Tuberous sclerosis complex is a disease caused by mutations in the TSC1 or TSC2 genes, which encode a protein complex that inhibits mTOR kinase signaling by inactivating the Rheb GTPase. Activation of mTOR promotes the formation of benign tumors in various organs and the mechanisms underlying the neurological symptoms of the disease remain largely unknown. We found that Tsc2 haploinsufficiency in mice caused aberrant retinogeniculate projections that suggest defects in EphA receptor–dependent axon guidance. We also found that EphA receptor activation by ephrin-A ligands in neurons led to inhibition of extracellular signal–regulated kinase 1/2 (ERK1/2) activity and decreased inhibition of Tsc2 by ERK1/2. Thus, ephrin stimulation inactivates the mTOR pathway by enhancing Tsc2 activity. Furthermore, Tsc2 deficiency and hyperactive Rheb constitutively activated mTOR and inhibited ephrin-induced growth cone collapse. Our results indicate that TSC2-Rheb-mTOR signaling cooperates with the ephrin-Eph receptor system to control axon guidance in the visual system.
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We thank B. Stevens and D. Shafer for assistance with multi-threshold LGN analysis, J. Twiss and T. Merianda for assistance with fluorescence recovery after photobleaching and M. Bear, E. Osterweil and D. Krueger for assistance with metabolic labeling experiments. The Tsc2loxP/loxP mice were a gift from M. Gambello, and the Tsc1loxP/loxP mice were gift of D. Kwiatkowski. We are also grateful to B. Stevens, C. Chen, Z. He and members of the Sahin laboratory for critical reading of the manuscript and to L. Mariani, A. Sadowski and S. Goldman for technical assistance. This work was supported in part by grants from the US National Institutes of Health (NS58956 to M.S. and HD025938 to E.B.P.), the John Merck Scholars Fund, Tuberous Sclerosis Alliance, the Manton Foundation and Children's Hospital Boston Translational Research Program to M.S. and the Children's Hospital Boston Mental Retardation and Developmental Disabilities Research Center (P01 HD18655). D.N. is supported by a Mentor Based Postdoctoral Fellowship from Autism Speaks. A.D.N. is supported by a grant from the Hearst Foundation. H.B. is supported by an Howard Hughes Medical Institute Research Training Fellowship for Medical Students.
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Nie, D., Di Nardo, A., Han, J. et al. Tsc2-Rheb signaling regulates EphA-mediated axon guidance. Nat Neurosci 13, 163–172 (2010) doi:10.1038/nn.2477
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