Project Summary The ability to heal from injuries is fundamental to survival and each body system has mechanisms built into its physiology to mitigate injuries and promote healing. In the central nervous system (CNS), astrocytes play a pivotal role in mitigating damage and promoting healing upon injury. Astrocytes undergo significant physiological changes following injury, straying from their many homeostatic functions in favor of injury directed roles. In the human CNS, the process of healing involves formation of a glial scar which is necessary for initial wound healing, but its persistence in the long-term has negative impacts on regenerative capacity leading to permanent disability. This is thought in large part to be due to the changes that occur in astrocytes following injury, however, the precise role of astrocytes in regeneration remains elusive, due in part to the heterogeneity in responses of astrocytes to different types of injury. Many genetic and molecular factors have been identified in the literature to be differentially regulated in astrocytes, but for many the causal relationship between astrocyte expression and their impact on regeneration remains elusive. Elucidating the direct astrocyte-neuron interactions that occur following injury and during regeneration represents the next frontier necessary to understand the cellular and molecular processes that promote functional regeneration in the CNS. Unlike most mammals, several other vertebrate species, including zebrafish used in this proposal, are capable of robust spontaneous regeneration and functional recovery even after severe CNS injuries. I hypothesize that astrocytes participate in the injury response in the zebrafish CNS and contribute to regeneration. Aim 1 of this proposal will define the dynamic behavior of astrocytes induced by neuronal injury in vivo. I will use advanced imaging approaches combined with molecular analysis and genetic manipulations to identify conserved astrocyte behaviors in a regeneration-capable model and identify those behaviors that promote regeneration. Aim 2 will address the molecular pathways that regulate astrocyte response to injury and their impact on regeneration by investigating the role of the conserved gene leucine rich repeat containing 15 (lrrc15). Mammalian homologues of lrrc15 have been shown to be upregulated in astrocytes around debris in the diseased brain, but its involvement in injury and regeneration has not been investigated. My preliminary data indicates that loss of lrrc15 negatively impacts axon regeneration in the spinal cord and this proposal will identify the specific role lrrc15 plays in astrocytes during injury and regeneration. I will use expression analysis and cell-specific rescue experiments to determine when and where Lrrc15 acts to promote regeneration. Together, this proposal will employ a variety of genetic and imaging approaches to identify the cellular and molecular processes used by astrocytes to promote fun...