Transcription Factors And Control Of Cell Differentiation In Vertebrates

Question 1

What do fibroblast cells normally form?

Answer 1

Extracellular matrix. They differentiate into muscle cells when gene for any of four transcription factors (MyoD, myogenin, Myf5, Mrf4) is expressed (artificially) in them. So, they can differentiate into muscle cells because muscle genes are turned on

Question 2

What is the purpose of the proteins MyoD, myogenin, Myf5, Myf4?

Answer 2

They can reprogramme fibroblast cell development . These proteins control normal muscle cell development. Many genes for muscle-specific proteins contain cisregulatory elements to which they bind

Question 3

What are somites and what do they differentiate into?

Answer 3

They are segmented blocks of cells that form along the sides of the notochord in vertebrate embryos. Cells from somites form (differentiate into) vertebrae, rubs, muscles, and limb

Question 4

What is the first step in the natural formation of muscle?

Answer 4

Signals from neighbouring cells induce transcription of genes for MyoD and Myf5. MyoD and/or Myf5 then convert undifferentiated somites cells to undifferentiated muscle precursor cells: myoblasts. Nice with both myoD and myf5 genes “knocked out” (limit it’s function)- don’t form myoblasts. Process is an example of determination; precedes differentiation. Determination involves chromatin remodelling (altered so they are accessible for transcription)- prepares genes for expression. MyoD and Myf5 have chromatin remodelling activity. MyoD includes transcription of its own gene-> switch. Positive feedback

Question 5

What happens in the second step in the two-step process of natural formation of muscle?

Answer 5

Myogenin gene is transcribed in myoblasts. Myogenin causes myoblasts to fuse and for multinucleate mature muscle cells: myotubes (muscle cell). Nice with myogenin gene knocked out then myoblasts don’t differentiate into myotubes- myogenin controls the process by which a myoblasts with other myoblasts for a myotubes, so if none then won’t get myotubes (Mrf4 functions later)

Question 6

How can the reprogramming of differentiation of stem cells have potential applications to regenerative medicine?

Answer 6

Four transcription factors (Oct4, Sox2, KIf4, Myc) in combination can reprogrammed fibroblasts to induced pluripotent (can turn into lots of different types of cells not any) stem cells (iPS cells), which can potentially give rise to many cell types and replace embryonic stem cells

Question 7

How can islet beta-cells (pancreatic cells) be used in reprogramming of differentiation/ have potential applications to regenerative medicine?

Answer 7

Three transcription factors (Pdx1, Ngn3, MafA) in combination can reprogrammed exocrine cells of the pancreas to differentiate into islet beta-cells, which produce insulin (could help to cure diabetes)

Question 8

Besides transcription, changes in mRNA stability and translation can change gene expression. For example iron availability regulates what?

Answer 8

1. Stability of mRNA for iron uptake protein into cells transferrin receptor
   - when iron concentration in cell is low, cell needs to take up more iron: transferrin receptor mRNA will becomes more stable - make the RNA last longer so have more
   - when iron concentration is high, cell does not need to take up more iron: transferrin receptor mRNA is degraded (less stable)
2. Translation of mRNA for iron storage protein ferritin- a storage protein

Question 9

What is ferritin?

Answer 9

An iron storage protein

Question 10

When iron levels are high is ferritin mRNA is translated or not translated?

Answer 10

Ferritin mRNA is not translated

Question 11

When iron levels are low is ferritin mRNA translated or not?

Answer 11

Ferritin mRNA is not translated

Question 12

What is the mechanism when iron in cells is low?

Answer 12

An iron sensor protein binds to mRNA and repressed translation. The iron sensor protein is cytosolic aconitase

Question 13

What does aconitase catalyse and how? What happens in the absence of iron?

Answer 13

Catalyses the conversion of citrate to isocitrate via cis-aconitate. It’s active site contains a 4Fe-4S ironsulphur cluster.

Question 14

What happens to aconitase in iron starvation?

Answer 14

Aconitase bund sto stem-loop, blocking passage of ribosomes

Question 15

What happens to aconitase in the presence of excess iron?

Answer 15

Aconitase is released; ribosomes can pass through stem-loop and start translating

Question 16

Are bottom of page 48 and top of page 49

Answer 16

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Question 17

How can changes in gene expression can occur?

Answer 17

. In response intracellular signals (e.g. levels of metabolites, metals.)
. In co-ordination of responses within a body (e.g. hormones) or between organisms (e.g. quorum sensing
. As part of a programme of differentiation in development of multicellular organisms (e.g. beta-globin, MyoD, myogenin, Myf5, Myf4 (transcription factors in muscle cells))