Differentiation Flashcards
What is meant by “terminal differentiation”?
the final cell form
cell can no longer differentiate into a more specialised form
What is meant by “developmental potency”?
how many different options a cell has to differentiate into
What are the three main areas of the germ layer?
ectoderm
mesoderm
endoderm
What cells can the ectoderm become?
the central nervous system: retina, photoreceptors, neurons
skin, hair and sweat glands
What cells can the mesoderm become?
bone
muscle: skeletal, cardiac (heart), smooth
kidney
connective tissue
What cells can the endoderm become?
liver
gut
lungs
pancreas: exocrine cells, endocrine cells
When are the germ layers formed?
during gastrulation, usually 14-21 days after fertilisation
What is meant by gene constancy?
the fact that all cells have all genes, just some are in an inactive state
What is a TATA box?
a DNA signal that binds the TATA-binding protein TFIID, a transcription factor
What is a helper protein?
a protein that directs RNA polymerase to gene transcription start sites
control where transcription starts not when gene is transcribed
used by all gene sequences transcribed by DNA polymerase II
What are the signal sequences next to genes to which transcription factors bind to?
enhancers
What ways can transcription factors recruit RNA polymerase to the TATA box
- direct recruitment
- indirect recruitment by altering chromatin structure
What proteins are recruited by TFs to alter chromatin structure?
- histone acetyl transferase (HAT)
- acetylation loosens histone interactions w DNA making the gene more accessible - chromatin remodelling complex
in each case these chromatin-modifying enzymes promote rna polymerase binding and function
What does a gene’s transcriptional activity depend on?
- what binding sites are in its DNA enhancer sequence
AND - whether the appropriate (cognate) TFs are present in cell
What is MyoD?
a transcription factor that activates expression of 100s of genes required for muscle differentiation including myosin II
What is the structure of MyoD?
binds to DNA as a dimer
has a basic-helix-loop-helix (bHLH) domain
its recognition sequence on genes is known as an E box
What is the result of transfecting a cell with a plasmid containing the MyoD gene?
can force the cell to become a muscle cell
What are plant trichomes?
small spikes on plant leaves that are spaced evenly
What are some benefits to plant trichomes?
deters insects, breaks up wind currents, reduces sun exposure
How do TF repressors prevent transcription?
- prevent binding of activators
- recruit proteins that tighten chromatin, making the gene less accessible
What is a feature of the GATA1 TF structure?
zinc-finger
What sequence does GATA1 bind to?
A/T -GATA-A/G
What are GATA1s target genes?
alpha and beta globin genes
erythropoietin receptor
heam biosynthesis enzymes
spectrin
What conditions have to be met to activate the beta-globin gene?
GATA1 and CP1 and NF1 have to be bound (present in erythroblasts)
beta globin encodes for the heamoglobin subunits
GATA1 is expressed in several blood lineages but only activate globin genes in which blood cell?
erythroblasts
thanks to CP1 and NF1
What is a common modification made to transcription factors and how does it affect them?
phosphorylation
negative charge causes a conformational change
regulated via a kinase enzyme
What is a GRN?
Gene Regulatory Network
a set of genes, or parts of genes, that interact with each other to control a specific cell function
How do growth factors promote cell proliferation?
activate a protein cascade
mitogen activated protein kinase enters the nucleus and phosphorylates transcription factors
What is EGF and how does it work?
epidermal growth factor is a mitogen
binding to egf receptors leads to phosphorylation of MYC, a bHLH-LZ (leucine zipper) TF which drives transcription of cyclin genes
Where is MYC phosphorylated on the EGF cell proliferation pathway?
on several serine and threonine residues (importantly ser-62)
How does erythropoietin (EPO) induce red blood cell differentiation?
secreted from the kidney
causes phosphorylation of GATA1 increasing its DNA binding affinity
What are transcription factors regulated by?
other transcription factors, and kinases
What are transcription factors important for with regards to differentiation?
orderly progression through to differentiation
control of cell fate choices
What 3 transcription factors are involved in the differentiation in sequential steps of guard cell specialisation?
- speechless (SPCH)
- mute
- Fama
What are somites?
populations of precursors cells that eventually give rise to important structures
What is Pax3?
a ‘paired box’ homeodomain TF expressed in somite involved in muscle cell differentiation
What are the closely related bHLH TFs involved in muscle cell differentiation?
MyoD
Myf5
Mrf4
Myogenin
What TFs are involved in MyoD gene regulation?
Pax3 and signal-activated Myf5, both have to be present
After the MyoD gene is activated it activates its own expression, what is this known as?
positive autoregulation
What signal activates Myf5?
Wnt
How are MyoD and Myf5 eventually degraded and why?
cyclin-dependent kinases phosphorylate them, targeting them for proteolytic degradation
this stops muscle differentiation allowing for enhancement of myoblast proliferation
How is Pax3 degraded and why?
it is only required for early muscle development and must be degraded for later stages to proceed
its mRNA is degraded by RNA interface, specifically regulatory RNA named microRNA miR-1
What TF controls the determination of the ‘eye primordium’ triggering the whole process of eye development?
PAX6
How is the cell fate of a myeloid progenitor decided?
antagonistic interaction between GATA1 and PU.1 TFs
autoregulate to try and boost themselves above the other
How does PU.1 repress GATA1?
can bind to GATA1 as its bound to the GATA1 gene and knock off a coactivator protein
the recruits a chromatin methylation protein which tightens chromatin making the GATA1 gene less accessible
What is the role of cdx2?
gives gut cells the potential to become pre-pancreatic cells
does this by activating pdx1 expression only if fgf2 signal is received from contact with the notochord
What is one way of triggering differentiation in myoblasts?
Removing growth factors to stop proliferation.
