Diff8 - 28 Flashcards
Four functions of muscle
Movement/posture, communication, body temperature, respiration
Three muscle wasting causes
Injury, ageing, dystrophies
What are the four broad stages of myogenesis?
Stem cell > muscle progenitor (myoblast) > differentiated muscle (myotubes) > myofibres
What is MyoD?
Regulatory gene in myogenesis
Who isolated MyoD and when?
Weintraub 1987
What family doe MyoD belong?
bHLH proteins
What does bHLH stand for?
basic helix-loop-helix proteins
What other members of the bHLH family are there?
MyoD, Myf5, Myogenin, MRF4
What is the function of the bHLH protein?
Transcription activator, forming heterodimers with E12 or E47, binding to E box (CANNTG)
What co-factors aid myogenesis?
Myogenic regulatory factors (MRFs)
Where are MRFs expressed?
Myoblasts during embryogenesis
Which group of muscles are medial?
Epaxial
Which group of muscle are lateral?
Hypaxial
Characterise Myf5 KO
Viable, no obvious muscle defect, delay in myotome formation until MyoD expression
Characterise MyoD KO
Viable, no obvious muscle defect, increased Myf5 expression compensates, slight delay in limb development, deficit in regenerative ability
Characterise Myf5/MyoD KO
Complete absence of skeletal muscle, no myoblasts
Characterise Myogenin KO
Mice die shortly after birth from diaphragm defect, reduced density of myofibers replaced by myoblasts
What are the three processes to muscle commitment?
Determination, differentiation, maturation
What specifies epaxial muscle lineage?
SHh + Wnt > Myf5 + MyoD
What specifies hypaxial muscle lineage?
Wnt7a > Myf5 + MyoD in lateral myotome; BMP4 > Pax3 + Lbx1, but represses Myo5 + MyoD in limb bud cells
What is HGF?
Hepatocyte growth factor
What is SF?
Scatter factor
What do limb bud cells secrete?
HGF/SF
How are HGF/SF receptors created in limb bud?
Pax3 > c-met (receptor)
Where do satellite cells originate?
Somites
Where are satellite cells?
Located just under basal lamina
What are satellite cells activated by?
Injury/exercise
What are the steps of regeneration by satellite cells?
Induction of Myf5 or MyoD; expression of both; proliferation/self renewal; differentiation and fusion to existing fibres
