Lecture 28

Question 1

Give a classical example of where cell adhesion was studied

Answer 1

H.V. Wilson in 1907 identified that the cells of sponges can re-aggregate following dissociate from each other. Interestingly this was seen in a species dependent manner whereby cells of the same species would clump together sorting themselves into species

Question 2

Transfection of L cells with cadherin family genes causes what

Answer 2

Homophilic binding between L cells expressing the same cadherins leading to adhesion

Question 3

What are the two families of cell adhesion molecules

Answer 3

Ca2+-dependant and Ca2+ independent

Question 4

Give an example of where cell adhesion molecules such as cadherins have roles other that in cell adhesion

Answer 4

VE-cadherin inactivation due to mutations causes abnormal vascular development and apoptosis of endothelial cells, indicating that it has roles in signalling

Question 5

Explain the role of selectins in neutrophil trapping

Answer 5

The amount of selectins can be changed in endothelial cells and expression of them is found to be increased in an immune response. Selectins act to catch lymphocytes near to the site of inflammation which ultimately leads to an increase in diapedesis (crossing of the lymphocytes over the vessel wall).Catching by selectins allows other CAM molecules also present in the lymphocytes to adhere with the corresponding CAMs of the endothelial wall. This allows the lymphocytes to cross the vessel wall into the site of inflammation

Question 6

Complex changes in selectin expression accompany the migration of neural crest cells, T or F

Answer 6

F – changes in cadherins do

Question 7

What is seen if the cells of embryonic tissues that have been separated are reintroduced

Answer 7

They also re-aggregate into distinct clusters consisting of cells of the same type

Question 8

What is significant about the number of genes involved in N-CAM expression

Answer 8

All of the N-CAM family of cell adhesion molecules are derived from a single gene. The original N-Cam transcript is subject to a vast array of alternative splicing and post translational glycosylation

Question 9

What is meant by graded sorting

Answer 9

By varying the degree and levels of cadherin family gene expression, you can influence the degree of sorting of the cells expressing these genes

Question 10

What can happen as a result of a failure of cell migration

Answer 10

Cell, tissue and organism dysfunction and death

Question 11

Larger re-aggregates of cells tend not to reorganise due to the number of different interactions, T or F

Answer 11

F – in fact large re-aggregates do show organisation into distinct clusters based on cell type. In addition, these clusters begin to show regionalisation where particular cells have stuck together

Question 12

What class of intracellular signalling proteins important in development have been found to bind to the intracellular domain of cadherins

Answer 12

Catenins (B-catenin)

Question 13

What is the major family of Ca2+-independent CAMs

Answer 13

Neural cell adhesion molecules (N-CAMs)

Question 14

Selectins are another type of cell surface membrane, Ca2+-dependant adhesion molecules. What attributes of cells do selectins recognise in order to elicit adhesion

Answer 14

Selectins recognise particular carbohydrate groups on proteins in neighbouring cells

Question 15

Explain the role of polysialic acid in N-CAM adhesion

Answer 15

N-CAMs show variations in the amount of polysialic acid present as a post-translational modification. More post-translational modifications and polysialic acid is found in immature neurons which results in less adhesion

Question 16

What happens following Ca2+ binding to cadherins

Answer 16

Causes a conformational change allowing interactions between cells

Question 17

What is the significance of hypervariable protocadherins

Answer 17

These CAMs are thought to have roles in specifying synapses as wells as mediating neurite self-avoidance

Question 18

Describe the basic structure of cadherins

Answer 18

Integral membrane glycoproteins that are 720-750 amino acids in length

Question 19

Monoclonal antibodies have been instrumental in identifying the vast array of CAM variants due to their ability to their ability to distinguish between very similar proteins. Explain how monoclonal antibodies are made

Answer 19

Firstly, the specific antigen (protein or epitope) is injected into a different animal so that these animals mount an immune response. After a certain period the animals are euthanised and the lymphocytes are extracted from the spleen. These lymphocytes will be the cells synthesising antibodies for the target antigen and are fused with lymphoma cells to create hybridoma cells. Lymphoma cells are used as they are hyperproliferative and can survive indefinitely whereas the extracted lymphocytes dies quickly outside the body. They hybridoma cells are selected for due to their ability to survive in harsher mediums. Once isolated the hybridomas are separated into wells containing one cell each. These cells are then allowed to proliferate and give rise to a clonal population of cells all expressing exactly the same antibody targeted for a single epitope of the target protein.

Question 20

Explain the significance of E and N-cadherin in the development of the early nervous system

Answer 20

Initially, only E-cadherin is expressed in the early embryo. However, newly formed mesodermal cells produced during gastrulation lose E-cadherin expression. Once the neural tube has formed this E-cadherin expression is replaced by N-cadherin

Question 21

To which CAM family do cadherins belong and what are the other subfamilies are there

Answer 21

Cadherins belong to the Ca2+-dependent CAM family along with selectins and integrins

Question 22

Cadherin family proteins only contain one Ca2+ binding site, T or F

Answer 22

F – they contain multiple

Question 23

What are L cells

Answer 23

L cells are a cell line used for investigating cell adhesions. This is because they do not express any of the cadherin family of cell adhesion molecules

Question 24

Give an example of where cell adhesion and migration play a vital developmental role

Answer 24

Formation of the early neural tube, the neural crest cells are required to detach from the dorsal neural tube, migrate, re-clump and then differentiate

Question 25

How do selectins bind to target cells

Answer 25

The lectin domain of selectin binds to sugar groups present on the surface of these cells