Differentiation, Development and Apoptosis Flashcards Preview

HLTH2210 > Differentiation, Development and Apoptosis > Flashcards

Flashcards in Differentiation, Development and Apoptosis Deck (23)
Loading flashcards...

Provide a brief overview of cellular development

- Genes are not gained of lost in the normal course of development
- Their expression is controlled
- Differentiation is determined by the selective expression of genes within a cell
- Thus different cells express different proteins
- Cells commit to certain fates


What is differentiation and how does it occur in a spatio-temporal manner

- Cells differentiate to carry out specialised functions, produce specific proteins
- Preceded by rapid proliferation
- DNA orchestrated set of cellular changes that normally occurs without error
- Development of specialised cells recognised morphologically
- Regulation of gene expression in a spatio-temporal manner (integration / coordination of events)
- Spatial: Cell fate / differentiation patterned in space
- Temporal: Involves the intricate patterning & timing of cell proliferation, activation of cell division in some regions, imposition of cell cycle arrest in others


What is symmetric vs asymmetric division

- Symmetric: Yields identical daughter cells that may have different fates if exposed to different external signals
- Asymmetric: Yields two different types of daughter cells with different fates, asymmetrical localisation of cell fate determinants lead to unequal daughters cells


What are stem cells and stem cell niches

- Undifferentiated cells that may or may not be committed to a particular fate
- Give rise to more stem cells (self renewal) and generate differentiated progeny
- Present at all stages of development
- Maintain stem cell population, increase stem cells or increase differentiating cells
- Stem cells are formed in niches that provide signals to maintain a population of undifferentiated stem cells but prevent excess proliferation
- Stem cells regenerate differentiated tissue cells that are damaged, sloughed, or aged
- Most stem cells are multi-potent and can undergo symmetric or asymmetric self-renewal divisions


What are the types of stem cells

- Totipotent: Ability to give rise to a new individual, given adequate maternal support (fertilised egg)
- Pluripotent: Ability to give rise to a wide range of somatic cells / tissues
- Multipotent: Can develop into a few cell types (blood, muscle, nerve, bone)


What are embryonic stem cells

- Embryonic blastocyst inner mass cells are pluripotent
- Give rise to all differentiated cell types of the organism
- Pluripotency is controlled by
state of DNA methylation, chromatin regulators, certain micro-RNAs, and TF (Oct4, Sox2, and Nanog)
- Can be isolated, cultured and maintained / grown indefinitely to form differentiated cell types


What are somatic stem cells

- Considered to be multipotent, limited capacity to divide (lack telomerase activity)
- Maintain / regulate homeostasis and repair / regeneration


What are induced pluripotent stem cells (iPS)

- Formed from somatic cells by expression of key TFs
- Treatment with therapeutic compounds, transplant genetically matched healthy cells
- Wound healing, blindness, deafness, stroke, bone marrow, spinal cord injury, arthritis, diabetes, cancer


What is the difference between differentially expressed and constitutively expressed genes

- DE: Inducible genes, only turned 'on' when needed, regulated
- CE: Housekeeping genes, always turned 'on', continually transcribed


What mediates development

- Transcriptional Regulation: inducible / housekeeping genes
- Cell Signalling: Direct cell-cell contact, soluble factors released by cells (morphogens)


How do gradients of maternally derived regulatory proteins establish polarity of the body axis and control transcriptional activation of zygotic genes

- Mother deposits material (mRNA and protein) that creates asymmetries and set up gradients that broadly define areas (basic body plan map)
- Gene interaction subdivides these areas (cells differentiate)
- These identities are remembered, asymmetries at poles, chemical longitude and latitude system
- Subdivide territory into broad domains and create finer subdivisions and commit them to memory
- Establish anterior-posterior (segments), dorsal-ventral (germ layers)


What is apoptosis

- Programmed cell death that is a normal and necessary event of normal development
- Triggered by variety of signals, active, physiological / pathological
- No inflammation, cell shrinkage
- Fragmentation / condensation of chromosomes / cytoplasm
- Organelle disruption
- Fragmentation of cell, sequential destruction of cell
- Release membrane bound fragments, phagocytosis


What is necrosis

- Death due to unexpected and accidental cell damage (toxins, radiation, heat, trauma, hypoxia)
- Swelling, holes appear in the plasma membrane, intracellular materials spill into surrounding environment
- Causes tissue damage, inflammation, oedema, recruitment of WBC’s
- Passive, pathological, inflammation, cell / mitochondrial swelling
- DNA degradation, breakdown of plasma membrane, loss of ion transport, cell lysis / dissipation


How is cell death regulated

- Cells have intrinsic apoptosis pathways for suicide without release of cytosolic contents
- Crucial for normal development
- Require trophic factors that bind surface receptors to repress apoptosis
- Balance between life and death
- Involves activation of cellular caspase proteases (death signals)


What is the function of apoptosis

- Embryogenesis, morphogenesis, cell selection, immunity
- Tissue remodelling, maintaining organ size / shape
- Protection against cancer, p53 / inducing apoptosis
- Cells lost are replaced by mitosis
- Occurs in all multicellular organisms


What are caenorhabditis elegans death (CED) proteins

- CED3 and CED4 are required for apoptosis
- CED9 prevents apoptosis
- CED3 (caspase) and CED4 (activates caspase activity)
- CED9 binds with CED4, localising on mitochondrial membrane and prevents
- Availability of CED4 in the cytoplasm depends on the concentration of CED9
- Isolate mutants with defective apoptosis and identify the affected gene / protein product


What are caspases and how are they activated

- Apoptosis is driven by activity of caspases
- Cysteine containing aspartate-specific proteases
- Normally present as inactive zymogens (harmless to cell), zymogen is activated by proteolysis
- Active caspases then target other proteins for destruction


What are the extrinsic and intrinsic activation mechanisms of apoptosis

- Extrinsic: Activated by extracellular ligands binding to cell-surface death receptors (TNF-R / FAS), physiological receptor
- Intrinsic: Activated by intracellular signals generated when cells are stressed (mitochondria), internal damage


What factors induce apoptosis

- Double strand breaks, stalled replication forks, DNA mismatches and nucleotide damage
- Activate ATM / ATR
- Activate CHK1 / CHK2 (kinases)
- Stimulate Cdc25 (stalls CC / DNA synthesis)
- Activates p53 protein, tumour suppressor, death of cancerous cell by inducing apoptosis, p21
- Cytotoxic T cells transfer serine proteases that permeabilise membrane


What are the consequences of dis-regulation

- Causes a variety of diseases that include cancer, autoimmune diseases and neurodegenerative diseases
- Diseases involve a failure of apoptosis to eliminate harmful cells (cancer) or the inappropriate activation of apoptosis leading to loss of essential cells
- Too much results in tissue atrophy, neuro degeneration / thin skin
- Too little results in hyperplasia, cancer and atherosclerosis


What is neuro-degeneration

- Neurons are post-mitotic (cannot replace themselves neuronal stem cell replacement is inefficient)
- Neuronal death caused by loss of proper connections, loss of proper growth factors and / or damage (oxidative)
- Neuronal dysfunction or damage results in loss of synapses (reversible) or loss of cell bodies (irreversible)
- Parkinsons, alzheimers and huntingtons


What is cancer

- Receptors Apoptosis eliminates damaged cells (damage to mutations to cancer)
- Tumour suppressor p53 controls senescence and apoptotic responses to damage
- Most cancer cells are defective in apoptotic response (damaged, mutant cells survive)
- High levels of anti-apoptotic proteins or low levels of pro-apoptotic proteins to cancer


What is ageing

- Ageing leads to both too much and too little apoptosis (evidence for both)
- Too much (accumulated oxidative damage) leads to tissue degeneration
- Too little (defective sensors, signals) leads to dysfunctional cells accumulate, hyperplasia (pre-cancerous lesions)