Journal of Neuroscience, Vol 8, 1747-1758, Copyright © 1988 by Society for Neuroscience
Axotomy-induced alterations in the synthesis and transport of neurofilaments and microtubules in dorsal root ganglion cells
MM Oblinger and RJ Lasek
Department of Biological Chemistry & Structure, Chicago Medical School, Illinois 60064.
Changes in the synthesis and axonal transport of neurofilament (NF)
proteins and tubulin were examined after various selective axotomies of
adult rat DRG cells. For axonal transport studies, DRGs were labeled by
microinjection of 35S-methionine 14 d after axonal injuries, and nerves
were retrieved 7 or 14 d after labeling. Slowly transported proteins were
examined by quantitative PAGE/fluorography. After distal peripheral nerve
crush (50-55 mm from the DRG), the cytoskeleton that entered undamaged
regions of peripheral branch DRG axons by slow axonal transport differed
from normal, while the cytoskeleton that entered dorsal root axons did not.
Specifically, smaller-than-normal ratios of labeled NF protein/tubulin were
transported in peripheral DRG axons after distal peripheral nerve crush.
This change was almost entirely due to a selective decrease in the output
of labeled NF proteins rather than to an increase in the amount of tubulin
transported with NF proteins. Since the efficiency of axonal regeneration
is known to be lower after cut injury than after nerve crush, we compared
the effect of cut versus crush axotomy of peripheral DRG axons on
cytoskeletal protein output. A more substantial reduction in the labeled
NF/tubulin transport resulted in peripheral DRG axons if the distal sciatic
nerve was cut rather than crushed but, even under these axotomy conditions,
the labeled NF/tubulin ratios in dorsal root axons were not reduced.
Peripheral cut axotomy did result in a lag in the advance of the labeling
peak of the NF/microtubule protein wave in dorsal root axons, suggesting
either that these proteins were delayed in exiting the cell body or that a
slowing of the rate of their transport occurred. Pulse- labeling DRGs in
vitro using 35S-methionine, and analysis of labeled proteins by
2-dimensional PAGE-fluorography demonstrated that the incorporation of
radioactivity into NF proteins was significantly reduced, while the
labeling of tubulins was unchanged 14 d after distal peripheral axotomy. In
contrast to the results of peripheral axotomy, dorsal root crushes made
close to the DRG (2-3 mm) or considerably distal (at the CNS entry zone
28-30 mm from the DRG) did not produce detectable changes in the amount of
labeled NF or tubulin transport in central or peripheral branch axons.
These findings indicate that the down-regulation of NF production/output
that is exhibited at 14 d after peripheral branch axotomy is not present
after central branch injury.(ABSTRACT TRUNCATED AT 400 WORDS)
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