Neural Crest Flashcards
what tissues are derived from neural crest cells?
- neurons and glia
- cartilage and bone
- connectie tissue
- sympatho-adrenal cells
- sensory neurons and glia
- pigment cells
how do neural crest cells migrate?
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
what molecule needs to be inhibite to allow neural crest formation?
BMP- they require intermediate levels of BMP
how is BMP inhibited to allow NC formation?
the organiser releases chordin etc to inhibit the formation of the neural plate
what kind of levels of BMP are required for NC to form
intermediate
how was it shown that intermediate levels of BMP are required for NC formation?
- 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
if you decrease the gradient of BMP, what happens to the NC pool?
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
when you have different concentration gradients specifying different tissues, hood does this occurs?
the concentration may activate different high or low affinity receptors on the same cell
how can you test whether that different levels of BMP- higher levels= one fate, lower levels = another and intermediate levels = NC.
- 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.
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?
- it is very hard to fix soluble molecules
- the gradient is very slight hard to differentiate
as well as intermediate levels of BMP, what other factor do you need and at what levels?
WNT at higher levels
is the BMP sufficient for neural crest induction?
no- it only induces the neural fold which is a prerequisite for neural crest formation but you also need WNT as well
what did mayor find when trying to form NC from xenopus ectoderm?
that you dont just need int BMP, you need high WNt too
what are the two main morphogens involved in the embryo patterning?
WNT and BMP- WNT is high in post and BMP high in ventral
how does the fate of the neural crest cells change from anterior to posterior?
A-P:
- head and neck
- heart
- skin
- gut
- adrenal gland
- peierphal nervous system
how do cells generally migrate?
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
how is a protrusion formed?
- ## the polymerisation of actin- pushes the membrane outward in the anterior direction
what are the two Rho GTPasses which control the polymerisation of actin
Rac1 and RhoA
which Rho GTPase is at the anterior?
Rac1
which Rho GTPase is at the posterior?
RhoA
what is the interaction between Rac and RhoA?
they inhibit each other
how is the cell polarised?
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
what is chemotaxis?
the movement of cels towards a chemoattractant
what is the type of migration that neural crest cells most first undergo to migrate?
epithelial to mesenchymal transition
how does a men to ep transition occur?
they reduce their cell-cell adhesion and they acquire motility
what disease is the EMT involved in?
in cancer- the metastasis
how do yo know that the EMTin nC migration and cancer metastasis is similar?
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
how is E-cadherin changed in EMT?
it is almost completely abolished in expression
which gene must be down regulated for the MET to occur?
E-cadherin
which factor binds and inhibits the expression of E-cadherin?
snail.
what is a better predictor of metastasis than E-cadherin down reg?
upreg in snail
how was it shown that the migration of cancer cells was basically synonymous with NC migration?
- 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
how did they find that snail inhibited E-cadherin?
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
how do neural crest cells generally migrate ?
they migrate in a very direction manner in basically a strip
what are the different models for the directional migration of neural crest cells?
- there is positive chemotaxis- there is negative chemotaxis
why is the idea that cells are attracted by a chemottractant not plausible?
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
what is a hypothesis in relation to cell interaction about how NC maintain their directionality?
that the cells know they have cell contact all around them apart from the front so they only send out prorusions to the front
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?
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
what is the name of the process by which NC cells migrate?
contact inhibition of locomotion
what is stimulating the polarity in the model of contact inhibition of locomotion?
the contact of the cells
what GTPase does cell-cel contact activate?
RhoA and inhibition of RAC- so Rac only expressed at the front
how can you test the mode of contact inhibition compared to random movement?
you can make a computer model
when you make a computer model what does this shown about the CIL model?
they dont move as a cluster they just move away from each other
how can you explain how the CIL can work with the cells moving as a cluster?
each cell releases a chemoattractant- this means that the cells are attracted to each other as they move
what is the initial stimulation to the direction of the cells?
initial asymmetry- they can only move in one direction
what are placodes and how to they interact with NCS?
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
what is the initial asymmetric trigger for NC migration?
the Ncs exert contact inhibition on the places which pushes them away and then the places attract the NCs
what did they test whether the placodes was the first asymm signal?
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
how did they test whether there was an asymmetric signal needed for the directional movement of the neural crest cells?
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
what precise combination of molecules is required for the specification of neural crest cells?
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
