4. D-V patterning in Drosophila Flashcards
What are the determinants of D-V patterning in Drosophila?
D-V determinants:
- nucleus pushed to one side in A -> determines D
- maternally deposited gurken in D
- PIPE RNA in V
How is the nucleus pushed in oocyte to pattern D?
In A-P organisation when microtubules reorganised - nulceus also pushed to a side which later forms D:
after microtubule reogranisation they take nucleus and push P->A on one side - that side will form D
HOWEVER not know if nucleus pushed to:
i) pre-determined D
ii) anywhere in A -> determines D
What was the experiment done to determine which of the two theories is followed when nucleus pushed to determine D?
HOWEVER not know if nucleus pushed to:
i) pre-determined D
ii) anywhere in A -> determines D
Experiment:
genotype produced which produces 2 oocytes -> 2 nuclei - observed the freq at which they were found at adjacent / 90 deg. / 180 deg. positions => seems like nuclear positions are independent - NOT going to a fixed site => hypothesis ii) probably correct - where nucleus ends up - determines D
Explain localisation of gurken in D determination
Once nucleus is moved to future D position - gurken RNA is transported by dynein (+) to (-) from P to A towards the nucleus location - translated into gurken protein - secreted to D surrounding follicle cells - determines those follicle cells as D
What is the role of gurken?
gurken determines D axis of oocyte: transported to the oocyte site where nucleus is located - gets translated into protein - signals surrounding follicle cells - defines them as D
What is gurken?
gurken - epidermal growth factor - signals follicle cells to become dorsal in oocyte D-V patterning
also used in other developmental processes at different developmental times
What maternal factor determines V?
PIPE RNA - located only in V side - indirect inhibition of PIPE by gurken - ex: if gurken deleted -> PIPE everywhere
What is the role of PIPE RNA?
PIPE RNA specifies V side in Drosophila oocyte by inducing secretion of a V cue into the vitelline membrane on the surface of late oocyte
That signal later in the embryo - syncytial blastoderm - activates SPATZLE which binds to TOLL membrane receptors -> Dorsal (DL) enters into ventral nuclei with V cue gradient => specifies D-V axis in embryo
What is the “Dorsal group” maternal effect genes?
“Dorsal group” maternal effect genes:
- spatzle
- nudel
- windbeutal
- pipe
- Toll
- dorsal (dl)
What are the ventral maternal effect genes?
Some V cue - unknown - in vitelline membrane - in perivitalline fluid
Perivitaline fluid contains polarising ventral signal
Some experiment determining what is secreted as the V cue into vitelline membrane
??
What zygotic gene expression do maternally deposited D-V factors activate?
Dorsal (DL) in V determines expression of:
- sog
- twist
- cactus
- snail
??
- dpp (BMP) - on in D but off in V <- because of dpp-sog diffusion and interaction - form a gradient to determine D-V
How is D-V patterning similar or different in other insects?
In Drosophila: initial cue - nucleus breaking symmetry - then determined by gurken, pipe, toll, DL, dpp (BMP)
Other insects: various different mechanisms of D-V patterning
=> Drosophila specific mechanism - didn’t originated in Diptera
Explain what influences morphogen gradient response
A response depends on:
- response threshold needed
- other morphogen interactions
- transcriptional regulation
Is Toll/Dorsal (DL) signalling specific to insects?
No, a very common signalling mechanism in animal immune systems - sensing for pathogens => but in Drosophila embryos used for D-V patterning
Toll - receptor
Dorsal (DL) - activated as a response
