Stability of myosin heavy chain isoforms in selectively denervated adult rat muscle spindles.
Rat intrafusal fibers consist of multiple isoforms of myosin heavy chains (MHCs) whose expression involves complex interactions among motor neurons, sensory neurons, and muscle cells during spindle development. Little is known about the roles of sensory and motor innervation in regulating and maintaining expression of MHC isoforms in adult rat muscle spindles.



MHC expression was investigated in deafferented or deefferented adult rat muscle spindles by reacting transverse sections of spindles with a panel of monoclonal antibodies specific for different MHC isoforms.



Deefferentation or deafferentation did not alter the number of intrafusal fibers expressing most MHC isoforms. However, the numbers of fibers expressing two MHC isoforms were altered in deefferented muscle spindles. Nuclear bag1 fibers ceased to express alpha-cardiac MHC and upregulated embryonic MHC after ablation of motor innervation. Likewise, bag2 and chain fibers downregulated avian neonatal/fast MHC following deafferentation, but chain fibers upregulated type 2A MHC and became more extrafusal-like in their pattern of MHC expression.



These data indicate that (1) perturbations in spindle sensory and motor nerve supplies produce less severe alterations in MHC expression in mature intrafusal fibers than do similar lesions in developing intrafusal fibers and (2) MHC expression in intrafusal fibers reflects a combination of inductive and suppressive effects of motor and sensory neurons.
Wang
J
J
Department of Anatomy, Northeastern Ohio Universities College of Medicine, Rootstown, USA.
McWhorter
D L
DL
Walro
J M
JM
D000818:Animals; D005260:Female; D005727:Ganglia, Spinal / Q000601:surgery; D009121:Muscle Denervation; D018485:Muscle Fibers, Skeletal / Q000201:enzymology* / Q000648:ultrastructure; D009470:Muscle Spindles / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000201:enzymology / Q000294:innervation; D018995:Myosin Heavy Chains / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D009475:Neurons, Afferent / Q000502:physiology; D009476:Neurons, Efferent / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
D018995:Myosin Heavy Chains; D009218:Myosins