Muscle Stem Cells

Question 1

What are satellite cells?

Answer 1

They are a type of stem cell found in muscle.

Question 2

What is an overview of skeletal muscle anatomy?

Answer 2

Myofibril
Muscle fibre.
Fascicle.
Skeletal muscle.

Question 3

Where are satellite cells found?

Answer 3

In the periplasmic space between each Fascicle.

Question 4

What is the satellite cell niche?

Answer 4

Myosatellite cells are located between the basement membrane and the sarcolemma of muscle fibres. They can lie in grooves either parallel or transversely to the longitudinal axis of the fibre.

Question 5

How can non-proliferative, quiescent myosatellite cells be identified? [5]

Answer 5

1. Distinct location between sarcolemma and basal lamina.
2. High nuclear-to-cytoplasmic volume ratio.
3. Few organelles.
4. Small nuclear size.
5. Large quantity of nuclear heterochromatin relative to myonuclei.

Question 6

How can activated satellite cells be identified?

Answer 6

1. Increased number of caveolae (type of lipid raft).
2. Increased number of cytoplasmic organelles
3. Decreased levels of heterochromatin.

Question 7

How can satellite cells augment muscle fibre?

Answer 7

They can differentiate and fuse to existing muscle to augment it or can form entirely new fibres.

Question 8

When do satellite cells become activated?

Answer 8

In response to mechanical strain - they can initially proliferate as skeletal myoblasts before undergoing myogenic differentiation.

Question 9

How can satellite cells be cultured?

Answer 9

Dissect EDL muscle (extensor digitorum longus).
Add collagenase digest
Plate individual fibres in culture dishes.

Question 10

Current thinking is that most satellite cells express which two markers?

Answer 10

PAX7

PAX3

Question 11

How do satellite cells in the head musculature differ in regard to what markers they express?

Answer 11

They are PAX7 + but PAX3 -

Question 12

Both quiescent and activated human satellite cells can be identified by what membrane-bound cell-surface glycoprotein?

Answer 12

Both types of satellite cell can be identified by the presence of neural cell adhesion molecule (N-CAM/CD56/Leu-19)

Question 13

What do N-CAM, CD56 and Leu-19 have in common?

Answer 13

They all refer to the same thing: neural cell adhesion molecule used in the identification of activated/inactivated satellite cells.

Question 14

How can the majority of quiescent satellite cells be indentified?

Answer 14

CD34

Myf5

Question 15

Why are activated satellite cells problematic to identify?

Answer 15

Their markers change with the degree of activation; for example, greater activation results in the progressive loss of PAX7 expression as they enter a proliferative stage.

Question 16

When would Pax7 expression decrease and increase in an activated satellite cell?

Answer 16

Pax7 expression decreases when they enter a proliferative stage.

Pax7 expression increases prominently after satellite cell differentiation.

Question 17

What do studies into satellite cell biology rely on?

Why is this unfortunate?

Answer 17

Flow cytometry and Fluoresence Activated Cell Sorting (FACS) analysis.

Gives no information about cell lineage or behaviour - therefore the satellite cell niche is relatively ill-defined and it is likely that is consists of multiple sub-populations.

Question 18

A positive test for Myf5 or Cd34 would indicate what type of satellite cell?

Answer 18

Inactive

Question 19

What markers do activated satellite cells express?

Answer 19

Pax7+
Myf5
MyoD

(MRF: myogenic regulatory factor family)