Lect. 24 - Muscular Development Flashcards
Myoblast stage
Derived from myogenic cells; postmitotic
Myotube stage
Formed when myoblasts line up and adhere to one another; requires Ca2++-dependent CAMs; involved in mRNA and protein synthesis; characterized by appearance of actin, myosin, troponin and tropomyosin; formation of sarcomeres; nuclei move to periphery
What is the role of satellite cells?
Located b/w sarcolemma and basal lamina; mitotic and myogenic; able to fuse w/ muscle fiber and provide for growth; note that satellite cells do not form new muscle fibers
Primary myotubes
Formed by fusion of earliest (embryonic) myoblasts; may already be distinguished as fast or slow in some species; differentiation occurs before innervation
Secondary myotubes
Smaller than primary; formed alongside primary from late (fetal) myoblasts; presence of motor axons may be necessary to form secondary myotubes; contained w/I same basal lamina and are electrically coupled
What is the role of FGF and TGF-beta in the differentiation of muscle tissue?
Maintain myogenic cells in the labile state
MyoD family
Able to convert non-muscle cells to cells capable of expressing muscle proteins; helix-loop-helix TF; forms dimer and binds to E box in enhancer region of myogenic genes; binding is enhanced when E12 replaces one member of the dimer to form a heterodimer; transcriptional inhibitor id can replace one member of the MyoD homodimer to form a heterodimer resulting in poor binding ability
Role of pax-3 and myf-5
Separately can activate MyoD and cause myogenic cells to become myoblasts; increasing Myf-5 along w/ MyoD results in expression of myoblast genes by myoblasts and expression of myogenin
Role of Myf-6
Myogenin results in expression of myotube genes myf-6; leads to expression of myofibers genes
Role of pax-7
Along w/ pax-3 induces MyoD w/ proliferation factors FGF and TGF-beta
Epaxial muscles of the trunk arise from ?
Dorsal lip of myotome
Epaxial tendons of the trunk arise from ?
Syndetome layer w/I somites
Hypaxial muscles of the trunk arise from?
Ventral buds of myotome
Tendons of Hypaxial muscles of the trunk arise from?
Lateral plate mesoderm
Limb muscles arise from?
Ventrolateral dermomyotome
Tendons of limb muscles arise from?
Lateral plate mesoderm
Muscles of the head and the neck are mostly derived from?
Par axial somitomeres
Extraocular muscles arise from?
Pre chordal plate
Most of the cranial musculature is derived from?
Unsegmented paraxial mesoderm
Some cranial musculature (lower jaw) is derived from ?
Splanchnic mesoderm
Cardiac muscle is derived from?
Splanchnic mesoderm
Myogenic cell stage
Originate in somites; resemble mesenchymal cells; restricted to muscle-forming line; mitotic cells
