Lecture 16- Neural crest II (migration and differentiation) Flashcards
What determines where neural crest cells migrate and what types of cells they form?
-the target sites and the cell types formed depend on the axial (rostrocaudal) level
What are the four divisions of the axial (rostrocaudal) level along the neural tube?
- Cranial
- Vagal
- Trunk
- Sacral
What are the 5 methods to study neural crest migration?
- Surgically remove defined regions of the neural crest, and then determine which structures fail to develop
- Construction of chick-quail chimeras
- Label pre-migratory cells with fluorescent dyes or radioactive substances
- Intrinsic markers of neural crest cells, including localization by immunohistochemistry or in situ hybridization
- Transgenic animals expressing reporter genes -Combinations of the above techniques can be used answer particular questions.
What are the advantages/disadvantages of method 1: Surgically remove defined regions of the neural crest, and then determine which structures fail to develop?
- Advantages: shows the importance of particular regions of neural crest
- Disadvantages: can’t see how the cells get there, or if other cells compensate for the loss of regions. Depends on high level of skill
- the first method used, cut out bits of the neural crest and see what doesn’t develop
What are the advantages/disadvantages of method 2: Construction of chick-quail chimeras?
Advantages: Can identify cells during migration (using fixed embryos). Cells are permanently identified.
Disadvantages:
- can’t imagine live cells during migration (using fixed embryos)
- Transplantations are difficult and somewhat variable.
- also look at sections of the embryos
- if you stop the embryo during development= so can see where they are
What are the advantages/disadvantages of method 3: Label pre-migratory cells with fluorescent dyes or radioactive substances?
- Advantages: Can image the cells in live embryos. Can label a variable number of cells (1 cell to hundreds or more). Can label different groups of cells or cells in precise locations (fate maps). Very useful for short- term labelling.
- Disadvantages:
- The labels are not permanent and are diluted out of the cells over time. -1970s -match with quail and chick chimeras
- can image cell in live embryos
more notes:
- can label in different colours and different groups of cells
- it is short term, dilute out of the cells over time as they divide, daughter cells have less and less with each division
What are the advantages/disadvantages of method 4: Intrinsic markers of neural crest cells, including localization by immunohistochemistry or in situ hybridization?
Advantages:
- Label specific genes or populations of neural crest.
- Can also use antibodies to other markers concurrently (eg look at proliferation or cell death).
- Can use to see how specific neural crest genes are affected following experimental manipulation.
Disadvantages:
-can only label fixed tissue (no live imaging).
What are the advantages/disadvantages of method 5: Transgenic animals expressing reporter genes?
Advantages:
- Can track cells using live imaging.
- Can permanently label cells using some approaches.
Disadvantages:
- Need to make/have the appropriate transgenic.
- Permanent transgenic more feasible in certain species (mice, zebrafish).
- Can make transient transgenic chick and Xenopus.
- the only live imaging and it is also permanent, hard to do
How do neural crest cells from different rostro-caudal levels migrate and what do they give rise to?
- Neural crest cells from different rostro-caudal levels:
- Follow different migratory pathways
- Give rise to different derivatives
Which neural crest cells migrate first?
-cranial region neural crest cells
Which neural crest cells migrate last?
-sacral region neural crest cells
In which order do the neural crest cells form and migrate?
- neural crest cells form and migrate in a rostrocaudal wave
- cranial, then vagal, then trunk, and lastly sacral region neural crest cells form and migrate
- this is due to the rostrocaudal wave in which the neural tube closes
What type of tissues do cranial neural crest cells give rise to?
- neurons and glia and cranial ganglia
- cartilage and bones
- connective tissue
What type of tissue do trunk crest neural cells give rise to?
- Pigment cells
- Sensory neurons and glia
- Sympatho adrenal cells
What type of cells do cranial neural crest cells give rise to?
- migrate first
- cranial sensory glia (together with placode cells)
- parasympathetic ganglia
- Schwann cells
- cartilage and bone
- smooth muscle
- connective tissue
- cornea
- teeth
- pigment cells (melanocytes)
What type of cells do vagal neural crest cells give rise to?
- cardiac outflow tract septum
- ventricular septum
- enteric neurons and glia
What type of cells do trunk neural crest cells give rise to?
- sympathetic ganglia
- dorsal root ganglia
- adrenal chromaffin cells
- schwann cells
- pigment cells
What type of cells do vagal neural crest cells give rise to?
- parasympathetic ganglia
- enteric neurons
Cranial neural crest, what does it form: details?
- form bone, cartilage and connective tissue in the head and neck
- the entire facial skeleton and much of the skull, including the upper and lower jaws, the palate and hyoid bone
- dermis, smooth muscle of the skin
- smooth muscles of blood vessels forming the aortic arch and the outflow tract of the heart (cardiac neural crest)
- connective components of striated muscle and glands in the head
- some endocrine cells, e.g parafollicular cells of the thyroid
Do placodes only produce neurons?
- yes
- glia are all from neural crest cells
What can happen if there are prblems on the development of cranial neural crest?
- can lead to caniofacial defect
- e.g. Treacher Collins syndrome: very rare, caused by a failure of the neural crest migrating to branchial arch 1 to survive (Tcof1 mutation), not enough of the migrating neural crest cells survive
- also cleft lip and palate:most common
- jaw malformation (micrognathia)
- these are not always due to neural crest cells problems but they can be involved
How are cranial ganglia formed?
- Cranial neural crest together with placodes form cranial ganglia.
- There are 2 sorts of cranial ganglia, sensory ganglia (associated with cranial nerves) and parasympathetic ganglia.
What can placodes give rise to?
-Placodes give rise to some neurons in sensory cranial ganglia and several other structures
What are placodes?
-specialised (thickened) regions of ectoderm
- develop from ectoderm
- induced by growth factors, different ones with different placodes
- get expression of genes, gets thicker
- two ways in which they develop=
- some invaginate (left) and
- on the right= undergo process of delamination (change from epithelial cell type and coming into the mesenchyme, don’t go very far, form a ganglion under the ectoderm
- Cells from the placodes enter the mesenchyme and combine with neural crest cells to make ganglia.
- Neurons in the cranial sensory ganglia arise from:
(a) placodes
(b) neural crest - Glia in the cranial ganglia arise from the neural crest.
What can neurons be made from?
-neural crest and placodes
Cranial neural crest cells give rise to to glia within ganglia and Schwann cells along nerves? true/false
true
What are the details about vagal neural crest cells and their derivatives?
- Somites 1-7: different targets:
- Enteric neural crest (neurons and glia)
- Cardiac neural crest: outflow tract of the heart (mesenchymal: smooth muscle and connective tissue)
- Connective tissues in branchial arches (overlap with cranial neural crest)
- Ganglia (neurons and glia)
What influence does neural crest have on cardiac development?
- Cardiac neural crest contribute to connective tissues in the outflow tract and ventricular septum
- Defects in the cardiac neural crest cause outflow tract abnormalities
T-his can be part of a larger defect in cranial (mesenchymal) derivatives, eg DiGeorge syndrome
-Can be caused by a problem in the neural crest themselves, or in the adjacent tissues.
Which parts of the neural crest give rise to the enteric system?
- Enteric neural crest give rise to enteric neurons and glia (enteric nervous system) along the gut.
- nerons and glia along the gut
- controls the motility of the gut and secretion
- The vagal neural crest contribute most of the neurons and glia, the sacral neural crest a small amount.
Defects in the migration of vagal enteric neural crest causes Hirsprung’s disease, these cells have to migrate the longest distance
Why is it difficult for neural crest cells to migrate along the gut?
- the gut is growing as the neural crest cells are migrating
- have to migrate fast to get to the end
What is Hirschprung’s disease?
-congenital aganglionisis
- occurs if neural crest cells fail to get to the end of the gut (the anal end)
- the neural crest cells allow for peristalsis and here don’t have it
- so constricted gut constantly, completely constipated
- get mega colon
- have to undergo surgery or fatal
- mega colon= normal neural crest cells migration up to there so have enteric neurons
- it is the region that is constricted, there no enteric neurons
What are the details about trunk neural crest and their derivatives?
- Trunk neural crest arise from somite levels 5-28 (last somite).
- Begin migration after cranial and vagal, but before sacral crest cells
- Trunk neural crest migrate along two major pathways:
- Ventral (between and through somites)
- Dorsolateral (underneath the ectoderm)
What are the two major pathways along which the trunk neural crest cells migrate?
- Ventral (between and through somites)
- Dorsolateral (underneath the ectoderm)
- ventral go first
- the ones that come later are in the dorsolateral pathway (mostly pigment cells)
What do the ventrally migrating trunk neural crest cells form? (5)
- Sympathetic ganglia (neurons and glia)
- Dorsal root ganglia (neurons and glia)
- Schwann cells along nerves
- Melanocytes
- Adrenal chromaffin cells
What do dorsolaterally migrating trunk neural crest cells form?
- become melanocytes.
- these cells migrate after the ventrally migrating cells.
What are the details about the sacral neural crest and its derivatives?
- Sacral neural crest arises from the neural tube caudal to the last somite.
- Begin migration last Sacral neural crest give rise to:
a )Neurons and glia in parasympathetic ganglia
b) Enteric neurons in the colon
How do cells migrate, and migrate directionally?
- It is more complex in three dimensions, cells can have multiple lamellipodia/processes.
- Neural crest cells express many cell surface receptors to allow them to interact with their environment.
- Downstream signalling from these receptors affects the migration and direction of migration of the cell.
What are the 7 mechanisms involved in neural crest migration?
- Chemoattraction
- Chemorepulsion
- Cell-matrix adhesion
- Cell-cell adhesion
- Matrix metalloprotease activity
- Contact inhibition of locomotion
- Growth factor signalling
- have to know 1 example of each
What are the basis for neural crest cell migration?
- Neural crest cells express receptors for various kinds of ligands in environment.
- Activation of the receptor affects various intracellular signalling pathways.
- This in turn affects many processes including adhesion to particular substrate, and ultimately controls whether the cell migrates and the direction a cell migrates.
What is the example of chemoattraction in neural crest cell migration we have to know?
- SDF1 is a chemokine(=chemoattrant), a small secreted protein, that binds to the G-protein coupled receptor Cxcr4 to mediate chemoattraction
- Cxcr4 is expressed by Xenopus cranial neural crest cells.
- Sdf1 is expressed by the mesenchyme in front of the neural crest.
- neural crest cells follow the gradient to the source
evidence:
-if knock out Sdf1 or Cxcr4 then have no migration
What is the example of chemorepulsion in neural crest migration we have to know?
- chemorepulsion regulates chick and mouse trunk neural crest migration
- chemorepulsion regulates migration in the ventral pathway through the somites (dorsal root ganglia), and in the dorsal pathway
- the dorsal root ganglia are segmental (thanks to the chemorepulsion)
- development of the dorsal root ganglia is linked to somite development
- migration occurs selectively in the rostral half of the somite and in the space between the somites.
-Class 3 Semaphorins are expressed in the posterior half of the somites and neuropilin 2 is expressed by neural crest
What are the secreted proteins and recptors involved in the chemorepulsion example?
- Class 3 Semaphorins are expressed in the posterior half of the somites and neuropilin 2 is expressed by neural crest
- Class 3 Semaphorins are secreted proteins that bind to Neuropilin receptors to inhibit migration.
What do class 3 semaphorins do?
-inhibit neural crest migration into posterior somite halves
What is some evidence for the chemorepulsion example?
- when don’t have the neurophilin2: don’t get proper migration
- if you knock out sempahorin 3 F: then don’t have the segmented pattern of migration
