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Birth and Death Cell
Organisation of the Body
| Question | Answer |
|---|---|
| How do normal cells develop | Cells are born from cell division Exponential growth - one cell divides to give two identical cells This is a rapid, clonal expansion |
| What makes a stem cell | The capacity for self-renewal through cell division The capacity for generating specialised cell types through differentiation |
| What are stem cells | Undifferentiated, are capable of renewal and can divide without limit They can divide to give two stem cells, two transit amplifying cells or one of each They experience progressive loss of developmental potential (loss of potency) |
| Different potencies of stem cells | Totipotent - everything Pluripotent - most Multipotent - many Unipotent - one |
| Adult stem cells | Important to maintain renewal of cell populations that last for long periods of time and must be renewed E.g. epithelium, blood, muscle, liver, brain Committed stem cells only give rise to a small subpopulation of cells |
| Renewal in epithelium (oesophagus) | Stem cells located in the stem cell proliferating layer (nuclear dense region under a microscope) Cells differentiate and migrate upwards towards the lumen where they are them lost |
| Renewal in epithelium (skin) | A stratified squamous keratinised layer Basal cell layer contains stem cells Cells move through skin to replace cells at surface, moving through states of gene expression to terminal differentiation Express different keratin proteins Last 30 days |
| Contents of skin basal layer | Contains very few stem cells and many transit amplifying cells Ture stem cells do not divide often, reducing chance of mutation This allows rapid repopulation as transit amplifying cells have a high differentiation potential - migrate upwards |
| Tissue renewal - Gut | Lining of small intestine renews itself every week Dividing stem cells line the crypts and travel upwards as they differentiate |
| Cell types in the small intestine epithelium | Absorptive cell - brush border, enterocytes, absorb nutrient with microvilli Goblet cell - secretes mucus Enteroendocrine cell - 15 subtypes, secrete serotonin and peptide hormones Paneth cell - innate immune system cells |
| Division in small intestine | Contains multipotent stem cells and transit amplifying cells Absorptive, goblet and enteroendocrine cells travel upwards Reach top of villus 2-5 days after leaving crypt Undergo apoptosis at tip Paneth cells migrate downwards Apoptosis after 20 days |
| Blood cells from a common stem cell | Blood cells are derived from multipotent hemopoietic stem cells, which differentiate and progressively lose potency Form multipotent hemopoietic progenitor, which divides into common lymphoid progenitor and common myeloid progenitor. |
| Bone marrow as a source of blood stem cells | Whole bone marrow transfer will resupply all haematopoietic tissue Can perform functional assay to identify stem cells, identify subpopulations using antibodies and transfer into irradiated mouse - as few as 5 stem cells will repopulate the mouse |
| Bone marrow transplantation | Haematopoietic stem cell transplantation Autologous (patient) or allogenic (matched donor) From bone marrow, blood or umbilical cord Treat severe aplastic anaemia, leukaemia, non-Hodgkin's lymphoma |
| Cardiac muscle regeneration | Almost no regenerative capacity beyond childhood Damaged heart muscle replaced by proliferation of connective tissue, forming myocardial scars |
| Skeletal muscle regeneration | Skeletal muscle fibres are post-mitotic Tissue can regenerate new muscle cells using satellite cells (muscle stem cells) Inactive mononuclear progenitor cells under basement membrane of myofibers Activated by hepatocyte growth factor on damage |
| Stem cells in the brain | Neurons are post mitotic and do no regenerate Neural stem cells exist in humans and mice through adulthood Subventricular zone - generate neurons for olfactory bulb Dentate gyrus of hippocampus - region of brain involved in learning and memory |
| Stem cells in the Subventricular zone | Neuronal stem cells lining ventricles produce new immature neurons (neuroblasts) These migrate to olfactory bulb along rostral migratory stream Form mature neurons at olfactory bulb which interrupt into circuits Experimentally we can grow these |
| Liver regeneration | Animal survive 75% loss of liver Number of cells return in a week, mass in 2-3 weeks Hepatocytes-High capacity for division. Unipotent stem cells used for most tissue repair Other stem cells exist e.g. oval cells (hepatocyte precursors) |
| Embryonic stem cells | Totipotent - from early mammalian embryo can form entire blastocyst (embryo and fetal placenta) Pluripotent - can form embryo but not surrounding tissue. Gives rise to 3 germ layers (Mesoderm, endoderm and ectoderm) |
| Totipotent embryonic cells | Early embryonic cells divide by cleavage These are totipotent - can obtain complete blastocyst from cells at 2 or 4 stage At 8 cell stage cells cannot generate a complete blastocyst, but are still pluripotent |
| Pluripotent embryonic stem cells | Can form an embryo but not the surrounding tissue Gives rise to ectoderm, endoderm, mesoderm Can be extracted from inner cell mass and cultured |
| Reprograming cells to for iPSC | Taking a primary cell type e.g. skin cell and placing it in reprogramming factors will return it to a pluripotent state 4 reprogramming factors - Oct4, Sox2, Klf4 and c-Mc Delivered via viral vectors or mRNA (shorter half life) |
| Disease in a dish models | iPS cells generated from health/unhealthy individuals can be differentiated into the desired cell types This allows us to study in vitro models of human disease, valuable for modelling inaccessible cells such an neurons Potential for self transplants |
| Example - using iPSCs to study Parkinson's | Use disease in a dish to model early neuron dysfunction Skin cells reprogrammed and differentiated into dopamine neurons by providing growth factors that trigger this. Varying concentration of these hormones produces neurons Can then compare function |
| Disease modelling for Parkinson's | Study iPSC dopaminergic neurons from patients to determine phenotype Extend phenotype to sporadic patient cells Understand how early dysfunction leads to disease e.g. synaptic failure, vesicle biology, calcium signalling Screen for novel drugs |
| Stem cell transplantation for spinal cord injury | Stem cells generate neurons, astrocytes, oligodendrocytes Replace dead neurons Reform myelin Scaffold bridge across injury Stimulate axon re-growth Protect from damage e.g. release of growth factor and removal of radicals Suppress inflammation |
| Stem cell transplantation for Parkinson's | Transplantation of dopaminergic neurons (fetal, ES derived or iPSC derived) Transplant into site of cell loss (nigra) or of dopamine loss (striatum) Experimental work in rats and monkeys successful but results on humans very mixed |
| Stem cell transplantation for Muscular Dystrophy | Using muscle stem cells or muscle precursor cells to regenerate diseased muscle Successful treatment in mice Unsuccessful in humans Alternative is genetically modified patient cells |
| Challenges of stem cell therapy for muscular dystrophy | Transplantation by intramuscular injection gives limited spread Massive death of injected cells Immune response of recipient Immunosuppression may permit survival of non-self cells Lifelong immunosuppression is unattractive |
| Apoptosis | Programmed cell death in a controlled manner Characteristic morphological changes |
| Necrosis | Accidental cell death Result of acute injury e.g. trauma, lack of blood supply |
| Mechanism of apoptosis | Molecular pathway involving activation of proteases and caspases e.g. Caspase 9 cleaves pro-caspase 3 to caspase 3 (executioner) Nucleus condensation and fragmentation - visible as laddering of DNA Membrane blebbing Apoptic bodies engulfed |
| Apoptosis in development | Important in interdigital cell death in correct limb development e.g. apoptotic cells between digits in a developing mouse paw Important in metamorphosis of tadpole into a frog. Apoptosis of cells in the tail causes tail to be lost |
| Apoptosis in bone development | At the epiphysial growth plate hypertrophic chondrocytes have been shown by TUNEL staining to undergo apoptosis before ossification occurs |
| Diseases of cell death - ischaemic stroke | Restriction of blood supply leads to tissue hypoxia. Core cells die by necrosis Penumbra cells survive but die later On reperfusion inflammatory and immune responses lead to cell death by apoptosis is the penumbra Caspase inhibitors may prevent this |
| Diseases of cell death - neurodegeneration | Loss of specific neuron, accumulation of protein aggregates Alzheimer's-death of cortical neurons Parkinson's-Death of midbrain dopaminergic neurons Huntington's-Death of medium spiny neurons in striatum Motor neuron disease-death of motor neurons |
| Mutation causing cancer | Ras - activating mutation driving cell division and oncogenesis (20-25% of cancers) p53 - inactivating mutation preventing apoptosis or cell cycle arrest in response to DNA damage (50% of cancers) Bcl2 - high levels inhibit apoptosis (B cell lymphoma) |
| Role of stem cells in cancer | Cancer stem cells drive formation of tumours These represent a small proportion of the tumour They are the required target for therapy, as if stem cells are left the tumour will regrow |
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