This application centers on the development of the visual system. The goal is to help us better understand how retinal ganglion cell (RGC) fibers target into the brain to hard-wire the eye with the CNS and bring about the neural connections important for vision. Previous studies in mice have implicated the B-subclass Eph receptor tyrosine kinases and their membrane-anchored Ephrin ligands as participating in three distinct aspects of RGC targeting: 1) within the retina as the RGC fibers funnel into the optic stalk to form the optic nerve, 2) at the optic chiasm as RGC fibers make the choice to project contralaterally or ipsilaterally to bring about binocular vision, and 3) within the superior colliculus as RGC fibers topographically map to mirror the ventral/dorsal axis of the eye into a medial/lateral axis in the colliculus. The Eph receptors and Ephrin ligands are unique molecules in that upon Eph-Ephrin engagement at sites of cell-cell contact, signals are transduce into both the Eph-expressing cell (forward signaling) and the Ephrin-expressing cell (reverse signaling). The bidirectional signals transduced by Eph-Ephrin interactions generally lead to alterations in the cytoskeleton that result in either repulsive or adhesive/attractive cell migration and guidance events. Indeed, the three forementioned examples of Eph-Ephrin signaling in RGC fibers appears to bring about either repulsion (examples 1 and 2) or attraction (example 3) events. In this application, we plan in vivo experiments to further dissect the molecular mechanisms by which bidirectional signaling controls wiring of the developing visual system. We will create and analyze new mutations and transgenic constructs in the mouse germline that are designed to selectively interfer with specific components of forward and reverse signaling. Our investigations will further advance our understanding of the molecular mechanisms by which Eph-Ephrin bidirectional signaling controls guidance events important for vision. As the sense of sight is crucial for normal life with loss of vision and blindness posing severe consequences to affected individuals and their families, it is hope that this research will provide important knowledge that may help form the basis for potential regenerative therapies of the future. [unreadable] [unreadable]