The guidance of axons from transplanted neurons through aneural Drosophila wings

The sensory neurons of the wing of Drosophila arise during the first 24 hr of metamorphosis, and their axons converge to form a stereotyped set of nerves projecting proximally from the peripherally located cell bodies through the wing and towards the CNS. To better characterize the cues guiding this stereotyped axon outgrowth, we have performed a series of transplantation studies in which neurons from a variety of sources (wing, eye, antenna, and leg disks) were placed into mutant, aneural wings. Axons growing from such implants in effect assay the host wing for the presence and location of guidance cues. Our results show, first, that such axons prefer to grow in the normal, proximal direction and, second, that they prefer to grow along the approximate site of one of the normal nerves, that of the third longitudinal vein. It therefore appears that the aneural wing epithelium contains cues capable of directing both the polarity and the location of axonal outgrowth. These cues are relatively non-specific, in that a variety of neuronal types are capable of responding to them.