Despite enormous clinical relevance for brain cancer and nervous system repair, the development and function of glial cells has received relatively little attention in vertebrate and invertebrate neurobiology. During development, the correct positioning of glia is crucial for the establishment of neural connectivity in the CNS of the embryo and the visual system of Drosophila, raising important questions regarding the mechanisms controlling the proliferation and migration of glia prior to the arrival of growing axons and regarding the cues presented by them to control axonal growth and pathfinding. Generally, little is known about the signals and mechanisms that control glial migration in vivo, and while important glia-derived guidance cues and their receptors have been identified in the Drosophila embryo, none of them appear to play a major role in the visual system. We have investigated the development of the subretinal glia, which proliferate and migrate into the developing Drosophila eye disc concomitant with the progressive differentiation of photoreceptors, and examined the role of different signaling pathways in controlling glial cell behavior. We found that the EGFr has a very pronounced, isoform-specific effect on subretinal glial migration that is not mediated by the canonical Ras-Raf-MAPK pathway. The proposed research aims to develop improved genetic and live imaging techniques for studying proliferative migrating cell populations, to use them to illuminate the mechanisms of glial migration in vivo, and to dissect the role of the EGFr isoforms in controlling different aspects of glial behavior by identifying the relevant ligands and effectors; a final aim is to search for additional RTKs and other receptors involved in controling glial behavior and glia-neuron interactions, using a layered reverse genetic approach that employs FACS sorting, GeneChip analysis and RNA interference. The objective of the proposed study is thus to further develop and investigate a much needed model for glial cell behavior in a genetic system, to provide material insights into novel aspects of EGFr function in the glia, and to expand the analysis towards non-canonical pathways of the EGFr and to other RTKs and receptors, with the ultimate goal of providing new targets for therapeutic interference in both malignant and regenerative situations in humans.