Lect. 24 - Muscular Development

Question 1

Myoblast stage

Answer 1

Derived from myogenic cells; postmitotic

Question 2

Myotube stage

Answer 2

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

Question 3

What is the role of satellite cells?

Answer 3

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

Question 4

Primary myotubes

Answer 4

Formed by fusion of earliest (embryonic) myoblasts; may already be distinguished as fast or slow in some species; differentiation occurs before innervation

Question 5

Secondary myotubes

Answer 5

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

Question 6

What is the role of FGF and TGF-beta in the differentiation of muscle tissue?

Answer 6

Maintain myogenic cells in the labile state

Question 7

MyoD family

Answer 7

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

Question 8

Role of pax-3 and myf-5

Answer 8

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

Question 9

Role of Myf-6

Answer 9

Myogenin results in expression of myotube genes myf-6; leads to expression of myofibers genes

Question 10

Role of pax-7

Answer 10

Along w/ pax-3 induces MyoD w/ proliferation factors FGF and TGF-beta

Question 11

Epaxial muscles of the trunk arise from ?

Answer 11

Dorsal lip of myotome

Question 12

Epaxial tendons of the trunk arise from ?

Answer 12

Syndetome layer w/I somites

Question 13

Hypaxial muscles of the trunk arise from?

Answer 13

Ventral buds of myotome

Question 14

Tendons of Hypaxial muscles of the trunk arise from?

Answer 14

Lateral plate mesoderm

Question 15

Limb muscles arise from?

Answer 15

Ventrolateral dermomyotome

Question 16

Tendons of limb muscles arise from?

Answer 16

Lateral plate mesoderm

Question 17

Muscles of the head and the neck are mostly derived from?

Answer 17

Par axial somitomeres

Question 18

Extraocular muscles arise from?

Answer 18

Pre chordal plate

Question 19

Most of the cranial musculature is derived from?

Answer 19

Unsegmented paraxial mesoderm

Question 20

Some cranial musculature (lower jaw) is derived from ?

Answer 20

Splanchnic mesoderm

Question 21

Cardiac muscle is derived from?

Answer 21

Splanchnic mesoderm

Question 22

Myogenic cell stage

Answer 22

Originate in somites; resemble mesenchymal cells; restricted to muscle-forming line; mitotic cells