Gene expression - Stem cells

What is the definition of a stem cell?

An undifferentiated cell which is not specialised to perform a particular function

What is differentiation?

The process by which a cell changes to become specialised for its job

Where are stem cells found?

In embryos and some adult tissues

Where are stem cells found in adults?

In tissues that need constant regeneration for example HSC's which are found in the bone marrow where they differentiate into blood cells

What is cell potency?

A cell's ability to differentiate into other cell types

What are the different kinds of cell potency?

Totipotent

Pluripotent

Multipotent

Unipotent

What is a totipotent stem cell?

Cells that can differentiate into any cell in the body. They are only found during the first four divisions of a zygote

What is a pluripotent stem cell?

A cell that can differentiate into any cell apart from cells in the placenta. They are present once the zygote has differentiated into a blastocyst

What is a multipotent stem cell?

Cells that can differentiate into a few different types of cells such as HSC differentiating into different kinds of cells found in the bloodstream but not into cells such as nerve cells

What are unipotent stem cells?

Cells that can only differentiate into a single type of cell

What potency do embryonic cells have?

Totipotent or pluripotent

What genes do stem cells contain?

All stem cells contain the same genes

During differentiation, what happens with genes?

Only certain genes are expressed

What can conditions stem cells are exposed to change?

Depending on conditions, some genes can be switched on and some can be switched off

What happens to genes that are expressed on stem cells?

They are transcribed into mRNA, which is then translated into a protein

Once a stem cell is specialised, why is it difficult to reverse?

Cell structures including the proteins made from the mRNA are specific to the function of the cell which means reversing those changes is difficult

Give the steps that occur when a gene is switched on in a stem cell to make it specialised (simple).

1. Genes switched on

2. mRNA transcribed from genes

3. Proteins are made from the translated mRNA

4. The proteins modify the cell which is now specialised

Give the steps that occur when a gene is switched off in a stem cell.

1. Genes switched off

2. The mRNA for these genes is not transcribed so proteins are not created at translation

What are cardiomyocytes?

They are specialised cells that make up the heart tissue

What makes cardiomyocytes specific to their function?

They are resistant to fatigue

What was believed historically about cardiomyocytes?

That they were unable to divide, which meant that if the heart were damaged, it would not be able to repair itself

What has recently been discovered about cardiomyocytes?

The cells have some degree of regenerative ability which means that some damaged cardiomyocytes can be replaced overtime

What has the discovery of regenerative cardiomyocytes implied about stem cells?

That the heart has its own supply of unipotent stem cells

What is stem cell therapy?

The use of stem cells to treat or prevent a disease or condition

Give an example of stem cell therapy currently used?

Bone marrow transplants, used to replace faulty bone marrow which may lead the production of abnormal blood cells e.g. treat leukaemia

What conditions do we hope stem cells will treat in the future?

Spinal cord injuries

Heart disease

Respiratory diseases

Organ transplants

What are our current sources of stem cells?

- Adult stem cells.

- Embryonic stem cells.

- Induced pluripotent stem cells (iPSCs)

Where are adult stem cells found?

Found in small numbers in most adult tissue. Most commonly sourced from the bone marrow of a donor. Multipotent so can only give rise to a limited number of cell types

Where are embryonic stem cells found?

Found in embryos between 3-5 days old. These embryos are created in laboratory settings using IVF. Pluripotent so can develop into all cell types in the body.

Describe iPSCs.

Created by reprogramming unipotent cells into pluripotent stem cells using transcription factors in laboratory settings

What are the ethical objections to embryonic stem cells?

- Embryos used in stem cell research are destroyed after 14 days. These embryos had the potential to become a foetus if implanted into a uterus.

- Others believe that life begins at the point of fertilisation. They argue it is morally wrong to destroy embryos

What are ethical considerations of adult stem cells?

- Individuals can give informed consent to have their stem cells harvested

- However, as adult stem cells are multipotent, they have more limited potential than embryonic stem cells

Describe the therapeutic potential of iPSCs.

As iPSCs are formed from adult tissue, the ethical concerns surrounding embryonic stem cells are not present. iPSCs have the same ability to differentiate as embryonic stem cells.

iPSCs could be used to grow replacement organs; these would be genetically identical to the donor, so the risks of organ rejection would be eliminated.

Why would stem cells be useful for organ transplants?

We can grow matching organs which means there wouldn't be huge waiting lists for organs

What can stem cells do to quality of life?

Their therapeutic use could provide life changing treatments