The EphA4 receptor tyrosine kinase is necessary for the guidance of nasal retinal ganglion cell axons in vitro

The retinotectal projection serves as a model system for the study of topog raphic projections. It has been shown in the past few years that members of the Eph family are strongly involved in establishing this projection. The analysis so far has focused on a characterization of Ephrin ligands which a re expressed in a gradient in both the tectum and the retina. Here we inves tigate the role of one of the multiple EphA receptors expressed on retinal ganglion cell axons, EphA4, which is uniformly expressed on nasal and tempo ral axons. We have adopted both a dominant negative approach and a method u sing neutralizing monoclonal antibodies in order to inactivate this recepto r. The results of these in vitro experiments suggest that EphA4 is cruciall y involved in the repulsive guidance of nasal but not of temporal axons.