Cell junction
Cell junction | |
---|---|
Details | |
Identifiers | |
Latin | junctiones cellulares |
TH | H1.00.01.0.00012 |
FMA | 67394 |
Anatomical terminology |
Cell junctions
Cell junctions are also especially important in enabling communication between neighboring cells via specialized protein complexes called communicating (gap) junctions. Cell junctions are also important in reducing stress placed upon cells.
In plants, similar communication channels are known as
Types
In vertebrates, there are three major types of cell junction:
- Adherens junctions, desmosomes and hemidesmosomes (anchoring junctions)
- Gap junctions[4] (communicating junction)
- Tight junctions (occluding junctions)
Anchoring junctions
Cells within tissues and organs must be anchored to one another and attached to components of the extracellular matrix. Cells have developed several types of junctional complexes to serve these functions, and in each case, anchoring proteins extend through the plasma membrane to link cytoskeletal proteins in one cell to cytoskeletal proteins in neighboring cells as well as to proteins in the extracellular matrix.[5]
Three types of anchoring junctions are observed, and differ from one another in the cytoskeletal protein anchor as well as the transmembrane linker protein that extends through the membrane:
Junction | Cytoskeletal anchor | Transmembrane linker | Ties cell to: |
---|---|---|---|
Desmosomes |
Intermediate filaments |
Cadherin | Other cells |
Hemidesmosomes |
Intermediate filaments |
Integrins | EC matrix |
Adherens junctions (Adhesion belt, Focal adhesion) | Actin filaments | Cadherin / Integrin / Nectins | Other cells / EC matrix |
Anchoring-type junctions not only hold cells together but provide tissues with structural cohesion. These junctions are most abundant in tissues that are subject to constant mechanical stress such as skin and heart.[5]
Desmosomes
Desmosomes, also termed as maculae adherentes, can be visualized as rivets through the
Hemidesmosomes
Hemidesmosomes form rivet-like links between cytoskeleton and extracellular matrix components such as the basal laminae that underlie epithelia. Like desmosomes, they tie to intermediate filaments in the cytoplasm, but in contrast to desmosomes, their transmembrane anchors are integrins rather than cadherins.[7]
Adherens junctions
Adherens junctions share the characteristic of anchoring cells through their cytoplasmic
Communicating (gap) junctions
Communicating junctions, or gap junctions allow for direct chemical communication between adjacent cellular cytoplasm through diffusion without contact with the extracellular fluid.[8] This is possible due to six connexin proteins interacting to form a cylinder with a pore in the centre called a connexon.[9] The connexon complexes stretches across the cell membrane and when two adjacent cell connexons interact, they form a complete gap junction channel.[8][9] Connexon pores vary in size, polarity and therefore can be specific depending on the connexin proteins that constitute each individual connexon.[8][9] Whilst variation in gap junction channels do occur, their structure remains relatively standard, and this interaction ensures efficient communication without the escape of molecules or ions to the extracellular fluid.[9]
Gap junctions play vital roles in the human body,
Tight junctions
Found in vertebrate
Physiological pH plays a part in the selectivity of solutes passing through tight junctions with most tight junctions being slightly selective for cations. Tight junctions present in different types of epithelia are selective for solutes of differing size, charge, and polarity.
Proteins
There have been approximately 40 proteins identified to be involved in tight junctions. These proteins can be classified into four major categories;signalling proteins.
Roles
- Scaffolding proteins – organise the transmembrane proteins, couple transmembrane proteins to other cytoplasmic proteins as well as to actin filaments.
- Signaling proteins – involved in junctions assembly, barrier regulation, and gene transcription.
- Regulation proteins – regulate membrane vesicle targeting.
- Transmembrane proteins – including junctional adhesion molecule, occludin, and claudin.
It is believed that claudin is the protein molecule responsible for the selective permeability between epithelial layers.
A three-dimensional image is still yet to be achieved and as such specific information about the function of tight junctions is yet to be determined.
Tricellular junctions
Tricellular junctions seal epithelia at the corners of three cells. Due to the geometry of three-cell vertices, the sealing of the cells at these sites requires a specific junctional organization, different from those in bicellular junctions. In vertebrates, components tricellular junctions are tricellulin and lipolysis-stimulated lipoprotein receptors. In invertebrates, the components are gliotactin and anakonda.[12]
Tricellular junctions are also implicated in the regulation of cytoskeletal organization and cell divisions. In particular they ensure that cells divide according to the Hertwig rule. In some Drosophila epithelia, during cell divisions tricellular junctions establish physical contact with spindle apparatus through astral microtubules. Tricellular junctions exert a pulling force on the spindle apparatus and serve as a geometrical clues to determine orientation of cell divisions.[13]
Cell junction molecules
The molecules responsible for creating cell junctions include various
Immunoglobulin superfamily are a group of calcium independent proteins capable of homophilic and heterophilic adhesion. Homophilic adhesion involves the immunoglobulin-like domains on the cell surface binding to the immunoglobulin-like domains on an opposing cell's surface while heterophilic adhesion refers to the binding of the immunoglobulin-like domains to integrins and carbohydrates instead.[20]
Cell adhesion is a vital component of the body. Loss of this adhesion effects cell structure, cellular functioning and communication with other cells and the extracellular matrix and can lead to severe health issues and diseases.
References
- ISBN 978-1-4160-2973-1.
- S2CID 237347708. Retrieved 23 January 2023.
- S2CID 11991859.
- ISBN 978-1-934115-46-6.
- ^ PMID 19856171.
- )
- PMID 3350210.
- ^ S2CID 20806078.
- ^ PMID 15109565.
- ^ PMID 18392995.
- ^ PMID 15473861.
- PMID 25982676.
- PMID 26886796.
- ISBN 978-1429203142.
- S2CID 8315194.
- PMID 7679406.
- PMID 10711736.
- PMID 16377174.
- S2CID 30326350.
- PMID 22272201.
External links
- Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter (2002). "Cell Junctions". Molecular Biology of the Cell (4th ed.). New York: Garland Science. ISBN 978-0-8153-3218-3.
- Intercellular+Junctions at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Cell-Matrix+Junctions at the U.S. National Library of Medicine Medical Subject Headings (MeSH)