Stem Cells Flashcards
What are stem cells?
Unspecialised cells - don’t have any tissue specific structures (specific proteins) that allow it to perform specialised functions
What are the two features of stem cells?
- They are capable of dividing (mitotic cell division) and renewing themselves for long periods - long term self renewal
- They are un specialised and are able to give rise to specialised cell types under appropriate conditions - differentiation
What is long term self-renewal ?
Stems cells being capable of making identical copies of themselves via mitotic cell division for the lifetime of the organism
What are the two possible outcomes when a stem cell divides by mitosis?
- Symmetrical division : both daughter cells retain the property of self-renewal to ensure that a pool of stem cells is constantly replenished in the adult organ
- Unsymmetrical division : one daughter cell remains a stem cell capable of self-renewal while the other daughter cell undergoes differentiation to become a specialised cell
What is differentiation?
The process where unspecialised stem cells give rise to specialised cells
What happens when a cell becomes specialised?
It has a limited capacity to produce new cells which are used to repair or replace damaged or diseased cells in the body
How is stem cell differentiation triggered?
Cell signalling triggers differentiation
- signals may lead to expression of specific genes to form tissue specific structures on the specialised cell
What is potency?
It specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cells
What are the 4 levels of potency?
(highest)
1. Totipotency : ability of cell to differentiate into any cell type to form the whole organism
2. Pluripotency : ability of the cell to differentiate into almost any cell type to form any organ or type of cell (except placenta or other extra-embryonic membranes)
3. Multipotency : ability of cell to give rise to a limited range of cells and tissues appropriate to their location
4. Unipotency : ability of cell to give rise to only one type of cell
(Lowest)
Which level of potency does zygotic stem cells have?
Totipotency - ability of cell to differentiate into any cell type to form a whole organism
What are zygotic stem cells?
Totipotent stem cells derived from cells in the zygote up to its development to morula (morula included)
Which level of potency does embryonic stem cell have?
Pluripotency - ability of a cell to differentiate into almost any cell type to form any organ or type of cell
What are embryonic stem cells?
Pluripotent stem cells derived from the inner cell mass - part of the early embryo (5 - 6 days) called the blastocysts
These cells would go on to form the entire foetus but not the whole organism
Can embryonic stem cells be removed?
In the lab, cells from the inner cell mass can be removed form the blastocyst and cultured into embryonic stem cells for research and medical purposes
- these stem cells can reproduce indefinitely and divide for long periods in an undifferentiated state
However, the embryo is destroyed in the process
What level of potency does adult stem cells have?
Multipotency - capable of renewing itself and producing all the specialised cell types of the tissue from where it originated
What are adult stem cells?
Undifferentiated cell that occurs in a differentiated tissue
Capable of making identical copies of themselves for the lifetime of the organism
What are the main functions of adult stem cells?
Replenish dying cells and regenerate damaged tissue
What are the two types of stem cells that adult stem cells can differentiate into?
Hematopoietic
Mesenchymal
What is an example of an adult multipotent cell?
Blood (hematopoietic) stem cell
- multipotent with the ability to differentiate into different blood cells and immune cells
- used to treat a range of blood disorders and immune system conditions such as leukaemia and sickle cell anemia
- sources : adult bone marrow and umbilical cord blood
What are the two types of cells a multipotent hematopoietic stem cell can differentiate into?
Myeloid stem cell
Lymphoid stem cell
What do myeloid stem cells differentiate into?
Red blood cells and platelets
What do lymphoid stem cells differentiate into?
White blood cells
- eg. T cells, B cells, natural killer cells
Where are blood cells produced?
All the various types of blood cells are produced in the bone marrow, arising from hematopoietic stem cells
How is the differentiation path taken by the cell regulated?
By cytokines (protein secreted by a cell to signal to other cells) and/or hormones
What is umbilical cord blood? And what is its use?
It is blood from the placenta and umbilical cord that is rich in hematopoietic stem cells
It is collected after the umbilical cord has been detached from the newborn and utilised as a source of stem cells for transplantation
What is the advantage of using umbilical cord blood stem cells in transplants ?
It is less prone to rejections than bone marrow blood stem cells (of the same person)
- cells in the umbilical cord blood have not yet developed features that can be recognised and attacked by recipient’s immune system
- umbilical cord blood also lacks well-developed immune cells so there is less chance that the transplanted cells will attack the recipient’s body
What are the potential uses of stem cells ?
- Replace damaged tissue
- Testing of new drugs
- Testing gene therapy methods
- Studying human development
- Toxicity testing
How are stem cells used to replace damaged tissue ?
Cell-based therapies : specialised cells or tissues grown from stem cells in the lab are transplanted into a patient
Stems cells could also be used to treat a range of conditions like heart failure, spinal injuries etc.
- ability of stem cells to replace damaged cells in body
Hoped that transplantation of appropriate stem cells in damaged tissue will regenerate various cell types of that tissue
How are stem cells used to test new drugs ?
Used for drug test before clinical trail
Stem cells can be directed to be differentiated into the particular cell the drug works on. These cells are more likely to mimic the response of human tissue to the drug tested as compared to animals
This makes drug testing safer, cheaper, and more ethically acceptable
Stem cells may also be useful for screening potential toxins in substances such as pesticides before they are used in the environment
How are stem cells used in testing gene therapy methods ?
Stem cells may prove useful during the development of new methods for gene therapy that may help people suffering from genetic illnesses
(Same as drug testing) Stem cells can be directed to be differentiated into the particular cell the drug works on. These cells are more likely to mimic the response of human tissue to the drug tested as compared to animals
How are stem cells used to study human development?
They can be used to study early events in human development and how cells differentiate and function
This may help researchers find answers as to why some cells become cancerous and how some genetic diseases develop, which may lead to clues as to how they may be prevented
How are stem cells used in toxicity testing?
Due to pluripotency of stem cells, it paves the way for an unlimited supply of primary human cells (eg. neurons) which are difficult to obtain in traditional ways for toxicity testing
What is toxicity testing ?
It is conducted to determine the degree to which a substance can damage living or non-living organisms
What are the four components of the ethical framework?
- Respect (rights) - informed consent
- Fairness ($$)
- Maximising good
- Do no harm
What are some ethical implications in stem cell research which falls under respect (rights)?
- The method used to retrieve embryonic stem cells requires the destruction of the embryo
- can be seen as murder by some - Whether the donor of the embryos have informed consent regarding the use for research
- Potential medical complications or health risks to donors from donation
- concerns of whether donors are fully informed or aware of the health risks involved with donation
What are some ethical implications regarding fairness?
Stem cell technologies are time consuming and expensive
- high cost of stem cell therapy make it available only to the rich and powerful = widen social divisions and enhance discrimination
What is one of the challenges faced in the use of adult stem cells for transplants?
Their limited ability to generate different cell types
What is plasticity/trans-differentiation?
Certain adult stem cells being able to generate cell types of a completely different tissue in the right conditions
What are induced pluripotent stem cells (iPSCs) ?
A type of pluripotent stem cells that can be generated directly from adult cells - expands the range of cell types stem cells can form
How are iPSCs formed?
The method involves taking mature somatic cells from an adult and introducing genes that regulate function of other genes important for early steps in embryonic development
How does iPSCs overcome ethical implications of stem cell research?
- they bypass the need to destroy embryos for stem cell extraction
- skin biopsy to obtain skin cells is less invasive and fewer risks are involved for the donors
- iPSCs can be made in a patient-matched manner : no risk of immune rejection during transplants
How are some of the ethical implications of stem cell research overcome?
Thought the use of induced pluripotent stem cells (iPSCs)
