Introduction of pluripotency Flashcards
How are cells arranged in a ‘state space’?
1) Give each gene a numerical value
2) Each different SET of genes will have a different numerical value
3) Arranged in an abstract space called a ‘state space’ depending on the SET of genes and their numerical values
What defines the state of a cell?
The combination of genes in the cell
In the ‘state space’, why would you not find cells represented at each position?
- Some combinations of genes are not compatible to be a cell
- Only STABLE configurations make cells and are shown in the state space
Ultimately, what defines a cell type?
The transcription factors present
Are the probabilities of changing between states equal? Why?
NO
- Difficulty due to how many genes need to be turned on or off
- If the two states are far away from each other on the state space
- More genes have to be turned on/off
- Harder to switch between the two states
What does the stability of a cell state depend upon?
- Where the state is positioned on the ‘state space’
(Think of the state space having hills and troughs:
- Hills are unstable
- Troughs are stable, as hard to roll around)
What is the metaphor for differentiation?
- It is like rolling a ball down a hill with valleys
- Only certain pathways can be taken
- When enter one valley (ie. switch certain genes on/off) it becomes much harder to switch to a different pathways
INEVITABILITY of differentiation
What is transdifferentiation? Is it difficult?
- Switching between different unipotent differentiated cells
(ie, jumping between valleys) - Some are more difficult than others
- Some can be overcome with the right factors
What must be reset in order to reset the cell state?
Doesn’t occur naturally
1) Gene expression
- Somatic genes turned off
- Embyronic genes turned on
2) Methylation
- Reset back to ‘totipotent’ configuration
3) Chromatin
- Remodelled
- Different patterns in different states
What POTENTIALLY be used to reset any cellular state and why?
Transcription factors as they are said to define a cell state
When fibroblasts are transfected with MyoD1 transcription factor what happens? How?
- Fibroblasts converted into muscle precursors
- MyoD1 turns on target genes
- Proteins coded for by target genes may switch on other genes
- This may form a cascade and switch the cell state as the genes expressed override the existing gene regulatory netowrk
How induce pluripotency in mouse or human?
Transfect somatic cells with transcripption factors that are known to be expressed in a pluripotent cell
Why does the induction of pluripotency have a low efficiency?
- As the genes which are expressed in a cell are changed, the cells may be able to respond to new signals
- These signals may cause the cell to change to a different state which is ‘off course’ of the original state that was the original target
What are the additional factors which must be added to make iPS cells?
Factors which help the cells to survive and divide such as:
- c-mvc
- hTERT
- SV40T
What are the problems with using viral transduction to create iPS cells?
1) Viruses insert into the genome and could cause a mutation
2) Viruses may not be silenced and could remain active in the cell, causing overexpression of genes which keep the cell in the stem cell stage, can’t differentiatte
