Intercellular Junctions

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This illustration shows two plant cells side-by-side. A gap in the cell wall, a plasmodesma, allows fluid and small molecules to pass from the cytoplasm of one cell to the cytoplasm of the other.
A plasmodesma is a channel between two adjacent plant cells’ cell walls. Plasmodesmata allow materials to pass from one plant cell’s cytoplasm to an adjacent cell’s cytoplasm. Source: OpenStax Biology 2e

OpenStax Biology 2e

Cells can also communicate with each other via direct contact, or intercellular junctions. There are differences in the ways that plant and animal and fungal cells communicate. Plasmodesmata are junctions between plant cells; whereas, animal cell contacts include tight junctions, gap junctions, and desmosomes.

Plasmodesmata

In general, long stretches of the plasma membranes of neighboring plant cells cannot touch one another because the cell wall that surrounds each cell separates them. How then, can a plant transfer water and other soil nutrients from its roots, through its stems, and to its leaves? Such transport uses the vascular tissues (xylem and phloem) primarily. There also exist structural modifications, which we call plasmodesmata  (singular = plasmodesma). Numerous channels that pass between adjacent plant cells’ cell walls connect their cytoplasm, and enable transport of materials from cell to cell, and thus throughout the plant.

Tight Junctions

A tight junction is a watertight seal between two adjacent animal cells. Proteins (predominantly two proteins called claudins and occludins) tightly hold the cells against each other.

This illustration shows two cell membranes joined together by a matrix of tight junctions.
 Tight junctions form watertight connections between adjacent animal cells. Proteins create tight junction adherence. (credit: modification of work by Mariana Ruiz Villareal)

This tight adherence prevents materials from leaking between the cells; tight junctions are typically found in epithelial tissues that line internal organs and cavities, and comprise most of the skin. For example, the tight junctions of the epithelial cells lining your urinary bladder prevent urine from leaking out into the extracellular space.

Desmosomes

Also only in animal cells are desmosomes, which act like spot welds between adjacent epithelial cells. Cadherins, short proteins in the plasma membrane connect to intermediate filaments to create desmosomes. The cadherins connect two adjacent cells and maintain the cells in a sheet-like formation in organs and tissues that stretch, like the skin, heart, and muscles.

This illustration shows two cells fused together by a desmosome. Cadherins extend from each cell and join the two cells together. Intermediate filaments connect to cadherins on the inside of the cell.
A desmosome forms a very strong spot weld between cells. Linking cadherins and intermediate filaments create it. (credit: modification of work by Mariana Ruiz Villareal)

Gap Junctions

Gap junctions in animal cells are like plasmodesmata in plant cells in that they are channels between adjacent cells that allow for transporting ions, nutrients, and other substances that enable cells to communicate. Structurally, however, gap junctions and plasmodesmata differ.

This illustration shows two cells joined together with protein pores called gap junctions that allow water and small molecules to pass through.
A gap junction is a protein-lined pore that allows water and small molecules to pass between adjacent animal cells. (credit: modification of work by Mariana Ruiz Villareal)

Gap junctions develop when a set of six proteins (connexins) in the plasma membrane arrange themselves in an elongated donut-like configuration – a connexon. When the connexon’s pores (“doughnut holes”) in adjacent animal cells align, a channel between the two cells forms. Gap junctions are particularly important in cardiac muscle. The electrical signal for the muscle to contract passes efficiently through gap junctions, allowing the heart muscle cells to contract in tandem.

– What are multi-protein junctional complexes whose general function is to prevent leakage of transported solutes and water and seals the para-cellular pathway. ?

– What are a specialized inter-cellular connection between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells?

– What are protein complexes that occur at cell–cell junctions in epithelial and endothelial tissues, usually more basal than tight junctions, and are defined as a cell junctions whose cytoplasmic face is linked to the actin cytoskeleton.?

Desmosomes are major cell-cell junctions that are particularly abundant in epidermal cells and cardiomyocytes. Arrhythmogenic Right Ventricular Dysplasia may be caused by genetic defects of the structure of myocardial desmosomes. Desmosomes are multiprotein complexes that form intercellular contacts on the surface of heart muscle cells. Mutations in many proteins that comprise desmosomes can have harmful effects on cardiomyocyte function. Defective desmosomes cannot sustain the constant mechanical stress inherent in contracting cardiomyocytes, resulting in cardiomyocyte detachment and the consequent impairment of mechanical and electrical cell junctions.

Source:

Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/biology-2e

https://en.wikipedia.org/wiki/Tight_junction

https://en.wikipedia.org/wiki/Gap_junction

https://en.wikipedia.org/wiki/Adherens_junction

https://www.sciencedirect.com/book/9780128170861/disease-pathways

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