cell junction

Definition

Target type: cellularcomponent

A cellular component that forms a specialized region of connection between two or more cells, or between a cell and the extracellular matrix, or between two membrane-bound components of a cell, such as flagella. [GOC:aruk, GOC:bc, GOC:mah, http://www.vivo.colostate.edu/hbooks/cmb/cells/pmemb/junctions_a.html, ISBN:0198506732, PMID:26820516, PMID:28096264]

Cell junctions are specialized structures that hold cells together, enabling communication and coordination between them. They are essential for maintaining tissue integrity, regulating cell behavior, and ensuring proper organ function.

Cell junctions can be broadly classified into three main types:

1. **Adherens junctions:** These junctions provide strong mechanical attachments between cells. They are characterized by the presence of cadherin proteins, which bind to each other in a calcium-dependent manner. Adherens junctions connect to the actin cytoskeleton inside the cell, providing a continuous network of support and allowing cells to maintain their shape and withstand external forces.

2. **Tight junctions:** These junctions form a seal between cells, preventing the leakage of fluids and molecules between them. They are composed of transmembrane proteins called claudins and occludins, which interact with each other and with intracellular proteins to create a barrier that regulates paracellular permeability. Tight junctions play a crucial role in maintaining tissue polarity and regulating the passage of substances across epithelial and endothelial barriers.

3. **Gap junctions:** These junctions provide direct communication channels between cells, allowing the passage of small molecules and ions. They are formed by connexins, which assemble into channels called connexons. Each connexon spans the plasma membrane of one cell and connects with another connexon from an adjacent cell to create a continuous channel. Gap junctions enable rapid communication between cells and play important roles in coordinating cellular activities, such as muscle contraction, electrical signaling, and development.

In addition to these three main types, there are other specialized junctions that contribute to cell-cell interactions and tissue organization. These include:

- **Desmosomes:** Similar to adherens junctions, desmosomes provide strong mechanical attachments between cells, but they connect to intermediate filaments instead of actin filaments. They are particularly important in tissues that experience significant mechanical stress, such as skin and heart muscle.

- **Focal adhesions:** These junctions act as anchoring sites for the cytoskeleton to the extracellular matrix, allowing cells to adhere to their surroundings and maintain their position. They are crucial for cell migration, wound healing, and tissue development.

Cell junctions are dynamic structures that can be assembled and disassembled in response to various cues, allowing cells to adapt to changing conditions. They are essential for maintaining tissue homeostasis and are implicated in various physiological processes, including development, differentiation, cell signaling, and disease.
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Proteins (31)

Compounds (738)