Why adult mammalian intrafusal and extrafusal fibers contain different myosin heavy-chain isoforms.
Multiple isoforms of the contractile protein myosin are present in mammalian skeletal muscles. The diversity of the heavy-chain subunits of myosin (MyHCs) in intrafusal fibers is thought to reflect a pathway of differentiation that is unique to muscle spindles. In fact, intrafusal MyHCs are developmental isoforms expressed by the prenatal precursors of both intrafusal and extrafusal fibers. In adult limbs, developmental MyHCs persist in intrafusal, but not extrafusal fibers principally due to the afferent neurons that arrest their maturational replacement by MyHCs associated with faster shortening velocities. The slow shortening velocities that are characteristic of developmental MyHCs might be adaptive for precise calibration of muscle spindles as sense organs.
Walro
J M
JM
Dept of Anatomy, Northeastern Ohio Universities College of Medicine, Rootstown, OH 44272-0095, USA.
Kucera
J
J
D000344:Afferent Pathways / Q000502:physiology; D000375:Aging / Q000378:metabolism; D000818:Animals; D019070:Cell Lineage; D005326:Fetal Proteins / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008322:Mammals / Q000033:anatomy & histology / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009024:Morphogenesis; D009119:Muscle Contraction; D024510:Muscle Development; D018485:Muscle Fibers, Skeletal / Q000737:chemistry* / Q000145:classification; D009124:Muscle Proteins / Q000172:deficiency / Q000502:physiology; D009470:Muscle Spindles / Q000502:physiology; D018482:Muscle, Skeletal / Q000737:chemistry / Q000196:embryology / Q000254:growth & development* / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000502:physiology; D020033:Protein Isoforms / Q000378:metabolism*; D051381:Rats
D005326:Fetal Proteins; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D018995:Myosin Heavy Chains