests as rupture of the basal epidermis when stress is applied.

Ectodermal dysplasia Ectodermal Dysplasia (ED) refers to a group of genetic disorders characterized by the abnormal development or function of two or more structures that originate from the ectoderm, the outer layer of an embryo. These structures include hair, teeth ...

or skin fragility syndrome is caused by plakophilin 1 mutations. This is manifested by detachment of intermediate filaments and desmoplakin from the desmosome.

History

The desmosome was first discovered by Giulio Bizzozero, an Italian pathologist. He named these ''dense nodules'' the ''nodes of Bizzozero''. In 1920, the term ''desmosome'' was originated by Josef Schaffer. The first

combining form Neoclassical compounds are compound words composed from combining forms (which act as affixes or stems) derived from classical languages (classical Latin or ancient Greek) roots. Neo-Latin comprises many such words and is a substantial componen ...

, '' desmo-'',

Neo-Latin Neo-LatinSidwell, Keith ''Classical Latin-Medieval Latin-Neo Latin'' in ; others, throughout. (also known as New Latin and Modern Latin) is the style of written Latin used in original literary, scholarly, and scientific works, first in Italy d ...

from Greek ''desmos'', bond, carries meaning of binding or bonding things together. Combined with '' -some'', which comes from ''soma'', body, it thus makes a desmosome a ''binding body''.

References

External links

* * – "Ultrastructure of the Cell: microvillous border, Junctional Complex of absorptive epithelium" * – "Ultrastructure of the Cell: microvillous border and Junctional Complex, desmosomes and zonula adhaerens" * – "Ultrastructure of the Cell: cardiac muscle, intercalated disk" {{Authority control Cell anatomy