The giant fiber system (GFS) of Drosophila melanogaster provides a con
venient system in which to study neural development. It mediates escap
e behaviour through a small number of neurons, including the giant fib
ers (GFs), to innervate the tergotrochantral jump muscle (TTM) and the
dorsal longitudinal flight muscles. The GFS has been intensively stud
ied physiologically in both wild-type and mutant flies, and is often u
sed as a system to study the effects of neural mutations on the physio
logy of the adult nervous system. Recently, much information has been
gleaned as to how and when synaptogenesis, with its major target neuro
ns, is achieved. However, little is known of the earlier development o
f this neuron. Here we have used an enhancer-trap, marking parts of th
e GFS, in conjunction with BrdU labelling, to attempt to follow the bi
rth, axonogenesis, and the early morphological meeting of the GFs with
their target neurons. From these anatomical observations we propose t
hat the GF cell is not born during the larval or pupal stages and, the
refore. appears to be a persistent embryonic cell. The axons of the GF
s develop during the third instar. During the early pupal stages the G
Fs contact other identified neurons of the GFS. In addition, we see so
me aberrant development of the network, with some flies carrying only
one GF, and yet others with extended axons. We present a model for the
initial joining of the GFs and tergotrochanteral motorneurons (TTMns)
. J. Comp. Neurol. 397:519-531, 1998. (C) 1998 Wiley-Liss, Inc.