MOLECULAR CHARACTERIZATION OF E587 ANTIGEN - AN AXONAL RECOGNITION MOLECULE EXPRESSED IN THE GOLDFISH CENTRAL-NERVOUS-SYSTEM

The E587 antigen (Ag) is a 200-Kd membrane glycoprotein originally ide ntified by a monoclonal antibody on new and regenerating retinal gangl ion cell axons in the adult goldfish. We report the isolation of CDNAs encoding the E587 Ag and identify it as a member of the L1 family of cell adhesion molecules (CAMs). The predicted amino acid sequence of E 587 Ag shows an approximately equal identity (405) to mouse L1, chick neuron-glia CAM, and chick neuron-glia-related CAN. Although the overa ll similarity is low, there is a high conservation of structural domai ns and specific sequence motifs. Wholemount in situ hybridizations wer e performed on goldfish between 34 hours and 3 days postfertilization (pf). A dramatic increase in E587 Bg mRNA was observed between 34 and 48 hours pf. The expression of E587 Ag mRNA in neurons shortly precede s axonogenesis. A marked decrease in expression occurs by 3 days pf, w hen the axonal scaffold has already been established. Wholemount immun ohistochemistry on embryos demonstrates expression of E587 Ag on all m ajor tracts. E587 Ag is absent from mature retinal ganglion cell axons , but its expression is induced by optic nerve transection. A correspo nding induction of E587 Ag mRNA in retinal ganglion cells is shown by in situ hybridization. Furthermore, E587 Ag mRNA was detected in the o ptic nerve, which suggests that nonneuronal cells also express this mo lecule. E587 Ag was previously shown to promote retinal axon fascicula tion and outgrowth in young fish and to mediate axon-glial interaction s in vitro. The expression pattern and developmental regulation of E58 7 Ag in the central nervous system, its reexpression in retinal gangli on cells following optic nerve transection, and its relation to the L1 family indicate that E587 Ag functions as a cell recognition molecule important during axonal growth and regeneration. (C) 1997 Wiley-Liss, Inc.