The Journal of Neuroscience, July 15, 2000, 20(14):5358-5366
The "Waiting Period" of Sensory and Motor Axons in Early
Chick Hindlimb: Its Role in Axon Pathfinding and Neuronal
Maturation
Guoying
Wang and
Sheryl A.
Scott
Department of Neurobiology and Anatomy, University of Utah School
of Medicine, Salt Lake City, Utah 84132
During embryonic development motor axons in the chick hindlimb grow
out slightly before sensory axons and wait in the plexus region at the
base of the limb for ~24 hr before invading the limb itself (Tosney
and Landmesser, 1985a). We have investigated the role of this waiting
period by asking, Is the arrest of growth cones in the plexus region a
general property of both sensory and motor axons? Why do axons wait?
Does eliminating the waiting period affect the further development of
motor and sensory neurons?
Here we show that sensory axons, like motor axons, pause in the plexus
region and that neither sensory nor motor axons require cues from the
other population to wait in or exit from the plexus region. By
transplanting older or younger donor limbs to host embryos, we show
that host axons innervate donor limbs on a schedule consistent with the
age of the grafted limbs. Thus, axons wait in the plexus region for
maturational changes to occur in the limb rather than in the neurons
themselves. Both sensory and motor axons innervate their appropriate
peripheral targets when the waiting period is eliminated by grafting
older donor limbs. Therefore, axons do not require a prolonged period
in the plexus region to sort out and project appropriately. Eliminating
the waiting period does, however, accelerate the onset of naturally
occurring cell death, but it does not enhance the development of
central projections or the biochemical maturation of sensory neurons.
Key words:
waiting period; chick; hindlimb; axon pathfinding; neuron
development; motor neuron; sensory; dorsal root ganglion; cell death; trkA; substance P; central projections
Copyright © 2000 Society for Neuroscience 0270-6474/00/20145358-09$05.00/0
Previous Article | Next Article
