Stem Cells & the Developing Brain

Question 1

WHY is stem cell proliferation is essential during development?

Answer 1

→ to understand how neural cell fates are determined

Question 2

2 key factors to consider in stem cell proliferation

Answer 2

Molecular factors = genes and transcription factors
Cellular factors = position and timing of cell birth

Question 3

neural cell fates are determined in…

Answer 3

a spatio-temporal manner (i.e., space & time - where and when a cell is born has a large influence on what it becomes)

Question 4

What is cell fate regulated by?

Answer 4

a number of factors - but ultimately depends on the integration of intrinsic signals which are genetically inherited from precursor cells and extrinsic signals that come from the environment

Question 5

Neural stem cell potential?

Answer 5

Multipotent - many potentials!
→ can become a neuron, astrocyte and oligodendrocytes

Question 6

Glial progenitor cell potetnial?

Answer 6

Bipotent - only gives rise to glia (there are only two types! Astrocytes & Oligodendrocytes)

Question 7

Where does the nervous system derive from

Answer 7

the ectoderm layer

Question 8

Bone Morphogenetic Proteins?

Answer 8

a key group of developmental signals

Question 9

Why would we antagonise BMPs?

Answer 9

to induce differentiation of the neural ectoderm, i.e., the blue print of the nervous system

Question 10

Importance of Neurogenic Vs Gliogenic signals?

Answer 10

to determine whether neural stem cells choose a neuronal or glial fate

Question 11

Which comes first in development - Neurogenesis or Gliogenesis?

Answer 11

Neurogenesis precedes gliogenesis in development of the NS

Question 12

Lateral inhibition?

Answer 12

inhibition of the cell lateral to another cell…
NB in the initial stages of development of the NS

Question 13

What is key to the behavior of neural progenitor cells?

Answer 13

the Neural tube under goes two types of division
- Symmetric division: - two identical daughter cells
- Asymmetric division: - two daughter cells, however only one continues dividing and the other migrates and differentiates into a neuron

Question 14

Symmetric Division

Answer 14

NB to increase the pool of neural progenitor cells in order to make the required amount of neurons that are needed by birth

Question 15

Asymmetrical divison

Answer 15

to maintain a stem cell, but also to give rise to a stem cell which will produce neurons

Question 16

What marks the onset of neurogenesis?

Answer 16

the switch from symmetric division to asymmetric division

Question 17

What is the Delta/Notch signaling pathway?

Answer 17

Neurogenic genes which inhibit neurogenin gene expression

Question 18

What are Neurogenins?

Answer 18

a family of proneural genes which drive neuronal differentiation

Question 19

When neurogenin expression is blocked..

Answer 19

When neurogenin expression is blocked in both cells to an equal extent, they have equal levels of delta and these stem cells will not differentiate and will maintain a stem cell fate (to increase the progenitor cell pool)

Question 20

What if one cell increases the expression of the delta ligand?

Answer 20

This will result in a greater signaling through the notch receptro in the blockade of neurogenin in the other stem cell, so this means it will maintain a stem cell fate - the cell with a greater expression of delta: switches on expression of other genes required for neuronal diffrentiation

Question 21

why can’t cells diffretniate at the same time to become a neuron?

Answer 21

Lateral inhibition - involves delta notch inhibition of neurogenesis which is NB in neuronal differentiation.
- When this process is unbalanced, one of them will undergo neuronal differentiation (asymmetrical)

Question 22

Most proneural genes encode..

Answer 22

basic helix-look-helix transcription factors
→ loss of proneural gene expression = decreased neuronal production etc

Question 23

Why is cell division so important in the neural tube?

Answer 23

for populating the developing nervous system with enough cells to ultimately generate the required number for what is needed for normal development

Question 24

asymmetric division is NB because..

Answer 24

not only does it allow the development of neurons, it also allows us to keep the progenitor cell pool intact

Question 25

Zika Virus

Answer 25

infects the proliferating neuronal epithelial stem cells, causing hypo morphism of brain development (smaller brains) because Zika virus kills these developing progenitor cells, meaning there isnt enough of them to make neurons needed for development

Question 26

Nestin

Answer 26

intermediate filament expressed by neuro epithelial stem cells

Question 27

Brain lipid bring protein (BLBP)

Answer 27

Cells which are Nestin positive & BLBP negative - they are undergoing symmetric division
Use of these markers very useful in identifying this process

Question 28

Describe mitotic spindle during asymmetric division

Answer 28

Parent cell attaches to apical complex. NPCs sit on the luminal surface, the spindle is horizontal to the luminal surface & provides cell division in which only one cell maintains contact with this surface. The other cell loses this contact and migrates out into the developing brain, starting neuronal differentiation

Question 29

Mitotic spindle during symmetric division

Answer 29

Vertical to the luminal surface

Question 30

Apical complex

Answer 30

Expresses Par3 protein - proteins in the apical complex (Par complex) at the apical pole of the cells activate delta notch signaling

Question 31

The basal complex

Answer 31

Consists of proteins NB for promoting neuronal differentiation (Ccnd2, Trim32)

Question 32

What is neural patterning?

Answer 32

the process through which cells in the developing nervous system acquire distinct identities according to their specific spatial position

Question 33

The area where neuronal patterning is most extensively studied

Answer 33

The spinal cord
- accesible
- small region in cross section
- the cellular architecture of the spinal cord is known very well

Question 34

Morphogens

Answer 34

e.g., Shh & BMP
a secreted signalling molecule; that elicits different cellular responses depending on its concentration

Question 35

What is a major determinant of neuronal cell fate in the spinal cord?

Answer 35

dorsal-ventral positioning

Question 36

2 signalling centres at the ventral and dorsal midline

Answer 36

• dorsal roof plate
• ventral floor plate

Question 37

What does the dorsal roof plate secrete?

Answer 37

BMPs (bone morphogenetic proteins)

Question 38

What does the ventral floor plate secrete?

Answer 38

Sonic hedgehog (Shh)

Question 39

The absolute concentration of the __ acting on any one cell determines developmental fate

Answer 39

morphogen (e.g. BMP, Shh)

Question 40

Does ventral patterning play a role in motor or sensory spinal circuitry?

Answer 40

Motor

Question 41

Does dorsal patterning play a role in motor or sensory spinal circuitry?

Answer 41

sensory

Question 42

Motor neuron progenitors express…

Answer 42

Nkx6.1 and Olig2

Question 43

Neuron progenitors in other ventral domains become …

Answer 43

Interneurons

Question 44

Nkx6.1 turns on expression of?

Answer 44

Olig2 (bHLH TF)

Question 45

Wnt ligands bind to

Answer 45

Frizzled receptors and co-receptors LRP5/6

Question 46

Mature BMP dimers exert their effects by binding to __, leading to…

Answer 46

BMPRs, leading to recruitment and phosphorylation of receptor-regulated Smad proteins (Smad-1/5), which then complex with Smad-4 and translocate to nucleus

Question 47

Neuron differentiation of Class __ interneurons is BMP/Wnt signalling-dependent

Answer 47

54

Question 48

The patterning of dorsal spinal cord interneurons requires __ signalling

Answer 48

BMP-Smad signalling

Question 49

Neurogenesis has mainly been studied in the __, whereas neural patterning has mainly been studied in the __

Answer 49

Cortex

Spinal Cord