7. Tissue repair Flashcards
How is the anterior - posterior axis positioned in central nervous system?
Which part of primary embryo brain develops into midbrain?
Mesencaphalon -> midbrain
What are the two main patterning structures of anterior-posterior axis of neural tube?
- isO: isthmic organiser (FGF8)
- nc: notochord (Shh)
How does dorso-ventral axis patterning occur in the neural tube?
Different signals secreted for patterning from:
- roof plate (rp)
- somites
- floor plate (fp)
—> different neurons protruced along dorso-ventral axis due to different signals
What neural cell subtypes and in which parts of the neural tube develop in dorso-ventral axis patterning?
Due to different signalling gradients in neural tube from roof plate / floor plate -> different neuron subtypes develop along dorso-ventral axis:
- dorsal root ganglion (drg)
- motor neurons (mn)
- spinal cord precursor
What are the main signalling molecules used for dorso-ventral axis formation in neural tube?
- Shh (floor plate)
- FGF8 (isthmic organiser)
- Wnt (roof plate)
Explain what part of neural tube secretes Shh and what activates
Shh released from
- notochord
- floor plate
in neural tube -> activates GLI TF: Shh conc highest in ventral - highest GLI activaion in ventral side
How is Shh signal transmitted?
Signal transduction:
- Off state: Shh not bound to PTCH1 - inhibits SMO activity -> GLI- - GLI repressed -> GLI targeted genes not transcribed
- On state: Shh binds to PTCH1 - binding activates SMO -> SMO activates GLI -> GLI targeted genes turned on by GLI TF
What is the gradient of Shh in neural tube?
Shh secreted by notochord and floor plate - highest Shh conc in ventral - lowest in dorsal axis => influences GLI TF activation - highest GLI activation in ventral - lowest in dorsal axis
What is the purpose of establishing Shh gradient in neural tube?
Different gradient -> different GLI TF activation -> different genes have different Shh thresholds for activation -> different neural cell identities developed
What is the mechanism behind negative feedback between two expressed genes for a single signalling molecule?
Complex gene expression patterns achieved by gene interaction:
Different genes have different signalling molecule thresholds for activation -> thresholds might overlap
Negative feedback:
when one threshold gene inhibits the overlaping gene expression
What are the anatomical parts of forebrain and hindbrain?
Forebrain: telencephalon, hypothalamus
Midbrain: -
Hindbrain: cerebellum
What is the pattern of Shh, Fgf8, Wnt expression in embryo?
What neurons induced by high Shh conc? What other signalling molecules contribute?
Dopaminergic (DA) neurons - form very close to neural floor plate
- Shh (high conc)
- Lmx1a
- Msx1/2
- Nurr1
Only midbrain tissue can form DA neurons
Can dorsal cells be induced to change to ventral cells?
Yes if Shh conc is increased:
dorsal cells -> ventral cells
Explain the function of isthmic organiser
isthmic organiser (isO) secretes FGF8 - important for dorso-ventral axis development in embryo
What is an organiser?
Organiser - a group of cells that transmit a signal to adjacent cells to influence their developmental fate
What Shh, Wnt, Fgf8 and their mixtures signal to develop?
Most important gradient - Wnt
How does the brain anatomy change in case of Alzheimer’s, Huntington’s and Parkinson’s?
Alzheimer’s: brain mass shrinks
Huntington’s: brain mass shrinks
Parkinson’s: DA neurons degenerate (no visible change in mass)
Where are DA neurones located?
Dopaminergic (DA) neurons in nigral midbrain (Substantia nigra)
What is the function of DA neurons?
Dopaminergic (DA) neurons supply dopamine to putamen in striatum -> DA loss -> slow movement, tremmor
What neural degeneration is involved in Parkinson’s?
DA neurons degenerate in Substantia nigra - no dopamine supply for putamen
How can stem cell therapy be used to treat Parkinson’s?
DA neurons lost -> trying to recover DA neurons by injecting stem cells (fetal ventral midbrain tissue / hESCs / iPSCs) - into Substantia nigra - DA neurons recovered
What happens if only one side of the brain exhibits DA neuron loss?
- Parkinson’s induced in rats by injecting 6-OHDA -> assymetric motor deficit
- when amphetamine given - hyperactive -> unilateral rotations (rotation direction depends on which side of the brain damaged)
What are the problems associated with using fetal tissues in Parkinson’s treatment?
- ethical issues
- poor / unpredictable supply of tissue
- poor quality / tissue heterogeneity
=> alternative - iPSCs
What are the types of pluripotent stem cells?
- embryonic stem cells (ESCs) - from IVF
- induced pluripotent stem cells (iPSCs) - tissues taken from adults - pluripotency induced by TF
How is DA neuron differentiation induced from stem cells?
- ESCs / iPSCs differentiate into primary neural tissue
- default path - forebrain cortical neurons
- if Shh, Wnt, FGF8 introduced (floor plate signalling) -> DA neurons
What tissue is the progenitor of DA neurons?
DA neuron progenitors - midbrain floor plate
What is the process of making DA neurons from hESCs / iPSCs?
DA neurons from midbrain tissue - need to make midbrain:
1. SMAD inhibition -> anterior neural tissue
2. High Shh -> ventral side
3. ‘Tuned’ Wnt gradient -> caudal side
4. ‘Timed’ FGF8b -> midbrain
What day of DA neuron development is best for transplant into Parkinson’s affected brain?
Day 16 - transplantable day
