Cell Junctions and Adhesion
Cell junctions and adhesion are the molecular structures and interactions that bind cells to one another and to the extracellular matrix, organising single cells into coherent tissues. They seal epithelial sheets against leakage, anchor cells mechanically, and provide direct channels for cell-to-cell communication, making them foundational to how multicellular tissue is built and maintained.
Definition
Cell adhesion is the binding of a cell to another cell or to the extracellular matrix through specialised membrane proteins; cell junctions are the organised multiprotein structures, classified as occluding, anchoring, or communicating, through which adhesion and intercellular continuity are achieved.
Scope
This area orients the reader to the main classes of intercellular junctions and adhesion systems: tight (occluding) junctions that form selective barriers, anchoring junctions (adherens junctions and desmosomes) that bear mechanical load, gap junctions that allow direct cytoplasmic communication, and the cell adhesion molecule families (cadherins, integrins, selectins, and immunoglobulin-superfamily CAMs) that mediate adhesion. It is treated as a reference topic in cell biology and histology, not as clinical guidance.
Sub-topics
Key concepts
- Occluding junctions (tight junctions)
- Anchoring junctions (adherens junctions, desmosomes, hemidesmosomes)
- Communicating junctions (gap junctions)
- Cell adhesion molecules (cadherins, integrins, selectins, Ig-superfamily CAMs)
- Junctional complex of epithelia
- Cytoskeletal anchorage and the extracellular matrix
- Epithelial barrier and tissue architecture
Mechanisms
Cells adhere through transmembrane adhesion proteins whose extracellular domains engage partners on neighbouring cells or in the matrix, while their cytoplasmic domains link to the cytoskeleton through adaptor proteins. Different junction types specialise this scheme: tight junctions seal the paracellular space; adherens junctions and desmosomes couple cadherin-based adhesion to actin and intermediate filaments respectively; and gap junctions form channels of paired connexin hemichannels that permit passage of ions and small molecules. Farquhar and Palade's classic ultrastructural description of the epithelial junctional complex established the spatial organisation of these elements along the lateral cell membrane, and the assembly and turnover of junctions are now understood as dynamic, regulated processes.
Clinical relevance
The integrity of cell junctions and adhesion underlies epithelial barrier function, tissue cohesion, and intercellular signalling, and disruption of these systems is a recurring theme in disease mechanisms studied across pathology. This entry describes structure and function for reference and education; it is not a basis for diagnosis or treatment.
History
The systematic understanding of cell junctions grew out of electron microscopy in the mid-twentieth century, when Farquhar and Palade (1963) distinguished the tight junction, intermediate (adherens) junction, and desmosome as components of the epithelial junctional complex. Subsequent molecular work identified the protein families responsible for each junction type and recast adhesion as the molecular basis of tissue architecture and morphogenesis.
Key figures
- Marilyn Farquhar
- George Palade
- Barry Gumbiner
- Kathleen Green
Related topics
Seminal works
- farquhar-palade-1963
- green-2009
- gumbiner-1996
Frequently asked questions
- What are the main types of cell junctions?
- They are usually grouped into occluding junctions (tight junctions) that seal cell sheets, anchoring junctions (adherens junctions and desmosomes) that provide mechanical attachment, and communicating junctions (gap junctions) that connect the cytoplasm of adjacent cells.
- How is cell adhesion different from a cell junction?
- Cell adhesion refers broadly to the binding of cells to each other or to the matrix via adhesion molecules, whereas a cell junction is the organised multiprotein structure through which such adhesion and intercellular continuity are achieved.