Muscle Development - Lecture 24

Question 1

Stages of differentiation of skeletal muscle cells

Answer 1

Starts are Myogenic cells - originate in somites, look like mesenchymal cells, restricted to pathway for forming muscle and are mitotic

Mitotic state requires FGF and TGF-β

Myoblasts - derived fro myogenic, postmitotic

Myotubes - myoblasts fuse to eachother, requires Ca-dependent CAMs, involved in mRNA and protein synthesis - presense of actin, myosin, troponin and tropomyosin. Myofibrils form with sarcomeric arrangment with nuclei on periphery

Then you have muscle fibers

Question 2

Satalite cells

Answer 2

Occur later in differentiation of myo-tissue

Located between sarcolemma and lasal lamina of myofiber

They are both mitotic and myo genic - they are able to fuse with existing muscle fiber for growth

They cannot form new muscle fibers

Question 3

Primary myocytes (myotubes)

Answer 3

Formed by fusion of earliest (embyronic) myoblasts

Can already be fast or slow fibers

Differenciation occurs before innervation

Bigger than secondary

Question 4

Secondary myocytes (myotubes)

Answer 4

Smaller than primary

Formed alongside primary from late, or fetal, myoblast

Motor axons may be necessary in the formation of secondary myotubes

Contained within same basal lamina and are electically coupled

Question 5

How does Myf-5 regulate myogenic differenctiation? Does it have a partner? If so, what is it? Where does this occur?

Answer 5

. Myf-5 along with Pax-3 each can activate MyoD. THey can work together but have the same funtion.

MyoD - causes myogenic cells to become myoblasts

Occurs in somites

Question 6

What is the general purpose of myogenic regulatory fibers?

Answer 6

Cause myogenic cells to produces p21, which causes loss of mitotic capability?

Question 7

What factors are required for a myogenic cell to be mitotically active?

Answer 7

FGF and TGF-β

Question 8

What leads to the expression of myogenin by myoblasts? What is myogenin’s function?

Answer 8

Induced by MyoD and Myf-f together

Myogenin causes expression of myotube genes and Myf-6

Question 9

What is Myf-6 function?

Answer 9

Causes expression of myofiber genes

Induced by myogenin

Question 10

What is the purpose of Pax-7?

Answer 10

Pax-7 has the same function of Pax-3, induced from somatic epithelium that causes activation of MyoD in myoblasts

Question 11

What is the origin of trunk muscles?

Answer 11

Epaxial muscles - dorsal lip of myotome

Epaxial tendoms - from syndetome layer in somites

Hypaxial muscles - ventral buds of myotome

Hypaxial tendons - lateral plate mesoderm

Question 12

What is the origin of limb muscles?

Answer 12

Limb from ventrolateral dermamyotome

Limb muscles tendons from lateral plate mesoderm

Question 13

What is the origin of head and neck muscles?

Answer 13

Derived from paraxial somitomeres

Extraocular muscles arise from prechordal plate

Most cranial muscle is from unsegmmented paraxial mesoderm

The rest, lower jaw mainly, is from splanchnia mesoderm

Question 14

What is the origin of cardiac muscle?

Answer 14

From splanchnic mesoderm

Early cardiac muscle lack myoD

express MADS (as does skeletal)

Begins contracting early, but retains mitotic ability by partial dissembly of contractile apparatus

Attach by intercalated discs

Question 15

Prune belly syndrome

Answer 15

Molecular deficiency - textbook

Question 16

Table 9.3 for axial and limb muscle precursors

Answer 16

.

Question 17

MyoD

Answer 17

Group of 4 helix-loop–helix tf - able to convert non-muscle cell to cells capable of expressing muscle proteins

Dimerizes and binds E box enhancer region of myogenic genes

Enhanced binding with E12 replacing one of the dimers. Weakened when id replaces a dimer and weakens the binding -> poor expression.