Compartments and the topography of leg afferent projections in Drosophila.

The legs of Drosophila are covered with mechanosensory bristles, innervated by sensory neurons that project to the CNS in a very orderly manner. We examined this afferent projection by staining the sensory neurons associated with identified bristles in wild-type, engrailed and scute flies. We observe that anterior neurons project to an anterior region of the ventral neuropil, while posterior neurons project to a more posterior region. We rule out that this difference depends on the compartment of origin of the receptors. Our results also argue against explanations based on other factors that might correlate to anterior/posterior position: peripheral organization of the leg nerve, competitive interactions, or differences in times of birth. We suggest that position itself is the primary determinant of this projection.