L12 - Myogenesis

Question 1

Four reasons myogenesis is important

Answer 1

Movement and posture
Communication
Maintencance of body temperture
Respiration

Question 2

What are the three processes the muscles go through

Answer 2

Specification/determination
Differentiation
Maturation

Question 3

Describe the heirarchy of muscle cells

Answer 3

Stem cells 
Muscle progenitor cells 
Myoblasts 
Diff muscle cells/myotubes 
Myofibres

Question 4

What is 5Aza

Answer 4

5Azacytidine demethylating agent

Question 5

Describe what happens when fibroblasts are exposed to 5Aza

Answer 5

Differentiate into myoblasts

Question 6

Descibe how myoD was isolated

Answer 6

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

Question 7

What is MyoD

Answer 7

A master regualtory gene

Question 8

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

Answer 8

Lead to dediffernetiation of the specilaised cell to muscle cells

Question 9

The dediff neural cells that are now muscle cells express what

Answer 9

Muscle specific proteins

Muscle specific receptors and membrane molecules

Question 10

What is the MyoD family

Answer 10

bHLH protein

Question 11

What is bHLH protein

Answer 11

Basic helix loop helix protein

Question 12

In the bHLH what is the role of:

Basic domain

Helix loop helix domain

Answer 12

Basic for DNA binding

HLH - dimerisation

Question 13

What dimerisation is MyoD family rpoteins involved in

Answer 13

E12 and E47

Question 14

What are members of the bHLH family

Answer 14

MyoD
Myf5
Myogenin
MRF5

Question 15

What is the function of MyoD familiy protein

Answer 15

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

Question 16

What are the 4 types of mesoderm

Answer 16

Axial mesoderm
Paraxial mesoderm
Intermeidate mesoderm
Lateral plate mesoderm

Question 17

Describe the axial mesoderm

Answer 17

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

Question 18

Describe the paraxial mesoderm

Answer 18

Immeidatly flanking the neural tube on either side

Question 19

Describe the intermediate mesoderm

Answer 19

Between the paraxial mesoderm and the lateral plate mesoderm

Question 20

Describe the lateral plate mesoderm

Answer 20

Beneath the surfac ectoderm

Question 21

Skeletal muscle originates from

Answer 21

The dermomyotome

Question 22

The dermomyotome contains

Answer 22

Progenitor cells for skeletal msuscle of the trunk and the limb

Question 23

Skeltal muscle progenitors express

Answer 23

The paired box transcription factor Pax3

Question 24

What are the two mytome domains

Answer 24

Epaxial

Hypaxial

Question 25

Where the the epaxial myotome

Answer 25

Medial

Question 26

Where is the hypaxial myotome

Answer 26

Lateral

Question 27

During emrbyogenesis where are MRFs expressed

Answer 27

In myoblasts

Question 28

Epaxial muscles are

Answer 28

Deep back muscles

Question 29

Hyaxial muscles are

Answer 29

Abdominal and limb muscles

Question 30

Describe the process of gene targetting in embryonic stem cells

Answer 30

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

Question 31

What is the effect of a Myf5 KO mouse

Answer 31

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

Question 32

What is the effect of a MyoD KO mouse

Answer 32

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

Question 33

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

Answer 33

Complete absence of skeletal muscle with no presence of myoblasts

Question 34

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

Answer 34

Myf5 or MyoD is required to generate myoblasts

Question 35

What is the phenotype of a myogenin KO

Answer 35

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

Question 36

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

Answer 36

Myogenin required for the differentiation of the muscle

Question 37

Determination is mediated by which MRFs

Answer 37

myf5 myoD MRF4

Question 38

What does MRF stand for

Answer 38

Myogenic regulatory factors

Question 39

What MRFs is required for the differentiation of muscle

Answer 39

Myogenin

Question 40

What MRF is reuired for the maturation of the muscle

Answer 40

MRF4

Question 41

Dtermination is from what cell to what cell

Answer 41

Pax3 positive somatic cell to a myoblast

Question 42

Differentiation is from what cell to what cell

Answer 42

Myoblast to a myotube

Question 43

Maturation is from what cell to what cell

Answer 43

Myotube to a myofibre

Question 44

In the epaxial myotome all progenitors express

Answer 44

Pax3

Question 45

In the epaxial myotome what signals are required

Answer 45

Low Shh and Wnt from the neural tibe and notochord

Question 46

All progenitors in the hypaxial myotome express

Answer 46

Pax3

Question 47

Cells in the hypaxial myotome require what signal

Answer 47

Wnt from the ectoderm

Question 48

In some of the cells of the hypaxial myotome what signal acts in an inhibotry manner Where is this required

Answer 48

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

Question 49

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

Answer 49

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

Question 50

Expression of the receptor to HGF/SF triggers

Answer 50

Migration of the muscle progenitor cells into the limb mesenchyme

Question 51

When migrating what do the migrating muscle progenitor cells split into

Answer 51

Dorsal and ventral route

Question 52

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

Answer 52

They proliferate

Question 53

Determination by expression of

Answer 53

Myf5 and MyoD

Question 54

Differentiation due to expression of

Answer 54

myogenin and MRF4

Question 55

What is the splotch mouse

Answer 55

Natural mouse mutant | Deletion - so loss of function of Pax3

Question 56

Describe the phenotypic effects of the splotch mouse What overall conclusion can be drawn from this

Answer 56

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

Question 57

Satellite cells are

Answer 57

Skeletal muscle stem cell progenitors

Question 58

Where do satelite cells derive from

Answer 58

The somites

Question 59

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

Answer 59

32% birth 5% adult

Question 60

When there is no stmuli | Describe the behaviour and appearance of the satelitte cells

Answer 60

Quiescent | Position themselves outside of the fibre under the basal lamina

Question 61

What stimuli cause activation of the satelitte cells

Answer 61

Injury, exercise etc.

Question 62

Describe activaiton process of the satelitte cells

Answer 62

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

Question 63

What do some of the satelitte cells remain as

Answer 63

Remain as satellite cells and return to quiescent This retains a stem cell pool

Question 64

Describe normal regernation

Answer 64

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

Question 65

Describe weak regernation

Answer 65

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

Question 66

What is sarcopenia

Answer 66

Loss of muscle due to ageing

Question 67

What is cachexia

Answer 67

Loss of muscle due to caner

Question 68

What is pertubed regernaeration

Answer 68

Too many satelitte cells are activated

Question 69

What cancer is caused by pertubed regeneration

Answer 69

Rhabdomyosarcoma