L8 - Muscle Development

Question 1

Where do satellite cells / muscle stem cells derive from in the somite?

Answer 1

The myotome

Question 2

What do activated satellite cells differentiate into?

Answer 2

Myoblasts

Question 3

What do myoblasts fuse together to form?

Answer 3

Myofibers

Question 4

Myf5 and Pax7 are both transcription factors involved in development and maintenance of muscle stem cells, including satellite cells. What is the role of Myf5?

Answer 4

It is expressed in embryonic muscle progenitor cells and allows them to become specific and differentiated into muscle cells. Also expressed in satellite cells where it helps regulate its activation and proliferation in response to muscle injury or exercise.

Question 5

What is the role of Pax7?

Answer 5

Expressed in both embryonic progenitor cells and adult satellite cells where it helps regulate its for their maintenance and self-renewal

Question 6

What is the first sign of differentiation in the somite?

Answer 6

In the ventral-medial region undergoes an epithelial to mesenchymal transition (EMT)

Question 7

The cells within each somite undergo EMT to form two distinct sets of cells. What are they?

Answer 7

Sclerotome and dermomyotome

Question 8

What do the sclerotome cells differentiate into after EMT?

Answer 8

Mesenchymal cells

Question 9

What do the mesenchymal cells form?

Answer 9

Vertebrae and associated connective tissues, such as cartilage, ligaments, and tendons

Question 10

What do the dermomyotome cells give rise to?

Answer 10

Muscles and skin of the body. Some dermomyotome cells also undergo EMT and migrate to other regions of the body to form various tissues, such as the diaphragm and some of the bones in the face.

Question 11

What is the role of the Pax3 gene?

Answer 11

Expression of this gene in muscle progenitor cells for regulation and proliferation of the muscle cells

Question 12

Future muscle cells migrate around the edges of the dermomyotome and form a layer underneath known as what?

Answer 12

Myotome

Question 13

What happens here?

Answer 13

Cells begin to differentiate and express muscle cell specific markers

Question 14

Which out of anterior the posterior end develops first into muscle cells?

Answer 14

Anterior cells

Question 15

What is the “in-out mechanism?

Answer 15

Myoblasts migrate into the limb and then back out to generate muscles. Migration of cells from the body wall into the developing limb buds.

Question 16

Which are the only muscles not derived from somites?

Answer 16

Head muscles (jaw, facial, and extraocular)

Question 17

Where are they formed from?

Answer 17

Unsegmented paraxial head mesoderm

Question 18

Where do the somites receive signalling from?

Answer 18

Notochord

Question 19

What is a grafting experiment?

Answer 19

A notochord from a donor embryo is transplanted into a host embryo which has had its own notochord removed. The results show that the transplanted notochord can induce formation of a second neural tube and other structures usually induced by the endogenous notochord.

Question 20

What is an ablation experiment?

Answer 20

The notochord is selectively destroyed in developing embryos, either partially, or completely. This leads to a variety of developmental defects and shows that the notochord is required for proper development of many structures in the embryo.

Question 21

Which transcription factors induce myogenesis?

Answer 21

Pax3 and Pax7

Question 22

Where are Pax3 and Pax7 expressed?

Answer 22

Dermomyotome in the proliferating myoblasts

Question 23

Myogenic Regulatory Factors (MRFs) are what kind of transcription factors?

Answer 23

Basic-loop-helix

Question 24

What do they bind to?

Answer 24

E proteins

Question 25

What is the role of E proteins?

Answer 25

They bind to DNA sequences known as “E boxes” which are found in regulatory regions of many genes. They can recruit chromatin remodelling factors.

Question 26

What will this lead to?

Answer 26

Activation of the expression of muscle specific genes

Question 27

Where are MRFs exclusively expressed?

Answer 27

Skeletal muscle