15 - Stem Cells and regenerative medicine Flashcards
What are the defining characteristics of stem cells?
- Primitive, undifferentiated
- Can divide indefinitely
- Self renewing
- Give rise to progeny that differentiate into specialised cells
What does totipotent mean?
can give rise to cells of the placenta and all three germ layers
What does pluripotent mean?
can differentiate into cell derived from any of the three germ layers (but not the placenta)
Multipotent
can give rise to several specialised cells or tissues of an organism – are often tissue-specific
Oligopotent
can generate a few cell types within a particular tissue
Unipotent
can produce only one type but are still capable of self-renewal
What is the link between niche and stem cells?
- 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
What is the difference between symmetric and asymmetric stem cells?
• Symmetric o stem cell + stem cell o differentiated cell + differentiated cell • Asymmetric o stem cell + differentiated cell
When does the fertilised egg form a blastocyst?
5-6 days
When does gastrulation occur? What is gastrulation?
• At 14-16 days, gastrulation occurs and forms three germ layers
What does embryonic stem cells give rise to?
cells of the endoderm, ectoderm and mesoderm
Why are there ethical issues with embryonic stem cells?
For stem cells to be obtained, blastocyst must be destroyed
What are the differences between immortality, clonality, undifferentiated and wide developmental potential?
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
What occurs during differentiation?
o Signals for commitment forms committed progenitor cells
o Signals for growth and differentiated form a large quantity of pure, mature, differentiated cells
What are the challenges of transplantation?
o Purity o Cancer development – can give rise to teratomas o Immunology problems – rejection o Ethical problems o Cost
What is therapeutic cloning?
- 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
What are adult stem cells?
- 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
What are induced pluripotent stem cells?
- Somatic cells reprogrammed to produce pluripotent stem cells
- Reduces risk of cancer
- No need to embryos
- No immune rejection
