BIT, an immune antigen receptor‐like molecule in the brain¹

Abstract

We previously found a brain‐specific glycoprotein in the rat brain. It postnatally increases and is rich in the mature brain. We cloned cDNA of this protein. It is composed of a signal peptide, a V‐type immunoglobulin domain, two C1‐type immunoglobulin domains, a transmembrane segment and a cytoplasmic region containing two tyrosine‐based activation motifs (TAM) that are variants of the antigen receptor signaling motifs. The overall structure is similar to those of immune antigen receptors. This molecule, BIT (brain immunoglobulin‐like molecule with TAMs), is a major endogenous substrates of brain tyrosine kinases in vitro. Cerebral cortical neurons could extend their neurites on BIT‐coated substrate and anti‐BIT monoclonal antibody specifically inhibited the effect. These findings and our recent study concerning BIT signal transduction mechanism suggest that BIT, an immune antigen receptor‐like molecule of the brain, functions as a membrane signaling molecule that may participate in cell–cell interaction.

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