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B io Factsheet www.curriculum-press.co.uk Number 238 Stem cells: research, potential, and the law Fig 2. Development of embryonic and adult stem cells What are stem cells? There are two types of stem cells: embryonic stem cells, and adult stem cells. Fertilised egg In humans, embryonic stem cells are formed when an egg, which has been fertilised by a sperm, divides to from new cells. Five days after fertilisation, the embryonic stem cells become a blastocyst, comprising the inner cell mass - which develops into the embryo - and an outer layer of cells known as the trophoblast which goes on to form the placenta (Fig.1). Totipotent embryonic stem cells Fig 1. Blastocyst Inner cell mass Pluripotent embryonic stem cells Blastocyst blastocyst cavity Embryonic development in uterus trophoblast Embryonic development in laboratory (up to 14 days) Immediately after fertilisation, the embryonic stem cells which are produced during the first few days of embryonic development are described as totipotent i.e. they are capable of developing into any of the different cell types found in the human body. After the formation of the blastocyst, the embryonic stem cells of the inner cell mass become pluripotent. They can still form any of the different cells in the adult human body, but as they can no longer become cells that form the trophoblast, they can no longer be described as totipotent. Long term culture of stable human embryonic stem cell line Adult stem cells blood brain muscle stem stem stem cell cell cell Why is stem cell research in the news so much? Stem cell research holds huge potential for allowing scientists to better understand how the human body works, and therefore to develop better treatments for when things go wrong. However, because stem cells theoretically have the potential to form an entire human being, the use of these cells in research is also highly controversial. The cells of the inner cell mass then go on to develop into adult stem cells. Adult stem cells are multipotent; they can still develop into multiple cell types, but can only produce cells with a related function. For example, multipotent adult blood cells are capable of producing all the different blood cells in your body, but not hair cells, skin cells, or muscle cells. Potential benefits of stem cell research Already, direct transplants of stem cells from one person to another are being used to treat cancer. Over 7,000 people are diagnosed in the UK every day with leukaemia (cancer of the blood) – which is equal to almost 19 people every day. By replacing the defective blood stem cells of the patient with those from a healthy donor, the symptoms can be relieved. The embryonic stem cells used in scientific research are extracted from the inner cell mass of blastocysts. These cells can be put into a laboratory environment which encourages them to continue to develop into embryos, or alternatively, the cells can be used to generate stable cell lines which remain in a stem cell-like state. 1 Bio Factsheet 238 Stem cells: research, potential, and the law www.curriculum-press.co.uk Additionally, work in the laboratory involving human embryonic stem cells is currently being used to: Typical Exam Question (a) How do adult stem cells differ from embryonic stem cells? (2) (b) Suggest two advantages of using adult stem cells rather than embryonic stem cells (2) 1. Test new drugs. Stem cells taken from patients with specific diseases can be used to trial new drugs for these diseases before testing them in animals or humans. (a) adult stem cells are pluripotent/ ultipotent/can only develop into certain cells; embryonic cells are totipotent/ can develop into any kind of cell (b) easier to obtain; can use patient’s own stem cells therefore no immunity problem; avoids the ethical issues associated with using embryonic stem cells; 2. Increase our knowledge of early human embryonic development. By understanding this process better, scientists and doctors could identify abnormalities during embryonic development that could potentially lead to problems during pregnancy or early childhood. 3. Understand how a stem cell develops into a different cell type. This process is known as differentiation. As stem cells differentiate, they switch off genes required for stem cell activity, and switch on genes required for specialised cell functions – for example, genes that allow a nerve cell to sense pain. If scientists can work out which genes are switched on to produce which different cell types, this information could potentially be used in the future to turn stem cells into new replacement organs for patients requiring transplants as a result of injury or disease. Markscheme What are the rules regarding human stem cell research in the UK? Typical Exam Question Human stem cells used in research are derived from embryos. Because embryos have the potential to become a human being, there are strict rules which scientists have to follow if they want to do research using human embryonic stem cells. Firstly, any research using embryonic stem cells has to be approved by the government. This will depend on: 1. Where the embryo comes from 2. The reason for the research The diagram below shows two different stem cells and the differentiated cells that they can form. Sources of embryos stem cell X red blood cell Currently, human embryonic stem cells can only be used for research if they come from an embryo which was created outside the human body. In most cases, these embryos are created in a laboratory for couples that are unable to have a baby naturally. This process is known as in vitro fertilisation (IVF). Because IVF is highly inefficient, more embryos are created in the laboratory than are used by the couple. Most human embryonic stem cell lines in use in the UK are produced from these surplus embryos – but this can only be done if the couple that donate the sperm and egg give their permission. stem cell Y many other cell types but not embryonic cells Research using human embryonic stem cells that IS allowed in the UK Scientists are allowed to do experiments on human embryos and embryonic stem cells for the following reasons: 1. To find out more about human embryonic development 2. To understand more about human diseases 3. To use this knowledge to develop treatments for human diseases (a) State one site where stem cell X may be found in an adult human (1) (b) Explain why stem cell B is described as pluripotent (2) (c) Explain how genetically identical cells produced from stem cells can have quite different functions (2) (d) Suggest why you might decide to keep a supply of live stem cells from your brain in a laboratory (2). Research using human embryonic stem cells that is NOT allowed in the UK (a) bone marrow e.g. of long bones / ribs); (b) it can give rise to many different types of cell; but not embryonic cells; (c) cell function is determined by which genes are switched on or off/ genetically identical cells will have different genes activated so have different functions; ref to transcription factors/promoters etc; (d) they would be genetically the same as the rest of your cells; allowing you to replace damaged brain cells if you had an accident/suffered brain deterioration;; you would be able to replace more than one kind of brain cell; in perpetuity; Embryos can be produced by fertilising an egg cell with a sperm cell. Embryos can also be produced by other methods, which scientists can use to create embryos with the genes they are interested in. In theory, these techniques could be used to create designer babies, or embryos with specific genes (e.g. for blonde hair or brown hair). It is illegal to produce a child using these techniques in the UK. What is the future for stem cell research? Stem cells are able to differentiate into any cell type found in the human body. Recently, scientists around the world have discovered that it is possible to reverse this process – to turn an adult cell back into a stem cell. .Markscheme 2 Bio Factsheet 238 Stem cells: research, potential, and the law www.curriculum-press.co.uk Why would you want to turn an adult cell back into a stem cell? (d) Complete the table below (6) Arguments for the use of embryonic stem cells to produce tissues Currently, many organ transplants are unsuccessful because the patient’s body recognises the donated organ as a foreign object, and fights the transplant as though it was an infection. Arguments against the use of embryonic stem cells to produce tissues If scientists are able to work out: a) How to turn an adult cell back into a stem cell b) How to turn stem cells into specific organs ...then it could be possible to take cells from an adult human and produce a new organ specifically for them, using their own cells. Because the DNA of the new organ matches the DNA of the patient, the risk of the body rejecting the transplant is reduced. Additionally, creating stem cells in this way would remove the ethical objections to using embryos created by IVF to produce stem cells for research, as this process does not involve loss of an embryo which has the potential to form a human being. This technology holds the potential to revolutionise the field of stem cell research, creating a plentiful supply of ethically acceptable human stem cells. Currently, this research is in its early stages. But watch this space... Step 6 cells stop dividing and differentiate human tissues for transplantation Markscheme Step 7 1. (a) cells which can divide; and differentiate into many different types of cell; (b) (i) IVF/superovulation; (ii) Blastocyst; (c) can use patient’s own stem cells therefore no immunity problem; overcomes problem of shortage of donors; less invasive technique/ less life threatening / reduced recovery time; may be cheaper; stem cells cultured in sterile petri dish (d) Step 5 Arguments against the use of embryonic stem cells to produce tissues stem cells isolated, rest of blastocyst discarded Arguments for the use of embryonic stem cells to produce tissues Step 4 Objection on religious/ethical grounds/ Increases pressure on women to produce surplus embryos grown to form blastocyst Potential for culturing patient’s own cells to provide replacement tissues/ organs or alleviate suffering Step 3 Embryonic stem cells are potential babies/people Spare embryos Embryos should not be considered human at this stage Step 2 Ref to unexpected harmful effects/ Problems with regulation/ ref to designer babies Fertilisation of egg with sperm Stem cells from IVF would otherwise be discarded Step 1 Research into the use of embryonic stein cells is unnecessary as it will soon be possible to use non-embryonic stem cells (a) What are stem cells? (2) (b) The diagram shows how embryonic stem cells may be used to produce human tissues. Use of non-embryonlc cells will need a development phase that used embryonic cells Practice Question (i) Suggest the likely source of ‘spare embryos’ (1) (ii) At what step do the cells lose their totipotency? (1) (c) Suggest two advantages of using stem cells rather than an organ transplant (2). Acknowledgements: This Factsheet was researched and written by Bryony Graham Curriculum Press, Bank House, 105 King Street, Wellington, Shropshire, TF1 1NU. Bio Factsheets may be copied free of charge by teaching staff or students, provided that their school is a registered subscriber. No part of these Factsheets may be reproduced, stored in a retrieval system, or transmitted, in any other form or by any other means, without the prior permission of the publisher. ISSN 1351-5136 3