Cell Siganlling In Embryo

Question 1

Induction process basic

Answer 1

One cell type induced change in another cell type
Secrete signalling molecules
Bind neighbouring cells receptors (can only respond if expressing right receptor)
Signal transfixed by receptor (confirmations change)
Results in change in expression profile of cell (phosphorylation signalling cascade - ends in in/activation of TFs)
Signalling cascade if conformational changes
Activation of second messengers - go between of receptor and nucleus
End of cascade something passes to nucleus and changes transcription

Question 2

ECM and signalling basic

Answer 2

ECM between cells
Mesh work of molecules
Signalling molecules need to diffuse through - won’t be free diffusion
ECM encounters alter - help or hinder- the diffusion

Question 3

FGF signalling

Answer 3

Homodimer receptor
Ligand binds
Dimerisation of receptor
Begins the cascade
Ends up at protein MEK and ERK
Pass through to nucleus and bind DNA alter transcription

In Several subfamilies of these signaling pathways eg FGF fibroblast growth factor The receptor Tyrosine kinase is itself ohospgoruykras and can phosphorylase the cascade

Question 4

Activin TGF-beta/Smad signalling

Answer 4

Heterodimer receptor
Used Smad
Ligand is a diner
Diffuses to meet receptor and causes receptor dimerisation into heterodimer
Phosphorylation of receptor
Leads to Smad intermediate molecule phosphorylation
Smad 1.5 first activated
Causes dimerisation with Smad 4 - universal Smad dimerises with others
Allows transfer to nucleus and altering of transcription

Each event in this pathway is activation events
Compared to WNT signalling

Question 5

Wnt signalling

Answer 5

Also includes antagonists of signalling secreted to ECM that can suppress signaling

When normal WNT ligand binds to 7 pass receptor
Receptor binds Dishevelled protein
In absence of WNT signalling Dishevelled can activate a certain protein complex
In presence of WNT this protein complex is suppressed

This protein complex degrades beta cafe in
So WNT binding causes beta fate in degradation to be suppressed
So beta catenins can go to nucleus and activate TFs

Question 6

Hedgehog signalling

Answer 6

Unbound Patched receptor inhibits Smoothened protein
Hh binds Patched and prevents this smoothened inhibition

Smoothened is now active
Cleaves Ci complex
Whole uncleaved Ci complex can go to nucleus and recruit CBP TF

Cleaved Ci blocks transcription as binds DNA but doesn’t recruit factors (recruiting but cleaved from binding bit)

So Hh binding receptor activated transcription

Question 7

Paracrine signalling

Answer 7

RTK
TgfBeta
WNT
Hh
All Paracrine signalling
Signaling to nearby cells

Question 8

Juxtaxeine signalling

Answer 8

Notch eg

Signaling only the neares next door neighbours (joined cells ig)

Question 9

Notch signalling

Answer 9

Delta ligand on one cells membrane
Notch receptor on the other
Delta binds notch and stimulates a conformational change
Makes it accessible to protease which cleaves intracellular part of notch
This part of notch can go to nucleus and activate transcription

Question 10

Endocrine signalling

Answer 10

V far range
Hormones Through blood eg
Targets all cells with the correct receptors to bind signal

Question 11

Steroid signalling

Answer 11

Endocrine
Ligand itself is small/hydrophylic
Passes through membrane
Binds to an intracellular receptor which is activated and does to nucleus to act as a TF and alter transcription

Question 12

Fate map of xenopus pre gastrulation mesoderm

Answer 12

On diagrams

Question 13

Pattering of mesoderm basic

Answer 13

Band in middle of pre gastrulation xenopus will become mesoderm
Notochord - ends up under neural tube
Blood - underneath belly on ventral side
Muscle - either side of neural tube

The mesoderm cells that make up the notochord pattern the rest of the mesoderm cells

Question 14

How does notochord pattern mesoderm

Answer 14

Transplant notochord region cells ectopicsly into blood region then it causes development of muscle cells there

Muscle cells get a Paracrine signal whereas blood ones don’t
Also has a top muscle and middle muscle fate too - MORPHOGEN GRADIENT in the Paracrine signal
(Morphogen - signal that has diff action at high and low concs)

But is not actually a morphogen even though it resembles it
It is a signalling relay

Question 15

How does different concentration of morphogen give a different effect

Answer 15

In practice
The individual receptors are either on or off

It’s the affinity of the DNA sequences for their TF binding sites that causes this
Lots of signalling = more receptors bound and on = more cascade events = more end part of pathways going into the nucleus = more active TF in nucleus = higher chance of low affinity DNA region to be activated

Question 16

Signalling relay

Answer 16

When notochord signalling induces muscle fate differentiating eg
Then those muscle fates cells induce neighbouring cells into bottom muscle

Signaling relay

Question 17

Patterning feathers in the extoderm

Answer 17

How to achieve the regular spaced pattern in feather promordia

Down with variation of juxtacrine signalling:
Lateral inhibition
Using the Notch signalling pathway

Question 18

Lateral inhibition using notch

Answer 18

Activation of notch receptor leads to up regulation of notch receptor and negative regulation of delta (ligand) in that cell

Used un drosophila neurogenesis

Question 19

Drosophila neurogenesis

Answer 19

All cells have potential in beginning to become neural cells
One just happens to become one by having more notch signalling than those around it
Higher notch signalling reinforced due to notch activation in this cell uotefuating the receptor and down regulating delta

Causes this cell to become one thing (neural progenitor)
And the cells around it to become another (higher notch in the first cell causes these ones to get delta up and notch down)
-this causes other cells next to these ones to go up notch and down delta

This repeats to form the regular pattern

Question 20

Signalling pathway conservation

Answer 20

Around 300 cell types in adult
Many signalling pathways would be needed for these and all the other ones in development to control these inductive events

So the same signalling pathway is recycled in different contexts

Context is v important sir he receiving molecules that the target cell has is as important to the response as the secreted signalling molecule

Question 21

Expression of hedgehog gene in diff stages in chick

Answer 21

Early chick embryo- Hh signalling patterns limb bud (posterior) and is expressed in notochord

Later patterns the feathers in the ectoderm

Question 22

How do we know about signalling pathways

Answer 22

Mutations in cancer
Genetic screens that cause mutations -sensitised mutations

Question 23

Screens for enhancers/suppressors if phenotype (signaling pathway stuff)

Answer 23

Mutantion I’m signalling pathway component that gives a viable BUT obvious mutant phenotype

Random mutagenesis in strain

Screen for mutations that suppress or enhance a certain phenotype

Question 24

Rough eye phenotype in flies

Answer 24

Cause: overwxpression of Egf receptor inhibitor -Argos

Mutation in sprouty sty gene acts as dominant suppressor of this rough eyed phenotype

Have two mutations come together to affect phenotype

Suggests a signaling pathway

Can find through enhancer and suppressor screen: components of signalling pathways