Critical Roles for EphB and Ephrin-B Bidirectional Signalling in Retinocollicular Mapping.

Graded expression of EphB and ephrin-B along the dorsoventral axis of the retina indicates a role for these bidirectional signalling molecules in dorsoventral-mediolateral retinocollicular mapping. Although previous studies have implicated EphB2 forward signalling in mice, the intracellular component of EphB2 essential for retinocollicular mapping is unknown as are the roles for EphB1, ephrin-B1, and ephrin-B2. Here we show that EphB2 tyrosine kinase catalytic activity and EphB1 intracellular signalling are key mediators of ventral-temporal retinal ganglion cell axon retinocollicular mapping, by likely interacting with ephrin-B1 in the superior colliculus. We further elucidate roles for the ephrin-B2 intracellular domain in retinocollicular mapping and present the unexpected finding that both dorsal and ventral-temporal retinal ganglion cell axons utilize reverse signalling for topographic mapping. These data demonstrate that both forward and reverse signalling initiated by EphB:ephrin-B interactions have a major role in dorsoventral retinal ganglion cell axon termination along the mediolateral axis of the superior colliculus.