The Journal of Neuroscience, June 15, 2002, 22(12):4955-4963
Axonally Transported Peripheral Signals Regulate
-Internexin
Expression in Regenerating Motoneurons
Tanya S.
McGraw1,
J.
Parker
Mickle2,
Gerry
Shaw1, and
Wolfgang J.
Streit1
Departments of 1 Neuroscience and
2 Neurological Surgery, University of Florida College of
Medicine and McKnight Brain Institute, Gainesville, Florida 32611
The class IV neuronal intermediate filament (IF) family
proteins includes the neurofilament (NF) triplet proteins NF-L, NF-M, and NF-H and also the more recently characterized
-internexin-NF66. It is well established that NF-L, -M, and -H protein and mRNA are
downregulated after peripheral nerve injury. We examined
-internexin protein expression after three facial nerve lesion paradigms: crush,
transection, and resection.
-Internexin immunoreactivity was absent
in the perikarya of uninjured facial motoneurons but increased
dramatically in all three injury paradigms, with maximum immunoreactivity observed at 7 d after injury. Twenty-eight days after nerve crush or transection, there was a dramatic decrease in the
number of
-internexin-positive cells. In contrast,
-internexin remained elevated 28 d after nerve resection, an injury that
hinders regeneration and target reinnervation. In situ
hybridization studies showed an increase in
-internexin mRNA
expression in the facial nucleus at 7 and 14 d after injury.
Retrograde transport of fluorogold from the whisker pads to the
facial nucleus was seen only in motoneurons that lacked
-internexin immunoreactivity, supporting the idea that target
reinnervation and inhibitory signals from the periphery regulate
the expression of
-internexin. Blockage of axonal transport through
local colchicine application induced strong immunoreactivity in
motoneurons.
-Internexin expression was also examined after central
axotomy of rubrospinal neurons, which constitutively show
-internexin immunoreactivity. After rubrospinal tractotomy,
-internexin immunoreactivity transiently increased by 7 d after
injury but returned to control levels by 14 d. We conclude that
-internexin upregulation in injured motoneurons suggests a role for
this IF protein in neuronal regeneration.
Key words:
axotomy; regeneration; axonal transport; neurofilament
proteins; motoneurons;
-internexin
Copyright © 2002 Society for Neuroscience 0270-6474/02/22124955-09$05.00/0