Morphogens Flashcards

1
Q

What is the definition of a morphogen?

A

A soluble secreted molecule which acts at a distance to specify the fates of cells. A morphogen may specify more than one cell type by forming a concentration gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is morphogenesis?

A

The creation of shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Which two people suggested the presence of morphogens?

A

AM Turing - The chemical basis of morphogenesis 1951

Lewis Wolpert - Positional Information and the Spatial Patterning of Cellular Differentiation 1969

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

A morphogen could either be….

A

An instructive signal
OR
A permissive signal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How can we test if a ligand is a morphogen?

A

Using ectopic expression:
Morphogens cause a mirror image to be created if expressed ectopically
Eg ZPA in the chick limb bud creates a mirror image as Shh is a morphogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What would happen if you exposed all cells to the same level of morphogen?

A

All cells would acquire the same fate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the two models for how morphogens move through tissues?

A

1) The ligand diffuses from the source cell

2) There is a ‘bucket brigade’ ie like chinese whispers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How can we show the bucket brigade system is not use by morphogens?

A

Test 1) Use genetic engineering to make the proposed molecule juxtacrine
This would not affect ligands using the bucket brigade model but the cells do not acquire their normal fates showing that morphogens diffuse
Test 2) Make a genetic mosaic that lacks a receptor for the source signal in one of the cells
All cells differentiate except the one without the receptor - if the BB system was used there would be no effect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How can the morphogen gradient be enhanced?

A

Morphogen binds to molcules in the ECM eh heparan sulphate proteoglycans

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is it called when morphogen gradients are made steeper?

A

Restriction diffusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How else could the gradient be made steeper?

A

Rapid degeneration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

HSPGs can also be called what?

A

co-receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do HSPGs regulate morphogen diffusion?

A

Sequestering or slowing diffusion eg BMP

Facilitating Diffusion eg Hedgehog

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is planar transcytosis?

A

Plays a role in establishing gradients when a pit forms in the cell membrane and engulfs the morphogen in a vesile

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the evidence for planar transcytosis in Dpp signalling?

A

Antibody staining shows Dpp is found in vesicles

Mutations that block vesicle formation cause Dpp to act in a juxtacrine manner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly