15 - Stem Cells and regenerative medicine

Question 1

What are the defining characteristics of stem cells?

Answer 1

• Primitive, undifferentiated
• Can divide indefinitely
• Self renewing
• Give rise to progeny that differentiate into specialised cells

Question 2

What does totipotent mean?

Answer 2

can give rise to cells of the placenta and all three germ layers

Question 3

What does pluripotent mean?

Answer 3

can differentiate into cell derived from any of the three germ layers (but not the placenta)

Question 4

Multipotent

Answer 4

can give rise to several specialised cells or tissues of an organism – are often tissue-specific

Question 5

Oligopotent

Answer 5

can generate a few cell types within a particular tissue

Question 6

Unipotent

Answer 6

can produce only one type but are still capable of self-renewal

Question 7

What is the link between niche and stem cells?

Answer 7

• Stem cells are maintained and defined by the environment surrounding them
• This environment is produced by differentiated cells which can secrete specific factors and communicate with cells via gap junctions
• Changes within the niche may induce the stem cell to die, divide or differentiate

Question 8

What is the difference between symmetric and asymmetric stem cells?

Answer 8

•	Symmetric
o	 stem cell + stem cell
o	 differentiated cell + differentiated cell 
•	Asymmetric 
o	 stem cell + differentiated cell

Question 9

When does the fertilised egg form a blastocyst?

Answer 9

5-6 days

Question 10

When does gastrulation occur? What is gastrulation?

Answer 10

• At 14-16 days, gastrulation occurs and forms three germ layers

Question 11

What does embryonic stem cells give rise to?

Answer 11

cells of the endoderm, ectoderm and mesoderm

Question 12

Why are there ethical issues with embryonic stem cells?

Answer 12

For stem cells to be obtained, blastocyst must be destroyed

Question 13

What are the differences between immortality, clonality, undifferentiated and wide developmental potential?

Answer 13

o Immortality – grow indefinitely
o Clonality - maintain normal karyotype and expression of telomerase
o Undifferentiated – presence of markers found in undifferentiated cells
o Wide developmental potential – able to divide into a wide range of cell types in vitro and vivo

Question 14

What occurs during differentiation?

Answer 14

o Signals for commitment forms committed progenitor cells

o Signals for growth and differentiated form a large quantity of pure, mature, differentiated cells

Question 15

What are the challenges of transplantation?

Answer 15

o	Purity 
o	Cancer development – can give rise to teratomas 
o	Immunology problems – rejection 
o	Ethical problems 
o	Cost

Question 16

What is therapeutic cloning?

Answer 16

• Unfertilised egg has nucleus removed
• Nucleus from somatic cell extracted
• Diploid oocyte formed using somatic nucleus
• Development initiated and blastocyst formed
• Embryonic stem cells extracted and grown in culture
• Cells are genetically identical to host so no immunological concerns

Question 17

What are adult stem cells?

Answer 17

• Undifferentiated cells found among differentiated cells in a tissue/organ
• Capable of differentiating to produce major specialised cell types of the tissue
• Multipotent – not pluripotent
• Primary role to maintain and repair the tissue in which they are found
• No legal or ethical concerns
• Using a patients own cells will remove the problem of immunological rejected
• Does not lead to tumour formation
• Currently can be sued for skin grafts and bone marrow transplants

Question 18

What are induced pluripotent stem cells?

Answer 18

• Somatic cells reprogrammed to produce pluripotent stem cells
• Reduces risk of cancer
• No need to embryos
• No immune rejection