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Nervous system development Flashcards

1
Q

What did Spemman and Mangold’s Organiser Experiment show?

A

That secreted signals can induce and pattern CNS development.

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2
Q

Give the 3 main steps in Spemman and Mangold’s Organiser Experiment.

A
  1. Remove dorsal blastopore lip from a donor
  2. Transplant into host on the opposite side (anterior)
  3. Will form a conjoined twin
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3
Q

Which organism was Spemman and Mangold’s Organiser Experiment first performed on?

A

Xenopus.

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4
Q

What is interesting about the conjoined twin formed in Spemman and Mangold’s Organiser Experiment? What does this show?

A

The majority of the conjoined twin is made of host tissue NOT donor tissue. Shows that the donor tissue has induced CNS formation in the host.

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5
Q

Give 4 examples of Organiser molecules.

A
  1. Chordin
  2. Noggin
  3. Follistatin
  4. Xnr3
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6
Q

What do the Organiser molecules all have in common?

A

They are antagonists of BMP signalling.

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7
Q

Where are the Organiser molecules found? Give 3 places.

A
  1. Dorsal endoderm
  2. Dorsal mesoderm
  3. Neural ectoderm
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8
Q

A combination of what 2 things causes neural induction in the ectoderm?

A
  1. Supression of BMP by antagonists

2. FGF signals

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9
Q

What is FGF signalling?

A

Fibroblast growth factor.

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10
Q

What 3 groups all promote posterior neural identity?

A
  1. Wnts
  2. Retinoic acid
  3. FGFs
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11
Q

The positive signals that promote posterior neural identity are known. What positive signals promote anterior neural identity?

A

No positive signals are known - anterior identity is established by protecting cells from caudalising agents

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12
Q

What is a caudalising agent?

A

One that is involved in the transformation of the posterior neural components.

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13
Q

Why does the embryo elongate in neurulation?

A

To move the anterior part away from caudalising agents.

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14
Q

To establish anterior neural identity which genes can be antagonised (inhibited)?

A

Wnt proteins

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15
Q

What happens to the anterior CNS if there is too much Wnt signalling?

A

It fails to form

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16
Q

What happens to the anterior CNS if there is not enough Wnt signalling?

A

It expands, not enough posterior CNS is established

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17
Q

How is the neural tube formed?

A

The neural plate rolls up on each side and fuses down the middle.

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18
Q

What happens to the neural crest cells as the neural tube is formed?

A

They delaminate and migrate away.

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19
Q

What is the notochord?

A

A solid rod of mesoderm down the dorsal side of the embryo which is important for tissue patterning.

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20
Q

Where do the motor neurones differentiate?

A

On the ventral side of the spinal chord.

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21
Q

What 3 events constitute as the dorsoventral patterning of the CNS?

A
  1. The formation of the neural tube
  2. The delamination of the neural crest cells
  3. The differentiation of the motor neurones
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22
Q

What is the neural floor plate?

A

A group of cells responsible for the differentiation of neurones and the ventralisation of tissues.

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23
Q

Where is the neural floor plate located?

A

On the ventral midline of the neural tube.

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24
Q

What happens if you transplant the developing notochord to a new location?

A

It will continue to produce neurones and floor plate cells.

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25
Q

In transplant experiments, in what proximity to the notochord are the floor plate cells it produces? What does this suggest?

A

Very close by, short-range signalling.

26
Q

In transplant experiments, in what proximity to the notochord are the neurones it produces?

A

Further away than the induced floor plate cells.

27
Q

What happens if the notochord is removed completely?

A

There are no neurones or floor plate cells produced.

28
Q

What signal is secreted by the notochord?

A

SHH (sonic hedgehog signalling molecule).

29
Q

What does SHH do?

A

Causes the ventral side of the neural tube to produce floor plate cells and other cell types.

30
Q

What is the gradient of SHH across the neural tube?

A

High (ventral) to low (dorsal).

31
Q

SHH could be regarded as a morphogen in neurulation. Why?

A

The concentration of SHH affects the cell types that are produced.

32
Q

What do homeodomain proteins do?

A

Establish discrete dorso-ventral domains.

33
Q

Where are homeodomain proteins located in regards to SHH?

A

Downstream.

34
Q

There are 2 classes of homeodomain factors. These become expressed at different concentrations of SHH. What are they?

A
  1. Class I = low levels of SHH (ventral)

2. Class II = high levels of SHH (dorsal)

35
Q

What are established by interactions between Class I and II homeodomain factors?

A

Mutually repressive boundaries.

36
Q

Dbx2 is a gene expressed in low levels of SHH. What does it repress?

A

Nkx6, expressed in high SHH.

37
Q

Pax6 is a gene expressed in low levels of SHH. What does it repress?

A

Nkx2, expressed in low SHH.

38
Q

What accounts for the huge disparity in size between organisms?

A

Growth and proliferation rates.

39
Q

Neural signalling is location dependent. What does this mean?

A

The same signalling molecules can produce different parts of the CNS based on location.

40
Q

What does SHH do in the spinal cord and brain respectively?

A
  1. Promotes neuron development

2. Induces the hypothalamus and parts of the eye.

41
Q

What happens if SHH is removed from the eye?

A

Cyclopia develops.

42
Q

What 2 things coordinate differentiation of cells?

A
  1. Position along the DV axis

2. Position along the AV axis

43
Q

What allows a single mother cell to form two different daughter cells. Give 2 factors.

A
  1. Polarised cell division

2. Asymmetric distribution of cytoplasmic determinants

44
Q

Where does newly formed neural tissue (ectoderm) and mesoderm aggregate?

A

At the caudal (posterior) end of the embryo.

45
Q

The caudal region of the embryo is divided into 3 parts. What are these?

A
  1. Differentiation zone
  2. Proliferating zone
  3. Zone at the very end where differentiated/proliferating cells move to.
46
Q

In which region of the embryo is retinoic acid expressed?

A

Anteriorly.

47
Q

In which region of the embryo is FGF expressed?

A

Caudally.

48
Q

What happens at the interface of retinoic acid and FGF expression?

A

Neural cells switch on expression of genes that make neurons.

49
Q

What does antagonising enzymes that degrade retinoic acid do?

A

RA helps to establish the anterior identity of the CNS.

50
Q

What affect does FGF expression have on RA production?

A

Switches it off.

51
Q

Once the nervous system has taken shape, the neurons migrate before fully differentiating. True or false?

A

True.

52
Q

Give an example of neuronal migration.

A

Those in the ventral part of the forebrain migrate to the dorsal forebrain and into the cortex.

53
Q

When are the axons of neurones generated?

A

After differentiation.

54
Q

What causes axonal growth?

A

The growth cone.

55
Q

What 3 factors guide axons to their target locations?

A
  1. Long-range repellents
  2. Long-range attractants
  3. Locally acting contact mediators
56
Q

What must be established when axons reach their target destinations?

A

Appropriate synapses between the correct neurones.

57
Q

Cell death is common in development. Why?

A

It kills off cells that are no longer needed.

58
Q

Which kind of experiments show cell death in the CNS?

A

Extra limb experiments - if there is an extra limb that needs innervation, there is less cell death.

59
Q

The majority of the CNS is morphologically symmetrical. In humans, where does asymmetry arise from?

A

There is a preference for ‘handedness’.

60
Q

There are asymmetries in the brain of all animals. What is this indicative of?

A

Lateralisation of the CNS, i.e. different brain hemispheres specialise in different things.

61
Q

Is left-right asymmetry easy to detect in zebrafish?

A

Yes.

Development (18 decks)

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