Damage to the central nervous system is devastating and debilitating. There are no effective clinical treatments for serious central nervous system damage. Paralysis affects ~5.5 million Americans, according to a study in 2008 (Reeve Foundation, One Degree of Separation). Research into why neurons can't regrow across injury sites has yielded some insight. Yet the regeneration-preventing factors identified thus far only explain a small part of why there is no recovery. To develop effective therapies, we need a more comprehensive understanding of extrinsic and intrinsic regeneration antagonists. Our lab has recently developed a system that uses a two-photon laser to cut either the axon or dendrite projections of neurons in flies. After injury, we observe the degeneration of these projections and any subsequent regeneration. Regeneration in the dendritic arborization (da) neurons in flies shares a number of important characteristics with regeneration in mammalian systems, and allows unbiased discovery of genes that influence this process. I aim to use this system to ask fundamental questions about axonal and dendritic regeneration. (1) What are the intrinsic differences that allow some neurons to have the capacity to regenerate when other cells do not, even in the same permissive environment? Similar classes of well-described da neurons show distinct regenerative capacities. We know transcription factors that define the characteristics of these cell types, including the pattern of dendritic arborization, axonal targeting, and receptor expression. Do these transcription factors also define regenerative ability differences, and by what mechanism? (2) How do external cues from glial cells regulate whether axon regeneration occurs? Glial cells engulf neurite fragments during degeneration after damage. We will characterize the role of glia in regeneration, and examine glial signals that may regulate whether a substrate is permissive for axon growth. To what extent do signals inside the neuron and in the surrounding tissue combine to regulate regeneration? (3) What novel antagonists of regeneration can we identify and validate? After screening for novel regulators of regeneration, we will investigate whether identified antagonists are components of known or unique pathways. With answers to these questions, we will be able to better explain why neuron regeneration fails and more effectively design ways to treat injury. My graduate experience provides a solid foundation for examining the nervous system using genetics and imaging, and the experiments proposed here represent significant opportunities for personal training and discovery in a stimulating and supportive environment.