Neural induction

Question 1

Neural induction

Answer 1

BMP antagonists prevent ligand from stimulating its receptor

Question 2

Cell differentiation

Answer 2

Process by which cells become different from each other and acquire specialized properties. Governed by changes in gene expression, which dictate the repertoire of protein synthesized.

Question 3

Gene expression in a cell can be governed by

Answer 3

extrinsic factors (eg morphogens) and intrinsic factors (eg transcription factors)

Question 4

Dpp/Sog dictate?

Answer 4

dorsal and ventral sides of inects/worms

Question 5

How does neurogenic region in invertebrates form?How the does neural plate in vertebrates form?

Answer 5

where dpp is inhibited by BMP antagonist Sog, the neurogenic region forms

where the BMP antagonist chordin inhibits BMPs

Question 6

Homologs in vertebrates and invertrbrates

Answer 6

Xenopus:Drosophila
BMP7:Screw
BMP1:Tolloid
BMP4:Dpp
Chordin: Sog (short gastrulation)

Question 7

Fates of ectoderm with BMP and ectoderm with no BMP signalling

Answer 7

BMP - Epidermal differentiatiion

No BMP - Neural differentiation (neural ectoderm)

Question 8

Cells in mesoderm

Answer 8

Organizer cells (spearman organiser) express TF’s (Gsc) which binds to enhancer and intrinsically transcriptionally activate genes that encode BMP antagonists (Chordin, noggin, follistatin). Once translated – diffuse into ectoderm and inhibit BMP signals/signalling.

Ventral centre in mesoderm express - BMP4, tolliod, Tsg

Question 9

Stages of mesoderm induction

Answer 9

and patterning:

1. Low level Nodal gives ventral mesoderm
2. High level Nodal gives organiser
3. 3.Signals (chordin, Noggin etc) from organiser act to inhibit BMPS- to ‘dorsalise’ and pattern the adjacent (ventral) mesoderm
4. At same time, antagonism of BMPs in ectoderm lead tissue to acquire neural identity

Question 10

Node in Chicks and humans:

Answer 10

A specialised mesoderm region, called the Node.
Secretes BMP antagonists, which induce the neural plate
Upregulating Sox2, changing fate and producing neural plate
Organiser = Node

Question 11

In Situ hybridization

Answer 11

it involves the hybridization of a labeled RNA or single-stranded DNA probe with a specific target nucleic acid (RNA or genomic DNA) within a cell.

Question 12

What happens when neural plate/organiser is induced?

Answer 12

Dorsal mesoderm involutes and undergoes convergent extension (to lie underneath the ectodermal, or top, layer of the embryo). As it does so, it self-differentiates into notochord (most of it) and prechordal mesoderm (right at front).
Neural plate lengthens to form neural tube.

Question 13

The two conclusions made from neural induction in Xenopus - the organiser graft experiment

Answer 13

The secondary neural tube was host-derived - ie showing that the neural tissue is induced from the ectoderm, in response to signal(s) from the organiser tissue.

The axial mesoderm (prechordal mesoderm and notcohord) and anterior endoderm were donor-derived showing that they had self-differentiated from the origaniser

Question 14

Types of experiments performed to prove that BMP antagonists are secreted from the organizer and induce neural plate

Answer 14

• Genes for BMP antagonists expressed in organiser
• BMP antagonists are secreted and act on adjacent cells
• Overexpression of BMP antagonists in an ectopic site lead to induction of secondary axis
• Inhibition of activity (eg via knock-out or injection of a dominant negative effector of the signalling pathway) prevents axis formation

Question 15

How were BMP antagonists discovered?

Answer 15

Discovered BMP antagonists by extracting ALL mRNA from organiser cells, reverse transcribing to cDNA, then testing each to look for a gene/protein that would mimic the organiser’s ability to induce a secondary neural plate