26. Satellite cells Flashcards
What is true about skeletal muscle cells?
Many nuclei- mitotically inactive- cannto divide
Highly active
Habe a high degree of plasticity (due to satellitte cells!)
How is skeletal muscle formed (embryology)
Mesodermal stem cells
Determined myoblasts
(removal of growth factors)
Differentiated myotubes (muscle fibres)
What transcription factors are released during terminal differentiation
Myogenin
MyoD
Myf5
MRF4
Discuss embryonic myogenesis
Mytome dervied myoblasts migrate into limb buds
Proliferatrion and initiation
Fusion to form skeletal muscle
Discuss the members of the myogenic family
What do they do?
MyoD, Myf 5, myogenin
regulate myogensis, convert one cell into a muscle cell
What is basic helix loop helix proteins
Bind to DNA sequence that activate muscle gene promotors
What is a dimer?
Not quite sure
How can BHLH be modulated?
Growth factors cause phosphorylatation to inactivate them.
Hence why removal of growth factors cause promotion
Growth factors can also restrict dimer formation to abolish myogenic regulators being active
Overall sum up the regulation of myogenesis
Mesodermal stem cell
Myogenic BHLH factors are expressed and are autoregualated and stimulate expression of muscle structural genes
Myogenic factors increase MEF2 (regulatory factor)
This also increases proliferation of muscle structure genes
How did removal of myodein D affect muscle differentation
How did removal of MyF5 affect muscle differentation
How did removal of myodein D and MyF5 affect differentiation
Muscle normal
Muscle normal
No muscle present
No myofibres
What is commitment
Muscle fibre cells can move to a new cell location and still maintain its original fate.
Where are satellite cells located?
Between the basal lamina and the muscle fibre
What is meant by quiescence?
Rest. Satellite cells sit in quiescence allowing them to be metabolically inactive but not dead.
How are satellite cells formed?
Progression of pre-cursor cells
Determination (quiescence)
Proliferation (re-activation)
Differentiation
How do satellite cells become quiescent?
Put aside after myogenesis
How is Pax7 related for satellite cells?
Essential for creating satellite cells.
Rudnicki’s theroy that if stem cells have pax-7 activtaed upon them that they will form satellite cells
When are myogenic regulatory factors expressed?
(Quiescent)
(Activated)
(Differentiation)
(Fusion of myotube)
(Activation of myofiber)
Quiescent- CD34, Pax7, Myf5
Activated- CD34, Pax7, Myf5, MyoD
Differentiation- Myf5,MyoD, Myogenin
Fusion of myotube- Myf5,MyoD, Myogenin
Maturation of myofiber- Myogenin
How does IGF affect satellite cells?
Increases proliferation in activaed satellite cells
IGF promotes differentiation in the prescence of Mef2 and other late MRF’s
How is satellite number affecetd in elderly and muscle dytrophies
Reduced
How can satellite cells affect muscles?
Change metabolic conditions
Repair in microtrauma to increase strength (everyday change)
How do satellite cells repair skeletal muscle?
Infilatrate gap via inflammatory mediators
satellite cells differnetiate and fse to existing myotubes to join up to each other
Small number of satellite cells go back to quiescence and refill the satellite pool
What is required to maintain the process of repair?
Balance between Pax and MRF’s to determine if satellite cells proliferate or initiate terminal differentiation
How is protein related to muscle hypertrophy
Protein synthesis increases and protein degredation decreases
Why do myotubes have multiple nuclei?
Too big to be controlled by one nucleus
Need multiple nuclei for protein synthesis
How are satellite cells affected in the elderly?
Falls off first in large fibres
Cytoplasmic atrophy
Returns to small fibres
