Neural Crest Flashcards
What do neural crest cells become?
Peripheral nervous system, endocrine cells, pigment cells, facial cartilage and bones, connective tissues
When are the neural crest cells specified? Where do they come from?
Very early on in the ectoderm. They come from the edge between the neural tube and the epidermis
What happens to the neural crest cells as the neural tube forms?
They undergo an EMT, delaminate, and migrate to become various cell types
What determines what cell type a neural crest cell will become?
Where it came from and which migration path it’s following
What are the 4 types of neural crest cells?
Cranial, cardiac, trunk, vagal/sacral
What types of cells do the cranial neural crest cells become?
Neurons, glia, melanocytes, facial cartilage
What are the two migratory pathways trunk neural crest cells can take?
Dorsal and ventral
Which of the two migratory pathways is the default for the trunk neural crest cells?
Dorsal
What features arise from the trunk neural crest cells that went through the dorsal pathway?
Melanocytes - skin pigment cells
What features arise from the trunk neural crest cells that went through the ventral pathway?
Sensory neurons in the dorsal root, sympathetic nervous system, adrenal medulla
How are pigmentation patterns created?
Migration or death of melanoblasts
What are the 3 steps required for trunk neural crest cells to take the ventral pathway?
- Cells are blocked from taking the dorsal pathway
- First set of NCC migrate between the somites then are blocked
- Second set of NCC migrate through the anterior parts of the somites
What is the sclerotome?
Anterior side of somites
How do the somites keep the neural crest cells out of the posterior end of the somite?
They express ephrin and semaphorin-3F, which repulses the NCCs
Why do the neural crest cells need to migrate through the anterior end of the somite?
Keeps all the motor neuron axons in one place
What part of the axon guides which direction it grows in?
The growth cone
What is the axon growth cone?
Extension off the axon with lamellipodia and filipodia constantly probing to make the axon grow one way or the other
Which protein complex in the axon growth cone controls directional growth?
CLASP/APC
How does the CLASP/APC complex in axon growth cones control directional growth?
Causing more microtubule growth and lamellipodial extensions when it is phosphorylated
What causes the CLASP/APC complex in the axon growth cones to become phosphorylated?
Attractive signals. Repulsive signals stop the phosphorylation from happening
What are the 3 steps in axon targeting?
Pathway selection: follows a general route through the to a general body region
Target selection: recognizing and going towards target cells in that general body region
Address selection: recognizing and going towards a specific subset of cells
What are the two signals that are guiding the growing axons to or away from limb buds?
Semaphorin and ephrin
How are semaphorin and ephrin signals arranged in the limb bud? How do neurons respond?
Semaphorin is expressed in the dorsal side of the limb bud, and neurons that are receptive to semaphorin signalling will grow towards that signal and will stay away from the ephrin signal. Ephrin is on the ventral side and will attract some neurons and repel others. Neurons that are repelled by both don’t go to the limb bud
What are the 3 subpopulations of sensory neurons? What order do they stop and what do they connect to?
Pain and temperature receptors: stop first in the dorsal part of the spinal cord and connect to interneurons
Mechanoreceptors: stop second in a slightly less dorsal part of the spinal cord and connect to interneurons
NT3 responsive neurons: stop last in the ventral part of the spinal cord and connect the motor neurons to form reflexes
What are the 3 diffusible signals involved in pathway selection in axon growth?
netrins/DCC receptor, Unc-6, Slit/Robo receptor
What is target selection?
A neuron will refine which signals it’s receptive to and will follow different signals than before. It will be simultaneously attracted by some signals and repelled by others
What are the 4 signals involved in target selection?
Neurotrophins, nerve growth factor, brain derived neurotrophic factor, endocannabinoids
Why are endocannabinoids important for neuron development?
Critical for finding their correct target and forming the correct connections
What is address selection?
Forming a synapse and then reducing the number of axons around through competition
How does address selection happen? What signals are involved?
The growing neurons detects beta2-laminin in the extracellular matrix and stops growing. The neuron produces agrin, which causes the muscle cell to cluster their neurotransmitter receptors. Then competition between axons will prune them so there’s not too many in one place
How many neurons will connect to a muscle cell in vertebrates?
One
