Cloning and characterization of a neural cell recognition molecule on axons of the retinotectal system and spinal cord.

Immunoglobulin superfamily molecules in the brain are involved in distinct aspects of nervous system histogenesis, for example neuronal migration and axonal growth. To identify novel members of this superfamily in the chick nervous system, we developed a polymerase chain reaction-based approach making use of sequence motifs of immunoglobulin-like domains. In the present study, we report the molecular cloning of three isoforms, the biochemical analysis and the immunohistochemical characterization of one of the proteins identified in this screen. This molecule has 91% sequence identity with the limbic system-associated membrane protein (LAMP) characterized in the rat and is therefore referred to as the chicken homologue of the latter (chLAMP). The molecule is a glycosylphosphatidyl-inositol-anchored 60 kDa protein with three immunoglobulin-like domains and contains 40% N-linked carbohydrate. We identify three different mRNA forms of chLAMP and show that two forms with distinct 5'-termini are differentially transcribed in neural development. In addition, we demonstrate using a fusion protein expressed in eukaryotic cells that chLAMP has homophilic binding activity. The protein was found on a subset of axons in the central and peripheral nervous system and is likely to be involved in specific cell-cell interactions in neurohistogenesis.