L4: Stem Cells + Reproductive Ethics

Q: What are stem cells?

A: Unspecialized cells that can reproduce indefinitely and differentiate into one or more specialized cell types (potency)

Q: What are the two main types of stem cells?

A: Embryonic stem cells and adult stem cells.

Q: What does "totipotent" mean?

A: Stem cells that can generate all tissues of the embryo and extra-embryonic tissues like the placenta (e.g., zygote).

Q: What does "pluripotent" mean?

A: Stem cells that can generate cells from all three germ layers but not extra-embryonic tissues (e.g., embryonic stem cells).

Q: What does "multipotent" mean?

A: Stem cells that can differentiate into multiple cell lineages but not all germ layers (e.g., hematopoietic stem cells).

Q: What does "unipotent" mean?

A: Stem cells that can differentiate along only one lineage (e.g., most adult stem cells).

Q: What is the difference between autologous and allogeneic stem cell use?

A: Autologous stem cells are derived from and returned to the same individual, while allogeneic stem cells come from one individual and are used in another.

Q: What is somatic cell nuclear transfer (SCNT)?

A: A cloning method where the nucleus of a differentiated cell is transplanted into an enucleated egg to reprogram it.

Q: Who achieved mammalian cloning and cloned Dolly the Sheep?

A: Scientists at the Roslin Institute in 1997 using nuclear transplantation.

Q: What are the challenges of reproductive cloning?

A:

low success rates

health issues in clones - incomplete reprogramming of the transplanted nucleus (aged 6, Dolly developed lung condition associated with older sheep)

don’t always look/behave identically​

Q: What is therapeutic cloning?

A: Using SCNT to produce patient-specific embryonic stem cell lines to replace injured or diseased tissues.

Q: What are human embryonic stem cells (hESC)?

A: Pluripotent cells derived from the inner cell mass (ICM) of blastocysts, capable of generating cells from all three germ layers.

Q: What are induced pluripotent stem cells (iPSCs)?

A: Somatic cells reprogrammed to behave like embryonic stem cells by introducing specific genes like Myc, Oct3/4, Sox2, and Klf4.

Q: What are potential applications of iPSCs?

A: Cell therapy to replace dysfunctional tissues and research to model diseases and test drugs.

Q: What is the significance of Yamanaka's research on iPSCs?

A: He demonstrated that mature mammalian cells could be reprogrammed into a pluripotent state, earning the Nobel Prize in 2012.

Q: What are the ethical concerns with hESC research?

A: hESCs are derived from embryos, raising questions about the definition of life and the morality of using embryonic material.

Q: What is teratoma formation?

A: A tumor containing tissues from more than one germ layer, which can arise if undifferentiated pluripotent cells are used in therapy.

Q: What are hematopoietic stem cells (HSCs) used for?

A: Replacing blood and immune systems in conditions like leukemia, sickle cell anemia, and after chemotherapy.

Q: What are the current clinical uses of bone marrow transplants?

A: Primarily for blood and immune system replacement, not for other tissue types.

Q: What are the challenges of scaling up stem cell therapies?

A: Immune rejection risks, potential for teratomas, and the need for large tissue banks for matching.

Q: What is a transgenic mouse?

A: A mouse genetically modified to express or suppress specific genes, often created using embryonic stem cells.

Q: What are the dual potentials of iPSCs?

A: Cell therapy for tissue replacement and research for understanding diseases and drug discovery.

Q: Why is stem cell therapy considered promising but challenging?

A: It offers solutions for regenerative medicine but involves scientific, ethical, and practical hurdles like safety and scalability.

what tissues can stem cells be isolated from?

- adult tissues i.e. bone marrow

- umbilical cord

- foetal tissue + organs (pregnancy termination)

SCNT steps:

differentiated animal cells – don’t divide in culture or develop into multiple lineages​

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removed nucleus of an egg (enucleated egg)​

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Replace it with nucleus of differentiated cell (nuclear transplantation or somatic cell nuclear transfer)​

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If nucleus from donor maintains full genetic potential, leads to development of the recipient cell into all tissues/organs of an organism

applications of embryonic stem cells

- basic research

- drug testing

- toxicology

- drug discovery

- therapy

Current concerns in the clinical use of hESC

Potential for teratoma formation from undifferentiated hESC​

mixed differentiation (need to define methods)

Small experimental scale, need to scale-up​

Off-the-shelf therapy would still require huge bank to tissue match, ​otherwise immune rejection issues​

Animal products used in culture, infection and immune risks

teratoma

An often benign tumour containing tissues of more than one germ layer, ​arising from totipotent cells

often occur in the ovary or testes

transgenic mice

mice into which the genetic material of another species has been introduced

knock-out mice

mice with a specific gene "knocked out" or made non-functional in all or only specific cells

adult stem cells

stem cells that are found in adults that can differentiate and form a limited number of cells (within their specific region)

four "stem cell" master regulatory genes

Myc

Oct3/4

Sox2

Klf4

Nanog and LIN28​ improve the efficiency of

iPS cells

advantages of iPSC

can make person-specific cell lines​

no embryos damaged

Make lines from people with genetic disease and study lineages ​eg: ALS (Lou Gerig disease, Motor neurone disease)​

disadvantages of iPSC

genetically modified

potential oncogenesis or damage to host genome

differentiation = hESC with similar limitations

Stimulus-Triggered Acquisition of Pluripotency

a proposed method (banned/not in use):

process of creating pluripotent stem cells by subjecting ordinary cells to specific types of stress