Sensory pathways in Drosophila central nervous system.

Abstract

We have analyzed the central projections of identified sensory neurons in wild type Drosophila and in the homeotic mutant bithorax postbithorax. The results indicate that: (i) the choice of a given pathway in the central nervous system of the adult depends on the developmental history of the neuron, namely on the type of sense organ of which it is part, and on the developmental compartment to which it belongs; (ii) the establishment of the projection involves the specific recognition of a preexisting "trail" in the central nervous system. Here we examine and rule out alternative explanations of our results, and conclude that the directed growth of an axon relies at least in part on a physical guidance mechanism to which specificity is conferred by programming the growing axon to recognize the appropriate guide. We speculate that the guides are preexisting, specifically marked nerve fibers and that the basic pattern of connectivity is largely laid down early during neurogenesis, at a time when a standard set of connections is relatively easy to specify.