Neural and PNS development 1, 2 and 3 Flashcards
If neurons have their cell body in the spinal cord where are they generated from?
(1 mark)
Neural tube
If neurons have their cell body elsewhere than the spinal cord where are they generated from?
(1 mark)
Neural crest
What gives rise to the neural crest and how?
(3 marks)
Neural plate border:
- Neural tube folds and starts to close, neural plate border gets closer together and end at most dorsal part of neural tube
- Tubes closing cells delaminate and migrate away
Where are the cell bodies of the PNS located?
(1 mark)
Dorsal root ganglion
and project to the spinal cord
What kind of components can the neural crest make?
(7 marks)
- Neurons
- Smooth muscle
- Cartilage and bone
- Pigment cells
- Sesnory neurons
- Glia
- Adrenal cells
What do cranial neural crest cells make?
Cartilage and bone
What do trunk neural crest cells make?
Sympathetic neurons
What neural crest cells are melanocytes made by?
ALL OF THEM xoxo
How do you find out if all neural crest cells are multipotent stem cells?
(4 marks)
- Mark cell
- Figure out where it is ending and what its descendants are
- SO when it divides all daughter cells maintain that marker
- Means you can check if they are all DRGs, neurons and glia
What is Cre-recombinase?
(1 mark)
Enzyme that recombines and stretches DNA that are located between 2 particular recognition sequences
What is a LoxP site?
(2 marks)
- 34bp sequence made up of 2 13bp recognition sites, seperated by 8bp spacer region
- 13bp are recognised by Cre protein and form dimer
What does Cre-recombinase do?
- Recognises LoxP sites and teh can switch DNA around depednig on orientation of sites and can recombinase what’s in the middle
What is the process of getting confetti mice with Cre?
(3 marks)
- Put different fluorescent proteins between LoxP sites
- Can create different colours as different sites can be recombined with different frequency
- Lables different cells with different colours
How does recombination with Cre and LoxP happen?
(2 marks)
- Target gene is floxed by inserting Lox sequence on either side of target gene - this line of mice is with the floxed gene then
- Gene is then crossed ith another transgenic mice carrying Cre recombinase which recognises LoxP and excises it out so offspring don’t have gene
Are neural crest cells multipotent stem cells?
Yes
xoxo
Does the cue for what a neural cell to produce come from its environment or is it intrinsic?
(2 marks)
- It does come from the environment
- If in a region where a specific kind of cell is meant to be produced it will switch from its original cell produced in old location to the one in the new environment
What are cranial placodes?
(2 marks)
- Specialized regions of ectoderm that give rise to various sensory ganglia and contribute to the pituitary gland and sensory organs of the vertebrate head
- Local and transient thickening of the ectoderm in head and neck between prospective neural tube and epidermis
What do cranial placodes do?
- Generate most of the peripheral neurons in head associated with smell, taste, hearing and balance
What does the neural border do?
(2 Marks)
- Gives rise to the pre-placodal region only happens v anteriorly in head as a lack of Wnt signalling
- shows you need inhibition of Wnt to form the head
Why is it necessary to limit the formation of the placodal field in the A-P domain and lateral domain?
- To form the epidermis in its place
- BMPs limit it laterally
- Wnt limits it anteriorly
How does neural crest specification occur? (4 marks)
- Neural plate induction signals induce expression of neural crest border specifiers (TF)
- INduces neural crest specifiers (2nd set TF)
- Cell expressed will become neural crest which triggers them to undergo Epithelial Mesenchymal Transition and start migrating away
What needs to happen to BMP in order to induce a neural fate?
Needs to be inhibited
In a late gastrula, what signalling factors are needed to allow these components to form correctly:
(8 marks)
- Ectoderm
- Preplacodal field
- Spinal cord
- Neural crest
- Ectoderm - high BMP gives rise to epidermis
- Preplacodal field - low Wnt/ low BMP - express Otx2
- Spinal cord - high Wnt, low BMP
- Neural crest - high Wnt/ high BMP
What markers are expressed in the:
a. ectoderm
b. preplacodal field
c. neural crest
(3 marks)
a. Ectoderm expresses keratins
b. Preplacodal expresses eya1 and Slv1
c. Neural crest expresses pax3 and Snail2, Max1/2
How do we know that BMP from ectoderm are inducing formation of cells at the very dorsal part of the spinal cord?
(4 marks)
- Because, if take cells from spinal cord that normally wouldn’t become neural crest and culture with BMP will express Pax6 and become spinal cord neurons
- Whereas, add ectoderm cells in cell culture will start expressing neural crest markers and same thing happens when add BMP4/7
What structures are involved in maintaining the structure of epithelial cells?
(3 marks)
- Epithelial cells form monolayer
- Connected to eachother by adheren junctions
- Have basal lamina that seperates them from underlying tissues
How does a mesenchymal cell form from an epithelial cell?
(3 marks)
- Epithelial cell reorganises its additions and cytoskeletons
- Not as tightly linked to neighbours as before
- Breaks through basal lamina and moves away and becomes mesenchymal cell
What does delamination mean?
Seperation of layers
During delamination of the neural crest, what do the neural tube and ectoderm express?
(2 marks)
- Ectoderm expresses e-cadherin and BMP which induces Wnt signalling
- Neural tube expresses n-cadherin
What are specialised cells to become the neural crest express in delamination?
- Cadherin-6B
Outline the process of delamination of neural crest cells.
(7 marks)
- BMP levels highest in premigratory domain
- Induce Wnt signalling
- Lead to expressino of core ‘EMT regulatory factors: Snail-2, Zeb-2, Foxd3 and Twist
- Snail-2 represses expression of E and N cadherin - therefore neural crest cells DOWN REGULATE these - so not attatched to neural tube cells
- Cadherin 6B activated only in apical ½ of pre-migratory cells and activates RhoA
- Snail-2 down regulates Cadherin 6B for delamination - C6B exp in one region of neural crest cells to reorganise cytoskeleton
- After migration, neural crest cells re-express cadherins
What are the core EMT regulatory factors?
(4 marks)
- Snail-2
- Twist
- Zeb-2
- Foxd3
What genes are upregulated in neural crest cell delamination?
(4 marks)
- RhoB - cytoskeleton remodelling
- ItgB1 - attatchment to ECM
- Cad11 - cell:cell adhesion
- Cad7 - cell:cell adhesion
What genes are down regulated in neural crest cell delamination?
(3 marks)
- Ncad - cell:cell adhesion
- Ecad - cell:cell adhesion
- Cad6B - cell:cell adhesion
Where do trunk and cranial neural crest cells migrate?
(2 marks)
Trunk - ventrally and laterally
Cranial - brachial arches
What does the ventral segmental pathway give rise to?
(3 marks)
- Sensory and autonomic neurons
- Adrenomedullary cells
- Glial cells
Where does ventral migration happen?
- Anterior half of each sclerotome
What does the sclerotome give rise to?
Cartilage of the spine
What are somite and what do they give rise to?
(2 marks)
- Balls of tissue generated on both sides of the neural tube
- Give rise to sclerotome and dermamyotome
What is the difference between neural crest cells that are born in the anterior ½ of somite and those born in the posterior ½ of the somite?
Anterior ones are able to migrate and the posterior ones can’t migrate
How does ephrin B1 cause neural cells to migrate around it?
(2 marks)
- in posterior ½ of sclerotome, ephrin B1 repels NC cells
- NC cells express EphB3 on its surface which interacts with EphB1 and transmits a repulsive cue
What are the external signals that guide trunk neural crest migration and how do they work?
(6 marks)
- Laterally migrating cells have a transcription which allows them to override repulsion of EphB1 (needed for them to migrate ventrally)
- Cadual part contains repulsive cues for NC cells - Sema 3A/F, EphB1, Versican, F-Spondin
- In anterior part, Sdf1 produced where sympathetic ganglia form
- NC cells go to the rostral region where DRG are formed
- Sympathetic ganglia also formed ^^ - have receptor CXCR4 which is attracted to Sdf1 - cells move towards it
Explain the process of nerual crest cell migration by ‘contact inhibition of local motion’.
(6 marks)
- 2 cells moving along and at some point they touch
- Contact triggers rearrangement of cytoskeleton and cells stop protruding into areas that their membranes are touching
- Start protruding ina reas membranes are not touching and move away
- Helps cells stay together
- Cells leading the way have space infront to make protrusions to advance
- Repulsive signals on the side
What proteins are secreted as cranial NC cells move by contact inhibition of locomotion?
- Low levels of N cadherin secrete C3a proein
What are the 3 major migratory streams?
(6 marks)
- NC in hindbrain and r1 and r2 - migrate 1st pharyngeal arch
- NC cells of r4 - migrate to 2nd oharyngeal arch
- NC cells of r6-r8 - migrate to 3rd and 4th pharyngeal arches
What are the signals guiding neural crest migration shown in r3?
(3 marks)
- r3 expresses Sema3f
- Cells that express the receptor for Sema3f are then repelled
- NC cells express receptors which encounter proteins that are repulsive
What proten is expressed in placodal cells?
(2 marks)
VEGF
- expressed to attract NC cells to move to together - NC cells only ones to encounter placodal cells
What is the ‘chase and run’ model?
(3 marks)
- Placode cells infront og NC cells and secrete SDF1 (chemoattractant)
- NC cells like SDF1 an move towards them when they touch it triggers CIL
- But since attractant is being secreted by neural cell it goes back anyway
