Myogenesis Flashcards
What kind of cells will migrate to the locations in the body where muscle development is needed?
Myotome cells
Describe the FIRST step of myogenesis.
A mesodermal stem cell (bone, fat, etc) will go through determination, which is where a cell becomes destined for a particular fate (cell type), and becomes a myoblast (which is a muscle precursor cell and contains a single nucleus).
Determination is triggered by the expression of MRFs (Myogenic Regulatory Factors) (transcription factors). The MRFs involved are MyoD and Myf5.
Describe the SECOND step of myogenesis.
The single myoblast will then go through proliferation and replicate into more myoblasts.
These myoblasts are not specialized and do not express muscle specific proteins.
True or False: Myoblasts are replication competent, meaning they are capable of progressing through the cell cycle and regenerating additional myoblasts
True!
Describe the THIRD step of myogenesis.
After myoblasts replicate, they withdraw from the cell cycle and stop dividing. Then, the cells align with one another. The membranes will fuse together and begin forming a myotube. MRFs (myogenin and MRF4) are going to be involved in early differentiation. Once differentiation and fusion are complete, it will have formed a myotube, which is an immature muscle fiber, it’s multinucleated, it cannot replicate, and it is now able to express muscle-specific proteins.
Describe the FOURTH step of myogenesis.
After the third step, the primary (1º) myotubes will form first! This is then followed by a second wave of myotubes, which create the secondary (2º) myotubes. Additional myoblasts (fetal myoblasts) will use the primary myotube as a scaffold to create the secondary myotube.
Describe the FIFTH step of myogenesis.
The primary (innervated and contains contractile proteins) and secondary myotube will then go through maturation and hypertrophy to create mature muscle fibers that contain adult satellite cells.
The formation of primary myotubes is __________.
Autonomous (independent)
The formation of secondary myotubes depends on _______________.
Contraction of the primary myotubes.
True or False: Animals may have 5-20+ x more primary fibers than secondary fibers.
FALSE - Animals may have 5-20+ x more secondary fibers than primary fibers.
Muscle fiber number is established by _________.
Birth
What does the muscle fiber number affect?
It affects the “potential” for overall muscle mass.
Who/what are the exceptions to the establishment of muscle fiber number?
1) Indeterminate growers
2) Senescence
3) Damage/repair
What are the two types of muscle growers?
1) Determinate growers
2) Indeterminate growers
What are determinate growers?
They reach a specific size postnatally with adequate nutrition provided. These include most mammals and avian species.
What are indeterminate growers?
They don’t have any predetermined mature weight. EX: that big fish in the slide - it had access to resources with a lot of nutrients
