DV axis by dorsal Flashcards
How were the genes important for determining DV axis determined?
Nusslein-Volhard and Wieschaus used mutants to identify genes. Fully ventralised when Dorsal present in nuclei of all cells. Fully dorsalised (shown by dorsal cuticle) when not in any nuclei.
What is the gene important for establishment of DV axis?
Dorsal
Where is Dorsal located?
Dorsal mRNA is delivered from nurse cells to oocyte. However, protein synthesis occurs 90 minutes after fertilisation - evenly distributed throughout the oocyte.
So how does dorsal act as a morphogen?
Despite being evenly distributed, dorsal can still act as a morphogen but in a slightly different way. It is translocated into the nucleus of ventral side cells only where it can activate or suppress transcription of certain genes.
What is the molecular pathway of the dorsal protein?
There must be another signal which triggers translocation of Dorsal.
- Gurken mRNA localised between oocyte nucleus and membrane
- It can only diffuse a short distance so only activate torpedo in dorsal cell which inhibits pipe
- Ventral cells therefore still produce pipe which is secreted
- Pipe interacts with Nudel which initiates three serine proteases - gd, snk, ea
- Nudel tethers and activates gastrulation defective (by cleavage)
- Gd cleaves Snake
- Snake cleaves Easter
- Easter cleaves Spatzle
- Spatzle binds Toll
- Toll activates Pelle
- Activate Pelle PK can phosphorylate cactus (bound to dorsal) so it is degraded
- Dorsal is free to to enter nucleus
How does this make gradient of dorsal?
Since signal transduction creates gradient of Spatzle highest in most ventral region, there is the most translocation of Dorsal to ventral cells nuclei.
What do high levels of dorsal induce?
Ventral mesoderm
- Twist, snail, rhomboid - these genes are only transcribed by high levels due low affinity enhancers for Dorsal
What do low levels of dorsal induce?
Dorsal amnioserosa
