Lecture 14 Drosophila appendage development Flashcards
What does the wing disc consist of?
- Dorsal part essentially forms the back and the shoulder
- Hinge area connects the wing to the shoulder/body wall
- Wing pouch that makes the wing proper (in blue)
What process results in the discs unfolding into their adult shapes? What is the result of this?
Eversion
As a result of eversion, surface area increases massively, but the height reduces
What happens to the cells of the wing pouch?
Cells of the wing pouch go from being columnar epithelium to squamous epithelium.
How are X-Y axes established in the wing disc?
Morphogen gradients.
The cells within the gradient, read their position in that gradient and take on different cell fates depending on the position on these axes.
Engrailed is what type of gene?
Segment polarity gene
Engrailed defines what?
It is a TF that defines the posterior compartment
What are doesn’t express engrailed?
Anterior portion
Presumptive imaginal discs inherit their A/P identity from…
the segmentation machinery
The expression of engrailed in the P part of the imaginal disc is set up within the first … hours of embryogenesis but…
Expression of engrailed in the P part of imaginal discs is set up within first 3 hours of embryogenesis, but maintained for the rest of the life
Why is Hh signalling not switched on posteriorly
To be competent to respond to hedgehog, cells must also be expressing Ci (as Hh blocks its expression). Therefore, in the P, although there is Hh, there is no Ci, so signalling cannot be switched on.
What is the expression of Hh signalling pathway A and why?
- In the anterior, there is Ci, but there is no engrailed present and so no Hh ligand. Engrailed prevents posterior cells from responding to their own Hh
Where is Hh pathway activity seen and why?
Pathway activity is only seen in the stripe of cells slightly anterior of the A-P border where there is Ci AND Hh which has diffused across the AP border. Because Ptc is a target gene of Hh, it is upregulated slightly anteriorly too i.e. cells in the anterior compartment CAN respond to Hh made posteriorly
Describe the pathway of Dpp
- Dpp is a secreted ligand of the TGF-beta superfamily
- It is an EC ligand and binds to and activates Type 1/11 receptor heterodimers Tkv/pnt
- These R’s phosphorylation a TF, Mad to form the active version, p-Mad
- p-Mad activates omb/sal but inhibits brinker
Describe a clone that is ptc-/- and dpp -/-
Hh pathway is switched on but there is no dpp to respond to Hh. Without ptc, Hh diffuses further through the tissue until it finds WT cells where normal development occurs to form. Patched binds to hh and is the pathway receptor. Dpp expression shifted anteriorly.
Demonstrates that Hh physically binds to the patched receptors
Wingless is a …
secreted signalling molecule
