Chapter 2 Flashcards
Syncytial:
A cell with multiple nuclei
How does the fly egg start the initial steps of development?
The cell becomes syncytial (multi-nucleated) through a series of synchronous nuclear divisions without cytokinesis. This allows transcription factors to be used and diffused through the cell and act as an effective early morphogen.
Ventral Furrow results in :
The internalization of the mesoderm
How does the dorsal ventral axis of a fly compare to that of a vertebrate?
It is inverted from ours. So a flies spinal cord is located on the ventral side.
Imaginal disks
Grow into the parts of the adult fly
Bicoid :
Maternal.
Sets of the cascade of anterior patterning.
Acts as both a transcription factor for gap genes and a specific translational inhibitor of caudal.
Nanos :
Sets of the cascade of posterior patterning
Acts as translational inhibitor of hunchback.
Torso :
Specifies the most anterior and the most posterior tips of the embryo.
Torso is a receptor tyrosine kinase (RTK).
Toll :
A toll like receptor (TLR), it is universally expressed in all cells
Maternal Bicoid and Nanos come in what form?
mRNA
How many independent genetic systems divide the anterior-posterior axis. How many divide the dorsal-ventral axis?
A-P : 3 independent systems ~50 maternal genes
D-V : 1 independent system
Define an independent system?
The loss of genes in this system does not affect the development of other systems. So there a 3 seperate ways to lose function in development of the A-P axis. While there is only one way to lose function in the D-V axis.
Maternal genes :
The embryo does not need to express these genes, only the mama.
The products of these genes will activate gap genes.
What genes do the products of maternal genes directly activate?
Gap genes.
Are nurse cells somatic or germline cells?
Anterior or Posterior?
Nurse cells are germline.
Anterior
Are follicle cells somatic or germline?
Anterior or Posterior?
They are maternal somatic cells
Surround the oocyte almost completely, however, there are some breaks at the anterior side of the cell, so follicles are more towards the right side of the cell.
The follicle cells will deliver the actual products used by maternal genes. (I believe)
In a female, the most anterior haploid germline cell will ______.
Develop/form an oocyte.
What is the importance of more mature germ-line cells signaling to less mature ones?
They help to set the A-P axis. The side of the oocyte closest to the more mature cells will be posterior. Signaled through a stalk which attaches the cells.
How are maternal mRNAs isolated onto one axis of the cell or another?
These mRNAs are moved across microtubules in order to isolate them onto one side or the other. (since one side of the microtubule is warm and one side is cold)
How can you determine that bicoid expression is a anterior morphogen?
You could make a loss of function for bicoid. The morphology of the anterior should change but not the posterior. You could then place bicoid in your loss of function embryo which and see if anterior characteristics develop there.
When is maternal mRNA for bicoid translated?
After fertilization.
Where is maternal mRNA localized? What forms the actual conc. gradient?
Anterior, translation of the mRNA forms actual gradient, meaning the protein product of translation.
Nanos :
Nanos mRNA is concentrated in the posterior of the embryo. When it is translated it acts as a translational inhibitor of hunchback mRNA.
Is hunchback maternal or zygotic?
Trick question! Hunchback is both maternal and zygotic.
How does maternal hunchback behave?
The mRNA for maternal hunchback is equally distributed throughout the embryo. But once translation is signaled areas with Nanos block the translation of Hunchback, Resulting in Hunchback protein being concentrated in the anterior of the cell. Hunchback specifies for anterior characteristics.
How does maternal hunchback behave?
The mRNA for maternal hunchback is equally distributed throughout the embryo. But once translation is signaled areas with Nanos block the translation of Hunchback, Resulting in Hunchback protein being concentrated in the anterior of the cell.
Hunchback specifies for anterior characteristics.
What occurs if the mother is Nanos-/hunchback-
Nothing out of the ordinary, the embryo develops normally
Caudal :
Maternal
Caudal mRNA is spread equally throughout the embryo
Caudal mRNA is translationally inhibited by Bicoid. This causes the protein to be concentrated in the front of the embryo.
perivitelline space:
The space between the oocyte and the Zona pellucida. The Zona pellucida is a glycoprotein coat which surround the embryo/oocyte.
Trunk :
Is the precursor to the ligand which activates the torso (RTK). Trunk is present in equal abundance throughout the entire perivitelline space.
How is torso activated only at the anterior and posterior poles?
Because only at these termini do we see trunk-specific protease activity. So only at the termini is torso RTK receptors bound to by there ligand.
Dorsal :
A transcription factor specifying ventral morphology.
Present in a concentration gradient, but not a cellular one, a cell nuclei based gradient. It is in roughly constant concentrations from cell to cell, but it is more concentrated in the nuclei of ventral cells.
When is dorsal concentrated into a nuclear gradient?
It is concentrated in the syncytial blastoderm. The mechanism may continue after the cell is no longer syncytial I do not know.
Spatzle :
Spatzle is the pro-protein (unactive form) or a protein which will be cut to form the ligand for Toll. Spatzle is located uniformly throughout the perivitelline space
Cactus
Cactus binds to Dorsal, and covers its nuclear localization signal one-one inhibition. If Cactus is phosphorylated, it is marked for degradation. Once gone, Dorsal will be localized to the nucleus.
What happens when spatzle fragments bind to Toll, in the perivitelline space.
The other end of the toll receptor carries out a process which results in phosphorylating cactus kinase. Cactus kinase phosphorylates cactus. Cactus can no longer bind to Dorsal once it is phophorylated, because it is busy being degraded. Dorsal, not bound by cactus, has a revealed nuclear localization signal and is therefor sent to the nucleus.
Dorsal acts as an _______ for Twist and an _______ for DPP (Decapentaplegic gene).
Activator (with low affinity binding sites)
Repressor (with high affinity binding sites.
Dorsal activates twist with a ____ affinity binding site. So what concentrations of Dorsal will Twist be active under?
A low affinity site. Therefore high concentrations of Dorsal are needed to activate twist.
Twist will be active on the ventral side of the embryo.
Dorsal activates DPP with a ____ affinity binding site. So what concentrations of Dorsal will DPP be active under?
High affinity. Therefor concentrations of Dorsal must be very low before DPP activity is seen. DPP is found in the dorsal region, and must cause activation of dorsal morphologies.
Will we see a gene active between Twist and DPP? Why or why not?
No. Because Twist has such a low affinity, and DPP has such a high affinity, we will see nothing in the middle ground between them.
If an embryo is a dorsal loss of function, what would the expression of DPP and Twist look like. Also what would be the morphology affect?
DPP would be expressed everywhere because its inhibitor is gone.
Twist would not be expressed at all lacking its activator.
The entire embryo would be dorsal morphology.
If an embryo greatly overproduces Dorsal, what would the expression of DPP and Twist look like. Also what would be the morphology affect?
DPP would be inhibited everywhere.
Twist would be expressed everywhere, if Dorsal is high enough, which it is since this is my hypothetical situation.
Morphology would be ventral, everywhere.
Dorsal Activates :
with what affinities
Twist (low affinity)
Snail (low affinity)
Rhomboid (medium affinity)
Twist activates :
Twist
Snail
Snail deactivates :
Rhomboid
From ventral to dorsal we see which genes expressed due to dorsal?
Ventral – Twist & Snail – Nothing – Rhomboid – DPP – Zerknullt (don’t learn) – Dorsal
What type of genes does Dorsal inhibit?
Dorsalizing genes.
What type of protein is DPP?
DPP is a ligand a TGF-Beta (transforming growth factor beta) ligand
What does SOG do?
Sog binds extracellularly to DPP, it inhibits DPP, and stops it from acting as a ligand. It is present up to the point where rhomboid stops, so it is likely activated by Dorsal.
