Muscle Development - Lecture 24 Flashcards

1
Q

Stages of differentiation of skeletal muscle cells

A

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

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2
Q

Satalite cells

A

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

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3
Q

Primary myocytes (myotubes)

A

Formed by fusion of earliest (embyronic) myoblasts

Can already be fast or slow fibers

Differenciation occurs before innervation

Bigger than secondary

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4
Q

Secondary myocytes (myotubes)

A

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

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5
Q

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

A

. 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

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6
Q

What is the general purpose of myogenic regulatory fibers?

A

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

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7
Q

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

A

FGF and TGF-β

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8
Q

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

A

Induced by MyoD and Myf-f together

Myogenin causes expression of myotube genes and Myf-6

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9
Q

What is Myf-6 function?

A

Causes expression of myofiber genes

Induced by myogenin

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10
Q

What is the purpose of Pax-7?

A

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

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11
Q

What is the origin of trunk muscles?

A

Epaxial muscles - dorsal lip of myotome

Epaxial tendoms - from syndetome layer in somites

Hypaxial muscles - ventral buds of myotome

Hypaxial tendons - lateral plate mesoderm

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12
Q

What is the origin of limb muscles?

A

Limb from ventrolateral dermamyotome

Limb muscles tendons from lateral plate mesoderm

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13
Q

What is the origin of head and neck muscles?

A

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

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14
Q

What is the origin of cardiac muscle?

A

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

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15
Q

Prune belly syndrome

A

Molecular deficiency - textbook

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16
Q

Table 9.3 for axial and limb muscle precursors

A

.

17
Q

MyoD

A

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.