7. Tissue repair

Question 1

How is the anterior - posterior axis positioned in central nervous system?

Answer 1

Question 2

Which part of primary embryo brain develops into midbrain?

Answer 2

Mesencaphalon -> midbrain

Question 3

What are the two main patterning structures of anterior-posterior axis of neural tube?

Answer 3

• isO: isthmic organiser (FGF8)
• nc: notochord (Shh)

Question 4

How does dorso-ventral axis patterning occur in the neural tube?

Answer 4

Different signals secreted for patterning from:
- roof plate (rp)
- somites
- floor plate (fp)
—> different neurons protruced along dorso-ventral axis due to different signals

Question 5

What neural cell subtypes and in which parts of the neural tube develop in dorso-ventral axis patterning?

Answer 5

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

Question 6

What are the main signalling molecules used for dorso-ventral axis formation in neural tube?

Answer 6

• Shh (floor plate)
• FGF8 (isthmic organiser)
• Wnt (roof plate)

Question 7

Explain what part of neural tube secretes Shh and what activates

Answer 7

Shh released from
- notochord
- floor plate

in neural tube -> activates GLI TF: Shh conc highest in ventral - highest GLI activaion in ventral side

Question 8

How is Shh signal transmitted?

Answer 8

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

Question 9

What is the gradient of Shh in neural tube?

Answer 9

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

Question 10

What is the purpose of establishing Shh gradient in neural tube?

Answer 10

Different gradient -> different GLI TF activation -> different genes have different Shh thresholds for activation -> different neural cell identities developed

Question 11

What is the mechanism behind negative feedback between two expressed genes for a single signalling molecule?

Answer 11

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

Question 12

What are the anatomical parts of forebrain and hindbrain?

Answer 12

Forebrain: telencephalon, hypothalamus
Midbrain: -
Hindbrain: cerebellum

Question 13

What is the pattern of Shh, Fgf8, Wnt expression in embryo?

Answer 13

Question 14

What neurons induced by high Shh conc? What other signalling molecules contribute?

Answer 14

Dopaminergic (DA) neurons - form very close to neural floor plate
- Shh (high conc)
- Lmx1a
- Msx1/2
- Nurr1
Only midbrain tissue can form DA neurons

Question 15

Can dorsal cells be induced to change to ventral cells?

Answer 15

Yes if Shh conc is increased:
dorsal cells -> ventral cells

Question 16

Explain the function of isthmic organiser

Answer 16

isthmic organiser (isO) secretes FGF8 - important for dorso-ventral axis development in embryo

Question 17

What is an organiser?

Answer 17

Organiser - a group of cells that transmit a signal to adjacent cells to influence their developmental fate

Question 18

What Shh, Wnt, Fgf8 and their mixtures signal to develop?

Answer 18

Most important gradient - Wnt

Question 19

How does the brain anatomy change in case of Alzheimer’s, Huntington’s and Parkinson’s?

Answer 19

Alzheimer’s: brain mass shrinks
Huntington’s: brain mass shrinks
Parkinson’s: DA neurons degenerate (no visible change in mass)

Question 20

Where are DA neurones located?

Answer 20

Dopaminergic (DA) neurons in nigral midbrain (Substantia nigra)

Question 21

What is the function of DA neurons?

Answer 21

Dopaminergic (DA) neurons supply dopamine to putamen in striatum -> DA loss -> slow movement, tremmor

Question 22

What neural degeneration is involved in Parkinson’s?

Answer 22

DA neurons degenerate in Substantia nigra - no dopamine supply for putamen

Question 23

How can stem cell therapy be used to treat Parkinson’s?

Answer 23

DA neurons lost -> trying to recover DA neurons by injecting stem cells (fetal ventral midbrain tissue / hESCs / iPSCs) - into Substantia nigra - DA neurons recovered

Question 24

What happens if only one side of the brain exhibits DA neuron loss?

Answer 24

• 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)

Question 25

What are the problems associated with using fetal tissues in Parkinson's treatment?

Answer 25

- **ethical** issues - poor / unpredictable **supply** of tissue - poor quality / tissue **heterogeneity** => alternative - iPSCs

Question 26

What are the types of pluripotent stem cells?

Answer 26

- embryonic stem cells (**ESCs**) - from IVF - induced pluripotent stem cells (**iPSCs**) - tissues taken from adults - pluripotency induced by TF

Question 27

How is DA neuron differentiation induced from stem cells?

Answer 27

- ESCs / iPSCs differentiate into **primary neural tissue** - **default** path - **forebrain cortical neurons** - **if** **Shh, Wnt, FGF8** introduced (floor plate signalling) -> **DA neurons**

Question 28

What tissue is the progenitor of DA neurons?

Answer 28

DA neuron progenitors - **midbrain floor plate**

Question 29

What is the process of making DA neurons from hESCs / iPSCs?

Answer 29

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

Question 30

What day of DA neuron development is best for transplant into Parkinson's affected brain?

Answer 30

**Day 16** - transplantable day