MCB Lecture 37 Junctions Flashcards
Where are Desmosomes localised? What do they connect?
They are localised in the apical region
They connect two cells
What is the function of Desmosomes?
Desmosomes connect two cells together.
Distribution of tensile forces
Describe the proteins involved in Desmosomes
Cadherin family proteins
Adaptor proteins: desmoplakin, plakoglobin
Intermediate filaments
What is the function of cadherin?
It forms the interaction between the two cells in a Desmosome
Which cytoskeletal element to Desmosomes connect to?
Intermediate filaments
What are two problems that can occur with Desmosomes ?
- Mutation in the intermediate filament (keratin)
2. Antibodies for the Desmosome interrupt it
What are focal adhesions? What is their function?
They are attachments between the cell and the extracellular matrix
They are involved with cell locomotion and signalling
Describe the protein involved with focal adhesions
Integrins attach cell to the ECM
Adaptor proteins: vinculin, Tallin
Actin filaments
Which cytoskeletal element is involved with focal adhesions?
Actin filaments
What is an integrin?
Describe its structure
How is there variability in integrin structure?
Which junctions have integrin?
It is a protein that connects cells together
It is made up of an alpha and beta subunit
Variability: different alpha and beta subunits present
Focal adhesions and hemidesmosomes have integrins
Describe how cells move
- Protrusion
- Adhesion
- Traction
What forces are produced by focal adhesions
Cell traction forces
CTF
Describe how focal adhesions are involved in cell signalling.
What are the two types?
- Inside out:
Ligand binds to a receptor (GPCR, tyrosine kinase) on the cell membrane. This starts a signal transduction pathway, leading to the activation of talin. Talin binds, and now extracellular matrix proteins can be engaged - Outside in:
Binding of an ECM protein to the integrin initiates a signal transduction pathway
Kinases (FAK) recruited
Gene expression, cell proliferation etc.
Describe inside-out signalling with focal adhesions
Ligand binds to a receptor (GPCR, tyrosine kinase) on the cell membrane. This starts a signal transduction pathway, leading to the activation of talin. Talin binds, and now extracellular matrix proteins can be engaged
Describe outside -in signalling in focal adhesions
Binding of an ECM protein to the integrin initiates a signal transduction pathway
Kinases (FAK) recruited
Gene expression, cell proliferation etc.
What is FAK?
It is Focal adhesion Kinase
It is activated when ECM proteins bind to integrins in focal adhesions
It initiates a cascade of transduction events
What is the function and location of hemi desmosomes?
These connect cells to the ECM
They give high tensile strength (eg in skin)
What proteins are involved in hemi desmosomes?
Integrins
Adaptor proteins
Intermediate filaments
Which cytoskeletal element is involved with hemi desmosomes?
Intermediate filaments
How are hemi desmosomes involved with cell proliferation?
When tension is detected by the integrins, a transduction pathway is initiated, leading to cell proliferation and G1 progression
What do mutations in integrins cause?
Skin blistering
What are the anchoring cell junctions?
Desmosomes
Adherens
Hemi desmosomes
Focal adhesions
Describe the function of Gap junctions
They allow for direct movement of materials from one cell to another through a small channel
Describe the structure of gap junctions
6 connexons form a connexon Two connexons (one on each cell) line up to form a channel
How much space is there between two cells linked by a gap junction?
2-4 nm
What is meant by homo and heteromeric connexons?
Homo: only one type of connexin present
Hetero: different types of connexin
What is meant by homo and heterotypic channels in gap junctions?
Homo: only one type of connexin
Hetero: different types of connexin in the channel
What are the functions of gap junctions? (3)
- Movement of metabolites
- Movement of ions in synapses
- Electrical signalling
What causes congenital deafness?
Defects in gap junction connexins
