13 Flashcards
What establishes the dorsal-ventral axis in a Drosophila embryo?
Gastrulation
How is Dorsal maternal mRNA distributed throughout the embryo?
Uniformly throughout the syncytial blastoderm
True or False: Dorsal protein is translocated evenly into nuclei on the ventral and dorsal side of the embryo?
False: Dorsal protein is only translocated into the nuclei on the ventral side of the embryo
What does Dorsal protein act as?
A maternal effect gene and morphogen
Why is Dorsal protein translocated into the nuclei in some but not all parts of the embryo?
Because in the dorsal side of the embryo, Cactus creates a complex with Dorsal in the cytoplasm which keeps it out of the nucleus. Ventrally, Cactus is degraded, leaving Dorsal free to enter the nuclei.
Name the vertebrate homologs of these Drosophila proteins: Dorsal, Toll, Gurken, Torpedo, Dpp, Sog, MAD
Rel/NF-kB transcription factor, Toll-like receptors, Epidermal Growth Factor, Epidermal growth factor receptor, BMP4, Chordin, SMADs1/5
What is the role of Gurken in dorsal-ventral patterning?
Gurken is an RTK ligand and after establishing anterior-posterior (helped anchor), the mRNA becomes localized between the oocyte nucleus (which has migrated anterior and dorsal) and cell membrane, and the protein product forms an ant-post gradient on the dorsal surface of the oocyte. It only diffuses a short distance, so it only signals to the closest follicle cells to the oocyte nucleus through Torpedo to become columnar dorsal follicle cells.
What happens in Dorsal mutants who have Cactus undegraded everywhere in the embryo? What about when it’s degraded everywhere? What mutation causes the former?
When Cactus is expressed everywhere, the Dorsal protein cannot enter any nuclei and the embryo becomes dorsalized, looking almost like a hydra with two heads. When Cactus is degraded everywhere, the Dorsal protein enters all nuclei and the embryo becomes ventralized with dendricles everywhere. A homozygous mutation in Snake will cause the former.
How is Dorsal protein related to invagination?
The cells with the most Dorsal protein in them (ventral cells) invaginate to form the mesoderm because Dorsal turns on Twist, which is a TF that specifies mesoderm cells.
What are the steps of Gurken mediated dorsal-ventral specification? What sort of cascade is occurring ventrally?
- The oocyte nucleus (with Gurken mRNA) moves to the dorsal and anterior side of the oocyte
- After fertilization, the oocyte’s Gurken is translated, and Gurken protein is received by Torpedo receptors on dorsal follicle cells.
3a. The signal from Torpedo causes these follicle cells to differentiate to a dorsal morphology (these cells are NOT part of the embryo)
3b. The signal from Torpedo inhibits Pipe synthesis in dorsal follicle cells - Gurken cannot diffuse ventrally because of the distance
5a. ventral cells thusly synthesize Pipe in the absence of inhibitory signals from Gurken->Torpedo
5b. Pipe sulfates ventral vitelline proteins, which starts the ventral differentiation pathway - A protease called Gastrulation Defective (GD) binds the sulfated vitelline membrane proteins
7a. GD cleaves the Snake protease to its active form
7b. The Easter protease is also cleaved to an active form by Snake - Easter binds and cleaves Spatzle protein, which then is able to bind to Toll on the embryo cell membrane
- Toll signaling after binding Spatzle activates the protein kinase Pelle within the embryo, Pelle phosphorylates Cactus leading to its degradation and the release of Dorsal
- Dorsal enters the ventral nucleus to act as a transcription factor
Ventrally, a protease cascade is occurring.
In mammals, has the Spatzle-Toll receptor pathway been conserved? If yes, how?
Yes, but not developmentally, it is present in our innate immune response. Interleukin or pathogen molecules bind to a Toll-like receptor. Signals from the TLR activate the PK IRAK, IRAK phosphorylates IkB which is then degraded and releases Rel/NFkB to the nucleus.
Describe the roles of these proteins in the development of the nervous system:
Dorsal/Rel/NF-kB transcription factor
decapentaplegic(dpp)/BMP4
Short Gastrulation(Sog)/Chordin
Is this mechanism conserved in vertebrates?
Dorsal inhibits dpp expression, which means dpp is only present dorsally (because Dorsal enters the nucleus ventrally). Sog further inhibits dpp activity after gastrulation by binding to it to induce neurulation, thereby preventing dpp activity from traveling ventrally.
This mechanism is conserved in vertebrates, though our nervous system is dorsal rather than ventral.