Dorsalization and neural crest formation

Question 1

How is the neural plate border created

Answer 1

BMP antagonists are secreted from the node/organiser and induce the neural plate in the adjacent cells - BMPs therefore become restricted to a region surrounding the neural plate

Question 2

What does neural crest formation and neural tube patterning happen before

Answer 2

Shh is expressed in the notochord

Question 3

What is the first stage of neural crest formation

Answer 3

Early border established between the surface ectoderm and the induced neural plate - Border begins to express msx (a transcription factor) Thought to be induced by intermediate levels of BMP signalling

Question 4

What is the second stage of neural crest formation

Answer 4

Wnts and FGFs act together with msx1 to turn on other transcription factors (Pax3,Pax6, Zic1) the combination of these factors characterises the neural plate border cell

Question 5

What is the third stage of neural crest formation

Answer 5

Wnt signals act together with NBD TFs to upregulate further TFs c-Myc, Id, Snail that characterise neural crest cells. Many of these TFs are known to give stem like behaviours - Proliferation and multipotency

Question 6

What is the fourth stage of neural crest formation

Answer 6

In response to c-Myc - genes that control proliferation and multipotency are transcriptionally activated, whereas, genes that control cell death are transcriptionally repressed

Question 7

What is the fifth stage of neural crest formation

Answer 7

At the same time: neural crest cell TFs upregulate a further set of genes that promote epithelial-mesenchymal cell transition (EMT). Neural crest cells delaminate from the border and begin to migrate away

Question 8

Give examples of neural crest cell final identity

Answer 8

PNS - schwann cells, sympathetic and Parasympathetic neurons, Adrenal medulla, Facial cartilage, dentine of teeth

Question 9

How are the different cell types a neural crest cell can become determined (3)

Answer 9

1. Determined by the position of origin of the neural crest cell - Determined partly by HOX gene so ultimately by posteriorising signals
2. The time of generation of the neural crest cell
3. The migratory pathway and the signals encountered on the way or at the target

Question 10

What are the three main pathways for neural crest cell migration and what might they produce

Answer 10

1. Superficial migratory pathway - just beneath the ectoderm - form pigment cells of the skin
2. Intermediate pathway vua the somites form sensory ganglia
3. Medial pathway form sympathetic ganglia and the cells of the adrenal medulla

Question 11

Do all neural plate border cells form neural crest cells

Answer 11

No, some are retained at the border and become roof plate cells - are important in the final step of neurulation and dorsal neural tube patterning

Question 12

What do roof plate cells upregulate

Answer 12

BMPs and Wnts - Secreted signals that act as morphogens - Once secreted they diffuse into the dorsal neural tube - induce expression of TFs Pax6,7,3 and Lim1)
These cause neural tube progenitors to acquire a dorsal identity

Question 13

How does the BMP/Wnt gradient effect the final identity of neurons in the dorsal spinal cord

Answer 13

By inducing different sets of progenitor cells that will ultimately differentiate to distinct subsets in the dorsal spinal cord