Neural Crest

Question 1

Ectoderm Overview

Answer 1

• forms neural structures, including the brain
• Ectodermal cells are bound by Cadherins, which ,must change to allow tissue separation during neurulation

Question 2

Neurulation Process:

Answer 2

1. Primary Neurulation
2. Hinge Points
3. Closure Dynamics

Question 3

Primary Neurulation

Answer 3

• formation of neural tube in three stages

1. Neural plate formation
2. Neural groove formation
3. Neural tube closure

Question 4

Neural Plate formation

Answer 4

• notochord secretes BMP inhibitors (Noggin, Chordin..) causing ectodermal cells to flatten

Question 5

Neural groove Formation

Answer 5

bending of the neural plate forms a groove, mediated by signals like shh form the notochord

Question 6

Neural Tube Closure

Answer 6

• Edges of the NG fuse
• transiotining cadherins from Ecads –> Ncads forming a closed tube

Question 7

Hinge points

Answer 7

Medial hinge points:
- forms above the notochord due to shh, causing apical constriction of cells

Dorsolateral Hinge points:
- Bring ectoderm together dorsally, completing closure

Question 8

Closure Dynamics

Answer 8

Frog Embryo:
- closure begins in the middle and zips bidirectionally

Chick Embryos:
- closure proceeds anterior to posterior, starting at Hensons node

Question 9

Closure Defects:

Answer 9

Anencephaly: failure in closing the anterior pore

Spina Bifida: Failure to close the posterior pore

Question 10

Role of Neural Tube Closure in Humans

Answer 10

• proper closure depends in Genes (pax3, shh) and nutrients (follic acid b12, and cholesterol)
• positive fluid pressure within the neural tube aids brain structure formation

Question 11

patterning of neural tube

Answer 11

Gradients of Shh and BMP. Gradient interactions determine diverse neuronal cell types within the spinal cord.

• Shh (ventral, floor plate): promotes motor neuron development
• BMP (Dorsal, roof plate): promotes sensory neuron differentiation

Question 12

Neural Crest Cells: “The Fourth Germ Layer” (origin and migration)

Answer 12

origin:
- Formed b/w the neural tube and epidermis, NCCs are pluripotent ad highly migratory

Migratory:
- Regulated by factors like Snail and Rho-GTPase
- Guided by chemoattractants, barriers, and positional cues (Ephrin, ECM)

Question 13

Snail function

Answer 13

Breaks Cadherin Bonds

Question 14

Rho-GTPase Function

Answer 14

Alter cytoskeleton during migration

Question 15

Cranial Neural Crest (CNC)

Answer 15

• contributes to pigement cells, cranial nerves, mandible, and skull
• Migrates before neural tube closure

Question 16

Cardiac Nerual Crest Cells

Answer 16

• Forms aortic arches, thyroid, parathyroid, and thymus
• attracted to Fgf signals in pharyngeal ectoderm

Question 17

Trunk Neural Crest Migration paths

Answer 17

Ventral Path:
- though anterior somite halves
- forming sympathetic ganglia and adrenal medulla

Dorsolateral Path:
- Along the epidermis forming melanocytes

Question 18

what is TNCs migration restricted by?

Answer 18

inhibitors:
- semaphorins, Ephrin
in posterior somites

Question 19

Vegal and Sacral Neural Crest

Answer 19

• contribute to enteric nervous systems development

Question 20

Factors influencing NCC migration

Answer 20

snail and slug: break cadherins, enabling cell movement

intergrins and Rho GTPase: Support adhesion and cytoskeleton changes

Question 21

Fate Determination of NCCs

Answer 21

NCCs remain pluiropotent until reaching their destination, except cranial NCs which are pre-specified

Question 22

Clinical Implications and NC development

Answer 22

failure in NCC migration or differentiation leads to congenital defects (cleft palate, adn hirschsprung’s disease)

Question 23

Neurulation and NCC formation depends on ?

Answer 23

Precise signalling Pathways (BMP and Shh) and Structural transitions (Cadherin changes)