NEURAL INDUCTION Flashcards
In worms, insects and vertebrates, neural precursors first form where?
At the surface, next to the future skin (ectoderm) on one side and next to the mesoderm on the other side.
What is happening for the ectoderm to change their identity and become neurogenic?
A signal coming from the mesoderm.
How does the body decide to put aside cells to become the neural plate?
Depends on how much BMP is or is not received.
What is BMP4 in Drosophila?
Decapentaplegic (dpp)
What is BMP7 is Drosophila?
Screw
What is BMP1 in Drosophila?
Tolloid
What is Chordin in Drosophila?
Short gastrulation
Although many genes have different names in vertebrates and non vertebrates, it shows what?
The body plan is conserved throughout vertebrates and there are surprising similarities between vertebrates and invertebrates.
What do early BMPs code for?
Non neural homeobox genes.
If BMP/dpp is antagonised, what happens.
The cells that do not receive BMP become neural.
How is BMP /dpp inhibited?
If chordin/short gastrulation binds to BMP/dpp, then BMP/dpp cannot bind to its receptor. If the receptor is not activated there is not pSMAD157 pathway - low SMAD4 and so the cell undergoes epidermal differentiation.
What other transcription factors are known for helping neural differentiation?
Sox genes
As vertebrate development progresses, what happens to the neural plate?
The neural plate rolls up to form the neural tube - this is neurulation.
Our understanding of how the neural plate forms and how neurulation occurs came from studies of which vertebrate?
Xenopus
Following fertilisation of Xenopus, the egg undergoes mitotic cleavages and give rise to a hollow ball of cells consisting of what?
Three germ layers: ectoderm, mesoderm, endoderm
What is the difference between the the Xenopus germ layers and the human germ layers?
The germ layers consist of the same ectoderm, mesoderm and endoderm but in Xenopus these are shaped in a hollow ball and in humans, this is flat plate.
What is meant by neural induction?
The neural embryonic plate is set aside from other parts of the ectoderm.
The neural pate forms when BMP antagonists prevent the BMP ligand from binding to its receptor.
The mesoderm is not uniform, a specialised type of mesodermal cells is induced that collectively is called what?
The organiser/node
What happens in the organiser/node?
The cells express a transcription factor that acts intrinsically to activate further genes that encode for BMP antagonists.
What is the transcription factor in the node/organiser that induces activation of BMP antagonist genes.
Goosecoid
Give examples of BMP antagonists.
Chordin
Noggin
Follistatin
BMP antagonists diffuse from the organiser/node. Where diffusion is highest, what happens to these cells?
They become neural.
In order to localise and visualise expression of different proteins, what studies should be done?
In situ hybridization
What are the stages of mesoderm induction and patterning?
- Low levels of Nodal gives for ventral mesoderm
- High levels of Nodal gives the Organiser/Node
- Signals from the organiser acts to inhibit BMPs
- Antagonism of BMPs in ectoderm lead tissue to acquire neural identity
What type of receptor is a BMP receptor?
TGF beta
As the neural plate is induced, what happens to the cells of the organiser/node?
The cells in the organiser/node self-differentiate into anterior endoderm, prechordal mesoderm and axial mesoderm (the notochord). These cells involute and extend (convergent extension/gastrulation) causing the neural plate sitting above to extend with it also, thereby changing the shape of the embryo.
What is invagination?
A sheet of cells bends inwards.
What is ingression?
Individual cells leave an epithelial sheet to become mesenchymal.
What is involution?
An epithelial sheet rolls inwards to from an underlying layer.
What is epiboly?
A sheet of cells spreads by thinning.
What is intercalation?
Rows of cells move between one another, creating an array of cells that is longer but thinner.
What is convergent extension?
Rows of cell intercalate but the intercalation is highly directional.
What will the anterior endoderm and prechordal mesoderm go on to produce?
Brain like transcription factors.
What will the notochord go onto produce?
Spinal cord like transcription factors.
What is the experimental proof that neural induction is by the organiser?
Spemann and Mangold Experiment.
They grafted an organiser from a donor to a host newt and found that a twinned embryo developed with a complete secondary neural axis.
What does BMP/Chordin boundary broadly dictate?
The dorsal and ventral sides of the body.
What are the conclusions that can be drawn from the Spemann Mangold experiment?
The neural tube was host derived since it responsded to the signals from the host organiser.
The axial mesoderm and anterior endoderm with donor derived as its own organiser had self differentiated.
How were BMP antagonists discovered?
All DNA was extracted from organiser cell, reverse transcribing to cDNA. The each were tested to look for a gene/protein that would mimic the organiser’s ability to induce a secondary neural plate.
How experimentally has it been shown that BMP anatagonists induce neural cells?
- Express BMP antagonists ectopically
2. Dominant negative experiments with BMP receptors/knock out
In the early stages of development, many of the stages are caused by extrinsic information. How was this figured out?
By GOF and LOF studies. Both studies can be done at the level of cells/tissues, proteins, mRNA and genes.
What examples of GOF studies are there?
- Transplant to and ectopic location - will this transform the fate of a Cell Z that does not usually does not see Cell X?
- Make a protein soaked bead and plant in an ectopic loaction - will Protein X induces the fate of Cell Z to become Cell X?
- Introduce Gene X into an ectopic cell near Cell Z. If ectopic gene produces Protein X. Cell Z now sees Protein X and tranforms into Cell X we can conclude that Gene X is sufficient for driving Cell fate X.
- Introduce gene encoding receptor for X into Cell Z (with no receptors). Ectopic gene expressed and receptor made. Cell Z now can respond to Protein X. If Cell Z transforms into Cell X we can conclude that stimulation of Protein X signalling pathway is sufficient for driving Cell fate X.
What examples of LOF studies are there?
- Cell ablation - if Cell B stays as Cell B upon ablation of Cell A, instead of changing to fate E then we can conclude Cell A is required to cause cell fate A.
- Prevention of the protein X (can be done with another protein to degrade or by KO, or interfering with stability of mRNA of protein X produced by Cell A). If B stays as B then we can conclude gene X and protein X are required to cause cell fate E.
- If you prevent a receptor on Cell B or prevent Cell B from functioning (by KO of receptor or introducing a dominant negative receptor.) If Cell B stays as Cell be then you can conclude Protein X signalling pathway is required for cell fate E.
