Cell junction
Multiprotein complexes that hold animal cells together.
Cell junctions, also known as junctional complexes, are a class of cellular structures composed of multiprotein complexes that provide contact or adhesion between neighboring cells or between a cell and the extracellular matrix in animals. They maintain the paracellular barrier of epithelia, control paracellular transport, and are especially abundant in epithelial tissues. Combined with cell adhesion molecules and extracellular matrix, cell junctions help hold animal cells together. They are also important in enabling communication between neighboring cells via specialized protein complexes called communicating (gap) junctions and in reducing stress placed upon cells. In plants, similar communication channels are known as plasmodesmata, and in fungi they are called septal pores.
- field
- Cell biology
- known_for
- Providing contact and adhesion between cells, maintaining paracellular barriers, and enabling intercellular communication
Lore & Background
In vertebrates, there are three major types of cell junctions: adherens junctions, desmosomes, and hemidesmosomes (anchoring junctions); gap junctions (communicating junctions); and tight junctions (occluding junctions). Invertebrates have several other types, such as septate junctions and the C. elegans apical junction. In multicellular plants, the structural functions of cell junctions are provided by cell walls, while communicative analogues are plasmodesmata. Anchoring junctions include desmosomes, which use cadherin molecules to bind adjacent cells; hemidesmosomes, which use integrins to link cytoskeleton to extracellular matrix; and adherens junctions, which anchor cells through cytoplasmic actin filaments and can form adhesion belts that encircle the cell. Gap junctions consist of connexin proteins forming connexons that create channels for direct chemical communication between adjacent cytoplasm. Tight junctions act as paracellular barriers regulating water and solute movement, with selectivity based on size, charge, and polarity. Tricellular junctions seal epithelia at corners of three cells and are implicated in regulating cytoskeletal organization and cell divisions.
Reader's Guide
Cell junctions are fundamental to the structural integrity and function of animal tissues. They provide mechanical cohesion, especially in tissues subject to constant stress such as skin and heart, through anchoring junctions like desmosomes and adherens junctions. Gap junctions enable direct chemical communication essential for coordinated activities, such as uniform contraction of heart muscle and signal transfers in the brain. Tight junctions regulate the paracellular pathway, controlling what passes between epithelial cells. The study of cell junctions has revealed a complex interplay of proteins—including cadherins, integrins, connexins, claudins, and tricellulin—that organize cellular architecture and signaling. Their roles extend beyond adhesion to include tissue morphogenesis, as adherens junctions participate in folding and bending of epithelial sheets. Tricellular junctions further ensure proper cell division orientation. Understanding these structures is critical for comprehending tissue development, homeostasis, and disease states where junctional integrity is compromised.
Did You Know?
- Cell junctions are especially abundant in epithelial tissues.
- Gap junctions allow direct chemical communication between adjacent cellular cytoplasm without contact with extracellular fluid.
- Tight junctions are classified as a paracellular barrier without directional discrimination, but solute movement depends on size and charge.
- Tricellular junctions ensure that cells divide according to the Hertwig rule.
Frequently Asked Questions
Who is Cell junction?
Cell junctions (aka junctional complexes) are multiprotein assemblies that act as the structural connectors between neighboring animal cells or between a cell and the extracellular matrix. They are the defining 'glue' of animal tissue architecture.
What are Cell junction's powers/role?
They hold the paracellular barrier of epithelia in place, regulate what substances can slip between cells, and open direct protein-mediated channels so neighbors can talk to one another. In short, they are simultaneously the wall and the doorway of a cell's neighborhood.
Where does Cell junction appear most prominently in the story?
They are especially abundant in epithelial tissues, where they form the backbone keeping a sheet of cells sealed and cohesive. They work hand-in-hand with adhesion molecules and the extracellular matrix to prevent animal cells from drifting apart.
Why is Cell junction important to the wider Cell biology franchise?
Without them, animal tissues would lose the cohesive barrier that separates body cavities and controls paracellular transport. They are also the physical basis for direct intercellular signaling, making them central to how multicellular animals coordinate.
What team does Cell junction work with?
It operates as part of a larger adhesion-and-communication crew that includes cell adhesion molecules and extracellular matrix components. Together these structures form the complete system that holds animal cells together and lets them exchange information.
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