Stem Cells

Question 1

What are stem cells?

Answer 1

Unspecialised cells - don’t have any tissue specific structures (specific proteins) that allow it to perform specialised functions

Question 2

What are the two features of stem cells?

Answer 2

1. They are capable of dividing (mitotic cell division) and renewing themselves for long periods - long term self renewal
2. They are un specialised and are able to give rise to specialised cell types under appropriate conditions - differentiation

Question 3

What is long term self-renewal ?

Answer 3

Stems cells being capable of making identical copies of themselves via mitotic cell division for the lifetime of the organism

Question 4

What are the two possible outcomes when a stem cell divides by mitosis?

Answer 4

1. 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
2. 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

Question 5

What is differentiation?

Answer 5

The process where unspecialised stem cells give rise to specialised cells

Question 6

What happens when a cell becomes specialised?

Answer 6

It has a limited capacity to produce new cells which are used to repair or replace damaged or diseased cells in the body

Question 7

How is stem cell differentiation triggered?

Answer 7

Cell signalling triggers differentiation
- signals may lead to expression of specific genes to form tissue specific structures on the specialised cell

Question 8

What is potency?

Answer 8

It specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cells

Question 9

What are the 4 levels of potency?

Answer 9

(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)

Question 10

Which level of potency does zygotic stem cells have?

Answer 10

Totipotency - ability of cell to differentiate into any cell type to form a whole organism

Question 11

What are zygotic stem cells?

Answer 11

Totipotent stem cells derived from cells in the zygote up to its development to morula (morula included)

Question 12

Which level of potency does embryonic stem cell have?

Answer 12

Pluripotency - ability of a cell to differentiate into almost any cell type to form any organ or type of cell

Question 13

What are embryonic stem cells?

Answer 13

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

Question 14

Can embryonic stem cells be removed?

Answer 14

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

Question 15

What level of potency does adult stem cells have?

Answer 15

Multipotency - capable of renewing itself and producing all the specialised cell types of the tissue from where it originated

Question 16

What are adult stem cells?

Answer 16

Undifferentiated cell that occurs in a differentiated tissue

Capable of making identical copies of themselves for the lifetime of the organism

Question 17

What are the main functions of adult stem cells?

Answer 17

Replenish dying cells and regenerate damaged tissue

Question 18

What are the two types of stem cells that adult stem cells can differentiate into?

Answer 18

Hematopoietic

Mesenchymal

Question 19

What is an example of an adult multipotent cell?

Answer 19

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

Question 20

What are the two types of cells a multipotent hematopoietic stem cell can differentiate into?

Answer 20

Myeloid stem cell

Lymphoid stem cell

Question 21

What do myeloid stem cells differentiate into?

Answer 21

Red blood cells and platelets

Question 22

What do lymphoid stem cells differentiate into?

Answer 22

White blood cells
- eg. T cells, B cells, natural killer cells

Question 23

Where are blood cells produced?

Answer 23

All the various types of blood cells are produced in the bone marrow, arising from hematopoietic stem cells

Question 24

How is the differentiation path taken by the cell regulated?

Answer 24

By cytokines (protein secreted by a cell to signal to other cells) and/or hormones

Question 25

What is umbilical cord blood? And what is its use?

Answer 25

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

Question 26

What is the advantage of using umbilical cord blood stem cells in transplants ?

Answer 26

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

Question 27

What are the potential uses of stem cells ?

Answer 27

1. Replace damaged tissue 2. Testing of new drugs 3. Testing gene therapy methods 4. Studying human development 5. Toxicity testing

Question 28

How are stem cells used to replace damaged tissue ?

Answer 28

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

Question 29

How are stem cells used to test new drugs ?

Answer 29

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

Question 30

How are stem cells used in testing gene therapy methods ?

Answer 30

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

Question 31

How are stem cells used to study human development?

Answer 31

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

Question 32

How are stem cells used in toxicity testing?

Answer 32

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

Question 33

What is toxicity testing ?

Answer 33

It is conducted to determine the degree to which a substance can damage living or non-living organisms

Question 34

What are the four components of the ethical framework?

Answer 34

1. Respect (rights) - informed consent 2. Fairness ($$) 3. Maximising good 4. Do no harm

Question 35

What are some ethical implications in stem cell research which falls under respect (rights)?

Answer 35

1. The method used to retrieve embryonic stem cells requires the destruction of the embryo - can be seen as murder by some 2. Whether the donor of the embryos have informed consent regarding the use for research 3. 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

Question 36

What are some ethical implications regarding fairness?

Answer 36

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

Question 37

What is one of the challenges faced in the use of adult stem cells for transplants?

Answer 37

Their limited ability to generate different cell types

Question 38

What is plasticity/trans-differentiation?

Answer 38

Certain adult stem cells being able to generate cell types of a completely different tissue in the right conditions

Question 39

What are induced pluripotent stem cells (iPSCs) ?

Answer 39

A type of pluripotent stem cells that can be generated directly from adult cells - expands the range of cell types stem cells can form

Question 40

How are iPSCs formed?

Answer 40

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

Question 41

How does iPSCs overcome ethical implications of stem cell research?

Answer 41

- 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

Question 42

How are some of the ethical implications of stem cell research overcome?

Answer 42

Thought the use of induced pluripotent stem cells (iPSCs)