The Draper signaling pathway in Drosophila glial immune functions

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Glia are the primary immune cell type in the nervous system. In response to neural infection or trauma they becoming "reactive", undergoing stereotypical changes in gene expression and morphology. However, the molecular details of glial responses to neural injury or death are poorly understood. We study glial immune functions in Drosophila because it has well-defined glial subtypes that resemble mammalian glia, and it is amenable to genetic analysis. This proposal focuses on the role of Drosophila glia and the newly-identified Drpr receptor in glial engulfment of dead neurons, and glial responses to neural injury in the CNS. Drpr encodes an engulfment receptor essential for glial removal of neuronal cell corpses; the Drpr receptor is also potently transcriptionally upregulated in glia after the axons they ensheath are severed. We will take a molecular genetic approach to understand how Drpr functions in glial responses to neural injury, glial engulfment of injured axons, and additional mechanisms of neuron-glia interactions after neural trauma. Our specific aims are: 1) Characterize Draper functions in the embryonic CNS: We will define the role for Drpr and specific Drpr receptor isoforms in cell corpse removal and glial morphogenesis in the Drosophila embryonic CNS. 2) Define glial responses to neural injury and roles for Draper in removing injured axons: We will define morphological and molecular changes exhibited by glia in response to neural injury, and determine the requirements for Drpr and glia in the removal of injured axons. 3) Define the cellular and molecular action of Wlds protein: The Wallerian degeneration slow (Wlds) protein protects injured axons from degeneration by unknown mechanisms. We found that Wlds can also spare severed Drosophila axons from degeneration. We will explore Wlds-mediated protection of Drosophila axons, and the consequences of Wlds expression on glial responses to neural injury. Mechanisms of neuron-glia communication after neural injury are likely well-conserved in flies and mice, since Drosophila glia also become reactive and Wlds can protect severed axons in flies. Characterizing genes that regulate neuronal and glial function in response to CNS trauma is essential to identify new avenues for the treatment of CNS injury and neurological disease.