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| Pregunta | Respuesta |
| Types of stem cells | 1. Fertilised egg stem cells - totipotent; can make extra-embryonic tissue, embryo, tissue and organs of the body. 2. Blastocyst stem cells- pluripotent aka embryonic stem cells. Give rise to tissue stem cells for all 3 germ layers. Endoderm, mesoderm, ectoderm. Tissue specific: multipotent: 3. Haemopoetic stem cells- give rise to blood cells 4. Neural stem cells- give rise to cells of the nervous system 5. Mesenchymal stem cells- connective tissue, bone, fat etc |
| What are stem cells | Stem cells are non-specialised cells with specific characteristics: - can self-renew and divide symmetrically - Can differentiate to make more specialised cells |
| Why are we interested in stem cells? | - Stem cells help us to understand human development - Help us to understand control of cell division in cancer - Aid in the development of cell based therapies; reducing need for organ and tissue donors/transplants replacing mutant/damaged cells in diseases such as parkinson's Act as a cell-based drug screening platform |
| Where to embryonic stem cells come from? | - Embryonic stem cells come from the blastocyst, which is the inner cell mass at day 4-5 of development. These can be derived from excess IVF embroyos. - Only around for a short time before they become tissue specific, however labs have come up with a way to keep them non-specific for longer: - Stem cells are grown on a culture of mouse embryonic fibroblasts (MEFS) and irradiated to form a mat so no longer divide. In this form they are pluripotent This serves 2 purposes: - Acts as a sticky substrate for embryonic stem cells to adhere to - secrete embryonic factors required for survival and division of embryonic stem cells Differentiation can then be controlled/manipulated in culture to generate specific cell types. |
| In order to study stem cells, they must remain undifferentated: how we do this... | 1. Inspect cells to see if they look healthy and undifferentiated 2. test the cells to see if they are capable of long-term self-renewal: 1) Isolate embryonic stem cells, place on mat of irradiated MEFS, should divide and fill up dish 2) disassociate either enzymatically or mechanically and replate them onto antother plate of MEFS 3) repeat multiple times. If they keep passaging for 6 months then they can be used as stem cells for studying 4) they then must be karyotyped to ensure that they are normal, and have normal protein expression/transcription factors 5) ensure that they can differentiate by removing them from feeder layer and seeing if they divide - They can then be transplanted into mice to see if they form tetranomas- benign tumors. Issues: -ethics -technique varies from lab to lab so difficult to compare results. |
| Experiment to show that EScs can give rise to all tissues | 1. ES cells taken from a black mouse fertilised in vitro 2. Inject fertilised ES cells of black mouse into the blastocyst of albino mouse 3. implant this into albino white mother mouse 4. this results in mixed-colour mice |
| Controversy over embryonic stem cells | - human embryonic stem cells are derived from the extra blastocysts generated during fertility treatment. This involves destroying the blastocyst. - Ethical questions: *Is it morally acceptable to use embryos for research? *Is an embryo a person? *When do we become a human being? |
| Tissue stem cells | - Generate tissues of the body during development - Includes stem cells isolated from fetal and cord blood - Retained in adult tissues where they are involved in repair and replacement: EG: Bone marrow stem cells Neural stem cells etc |
| Examples of stem cells and what they generate | - haemopoetic stem cells in the immune system: *These are multipotent and when they divide go down either a myeloid stem cell lineage (form erythrocytes, neutrophils etc) or the lyphoid cell lineage (lymphocytes). * Can be used to treat lymphomas, taken from bone marrow. - Mesenchymal stem cells (MSCs) * differentiation along specific lineages eg osteoblasts, muscle cells, tendons, fat etc. Tested in clinical trials for abiliy to replace cartliage, injection of MSCs into joints w/damaged cartlliage |
| Neural stem cells | - Neural stem cells can self-renew or differentiate into - Neural progenitor cells, which have limited self-renewal, or can differentiate into - Lineage specific progenitor cells ie neurons, ogliodendrocytes, astrocytes etc There are 2 regions in the brain that generate new neurons throughout our lives: 1. Subventricular zone- lining lateral ventricles, involved with sensory info associated w/olfaction and memory 3. Subgranular zone of the hippocampal dentate gyrus; spacial learning, memory, pattern seperation, cognitive flexibility and memory clearance. |
| Summary of basic stem cell characteristics | stem cell- committed progenitors- specialised cells |
| The stem cell niche | Stem cell niche: the microenviroment around stem cells that provide support and signals regulating self-renewal and differentiation Chacteristics common in all stem cell niche: - extracellular matrix - stem cells - daughter cells - humoural factors/blood |
| Cancer stem cells | - Standart unspecific therapy on tumour kills off many of the tumour cells, resulting in the tumour shrinking. However, if cancer stem cells remain, relapse is common. Therefore, in order to acheive tumour regression tumour stem cells must be destroyed. |
| Reproductive cloning and stem cell research: showing that pluripotency resides in cell cytoplasm | Experiment in frogs to show that pluripotency resides in the cell cytoplasm: 1. ennucleate egg from froh A 2. Replace egg nucleas with nucleus from differentiated sking cell from frog B 3. Egg transplanted back into tadpole, resulting in a clone of frog B: * this shows that pluripotency resides in the cell cytoplasm* |
| Yamanaka factors | - Shinya Yamanaka found 24 pluripotency factors, which he whittled down to 4 Yamanaka factors. These factors, if transduced into cell, made it pluripotent. - these have similar properties to embryonic stem cells - can create stem cells directly from the patient - nypass ethical issues of using embryonic stem cells. Yamanaka factors: *OCT4 *SOX2 *KLF4 *CMYX |
| Current applications of reproductive cloning and stem cell research | - Treat blood diseases - treat burns - repair corneal damage - bone and cartliage repair - organogenesis eg: cortical tissue, thyroid tissue, cardiomyocytes. |
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