Neurulation

Question 1

What main structures form from the neural tube?

Answer 1

Whole brain
Spinal cord
Cranial & spinal nerves,

Question 2

Around how many weeks of gestation does neurulation occur?

Answer 2

3-4 weeks

Question 3

Name the 3 main structures the ectoderm gives rise to.

Answer 3

Outer ectoderm
Neural crest
Neural tube

Question 4

Outline the basis of neurulation.

Answer 4

A-P axis established 
Induction of neural plate 
Morphogenesis and closure of neural tube 
Neural tube patterning (A-P/D-V)
Regionalisation of the neural tube

Question 5

When is the A-P axis patterned, and what direction does this occur in?

Answer 5

Prior to gastrulation

Caudal to cranial

Question 6

What 3 major molecule are responsible for A-P patterning? How does this mechanism work?

Answer 6

Nodal, Wnt, BMP

Nodal expressed in the posterior end in the extra embryonic tissue (ExE). It induces and maintains BMP4 signalling. BMP induces Wnt signalling. Wnt induces further nodal signalling, creating a feed-forward loop.

Nodal then

Question 7

What is nodal and what signalling pathway does it activate?

Answer 7

Nodal is a secretory protein that is inactive until it’s proteolytically cleaved. Part of the TGFbeta superfamily and activates SMAD2/3 signalling pathway.

Induces signals from the node, in the anterior primitive streak, to the lateral plate mesoderm (LPM).

Question 8

Name a molecule that can inhibit A-P patterning.

Answer 8

Lefty can inhibit nodal itself or via a co receptor to the nodal signalling pathways called cripto.

Question 9

What is the name of the first reliable landmark of the anterior pole of the body?

Answer 9

Anterior visceral endoderm (AVE)

Question 10

BMP is inhibited in the pre-sumptive neural plate cells in the ectoderm. What is the name of the inhibitory molecule and where does it initiate from?

Answer 10

Chordin is a BMP antagonist expressed in the mid-gastrula organiser that induce neural plate formation

Question 11

Closure points of the cranial and caudal neuropores occur in waves. How many closure point are there in humans.

Answer 11

Five

Question 12

What is the difference between primary and secondary neurulation?

Answer 12

Primary neurulation is rolling-up of tube.

Secondary neurulation is tunnelling or hollowing of tail bud

Question 13

Name the 5 steps of primary neurulation.

Answer 13

Shaping, folding (notochord/MHP), elevation, convergence (DLHP) and closure (neural crest cell migration)

Question 14

What are the three main structures involved in primary neurulation?

Answer 14

Neural plate, neural crest and epidermis

Question 15

Explain briefly the mechanism of secondary neurulation.

Question 16

What happens if we graft and extra notochord?

Answer 16

Extra MHP occur + ventral floor plate of the neural tube.

Question 17

What changes happens to cells at the hinge points, and what drives these changes?

Answer 17

Cell wedging at hinge points: driven by changes in the microtubules & actin filaments

Question 18

Explain the term ‘convergence-extension’ of the neural tube. Name a defect associated with poor C-E.

Answer 18

A process of lengthening by narrowing, which requires cells to become polarized, in the plane of the cell layer. It allows elongation and narrowing of the neural tube.

Mutants have closure point 1 failure and are presented with craniorachischisis. The neural plate is abnormally broad with a non-bending region between neural folds – broadness prevents neural tube closing in sufficient time.

Question 19

Name a gene mutated in mice with craniorachischisis.

Answer 19

Loop-tail, crash, circletail, dishevelled 1&2