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The mystery of tight junctions: Why do some cells form an impermeable barrier?
Direct interactions between cells are crucial in the development and function of multicellular organisms. The ability of cells to signal changes in their microenvironment is critical for cell survival. Interactions between cells can be stable, through cell junctions, or transient, such as interactions between cells of the immune system.
Stable interaction
Stable cell-cell interactions are required for the control of cell attachment, shape, and function within tissues and these interactions involve cellular engagement by multiprotein complexes. These junctions not only maintain epithelial cell function but also ensure the overall structure of the tissue.
Tight fit
Tight junctions are multi-protein complexes that tightly connect cells of the same tissue and prevent water and water-soluble molecules from passing through the spaces between cells. These junctions are present in epithelial cells and their main function is to separate the external fluid of the cell from the basement membrane.
These tight junctions form a sealed barrier between different tissues and cavities of the body, ensuring selective permeability.
Anchor Joint
Among anchoring junctions, only two types of junctions involve cell-cell interactions: adhesion junctions and decussation junctions. Both are present in many cell types and provide close connections and support between cells.
Channel Bonding
Channel junctions are the primary site of intercellular signaling, allowing small molecules to diffuse between neighboring cells. These channels are composed of transmembrane proteins called connexins.
Transient Interaction
Immune systemWhite blood cells destroy abnormal cells and fight infection; these interactions are often transient but are an essential part of the immune response. Both the migration of white blood cells within blood vessels and the transmission of information between them must be achieved through a series of intercellular interactions.
Blood coagulation
The clotting process also depends on the interaction between platelets. When the endothelium of a blood vessel is damaged, platelets quickly attach to the exposed connective tissue, triggering their aggregation and activation.
Interactions between bacteria
Communities of bacteria interact similarly to cells in tissues, using physical interactions and signaling molecules to regulate their metabolic rates and growth.
Pathological implications
CancerCancer formation is often triggered by the loss of cell-cell interactions. In normal cells, contact inhibition controls growth, but aberrant expression of this gene in cancer cells results in a loss of this ability, leading to unbridled proliferation.
Bacterial pathogensPathogen invasion requires communication with host cells, often characterized by strong attachment, to prevent being flushed out before infection can occur.
Diseases
Cell-cell interactions are highly specific and tightly regulated, and genetic defects or dysregulation of these interactions can lead to the development of many diseases.
As people gradually understand the physiological and pathological significance of cell-cell interactions, we can't help but wonder how these subtle interactions between cells play a more profound role in human health?
