Cell Adhesion Molecules

Question 1

What is the importance of cell adhesion?

Answer 1

Sperm adhere to the eggs to transfer material
Brings cells within the egg together to form to morula (E-cadherin)
Inner cell mass and trophoblasts of embryos expressed different adhesion properties
Implantation of egg into endometrium wall
Over time more cell types develop which form due to differential adhesion
Neural crest cells becoming nerve cells involves adhesion

Question 2

What makes L-cells useful for studying cadherins?

Answer 2

They don’t express any cadherins so they can be transfected and studied

Question 3

What is the outcome of transfecting L-cells with E-cadherin and N-cadherin?

Answer 3

Homophillic sorting

Question 4

What is the outcome of transfecting L-cells with E-cadherin but at different levels of expression?

Answer 4

Graded sorting

Question 5

Describe cadherin linkage

Answer 5

Calcium binds to the hinge regions to stabilise them which allows them to interact with neighbouring cells

Question 6

How do rows of cadherins interact?

Answer 6

Perpendicular (these perpendicular arrays act like velcro and allow adhesion)

Question 7

What are the roles of hypervariable protocadherins?

Answer 7

Specifying synapses within the brain, neurite self avoidance

Question 8

What are a couple of intracellular proteins that are important in cadherin function?

Answer 8

Catenins, bind to intracellular region of cadherin to link cadherin to cytoskeleton
Beta-catenin can regulate proliferation via c-Myc
They can sense when cells are interacting with neighbouring cells
When cadherin interacts with a neighbouring cell you get tension that stretches out the cell membrane that causes a conformational change of catenin to a folded to an open state, vinculin can bind

Question 9

How can Rho be activated?

Answer 9

B-catenin activated junction formation, strong actin filaments form

Question 10

What does mutant Rho lead to?

Answer 10

Constitutive activation of Rho leading to stress fibre formation

Question 11

How does cadherin expression change in the early nervous system?

Answer 11

Only E-cadherin expressed in the early embryo
Newly formed mesoderm cells lose E-cadherin
N-cadherin replaces E-cadherin in the neural tube
Cadherin 7 - neural crest cell identity

Question 12

What are the features of selectins?

Answer 12

Cell surface, Ca2+ dependent, bind carbohydrates on neighbouring cells

Question 13

What are the roles of selectins?

Answer 13

Neutrophil trapping

Question 14

What are the roles of Ca2+ independent CAMs?

Answer 14

Mediate homophillic binding, mediate interactions with ECM and between neighbouring cells

Question 15

How do Ca2+ independent CAMs arise?

Answer 15

Alternative splicing