IDENTIFICATION OF THE BORDER BETWEEN FIBRONECTIN TYPE-III HOMOLOGOUS REPEAT-2 AND REPEAT-3 OF THE NEURAL CELL-ADHESION MOLECULE L1 AS A NEURITE OUTGROWTH-PROMOTING AND SIGNAL-TRANSDUCING DOMAIN

To determine the domains of the neural cell adhesion molecule L1 invol ved in neurite outgrowth, we have generated monoclonal antibodies agai nst L1 and investigated their effects on neurite outgrowth of small ce rebellar neurons in culture. When the 10 antibodies were coated as sub strate, only antibody 557.B6, which recognizes an epitope represented by a synthetic peptide comprising amino acids 818 to 832 at the border between the fibronectin type III homologous repeats 2 and 3, was as e fficacious as L1 in promoting neurite outgrowth, increasing intracellu lar levels of Ca2+, and stimulating the turnover of inositol phosphate s, These findings suggest that neurite outgrowth and changes in these second messengers are correlated. Such a correlation was confirmed by the ability of Ca2+ channel antagonists and pertussis toxin to inhibit neurite outgrowth on L1 and antibody 557.B6. These observations indic ate for the first time a distinct site on cell surface-bound L1 as a p rominent signal-transducing domain through which the recognition event s appear to be funneled to trigger neurite outgrowth, increase turnove r of inositol phosphates, and elevate intracellular levels of Ca2+. (C ) 1995 John Wiley & Sons, Inc.