DNA and the Genome Key Area 4b Stem Cells

Embryonic and tissue (adult) stem cells Learning Intentions By the end of this topic you should be able to: Embryonic and tissue (adult) stem cells Describe 3 examples of present or future therapeutic uses of stem cells Describe 3 other areas in which stem cell research can be useful Describe the main ethical issues relating to the different types of stem cell use

Embryonic and Tissue Stem Cells

Differential Gene Expression in Development Multicellular organisms, such as humans, contain around 100-200 different cell types Although every cell contains identical genetic material only 3-5% of genes will be expressed in a given cell. On average each of the 200 cell types express 100-200 unique “signature” genes

Embryonic Stem cells (ESCs) Embryonic stem cells have the potential to differentiate into all of the cell types that make up the organism (pluripotent). This is because all of the genes in ESCs can be switched on so these cells can differentiate into any type of cell.

Embryonic stem cells

Embryonic stem cells come from very early embryos (5-14 days after fertilisation) called blastocysts.

Tissue (Adult) stem cells Tissue stem cells are involved in the growth, repair and renewal of the cells found in tissue. They are said to be multipotent as they can differentiate into all of the types of cell found in a particular tissue type For example, blood stem cells located in bone marrow can give rise to all types of blood cell.

Adult stem cells are found at several locations around the body. Hematopoietic stem cells give rise to different blood cells. Mesenchymal stem cells give rise to bone, cartilage, adipose tissue.

Therapeutic and Research uses of Stem Cells

Uses of Stem Cells Scientists have used their knowledge of stem cells in many different areas of research: Therapeutic uses of stem cells – as stem cells from the embryo can self-renew under the right conditions in the lab they can be used to repair damaged/diseased organs or tissues Understanding cellular processes – cell growth, differentiation, gene regulation Model cells – disease development, drug testing

Therapeutic Uses of Stem Cells There are many examples of therapeutic uses of stem cells: Regenerate damaged skin Tissue stem cells associated with the skin can be used to treat burn victims. The stem cells are extracted and grown in the lab before being grafted on. This removes the need to take healthy skin from undamaged parts of the body and so reduces the risk of infection

Therapeutic Uses of Stem Cells Corneal Damage More recently, stem cells have been used to treat cornea in the eye that have been damaged by chemical burning. Stem cells from the patients own healthy cornea are grafted onto the damaged cornea resulting in most patients regaining their full eye sight

Understanding Cellular Processes Stem cells can be grown under laboratory conditions if provided with optimum culture conditions in the presence of certain growth factors When some of these growth factors are removed, the stem cells start to differentiate By looking at the combination of different growth factors, scientists are starting to understand more deeply the processes of cell growth and differentiation In the future, specific cell types will be able to be produced from undifferentiated stem cells and a better understanding of gene regulation gained

Model Cells Other uses of stem cells involve using the as model cells to look at how particular diseases develop and to look at the effect of particular drugs on specific cell types Disease Development Different microbes have different routes of infection and their pathways to disease differ. A greater understanding of these pathways is now possible by looking at the effect of the microbe on the stem cell which leads to better prevention and treatment of these diseases

Model Cells Drug Testing New data is being gained on the effectiveness of dugs used to treat disease. In the past, drug testing was carried out under trials on volunteers where the side effects were not fully understood. With the use of stem cells, there is a reduced risk to patients as the drugs can first be tested on stem cells before proceeding to human trials

Ethics use of Stem Cell Research

Ethical Issues The use of stem cells can offer effective treatments for disease and injury. However, stem cell research has caused a lot of controversy and debate within the public. Is it morally right to extract and use stem cells for research? Stem cells are obtained and used for various processes: The creation of a continuous stem cell line results in the destruction of a human embryo. Is this unethical? Is it ok to use induced pluripotent stem cells? Nuclear Transfer Techniques - mix material from a human cell with material from animal cells (eg cow). Should these hybrid cells be produced?

Continuous Stem Cell Lines The production of a continuous stem cell line from human embryonic cells (no older than 14 days) results in the destruction of the embryo which some view as murder The main debate about the production of the cell line is centred on the question of whether “…a human embryo of less than two weeks is a person?”

Those against claim… … a human life begins when a sperm cell fuses with the egg cell and it is inviolable (sacred and must not be harmed) … a unique version of human DNA is created at conception … a fertilised egg is a human being with a soul .. stem cell research violates the sanctity of life

Those in favour claim… … an embryo is not a person although it has the potential to develop into a person … at 14 days or less an embryo is not sentient (no brain, nervous system, consciousness or powers of sensation) … the death of a very young embryo is not of serious moral concern when it has the potential to benefit humanity … abortion is legal in many countries including the UK – destroying a 14 day embryo is much less objectionable to most people than terminating a fetus at 20 weeks … stem cell research uses embryos generated by IVF but which were not used and would be destroyed as a matter of course

A possible solution… … could be the use of induced pluripotenet stem cells and the increased use of stem cells from amniotic fluid that would not require destruction of the embryo

Induced Pluripotenet Stem Cells A pluripotent stem cell is one that is able to differentiate into any type of cell and give rise to a whole organism It is possible to turn differentiated cells into pluripotent stem cells by switching back on some of the genes that have previously been switched off The differentiated cell is genetically reprogrammed using transcription factors and as a result the induced pluripotent stem cell created can be used for research purposes in place of the embryonic stem cell

Nuclear Transfer Technique The nucleus from an egg is removed and replaced with the nucleus from a donor cell (not always from the same species) The cell produced is known as a cytoplasmic hybrid cell and when it begins to divide, stem cells can be removed after 5 days and be used for research However, as these cells are not 100% human, they are not allowed to be used for therapeutic procedures Nuclear Transfer Technique

Some people believe it unethical to mix material from 2 different species whereas others see it as a means to relieve the shortage of human embryonic stem cells available for research However, all stem cell research is monitored and there are a set of regulations researchers must abide by