Myogenesis Flashcards
What are 4 reasons for skeletal muscle?
1) Movement and posture
2) Communication
3) Maintain body temperature
4) Respiration
How does skeletal muscle help to maintain body temperature?
Heat released through muscle contraction participates in the control of body temperature (thermoregulation)
How is muscle important in respiration?
Diaphragm
What are muscle wasting diseases?
Injuries
Ageing
Muscle-degenerating disease (dystorophy)
What is understanding how muscles form and differentiate a paradigm for?
Studying cell differentiation
What are muscles made from?
Bundles of muscle fibres
How do you get the defined structure of a muscle fibre?
Gradual process of:
- Specification
- Determination
- Differentiation
- Maturation
What happens in the differentiation step of skeletal muscle formation?
- Fusion between many MYOBLASTS to from a MYOTUBE
- And the coordinated ACTIVATION of skeletal muscle specific genes
What is a myoblast?
A muscle progenitor cell
What happens during the maturation of a muscle fibre?
- Innervation of the muscle
- Refinement of the TYPE of muscle fibre (into slow, fast or intermediate)
What is the myogenesis determination gene?
myoD
How can myoD be isolated?
1) Start with fibroblast cell line
2) Have to groups of the fibroblast cell line: one cultured in the presence of 5Azsa and one untreated
3) Collect mRNA from both cell lines and convert into cDNA - get 2 populations of cDNA
4) Subtract the populations of cDNA using hybridisation
5) Screen single strand using myoblast specific probes
Under certain conditions, what does the fibroblast cell line C3H10T1/2 give rise to?
Number of cell types, including MYOBLASTS
What is 5Azsa?
Why is it used to culture fibroblasts?
A de-methylating agent
Used to get a high percentage of myoblasts from the fibroblasts (instead of other cell types)
How will the cDNA of the fibroblasts treated with 5Azsa be the same/different to the untreated fibroblasts? Why?
- Genes will be similar as they come from the SAME mother cell
- BUT, some genes will be different - treated cell line will be PARTIALLY converted to myoblast cell type
When is hybridisation on the populations of cDNA performed?
How are the unique genes in either sample isolated?
After denaturing the DNA
- Identical genes will hybridise together - can be eliminated through filtration
- Unique genes (present in only ONE population) - will NOT hybridise and will remain as SINGLE strands
What does demethylating cells do?
Transform heterochromatin into euchromatin and release chromatin from a silenced state
Allowing the transcription of genes that would normally be silenced
What is heterochromatin?
Highly condensed DNA
What is euchromatin?
Uncondensed DNA
What did Weintraub do?
What were the results of this?
What did this show?
- Isolated myoD
- Inserted myoD into a viral vector and into a number of cell types that were already DIFFERENTIATED (eg. pigment cells, nerve cells, fibroblasts)
Results:
- Cells lost their differentiation characteristics and converted into MYOBLASTS
- That were capable of differentiating and fully forming DIFFERENTIATED myotubes
Showing:
- Introduction of myoD into a DIFFERENTIATED cell is SUFFICIENT to reprograme the cell into skeletal muscle
AND
- Carry out the WHOLE myogenetic programme (including the expression of genes responsible for contractile proteins)
What type of gene is myoD
A MASTER REGULATORY gene
What is the myod protein family characterised by?
2 domains:
- Basic domain
- Helix-loop-helix
What does the basic domain of the myoD protein do?
Binds to DNA
What does the helix-loop-helix domain of the myoD protein do?
What is this required for?
Forms DIMERS with the proteins that belong to the E12 or E47 family
Dimerisation is required for the FUNCTION of the protein