Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
22 Cards in this Set
- Front
- Back
|
1. What are three features along the D/V axis in the Drosophila embryo? What does this suggest regarding the time when the D/V axis is established?
|
-Egg shape (flatter on ventral side),
-Chorionic appendages (remember: PM, vitellin membrane, chorion), micropyle being positioned more dorsally. The fact that each of these is specifically positioned either dorsally or ventrally is evidence that the dorsal/ventral axis is established during oogenesis, otherwise there wouldn’t be a reproducible way to localize them. |
|
|
2. What are features that are along the D/V axis during the embryogenesis of Drosophila? How is this axis perpetuated in the adult fly?
|
-First is the GERM BAND which begins extending during gastrulation though mostly after.
-Second you begin to see the very transient PARASEGMENTAL GROOVES which disappear and the germ band retracts. -Then the PS grooves are replaced by the SEGMENTAL GROOVES (ventral), and the retraction of the germ band leaves bare amnioserosa on as the ventral-most aspect of the embryo. Finally you have DORSAL CLOSURE, where the amnioserosa is internalized, segmental grooves completely wrap around the embryo. |
|
|
3. What genetic evidence suggested that the maternal genome established the D/V axis during oogenesis?
|
All of the genes that form the dorsal ventral differentiation form in response to dorsal; a maternal protein.
“Mutations in maternally expressed genes alteres the D/V axis in the embryo (toll, dorsal, easter, spatzle, etc.) |
|
|
4. Why are eggs from Toll- mothers dorsalized? Where is the Toll receptor distributed on the surface of the egg? How is it activated?
|
Toll is a TRASNMEMBRANE PM ligand binding protein found in all cells in the early embryo. Inactive Spatzle (toll ligand) is uniform in the perivitelline, but the active form is localized to the ventral aspect because it is cut by the maternal protein EASTER, WHICH IS VENTRALLY ACTIVATED. Active spatzle binds to toll which causes dorsal protein to translocate into the nucleus. Direct correlation between concentration of active spatzle and nuclear dorsal concentration. Since dorsal protein is responsible for causing ventralization, toll- mutants have no way of allowing this ventralizing protein into the nucleus, and therefore are uniformly dorsalized. So in these embryos, dpp is expressed all over the place, and twist/snail are not expressed at all.
|
|
|
5. How is the ligand of the Toll receptor activated only in the ventral third of the egg? Describe the proteins involved.
|
EASTER is a protease that is activated in the VENTRAL third which cleaves and activates SPATZLE, which then binds to the toll receptor.
|
|
|
6. What is the effect of activation of the Toll receptor protein? What are the proteins involved in this pathway and what is the ultimate result?
|
Toll activates CACTUS KINASE, which phosphorylates CACTUS (the chaperone of dorsal), and thus allows the free dorsal protein to translocate into the nucleus.
|
|
|
7. What are the genes that are transcriptionally activated in the presence of: high dorsal nuclear protein, just under high dorsal nuclear protein, intermediate dorsal nuclear protein and low dorsal nuclear protein?
|
High Dorsal Protein -> Snail (DNA binding repressor that represses genes that would disrupt mesodermal determination t), Twist (activates genes that are necessary for cell shape changes to form ventral furrow/mesodermal cell determination, cytoskeletal stuff)
Just under High -> Sim Intermediate -> Rho Low -> Sog No Dorsal Protein –> Dpp, Zen |
|
|
9. What are three gene products that limit dpp protein to the dorsal apex of the embryo? How do they act on dpp?
|
Short Gastrulation (SOG) – intermediate dorsal conc. Binds/inactivates dpp
Twisted Gastrulation (TSG) – I’m guessing around the same area as sog. Binds/inactivates Tolloid (TLD) – degrades sog when bound its to dpp, thus releases dpp |
|
|
10. How is the Sog gradient refined and what cell type does it specify?
|
Sog is degraded by TLD, so its high point is in neuroectoderm, and low point is at the dorsal midline.
|
|
|
11. What are the four different cell types specified by the dpp/sog pathway along the d/v axis?
|
Mesoderm
ventral ectoderm(becomes neuroectoderm) dorsal ectoderm amnioserosa |
|
|
12. What are the dpp/sog homologs in vertebrates? What cell fates are associated with dpp, sog in invertebrates and BMP-4 and Chordin in vertebrates? What is the curious difference between the d/v axis in vertebrates and invertebrates?
|
In vertebrates:
DPP=BMP-4 (for memorization: in vertebrates, vertebrae bones ventral to spinal cord) SOG = Chordin (as in spinal cord) Additionally: TOLLOID = XLD TSG = TSG (same protein) BMP-4 and Chordin are both involved in determining the dorsoventral axis in vertebrates, however the vertebrate d/p axis is reversed relative to the invertebrate axis, which is evident in the fact that the vert. spinal cord is dorsal, while the invert. Is ventral. |
|
|
What does toll do?
|
Transmembrane receptor on PM of syncytial blastoderm. Activates cactus kinase.
|
|
|
What does spatzle do?
|
Toll ligand. Activated ventrally by Easter and spatzle processing enzyme. Uniform in perivitrelline space.
|
|
|
What does easter do?
|
Serine endoprotease. spatzle activator. Activated ventrally
|
|
|
What does dorsal do?
|
maternal TF that regulates the d/v zygotic genes. Translocation into nuclei regulated by toll/spatzle and is in gradient concentrated ventrally.
|
|
|
What does snail do?
|
ventrally localized. Inhibits genes that would interfere with ventralization.
|
|
|
What does twist do?
|
Activates genes that control invagination of mesoderm. (cytoskeletal stuff)
|
|
|
What does short gastrulation do?
|
Defines neuroectoderm from amnioserosa. binds/inactivates DPP. Bound SOG is degraded by tolloid
|
|
|
What does twist gastrulation do?
|
secreted by dorsal ectoderm to affect cells in dorsal midline. Also binds/ inactivates dpp.
|
|
|
What does tolloid do?
|
Metaloprotease/BMP-4 homologue. ENHANCES DPP function by processing somehow and degrades sog bound to dpp. Confining sog to neuroectoderm
|
|
|
What does decapentaplegic do?
|
Secreted morphoegen. Repressed by dorsal. Required for amnioserosa formation. Activated by UBX later in development to define position of antenna, wings, legs.
|
|
|
Where is zen
|
Dorsal area.
|
