Neurite outgrowth promoting activity of G4 and its inhibition by monoclonal antibodies.

The chick G4 molecule is a cell surface glycoprotein which is a member of the L1/NILE/NgCAM/8D9 group of neural cell adhesion molecules. Polyclonal antisera against G4 have been shown to decrease sympathetic neurite outgrowth on sympathetic axons and to de-bundle retinal axons growing on a tectal membrane substrate. We have extended the specificity of these results by showing that a panel of monoclonal antibodies against G4 is also effective in reducing sympathetic neurite outgrowth on sympathetic axons. Furthermore, purified G4 adsorbed onto an inert substrate promotes extensive neurite outgrowth. Monoclonal antibodies to G4 completely inhibit the activity of purified G4. These data show that G4 is a cell surface neurite outgrowth promoting molecule, a function which was first suggested by antibody perturbation experiments and now is confirmed directly.