5b Flashcards
Drosophila oogenenis
Cystoblast: daughter cell of stem cell undergoes 4 mitotic divisions
-16 cells now two, one of the two with four connections becaomes the oocyte
-other 15 become polyploid nurse cells that feed the oocyte so gene products are dropped here
-15 cells called ring canal
stage 10 drosophila
The localization of oskar, bicoid, and gurken mRNAs in the Drosophila oocyte defines the anterior-posterior and dorsal-ventral axes of the embryo.
n situ hybridizations to oskar (top) forms abdominal and germline determonntn, bicoid(middle) forsm head and thoraxand gurken (bottom) sets up axis (DV or AP) mRNAs in stage 10 Drosophila egg chambers.
What establishes oocyte ap polarity
gurken gene
-made by nurse cells and transported towrds oocyte nucleus,
found betweel oocyte nucleus and oocyte membrane
-follicles habe receptor for gurken
gurken = epidermal growth facotor
-follicles send signal back to oocyte which recruits par 1 protein, which organizes microtubules such that their plus ends are posterior
What is par 1
in drosophila, regulates microtubules cytoskeleton
Motor proteins
use atp to drive changes, hydrolysis of atp is dependent on attachment of cytoskeletal filament
-proteins mediate movement of filaments against eachother and /or can transport cargo along a filament, using filament as a track
-all motor proteins that move on actin are myosin family members
Kinesins: move towards plsu end
dynesin: move toward negative
What end are plus ensd found on and in relations to oskar mra movement
posterior,
so oskar mrNA is transported by kinesin (moves to plus end)to the posterior end
only in posterior oocyte OKSAR is translated and it recruits more par1 which reinforces microtubles organization
causes posterior pole to be distinctive (POLE PLASM) contains determinants for producing adominal segemnts of embryo and germ cell determinants
what is the AP polarity oocyte mt polartiy
anterior end (negative) so dyneines move things here
posterior end (positive) so kinesins move things here
cargo can be tied on to specific motor proteins so this can bring things to either end
using this
BICOID mRNA is moved to oocyte anterior by dynesins
Nanos mrna localized to posterior (bc its bound to oskar)
Dorsal Ventral polarity
as it grows, nucleus of oocyte moves to anterior dorsal potion
Gurken used again to have localized expression between nucles and oocytem membrane to form gradient
What causes ventralizatin of eggs and embryos
maternal mutants of gurken
or
torpedo mutants
Where is gurken activity required? Torpedo?
Gurken: oocyten (germline cells)
torpedo: follicle cells (somatic cells
-neeed for proper dorsaliztion of egg and embryo
-if there is a mutant in torpedo: we would have an entirely ventral embryo
-this isa maternal mutant,so if the mothre had a mutation of the gene b ut the children don,t it would still result in an entirely ventral egg
-if the maternal was heterogenoously effected and so was the paternal,and the offspring has mutant, the offspringwould not have any disruptions since the mother had one good working gene
pole cell transplants and germline/somatic mosaics
sucessful mosaic means that the egg develops properly with germ cell adn somatic cells
saying that u can use a donor that has a genetic mutation and implant it in pole into a embryo that does have the mutation and the donor cells would do their job and create a sucessful mosaic with the donor cells being the germ cells and the somatic cells developing from follicle
dorsilization
-binding of gurken (ligand) to receptor torpedo starts cascade that lead tothe creation of the dorsal/ventral axis
-activated torpedo->activates Mirror which inhibits pipe (pipe is only found where there is no gurken signal (ie ventral cells)
pipe when it is thereis secreted into the ventral side of vitelline envelope, results in protease activity only on ventral side of embryo
pipe modifies the ventral vitelline membrane – creating a positional cue
What does gurken and torpedo do
if mutant torpedo is found in somatic cells: ventralized so we need unmutated torpedo in somatic cells tohave normal development
if mutant gurken is found in germ line: ventralized so we need unmutated gurken in germ line to have normal development
what does no gurken mean for dorsalization
no gurken means thats gurken as a ligand wont bind to torpedo receptor, so mirror wont be activated and pipe would be on, meaning that the sulfation of viteline envelope will occur everywhere so sulfated viteline envelope develops on both dorsal and ventral side. SO VENTRAL FATE IS THE OUTCOME
If the Gurken signal is not present, the signalling pathway is off and ventral fate is the outcome
when there is gurken , pipe is off so the sulfation of the vitilline envelope will not really be there on dorsal side leading to dorsalization
WHAT DOES LESS SULFATION OF THE VITELINE ENVELOPE MEAN
DORSAL FATE ALLOWS FOR THE SPECIFICIATION OF THE DORSAL AND VENTRAL CELL FATE
MEANS THAT IT WOULD BE LESS ON DORSAL SIDE SO ITS NOT VENTRAL FATE
VENTRAL FATE IS WHEN THERE IS NO PRESENCE OF GURKEN AS A LIGAND
