Retinal Axon Growth at the Optic Chiasm: To Cross or Not to Cross Timothy J. Petros, Alexandra Rebsam, and Carol A. Mason Department of Pathology and Cell Biology, Department of Neuroscience, Columbia University, College of Physicians and Surgeons, New York, New York 10032; email: tjp2001@columbia.edu, adr2111@columbia.edu, cam4@columbia.edu Annu. Rev. Neurosci. 2008. 31:295–315 First published online as a Review in Advance on April 2, 2008 The Annual Review of Neuroscience is online at neuro.annualreviews.org This article’s doi: 10.1146/annurev.neuro.31.060407.125609 Copyright c  2008 by Annual Reviews. All rights reserved 0147-006X/08/0721-0295$20.00 Key Words axon guidance, binocular vision, growth cone, Ephs/ephrins, patterning, transcription factors Abstract At the optic chiasm, retinal ganglion cell axons from each eye con- verge and segregate into crossed and uncrossed projections, a pattern critical for binocular vision. Here, we review recent findings on optic chiasm development, highlighting the specific transcription factors and guidance cues that implement retinal axon divergence into crossed and uncrossed pathways. Although mechanisms underlying the formation of the uncrossed projection have been identified, the means by which retinal axons are guided across the midline are still unclear. In addi- tion to directives provided by transcription factors and receptors in the retina, gene expression in the ventral diencephalon influences chiasm formation. Throughout this review, we compare guidance mechanisms at the optic chiasm with those in other midline models and highlight unanswered questions both for retinal axon growth and axon guidance in general. 295 Click here for quick links to Annual Reviews content online, including: • Other articles in this volume • Top cited articles • Top downloaded articles • Our comprehensive search Further ANNUAL REVIEWS Annu. Rev. Neurosci. 2008.31:295-315. Downloaded from arjournals.annualreviews.org by Columbia University on 01/06/09. For personal use only.