Localized FGF-receptor signaling controls differentiation of wrapping glial cells of Drosophila

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Efficient neuronal conductance requires insulation of axons by glial cell processes. Inver-tebrates, such as Drosophila, show a relatively simple extension of glial membranes around the axons, resembling Remak fibers formed by Schwann cells in the mammalian peripheral nervous system. In the framework of tthis appliaction we want to unravel the molecular pathways underlying glial differentiation using the developing Drosophila visual system as a model. Here the wrapping glial cells first form thin processes along photore-ceptor axon fascicles to then ensheath the entire axon bundle. This differentiation is con-trolled by fibroblast growth factor (FGF)-signaling. The FGF-receptor is expressed at the neuron-glia interface along the entire length of the photoreceptor axon fascicle and is acti-vated by axonally secreted FGF. This suggests that localized activity of the FGF-receptor is important to trigger glial membrane growth around the axonal fascicle. Preliminary data suggest that additional transmembrane proteins are required for normal differentiation of the wrapping glia. We will identify these factors and address the molecular mechanisms that direct glial growth around the axon.