Cell junctions definition
Cell junctions refers to specialized regions through which cells adhere and communicate with each other or with the extracellular matrix.
Cellular Communication
Cells are small, with a thin, malleable plasma membrane and internally composed by liquid with suspended organelles. In addition to these characteristics, different types of cells are in line in a tissue or organ; each cell type having its shape and function. Nevertheless, in multicellular organisms, cells are able to associate and form compact, resistant, and functional tissues and organs. To do this, it is essential that there is intercellular communication and communication with the extracellular environment. This communication is done through cell-to-cell junctions or extracellular cell-matrix junctions, respectively, and aims to coordinate the growth, differentiation and metabolism of each cell. In addition to communication, there must also be adhesion between cells, otherwise tissues/organs/organisms would disintegrate.
Types and Characteristics of Cellular Junctions
There are different types of cell junctions, each with different functions:
- anchoring junctions (figure 1B),
- gap junctions (figure 1A),
- occluding junctions (figure 1C),
- cell-matrix junctions.
Figure 1 – Schematic image illustrating the different types of cellular junctions. A) gap junction; B) anchoring junction; C) occluding junction.
Occluding junctions are present in epithelial tissues and are responsible for the formation of a barrier that prevents the movement of water and some solutes between compartments. Epithelial tissue is present, for example, throughout the digestive system. Anchoring junctions, together with the extracellular cell-matrix junctions, are responsible for cell shape and rigidity and for holding cells together in a tissue. In the case of gap junctions, these are responsible for the passage of ions between cells, without contact with the extracellular fluid.
Cell-to-cell junctions, present in tissue and organ cells, are stable and arise when each cell grows and differentiates. On the other hand, in the case of immune system cells, cell-to-cell junctions are temporary and are formed only in case of tissue inflammation/infection, leading to leukocyte migration to a particular tissue.
Electronic microscopy is used to study cellular junctions.
References:
Alberts B., Johnson A., Lewis J., Raff M., Keith R., Walter P. (2007). Molecular Biology of the Cell (5th edition). Garland Science, New York.
Cooper G.M. (2000). The Cell: A Molecular Approach (2th edition). Sinauer Associates, Sunderland (MA).
Lodish H., Berk A., Zipursky S.L., Matsudaira P., Baltimore D., Darnell J. (2000). Molecular Cell Biology (4th edition). W. H. Freeman, New York.
