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BMS242 Developmental Biology > L12 - Myogenesis > Flashcards

L12 - Myogenesis Flashcards

1
Q

Four reasons myogenesis is important

A

Movement and posture
Communication
Maintencance of body temperture
Respiration

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2
Q

What are the three processes the muscles go through

A

Specification/determination
Differentiation
Maturation

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3
Q

Describe the heirarchy of muscle cells

A 
Stem cells 
Muscle progenitor cells 
Myoblasts 
Diff muscle cells/myotubes 
Myofibres
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4
Q

What is 5Aza

A

5Azacytidine demethylating agent

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5
Q

Describe what happens when fibroblasts are exposed to 5Aza

A

Differentiate into myoblasts

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6
Q

Descibe how myoD was isolated

A

Extract mRNA from both 5Aza treated fibroblasts and normal fibroblasts
Reverse transcribe the two sets to cDNA
Subtracted cDNA enriched in muscle specific genes
Screen using myoblast specific probes
Lead to the identification of MyoD cDNA

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7
Q

What is MyoD

A

A master regualtory gene

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8
Q

Describe what occurs when a neural cell was transfected with MyoD being expressed under n active viral promoter

A

Lead to dediffernetiation of the specilaised cell to muscle cells

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9
Q

The dediff neural cells that are now muscle cells express what

A

Muscle specific proteins

Muscle specific receptors and membrane molecules

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10
Q

What is the MyoD family

A

bHLH protein

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11
Q

What is bHLH protein

A

Basic helix loop helix protein

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12
Q

In the bHLH what is the role of:

Basic domain

Helix loop helix domain

A

Basic for DNA binding

HLH - dimerisation

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13
Q

What dimerisation is MyoD family rpoteins involved in

A

E12 and E47

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14
Q

What are members of the bHLH family

A

MyoD
Myf5
Myogenin
MRF5

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15
Q

What is the function of MyoD familiy protein

A

Transcriptional activator
Forms heterodimers with E12 or E47
Binds to E box: CANNTG

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16
Q

What are the 4 types of mesoderm

A

Axial mesoderm
Paraxial mesoderm
Intermeidate mesoderm
Lateral plate mesoderm

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17
Q

Describe the axial mesoderm

A

Formed of the notochord - involutes beneath the neural plate during gastrulation

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18
Q

Describe the paraxial mesoderm

A

Immeidatly flanking the neural tube on either side

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19
Q

Describe the intermediate mesoderm

A

Between the paraxial mesoderm and the lateral plate mesoderm

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20
Q

Describe the lateral plate mesoderm

A

Beneath the surfac ectoderm

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21
Q

Skeletal muscle originates from

A

The dermomyotome

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22
Q

The dermomyotome contains

A

Progenitor cells for skeletal msuscle of the trunk and the limb

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23
Q

Skeltal muscle progenitors express

A

The paired box transcription factor Pax3

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24
Q

What are the two mytome domains

A

Epaxial

Hypaxial

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25
Q

Where the the epaxial myotome

A

Medial

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26
Q

Where is the hypaxial myotome

A

Lateral

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27
Q

During emrbyogenesis where are MRFs expressed

A

In myoblasts

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28
Q

Epaxial muscles are

A

Deep back muscles

29
Q

Hyaxial muscles are

A

Abdominal and limb muscles

30
Q

Describe the process of gene targetting in embryonic stem cells

A

Electroporation - transgenic DNA able to enter
Selection of the cells which have taken up the vector
Colonies genotyped
Targetting ES cells then implanted into early stage blastocyst
Offspring tested for chimerism
Breed for germline transmission
Cross heterozygotes
Analyse the offspring for a phenotype

31
Q

What is the effect of a Myf5 KO mouse

A

Viable with no obvious defects
Delay in myotome formation until the onset of MyoD
Cells migrate abberantly into the sclerotome and dermatome

32
Q

What is the effect of a MyoD KO mouse

A

Mice viable with no obvious defect at birth
Increased Myf5 expression in the somites - compensates for lack of MyoD
Slight delay in limb muscle development and deflict in muscle regeneration in adult mice

33
Q

What is the phenotpye of a Myf5/MyoD double k/o

A

Complete absence of skeletal muscle with no presence of myoblasts

34
Q

What are the conclusions which can be drawn from the Myf5/MyoD double KO

A

Myf5 or MyoD is required to generate myoblasts

35
Q

What is the phenotype of a myogenin KO

A

Mice die shortly after birth due to a defect in the diaphragm
Reduced density of myofibers - replaced instead by myoblasts

36
Q

What is the conclusion which can be drawn from the myogenin KO mouse

A

Myogenin required for the differentiation of the muscle

37
Q

Determination is mediated by which MRFs

A

myf5 myoD MRF4

38
Q

What does MRF stand for

A

Myogenic regulatory factors

39
Q

What MRFs is required for the differentiation of muscle

40
Q

What MRF is reuired for the maturation of the muscle

41
Q

Dtermination is from what cell to what cell

A

Pax3 positive somatic cell to a myoblast

42
Q

Differentiation is from what cell to what cell

A

Myoblast to a myotube

43
Q

Maturation is from what cell to what cell

A

Myotube to a myofibre

44
Q

In the epaxial myotome all progenitors express

45
Q

In the epaxial myotome what signals are required

A

Low Shh and Wnt from the neural tibe and notochord

46
Q

All progenitors in the hypaxial myotome express

47
Q

Cells in the hypaxial myotome require what signal

A

Wnt from the ectoderm

48
Q

In some of the cells of the hypaxial myotome what signal acts in an inhibotry manner

Where is this required

A

BMP4 required to inhibit expresison of myf5 and myoD

Required in cells of the myotome in limb region - since they first must migrate in the limb

49
Q

In cells migrating into the limb what is the effect of Pax3

A

Induces expression of c-met which is a receptor for HGF/SF

50
Q

Expression of the receptor to HGF/SF triggers

A

Migration of the muscle progenitor cells into the limb mesenchyme

51
Q

When migrating what do the migrating muscle progenitor cells split into

A

Dorsal and ventral route

52
Q

When they reach their position what happens to the muscle progenitor cells

A

They proliferate

53
Q

Determination by expression of

A

Myf5 and MyoD

54
Q

Differentiation due to expression of

A

myogenin and MRF4

55
Q

What is the splotch mouse

A

Natural mouse mutant

Deletion - so loss of function of Pax3

56
Q

Describe the phenotypic effects of the splotch mouse

What overall conclusion can be drawn from this

A

Expression pattern of myoD normal in the somites but no expression of myoD in the limb - cells have failed to migrate

Shows pax3 is required to induce c-met

57
Q

Satellite cells are

A

Skeletal muscle stem cell progenitors

58
Q

Where do satelite cells derive from

A

The somites

59
Q

What % of muscle are satellite cells at birth, what about during adulthood

A

32% birth

5% adult

60
Q

When there is no stmuli

Describe the behaviour and appearance of the satelitte cells

A

Quiescent

Position themselves outside of the fibre under the basal lamina

61
Q

What stimuli cause activation of the satelitte cells

A

Injury, exercise etc.

62
Q

Describe activaiton process of the satelitte cells

A

Induction of Myf5 or myoD
Expression of both myf5 and myoD
Proliferation/self renewal
Differentiatie and fuse to the existing fibres

63
Q

What do some of the satelitte cells remain as

A

Remain as satellite cells and return to quiescent

This retains a stem cell pool

64
Q

Describe normal regernation

A

Some satelitte cells become active to repair damaged fibers some then return to quiescent and retain the stem ell pool

65
Q

Describe weak regernation

A

Not enough satelitte cells - not enough to proliferate or they fail to proliferate to self renew so stem cell pool is depleted - causes degeneration over time

66
Q

What is sarcopenia

A

Loss of muscle due to ageing

67
Q

What is cachexia

A

Loss of muscle due to caner

68
Q

What is pertubed regernaeration

A

Too many satelitte cells are activated

69
Q

What cancer is caused by pertubed regeneration

A

Rhabdomyosarcoma

BMS242 Developmental Biology (17 decks)

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