10 Questions
What type of cells are desmosomes particularly numerous in?
Epithelial cells
What type of proteins link the two cells across a narrow extracellular gap in desmosomes?
Cadherins
What is the term used to describe the cadherins found in desmosomes?
Desmogleins and desmocollins
What is the function of the dense cytoplasmic plaques on the inner surface of the plasma membranes in desmosomes?
Sites of anchorage for looping intermediate filaments
What is the term used to describe the process of transferring information across the plasma membrane?
Transmembrane signaling
Which type of cell-adhesion molecules can transmit signals from the extracellular environment to the cytoplasm?
Both integrins and cadherins
What is the term used to describe the type of proteins that link the cytoskeleton to the plasma membrane?
Plakoglobin and Desmoplakin
What is the function of the intermediate filaments in desmosomes?
Provide structure and tensile strength to the entire sheet of cells
What is the term used to describe the process of linking the cytoskeleton to the plasma membrane?
Cytoskeleton anchorage
What type of molecules can transmit signals from the extracellular environment to the cytoplasm in addition to integrins and cadherins?
Selectins
Study Notes
Cadherins
- Cadherins join cells of similar type to one another by binding to the same cadherin on neighboring cells.
- Cells expressing one species of cadherin preferentially adhere to other cells expressing the same cadherin.
Structure of Cadherins
- Classical cadherins have a modular construction consisting of:
- A large extracellular segment with five tandem domains
- A single transmembrane segment
- A small cytoplasmic domain associated with catenin family proteins
- Catenin family proteins:
- Tether cadherins to the cytoskeleton
- Transmit signals to the cytoplasm and nucleus
Role of Calcium
- Calcium is essential for cell-cell adhesion
- Calcium forms bridges between successive domains of a given molecule
- Maintains the extracellular portion of each cadherin in a rigid conformation required for cell adhesion
Adhesion Between Cells
- Adhesion between cells results from the interaction between the extracellular domains of cadherins
- Cadherin interdigitation forms a "cell-adhesion zipper"
- The greater the number of interacting cadherins in a cluster, the greater the strength of adhesion between apposing cells
Cadherin-Mediated Adhesion
- Cadherin-mediated adhesion is responsible for the ability of like cells to "sort out" of mixed aggregates
- Loss of cadherin function may play a key role in the spread of malignant tumors
Specialized Intercellular Junctions
- Cadherins participate in the formation of specialized intercellular junctions:
- Adherens Junctions
- Desmosomes
- Desmosomes are particularly numerous in tissues subjected to mechanical stress
Adherens Junctions and Desmosomes
- Anchoring cells to other cells through specialized calcium-dependent adhesive junctions
- Desmosomes contain cadherins that link the two cells across a narrow extracellular gap
- Dense cytoplasmic plaques on the inner surface of the plasma membranes serve as sites of anchorage for looping intermediate filaments
Transmembrane Signaling
- Integral membrane proteins, including cadherins, can transfer information across the plasma membrane through transmembrane signaling
- Cadherins can transmit signals from the extracellular environment to the cytoplasm by means of linkages with the cytoskeleton and with cytosolic regulatory molecules
Test your knowledge on how cadherins facilitate cell adhesion by binding to the same cadherin on neighboring cells, as demonstrated through genetic engineering experiments mixing cells expressing different cadherin species.
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