Flashcards in Muscular Development Deck (15):
What are myoblasts?
-derived from myogenic cells
What are myotubes?
-formed when myoblasts line up and adhere to one another
-requires calcium dependent CAMs
-involved in mRNA and protein synthesis
-characterized by appearance of actin, myosin, troponin, and tropomyosin
-formation of sarcomeres
-nuclei move to periphery
All skeletal muscle originates in what?
Somites or somitomeres
What are satellite cells?
-located between sarcolemma and basal lamina
-mitotic and myogenic
-able to fuse with muscle fiber and provide for growth
-satellite cells do not form new muscle fibers
Differentiate between primary myotubes and secondary myotubes.
-formed by fusion of earliest embryonic myoblasts
-may already be distinguished as fast or slow in some species
-differentiation occurs before innervation
-smaller than primary
-formed alongside primary from fetal myoblasts
-presence of motor axons may be necessary to form secondary myotubes
-contained within same basal lamina and are electrically coupled
What two things maintain myogenic cells in labile state?
-FGF and TGF-beta
What causes a loss of mitotic capability?
What are the stages of differentiation in myogenic cells?
-originate in somites
-resemble mesenchymal cells
-restricted to muscle forming line
What does the MyoD family do?
-able to convert non-muscle cells to cells capable of expressing muscle proteins
-helix loop helix transcription factors
-forms dimer and binds to E box in enhancer region of the myogenic genes
-binding is enhanced when E12 replaces one member of the dimer to form a heterodimer
-transcriptional inhibitor id can replace one member of the MyoD homodimers to form a heterodimer, resulting in poor binding ability
What regulates MyoD?
Pax-3 and Myf-5 separately can activate MyoD and cause myogenic cells to become myoblasts
What can increasing levels of MyoD result in?
-along with Myf-5, can result in expression of myoblast genes by myoblasts and expression of myogenin
-myogenin results in expression of myotubes genes and Myf-6
-Myf-6 leads to expression of myofiber genes
What are the origins of the muscles of the trunk?
-epaxial muscles arise from dorsal lip myotome
-epaxial tendons arise from syndetome layer within somites
-hypaxial muscles arise from ventral buds of myotome
-tendons arise from lateral plate mesoderm
What derives the muscles of the limbs?
-limb muscles arise from ventrolateral dermomyotome
-tendons from lateral plate mesoderm
Where are muscles of the head and neck derived from?
-mostly from paraxial somitomeres
-extra ocular muscles from prechordal plate
-most of the cranial musculature from unsegmented paraxial mesoderm
-cranial musculature (lower jaw) from splanchnic mesoderm