Journal of Neuroscience, Vol 6, 3552-3563, Copyright © 1986 by Society for Neuroscience
Guidance of neuronal growth cones in the grasshopper embryo. IV. Temporal delay experiments
CQ Doe, MJ Bastiani and CS Goodman
In the previous 3 papers, we demonstrated that neuronal growth cones
display selective affinities for both specific axonal and glial pathways in
the grasshopper embryo; for example, the pCC growth cone selectively
recognizes the MP1/dMP2 axons, while the aCC growth cone selectively
recognizes the U axons and a specific glial cell (the segment boundary
cell). We were interested in further testing the temporal specificity of
these affinities. To address this issue, we performed specific temporal
transplant experiments by using a laser microbeam in ovo to ablate the
neuronal precursor cell, neuroblast (NB) 1-1, that generates the aCC and
pCC neurons. Neighboring ectodermal cells regulate and replace the ablated
NB 1-1; the new NB 1-1 then generates the aCC and pCC neurons with a
temporal delay of 10-20 hr (2- 4% of development), depending upon the
experimental paradigm. The results of these temporal delay experiments
further demonstrate the selective affinities of the aCC and pCC growth
cones for specific axonal and glial surfaces and confirm that these
specificities are absolute and not hierarchical. Furthermore, they suggest
that precise timing is not important; both the pCC and aCC growth cones are
able to selectively recognize their appropriate axonal and glial pathways
after delays of 10-20 hr despite being confronted with the surfaces of many
additional axons and pathways.