Neurotractin, a novel neurite outgrowth-promoting Ig-like protein that interacts with CEPU-1 and LAMP

The formation of axon tracts in nervous system histogenesis is the result o f selective axon fasciculation and specific growth cone guidance in embryon ic development. One group of proteins implicated in neurite outgrowth, fasc iculation, and guidance is the neural members of the Ig superfamily (IgSF). In an attempt to identify and characterize new proteins of this superfamil y in the developing nervous system, we used a PCR-based strategy with degen erated primers that represent conserved sequences around the characteristic cysteine residues of Ig-like domains. Using this approach, we identified a novel neural IgSF member, termed neurotractin. This GPI-linked cell surfac e glycoprotein is composed of three Ig-like domains and belongs to the IgLO N subgroup of neural IgSF members. It is ex-pressed in two isoforms with ap parent molecular masses of 50 and 37 kD, termed L-form and S-form, respecti vely. Monoclonal antibodies were used to analyze its biochemical features a nd histological distribution. Neurotractin is restricted to subsets of deve loping commissural and longitudinal axon tracts in the chick central nervou s system. Recombinant neurotractin promotes neurite outgrowth of telencepha lic neurons and interacts with the IgSF members CEPU-1 (K-D = 3 x 10(-8) M) and LAMP. Our data suggest that neurotractin participates in the regulatio n of neurite outgrowth in the developing brain.