Neurolin Ig domain 2 participates in retinal axon guidance and Ig domains 1 and 3 in fasciculation

The optic disk-directed growth of retinal ganglion cell axons is markedly d isturbed in the presence of polyclonal antineurolin antibodies, which mildl y affect fasciculation (Ott, H., M. Bastmeyer, and C.A.O. Stuermer, 1998, J . Neurosci. 18:3363-3372). New monoclonal antibodies (mAbs) against goldfish neurolin, an immunoglobul in (Ig) superfamily cell adhesion/recognition molecule with five Ig domains , were generated to assign function (guidance versus fasciculation) to spec ific Ig domains. By their ability or failure to recognize Chinese hamster o vary cells expressing recombinant neurolin with deletions of defined Ig dom ains, mAbs were identified as being directed against Ig domains 1, 2, or 3, respectively. Repeated intraocular injections of a mAb against Ig domain 2 disturb the disk-directed growth: axons grow in aberrant routes and fail t o reach the optic disk, but remain fasciculated. mAbs against Ig domains 1 and 3 disturb the formation of tight fascicles. mAb against Ig domain 2 significantly increases the incidence of growth con e departure from the disk-oriented fascicle track, while mAbs against Ig do mains 1 and 3 do not. This was demonstrated by time-lapse videorecording of labeled growth cones. Thus, Ig domain 2 of neurolin is apparently essential for growth cone guida nce towards the disk, presumably by being part of a receptor (or complex) f or an axon guidance component.