Cell junction

Some examples of cell junctions
This image shows a desmosome junction between cells of the epidermal layer of the skin.
The cartoon of epithelium cells connected by tricellular junctions at the regions where three cells meet.

Cell junctions (or intercellular bridges ) are a class of cellular structures consisting of multiprotein complexes that provide contact or adhesion between neighboring cells or between a cell and the extracellular matrix in animals.

- Cell junction

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Epithelium

One of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue.

Types of epithelium
Summary showing different epithelial cells/tissues and their characteristics.
Forms of secretion in glandular tissue
Different characteristics of glands of the body
Epithelial cell infected with ''Chlamydia pneumoniae
Squamous epithelium 100x
Human cheek cells (Nonkeratinized stratified squamous epithelium) 500x
Histology of female urethra showing transitional epithelium
Histology of sweat gland showing stratified cuboidal epithelium

Cell junctions are especially abundant in epithelial tissues.

Tight junction

Diagram of Tight junction
Depiction of the transmembrane proteins that make up tight junctions: occludin, claudins, and JAM proteins.
TEM of negatively stained proximal convoluted tubule of Rat kidney tissue at a magnification of ~55,000x and 80 kV with Tight junction. Note that the three dark lines of density correspond to the density of the protein complex, and the light lines in between correspond to the paracellular space.

Tight junctions, also known as occluding junctions or zonulae occludentes (singular, zonula occludens) are multiprotein junctional complexes whose canonical function is to prevent leakage of solutes and water and seals between the epithelial cells.

Desmosome

Cell structure specialized for cell-to-cell adhesion.

A desmosome.

A type of junctional complex, they are localized spot-like adhesions randomly arranged on the lateral sides of plasma membranes.

Gap junction

Gap junctions are specialized intercellular connections between a multitude of animal cell-types.

Vertebrate gap junction
Light microscope images do not allow us to see connexons themselves but do let us see the fluorescing dye injected into one cell moving into neighboring cells when gap junctions are known to be present
Annular gap junction cross section in TEM thin section. Gap junctions are usually linear rather than annular in TEM thin sections. It is thought that annular gap junctions result from engulfment by one of the two cells of the membrane plaque to form a vesicle within the cell. This example shows three layers to the junction structure. The membrane from each cell is the dark line with the whiter narrow gap between the two darkly stained membranes. In such electron micrographs there may appear to be up to 7 layers. Two lipid mono-layers in each membrane can stain as 3 layers plus one layer from the gap between them, similar to two stacked bread sandwiches with space between them

A similar narrow regular gap was not demonstrated in other intercellular junctions photographed using the TEM at the time.

Junctional adhesion molecule

Protein that is a member of the immunoglobulin superfamily, and is expressed in a variety of different tissues, such as leukocytes, platelets, and epithelial and endothelial cells.

Crystallographic structure of junctional adhesion molecules linked together
Tight junctions are formed from action of different JAM proteins working in conjunction. Many of these JAM proteins will be localized in these junctions.

JAM-1interacts with cells in a homophilic manner in order to preserve the structure of the junction while moderating its permeability.

Hertwig rule

Hertwig's rule or 'long axis rule' states that a cell divides along its long axis.

Cartoon of the dividing epithelium cell surrounded by epithelium tissue. Spindle apparatus rotates inside the cell. The rotation is a result of astral microtubules pulling towards tri-cellular-junctions (TCJ), signaling centers localized at the regions where three cells meet.

The study indicates Cell junction participation in determining the spindle orientation.

Cell signaling

Ability of a cell to receive, process, and transmit signals with its environment and with itself.

Different types of extracellular signaling
Differences between autocrine and paracrine signaling
Figure 2. Notch-mediated juxtacrine signal between adjacent cells.
Transmembrane receptor working principle
The AMPA receptor bound to a glutamate antagonist showing the amino terminal, ligand binding, and transmembrane domain, PDB 3KG2
A G Protein-coupled receptor within the plasma membrane.
VEGF receptors are a type of enzyme-coupled receptors, specifically tyrosine kinase receptors
Figure 3. Key components of a signal transduction pathway (MAPK/ERK pathway shown)
Signal transduction pathways that lead to a cellular response

2) A communicating junction links the intracellular compartments of two adjacent cells, allowing transit of relatively small molecules.

Organoid

Miniaturized and simplified version of an organ produced in vitro in three dimensions that shows realistic micro-anatomy.

Intestinal organoid grown from Lgr5+ stem cells.

Comparative transcriptional profiling of epithelial cells purified from patient and control organoids highlighted pathways involved in cell polarity, cell-cell junctions and dynein motor assembly, some of which had been implicated for other genotypes within the phenotypic family of renal ciliopathies.

Embryoid body

Embryoid bodies (EBs) are three-dimensional aggregates of pluripotent stem cells.

Phase image of EBs in suspension culture. Individual EBs are composed of approximately 1000 mESCs

EBs are formed by the homophilic binding of the Ca2+ dependent adhesion molecule E-cadherin, which is highly expressed on undifferentiated ESCs.

Intercalated disc

Intercalated discs or lines of Eberth are microscopic identifying features of cardiac muscle.

Cardiac muscle, an intercalated disc can be seen joining cardiomyocytes in magnified section
Ruptured intercalated discs, in this case regarded as a visual artifact.
Square-shaped nuclei, indicating forceful myocardial contraction.

The three types of cell junction recognised as making up an intercalated disc are desmosomes, fascia adherens junctions, and adherens junctions.