The Journal of Neuroscience, September 15, 1999, 19(18):7901-7912
Effects of roundabout on Growth Cone Dynamics,
Filopodial Length, and Growth Cone Morphology at the Midline and
throughout the Neuropile
Michael J.
Murray and
Paul M.
Whitington
Molecular and Cellular Biology, School of Biological Sciences,
University of New England, Armidale, NSW 2351, Australia
roundabout (robo) encodes an axon
guidance receptor that controls midline crossing in the
Drosophila CNS. In robo mutants, axons
that normally project ipsilaterally can cross and recross the midline.
Growth cones expressing Robo are believed to be repelled from the
midline by the interaction of Robo and its ligand Slit, an
extracellular protein expressed by the midline glia. To help understand
the cellular basis for the midline repulsion mediated by Robo, we used
time-lapse observations to compare the growth cone behavior of the
ipsilaterally projecting motorneuron RP2 in robo and
wild-type embyros. In wild-type embryos, filopodia can project across
the midline but are quickly retracted. In robo mutants,
medial filopodia can remain extended for longer periods and can develop
into contralateral branches. In many cases RP2 produces both
ipsilateral and contralateral branches, both of which can extend into
the periphery. The growth cone also exhibits longer filopodia and more
extensive branching both at the midline and throughout the neuropile.
Cell injections in fixed stage 13 embryos confirmed and quantified
these results for both RP2 and the interneuron pCC. The results
suggest that Robo both repels growth cones at the midline and inhibits
branching throughout the neuropile by promoting filopodial retraction.
Key words:
Drosophila melanogaster; roundabout; growth
cone; time-lapse; filopodia; repulsion
Copyright © 1999 Society for Neuroscience 0270-6474/99/19187901-12$05.00/0
Previous Article | Next Article
