L12: Branching Morphogenesis 1 Flashcards
Why is branching effective?
- Increase surface area for metabolic exchange while minimizing volume
- Enable targeted delivery of nutrients while maximizing cell to cell contact
What are three main types of branching with examples?
- Single cell extension. (neurons)
- Collective cell migration (trachea)
- Non migratory mechanisms
What molecules acts as the internal guiding cue for filopodia retraction/extension?
++ pMLC leads to retraction through severing f-acting.
– pMLC and anchoring leads to extension
What are some positive external cues for neural path navigation?
- Nerve growth factor
- Brain derived growth factor
- Netrin
What are some negative external cues for neural path navigation?
- ephrin
- slit
NGF or BDGF pathway
> Receptor Tyrosine kinase > PI3K > PIP3 > GEFs > activate Rac > actin poly
Netrin Pathway
> activate FAK/src
activate Rac/Cdc42
acting poly
Which molecule does slit activate for actin depoly?
cofilin
Three reasons why drosophila trachea system is studied?
- very simple model (~50genes, ~1600 cells)
- Well documented
- fluorescence microscopy
What are 3 stages of Tracheal development?
- cell commitment
- tracheal pit formation
- primary branching
What is the earliest sign of cell commitment?
Expression of Trh
How many placeodes are formed and how are they distributed?
20 bilaterally
Which sort of cell movement occurs during tracheal put formation?
Invagination
During invagination in pit formation, cells on which side forms the pits?
dorsal
Trh pathway?
Trh > EGFr > Rho-GAP > Apical acto-myosin enrichment > cell constriction (trapezoid like look) > cell invagination
Which element in the Trh pathway is self inhibitory?
EGFr / Trh / Rho-GAP
EGFr
Do cells divide after invagination?
No
Name some receptor tyrosine kinases
FGFr
How many cells are usually in the primary branch?
4-20
What is the earliest sign of cell commitment?
Expression of Trh
How many placeodes are formed and how are they distributed?
20 bilaterally
Which sort of cell movement occurs during tracheal put formation?
Invagination
During invagination in pit formation, cells on which side forms the pits?
dorsal
Trh pathway?
Trh > EGFr > Rho-GAP > Apical acto-myosin enrichment > cell constriction (trapezoid like look) > cell invagination
Which element in the Trh pathway is self inhibitory?
EGFr / Trh / Rho-GAP
EGFr
Do cells divide after invagination?
No
Name some receptor tyrosine kinases
FGFr
How many cells are usually in the primary branch?
4-20
How many stereotypical positions for cell migration is there in primary branches?
6
FGFr adapter protein is called
Dof
Which chemoattractants are the 6 primary branches moving towards?
- FGF
- WG
- BMP
[T/F] Suppression of FGF through only FGF mutation (bnl) causes issues in tracheal development.
False. Any mutations in FGF signalling (i.e. FGFr mutant btl) can cause issues.
How many types of FGF in drosophila?
3
How many types of FGF in humans?
22
What are some cellular mechanism FGF is used for?
Branching Patterning Differentiation Cell proliferation Cell survival
How many types of FGFr in drosophila?
2
How many types of FGFr in humans?
4
[T/F] FGF is a powerful chemoattractant that promotes cell extension to the direction of the FGF source.
True
FGFr adapter protein is called
Dof
Describe one pathway downstream to FGF
FGF > bind to FGFr > Dof (adapter) >
> Grb2/drk > Sos > phosphorylate Ras >
> src64 >
> Raf > MEK/Dsor > MAPK/erk > Pnt + Ap1
What is one possible explanation of the FGF source locations being the same in every scenario.
Global segment patterning system
[T/F] Activation of Raf is essential to FGF signalling pathway
True. Raf is the only protein that can activate MAPK and lead to transcription factor Pnt to be activated
In a normal circumstance where placeodes are already formed, do the pit formation mechanism also follow? Why?
Yes it does. Trh which leads to placeodes, also activate btl, dof and rho
Which 3 proteins are produced downstream of Trh>
btl, dof, rho
What are the cells closest to FGF sources called?
tip cells
How many tip cells follow FGF sources in primary branching?
2
[T/F] FGF leads to lamillepodia formation in tip cells
False. Filopodia is formed
Can filopodia formation be rescued with ectopic insertion of FGF?
Yes
[T/F] There is a pulling behaviour by tip cells on cells in the back.
True
What is one possible explanation of the FGF source locations being the same in every scenario.
Global segment patterning system
How many secondary branches come from 1 placeode?
~24
[T/F] All secondary branches merge with neighbouring secondary branches.
No. Only fusion cells are responsible for that. T
How many fusion cells per placeode?
~5
When in AEL do secondary branches start growing?
~10
When in AEL do fushion cells start growing?
~10-12
Describe how FGF expression is different in 2* branches compared to 1* branches.
In 2* branches, FGF sources are dynamic. The FGF concentrations come in multiple concentrations at different time intervals. The sources also move slightly farther in each interval. The second wave causes 2* branches.
3* branches are formed in response to what?
hypoxia
Sprouty inhibits what?
Tyrosine Receptor Kinase signalling
What problems are seen in the absence of sprouty?
Excessive 2* branches in wrong time and place
[T/F] Branching is followed by physical and adhesion molecules, other than just chemoattractants
True.
Draw the reiterated pathways for 1/2/3* branching.
Which transcription factor is needed for 2* branching
pnt
Which transcription factor is needed for 2* branching
blistered