Musculoskeletal Development II Flashcards
4 Stages of muscle development?
All skeletal muscle originates in somites or somitomeres.
Goes into myogenic cells which are mitotic. Then to myoblasts derived from myogenic cells and postmitotic.
Then myotubes and muscle fibers.
First stage of muscle differentiation?
Myogenic cells which originate in somites and resemble mesenchymal cells. They aremitotic and kept in labile state by FGF and TGF-B
Second stage of muscle differentiation?
Myoblasts derived from myogenic cells they are post mitotic
Third stage of muscle differentiation?
Myotubes which are formed when myoblasts line up and adhere to each other. Requires calcium dependent CAMs and involved in mRNA and protein synthesis. Appearance of actin myosin troponin and tropomhyosin formation of myofibrils with sarcomeric arrangement. Nuclei move to periphery
Fourth stage of muscle differentiation?
Muscle fibers
Role of satellite cells?
Attach to myotubes before basal lamina is laid down and found between sarcolemma and basal lamina of myofibers. Mitotic and myogenic, can fuse with muslce fiber and provide for growth. function as stem cells. can become mitotic with stress and give rise to myyogenic precursor cells
What is the difference between primary and secondary myotubes?
Primary myotubes are formed by fusion of early embryonic myoblastas and can be distinguished as fast or slow. Differentiation occurs before innervation.
Secondary myotubes are smaller than primary formed alongside primary from late fetal myoblasts. Presence of motor axons necessary to form secondary. Contained within same basal lamina and electrically coupled
How can satellite cells become mitotic?
C-Met receptor and HGF expression during stress
Changes in myosin subunits during development of muscle fibers? pg. 186
book
Mitotic capability of myogenic cells and loss?
FGF and TGF-B keep myogenic cells in labile state.
Loss of mitotic capability due to p21 produced by myogenic cells in response to myogenic reg factors
MyoD family?
Can convert non muscle cells to cells that express, muscle. Helix loop helix TF that forms dimer and binds to E box in enhancer region of myogenic genes.
Binding is enhanced when E12(TF) replaces one member of the dimer to form heterodimer.
Transcriptionbal inhibitor id can replace one member of MyoD homodimer to form heterodimer
Molecular regulation of muscle development?
Pax-3 and Myf-5 separately activate MyoD and causes myogenic cells to become myoblasts. Increasing levels of MyoD with Myf-5 results in expression of myoblast genes by myoblasts. Myogenin results in expression of myotube genes and Myf-6. Myf-6 leads to expression of myofiber genes.
