Analysis of ephrin‐A2 in the chick retinotectal projection using a function‐blocking monoclonal antibody

Eph receptor tyrosine kinases and their ligands have been shown to be involved in processes of cell migration and axon guidance during embryonic development. Here we describe the development of a function‐blocking monoclonal antibody against chick ephrin‐A2, and its effect on retinal ganglion cell axons studied both in vitro and in vivo. In the stripe assay, the blocking antibody completely abolished the repulsive effect of posterior tectal membranes. In vivo, in a loss‐of‐function approach, hybridoma cells secreting the antiephrin‐A2 antibody were applied to chick embryos from embryonic day 3 (E3) on, and the retinotectal projection was subsequently analyzed at E16. DiI tracing analyses showed that although the projection of both temporal and nasal retinal ganglion axons in the tectum was, overall, normal, occasionally diffuse and extra termination zones were observed, in addition to axons over‐shooting their termination zones. These data support the idea that ephrin‐A2 contributes to the establishment of the chick retinotectal projection. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 245–254, 2001