Neural Crest

Question 1

what tissues are derived from neural crest cells?

Answer 1

• neurons and glia
• cartilage and bone
• connectie tissue
• sympatho-adrenal cells
• sensory neurons and glia
• pigment cells

Question 2

how do neural crest cells migrate?

Answer 2

they migrate away from the dorsal midline when the neural tube fuses - from the area at the interface between the epidermis and the neural plate

Question 3

what molecule needs to be inhibite to allow neural crest formation?

Answer 3

BMP- they require intermediate levels of BMP

Question 4

how is BMP inhibited to allow NC formation?

Answer 4

the organiser releases chordin etc to inhibit the formation of the neural plate

Question 5

what kind of levels of BMP are required for NC to form

Answer 5

intermediate

Question 6

how was it shown that intermediate levels of BMP are required for NC formation?

Answer 6

• different mutant embryos which expresses different levels of BMP
• wild type has higher levels and other mutants have lower levels
• when you analyse the expression of genes expressed in the neural crest - fkd6
• if you get rid of neural BMP expression completely then the NC disappear- so you need some
• if you increase the level of BMP-intermediate- the entire ectoderm is turned into neural crest cells
• then if you increase even more but less than WT, it reduces again
• need an intermediate level

Question 7

if you decrease the gradient of BMP, what happens to the NC pool?

Answer 7

it increase in size because the neural crest cell tissue begins earlier because the threshold is reached earlier and the gradient decreases at a slower rate so the tissue within the NC concentration threshold is larger than normal

Question 8

when you have different concentration gradients specifying different tissues, hood does this occurs?

Answer 8

the concentration may activate different high or low affinity receptors on the same cell

Question 9

how can you test whether that different levels of BMP- higher levels= one fate, lower levels = another and intermediate levels = NC.

Answer 9

• in the xenopus you can cut the ectoderm and culture it when exposed to different levels of BMP and you show that different levels give rise to different tissues- high for ectoderm, intermediate to neural crest, low for neural tube.

Question 10

why is it not possible to use immunocytochemistry to measure the gradient of BMP in the ectodermal tissue to see if intermediate levels induce NC populations?

Answer 10

• it is very hard to fix soluble molecules

- the gradient is very slight hard to differentiate

Question 11

as well as intermediate levels of BMP, what other factor do you need and at what levels?

Answer 11

WNT at higher levels

Question 12

is the BMP sufficient for neural crest induction?

Answer 12

no- it only induces the neural fold which is a prerequisite for neural crest formation but you also need WNT as well

Question 13

what did mayor find when trying to form NC from xenopus ectoderm?

Answer 13

that you dont just need int BMP, you need high WNt too

Question 14

what are the two main morphogens involved in the embryo patterning?

Answer 14

WNT and BMP- WNT is high in post and BMP high in ventral

Question 15

how does the fate of the neural crest cells change from anterior to posterior?

Answer 15

A-P:

• head and neck
• heart
• skin
• gut
• adrenal gland
• peierphal nervous system

Question 16

how do cells generally migrate?

Answer 16

a protusion is formed

• once formed, the membrane in the anterior needs to attach to the platform along which the cell the moving by attached to the cell membrane - focal complex formation
• then the trailing edge focal adhesion must undergo dissolution
• then there is myosin based contractility to move the posterior of the cell forward

Question 17

how is a protrusion formed?

Answer 17

• ## the polymerisation of actin- pushes the membrane outward in the anterior direction

Question 18

what are the two Rho GTPasses which control the polymerisation of actin

Answer 18

Rac1 and RhoA

Question 19

which Rho GTPase is at the anterior?

Answer 19

Rac1

Question 20

which Rho GTPase is at the posterior?

Answer 20

RhoA

Question 21

what is the interaction between Rac and RhoA?

Answer 21

they inhibit each other

Question 22

how is the cell polarised?

Answer 22

chemotractant- the gradient is sensed by the cell and because it is higher at the front which will stimulate Rac1 and because Rac1 is more stimulated at the ‘front” of the cell, then RhoA is inhibited here and RhoA is therefore expressed at the ‘back of the cell

Question 23

what is chemotaxis?

Answer 23

the movement of cels towards a chemoattractant

Question 24

what is the type of migration that neural crest cells most first undergo to migrate?

Answer 24

epithelial to mesenchymal transition

Question 25

how does a men to ep transition occur?

Answer 25

they reduce their cell-cell adhesion and they acquire motility

Question 26

what disease is the EMT involved in?

Answer 26

in cancer- the metastasis

Question 27

how do yo know that the EMTin nC migration and cancer metastasis is similar?

Answer 27

when yo do an expression pro-life to look at the factors that are upregulated in both- you find the factors are very similar and the pathways

Question 28

how is E-cadherin changed in EMT?

Answer 28

it is almost completely abolished in expression

Question 29

which gene must be down regulated for the MET to occur?

Answer 29

E-cadherin

Question 30

which factor binds and inhibits the expression of E-cadherin?

Answer 30

snail.

Question 31

what is a better predictor of metastasis than E-cadherin down reg?

Answer 31

upreg in snail

Question 32

how was it shown that the migration of cancer cells was basically synonymous with NC migration?

Answer 32

- the grafted a group of human melanoma cells into an embryo into the dorsal midline where the NC region is, the cancer cell migrate using the same pathway of the NC from the same region- they found that the cancer cells in the environment instead become neural crest cells! SO the process is very similar

Question 33

how did they find that snail inhibited E-cadherin?

Answer 33

they sequences the premier region and found an inhibitory binding region called E-pal. They then cloned this sequence upstream of a HIS3 gene and recombined it from a plasmid into a chromosome on the yeast and grew on a histidine lacking medium. The then took a cDNA library fused with a Ga4 activation domain and transfected into eh yeats- those containing genes that bound to the E-pal region would activate the expression of the resistance gene via the Gal4 activation domain . They found snail this way

Question 34

how do neural crest cells generally migrate ?

Answer 34

they migrate in a very direction manner in basically a strip

Question 35

what are the different models for the directional migration of neural crest cells?

Answer 35

- there is positive chemotaxis- there is negative chemotaxis

Question 36

why is the idea that cells are attracted by a chemottractant not plausible?

Answer 36

because NCs travel a very long way for cels- unlikely that there could be a strong enough gradient because the ventral region is so far away

Question 37

what is a hypothesis in relation to cell interaction about how NC maintain their directionality?

Answer 37

that the cells know they have cell contact all around them apart from the front so they only send out prorusions to the front

Question 38

how could you the theory that cells at the front send out prjection forwards because they know they are surrounded by other cells so can only go forward?

Answer 38

you can compare the movement of the individual cell to a cell leading a group of cells- you see that the individual cells moves very randomly but the group leader cell has great directionality

Question 39

what is the name of the process by which NC cells migrate?

Answer 39

contact inhibition of locomotion

Question 40

what is stimulating the polarity in the model of contact inhibition of locomotion?

Answer 40

the contact of the cells

Question 41

what GTPase does cell-cel contact activate?

Answer 41

RhoA and inhibition of RAC- so Rac only expressed at the front

Question 42

how can you test the mode of contact inhibition compared to random movement?

Answer 42

you can make a computer model

Question 43

when you make a computer model what does this shown about the CIL model?

Answer 43

they dont move as a cluster they just move away from each other

Question 44

how can you explain how the CIL can work with the cells moving as a cluster?

Answer 44

each cell releases a chemoattractant- this means that the cells are attracted to each other as they move

Question 45

what is the initial stimulation to the direction of the cells?

Answer 45

initial asymmetry- they can only move in one direction

Question 46

what are placodes and how to they interact with NCS?

Answer 46

the placodal cells that are infant of the neural crest cells in a strip but when the NC start to migrate they forma tripe and go between strips of placodes - the placodes release Sdf-1 which attracts the NC but then the NCs touch the places there is contact inhibition so the places move away

Question 47

what is the initial asymmetric trigger for NC migration?

Answer 47

the Ncs exert contact inhibition on the places which pushes them away and then the places attract the NCs

Question 48

what did they test whether the placodes was the first asymm signal?

Answer 48

they made a computer model of the placodes without and with the contact inhibition and showed that they didn't move but with contact inhibition they did move

Question 49

how did they test whether there was an asymmetric signal needed for the directional movement of the neural crest cells?

Answer 49

they did a model of the NC clusters starting in the middle and they found that they randomly moved in either one direction or the other- not just in one direction- so needs to be asymmetry

Question 50

what precise combination of molecules is required for the specification of neural crest cells?

Answer 50

The NC is induced within the neural plate border region by a precise combination of bone morphogenetic protein (BMP), Wnt, fibroblast growth factor (FGF), retinoic acid and Notch signals produced by the ectoderm, the neuroepithelium and the underlying mesoderm