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developmental biology > myogenesis > Flashcards

myogenesis Flashcards

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1
Q

what is the importance of muscle?

A
  • movement and posture
  • regulation of temperature
  • communication
  • respiration
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2
Q

making of a muscle (from stem cell to muscle)

A
  1. myoblast
  2. myotube
  3. myofibril
  4. myofibre
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3
Q

describe how myoD was isolated

A
  1. culture fibroblast cell line in 5Aza = demethylating agent
  2. isolate RNA from untreated fibroblast cell line and fibroblast cell line treated with 5Aza & converted to cDNA
  3. subtract populations of cDNA by hybridisation:
    - identical genes hybridise –> remove by filtration
    - genes in one population but not the other will remain as single cDNA strands
  4. separate and sequence these genes
  5. screen cDNA using probes derived from mRNA of myoblasts
  6. myoD cDNA isolated
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4
Q

MyoD

A
  • master regulatory gene
  • introduction of MyoD in differentiated cell is sufficient to reprogram cell into skeletal muscle + activate genes responsible for synthesising contractile proteins
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5
Q

what is the structure of proteins in the MyoD family?

A

basic helix loop helix

  • basic domain binds DNA
  • helix loop helix domain forms dimers with E12 and E47 proteins
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6
Q

what is the E box?

A

CANNTG

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7
Q

where are skeletal muscles and dermis derived from?

A

dorsal somite —> dermomyotome —-> skeletal muscles + dermis

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8
Q

where is epaxial muscle derived from?

A

medial somite —> myotome —> epaxial muscle

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9
Q

where is hypaxial muscle derived from?

A

lateral somite –> myotome –> hypaxial muscle

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10
Q

what does the syndotome give rise to?

A

tendons

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11
Q

describe the series of events that occur during the specification of skeletal muscle

A
  1. epithelial-to-mesenchymal transition of ventral somite cells = sclerotome
  2. dorsal somite remains epithelial = dermomyotome
  3. medial and lateral somite undergo epithelial-to-mesencymal transition to form 2 regions of myotome:
    - medial somite = epaxial muscle
    - lateral somite = hypaxial muscle
  4. cells in the dorsal somite remaining epithelial = dermatome
  5. thin layer of cells forms sclerotome and endothelial cells
  6. when the myotome cells delaminate they become specified to form skeletal muscle. skeletal muscle progenitors express Pax3
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12
Q

MRFs

A

myogenic regulatory factors

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13
Q

in a genetic KO, what do high levels of chimerism correspond to?

A

higher chance that the disrupted gene will be integrated into germ cells and transmitted to descendants

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14
Q

what would be observed in a Myf5/MyoD double KO and what can be concluded?

A

complete absence of muscles
no myoblasts
need at least 1 allele of either Myf5 or MyoD to obtain myoblasts

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15
Q

what is the role of myogenin?

A

differentiation of myoblasts into myotubes

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16
Q

what is the role of MRF4?

A

maturation of myotubes into myofibre

specification of progenitor into myoblast

17
Q

what drives Myf5 expression in the epaxial muscle?

A

Shh and Wnt signalling from neural tube and notochord

18
Q

what drives and inhibits Myf5 expression in the hypaxial mesoderm?

A

drives? - Wnt signalling from ectoderm
inhibits? - BMP4 - allows migration of cells that will migrate to the limb to form limb muscles so no need to differentiate yet

19
Q

describe the process of limb myogenesis

A
  1. hypaxial muscle cells (progenitors) express pax3
  2. pax3 drives cMet expression
  3. hypaxial muscle cells delaminate and migrate into limb bud
    - cMet = receptor for HGF and SF
    - HGF released by limb bud mesenchyme and acts as a chemoattractant
  4. cells follow dorsal route or ventral route
  5. proliferation of cells
  6. cells express Myf5 and MyoD -> differentiate and form limb muscles
20
Q

splotch mouse

A

LOF pax3
normal MyoD expression in somites
no MyoD expression in limb because cells failed to migrate to limb bud

21
Q

what are satellite cells?

A

skeletal muscle specific stem cells

22
Q

describe the activation of satellite cells

A
  1. satellite cells are quiescent and remain under basal lamina
  2. activated by stimuli = injury, exercise, disease etc.
  3. induction of Myf5 & MyoD
  4. expression of Myf5 & MyoD
  5. proliferation/self-renewal
  6. differentiation
  7. muscle cells fuse to existing muscle fibres
  8. subset of cells do not differentiate to maintain stem cell pool + return to quiescence
23
Q

DISEASE: sarcopenia

A

loss of muscle due to ageing

24
Q

DISEASE: cachexia

A

loss of muscle due to cancer

developmental biology (12 decks)

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