The Journal of Neuroscience, June 15, 1999, 19(12):4899-4906
A Single Growth Cone is Capable of Integrating Simultaneously
Presented and Functionally Distinct Molecular Cues during Target
Recognition
Demian
Rose and
Akira
Chiba
Department of Cell and Structural Biology, University of Illinois,
Urbana, Illinois 61801
A variety of cell recognition pathways affect neuronal target
recognition. However, whether such pathways can converge at the level
of a single growth cone is not well known. The RP3 motoneuron in
Drosophila has previously been shown to respond to the
muscle cell surface molecules TOLL and fasciclin III (FAS3),
which are normally encountered during RP3 pathfinding in a sequential
manner. TOLL and FAS3, putative "negative" and "positive"
recognition molecules, respectively, affect RP3 antagonistically. Under
normal conditions, TOLL and FAS3 together improve the accuracy of its target recognition. Here, we show that, when presented with concurrent TOLL and FAS3 expression, RP3 responds to both, integrating their effects. This was demonstrated most succinctly by single cell visualization methods. When a balance in relative expression levels between the two antagonistic cues is achieved, the RP3 growth cone
exhibits a phenotype virtually identical to that seen when neither TOLL
nor FAS3 is misexpressed. Thus, growth cones are capable of
quantitatively evaluating distinct recognition cues and integrating
them to attain a net result, in effect responding to the "balance of
power" between positive and negative influences. We suggest that the
ability to integrate multiple recognition pathways in real-time is one
important way in which an individual growth cone interprets and
navigates complex molecular environments.
Key words:
axon guidance; Drosophila; fasciclin III; growth cone; neuromuscular; neuronal recognition; signal integration; synaptic target recognition; pathfinding; TOLL
Copyright © 1999 Society for Neuroscience 0270-6474/99/19124899-08$05.00/0