Muscle Development - Lecture 24 Flashcards
Stages of differentiation of skeletal muscle cells
Starts are Myogenic cells - originate in somites, look like mesenchymal cells, restricted to pathway for forming muscle and are mitotic
Mitotic state requires FGF and TGF-β
Myoblasts - derived fro myogenic, postmitotic
Myotubes - myoblasts fuse to eachother, requires Ca-dependent CAMs, involved in mRNA and protein synthesis - presense of actin, myosin, troponin and tropomyosin. Myofibrils form with sarcomeric arrangment with nuclei on periphery
Then you have muscle fibers
Satalite cells
Occur later in differentiation of myo-tissue
Located between sarcolemma and lasal lamina of myofiber
They are both mitotic and myo genic - they are able to fuse with existing muscle fiber for growth
They cannot form new muscle fibers
Primary myocytes (myotubes)
Formed by fusion of earliest (embyronic) myoblasts
Can already be fast or slow fibers
Differenciation occurs before innervation
Bigger than secondary
Secondary myocytes (myotubes)
Smaller than primary
Formed alongside primary from late, or fetal, myoblast
Motor axons may be necessary in the formation of secondary myotubes
Contained within same basal lamina and are electically coupled
How does Myf-5 regulate myogenic differenctiation? Does it have a partner? If so, what is it? Where does this occur?
. Myf-5 along with Pax-3 each can activate MyoD. THey can work together but have the same funtion.
MyoD - causes myogenic cells to become myoblasts
Occurs in somites
What is the general purpose of myogenic regulatory fibers?
Cause myogenic cells to produces p21, which causes loss of mitotic capability?
What factors are required for a myogenic cell to be mitotically active?
FGF and TGF-β
What leads to the expression of myogenin by myoblasts? What is myogenin’s function?
Induced by MyoD and Myf-f together
Myogenin causes expression of myotube genes and Myf-6
What is Myf-6 function?
Causes expression of myofiber genes
Induced by myogenin
What is the purpose of Pax-7?
Pax-7 has the same function of Pax-3, induced from somatic epithelium that causes activation of MyoD in myoblasts
What is the origin of trunk muscles?
Epaxial muscles - dorsal lip of myotome
Epaxial tendoms - from syndetome layer in somites
Hypaxial muscles - ventral buds of myotome
Hypaxial tendons - lateral plate mesoderm
What is the origin of limb muscles?
Limb from ventrolateral dermamyotome
Limb muscles tendons from lateral plate mesoderm
What is the origin of head and neck muscles?
Derived from paraxial somitomeres
Extraocular muscles arise from prechordal plate
Most cranial muscle is from unsegmmented paraxial mesoderm
The rest, lower jaw mainly, is from splanchnia mesoderm
What is the origin of cardiac muscle?
From splanchnic mesoderm
Early cardiac muscle lack myoD
express MADS (as does skeletal)
Begins contracting early, but retains mitotic ability by partial dissembly of contractile apparatus
Attach by intercalated discs
Prune belly syndrome
Molecular deficiency - textbook