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Advanced Developmental > Myogenesis > Flashcards

Myogenesis Flashcards

1
Q

List the functions of skeletal muscle

A

Movement and posture
Communication
Body Temperature maintenance
Respiration

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2
Q

Give two examples of muscle wasting diseases

A

Duchenne dystrophy

Becker’s dystrophy

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3
Q

What is Duchenne dystrophy?

A

Progressive muscle degeneration
Onset 3 to 5 year olds
Mainly affects boys as it is X-linked recessive

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4
Q

What is Becker’s dystrophy?

A

Variant of duchenne dystrophy

Voluntary muscles function slightly better than in duchennes

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5
Q

What are the steps in making a muscle?

A

1) Stem cells have to be specified to differentiate
2) Muscle progenitor cells differentiate = MYOBLAST
3) Differentiated muscles cells express enzymes and contractile elements to form myotubes
4) Maturation of myotubes to myofibers

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6
Q

What usually dictates the speed of a muscles metabolism?

A

Their innervation

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7
Q

Who isolated MyoD?

A

Weintraub 1987

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8
Q

What is 5Aza?

A

A demethylating agent which causes histone demethylation

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9
Q

Which cell line was identified to sometimes turn into myoblasts if treated with 5Aza?

A

Fibroblats C3H10T1/2

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10
Q

If demethylatng agents are applied to a cell what is the effect?

A

The depress the state of the chromatin in the cell

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11
Q

What did Weintraub do in his experiment?

A

1) He took 5 Aza treated and untreated fibroblasts and converted their mRNA to cDNA
2) He then hybridised the two cDNA populations together to identify the muscle specific genes from the house keeping genes
3) Where there are two copies of genes from each population the DNA hybridises, but where there isn’t it remains single stranded
4) This is how he identified MyoD cDNA

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12
Q

What is MyoD referred to as?

A

A master regulatory gene

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13
Q

What happens if MyoD is put into any cell type?

A

The cell will be converted into a myoblast as it is a master regulator

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14
Q

Which other proteins are in the MyoD family?

A

MyoD, Myf5, Myogenin, MRF4

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15
Q

What do bHLH proteins stand for?

A

Basic helix loop helix

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16
Q

What is a bHLH?

A

A protein structural motif that characterises one of the largest families of dimerising transcription factors

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17
Q

Which cofactors dimerise with the helix - loop - helix domain?

A

E12 and E47

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18
Q

What are the three functions of the MyoD protein families?

A

1) Transcription activator
2) Form heterodimers with E12 or E47
3) Binds to E boc: CANNTG

19
Q

Where does skeletal muscle originate from?

A

The dermyotome

20
Q

Skeletal muscle progenitors express which paired box transcription factor?

A

PAX3

21
Q

In the trunk PAX3 positive cells contribute to what?

A

The myotome

22
Q

What are the two myotome domains?

A

Epaxial (medial)

Hypaxial (lateral)

23
Q

When are MRFs expressed?

A

In myoblasts during embryogenesis

24
Q

In an embryo stained for MRF what does the staining correlate to?

A

To where the skeletal muscle is forming

25
Q

Which is the earliest gene to be expressed from the MyoD protein family and when is it expressed?

A

Myf5

8 days of gestation (somites form at 7.5 days)

26
Q

How are genes targeted in ES cells?

A

1) electroporate the cell with mutated gene
2) Select cells which have taken up the DNA
3) Analyse colonies using gel electrophoresis
4) Make chimeras
5) Implant into the the mother
6) Test offspring for chimerism
7) Test germline for transmission
8) Cross the heterozygotes to analyse the offspring for the phenotype

27
Q

What happens in a Myf5 knockout?

A

Mice are viable
No obvious muscle defect at birth
During embryogenesis there is a delay in the myotome formation until the expression of MyoD
Myf5-/- cells migrate aberrantly into sclerotome and dermatome

28
Q

What happens in a MyoD knockout?

A

Mice are viable
No muscle defect at birth
During embryogenesis increases Myf5 expression in somites to compensate
Slight delay in limb muscle development
Deficit in muscle regeneration in adult mice

29
Q

What happens when both MyoD and Myf5 are knocked out?

A

Complete absence of skeletal muscles, no presence of myoblasts
Shows the you need one of them to generate myoblasts

30
Q

What happens in a myogenin knockout?

A

Mice die shortly after birth from diaphragm defect
Rediced density of myofibers replaced by myoblasts
Shows myogenin is required for muscle differentiation

31
Q

Which genes are involved for a Pax3 positive cell to be determined to form a myoblast?

A

Myf5
MyoD
MRF4

32
Q

Which gene is required for a myoblast to differentiate into a myotube?

A

Myogenin

33
Q

Wghcih gene is required for a myotube to mature into a myofiber?

A

MRF4

34
Q

Which two signalling pathways are involved in controlling muscle gene activation in the epaxial myotome?

A

Wnts - come from the notochord

Shh - comes from the dorsal part of the neural tube

35
Q

Which two signalling pathways are involved in controlling muscle gene activation in the hypaxial myotome?

A

Wnts

BMPs - lateral plate mesoderm

36
Q

Why does a PAX3 mutant mouse have a white spot on their belly?

A

PAX3 is important for neural crest formation and therefore pigmentation

37
Q

PAX3 mutant mice show what phenotype in the limbs?

A

They lack muscles in the limbs

38
Q

How do muscle cells migrate into the limb bud?

A

Mesenchymal cells from the limb bud secrete HGF/SF
PAX3 induces expression of c-met, the receptor for HGF/SF, in the limb muscle progenitor cells
Following c-met induction, cells migrate into the limb

39
Q

PAX7 knockouts do not have what ability?

A

To repair muscles in the adult

40
Q

When are satellite cells visible in mice?

A

E17.5 in the limbs

41
Q

Where are satellite cells seen?

A

Located under the basal lamina (inbetween the basal lamina and the muscle fibres

42
Q

What happens to our satellite cells over time?

A

The amount we have decreases due to the postnatal growth of muscles

43
Q

What activates satellite cells?

A

Injury causes themm to be activated due to reactive oxygen species

44
Q

Satellite cells represent the what percentage of muscle cells in the embryo and the adult

A

32% embryo

5% adult

Advanced Developmental (25 decks)

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