Exam3Lec9Neurogenesis Flashcards
What are the necessary conditions to be considered a stem cell?
- Proliferation
- Self-renewal
- Production of differentiated functional progeny
- Regenerating the tissue after injury
What is a totipotent stem cell?
it is a Embryonic Stem cell (ESC) Found in the inner cell mass of the blastocyst (fertilized egg)
From there it can begin differentiation to produce the three germ layers and their respective stem cells, committed progenitors, and ultimately differentiated cells.
Are there unique markers to identify NSC? If so, what are they?
NO
ex: nestin was found among embryonic, neural and hematopoietc stem cells when cultured the same way, but it isn’t unique to neural
What gives rise to our CNS?
ectoderm
Where does microglia develop from?
The mesoderm NOT ectoderm
hy
it was a macrophage stuck in brain during early development
not made from neural stem cells
Fill in the blanks
Neurogenesis is dependent on what 3 main processes?
- Proliferation
- Differentiation
- Migration
These processes are not necessarily sequential, occurs simultaneously
Explain how neurogenesis occurs (cell birth)
- In G1: the nucleus is near the ventricular surface (neural tube)-1 cell layer thick b/w pia and lumen ventricle (this is where our brain is growing)
- During S stage: nucleus and surrouding cytoplasm migrate toward the pial surface and DNA replicates.
- During G2: cell grow and nucleus migrates toward lumen again.
- It comes back to the ventricle and undergoes mitosis and can undergo asym ( a neuroblast and a progenitor cells generated) or symm division ( 2 neural stem cells generated)
Migration of the nucleus (toward and away from pial surface) throughout the cell cycle is known as ?
interkinetic nuclear migration. This process involves molecular motor proteins Dynein and Kinesin and is guided by radial glia
What is the diffference between cell proliferation and cell differentiation?
Cell proliferation : process of multiplying the number of cells.
Cell differentiation: process of forming different cell types which form tissues and organs that have specific functions within the body.
What are the 2 types of division that can occur once the cell is large enough and makes it way back down to the ventricle ?
What determines whether a stem cell goes through prolif or differ?
Symmetrical/Vertical Division
Asymmetric/Horizontal Division
What is symmetric/vertical division?
Splitting neural stem cells vertically and they migrate up and down and proliferate
Same fate: expansion of cells population (neural stem stells)- (2 copies of original: making more neural stem cells)
What is asymmetric/horizontal division?
Neuron split horizontally and its asymm b/c 2 daughter cells are differennt. One daughter is going to proliferate and another is going to be a differentiated stem cell. (once becomes a neuroblast and once becomes a copy of original stem cell -AKA stays as a progenitor cell)
Different fate:Expansion of stem cell population while also producing differentiated cells (neurons).
it does both prolif and differentiation
Which facors influence proliferation?
Growth/Trophic Factors
* FGF-2 (bFGF)
* EGF
* Neurotrophins (BDNF/NT3/NT4)
How does FGF-2 (bFGF) influence proliferation?
- In early embryonic NSCs & predisposes toward a neuronal fate
- Induces a slow proliferation
- Lack bFGF receptors during development leads to reduced neurons & glia in cortex while administering bFGF leads to increased neurons in cortex
How does EGF influence proliferation?
- Expressed later in development around the time of gliogenesis
- Vigorous proliferation (quick)
- Deletion of receptors leads to defect in cortical neurogenesis
How does Neurotrophins (BDNF/NT3/NT4) influence proliferation?
- Act through tropomyosin (trk) receptors B and C
- Enhance NSC survival
not impt for prolif
What are other factors that can influence proliferation?
Ephrins & Eph receptors
Adhesion Molecules
Polycomb group (PcG) proteins
Hedgehog
How can Ephrins & Eph receptors influence proliferation?
- Ephrin B2 and EphB2 ↑ proliferation
- Ephrin A2 decr differentiation
How can adhesion molecules influence proliferation?
NCAM & CD24 ↑ proliferation & modify migration
How can polycomb (pcG) proteins influence proliferation?What os it essential for?
What factors are involved?
- Form multiple polycomb repressive complexes (PRCs) which bind to DNA & modify chromatin structure, silencing genes
- Essential for earliest stages of vertebrate development
- Components of PRC2 that are required for activity: EZH2, SUZ12, EED
What is SuZ12?
It’s a suppressor of zeste 12 and 8% of all ESC genes are bound by SUZ12
How does hedgehog influence proliferation
Hedgehog ↑ leads to ↑ in proliferation
What 2 pathways induces differentiation (what determined cell fate)?
Intrinsic and Extrinsic factors
Explain the intrinsic pathway of differentiation
- Molecules that triggeres differention is expressed withinin progenitor
- Forwarded to progeny through invariant pattern of mitosis
Explain the extrinsic pathway of differentiation
- Receptor mediated
- Autocrine (itself), paracrine (neighboring cell) or endocrine(far, blood borne signaling)
- Modify transcription
comes from the the environemnt
What are the extrinsic factors of cell determination?
facors=ligands/families
hy
- BMP/TGF-β
- PDGF/EGF
- Cytokines (IL-6/CNTF/LIF)
- EGF-like receptor/Notch
hy
these are facotrs outrside the cell that lead to extrinsic diff
What is the fxn of the BMP/TGF-β extrinsic factor?
induce neurons or astrocytes
What is the fxn of the PDGF/EGF extrinsic factor?
hy
earliest marker of an oligodendrocyte precursor
* Once fate committed, both PDGF-a & b present
* Once fate committed, EGF promotes further differentiation
hy
only new born cell that has this specifc receptor will becoems an oligo
What is the fxn of Cytokines (IL-6/CNTF/LIF) extrinsic factor?
Important for astrocyte & oligodendrocyte fate
What is the fxn of EGF-like receptor/Notch extrinsic factor?
Required for glial fate specification
What are the intrinsic factors of cell determination?
bHLH
Co-associating protein
Co-activators and Co-repressors
What is the fxn of bHLH
intrinsic factor?
Mash-1, Neurogenin 1&2→neurons
Olig 1&2→Oligodendrocytes
What is the fxn of Co-associating Proteins
as an intrinsic factor?
- Hes-1, Prox-1, Inhibitor of Differentiation (ID)
- Antagonize Mash-1
you get astrocytes not neurons
What is the fxn of Coactivators and Corepressors as an intrinsic factor?
- CREB binding protein (CBP)/p300→astrocytes
- Acts at the STAT binding element within the GFAP promoter
Migration
During neural development, what are the 1st differentiated cells in the VZ?
Radial glia (scaffolding cells)
What is the fxn of the radial glia?
Their radial foot processes extend from ventricular zone to pial zone
Act as primary guidance pathway for postmitotic neurons
acts as scaffold for neural stem cells to come to top and start the process
What are 5 factors the are expressed that play a role in the Migration Process?
Reelin: Push migrating neurons off radial glial
Vimentin
Nestin
S-100B
GLAST
All factors EXCEPT Reelin play a “structural role” as it relates to migration
these work together to pull neuroblast up to cortex and reelin pushes it off so it can migrate to its spot in the cortex
During migration, radial migration occurs ____ as the cortical layers are established
first
early in neural development
In later stages of development, what migration occurs?
Tangential migration and Anterior-Posterior migration
What is tangential migration and its factors that mediate it?
- Formation of cortical interneurons
- Factors: Nkx2.1, Dlx1, Dlx2, Mash1
“my X sMASHed my TANGerines”
What is anterior-posterior migration and the factors that mediates it?
- Newborn neurons from the subventricular zone travel to the olfactory bulb through the rostral migratory stream
- Factors: PSA-NCAM, Reelin, Ephrins, Tenascin-R
this is migration you see in adulthood
neurons from RMS detatch to become neurons w/in OB
What are 3 primary differences between fetal neurogenesis and Adult Neurogenesis?
- It must occur in a permissive environment
- Individualized (smaller scale) process NOT a population event.
- Quiescence Hypothesis
Where can adult neurogenesis occur?
what are the permissive envrionments?
Subventricular Zone (SVZ)
Subgranular Zone (SGZ-Denate Gyrus)
Regions are well vascularized and be influenced by local and circulating regions.
It protectes from anti-neurogenic influences
In adult neurogenesis, what is being made in the the SVZ and SGZ?
SVZ→Mainly neurons
SGZ→Some neurons and some glia
neurons of all developmental stages can be found at any time point, making it an individualized process.
not trying to”build” cortical layers
What is the Quiescence Hypothesis of adult neurogenesis?
NSC’s slowly proliferate and produce transit amplifying cells which are neuroprogenitor cells proliferating fast to form neuroblasts
refers to the stem cells
Parellels the hematopoietic system in which some stem cells would be noncycling quiescent stem cells locked in G0 while others are actively engaged in the cell
Glia as stem cells
If you deplete all proliferating cells in SVZ, ____ can repopulate
GFAP+ astrocytes
the original and later neural stem cells are radial glia or their descendants
What is the order of receptor formation in Embryo Neurogenesis?
hy
- Voltage dependent Na+→Action Potential
- GABAa-R→Depolarization
- NMDA-R→Depolarization
- AMPA-R→Depolarization
What is the order of receptor formation in Adult Neurogenesis?
hy
- GABAa-R→Depolarization (?)
- AMPA-R→Depolarization
- NMDA-R→Depolarization
- Voltage dependent Na+→Action Potential
hy
What is the main difference between the receptor formation of embryo and adult neurogensis? Why does this occr?
- Developing adult neurons DELAY the formation of voltage-gated Na+ channels UNTIL they are fully integrated into the neural circuitry
- This is to prevent unwanted AP firing during migration.
As the cells radially migrate in the olfactory bulb (OB) they recieve synaptic inputs but they remain unable to fire they are fully integrated into the neural circuitry (not electrically active until they reached their newhome)
During adult neurogenesis, what do the new neurons born in the SVZ do?
replace older neurons within the olfactory bulb.
In adult neurogenesis, how do new neurons born in the SVZ replace older neurons within the olfactory bulb?
- Migration via the RMS is mediated by PSA-NCAM and other chemoattractive/repulsive signals in the RMS including integrins, ephrins, astrocytes
- Once the cells reach OB, reelin mediates detachment and Tenascin directs cells to final destination in granule cell layer.
- New cells become interneurons NOT projection neurons
During Adult Neurogenesis in the SVZ, why do new cells become interneurons and not projection neurons?
Granule neurons have no axons, and their output is mediated by bidirectional dendrodendritic synapses with mitral and tufted cells
Adult Neurogenesis in the SVZ takes how long?
15-30 days
1% of the NSC becomes preglomerular cells
In adult neurogenesis, what is occuring in the SGZ?
Cellular proliferation occurs in sub-granular layer of the dentate gyrus.
During adult Neurogenesis in the SGZ, how is cellular proliferation occuring in sub-granular layer of the dentate gyrus?
- Cells migrate into the granular cell layer where they extend dendrites then axons through the hilus and into Ammons horn/ CA3 (No long distance-migration)
- Neurogenesis is interspersed with gliogenesis
- Then most newly generated cells die
How long does Adult Neurogenesis in the SGZ?
Process occurs over 4-7 weeks (proliferation is much slower)
mentioned that is is a big difference
What are 4 characteristics of Adult Neurogenesis in the SGZ?
- Responsive to FGF-2
- Do NOT form neurospheres in culture
- Do NOT undergo long-distance migration
- About 15% form glial cells
What are some differences you see in adult neurogenesis in the SVZ vs DG in young rats?
Why does neurogensis decrease with Age?
Fewer Stem Cells
Environmental Changes
Age Related Changes
What the main diffeerences between neurogenesis while you are young vs when you are old
Why are there fewer stem cell with decr neurogenesis as we age?
- ↑ cell cycle time
- Terminal differentiation
- Cell death
What environmental changes occur that cause decr neurogenesis as we age?
- ↓ trophic support
- ↓ migration
- Altered local cues
What age-related changes occur that causes decr neurogenesis as we age?
- ↓ cellular metabolism
- Oxidative damage
- DNA & protein damage
- ↓ mitochondrial function
- Altered telomerase biology
- Altered gene expression
Is there adult neurogenesis after injury (i.e. stroke)?
YES
Study 1: Neurogenesis increases in SVZ and SGZ after MCAO
Study 2: Neurogenesis increases in SVZ in people after ischemic stroke
Do the newborn cells integrate into existing neurocircuitry after injury?
YES
Study 1: It is believed that astrocytes/microglia release factors which draw newborn cells to sites of injury.
Study 2: Newborn cells release the appropriate neurotransmitters.
Study 3: Newborn cells are electrically active.
Are Endogenous Stem Cells reparative?
NO
Study 1: Newborn cells don’t necessarily target the appropriate neurons and could lead to epilepsy due to unwanted AP firing.
Can Endogenous Neurogensis be enhanced by adding growth/trophic factors?
NO
Study 2: We do some increases in neural stem cell proliferation but its not enough.
Some factors shown effective: Erythropoeitin (EPO), Neutrophins, IGF-1, VEGF
Can stem cell transplants repair a damaged brain?
YES
Study 1: Showed improved behavioral outcome, increased differentiated cells surrounding the lesion and decreased the size of the lesion.
What is the mechanism of recovery for stem cell therapy?
4 studies
Study 1: Production of appropriate neurotransmitters at appropriate locations.
Study 2: Neurotrophic factors (i.e. NT-3) lead to increases in neuronal fibers.
Study 3: 2hr IV infusion of Neural Stem Cells (NSC) led to significant decreases in inflammation.
Study 4: NSC migrate to the site of tumors. In other words, they can be used as a targeted delivery system to fight injury/disease
adding trophic factors did a better job the neural cells itselfs
What are the 5 advantages of Stem Cell Transplantation
- Can expand the cell population
- Can differentiate into many different cell types
- The cell migrate
- The cells have the potential to integrate into mature brain circuity
- Low immunogenicity if using fetal cells
There are many stem cell niches throughout the body, such as embryonic stem cell, adipose derived, induced pluripotent stem cells, how do you choose which one the use for transplant?
depends on what you think the most impt mechanism of repair is
What are Induced Pluripotent Stem Cells (iPSCs)?
a type of pluripotent stem cell that can be generated directly from a somatic cell. These cells can develop into MANY different types of cells or tissues in the body (one size fits all).
Explain genesis of Induced Pluripotent Stem Cells (iPSCs)
Patient fibroblasts are reprogrammed with master regulators of pluripotency: c-Myc, OCT4, Klf-4, and SOX2.
iPSC colonies are then formed (return to embyronic like stage) which can be used to form neural precursor cells via dual-SMAD inhibition.
What is the Best Cell Type to Transplant? Why?
hy b/c her study
Umbilical Cord blood cells
Results: 48 hours post-stroke , there was an 80% decrease in damage due to an interruption of inflammatory and apoptotic responses.
