Journal of Neuroscience, Vol 7, 2397-2411, Copyright © 1987 by Society for Neuroscience
Axonal transport of cytoskeletal proteins in oculomotor axons and their residence times in the axon terminals
P Paggi and RJ Lasek
Cytoskeletal protein transport and metabolism are studied in the somatic
motor and parasympathetic axons of the chicken oculomotor system. Kinetic
analyses of pulse-labeled proteins indicate that the neurofilaments are
transported 2-3 times more rapidly in the somatic motor axons than in the
parasympathetic axons. By contrast, the transport rates of the slow
component b (SCb) proteins are very similar in these axons. The
parasympathetic axons terminate in the ciliary ganglion, and radiolabeling
curves from the ciliary ganglion can be used to study the kinetics of
cytoskeletal protein removal from the terminals. The rate of removal
directly determines the residence time of the cytoskeletal proteins in the
ciliary ganglion, and the residence time directly affects the shape and
amplitude of the transport curves of the ganglion. A computer model was
used to analyze these transport curves and to determine the half-residence
time of the cytoskeletal proteins in the terminal regions. From the
computer experiments, we estimate that the half-residence times of the
neurofilament proteins actin and tubulin are 2, 3.5, and 7 d, respectively.
The differences between the half-residence times of the cytoskeletal
proteins indicate that the rate of protein removal from the terminals
differs for these proteins. On the basis of these results, we propose that
the removal mechanisms critically control the composition of the
cytoskeleton in the terminal regions. Through their effects on its
composition, the removal mechanisms have a crucial role in converting the
cytoskeleton of the axon proper into the specialized cytoskeleton of the
axon terminal.