Stem Cells and Human Neurogenesis Flashcards
1
Q
Define stem cells
A
2 important properties
- Differentiation gives rise to specialised cell types
- Self-renewal means stem cells can give rise to daughter cells equivalent to the parent cell
2
Q
Describe cell potency
A
- Range of commitment options available to a cell (how many cells can they generate?)
- Totipotent (capacity to form an entire organism eg. zygote)
- Pluripotent (able to form all cell lineages, including germ cells - ectoderm, mesoderm, endoderm)
- Multipotent (can generate multiple cell types that constitute to an entire tissue or tissues - blood cells)
3
Q
Describe embryonic germ layers
A
- Zygote divides into a blastocyst.
- At blastocyst stage divides
- In gastrulation the inner cell mass forms the endoderm, mesoderm and ectoderm with some germ cells
- Ectoderm: neural and skin
- Mesoderm: Bone muscle blood cells
- Endoderm: liver pancreas lung
4
Q
How are stem cells categorised
A
- Self renewal requirements
- Differentiation potency
- Where they come from
Types:
- Pluripotent stem cells
- Somatic (adult/tissue specific, also exist in embryois)
- Cancer stem cells (not a physiological stem cell)
5
Q
Describe pluripotent stem cells
A
- Self renewal is unlimited
- Derived from inner cell mass of embryos (embryonic stem cells - only from culture dish, as can self renew and have pluripotency)
- Somatic human cell types eg. skin (reprogrammed to induce PSCs) - induced
6
Q
Describe regulation of self renewal in PSCs
A
- Intrinsic factors (Oct4, sox2 and nanog - form transcriptional network and regulate gene expression)
- Extrinsic factors (growth factors, ECM, affect expression of intrinsic factors)
7
Q
How do we assess for pluripotency?
A
- Embroid body formation should create 3 germ layers (endoderm, mesoderm, ectoderm)
- Teratoma formation (inject cells with cancer to form teratoma. The teratoma should contain tissue from all 3 layers)
- Chimera formation (mouse pluripotent stem cells into a blastocyst, transplant resulting embryos into a mouse the same as the blastocyst donor. If the cell is pluripotent there should be chimeric colour)
8
Q
Describe somatic stem cells
A
- Neural, skin, blood (bone marrow), intestinal (bottom of crypts)
- Replace injured or damaged cells in our body
- In the brain: subventricular zone and subgranular zone
- Limited self renewal, as they are niche dependent. They are capable of life long self renewal.
- Lower plasticity and will not form teratoma.
9
Q
Describe stem cell niche
A
- Microenvironment that surrounds and nurtures stem cells and enables them to maintain tissue homeostasis
- Neural: cellular elements (astrocytes, endothelial cells, ependymal) and molecular factors (eg. GF, ECM, CSF)
10
Q
Describe multipotent stem cells
A
- Can form all the cell types within one system
- Eg. neural stem cells can make neurons, astrocytes and microglia
11
Q
Where do pluripotent cells exist?
A
- In our body
- All germ cells in our body are pluripotent
- Also in culture
12
Q
Why are PSCs best for neuroscience research?
A
- Limited accessibility of brain tissues, particularly for studying human brain
- Limitation of plasticity of neural stem cells
- Difficulty in creating stem cell niche for neural stem cells in vitro to maintain their self renewal
13
Q
List uses of PSCs in biological research
A
- An in vitro model for studying embryonic development (brain development/neurogenesis)
- A valuable cell model to elucidate molecular mechanisms underlying stem cell differentiation/self-renewal and diseases
- A model to study function of specific genes in vitro and in vivo (mouse ES cells) through genetic manipulation
14
Q
Compare embryonic development of mice and humans
A
- Preimplantation stage human and mice look very similar.
- However, after implantation the mouse has a very different structure to human
- Mouse has a cylindrical shape, and human a disc like shape
15
Q
Compare human and mice brain
A
- Human brain is 1500g with 86 billion neurons, amnd mouse only 0.4g with 70 million neurons
- Human brain has many sulci and gyri, while mouse brain has much less
16
Q
Describe neural differentiation from PSCs
A
Must inhibit BMP as this inhibits pluripotency
17
Q
List uses of PSCs in medicine
A
- Disease modelling (take patients primary cell, make iPSCs and then look for genetic cause, can then test drugs)
- Drug discovery (could also take hESC and manipulate for gene defect then test with drugs)
- Cell therapy
18
Q
Describe cell replacement therapy
A
- Injecting or implanting live cells into a patient, to replace damaged or died cells for the recover of proper physiological functions
19
Q
List challenges for using PSC for cell replacement therapy
A
- Differentiation of specific cell types
- Integration and survival (will form teratoma)
- Immune rejection
- Tumorigenesis
20
Q
List possible methods to prevent tumorigenesis
A
- Generation of iPSCs without changing genomic DNA using small molecules, RNAs and proteins
- Optimal culture conditions to maintain genome stability
- Eliminate undifferentiated cells before transplantation
- Genetic modification of hPSC to prevent tumour formation (toxic ablation - integrate potential toxic gene, administer an inducer and the toxic protein is activated then cells will be killed)
21
Q
Define neural induction
A
- Induction is a developmental mechanism:
- One tissue secrets signalling factors that instruct an abutting (neighbouring) tissue
to differentiate to a new cell fate - Organiser secretes neural inducing signals capable of organising the surrounding cells into the brain and head (eg. hensens node in chicks)
22
Q
Where is the mammalian node?
A
- At the gastrulation front
- The gastrulation primitive streak formation generates 3 new layers (2nd week in human)
23
Q
Describe the 3 germ layers
A
Mesoderm:
- PS derived layer of cells migrates adjacent to the epiblast.
- It gives rise to the mesenchyme; and organs: spleen, kidney, gonads, heart, blood vessels and blood. It also gives rise to paraxial mesoderm: somites which are transient structure containing the precursors of muscle and skeleton of the trunk portion of the body
Definitive Endoderm
- PS derived layer forming on top of the mesoderm. There it displaces/replaces the external epithelial layer (extraembryonic epithelium) “visceral endoderm” which surrounds the epiblast prior to gastrulation.
- The endoderm gives rise to the gastrointestinal tract and organs: liver, pancreas, stomach, gut and lungs
Ectoderm:
- Forms by conversion of the epiblast cells that do not ingress through the PS and will give rise to neuroectoderm and epidermis.
- This neuroectoderm will form only the brain, which will also give rise to the craniofacial muscle and bone of the head
24
Q
List tissues that divide form the primitive node
A
- Anterior endoderm
- Node
- Node derived notochord and prechordial plate
- Loss of node in mouse embryos causes no brain, no notochord but there is a spinal cord
25
Which signals induce brain formation?
- Antagonists of primitive streak signals
26
Summarise brain development
- Brain forms on the “ectoderm” that consists of epiblast cells which do not ingress into the Primitive Streak (PS)
- Brain is induced by signals emanating from tissues derived from the Anterior-PS (mammalian equivalent to Spemann Organiser):
- The Anterior Endoderm (AE) and
- The Node and the mesendoderm (notochord & prechordal plate)
- The AE signals are Antagonists of the signalling pathways: BMP, NODAL and WNT
- The brain grows inside out, from the ventricular zone to the pia surface
27
Describe spinal cord development
- The primitive Streak (PS) generates Mesoderm and Endoderm, but recently it has been shown that the PS mesoderm behind the Node generates neuromesodermal (NMPs) precursors
- Neuromesoderm gives rise to the somites: two rows of condensed structures, which are separated by the node-derived mesendoderm and the neural tissue (neural plate) above the somites that will form the spinal cord neural plate
- WNT and FGF Signals together generate NMPs
- Then FGF alone differentiate NMPs to neuronal precursors; then + Retinoic Acid => spinal cord
- While WNT alone convert the NMPs to somites
28
Where does the PNS develop from?
Neural crest cells
29
List examples of neurocristopathies
- Goldenhar syndrome
| - Waardenburg syndrome
