BIG-1 - A NEW TAG-1 F3-RELATED MEMBER OF THE IMMUNOGLOBULIN SUPERFAMILY WITH NEURITE OUTGROWTH-PROMOTING ACTIVITY

We have cloned a rat cDNA for a novel brain-derived immunoglobulin (Ig ) superfamily molecule, BIG-1, by using PCR based on the amino acid se quences of the two closely related and well known Ig superfamily membe rs, rat TAG-1 and mouse F3. BIG-1 is a glycosylphosphatidylinositol-an chored membrane protein with six Ig-like domains and four fibronectin type III repeats, belonging to the TAG-1/F3 subgroup. The expression o f BIG-1 mRNA is developmentally regulated with the highest level in th e adult brain. It is restricted to subsets of neurons such as Purkinje cells of the cerebellum, granule cells of the dentate gyrus, and neur ons in the superficial layers of the cerebral cortex. Recombinant BIG- 1 protein has a neurite outgrowth-promoting activity when used as a su bstrate for neurons in vitro. These results suggest that BIG-1 may be involved in the formation and maintenance of neuron type-specific netw orks in the brain.