Lecture 5- Basic Mechanisms Flashcards
in cell regulation, what are intrinsic factors?
Transcription factors than either increase or decrease transcription - come from inside of cell
does 1 trascription factor regulate one gene?
no- often goes on to regulate several genes
what are extrinsic factors?
signals coming from outside the cell
ligands than bind and activate a receptor, causing a conformational change in a second messenger/ signal cascade
in early development how many cell fates are there?
4
what are these 4 cell fates?
endoderm, ectoderm, neuroectoderm and mesoderm
what controls which of the 4 cell fates is formed?
a morphegen (extrinsic factor) which interacts with receptors to give a second messenger and affect a master TF
what happens if an embryonic stem cell goes long enough without being induced?
it will follow it’s pre-determined path- so will become neuroectoderm
what does each of the 4 pathways need to do to secure their cell fate is formed?
increase a master TF above a particular threshold.
what 2 factors determine whether or not TF threshold is overcome?
- morphogen concentration (higher conc.= quicker decison)
- length of time exposed to morphogen (low dose can have a cummulative effect over prolonged time)
what are the 4 main morphogen pathways?
- TGF1 (transposing growth factor pathway)
- BMP4 (bone morphogenetic pathway)
- WNT pathway
- FGF pathway
what pathway does TGF1 take stem cells?
endoderm/endomesoderm/ mesoderm
what pathway does BMP4 take stem cells?
ectoderm
what pathway does WNT take stem cells?
mesoderm
what pathway does FGF take stem cells?
neuroectoderm
is FGF required to give neuroectoderm?
probably not as it’s the pre-determined cell fate
what MTF genes are needed to be upregulated to give neuroectoderm?
OCT4 and SOX2
what happens once the 4 main cell type pathways have done their work and main cell types have matured?
the cells go on to switch on new gradients
what is competence?
switching on other gradients in an area where it was previously absent
what is digital function?
where there’s a TF threshold above which genes are activated to drive the cell down a different fate pathway (e.g cell A or cell B)
what’s analogue function?
where high, intermediate and low affinity genes are activated to give different cell substrates (e.g. Cell Ba, Cell Bb or Cell Bc)
in an analogue function, what will low TF concentrations bind to?
only genes with a high affinity
in an analogue function, what will high TF concentrations bind to?
activate additional genes. Those with the highest affinity, 2nd highest and so on… (allows a single TF to give multiple cell fates)
what happens at border/ centre cells (cells between 2 cell types which haven’t recieved a high enough TF conc. to become cells on either side?
these are Naive cells which can be instructed to make different cell types
what are the 2 possible outcomes of border/centre (naive cells)?
they may be influenced bu the newly committed cells on either side
or
the unique boundary cells will now generate and secrete a new gradient signal that subpatterns them
