Introduction
What are intercellular junctions?
A way of contact where adjacent cells can communicate and coordinate their activities through a network of structures
These structures enable signalling between cells
Why they are important: maintain tissue integrity, cell communication, selective permeability, embryologic development. maintain homeostasis
Most commonly, epithelial cells have many intercellular junctions
Types of intercellular junctions
Tight junctions – Create selective barrier
Desmosomes – Create strong adhesion between cells
Gap junctions – Allow passage of ions between cells, enabling cell communication
Tight Junctions
Structure:
- Tight
Continuous belt-like structure at the apical ends of adjacent cells, completely surrounding cell
40 proteins within tight junctions: 1. Scaffolding protein, 2. Signaling protein, 3. Regulation protein, 4. Transmembrane protein
Made up of proteins: Claudins and Occludins.
Function:
- Maintain controlled environment in epithelial tissue as form a strong selective barrier, therefore regulating what comes in and goes out of the cell
Desmosomes
Structure:
Disc like structures
Function:
-Maintain tissue integrity
-Strong adhesion between cells
-Distributes mechanical stress
-Linked to cytoskeleton, specifically the intermediate filaments (keratin filaments)
-Found in skin and heart cells
Difference between adhering junction and desmosomes:
Similar functions (adhesion of cells to withstand forces) but:
- Desmosomes deal with longer lasting forces like mechanical stress (stretching) whereas adherent junctions deal with transient forces
Made up of different proteins (adhering = E – cadherin, desmosomes = desmogleins etc),
Both connect to cytoskeleton but different areas, adhering = actin filaments, desmosomes = intermediate filaments
Gap Junctions
Structure:
Consist of connexin proteins (transmembrane proteins) – form channels called connexons
Join cytoplasm of adjacent cells together this way
Function:
Allow direct communication between adjacent cells through passage of ions and other small molecules (cell signaling)
Allow for cell synchronization so found mostly in heart as these cells need to contract together
Found in the brain, heart