L8 - Muscle Development Flashcards
Where do satellite cells / muscle stem cells derive from in the somite?
The myotome
What do activated satellite cells differentiate into?
Myoblasts
What do myoblasts fuse together to form?
Myofibers
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?
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.
What is the role of Pax7?
Expressed in both embryonic progenitor cells and adult satellite cells where it helps regulate its for their maintenance and self-renewal
What is the first sign of differentiation in the somite?
In the ventral-medial region undergoes an epithelial to mesenchymal transition (EMT)
The cells within each somite undergo EMT to form two distinct sets of cells. What are they?
Sclerotome and dermomyotome
What do the sclerotome cells differentiate into after EMT?
Mesenchymal cells
What do the mesenchymal cells form?
Vertebrae and associated connective tissues, such as cartilage, ligaments, and tendons
What do the dermomyotome cells give rise to?
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.
What is the role of the Pax3 gene?
Expression of this gene in muscle progenitor cells for regulation and proliferation of the muscle cells
Future muscle cells migrate around the edges of the dermomyotome and form a layer underneath known as what?
Myotome
What happens here?
Cells begin to differentiate and express muscle cell specific markers
Which out of anterior the posterior end develops first into muscle cells?
Anterior cells
What is the “in-out mechanism?
Myoblasts migrate into the limb and then back out to generate muscles. Migration of cells from the body wall into the developing limb buds.
Which are the only muscles not derived from somites?
Head muscles (jaw, facial, and extraocular)
Where are they formed from?
Unsegmented paraxial head mesoderm
Where do the somites receive signalling from?
Notochord
What is a grafting experiment?
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.
What is an ablation experiment?
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.
Which transcription factors induce myogenesis?
Pax3 and Pax7
Where are Pax3 and Pax7 expressed?
Dermomyotome in the proliferating myoblasts
Myogenic Regulatory Factors (MRFs) are what kind of transcription factors?
Basic-loop-helix
What do they bind to?
E proteins
What is the role of E proteins?
They bind to DNA sequences known as “E boxes” which are found in regulatory regions of many genes. They can recruit chromatin remodelling factors.
What will this lead to?
Activation of the expression of muscle specific genes
Where are MRFs exclusively expressed?
Skeletal muscle
