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BMS 249 - Developmental Neurobiology > Formation of the neural plate and neurulation > Flashcards

Formation of the neural plate and neurulation Flashcards

1
Q

Which organism was it first indicated how the neurogenic region arose?

A

Drosophila

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2
Q

What is cell differentiation?

A

Process in which cells become different to each other and acquire specialised fates

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3
Q

How does differentiation occur?

A

By CHANGES in the gene expression in a cell, which dictate the repertoire of protein synthesise - determines shape, function and behaviour

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4
Q

What is gene expression governed by?

A

Extrinsic factors (morphogens) and intrinsic factors (transcription factors) which determine if a particular TF is expressed in the cell - can bind to enhancers/promotors

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5
Q

What happens to cell fate and potency as a cell differentiates

A

Potency decreases - cell gets more committed to cell fate

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6
Q

What is the homologue of BMP7 in drosophila?

A

Screw

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7
Q

What is the homologue of BMP4 in drosophila?

A

dpp (decapentaplergic)

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8
Q

What is the homologue of chordin in drosophila?

A

sog (short gastrulation)

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9
Q

What is the function of chordin and what type of protein is it?

A

Secreted factor which prevents BMP signalling

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10
Q

What type of molecules are BMPs?

A

Secreted molecules

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11
Q

When does neurogenic fate occur?

A

When BMP/dpp signalling is in inhibited - by chordin/sog

Originally, all cells have BMP signalling

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12
Q

What happens when BMP/dpp binds to a receptor?

A

1) Phosphorylation of SMAD
2) Phosphorylated SMAD can enter the nucleus - as a key part of the transcription machinery
3) Dictates if a gene is transcribed

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13
Q

How does chordin/sog prevent BMP/dpp signalling?

A
  • Mop up the BMP/dpp (act as ‘sponges’)
    OR
  • By competitive inhibition
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14
Q

Where is chordin/sog expressed in invertebrates and vertebrate and why?

A

Vertebrates - Dorsal side

Invertebrates - Ventral side

Where chordin/sog is expressed, BMP/dpp signalling is inhibited and a neural fate is induced

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15
Q

Why does the nervous system of the vertebrates lie dorsally?

A

Vertebrates and invertebrates developed from the same common ancestor, but as vertebrates develop, their head twisted

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16
Q

What is the molecular pathway for the development of epidermal cells?

(in a blastoderm??)

A

1) Ectodermal cell - BMP signalling pathway, induced by BMP release from neighbouring cells.
Releases BMP also.

2) BMP signalling - Phosphorylate SMAD (High SMAD 1)
3) Switch on TFs which dictate epidermal fate - MSX1, GATA1 and vent
4) These TFs act in an autonomous manner, switching on higher level TF LEF1
5) LEF1 commits cells to skin epidermal fate by restricting potency over time

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17
Q

What is the molecular pathway for the development of neurogenic cells?

(in a blastoderm??)

A

1) BMP signalling is prevented in these cells by chordin
2) A different SMAD is phosphorylated (High SMAD 7)
3) Upregulates a set of TF (Sox TF)
4) Autonomously upregulate NEUROGENIN
5) Autonomously upregulate NeruoD which commits the cell to neural differentiation

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18
Q

What are the levels of SMAD 1 and 7 in cells that have BMP signalling?

A

High SMAD 1, low SMAD 7

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19
Q

What are the levels of SMAD 1 and 7 in cells that DON’T have BMP signalling?

A

Low SMAD 1, high SMAD 7

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20
Q

What is neurulation?

A

The folding up of the neural plate to form the neural tube

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21
Q

What is caused if the neural tube doesn’t close properly in development?

A

Spinal bifida

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22
Q

Where did the understanding of the neural plate and neurulation come from

A

Studies in Xenopus

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23
Q

How do we know that the 3 germ layers in the early stages of Xenopus development, are different to each other?

A

Using in situ hybridisation, can see that the 3 layers express different transcription factors and proteins

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24
Q

How is the neural plate established in the xenopus?

A

1) After fertilisation - 3 germ layers form
2) Subset of cells in the mesoderm start to become specialised - called the ‘organiser’
3) The organiser expresses specialised TF (siamois and goosegoid)
4) TF act in an autonomous manner - upregulate transcription of chordin, noggin, follistatin
6) These TFs diffuse into the immediate ectoderm (directly next to the organiser) and antagonise BMP signalling
7) This part of the ectoderm no longer has active BMP signalling and therefore becomes the future CNS (neural plate)

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25
Q

What is the ‘organiser’ called in humans and chicks?

A

The node

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26
Q

What are the transcription factors which upregulate chordin, noggin and follistatin?

A

Siamois

Goosecoid (Gsc)

Xnot

Xlim1

27
Q

What are chordin, noggin and follistatin?

A

Secreted molecules which antagonise BMP signalling - causing a neural fate

28
Q

What is ‘neural induction’?

A

The process through which the neural plate forms when BMP antagonists prevent the BMP ligand from stimulating its receptor

29
Q

What are BMPs?

A

Bone morphogenic proteins

30
Q

What are BMP receptors?

A

TFb

31
Q

Where are BMP receptors present?

A

In all ectodermal cells

32
Q

As long as the BMP signalling pathway is activated, what fate will ectodermal cells assume?

A

Epidermis

33
Q

If the BMP signalling pathway is inhibited, what fate will ectodermal cells assume and why?

A

Neural tissue, due to the upregulation of transcription factors which direct the cell down the neural pathway

34
Q

What do BMP antagonists do?

A

Diffuse into the extracellular spaces of ectodermal tissue and compete with BMPs for the TGFb receptor - inhibiting BMP signalling

35
Q

What do chicks and humans develop from?

A

Flattened sheet with 3 layers

36
Q

Where there is high levels of Nodal, what develops?

A

The organiser

37
Q

Where there is low levels of Nodal, what develops?

A

Ventral mesoderm

38
Q

Where does the organiser develop?

A

Dorsal mesoderm

39
Q

What is expressed in the ventral mesoderm?

A

BMP

Tolloid

40
Q

Where does the node develop in vertebrates?

A

In the centre of the flattened sheet, above the primitive streak

41
Q

What is sox2 and where is it expressed?

A

TF in cells which are going to aquire neural fates

42
Q

What happens at the same time as gastrulation?

A

NERULATION

Neural plate gets extends along the AP axis and folds up into a neural tube

43
Q

What do the master regulators (siamois and goosegoid) cause the cells in the organiser to do?

A

Develop into 3 different cell types:

1) Anterior endoderm
2) Pre-chordal mesoderm
3) Chordamesoderm (notochord)

44
Q

What are is the axial mesoderm?

A

The collective name for the pre-chordal mesoderm and the notochord

45
Q

What happens to the organiser later on in development?

A

1) Differentiates into 3 cell types under the influence of the master regulators (siamois, goosegoid)
2) Cells involute, intercalate and undergo convergent extension, come to lie beneath the ectoderm

46
Q

From the organiser, which cells involute in which order?

A

1) Anterior endoderm
2) Pre-chordal mesoderm
3) Notochord

47
Q

What is involution?

A

Sheet of cells roll inwards to form an underlying layer

48
Q

What is invagination?

A

Sheet of cells bend inwards

49
Q

What is epiboly?

A

Sheet of cels spreading out by thinning

50
Q

What is intercalation?

A

Rows of cells move between one another - create array of cells which is longer but thinner

51
Q

What is ingression?

A

Individual cells leave an epithelial sheet and become freely migrating mesenchyme cells

52
Q

What is convergent extension?

A

Rows of cells intercalate with high directionality

53
Q

Where do the cells of the pre-chordal mesoderm come to lie after involution and convergent extension?

A

Underneath the developing forebrain and are followed by cells of the notochord

In close contact with the developing mouth

54
Q

What is the shape of the prechordal mesoderm?

A

Fan-like

55
Q

Describe the experimental proof for neural induction

A

‘Organiser graft’ by Spemann and Mangold

  • Graft organiser from donor to host newt (with different pigment) in an ECTOPIC location
  • Donor organiser produced BMP agaonists and induced the cells of the host to become neural (will become the neural plate and then neural tube)
  • Self-differentiated into anterior endoderm and axial mesoderm
  • This underwent involution and convergent extension to lie underneath the neural plate
  • Created a second ‘twinned’ embryo, with a secondary neural tube, underlied by a second axial mesoderm
56
Q

What were the 2 conclusions of the ‘organiser graft’?

A

1) Host cells were induced to a neural identity - due to signals from the grafted organiser
2) Axial mesoderm and anterior endoderm all came from the donor organiser self-differentiating

57
Q

How was the ‘organiser graft’ done similarly in the chick?

A

Quail node grafted into a host chick

58
Q

How were BMP antagonists discovered?

A

1) Dissecting out the organiser from xenopus
2) Extract all mRNA from Xenopus cells and reverse transcribe to cDNA
3) Tested each to look for gene/protein that would mimic organisers ability to induces a second neural plate and ectopic axis

59
Q

What experiments could be done to prove that a molecule is a ‘neural inducer’?

A

1) Make cDNA (antisense mRNA)
2) Probe for the complimentary mRNA - expressed in the right time and place?
3) Ectopically express the molecule - if cause a 2nd axis to form, it is sufficient
4) Knock-out the molecule - if no development, it is necessary
5) Is the molecule secreted?

60
Q

How is neurulation driven?

A

By the change in cell shape:

1) Band of F-actin (filementous) at the apical domain of neuroepithelial cells contracts
2) Pulls the actin tight, causing cells to be constricted at that edge - change shape

61
Q

What causes F-actin to contract?

A

Interaction with many molecules

Eg. folate in pregnant women

62
Q

What can happen if pregnant women don’t get enough folate?

A

F-actin cannot contract

Neural tube cannot close

Cause spinal bifida

63
Q

What TF commits cells to an epidermal fate?

A

LEF1

64
Q

What TF commits cells to a neural fate?

A

NeuroD

BMS 249 - Developmental Neurobiology (16 decks)

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