Tissue stem cells Flashcards
What potency are postimplantation epiblast ?
pluripotent
what potency are adult stem cells
multipotent
what are the function of adult stem cells
long term hemeostasis and repair, replenish the cells
lost through normal wear-and-tear and are ready to rapidly expand upon injury
when does multipotent progenitors exist
towards the end of gastrulation
what do multipotent progenitors do
they receive signals from surrounding tissues and start to differentiate into a more restricted progenitor or terminally differentiated cell types
compare self-renew ability between tissue stem cells and progenitors
TSC can self renew without losing potential. Progenitor cannot, it is highly proliferative but potential decreases over time and become more and more specialised
when does adult stem cells appear
appear in fetal stem cells at around the time of birth
function of hematopoietic stem cells
it can give rise to all cells
what can replenish hematopoietic stem cell after irradiation
bone marrow transplant
do all adult tissue have resident stem cells?
no eg. pancreas, n patients with type I diabetes, where the immune system wrongly targets the beta cells of pancreas that
produce insulin in response to elevated blood sugar levels. In the absence of these cells, the pancreas is not able to produce insulin and blood sugar levels
are left unchecked leading to high blood sugar (hyperglycaemia)
name another organ with no resident stem cells
brain, can lead to neurodegenerative diseases resulting in loss of function due to neuronal dysfunction
what are transit amplifying cells
an undifferentiated population in transition between SCs and differentiated cells
How do you identify tissue stem cells
by label retaining assay, giving post-natal mice labelled nucleotide analogue (IdU) which incorporates DNA in all proliferating cells and some number of cells were found to retain label and designated as label retaining cells
what cells can Label retaining assay identify
stem cells in intrafollicular epidermis giving rise to stratified epithelium of skin , neural stem cells at SVZ and dentate gyrus, satellite cells (muscles stem cells, precursor of muscle cells) in muscles
What is the function of paneth cells
support stem cells
what can be observed in label retaining assay in small intestine
paneth cells are retained and there is constant turnover of intestinal stem cells that continuously divide and are retained as stem cells or TA cells
how do stem cells maintain undifferentiated
by staying in stem cell niche. Niche provides a specific microenvironment composed of extracellular matrix and various support cell types which provides the right biochemical and physical environment to maintain stem cells undifferentiated
what is key to keep stem cells undifferentiated
cell position, Differentiation often occurs as cells leave the niche and those
move away from the signals the stem cells need.
How does paneth cells affect stem cell differentiation
paneth cells, fibroblast, myofibroblast, smooth muscle cells and endothelial cells located in the crypt base produce signalling molecules to activate Wnt signalling and inhibit BMP signalling. cells move away from crypt base and paneth cells and decrease Wnt signalling and increase BMP signalling, diving stem cell differentiation
Function of stem cell niche
to recreate stem cell niche to expand TSC in vitro, study the pathological expansion of stem cell pool through dysregulation of niche or signals emanating from niche
how do you capture progenitor cells in vitro
immortalising the cell type of interest by forcing expression of oncogene, yielding mixed cultures where differentiated and undifferentiated cells are mingled, progenitors can be maintained in a homogenous self-renewal state, preserving the capacity to re-enter development and differentiation
what cells can be captured in vitro ?
embryonic stem cells, epiblast stem cells, neural stem cells and neuroepithelium stem cells
what similarities do NS cells and NES cells have
they both grow in same culture condition- basal medium supplemented with EGF and bFGF
Where are NES cells derived from
from human fetal tissue during short window of time in development (week 5-7)
What do NES cells differentiate into
hindbrain-specific cell types
Where are NS cells derived from
from mouse and human fetal cortex at later stage (E16.5 in mouse, week>7 in human)
What can NS cells give rise to
neurons, astrocytes, retaining characteristics of radial glial cells
Why are adult stem cells hard to grow in vitro?
ASC reply heavily on complex niche to direct between self-renewal and differentiation,
What are organoids
miniature organ-like structures that grow in 3D and contain stem cells and differentiated cell progeny.
arranged in a manner very reminiscent of tissue of origin and can be propagated
How are organoids derived ?
Lgr5 is a protein expressed by the intestinal stem cells (also called Crypt base columnar cells).
These cells can be purified and isolated. Under the right culture conditions organoids can be derived. The organoids self-assemble into mini-guts, with Lgr5
positive cells, interspersed with Paneth cells, giving rise to differentiated cells of the villus.
How do you find adult stem cells ?
label retaining assay, lineage tracing, cell isolation and serial transplantation, molecular profiling of stem cells,
what is the methodology behind label retaining?
a short of pulse of nucleotide analogue given to tissue, nucleotide incorporated into DNA. If cells are highly proliferative, labelled nucleotide will be diluted over time and if cells proliferate slowly, label will be retained
What are the limitations of label retaining
only useful to identify slowly proliferating cells, If the stem/progenitor cell proliferates very rarely, it will be difficult for the cell to be labelled in the first place, no information on potential
What limitations do lineage tracing has
- Dyes dilute over time and not all systems are readily accessible for injection
What do cell isolation and serial transplantation of HSCs do
- HSCs are extracted from bone marrow and purified by means of combination of cell surface markers
- HSCs can be isolated from second individual and transplant onto third -> serial transplantations (prove self-renewal) to reconstitute entire blood lineage
What does molecular profiling tells us
can start designing strategies for locating the different cell types within tissues, isolating them for in vitro experiments or
using lineage tracing to study what types of cells they can give rise to, identify growth
factors or matrix proteins they might produce, and look for signs of signalling pathway activity in the tissue stem cells themselves.
How can you find out if it is a progenitor or a stem cell?
Generic lineage trace. If it is a stem cell, undifferentiated descendants of that labelled cell will still be present over a long period of time. If cell in progenitor, descendants will not be present as undifferentiated cells but only as differentiated progeny.
How can you start to determine what culture condition might allow you to grow organoids from this putative stem cell?
Look at what genes (and therefore likely proteins) are expressed in the stem cell and surrounding cells. Analyse pathways which might be active. The important growth factors and activated pathways might give you a clue what to add to the growth medium for your organoids.
Cancer is thought to arise from mutated tissue stem cells rather than terminally differentiated cells. Can you think why?
Stem cells already have many of the properties that characterise cancer cells (cell cycle, telomerase activity, etc). Therefore the threshold for these cells to become cancerous is lower than that of a terminally differentiated cell, which would have to acquire many more mutations.
- Name 3 things that the niche can provide stem cells with.
- signals to keep the SC undifferentiated
- signals to push the SC to differentiate at the right time
- the right physical/mechanical environment
