Regulation of ephrin-A expression in compressed retinocollicular maps

Authors

  • Tizeta Tadesse,

    1. Neuroscience Institute, Georgia State University, Atlanta, Georgia
    2. Department of Biology, Graduate Program in Neurobiology & Behavior, Georgia State University, Atlanta, Georgia
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    • These authors contributed equally to this study.

  • Qi Cheng,

    1. Neuroscience Institute, Georgia State University, Atlanta, Georgia
    Current affiliation:
    1. Department of Human Genetics, Emory University Medical School, Atlanta, GA, USA
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    • These authors contributed equally to this study.

  • Mei Xu,

    1. Department of Biology, Graduate Program in Neurobiology & Behavior, Georgia State University, Atlanta, Georgia
    Current affiliation:
    1. Philadelphia College of Osteopathic Medicine, Anatomy, Philadelphia, Pennsylvania, USA
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    • These authors contributed equally to this study.

  • Deborah J. Baro,

    1. Neuroscience Institute, Georgia State University, Atlanta, Georgia
    2. Department of Biology, Graduate Program in Neurobiology & Behavior, Georgia State University, Atlanta, Georgia
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  • Larry J. Young,

    1. Center for Translational Social Neuroscience, Department of Psychiatry and Behavioral Sciences, Yerkes National Primate Research Center, Emory University, Atlanta Georgia
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  • Sarah L. Pallas

    Corresponding author
    1. Neuroscience Institute, Georgia State University, Atlanta, Georgia
    2. Department of Biology, Graduate Program in Neurobiology & Behavior, Georgia State University, Atlanta, Georgia
    • Neuroscience Institute, Georgia State University, Atlanta, Georgia
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Abstract

Retinotopic maps can undergo compression and expansion in response to changes in target size, but the mechanism underlying this compensatory process has remained a mystery. The discovery of ephrins as molecular mediators of Sperry's chemoaffinity process allows a mechanistic approach to this important issue. In Syrian hamsters, neonatal, partial (PT) ablation of posterior superior colliculus (SC) leads to compression of the retinotopic map, independent of neural activity. Graded, repulsive EphA receptor/ephrin-A ligand interactions direct the formation of the retinocollicular map, but whether ephrins might also be involved in map compression is unknown. To examine whether map compression might be directed by changes in the ephrin expression pattern, we compared ephrin-A2 and ephrin-A5 mRNA expression between normal SC and PT SC using in situ hybridization and quantitative real-time PCR. We found that ephrin-A ligand expression in the compressed maps was low anteriorly and high posteriorly, as in normal animals. Consistent with our hypothesis, the steepness of the ephrin gradient increased in the lesioned colliculi. Interestingly, overall levels of ephrin-A2 and -A5 expression declined immediately after neonatal target damage, perhaps promoting axon outgrowth. These data establish a correlation between changes in ephrin-A gradients and map compression, and suggest that ephrin-A expression gradients may be regulated by target size. This in turn could lead to compression of the retinocollicular map onto the reduced target. These findings have important implications for mechanisms of recovery from traumatic brain injury. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013

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