After MT2 - The Neural Crest

Question 1

What are the five types of neural crest cells (NCCs)?

Answer 1

Cranial neural crest cells
Cardiac neural crest cells
Vagal neural crest cells
Sacral neural crest cells
Trunk neural crest cells

Question 2

1. What do cranial neural crest cells give rise to?
2. What do cardiac neural crest cells give rise to?
3. What do vagal and sarcral neural crest cells give rise to?
4. What do trunk neural crest cells give rise to?

Answer 2

1.

• the neurons and glial cells of cranial ganglia
• connective tissue, cartilage and bone of the face

2. • melanocytes, neurons, cartilage, connective for the 3rd, 4th and 6th pharyngeal arches
   • parts of the circulatory system (septum of the heart, connective tissue of the large arteries…)

3.
form the enteric ganglia of the gut

4. a) Ventrolateral pathway: give rise to sensory neurons, peripheral glia, autonomic neurons, adrenal medulla

b) Dorsolateral pathway: give rise to melanocytes, connective tissue, skeletal tissue

Question 3

before the neural tube closes, where are the presumptive neural crest cells located?

Answer 3

They are located in the transitional region between the neural plate and the epidermal tissue.

Question 4

where are neural crest cells located after the neural tube has closed?

Answer 4

Dorsal part of the neural tube.

Question 5

The transition from the pre-migratory to migratory neural crest cell is referred to as _____________

Answer 5

EMT/ingression or delamination.

(it isn’t actually delamination, it is ingression/EMT, but the literature often incorrectly calls it delamination).

You should use EMT via ingression to be accurate.

Question 6

Neural plate cells have _______ levels of BMP.

Neural crest cells have _______ levels of BMP.

Epidermal cells have _______ levels of BMP.

Answer 6

Neural plate cells have _ low _ levels of BMP.

Neural crest cells have _ intermediate _ levels of BMP.

Epidermal cells have _ high _ levels of BMP.

Remember that BMP levels go from low to high as you go medial to lateral, or in other words, neural to epidermal.

Question 7

What are confetti mice?

Answer 7

These are tools used to trace the migration path of neural crest cells. Certain types of NCCs, have a certain colour, and that colour depends on the migratory pathway the NCC takes.

Question 8

Neural crest cells are multipotent cells. What does this mean?

Answer 8

It means that the fate of what they become is attached to what (1) migratory path they take and (2) what factors or morphogens they get exposed to while migrating

Question 9

Neural crest cells form where we have intermediate levels of BMP. How does Wnt fit in here i.e. how does the Wnt gradient change medially to laterally?

Answer 9

We already discussed that Wnt is low in anterior region, high in posterior regions, in the Xenopus.

BUT, recall that the pharyngeal endoderm, which produces the Wnt inhibitors, is a MEDIAL structure, so when considering the Wnt gradient medial to laterally, across the entire A-P axis, Wnt is low at medial regions and increases as you go laterally.

Remember that neural crest cells are in the transition area between neural plate cells and epidermal cells, so neural crest cells appear not only where BMP is at intermediate levels, but also where Wnt is at intermediate levels!

Question 10

In that border region between the neural plate cells and the epidermis, you either get neural crest cells or you get _______

Answer 10

Placodes

Question 11

What are placodes?

Answer 11

Thickenings of epidermis important for eye development.

Question 12

The combination and length of exposure of what two morphogens determines whether we get placodes or neural crest cells?

Answer 12

Wnt and BMP.

Question 13

Ectoderm that is exposed to both Wnt and BMP for an extended period of time give rise to _________

Answer 13

Epidermis

Question 14

Ectoderm where we have no BMP signalling at all, but exposure to Wnt for long periods of time, you get the induction of trunk_____________

Answer 14

NEURAL cells (not neural crest cells)

Question 15

If Wnt signalling is followed by BMP signalling later, but Wnt signalling remains active the cells in that border region between the epidermis and neural plate become _____________

Answer 15

neural crest cells.

so we get neural crest cells, instead of placodes, if Wnt signalling (at intermediate levels) is followed by BMP signalling (at intermediate levels), and Wnt signalling remains active when BMP signalling happens

Question 16

If Wnt signalling is followed by BMP signalling but then the Wnt signalling is inhibited right after that, the cells in that border region (between the neural plate and epidermis) become _________

Answer 16

Placodes.

so we get placodes, instead of NCCs, if Wnt signalling (at intermediate levels) is followed by BMP signalling (at intermediate levels), but then Wnt signalling is inhibited after BMP signalling happens

Question 17

What are genes that are expressed by neural crest cells? (you can stain for these to stain for neural crest cells!)

Answer 17

Pax7, Snail2 and Sox9

Question 18

What are genes that are expressed by placodes? (you can stain for these to stain for placodes!)

Answer 18

Six1, Six4, Eya2

Question 19

True or false. The timing of BMP and Wnt signalling is what determines whether we get placodes or neural crest cells.

Answer 19

true.

Question 20

What type of cadherin do pre-migratory neural crets cells have?

Answer 20

Cadherin6B.

Question 21

After neural crest cells transition from pre-migratory to migratory, what kind of cadherin do they start to express?

Answer 21

Cadherin7

Question 22

Describe the process of EMT that makes pre-migratory NCCs to migratory NCCs.

Answer 22

• Neurulation is about to end
• noggin levels drop
• noggin is a BMP inhibitor, so its levels dropping means BMP levels increase
• BMP activates an EMT-regulatory factor; Snail-2
• Snail-2 inhibits N-cadherin, E-cadherin and cadherin6B expression, allowing expression of cadherin7.
• Snail-2 also activates actin remodelling to increase motility of pre-migratory neural crest cells.
• Snail-2 upregulates integrin expression, increasing the pre-migratory NCCs interaction with the extracellular matrix.

Question 23

Describe an experiment that can test the importance of Snail-2 in migration of neural crest cells.

Answer 23

If you inject snail-2 into one blastomere of a 2-cell stage embryo, the side injected will show increased migration of neural crest cells (trailing edge travels further than the control side).

Or, you can inject a mutant snail-2 into one blastomere of a 2-cell stage embryo. The injected side will show decreased migration of neural crest cells (trailing edge travels less than the control side).

Question 24

After neural crest cells go migratory, they undergo a process called contact inhibition. What is this? Don’t describe how it works

Answer 24

Contact inhibition is the process that moves NCCs away from one another when they collide with one another.
This allows NCCs to move away from the dorsal neural tube.

Question 25

Describe the mechanism of contact inhibition

Answer 25

• Every NCC has a cell-adhesion molecule (CAM) expressed on their plasma membranes.
• when two NCCs collide, their respective CAMs interact via heterophillic binding.
• this interaction is felt as a repulsive cue, that decreases actin polymerization at the point of contact, and increases actin polymerization at the opposite end, making the NCC move in that specific direction.

Question 26

Do pre-migratory NCCs show contact inhibition?

Answer 26

No, this is a process that is seen in migratory NCCs only.

Question 27

After neural crest cells move away from the neural tube because of EMT and contact inhibition, the ones in the trunk region first move via the _________pathway, then the _________pathway

Answer 27

The Ventrolateral pathway first, then later on the dorsolateral pathway

Question 28

When it comes to trunk neural crest cells, which pathway is initially blocked?

Answer 28

The dorsolateral pathway.

Question 29

True or false. Trunk NCCs travel via the ventrolateral pathway first, because the dorsolateral pathway is initially blocked

Answer 29

true

Question 30

True or false. Trunk NCCs travelling the ventrolateral pathway either travel between somites (the earliest ones do) or through the somites (which most trunk NCCs do)

Answer 30

True

Question 31

Trunk NCCs travelling the ventrolateral pathway travel through the ________ portion of sclerotomes.

Answer 31

Anterior

Question 32

Why do trunk NCCs only travel via the anterior portion of sclerotomes?

Answer 32

1. ) The anterior half has many fibronectins and laminins, that attract NCCs (because NCCs express integrin, remember snail-2 upregulates integrin!). This acts as an attractive cue, attracting trunk NCCs to the anterior portion.
2. ) The posterior half has ephrin and sematophorin, whose receptors (eph and neuropilin receptor) are expressed on the NCCs. When these ligands bind to the receptor, it acts as a repulsive cue, making NCCs have changes in actin polymerization, that facilitates moving away.

Question 33

What happens to pre-migratory trunk NCCs that sit near the posterior halves of sclerotomes of somites?

Answer 33

They travel either anteriorly or posteriorly, along the A-P axis, so that they can travel through an anterior portion of a sclerotome, perhaps the next somite downstream.

Question 34

What happens if we block ephrin, so that now NCCs can move via the posterior portions of sclerotomes?

Answer 34

The fate of NCC’s is connected to the pathway they take. Certain tissues that are made by trunk NCCs going the ventrolateral pathway correctly will now not form properly, because those NCCs have changed their fate by going through an incorrect pathway.

Question 35

Describe in one sentence the dorsolateral pathway

Answer 35

The pathway in which trunk NCCs travel in the region between the epidermis and the dermis.

Initially blocked.

Question 36

What causes the dorsolateral pathway to be initially blocked?

Answer 36

The expression of ephrin in that region between the epidermis and dermis.

Question 37

Trunk NCCs in the chick begin migrating via the dorsolateral pathway after about _____hours after migration via the ventrolateral pathway

Answer 37

24 hrs

Question 38

A significant portion of cells that take the dorsal-lateral pathway form cells such as _______ (pigmented cells).

Answer 38

melanocytes

Question 39

How do trunk NCCs suddenly go through the dorsolateral pathway (eventually)?

Answer 39

There’s a flip where ephrin-eph interaction goes from being a repulsive cue to an attractive cue.