Regulation of the intermediate filament protein nestin at rodent neuromuscular junctions by innervation and activity.
The intermediate filament nestin is localized postsynaptically at rodent neuromuscular junctions. The protein forms a filamentous network beneath and between the synaptic gutters, surrounds myofiber nuclei, and is associated with Z-discs adjacent to the junction. In situ hybridization shows that nestin mRNA is synthesized selectively by synaptic myonuclei. Although weak immunoreactivity is present in myelinating Schwann cells that wrap the preterminal axon, nestin is not detected in the terminal Schwann cells (tSCs) that cover the nerve terminal branches. However, after denervation of muscle, nestin is upregulated in tSCs and in SCs within the nerve distal to the lesion site. In contrast, immunoreactivity is strongly downregulated in the muscle fiber. Transgenic mice in which the nestin neural enhancer drives expression of a green fluorescent protein (GFP) reporter show that the regulation in SCs is transcriptional. However, the postsynaptic expression occurs through enhancer elements distinct from those responsible for regulation in SCs. Application of botulinum toxin shows that the upregulation in tSCs and the loss of immunoreactivity in muscle fibers occurs with blockade of transmitter release. Extrinsic stimulation of denervated muscle maintains the postsynaptic expression of nestin but does not affect the upregulation in SCs. Thus, a nestin-containing cytoskeleton is promoted in the postsynaptic muscle fiber by nerve-evoked muscle activity but suppressed in tSCs by transmitter release. Nestin antibodies and GFP driven by nestin promoter elements serve as excellent markers for the reactive state of SCs. Vital imaging of GFP shows that SCs grow a dynamic set of processes after denervation.
Kang
Hyuno
H
Section of Neurobiology, Institute of Neuroscience, University of Texas, Austin, Texas 78712, USA.
Tian
Le
L
Son
Young-Jin
YJ
Zuo
Yi
Y
Procaccino
Diane
D
Love
Flora
F
Hayworth
Christopher
C
Trachtenberg
Joshua
J
Mikesh
Michelle
M
Sutton
Lee
L
Ponomareva
Olga
O
Mignone
John
J
Enikolopov
Grigori
G
Rimer
Mendell
M
Thompson
Wesley
W
D000818:Animals; D004742:Enhancer Elements, Genetic / Q000502:physiology; D007381:Intermediate Filament Proteins / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000166:cytology / Q000294:innervation* / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000502:physiology*; D064231:Nestin; D009469:Neuromuscular Junction / Q000166:cytology / Q000502:physiology*; D051381:Rats; D012583:Schwann Cells / Q000166:cytology / Q000502:physiology; D020426:Sciatic Neuropathy / Q000473:pathology
D007381:Intermediate Filament Proteins; D009419:Nerve Tissue Proteins; C577485:Nes protein, mouse; C577486:Nes protein, rat; D064231:Nestin