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Lecture notes of 15 pages for the course Cell Biology and developmental genetics at QMUL
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Cells and Tissues: Stem cells and asymmetric cell division ASLearning objectives:
1. Proneural genes and neurogenic genes are responsible for the formation of neural stem cells
2. Spatial and temporal mechanisms determine the identity of individual stem cells and their progeny
Question:
• How do Schwann cells cause axon growth and sprouting in the peripheral NS?
Answer: Processes of regeneration
• Depending on the severity of the injury it is possible for the peripheral nerve to regenerate
• The peripheral NS have glial cells, which are Schwann cells that are wrapped around the nerve for protection
• Schwann cells are activated in the course of an inflammation, which results post injury
• If the gap is not big, the Schwann cells can align themselves in the gap to make it possible for the axon to grow towards
the target
1. Injury
2. Inflammation, activation of Schwann cells
3. Sprouting (outgrowth)
4. Traverse region of injury, navigate back to original target
5. Re-establish synaptic contact, re-myelination.
• The further away from the cell body the better the survival rate.
Properties of Schwann cells:
• Fill the gap between distal and proximal nerve so that regenerating axons can grow on their surfaces.
• Secrete ECM, which contains growth-promoting factors.
• Secrete neurotrophin and other factors that support neuronal survival.
, The development of the nervous system
Neurogenesis can be subdivided into four processes
• Image showing neuroectoderm
- Neuroectoderm = is ectoderm which receives bone morphogenetic protein-inhibiting signals from proteins such as
noggin, which leads to the development of the NS from this tissue.
1. Generation of neural stem cells in neuralectoderm.
2. Establishment of neural stem cell identity
- Each neural stem cell knows which part of the NS it is supposed to form.
- Therefore, each neural stem cells needs to have specific identity
- Cells in certain area of the brain give rise to different neurons as supposed to stem cells in the spinal cord.
Same in drosophila, in different segment there is different neurons.
3. Differentiation of neural precursors
- Stem cells divide in a specific way, which gives rise to neurons which the differentiate and obtain their specific
morphology (cell body, dendrites, axon, etc.)
- At the same time other cells (supporting cells i.e. glial cells )in the NS will differentiate
4. Establishment of neuronal networks
- Once the axons have grown out, they have to find a target neuron and form synapses to establish a whole
neuronal network
The regions that will give rise to the different parts of the embryo are already determined at the blastoderm stage
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