NEURAL INDUCTION

Question 1

In worms, insects and vertebrates, neural precursors first form where?

Answer 1

At the surface, next to the future skin (ectoderm) on one side and next to the mesoderm on the other side.

Question 2

What is happening for the ectoderm to change their identity and become neurogenic?

Answer 2

A signal coming from the mesoderm.

Question 3

How does the body decide to put aside cells to become the neural plate?

Answer 3

Depends on how much BMP is or is not received.

Question 4

What is BMP4 in Drosophila?

Answer 4

Decapentaplegic (dpp)

Question 5

What is BMP7 is Drosophila?

Answer 5

Screw

Question 6

What is BMP1 in Drosophila?

Answer 6

Tolloid

Question 7

What is Chordin in Drosophila?

Answer 7

Short gastrulation

Question 8

Although many genes have different names in vertebrates and non vertebrates, it shows what?

Answer 8

The body plan is conserved throughout vertebrates and there are surprising similarities between vertebrates and invertebrates.

Question 9

What do early BMPs code for?

Answer 9

Non neural homeobox genes.

Question 10

If BMP/dpp is antagonised, what happens.

Answer 10

The cells that do not receive BMP become neural.

Question 11

How is BMP /dpp inhibited?

Answer 11

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.

Question 12

What other transcription factors are known for helping neural differentiation?

Answer 12

Sox genes

Question 13

As vertebrate development progresses, what happens to the neural plate?

Answer 13

The neural plate rolls up to form the neural tube - this is neurulation.

Question 14

Our understanding of how the neural plate forms and how neurulation occurs came from studies of which vertebrate?

Answer 14

Xenopus

Question 15

Following fertilisation of Xenopus, the egg undergoes mitotic cleavages and give rise to a hollow ball of cells consisting of what?

Answer 15

Three germ layers: ectoderm, mesoderm, endoderm

Question 16

What is the difference between the the Xenopus germ layers and the human germ layers?

Answer 16

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.

Question 17

What is meant by neural induction?

Answer 17

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.

Question 18

The mesoderm is not uniform, a specialised type of mesodermal cells is induced that collectively is called what?

Answer 18

The organiser/node

Question 19

What happens in the organiser/node?

Answer 19

The cells express a transcription factor that acts intrinsically to activate further genes that encode for BMP antagonists.

Question 20

What is the transcription factor in the node/organiser that induces activation of BMP antagonist genes.

Answer 20

Goosecoid

Question 21

Give examples of BMP antagonists.

Answer 21

Chordin
Noggin
Follistatin

Question 22

BMP antagonists diffuse from the organiser/node. Where diffusion is highest, what happens to these cells?

Answer 22

They become neural.

Question 23

In order to localise and visualise expression of different proteins, what studies should be done?

Answer 23

In situ hybridization

Question 24

What are the stages of mesoderm induction and patterning?

Answer 24

1. Low levels of Nodal gives for ventral mesoderm
2. High levels of Nodal gives the Organiser/Node
3. Signals from the organiser acts to inhibit BMPs
4. Antagonism of BMPs in ectoderm lead tissue to acquire neural identity

Question 25

What type of receptor is a BMP receptor?

Answer 25

TGF beta

Question 26

As the neural plate is induced, what happens to the cells of the organiser/node?

Answer 26

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.

Question 27

What is invagination?

Answer 27

A sheet of cells bends inwards.

Question 28

What is ingression?

Answer 28

Individual cells leave an epithelial sheet to become mesenchymal.

Question 29

What is involution?

Answer 29

An epithelial sheet rolls inwards to from an underlying layer.

Question 30

What is epiboly?

Answer 30

A sheet of cells spreads by thinning.

Question 31

What is intercalation?

Answer 31

Rows of cells move between one another, creating an array of cells that is longer but thinner.

Question 32

What is convergent extension?

Answer 32

Rows of cell intercalate but the intercalation is highly directional.

Question 33

What will the anterior endoderm and prechordal mesoderm go on to produce?

Answer 33

Brain like transcription factors.

Question 34

What will the notochord go onto produce?

Answer 34

Spinal cord like transcription factors.

Question 35

What is the experimental proof that neural induction is by the organiser?

Answer 35

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.

Question 36

What does BMP/Chordin boundary broadly dictate?

Answer 36

The dorsal and ventral sides of the body.

Question 37

What are the conclusions that can be drawn from the Spemann Mangold experiment?

Answer 37

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.

Question 38

How were BMP antagonists discovered?

Answer 38

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.

Question 39

How experimentally has it been shown that BMP anatagonists induce neural cells?

Answer 39

1. Express BMP antagonists ectopically

2. Dominant negative experiments with BMP receptors/knock out

Question 40

In the early stages of development, many of the stages are caused by extrinsic information. How was this figured out?

Answer 40

By GOF and LOF studies. Both studies can be done at the level of cells/tissues, proteins, mRNA and genes.

Question 41

What examples of GOF studies are there?

Answer 41

1. Transplant to and ectopic location - will this transform the fate of a Cell Z that does not usually does not see Cell X?
2. Make a protein soaked bead and plant in an ectopic loaction - will Protein X induces the fate of Cell Z to become Cell X?
3. 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.
4. 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.

Question 42

What examples of LOF studies are there?

Answer 42

1. 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.
2. 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.
3. 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.