L21 - Cell Adhesion - Migration and Motility

Question 1

What are some examples of adhesion within the embryo?

Answer 1

Adhesion of sperm to the oocyte
Embryos go through a stage of compaction – begin to express adhesion molecules
- Embryo forms a morula
Egg has to implant in uterine wall by binding to endometrium wall

Question 2

What are some examples of adhesion when forming the neural tube?

Answer 2

Cells in dorsal side of neural tube delaminate – neural crest cells

• Lose adhesion with neighbouring cells
• Migration involves adhering to various molecules
• They then aggregate again once they have finished migrating

Question 3

What is an example of a classical cell aggregation experiment?

Answer 3

Sponges can reaggregate if broken apart

Cells self-organise based upon their adhesion

Question 4

What happens if large reaggregations occur?

Answer 4

You see regionalisation?

Question 5

What are L cells?

Answer 5

A cell line that expresses no cadherins?

Question 6

What two things does transfection of L cells induce?

Answer 6

Homophilic sorting
- Some cells express E-cadherin some express N-cadherin
Graded sorting
- Some cells express high level of E-cadherin some express low levels

Question 7

What are cadherins?

Answer 7

Integral membrane glycoproteins with 720-750 amino acids

Question 8

How do cadherins interact?

Answer 8

Extracellular regions of two cadherins interact

• Ca binds to hinge regions to stabilise them
• Leads to conformational change and binding
• Allows them to interact with neighbouring cells

Question 9

What does Ca control about cadherins?

Answer 9

Ca can control their levels of interaction

Question 10

How do perpendicular arrays of cadherins act?

Answer 10

Perpendicular arrays of cadherins act like velcro

Arrays are localised to regions of the cell membrane

Question 11

What are hypervariable protocadherins?

Answer 11

Evolved to form many different isoforms – via alternative splicing
Thought to have a role in specifying synapses
Though to have a role in neurite self-avoidance

Question 12

What are the two different subtypes of cadherins?

Answer 12

Classical

• E-cadherin
  
  • Found in many epithelia
  • Involved in adheren junctions

Non-classical - more specific functions

• Cadherin 23
  
  • Found in the inner ear

Question 13

Cadherin family structure

Answer 13

Most have single transmembrane domains but can have multiple
All have repeated extracellular domains – some have added extra molecules

Question 14

What do catenins connect?

Answer 14

Connect cadherins to actin filaments

Question 15

What are the role of catenins?

Answer 15

Signalling

Building junctions

Question 16

How are catenins involved in signalling?

Answer 16

B catenin can regulate proliferation via c-myc

Question 17

How are catenins involved in building junctions?

Answer 17

1. Myosin / actin interaction
2. Exposes vinculin binding site
3. Cross-linking in more actin filaments
4. Myosin pulls on actin extending a-catenin
5. This pulls on the attached cadherin which is attached to another cadherin

Question 18

How do Rho mutants affect the actin cytoskeleton?

Answer 18

Constitutively active Rho activation leads to stress fibre formation
Changes the cell shape

Question 19

What cadherin is expressed in the early embryo?

Answer 19

E-cadherin

Question 20

When is E-cadherin lost in the embryo?

Answer 20

Newly formed mesoderm cells lose E-cadherin – mesoderm needs to migrate inwards

Question 21

What is E-cadherin replaced by in the neural tube?

Answer 21

N-cadherin replaces E-cadherin in the neural tube

Question 22

What happens to neural crest cells during migration?

Answer 22

Complex changes in neural crest cells during migration

Express cadherin 7 when they first migrate

Question 23

Selectin structure

Answer 23

Intracellular domain - anchored to actin (like which cadherins)
Extracellular domain – many repeated domains and unique domains at the end

Question 24

What s the role of selectins?

Answer 24

Major role in neutrophil trapping

• Cells become adhered to outside wall of blood vessel
• Cells keep rolling slowly - selectin dependent
• Once cells stop rolling they move between endothelial cells into tissue – integrin dependent

Question 25

What do selectins bind to?

Answer 25

Ca dependent binding

Bind carbohydrates on neighbouring cells

Question 26

Where do selectins bind?

Answer 26

Cell surface - single transmembrane domain

Question 27

Ca independent CAMs structure?

Answer 27

Can be extracellular or transmembrane

Question 28

What is the major part of the Ca independent CAMs family?

Answer 28

Neural cell adhesion molecules (N-CAMs)

Question 29

What do Ca independent CAMs mediate?

Answer 29

Homophilic binding

Interactions with ECM and between different cells

Question 30

Where do Ca independent CAMs come from?

Answer 30

Arise from alternative splicing and can undergo post translational glycosylation

Question 31

What do variable polysialic acid concentrations in Ca independent CAMs do?

Answer 31

More N-CAMS in immature tissue in the neural tube

Means there is less adhesion

Question 32

Summary

Answer 32

Expression of CAM’s is regulated
CAM expression correlates with migration and aggregation
CAM expression may delineate regions of a cell’s membrane