THE LEG OF DROSOPHILA AS A MODEL SYSTEM FOR THE ANALYSIS OF NEURONAL DIVERSITY

The neurons innervating insect sense organs vary in number, shape, den dritic morphology, axonal projections and connectivity, providing abun dant material for the genetic analysis of neuronal diversity. Here we describe the leg of Drosophila as a potential model system for this an alysis. The leg of Drosophila comprises a variety of sense organs arra nged in a precise and reproducible pattern. The cell bodies of the sen sory neurons are located near the organ they innervate, which greatly facilitates their identification and accessibility. The development of the leg from its progenitor structure, the imaginal disc, is known in good detail. In particular, the time of appearance and of divisions o f the sense organ precursors is known. The origin and mode of formatio n of the leg nerve (through which all sensory axons project into the c entral nervous system) has been described. The central projections of some of the sensory neurons have been examined by horseradish peroxida se backfill or DiI labelling. Finally, the expression of several genes that control the differentiation of various types of sensory neurons can be manipulated at will. We illustrate these different aspects, and discuss the potentials and shortcomings of this system.