A role for the EphA family in the topographic targeting of vomeronasal axone

We have investigated the role of the Eph family of receptor tyrosine kinase s and their ligands in the establishment of the vomeronasal projection in t he mouse. Our data show intriguing differential expression patterns of ephr in-A5 on vomeronasal axons and of EphA6 in the accessory olfactory bulb (AO B), such that axons with high ligand concentration project onto regions of the AOB with high receptor concentration and vice versa. These data suggest a mechanism for development of this projection that is the opposite of the repellent interaction between Eph receptors and ligands observed in other systems. In support of this idea, when given the choice of whether to grow on lanes containing EphA-F-c/laminin or F-c/laminin protein (in the stripe assay), vomeronasal axons prefer to grow on EphA-(c)/laminin. Analysis of e phrin-A5 mutant mice revealed a disturbance of the topographic targeting of vomeronasal axons to the AOB. In summary, these data, which are derived fr om in vitro and in vivo experiments, indicate an important role of the EphA family in setting up the vomeronasal projection.