L6 - Dorsalisation

Question 1

BMPs become restricted to?

Answer 1

Region around neural plate

• Cells that were too far away to be affected by BMP antagonists
• A neural plate border develops at the neural-ectoderm boundary
• When the neural plate folds the neural plate borders on either side come together

Question 2

Neural crest formation method

Answer 2

1. A border is established between induced neural plate and surface ectoderm
   - Border expresses Msx1 (induced at intermediate BMP signalling levels)
2. Wnts and FGFs act with Msx1 to turn on transcription factors
   - Characterise the neural plate border cell
3. Wnt signals act with NPB transcription factors to upregulate transcription factors
   - Characterise neural crest cells
   - Give cells stem-like behaviours – proliferation and multipotency
4. Transcription factors triggers genes that control proliferation, multipotency and survival to be transcriptionally activated
5. Neural crest cell transcription factors upregulate genes promoting epithelial-mesenchymal transition
   - Neural crest cells delaminate from the border region and migrate away

Question 3

Main neural crest cell migration pathways

Answer 3

They all delaminate from top of forming neural tube and

• Migrate into somites
• Migrate between notochord and aorta and aggregate to form sensory and autonomic ganglia
• Migrate below the aorta and aggregate to form the adrenal medulla

Question 4

BMPs from roof plate induce expression of

Answer 4

RhoB

Slug

Question 5

What does Slug do?

Answer 5

Activates factors that dissociate tight junctions between cells

Question 6

What does RhoB do?

Answer 6

Establishes cytoskeletal conditions that promote migration

Question 7

Different cell types are determined by?

Answer 7

Position of origin of neural crest cells – partly by Hox genes
Time of generation of neural crest cells
Migratory pathway and the signals they encounter on route or at target

Question 8

What do BMPs do?

Answer 8

Differentiation of neural crest cells into sympathetic neurons

Question 9

What do FGFs do?

Answer 9

Differentiation of bipotential neural crest cells into sympathetic neurons/adreno-medullary cells

Question 10

What 3 things does ectoderm form?

Answer 10

Neural crest cell
Outer ectoderm
Neural tube

Question 11

What do neural crest cells form?

Answer 11

Peripheral nervous system – Schwann cells, neuroglial cells
Enteric nervous system 
Adrenal medulla 
Melanocytes
Facial cartilage 
Dentine of teeth

Question 12

When do roof plate cells form?

Answer 12

Not all neural plate border cells form neural crest cells
A few remain at the border and form roof plate cells
- Important in the final stage of neurulation and in dorsal neural tube patterning

Question 13

What do roof plate cells upregulate?

Answer 13

BMPs and Wnts

• Diffuse into the dorsal neural tube
• Non-autonomous, cell extrinsic
• Induce expression of a set of transcription factors (Pax6, pac7, Pax3, Lim1)
• Cause neural tube progenitors to acquire dorsal identities

Question 14

What do BMPs in roof plate cells do?

Answer 14

Roof plate expresses different BMPs each inducing a particular dorsal cell type

• Blocks of cells defined through transcription factors
• Each progenitor gives rise to a different class of neuron