Stem Cells 2 Flashcards
What are tissue specific stem cells?
These are multipotent not pluri.
e.g. Neurone stems cells make neuronal tissue.
Primarily held in G0
You can find stem cells in tissues by identifying cells that divide using antibodies that identify cell cycle stages. What are the 3 given example of this?
- BrdU taken up by DNA when it is being replicated in S phase; label with antibodies
- Fluorescent activated cell sorting - Dissociate tissue, label w antibodies, gently put through machine; lasers push out any cells with marker
- Label with DNA dye e.g. DAPI to work out relative levels of DNA (work out which cell cycle phase they’re in)
Adult stem cells are often in G0. Label retaining assay can be used to overcome this to help identify stem cells in adult tissues. Name a label retaining assay?
A pulse chase: you pulse with label for division and chase later to see which labels have been retained
Outline an example Pulse Chase.
H2B GFP (Histone 2B) fusion can be incorporated within chromatin of all cells. Takes place in culture. Any cells dividing will dilute the label quickly. Stem cells wont divide often so will retain label histones and glow green under microscope (label-retaining cells). Will need further characterization but likely to be stem cells.
Why is stem cell division kept to a minimum?
Division risks mutations therefore division is kept to a minimum.
How is stem cell division in adult tissues kept to a minimum?
Stems cells divide once and then the daughters divide alot. It’s less important to keep daughter cells mutation free because they die quickly.
Why do some older tissues have fewer stem cells?
Some may have undergone apoptosis. This leads to the tissue being unable to repair itself and homeostasis is lost.
What is a stem cell niche?
The environment that regulates everything about a stem cell.
Niche can include so many signals.
What factors make up the niche?
- Chemical signals, including those from blood vessels
- Mechanical forces
- Neuronal inputs (e.g. from hippocampus)
- Cell adhesion
Give an example of a physical anchor in a stem cell niche.
DE-cadherin in Drosophila testes, N-cadherin in bone marrow hematopoietic
Why is symmetry of division important for stem cells?
In early division you make lots of cells and they are symmetrical and then you start to make asymmetrical and can differentiate cell type layers.
Motor protein can be key in this process. If you are not able to orientate mitotic spindle properly you will get abnormal division.
What is the most rapidly renewing mammalian tissue?
The gut (10^11 epithelial cell ~200g lost everyday in small intestine)
Why is a lot of stem cell activity require in the gut?
It is a really harsh environment
Where are stem cells found in the gut?
In the crypt which is at the base of the villi
What is the stem cell niche in the gut like?
Surrounded by cell. There is continual division of stem cells with trans-amplifying cells at the top which differentiate and get lost
Why don’t mutations in the trans-amplifiers not matter as much?
It is the mutations in the stem cells that cause gut cancer. transamplifier cells mutations don’t exist for the life of the organism like stem cells do.
