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Trends in stem cell biology (NWI-BM073)
Summary of the lectures of Trends in stem cell biology (NWI-BM073) given in year .
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Trends in stem cell biologyMedical biology master
Lecture 1: Introduction to ethical models
Ethical things concerning stem cells:
- Purpose – enhancements
- Discarding embryonic stem cells
- Justification in principle of using embryonic stem cells
- Source
- Feasibility
- Economics
Ethical subjectivism: is the idea that moral opinions are based on our feelings and nothing
more. On this view, there is no such thing as “objective” right and wrong.
- Do you agree on this or not?
If there would be no criteria/ no ways to evaluate factors in making decisions, it would be a
mess.
How to think about a norm? (normativity)
Ethical models help us build arguments. We still need to be able to discuss.
What are ethical theories?
- Explain what makes an action right or wrong
Ethical theories vs. particular ethical judgements
Analogy with scientific theories and observations
Ethics is not morals!!
Ethics is not law!!
Some kinds of ethical theory
- Consequentialism
- Deontology
- Virtue ethics
- Contractarianism
- Natural law
- Relativism
Consequentialism:
The rightness/wrongness of an action is determined by its consequences
Action Result
Example: utilitarianism the right action is the one that promotes the greatest happiness of
the greatest number (maximizes social utility)
Example: Ethical egoism the right action is the one that promotes the greatest happiness
of the agent (maximizes the agent’s utility)
- An agent is the one doing the action
Deontology:
The rightness/wrongness of an action is determined by inherent features of the action itself,
or by an inherently valid rule
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, Trends in stem cell biology
Medical biology master
Rule action
If an action is of the wrong kind, it is forbidden, no matter how good its consequences are
Rejects both utilitarianism and ethical egoism
“The end doesn’t justify the means” no matter how good the consequences are.
Example: Kantianism right actions must be universalizable and must treat rational agents
as ends, not mere means.
Virtue ethics:
The rightness/wrongness of an action is determined by the character traits it expresses
Character action
Emphasize what kind of person you should be focus on the agent
Possible criticism:
- Relativism?
- Who decides what constitutes a virtue?
- “moral luck”
- Too situational
Lecture 2: Epigenetics and pluripotency in mouse embryonic stem cells.
What are stem cells:
- Stem cells are biological cells that can differentiate into other types of cells and can
divide to produce more of the same type of stem cells (self-renewal).
- In mammals, there are two broad types of stem cells: embryonic stem cells, which
are isolated from the inner cell mass of blastocysts, and adult stem cells.
1. Different forms of cell potency during development in vivo.
- First commitment of cells to inner cell mass and trophoblast.
- Second commitment from inner cell mass to ecto, endo and mesoderm
Conclusion: Cells loose potency during in vivo development
2. Different pluripotent cells in vitro (mouse)
Take an embryo, take out the inner mass and culture them.
You can also capture the cells a little later epiblast cells
Five different types of pluripotent cells:
- Embryonic stem cells (ESCs)
- Epiblast stem cells (EpiSCs; primed ES cells)
- Embryonal carcinoma cells
- Embryonic germ cells
- Induced pluripotent stem cells (iPSCs)
We have to adapt culture conditions so that the cells not start differentiating.
To test for pluripotency, they should be able to multiply and keep on multiplying over time.
Inject them to see if they can contribute to all somatic lineages/produce germ line (e.g. with
GFP).
Detect known marker genes/proteins for pluripotency (Oct4, Nanog, Sox2, SSEA, etc.)
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, Trends in stem cell biology
Medical biology master
Teratomas: inject an embryonic stem cell under the skin of mice and here you can see if a
tumour is being formed, whether all the different tissues are present
(endoderm/mesoderm/ectoderm) strong indication that the cell is pluripotent
Human:
- Multi lineage differentiation in vitro (/ vivo NOT) (germline colonization)
- Normal, stable karyotype
- Extensive proliferation in vitro under well-defined culture conditions
- Known marker genes/ proteins (Oct4, Nanog, Sox2, SSEA, etc.)
NOT In practice absolute proof: contribute to all somatic lineages/produce germ line
(chimerism). Teratomas with differentiated cells of all three germ layers (could be
performed in mice)
Conclusion: ES cells, like some other in vitro cultured cells, are pluripotent.
3. Application of ES cells
Why are ES cells so interesting?
Pluripotent, self-renewal
ES cells are the only ones that will form the complete body!
Model for embryonic development:
- Regenerative medicine (grow in large quantities + differentiate)
- Generation of KO mouse
- Disease model (because differentiate into desired specialisation)
- Cytotoxicity tests (esp. during pregnancy for foetus)
Ethical concern: can we use human ESCs?
- Are human embryonic stem cells human beings with full moral status?
(Embryonal) stem cell therapies:
Replace lost cells, might be useful in:
- Stroke (heart attack): loss of muscle cells
- Duchenne muscular dystrophy: muscle degeneration (eventual death)
- Parkinson’s disease loss of dopamine-generating cells in the substantia nigra, a
region of the midbrain)
- Alzheimer
Dangers:
- Graft rejection (but not when it’s from the patient itself; cord blood!)
- Graft-versus-host: the cells that are injected attack other cells in the body
- Teratocarcinoma
Conclusion: ES cells are very useful for regenerative medicine and to study embryonic
development
4. Molecular mechanisms to maintain pluripotency
Pluripotent, (clonal) self-renewal:
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, Trends in stem cell biology
Medical biology master
- Pluripotency is transient in the embryo
- ES cells are a culture phenomenon
- ES cells are primed to differentiate due to autocrine FGF4
Different ways to inhibit differentiation in vitro:
- Feeders + serum (serum is undefined we don’t know what exactly is in there)
- Lif (leukaemia inhibitor factor) + serum
- 2i (+LIF) (2i= 2 small molecule inhibitors)
Regulatory pluripotency network in ES cells
The pluripotency network acts to:
- Self-induce its own expression, and of other pluripotency genes, by binding in the
promotor
- Repress genes that induce differentiation (silent differentiation factors)
Colocalization of pluripotency network proteins
ChIP-Seq: see where proteins bind. Pluripotency factors (Pct4/Nanog/Sox2) bind at the
same location.
Oct4/Nanog/Sox2 not only bind promotors, but also bind to enhancers (= master regulators)
Effect of manipulation of pluripotency transcription factors
- Not only overexpression and absence of these factors cause differentiation, but also
the reduced expression
- So in vivo, perturbation of this loop is also required to trigger differentiation.
General concept in stem cells that there are a few master regulators
Conclusion: Autoregulatory loop between Oct4, Sox2 and Nanog maintains pluripotency in
ES cells
5. Pluripotency and chromatin structure (epigenetics)
Epigenetics: add groups to genomes/histones or remove it.
Different chromatin structures:
- Euchromatin
- Heterochromatin
Chromatin modifiers are important in
development. Cells need to change their
chromatin when they differentiate.
Also, chromatin modifiers can assist
reprogramming. (next lecture)
Conclusion: Open and unique chromatin conformation is associated with pluripotency.
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