Diff5 - 36 Flashcards
What causes different cytoplasmic determinants to sink in the egg?
Gravity in xenopus, placenta interaction in mammals
What does cytoplasmic determinants sinking cause?
Cells in this region to be different - they then have specific transcription factors localised and activated
What specific transcription factors are localised and activated in the Xenopus egg?
Vegetal portion - the heavy yolk - has VgT activated
What is VgT?
T box transcription factor
What does the vegetal section induce?
Dorsal and ventral mesoderm
Example of dorsal mesoderm derivative
Notochord
Example of ventral mesoderm derivative
Blood
Why are two forms of mesoderm induced by vegetal section?
Differential gene expression
What causes differential gene expression in the vegetal section?
Sperm induced cortical rotation
What does sperm induced cortical rotation cause the expression of?
Wnt signalling from the dorsal side
What does activation of Wnt signalling lead to?
The stabilisation of a factor called beta-catenin, which enters the nucleus and changes the transcriptional profile
What does Wnt bind to?
Frizzled
What does frizzled signal to?
Dishevelled
What does dishevelled interact with?
Axin - to prevent GSK3 from degrading free beta-catenin
How does Wnt induce a difference in vegetal cells?
Wnt on the dorsal side, VgT on vegetal = 3 dimensional gradient
What is the region of Nodal and Wnt expression overlap called?
Nieuwkoop centre
What is the name for Nieuwkoop progeny?
Organiser/Dorsal mesoderm
Summarise early morphogenetic gradients in the Xenopus embryo
Outline the properties of the organiser
Ability to self-differentiate into axial mesoderm, ability to dorsalise adjacent mesoderm, ability to induce adjacent extoderm to a neural fate
What controls the properties of the organiser?
Siamois, then goosecoid later
What is the axial mesoderm?
Rod of cells around which the future body’s axis forms
How is the axial mesoderm created?
Convergent extension - cells in a circle or sheet, then all desperately want to be in the centre
What three cell types form axial mesoderm?
Prechordal mesendoderm, prechordal mesoderm, notochord
What form dorsal aspects of the axial mesoderm?
Prechordal mesendoderm, prechordal mesoderm
What is important to note about Nodal expression in the Xenopus?
Doesn’t differentiate all the way to the top of the animal hemisphere, only changes the fate of a band of animal hemisphere cells that areimmediately adjacent to the vegetal hemisphere.
What does convergent extension cause in the developing embryo?
Complete change in shape - from sphere to larva-like shape
Why does convergent extension cause a change in embryo shape?
The yolk from the yolky vegetal cells is being used, so they all but disappear; top animal cap cells now have the induced mesoderm cells arranged in rod-like sturcutres inside of them, running down the AP extent of the body
What do the three main precursors form of the organiser region form?
Pharyngeal endoderm, prechordal mesoderm and notochord
What does the rod follow during convergent extension?
Fibronectin rich pathways
When does gastrulation occur in vertebrates?
Shortly after blastocyst stage, when the trophextoderm and inner cell masses have formed, and it has implanted into the uterine wall
What causes gastrulation in vertebrates?
Signals coming from the developing placenta, forcing the ICM to start differentiating into hypoblast or epiblast
What does epiblast go on to be?
Embryo proper - equivalent to Xenopus animal hemisphere
What can the hypoblast be considered equivalent to?
Xenopus vegetal hemisphere
Where does the vertebrate version of the Nieuwkoop centre form?
The hypoblast
What does the organising part of the hypoblast induce?
Some epiblast cells to become mesoderm and definitive endoderm
What occurs to the vertebrate organiser, and what does this form?
Moves from propective posterior to anterior, creating the primitive streak
