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Roles of peripheral glia in embryonic nervous system development of drosophilia Sepp, Katharine Julia


Peripheral glial cells are major constituents of the PNS and are required for insulation of peripheral nerves. Their function during Drosophila nervous system development has not been previously studied largely due to a lack o f cellular markers. To determine what roles peripheral glia have in Drosophila embryonic nervous system development, a series of peripheral glial enhancer trap lines were first generated by converting previous glial nuclear lacZ enhancer traps to the GAL4 system. The targeted transposition technique, which is a direct exchange of one P element for another, successfully generated the desired peripheral glial GAL4 lines at a high efficiency. Potentially, targeted transposition is a widely applicable technique for generation of many other desirable GAL4 lines in the future. The new GAL4 lines were used to characterize peripheral glia in relation to neuronal growth. Peripheral glial proliferation, migration, cell contacts, morphological changes, and nerve wrapping were described. Peripheral glia are born at the lateral edge of the CNS. Motor and sensory neurons make physical contacts with the peripheral glia as they migrate across the CNS/PNS border. The peripheral glia then migrate into the PNS along preestablished neuronal tracts while extending long cytoplasmic processes. The peripheral glia completely wrap all sensory axon tracts by the end of embryogenesis, but do not wrap the distal tips of motor neuron branches. The migrational patterns and neuronal associations of peripheral glia during development are very similar to vertebrate glia and suggest that Drosophila may be a powerful model system to understand many aspects of glial development. The GAL4 lines were then used to ablate peripheral glia early in development by ectopic expression of apoptosis genes. The analysis provides insight into the major roles peripheral glia play in generation of the nervous system. Peripheral glia mediate axon migration over the CNS/PNS border and glia are required to prepattern the neuronal CNS exit/entry sites. When the glia are ablated, axons project across the CNS/PNS border at abnormal positions and proper nerve bundling never forms in the region. Peripheral glia also appear to stimulate axogenesis and promote sensory neuron survival. The glia also may provide contact-mediated cues for centrally directed sensory axon migration. Peripheral glia are also essential for maintenance of tight axon fasciculation and compact nerve bundling. Overall, the results suggest that peripheral glia have important functions in early and late development of the nervous system which also may be common to vertebrate PNS glia.

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