Term
| How does β-catenin activate the expression of siamois? |
|
Definition
Tcf3 downregulates the expression of twin and siamois (these two genes are key for axis formation).
β-catenin enters the nucleus and changes the protein's behavior from inhibiting to activating.
This causes expression of the two genes and formation of a new axis. |
|
|
Term
| How does siamois activate the transcription of goosecoid? |
|
Definition
Siamois needs to interact with Smad2/4 from the TGF-β pathway to activate the transcription of goosecoid.
Goosecoid then specifies the dorsal mesoderm. |
|
|
Term
| Explain general vertebrate embryo growth till gastrulation. |
|
Definition
- Fertilization
- Polarity established
- Cleavage to form a blastula (vegetal pole and animal pole)
- Gastrulation forms three germ layers
- Gastrulation brings the mesoderm and the endoderm inside the embryo through the blastopore
- Once the three layers are present neural induction can take place.
|
|
|
Term
| How does neural induction occur in the Xenopus? |
|
Definition
- Small invagination of the smooth surface opposite sperm entry in the blastopore
- This is caused by the Involution Marginal Zone (IMZ) and forms the blastocel
- Neural induction transforms the neurogenic region to the neural plate
- This forms above the ring of mesoderm inbetween the ring of ectoderm.
|
|
|
Term
| How does neural induction happen in Gallus? |
|
Definition
- Cells of the are opaca move downwards and converge to form a groove
- The embryo elongates
- The primative groove (equivalent to the blastopore) elongates into a streak
- The anterior end of the streak becomes enlarged to form Hensen's node
- The streak moves anteriorly and defines the axis of the embryo (then cranially before regressing).
|
|
|
Term
| How can we determine when the ectoderm acquires neural fate? |
|
Definition
Isolate the animal caps pre gastrulation.
This gives rise to epidermal cells (undetermined).
Isolate caps post gastrulation, and this gives rise to neural tissue (determined).
Transplant pigmented DLB on to vegital cells and this creates a second spemann organiser and a mirrored d-v axis. |
|
|
Term
| What do experiments whereby secondary mesoderm is generated tell us? |
|
Definition
If we place prospective ectoderm (animal pole) and prospecive endoderm (vegetal pole) together without mesoderm in the middle they create a secondary mesoderm.
If we iscolate prospective ectoderm tissue it induces the formation of a secondary mesoderm also.
This means that vegetal cells induce the formation of the mesoderm. |
|
|
