Stem cells

Question 1

What are stem cells?

Answer 1

A stem cell is an unspecialised cell that can divide and self-renew indefinitely and has the ability to differentiate into specialised cells under appropriate conditions

Question 2

Features of stem cells

Answer 2

1. They are unspecialised
2. They are capable of dividing and renewing themselves for long periods
3. They can give rise to specialised cell types under appropriate conditions
   -> triggering cell differentiation -> internal signals are controlled by a cell’s genes while external signals include chemicals secreted by other cells, physical contact with neighbouring cells, and certain molecules in the microenvironment

(All stem cells have the complete set of genetic info. but, due to differential gene expression, different set of genes are expressed during different stages of embryonic development)

Question 3

Potency specifies the stem cell’s potential to differentiate into different cell types:

Answer 3

1. Totipotent (Zygotic stem cells)
   -> they are totipotent because they have the ability to differentiate into any cell type to form whole organisms and so are also pluripotent and multipotent
2. Pluripotent (Embryonic stem cells)
   -> embryonic sc are found in the inner cell mass of blastocyst
   -> they are pluripotent because they have the ability to differentiate into almost any cell type to form any organ or type of cell and so are not totipotent but are also multipotent
3. Multipotent (Myeloid and lymphoid stem cells)
   - they are undifferentiated and have the ability to differentiate into a limited range of cell types, usually closely related family of cells
   - they are not pluripotent or multipotent.
   eg. RBC

Question 4

Embryonic stem cells

Answer 4

• es cells are obtained from the inner cell mass of the blastocyst and are pluripotent, giving rise to all derivatives of the three primary germ layers: ectoderm, endoderm and mesoderm during development
• these germ layers subsequently give rise to the multiple specialised cell types that make up the heart, lung, skin and other tissues

Question 5

Blood stem cells

Answer 5

• their primary function is to maintain the steady state functioning of tissues by replacing cells lost through diseases, tissue injury or normal wear-and-tear
• myeloid stem cells give rise to red blood cells, platelets and white blood cells such as granulocytes
• lymphoid stem cells give rise to white blood cells such as B lymphocytes, T lymphocytes and natural killer cells

Question 6

ethical issues

Answer 6

1. informed and voluntary consent during the Donation of biological materials
2. Destruction of embryos during research with hESCs
3. creation of embryos specifically for research purposes during research with hESCs
   -> payment to oocytes donors
   -> medical risk of oocyte retrieval
   -> protecting reproductive interests of women in infertility treatment
4. Conflicting legal and ethical standards when using SCs derived at another institution
5. Risks and benefits of experimental intervention. and informed consent. during stem cell clinical trials
6. the use of hECSc for research and medical applications is often viewed as tampering with nature and hence going against the natural way of life

Question 7

moral dilemma in using human ES cells (hESCs)

Answer 7

• dilemma between to prevent or alleviate human suffering and to respect the value of human life
• to obtain hESCs, the early human embryo has to be destroyed and this means destroying a potential human life.
• but research can also lead to new medical discoveries that may alleviate the suffering of many people

Question 8

Features of induced pluripotent stem cells (IPSCs) - alternative method to obtain embryonic SCs

Answer 8

1. Differentiated adult cells that are induced through chemical signals to regain pluripotency
2. self-renewing
3. pluripotent

Question 9

Potential uses and advantages of IPSCs

Answer 9

1. bioethics
2. genetically matched cells lines: minising cell/tissue rejection issues
3. easier to create
4. IPSCs used as model for the study of diseases

Question 10

Limitations of IPSCs

Answer 10

1. not fully understood if IPSCs and ES cells differ in significant ways (uncovered differences in gene expression and other cellular functions like cell division)
2. safety issues need to be resolved as IPSCs can still become abnormal and be potentially unsafe for therapeutic procedures