Regulation of ephrin-A expression in compressed retinocollicular maps

• Type of Material: Article
• Authors: T. Tadesse, Georgia State University; Q. Cheng, Georgia State University; M. Xu, Georgia State University; D. J. Baro, Georgia State University; Larry Young, Emory University; S. L. Pallas, Georgia State University
• Language: English
• Date: 2013-04-01
• Publisher: Wiley: 12 months
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2012 Wiley Periodicals, Inc.
• Final Published Version (URL): http://dx.doi.org/10.1002/dneu.22059
• Title of Journal or Parent Work: Developmental Neurobiology
• ISSN: 1932-8451
• Volume: 73
• Issue: 4
• Start Page: 274
• End Page: 296
• Grant/Funding Information: Support contributed by: NIH EY-12696 (SLP); NSF 0078110 (SLP); NSF STC IBN-9876754 (LJY); NIH NS-38770 (DJB); and the GSU Research Foundation (SLP and DJB).
• Keywords: Neurosciences & Neurology; axon guidance; RETINOTECTAL PROJECTION; RECEPTOR TYROSINE KINASES; Developmental Biology; HALF RETINAL PROJECTION; TOPOGRAPHIC MAPS; neural plasticity; topographic map; Life Sciences & Biomedicine; SUPERIOR COLLICULUS; HAMSTERS MESOCRICETUS-AURATUS; PARTIAL TECTAL ABLATION; GOLDEN-HAMSTER; retinotectal; Science & Technology; population matching; VISUAL-SYSTEM; Neurosciences; GANGLION-CELL AXONS
• Research Categories: Biology, Neuroscience

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.