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Developmental Biology > L9 - Neural Induction and Neural Tube Patterning > Flashcards

L9 - Neural Induction and Neural Tube Patterning Flashcards

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1
Q

What is the function of the organiser?

A

Neural inducing

Mesoderm dorsalisation properties

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2
Q

Where is the organiser induced?

A

The organiser is induced mesoderm that lies directly above the Nieuwkoop centre

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3
Q

During neural induction in the organiser what do ectoderm cells do?

A

Make and secrete BMPs
Diffuse out and act locally, binding to BMP receptors on adjacent cells
Trigger the BMP signalling pathway
BMP signaling pathway active - differentiation into epidermal ectoderm

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4
Q

During neural induction in the organiser what do organiser cells do?

A

Intrinsically expresses secreted products (under influence of siamois and gsc)
Antagonists of BMP or components of BMP signalling pathway
- Chordin and noggin
Diffuse into extracellular space and compete for binding to BMPs in adjacent ectoderm cells
BMPs no longer able to activate their receptors
BMP signaling pathway not active – differentiation into neural

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5
Q

What else do BMP antagonists act on?

A

Act on rest of non-organiser mesoderm to refine mesodermal fates

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6
Q

Where do organiser derived signals diffue?

A

Diffuse through ventral mesoderm and pattern it

Diffuse locally into the ectoderm, resulting in the induction of neural tissue in part of ectoderm

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7
Q

Low levels of nodal produces?

A

Ventral mesoderm

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8
Q

High levels of nodal produces?

A

Organiser

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9
Q

What experiment was carried out to prove neural induction by the organiser?

A

1920 - organiser graft experiment
Spemann and Mangold
Grafted an organiser from a donor to a host newt

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10
Q

What were the results of the organiser graft experiment?

A

Another embryo developed whose secondary axis was host-derived
Neural tissue is induced from ectoderm, in response to signals from organiser tissue

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11
Q

What is induction?

A

Example of a change in fate mediated by an extrinsic/ non-autonomous event

  • Cell A makes a signal that acts on neighbouring Cell B
  • Cell B is induced to become Cell C
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12
Q

What is autonomous/cell-intrinsic differentiation?

A

Cell A divides asymmetrically

  • One daughter has same fate as mother
  • Second daughter inherits different components and cell-autonomously differentiates to alternate Cell fate X
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13
Q

As the A-P axis begins to form what has already formed?

A

Neural tissue has already begun to form

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14
Q

What starts the formation of the A-P axis?

A

Organiser autonomously differentiates and undergoes convergent extension – gastrulation

  • As it does so, it self-differentiates into
    • Anterior endoderm - anterior
    • Prechordal mesoderm – anterior
    • Notochord – posterior
  • Axial mesendoderm collectively
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15
Q

What does development of axial mesendoderm drive?

A

Drives elongation and transition from neural plate to neural tube

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16
Q

Gastrulation method

A
  1. Organiser cells try to coalesce and form a rod
  2. Rod migrates inside the cells of the animal hemisphere
  3. First cells to migrate in - prechordal mesoderm cells
    - Mark future anterior endoderm
  4. Last cells to migrate in - notochord cells
    - Underlie most of the body and mark future posterior end
  5. Neural plate grows and elongates along A/P axis
17
Q

At the end of gastrulation..?

A

The rest of the body is built around the notochord cells/rod of mesoderm cells
Axial mesendoderm now underlies the midline of induced neural plate/prospective neural tissue

18
Q

What is the activation transformation model?

A

The basis for formation of forebrain versus hindbrain and spinal cord
Helps explain how the neural plate elongates

19
Q

How does the neural plate elongate?

A

Signals from notochord

  • Cause cells at the back of the neural plate to proliferate
  • Transform these cells from an anterior to a posterior identity
    • Represses anterior transcription factors
    • Promotes posterior transcription factors
20
Q

What signals are released by anterior tissues to establish early A-P regional identity?

A

BMP antagonists

Wnt antagonists

21
Q

What signals are released by posterior tissues to establish early A-P regional identity?

A

FGFs
Wnts
Retinoic acid

22
Q

Different domains of hindbrain and spinal cord are defined through?

A

Hox signature

23
Q

Retinoic acid gradient induces?

A

Different patterns of Hox transcription
As a result, different regions of the axis express different Hox genes
Important in rhombomeres of the hindbrain

24
Q

What does the interaction between hindbrain and forebrain cells produce?

A

Interaction induces midbrain cells at the boundary

Further events result in regionalisation of forebrain into diencephalon and telencephalon

25
Q

How is the D-V axis patterned?

A

After neuroepithelium is induced, it rolls up into the neural tube
- Transforms medio-lateral axis into D-V axis
Lateral edges fuse to become dorsal part of neural tube
Neural tube pinches off from the overlying surface ectoderm

26
Q

Where are roof plate cells found?

A

Found in the most dorsal part of the neural tube

  • Induced in response to BMPS
  • They are neural plate border cells that have been retained
27
Q

What do roof plate cells upregulate?

A

BMPs

Wnts

28
Q

What do the signalling molecules released by roof plate cells do?

A

Diffuse into dorsal neural tube
Induce expression of a set of transcription factors - Pax6, Pac7, Pax3, Lim1
- Induce dorsal identities in adjacent neural tube progenitors

29
Q

How many BMPs are expressed by the roof plate?

A

Many different BMPs expressed each of which induces a particular dorsal cell type

30
Q

What do BMPs and Wnts induce?

A

Induce different sets of progenitor cells

  • Through transcription factors
  • Will differentiate to distinct neuronal subsets in dorsal spinal cord
31
Q

What are the examples of cells that differentiate dorsally?

A

Roof plate cells
Neural crest cells
Dorsal sensory relay interneurons - D1-D3

32
Q

When is Shh released?

A

After BMPs have begun to pattern neural tube, the notochord upregulates Shh

  • Induces floor plate cells in ventral midline of neural tube
  • Floor plate also expresses Shh
33
Q

What is the role of Shh?

A

Acts as a morphogen

Induces floor plate cells

34
Q

What is the Shh gradient translated into?

A

Translated into an intrinsic GliA-GliR gradient in responding cells
In turn, begin to express particular homeodomain transcription factors
- These transcription factors are the upstream regulators of particular neuronal fate

35
Q

High Shh leads to?

A

High GliaA activity

36
Q

Low Shh leads to?

A

High GliaR activity

37
Q

As cells differentiate where do they move?

A

Laterally

38
Q

Overall what patterns the DV axis?

A

BMPs and Shh

Developmental Biology (16 decks)

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