4/ differentiation Flashcards
what causes cell diversity?
differences in gene expression
what is the final fate of the cell called
terminally differentiated state - will perform that function until it dies
steps in restricting potency - progressive loss of totipotency
totipotent, pluripotent, multipotent, bipotent, unipotent
what do the stages of differentiation correlate with?
stepwise expression of different regulatory transcription factors
what is the transcriptome?
- all genes being transcribed into mRNA
- More easy but less accurate to measure than proteome
- Amount of mRNA tends to correlate to amount of protein
- not all RNA and mRNA into proteins
what is differential gene expression
different cells/tissues that express different genes
how do TFs bind to DNA
- Bind to DNA backbone
- reach into the major groove to form very specific bonds
- binds through H bonds at recognition sequences
- not entirely stable, can fall off and reattach
- bind in clusters
other names for DNA binding site
cis acting element, regulatory element, enhancer, silencer
enhancers and silencers
- enhancers are binding site for transcriptional activators
- silencers are binding site for transcriptional repressors
- enhancer often refers to both (same stretch of DNA can be on or off switch)
- enhancers are promiscuous (will work on any gene)
insulator elements? barrier sequence?
- insulator: blocks promiscuity of enhancers - they only transcribe desired gene
- barrier sequence: prevents transcription between heterochromatin and euchromatin
inputs that alter gene expression
- many inputs for single expression
- like a computer sensing all inputs before reaching a decision
- each input is a genetic switch responding to extrinsic or intrinsic regulation
expression profile
- created by a single transcription factor
- causes some genes to be switched on and others off
- regulate expression of many genes
—| what does this symbol mean
represses
how can gene activity be regulated by feedback loops
- positive feedback loop: stabalise expression of a gene
- negative: reduce expression of a gene
- transcription factors can also interact with themselves
list muscle specific proteins
- muscle-specific actin
- myosin II
- tropomyosin
- muscle-specific enzymes (eg creatine phosphate kinase)
MyoD
- TF
- Expressed only in muscle precursors and muscle cells
- controls expression of genes for muscle differentiation
- maintains own expression (positive feedback)
experiment working out if MyoD is sufficient for muscle cell differentiation
- took fibroblasts (don’t usually express MyoD or other muscle proteins)
- transfect fibroblasts with MyoD gene
- fibroblasts differentiated into muscle
- MyoD is sufficient to direct muscle cell fate in fibroblasts
fibroblasts
connective tissue cells related to mesechymal cells, commonly used in tissue culture
experiment MyoD required for muscle differentiation?
- mice lacking MyoD develop with normal skeletal muscle
- so MyoD not requied
- 2nd gene Myf5 acts redundantly with MyoD
- mice lacking Myf5 and MyoD lack all skeletal muscle
- determination (mesodermal progenitor to myoblasts):
- mrf4: 1st TF. activates myoD and myf5
- both of those positively act on their own expression
- pax3 also activates myoD
- DIFFERENTITATION (myoblasts to multinucleate myotube):
- inhibited by growth factors
- myoD and myf5 activate myogenin
- MATURATION (multinucleate myotube to muscle fibre)
embryonic vs adult stem cells for muscle
- embryo: most muscle cells from somites
- adult: muscle cells renewed by satellite stem cells that line muscle fibres - form a sheath
- satellite cells have pax7 as a TF.
blood cells as a model for differentiation
- embryo: blood cells made in yolk sac then liver
- adults: bone marrow
- hematopoietic stem cells
- towards terminal differentiation, express different TFs
- erythroid lineage, myeloid lineage, lymphoid lineage
