MOLECULAR CORRELATES OF NEURONAL SPECIFICITY IN THE DEVELOPING INSECTNERVOUS-SYSTEM

The development of the nervous system in insects, as in most other hig her animals, is characterized by the high degree of precision and spec ificity with which synaptic connectivity is established. Multiple mole cular mechanisms are involved in this process. In insects a number of experimental methods and model systems can be used to analyze these me chanisms, and the modular organization of the insect nervous system fa cilitates this analysis considerably. Well characterized molecular ele ments involved in axogenesis are the cell-cell adhesion molecules that underlie selective fasciculation. These are cell-surface molecules th at are expressed in a regional and dynamic manner on developing axon f ascicles. Secreted molecules also appear to be involved in directing a xonal navigation. Nonneuronal cells, such as glia, provide cellular an d noncellular substrates that are important pathway cues for neuronal outgrowth. Once outgrowing processes reach their general target region s they make synapses with the appropriate postsynaptic cells. The mole cular mechanisms that allow growth cones to recognize their correct ta rget cells are essential for neuronal specificity and are being analyz ed in neuromuscular and brain interneuron systems of insects. Candidat e synaptic recognition molecules with remarkable and highly restricted expression patterns in the developing nervous system have recently be en discovered.