Neural Pathfinding in an Insect Wing

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To understand how axons of nerve cells navigate in particular directions along defined pathways, the substratum for axonal growth is being examined in the simple system. Growth of axons can easily be studied in an insect wing where neurons form a simple, two- dimensional network nestled in the space between two monolayers of epithelial cells. Transposition of grafts from the upper monolayer suggests that growing axons are guided in a distal to proximal direction by graded cues in their epithelial substratum. Using scanning electron microscopy, the topography of this substratum has been viewed in its entirety. Axons encounter an increasing density of basal cellular processes as they grow proximally. The distribution of surface molecules along the neural pathway can be modulated by extension and retraction of these basal processes. A novel protein (2F5) found on surfaces of the substratum at the time of axonal outgrowth is thought to be involved in the interaction of axons with substrata. This protein has been purified and its ability to promote outgrowth of axons will be studied using functional assays in situ and scanning electron microscopy. In addition, an immunosuppression technique will be used to generate antibodies to other surface proteins that may be involved in axonal pathfinding. These studies promise to identify novel molecules that play a role in neuronal development and regeneration, not only in the insect, but in other species, as well.