GSK-3B/APC in developmental & regenerative axon growth

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DESCRIPTION (provided by applicant): Links between neurotrophin signals that regulate neuronal morphology and the neuronal cytoskeleton have remained elusive. In vitro, we have identified a pathway downstream of NGF involving spatially localized PI3K and GSK-3b signaling and binding of the Adenomatous Polyposis Coli protein (APC) to microtubule + ends at the growth cone. We hypothesize that this pathway mediates microtubule assembly during NGF induced axon growth. Both APC and GSK-3b are also strikingly localized to the distal axon tips and growth cones of rapidly growing axons of "precondition lesioned" DRG neurons in vitro. Thus we hypothesize the GSK-3b/APC pathway mediates microtubule assembly in regenerative axon growth as well. In vivo functions of GSK-3b and APC related to nervous system development have not yet been explored because of embryonic lethality in gene targeted mice and because each has a related family member also heavily expressed in the mammalian nervous system that may have a "compensatory" function. We plan to address in vivo roles of these proteins in the current proposal. We will generate inducible, DRG-specific knock-outs for GSK-3a, GSK-3b, APC, APC-L, and an upstream kinase, ILK. Using DRG specific axonal reporter mice, we will determine the roles of the GSK-3b/APC pathway in the development of peripheral and spinal cord DRG projections and in the axon regeneration normally induced by a peripheral nerve crush. If GSK-3b and APC are found to be required for assembly of microtubules during axon regeneration in vivo, and if key upstream regulators can be identified, our studies would provide a new pharmacological approach to enhancing axon regeneration after injur