Journal of Neuroscience, Vol 9, 436-446, Copyright © 1989 by Society for Neuroscience
Transport of cytoskeletal elements from parent axons into regenerating daughter axons
IG McQuarrie and RJ Lasek
Department of Developmental Genetics and Anatomy, Case Western Reserve University School of Medicine, Cleveland, Ohio.
The kinetics of slow axonal transport in newly regenerating axonal sprouts
were compared with those in nonelongating axons. The slowly transported
cytoskeletal proteins of ventral motor axons were prelabeled by
microinjection of 35S-methionine into the spinal cord. Pulse-labeled slow
transport "waves" were observed as they progressed from the surviving
"parent" axon stumps (located proximal to a crush lesion) into regenerating
"daughter" axon sprouts (located distal to the lesion). Prelabeled
cytoskeletal elements of the parent axons were transported into daughter
axons, to become distributed into 2 transport waves, "a" and "b." The rate
and composition of these waves corresponded to the slow transport
subcomponents, SCa and SCb. The shapes of the "a" and "b" waves suggested
that the cytoskeletal elements had been reorganized at the junction between
the parent and daughter axons. This hypothesis was supported by
quantitative analyses of the transport distribution for individual
radiolabeled cytoskeletal proteins (actin, spectrin, a 58-67 kDa group that
includes microtubule- associated proteins, calmodulin, and tubulin).
Specifically, during the first week of outgrowth, the amounts of
radiolabeled calmodulin and 58- 67 kDa proteins were greater in daughter
axons than in nonregenerating control axons. These results support Paul
Weiss's "conservative" model of axonal regeneration, which holds that the
preexisting transported cytoskeletal elements that continually maintain
axonal structure can also provide the cytoskeletal elements required for
axonal regeneration. In addition, the results elucidate some of the
reorganizational changes in cytoskeletal elements that occur when these are
recruited from the parent axon to form daughter axons.