1.11 Normal Control of Cell Growth and Differentiation Flashcards
1
Q
What routes can undifferentiated cells follow?
A
- Differentiation (possibly leaving the cell cycle)
- Apoptosis (mediated cell death)
- Proliferation and/or growth (mitotic divisions and/or increase in cell size)
2
Q
What determines body and organ size?
A
Cell growth
3
Q
What can be used to counter cell growth?
A
Apoptosis or necrosis (good and bad cell death respectively)
4
Q
What does cell growth require?
A
- Incr in cell mass and volume
- Macromolecular synthesis (i.e. proteins, lipids, carbohydrates)
- > these have a relative movement on the cell surface
- > change in cell volume and shape
5
Q
Why is regulation of cell growth/organ size important?
A
- Maintains a massive and consistent size increase during development
- Organs need to be maintained in proportion to one another (typically, in hypoplasia or agenesis then the other organ may increase in size to compensate)
- Cells continue to grow in adults, so must still be controlled
- Defective growth can be seen in a series of human diseases, including cancer
6
Q
How are cell growth and proliferation connected?
A
Usually - but not always - coupled
7
Q
How is cell growth and proliferation typically influenced?
A
By the presence of extracellular growth factors and growth inhibitors, or through contact with the extracellular matrix (ECM)
8
Q
Should organs grow to a fixed size?
A
Under normal conditions, yes - this is the intrinsic control of growth
9
Q
How can organ growth be externally regulated?
A
By reduced/excess extrinsic growth factors and global nutrition regulation (nutrition has a huge effect on growth)
10
Q
When does cell growth occur?
A
- Fertilised egg -> embryo -> foetus -> adult = 10^9 fold increase in size
Growth in adults:
- Hypertrophy (just growth, no proliferation) e.g. in skeletal muscle
- Hyperplasia (growth and proliferation), seen in renewing tissues e.g. stem cells (epidermis of skin, red blood cells), and also in ‘resting tissues’, e.g. thyroid or liver regeneration (usually self limiting, often reversible)
In disease:
- Neoplasia, tumour growth (abnormal growth and division)
11
Q
When does cell/tissue loss occur in development?
A
- Tissue patterning, e.g. digit formation (anterior and posterior death zones seen on the digits)
- Neural patterning e.g. retinal ganglion cells, neural growth factors (NGF) present (necessary to allow correct connections of neurons)
12
Q
When does cell/tissue loss occur due to physiological atrophy?
A
- Ductus arteriosus (pulmonary artery/aorta) at birth
- Thymus as puberty (tends to die off slowly, decreases in function)
- Epithelial cells (e.g. keratinocytes)
13
Q
What is the difference between pathological and physiological atrophy?
A
Pathological is due to -ve external pressures on the tissue
Physiological is often due to natural cellular processes, linked with apoptosis
14
Q
- What are some physiological/developmental disorders?
A
- Hypoplasia and atrophy, e.g. in Klinefelter’s syndrome (XXY) where the testes decrease in size
- Skeletal muscle degeneration after denervation
- Neurodegenerative diseases of ageing (e.g. Alzheimer’s)
15
Q
How can cell growth be studied?
A
- Analysis in cultured cells
- Experimental manipulation of organs/tissues in whole animals
- Genetic analysis in whole animals (humans or model systems such as mice, yeast or fruit flies, can use these due to high level of evolutionary conservation)
16
Q
What drives the cell cycle?
A
Growth (not the other way round as previously thought)
- Certain restriction points within the cell cycle require input from growth factors before a cell is allowed to enter the next stage of the cell cycle
17
Q
What are some examples of growth factors involved in the cell cycle?
A
G1/S cyclin-dependant kinases (CDKs) - controls G1-S phase transition
G2 cyclin-dependant kinases (CDKs) - controls G2-M phase transition
18
Q
- What effect does the upregulation of factor E2F have on cell growth?
A
G1 Cdk is upregulated, causing mass proliferation but skipping the initial growth stage (mass increase in number, none in mass)
19
Q
- What effect does the upregulation of the retinoblastoma protein (Rb) have on cell growth?
A
G1 Cdk is down-regulated, causing the cell cycle to be blocked but G1 stage is still allowed to occur, so increase in cell size but no division
20
Q
What effect does the upregulation of growth factor signalling result in?
A
Upregulation of growth and G1 Cdk, supporting the balanced growth and proliferation of cells
21
Q
What is an example of a time where just proliferation occurs?
A
During development (cleavage stage of embryonic development is just proliferation, no growth occurs)
22
Q
What is an example of when just growth occurs?
A
Skeletal muscle hypertrophy (in response to exercise, cells already fused)
23
Q
What are some examples of when cell growth and DNA replication occur, but no cytokinesis/cell division?
A
- Many myocardial cells are seen to have this (often tetraploid/4N, has many nuclei - unlike muscle cells which are multinucleate because they fuse together)
- Polyploidy in salamanders, some are 2N some are 4N
- Polyploidy in insects etc
24
Q
- What is an example of a growth inhibitor? And the evidence for them?
A
Myostatin, a homologue of TGF-beta
Evidence can be seen in mice with knockout myostatin, can have up to a 3 fold mass increase
25
What molecules can affect growth?
```
Growth inhibitors (decr)
Growth factors (incr - as growth drives proliferation, these can also act as mitogens)
```
26
How were cell growth factors discovered?
Through cell cultures
27
* How can a primary eukaryotic cell culture be developed?
- Normal tissue explant e.g. piece of skin needs to be minced and digested using trypsin
- Leaves single cells and small clumps of cells
Result: monolayer of mixed diploid cell types on glass or plastic, but has predominating fibroblasts
28
* What should a medium for a cell culture consist of?
- Amino acids
- Balanced salts
- Bicarbonate buffer (24mM = arterial)
- 5% CO2 in gas phase
- Glucose
- Vitamins
- For eukaryotes, a 10% calf serum is also useful
29
* How can a secondary eukaryotic cell culture be developed?
Primary culture (mixed but predominantly fibroblasts) is trypsinised and subcultured repeatedly to result in a secondary culture of pure fibroblasts
Growth is anchorage and serum dependant, as well as needing contact with the ECM
30
What are fibroblasts?
Cells in connective tissue that produces collagen and other fibres
31
* Why is serum necessary for cell cultures?
Because growth factors are a key constituent of serum
32
* What is PDGF?
Platelet-derived growth factor (discovered by Gospodorawicz)
- Dimeric glycoprotein
- Stimulates growth/mitogenesis in many (mesodermal) cell types, e.g. fibroblasts and vascular smooth muscle
33
What is mitogenesis and mitogens?
```
Mitogenesis = the process of inducing mitosis in a cell
Mitogens = peptides or small proteins that induce mitosis in cells
```
34
* How can action of PDGF be shown?
- Citrate blood (citric acid prevents coagulation)
- Centrifuge at a low speed
- Centrifuge to remove platelets and replace calcium ions, normal cells fail to grow in platelet-free plasma
- Replace Ca^2+ in solution still containing platelets, they will aggregate and form a clot - remove the clot and then the remaining serum will stimulate cell growth in normal cells
35
How do growth factors work?
Through cascade reactions:
- Interaction with a cell receptor or entry into the cell can allow the activation or inactivation of other intracellular signalling molecules
- This can allow the control of target genes through interaction with transcription factors
- And/or encourage the synthesis of macromolecules (e.g. translational factors) which stimulates the cell growth cycle
36
What are some examples of global growth factors with global effects?
Growth hormones like IGF-1 and IGF-2 (insulin-like growth factors from the liver and embryo respectively)
37
What are some examples of global growth factors with specific effects?
Erythropoietin (glycoprotein cytokine), produced in the kidney but only affects erythrocyte precursors in rec bone marrow (example of an endocrine factor as secreted directly into the blood)
38
What are some examples of local growth factors with local effects?
NGF (nerve growth factor), TGF-alpha (transforming growth factor-alpha)
These are usually paracrine or autocrine
39
What does autocrine mean?
A hormone that only affects the cell it is secreted by
40
What does paracrine mean?
A hormone that only affects cells in the gland and immediate vicinity of the gland secreting it
41
What different types of growth do local and global growth factors regulate?
- Local: often control growth in specific organs
| - Global: able to regulate coordinated growth in multiple organs (therefore can be highly dependant on nutrition)
42
* How can autonomous and non-autonomous control of organ growth be shown experimentally?
Multiple foetal thymuses transplanted into a mouse, all grow to full/adult size - organ already knows what size to grow to
BUT multiple foetal spleens transplanted and their total mass at the end of growth = mass of a normal spleen, showing coordination and regulation - non-autonomous control
43
* How much is the hepatocyte able to regenerate itself?
It is able to regenerate 2/3s of itself
44
What is non-autonomous control and how can it be controlled?
This is where the growth of an organ is not regulated by the organ/final size not 'known', but instead regulated by other factors - has a link to NUTRITION, seen in birth weight and health, majorly affects lifespan
Factor example:
- Growth hormones (e.g. IGF-1, regulates growth of the liver and other organs)
45
* What can be the result of an insulin receptor mutant?
Leprechaunism/Donahue syndrome in humans, lifespan will be limited and short of stature, but everything will be fully formed (just smaller than usual)
46
* What is a major determinant of size in various dog breeds?
IGF-1 gene variants
47
* What is the general function of insulin-like growth factors (IGFs)?
- Global nutritional regulation, they are modulated by local nutrient and growth signals
Can be seen in growth hormone and IGF1 deficient/knockout mice, still fully formed just far smaller than the wild type
48
How is growth of neurones controlled?
Through signals from neighbouring structures, e.g. nerve growth factors (NGFs)
- Size of SYMPATHETIC neurons is controlled by NGFs
- Survival of RETINAL GANGLION axons is controlled by NGFs
The NGFs are obtained through connections with neighbouring cells and neurons, if no connections/incorrect connections made, then neuron won't be able to grow/survive
49
What must growth also be coupled with to form specific organs?
Growth must be coupled with patterning/the structuring of different tissues
Many factors are currently not well understood, but localised expression of growth factors has been shown to be important
50
What is FGF7 and what effect does it have on the dermis?
Fibroblast growth factor 7 (FGF7) is a locally expressed growth factor in the dermis, stimulating growth and proliferation of epidermal basal cell layer above the dermis (involved in wound healing, controls stem cells)
If wounded, more FGF7 will be produced, resulting in more stem cells being stimulated and repair of tissue
51
What effect does FGF8 (and FGF4) have on the apical epidermal ridge (AER) in embryos?
They stimulate growth and proliferation of underlying mesenchymal/mesodermal cells during limb bud formation
52
What hormones regulate bone growth from the cartilage model at the epiphyseal plate?
- IGF-1, made by local chondrocytes stimulated by growth hormones (GHs control how long your bones)
- FGFs (fibroblast growth factors), instruct cells to differentiate into cartilage/not divide (dominant mutation in FGF receptor 3 is linked to achondroplasia/form of dwarfism)
- Steroids, oestrogen and testosterone regulate growth before puberty and cessation of growth afterwards (e.g. males lacking oestrogen receptors keep growing)
- Thyroid/parathyroid related hormones, affect hypertrophy and maturation
53
* What are the only types of cells that are able to grow in free suspension?
Cancer cells
54
What is morphogenesis?
The biological process that allows an organism to develop its shape. Seen especially during development, the third vital process next to cell differentiation and growth
55
What are some examples and features of renewing tissues?
Skin and gut epitheliums, constantly renewing and dividing stem cells
56
What are some examples and features of resting tissues?
Liver, cells only multiply in order to repair damage
57
What are some examples and features of non-dividing tissues?
Neurones - they won't divide after birth
58
What is apoptosis?
Programmed cell death - a series of processes go on within the cell to cause this process to occur, including blebbing, nuclear fragmentation, cell shrinkage and even the changing of phospholipid proportions on the inside and outside of the phospholipid bilayer
59
What do all terminally differentiated cells have in common?
- Should typically contain the same set of organelles
| - They will express some common proteins ('housekeeping genes/proteins)
60
What causes terminally differentiated cells to be different?
They will express cell type-specific proteins that are not expressed in the precursors/non-differentiated cells which will lead to:
- Specialised functions (e.g. specific enzymes, keratin)
- Specialised structures (e.g. melanosomes, sarcomeres, secretory lysosomes)
61
How many cell types are there?
>200 specific cell types, although some cells have subtypes
62
What is a necessary factor for regulating the nervous system and what does it control?
Caspase 9, regulates apoptosis /programmed cell death
63
* What happens in caspase knockout mice?
No apoptosis occurs during foetal cranial development, resulting in too much brain tissue, as roughly 50% of neurones usually die/undergo apoptosis to ensure that the correct neuronal connections are formed
64
At what point in the cell cycle do cells leave to become terminally differentiated?
Before/during G1
65
What is the name for the stage fully differentiated cells enter after leaving the cell cycle?
G0
66
What is terminal differentiation?
Where a precursor cell leaves the cell cycle and begins to express features that will aid the cell's final function - after this point, the cell will no longer divide (except for a few exceptions) and the process is irreversible
67
What are some of the exceptions of terminal differentiation?
- Hepatocytes, due to stimulation from growth factors they are able to reverse their terminal differentiation and re-enter the cell cycle in order to repair damage caused to the organ
- Chondrocytes are programmed to divide once or twice more after becoming terminally differentiated/embedded in the ECM
68
At what point do humans start to differentiate?
During cleavage, around the point where 8 cells are present
69
What happens to developmental potential of cells over time?
- Potency of cells becomes more restricted
- Differentiation is a complex, multistep process that results in GRADUAL specialisation
- Over time, gene expression becomes cell-type specific
70
What are totipotent stem cells?
Cells that can differentiate to become anything, including the placenta, this only occurs for the first four days of embryonic development, after this the embryonic cells are only pluripotent
Good experimental/extra evidence is the banded armadillo, where the first four cells produced will all go on to form an animal
71
What are pluripotent stem cells?
Cells that can divide to form the 3 germ layers (ectoderm, mesoderm, endoderm) within an embryo (and therefore any tissue within the organism) but have lost the ability to form extra-embryonic tissues such as the placenta
72
What are multipotent stem cells?
Stem cells that are more restricted in the cell types that they can differentiate into, but still have the ability to differentiate into more that one cell type - an example would be the haematopoietic cells in bone marrow which can give rise to any of the blood cells. Most adult stem cells are in this form
73
What are unipotent stem cells?
Stem cells that are committed to terminal differentiation and can only form one cell type at this point, so potency is extremely limited, for example skin stem cells
74
What are the stages of terminal differentiation?
Specification
Determination
Differentiation
Likely to exit the cell cycle prior to differentiation
75
What is specification?
Autonomous differentiation, but can be reversed (for example, if in contact with a different type of cell)
76
What is determination?
Autonomous differentiation, but in all circumstances - cannot be reversed
77
What is commitment?
Can involve proliferation, including the germ layers, but is involved in the different developmental transitions that occur, 'commits' cells to a certain developmental path
78
Is development plastic?
Yes, cells can 'change their mind' and respond to their environment in order to allow the correct developmental stages to continue
79
* What is an experimental example of the plasticity of development?
In embryonic development (shown in Xenopus):
- Ectoderm, mesoderm and endoderm are all specified, but ectoderm has yet to become committed, and several other specification/commitment events have yet to occur
- If the mesoderm is removed, and the 'animal cap' of the ectoderm made to come into contact with the endoderm, it will differentiate into mesodermal cells due to factors released from the endoderm
80
Is the genome affected by differentiation?
No, and this is shown through cloning experiments
- DNA is still present and can be reorganised to allow differentiation from a somatic cell, same genome as at start of development is present
- If an oocyte is 'pricked', activating it through convincing the cell that fertilisation has occurred, a nucleus can be removed from a somatic cell from another organism of the same species (preferably with a distinctive phenotype) and inserted into the activated oocyte
- The factors within the activated egg will reverse the chromosomal modifications from terminal differentiation of the somatic cell, resulting in the development of a 'clone', or genetically identical organism to that of the organism the nucleus was derived from (NOT the oocyte)
Gurdon won the Nobel prize for this discovery in 2012
81
How are the genomes of specific cell types formed?
Through cell specific transcripts and cell specific transcription factors
82
* What is an example of a cell-specific transcript in muscles?
MyoD is a basic helix-loop-helix protein that regulates muscle specific genes - it inhibits G1 cyclin accumulation and proliferation, whereas growth factors inhibit MyoD's DNA binding ability. In muscle development, the cell cycle and terminal muscle differentiation are mutually exclusive processes
83
* What is the effect of knocking out both MyoD and Myf5 in muscle development?
Mice with the double knockout form no muscle at all, but if only one is knocked out, muscle still forms as normal
84
How stable are differentiated states?
Very stable, only very few cell types (e.g. hepatocytes) are able to reverse the process with aid of growth factors
85
What enables stability of the differentiated state?
- Transcription factors show positive autoregulation, so bind to and activate their own gene, causing rapid proliferation
- Factors that drive differentiation block the cell cycle, leading to G0 and terminal differentiation
- Promoters of inactive genes will be methylated and associated histones deacetylated, forming heterochromatin (stably deactivated, dense chromatin)
- Active genes are stably activated using the opposite methods, so their chromatin is euchromatic (loosely packed)
86
What is a critical feature of somatic cloning technology?
That the stable activation and inactivation must be reversed - oocytes contain many of the molecules and factors that can reverse the blockage of genes
87
What are iPS cells?
Induced Pluripotent Stem Cells, where differentiated cells are artificially reprogrammed to become stem cells through the expression of transcription factors that are specific to that level of potency
They can be reprogrammed into a huge variety of different cells, so have huge clinical potential
88
What are the limitations of iPS cells?
They have a lower proliferation rate and earlier senescence period than embryonic stem cells, so can produce a lower number overall and take longer to do so
89
How can terminal differentiation be maintained?
Some cells obtain this through the presence of specific transcription factors
90
* What is some experimental evidence for how terminal differentiation can be maintained through specific transcription factors?
B cells/immune cells:
- Removal of the Pax 5 transcription factor in mature B cells results in the production of uncommitted progenitor cells that can then differentiate into different cell types (Cobaleda, 2007)
91
How can differential gene expression be regulated through alternative splicing?
Alternative splicing is where splicing can occur at different places along the same transcript in different cells due to the presence of different associating factors strengthening or weakening splice sites (e.g. neurexin, which has hundreds of forms, and fibronectin, which has secretory (liver) and adherent forms)
92
How can differential gene expression be regulated through RNA editing?
RNA editing is where different editing events can result in the formation of different transcripts, resulting in different proteins, or different functional RNA molecules may cause transcripts to have different fates in different cells (e.g. Apo-B100 in the liver as opposed to edited Apo-B48 is involved with intestinal epithelial chylomicrons)
93
How can differential gene expression be regulated through genomic arrangements?
THIS IS SPECIFIC TO B CELLS AND LYMPHOCYTE PRODUCTION
| Here, the genome is edited and rearranged to ensure that different antibodies can be made in different cells
94
How is cell type-specific commitment and differentiation most commonly achieved?
Through the instructions and signalling from neighbouring cells - this is called induction or regulative development
95
What are some methods of cell-cell signalling?
- Diffusible ligands bind to a cell surface or intracellular receptor, with the ligand being secreted from a cell in the direct vicinity (juxtacrine or paracrine)
- Interactions between a cell-surface ligand and a receptor (juxtacrine)
- Gap junctions, which are specific cell connections that allow the transfer of some molecules (juxtacrine), these are important in controlling how many new cells are formed
96
What does paracrine signalling mean?
This is a type of cell-cell or cell-ECM signalling where a cell can induce changes in nearby cells (wider range than juxtacrine)
97
What does juxtacrine signalling mean?
This is a type of cell-cell or cell-ECM signalling that occurs in multicellular organisms where the cells are in very close proximity/requires contact (smaller range than paracrine)
98
How are somites affected by different growth factors and signals?
Through the establishment of a gradient of factors such as Wnt1/Wnt3 or SHH from the neural tube and notochord respectively, and also input of BMP4 (bone morphogenic protein 4) from the lateral plate mesoderm, different regions of the somite differentiate slightly and commit to become different parts of the body, like the dermis, hypaxial muscles, epaxial muscles or the sclerotome. Somites are partly involved with limb bud formation also.
99
* What is an experiment showing the effect of Hox genes?
Drosophila Antennapedia, where a dominant mutation in the antennapedia Hox gene (Antp) results in a failure of fly development where legs are produced in the place of the antennae
100
* What Hox gene causes synpolydactyly?
Human HoxD13, and this is where too many digits are produced along with some becoming fused
101
* What happens if the 4 cells in an early blastomere of a sea urchin are split up and then allowed to grow normally?
A normal larvae is produced - the cells retain their totipotency and so can differentiate and proliferate to form a whole organism
102
* What is mosaic development?
A type of developmental process/regulation of differentiation that doesn't require cell-cell interactions - this is where each cell is partially differentiated on its own, so polarity already exists and it can be predicted what tissue each cell will become
103
* When is mosaic development seen in mammals?
During stem cell development:
- Asymmetric division is controlled by highly evolutionarily conserved proteins such as PAR and Numb proteins amongst others
- These regulate stem cell division in all higher animals and are asymmetrically located
104
Is the genome of a differentiated cell altered in sequence?
No, not usually - different modifications will occur as different signals are received
105
Do stem cells have specialised gene expression programs?
Yes, but typically they are still able to proliferate
106
What are the different ways through which a cell can be born?
Exponential growth
- Cells born from cell division
- Rapid, clonal expansion
Stem cell growth
- Stem cells are self-renewing, meaning that one cell after cell division will remain a stem cell
- Stem cells have the capacity for generating specialised differential cell types through division and then differentiation
107
What are stem cells?
- Undifferentiated
- Capable of renewal
- Can divide without limit
- Do experience a progressive loss of potency during development (totipotent cells in first four divisions of embryo to multi- or unipotent cells in adults)
108
In which tissues are stem cells particularly important and why?
- Epithelium
- Blood
- Liver
- Muscle
- Brain
Important to maintain cell populations, last for a long time but must be renewed
109
* Where does renewal in the oesophagus occur?
- Starts in nuclear dense proliferating region, where the stem cells are
- Cells divide here and then migrate upwards through the stratified squamous structure, differentiating the further up they go
- These cells replace those constantly being sloughed off the surface into the lumen
110
* Where are the stem cells in skin tissue?
- In the basal cell layer
- Contains a few true stem cells (don't divide often) and many transit amplifying cells (amplify the divisions of true stem cells that do occur)
- Cells express a series of different keratin proteins during differentiation
111
* Where are the stem cells in gut tissue?
- Dividing cells lie in the 'crypts' then move upwards
| - Shortest known turnover time (~1 week)
112
What are the four cell types produced by multipotent epithelial stem cells?
- Absorptive cells (brush border cells, enterocytes, absorb nutrients, multiple microvilli)
- Goblet cells (secrete mucus)
- Enteroendocrine cells (15 subtypes, secrete serotonin and peptide hormones
- Paneth cells (innate immune system cells, migrate downwards in small intestine epithelial tissue)
113
From which stem cell do platelets, red blood cells and white blood cells all derive?
Found in bone marrow, haemopoietic stem cell, produces both lymphoid and myeloid progenitors which then form all the different types of cells in the blood
114
How can different subpopulations of cells be identified within bone marrow and then used?
Functional assays:
- Labelled cell surface antibodies (e.g. using GFP) can identify specific cells, these can then be removed and transferred if necessary (e.g. if an irradiated mouse has lost all of its own haemopoietic tissue, just 5 transplanted bone marrow cells can restore the entire population of cells in the irradiated mouse's blood)
115
* What can a bone marrow transplant treat?
Bone marrow transplant = haemopoietic stem cell transplantation
Has to be autologous (from patient) or allogenic (from a HLA (human leukocyte antigen) matched donor and then from the bone marrow, peripheral blood or umbilical cord blood
Can treat:
- Severe aplastic anaemia (bone marrow failure)
- Leukaemia (cancer of the white blood cells)
- Non-Hodgkin's lymphoma (cancer of the lymphatic system)
- Genetic blood and immune system disorders (e.g. sickle cell anaemia and thalassaemia)
116
How does skeletal muscle regenerate?
- Fibres are post-mitotic, but tissue can regenerate new muscle cells through using satellite cells (muscle stem cells)
- Satellite cells in muscle are long, spindle-shaped mononuclear progenitor cells that lie under the basement membrane of individual muscle fibres, usually quiescent
- Activated by hepatic growth factors (HGFs) which are released by damaged fibres upon injury
- The satellite cells then proliferate and fuse to make new muscle fibres
117
Can cardiac muscle regenerate?
No, any damage to cardiac myocytes will only result in scarring as connective tissue instead proliferates
118
Are neurons able to regenerate?
No, they are post-mitotic cells which are unable to divide and regenerate. However, neuronal stem cells can be found in adults
119
Where can neuronal stem cells be found in adults?
- Subventricular zone (generates neurons for olfactory bulb, especially in mice, neuronal stem cells line ventricles and then the neurons migrate to the olfactory system)
- Dentate gyrus of hippocampus (involved in learning, memory and plasticity so requires stem cells)
120
What are the hepatocyte precursor cells?
Oval cells
121
What can pluripotent stem cells give rise to?
The three germ layers:
- Ectoderm (skin and nervous system)
- Mesoderm (muscle, connective tissue, gonads, organs)
- Endoderm (gut epithelium)
122
* How can cells be reprogrammed into iPS cells?
iPS cell = induced pluripotent stem cell
- Four reprogramming factors been able to convert primary cells (e.g. fibroblasts) into pluripotent stem cells:
- > Oct4
- > Sox2
- > Klf4
- > c-Myc
- Other factors also shown to work in combination:
- > Lin28
- > Nanog
- Delivered by viral vectors
- Can use mRNA or protein transfection (transfection is the process of delivering nucleic acids)
123
What is the potential for iPS cells?
- Can be used to study healthy or disease cases (cells generated from specific individuals with their genome)
- Can be differentiated into different cell types
- 'Disease in a dish' allows us to study in vitro models of human disease, even compare them to healthy models
- Valuable for modelling inaccessible cells and tissues such as neurons (has allowed models of diseases such as Parkinson's as Noggin and other factors cause the differentiation of cells into dopaminergic neurons)
- Also provides ultimate therapy for transplantation of 'self' cells (e.g. treatment for spinal cord injuries - replace neurones that have died as a result of the injury, potentially reversing the paralysis)
124
What is the difference between apoptosis and necrosis?
- Apoptosis is programmed, cells kill themselves in a controlled way
- Necrosis is accidental e.g. the result of acute insult such as trauma or ischaemia
125
What are the features and mechanisms of apoptosis/programmed cell death?
- Necessary for neuronal development and digit formation
- Kills and removes cells without spilling bioactive contents
- Molecular pathway involving activation of proteases ad caspases, e.g. caspase 9 cleaves pro-caspase 3 to mature form (caspase 3), which is the executioner (cascade reaction)
- Nucleus condensation and fragmentation
- Membrane 'blebbing' (breaking up/exploding)
- DNA fragmentation (laddering of genetic material seen)
- Apoptotic cell fragments into apoptotic bodies engulfed by phagocytotic cells before bioactive contents can spill out and cause damage
126
Where does apoptosis occur in the epiphyseal plate?
As chondrocytes reach bone after going through the hypertrophic phase, they undergo apoptosis and become ossified bone
127
What stain can pick out cells undergoing apoptosis?
Tunel stain
128
* Describe necrosis and apoptosis during an ischaemic stroke.
Ischaemic stroke: blood supply to the brain is blocked, causing lack of oxygen and nutrients which results in tissue hypoxia and cell death
- Core: cells die via necrosis due to ischaemia
- Penumbra (peripheral affected area): cells survive but are likely to die later via apoptosis due to reperfusion injury
- Reperfusion injuries are where restoration of blood flow and re-oxygenation results in an inflammatory and immune response, causing cells in penumbra to die at a later date
- Caspase inhibitors may be useful drugs to preserve as much nerve tissue as possible
