Glial cells are thought to play a role in growth cone guidance, both in insects and in vertebrates. In the developing central nervous system of the Drosophila embryo, the interface glia form a scaffold prior to the extension of the first pioneer growth cones. Growing axons appear to contact the glial scaffold as the axon tracts are established. We have used a novel technique for targeted cell ablation to kill the interface glia and thus to test their role in establishment of the embryonic axon tracts. We show that ablation of the interface glia early in development leads to a complete loss of the longitudinal axon tracts. Ablation of the glia later in embryonic development results in defects comprising weakening and loss of axon fascicles within the connectives. We conclude that the interface glia are required first for growth cone guidance in the formation of the longitudinal axon tracts in the Drosophila embryo and then either to direct the follower growth cones, or to maintain the longitudinal axon tracts.

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