Journal of Neuroscience, Vol 15, 5956-5965, Copyright © 1995 by Society for Neuroscience
The notochord and floor plate guide growth cones in the zebrafish spinal cord
S Greenspoon, CK Patel, S Hashmi, RR Bernhardt and JY Kuwada
Department of Biology, University of Michigan, Ann Arbor 48109-1048, USA.
Elimination of the floor plate, a row of distinctive cells at the ventral
midline of the spinal cord, dramatically increased the frequency of errors
made by specific growth cones in the zebrafish embryo. This demonstrated
that the floor plate participated in guiding specific growth cones at the
ventral midline of the spinal cord. However, since a significant proportion
of these growth cones followed their normal pathway despite the absence of
the floor plate, we hypothesized that a second source of cues must exist at
or near the ventral midline. We tested whether the notochord, which is
located just ventral to the spinal cord, was an additional source of
pathfinding cues by eliminating it prior to axonogenesis. Laser ablation of
the notochord in wildtype embryos increased errors by spinal growth cones.
Likewise, spinal growth cones made errors in no tail mutants that are
missing the notochord but not the floor plate. These results demonstrate
that the notochord also participates in guiding growth cones at the ventral
midline. Furthermore, removal of both the floor plate and notochord
resulted in a higher error rate than removal of either one alone. These
results suggest that the notochord and floor plate normally act in concert
to guide spinal growth cones at the ventral midline.
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