L8 - Germ Layer Induction and Gastrulation Flashcards
What is cell differnetiation
Process by which cells become different from each other and are able to acquire specialised properties
What is cell dif governed by
Changes in gene expression which dictate the repertoire of proteins synthesised
Describe extrinsic control
Cell non autonomous
Describe intrinsic control
Cell autonomous
Example of intrinsic control
Transcription factors
Example of extrinsic control
Morphogens
What does the ectoderm give rise to
Skin
Nervous system
Pigmented cells
What does the mesoderm give rise to
Muscle
Kidney
Blood
What does the endoderm give rise to
Lung
Thyroid
Pancreas
What layer gives rise to the sperm and egg
The germ layer
Gastrulation is best kniw through studies in ____
Xenopus
What occurs at the four cell stage
What does this give rise to
What are these two known as
Horizontal clevage
4 cells on the top, 4 cells on the bottom
Animal and vegetal cells
What are animal cells known as in chicks and human
Epiblast
What are vegetal cells known as in chicks and humans
Hypoblast
What is given rise to after the four cell horizontal cleavage
Morula
What is the morula
Hollow sphere of many cells which has a clear define animal and vegetal hemisphere
Where is the polarity in the oocyte seen
Why is this the case
Even before fertilisation
Due to gravity causing different cytoplasmic determinantns to sink to one part of the egg
Leads to the formation of the animal and vegetal pole
What is turned on in the cells in the vegetal pole
TFs come to be turned on in the vegetal pole - example of hich is Vgt
What is VgT
Vegetal- T-boc
Where is VgT localised to
Localised to the nucelus in the vegetal hemisphere cells
What does VgT bind to
What is the result of this
The promoter of nodal
Causes activation of Nodal
What is Nodal
Where does it act
How does it act
Secreted morphogen that can diffuse out of the vegetal cells into animal hemisphere
Acts on the cells in animal hemisphere were there are receptors
Activates the nodal signal trnasduction pathway
What is the effect of cells that recieve high nodal
Endoderm
What is the effect of cells that recicve intermediate nodal
Mesoderm
What is the effect of no nodal
Ectoderm
Where is the Wnt pathway activated
On the dorsal side of the embryo
What does the point of Wnt activation mark for the future
Marks the future posterior dorsal part of the body
Where does sperm always fertilise the egg
Sperm always the animal side of the egg
What happens where the Wnt pathway is activated
Movements of gastrulaion begin
What forms directly opposite the point where the sperm enters
Organiser forms
This is brought about by the fact that when the sperm enters the egg it initiates the rotation of the cortex
How many sides is the Wnt pathway activated
JUST the one side of the cell
What is the crucial TF involved wwith canonical Wnt signalling
B-catenin
What is the effeect of active Wnt singalling on B-catenin
Stabilises - allowing the entry of B-catenin to enter the nucleus and gene expression to be changed
What is the effect of B-catenin on Nodal
Increases levels of Nodal
So transforms Nodal into a gradient
What is the region of overlap of Nodal and active Wnt
Nieuwkoop centre
Once Nodal has been transformed to a gradient what is it acting as
Morphogen
What occurs at the dorsal where Nodal is high
Forms the organiser
What forms at the ventral end where Nodal is low
Ventral mesoderm froms
Why is Nodal high at the dorsal end
Interaction of B-catenin (from active Wnt signalling) and VgT - gives high Wnt
Why is Nodal low at the ventral end
Only Vgt
The organiser forms under what conditions
Where cells recieve very high nodal and Wnt
What is the main gene expressed at the organiser
Gsc
Decribe the upstream enhancers of Gsc
Proximal element - Wnt/B catenin
Distal element - TGF-B/Nodal
Describe the conditions for when Gsc is produced
BOTH proximal and distal elements must be activate by Wn/B-catenin and TGf-B/Nodal
What do cells of the organiser differentiate into
Axial mesoderms
Describe the migration of axial mesoderm
Migrate collectively in a process called convergent extension
Why are different types of axial mesoderm cells produced
Siamois and Gsc are expressed at fractionally different leveles
Gastrulation is driven by movement of cells from __________ to _________
Posterior to anterior
What does the organiser undergo
Self differentiation
What does the organsier give rise to
Mix of progenitor cells
Prechordal mesendoderm
Prechordal mesoderm
Notochord
Together forming the axial mesoderm
What are the three main cell type of precurrsor form in the organiser region
Pharyngeal (anterior) endoderm
Prechordal mesoderm
Notochord
What is the shape of the involuting axial mesoderm
Rod shape
What does the axial mesoderm move over
Blastocoel
As the preaxial mesoderm moves what does it form
Fibronectin rich pathwya which binds to inegrins
Integrins are expressed on the
Organiser cells
The pahryngeal endoderm and the prechordal mesoderm mark the
Furture anterior part of the embryo
What are the last cells to migrate
The notochord cells
What do the notochord cells form
The future posterior part of the embryo
Explain how the blastocoel forms
At some point there is a change in osmolarity
Results in an influx of water so morulla changes to a hollow sphere with a central fluid filled blastocoel
