Journal of Neuroscience, Vol 13, 115-126, Copyright © 1993 by Society for Neuroscience
Cell-cell interactions during the migration of an identified commissural growth cone in the embryonic grasshopper
PZ Myers and MJ Bastiani
Department of Biology, University of Utah, Salt Lake City 84112.
One of the fascicles of the posterior commissure of the embryonic
grasshopper is pioneered by an individually identifiable neuron named Q1.
Q1 initially grows along a longitudinal pathway established by another
pioneer neuron, MP1, and then crosses to the midline, where it meets and
fasciculates with the axon of the contralateral Q1. The Q1 growth cone
follows the contralateral Q1 axon to the contralateral longitudinal
pathway, where it then fasciculates with axons of the MP1/dMP2 fascicle. In
this work, we have identified a small set of early neurons that Q1 could
use as guidance cues while negotiating its way along a specific and
stereotyped pathway to the midline. Furthermore, we have observed
characteristic morphological changes in the Q1 growth cone that could
indicate responses to changing adhesivity in the substrates it contacts. We
have also quantified the pattern of dye coupling between neurons in this
system. Most of the neurons to which Q1 becomes coupled retain a strong,
consistent pattern of dye coupling that shows no recognizable variation at
times when growth cones are making pathway decisions. However, we have
found one clear instance of transient, site-specific dye coupling between
the Q1 growth cone and the ipsilateral MP1 soma. The timing and pattern of
dye coupling in this system suggest that dye coupling may play a role in
synchronizing the initiation of axon outgrowth among a small population of
neurons. Although dye coupling may not play a direct role in neuronal
pathfinding, it may exert a profound indirect influence on neuronal
interactions by regulating the timing of axon outgrowth.