CHICKEN ACIDIC LEUCINE-RICH EGF-LIKE DOMAIN-CONTAINING BRAIN PROTEIN (CALEB), A NEURAL MEMBER OF THE EGF FAMILY OF DIFFERENTIATION FACTORS,IS IMPLICATED IN NEURITE FORMATION

Chicken acidic leucine-rich EGF-like domain containing brain protein ( CALEB) was identified by combining binding assays with immunological s creens in the chicken nervous system as a novel member of the EGF fami ly of differentiation factors. cDNA cloning indicates that CALEB is a multidomain protein that consists of an NH2-terminal glycosylation reg ion, a leucine-proline-rich segment, an acidic box, a single EGF-like domain, a transmembrane, and a short cytoplasmic stretch. In the devel oping nervous system, CALEB is associated with glial and neuronal surf aces. CALEB is composed of a 140/130-kD doublet, an 80-kD band, and a chondroitinsulfate-containing 200-kD component. The latter two compone nts are expressed in the embryonic nervous system and are downregulate d in the adult nervous system. CALEB binds to the extracellular matrix glycoproteins tenascin-C and -R, In vitro antibody perturbation exper iments reveal a participation of CALEB in neurite formation in a permi ssive environment.