DEVELOPMENT OF THE GIANT FIBER NEURON OF DROSOPHILA-MELANOGASTER

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.