USE OF ELISA TO G4 ANTIGEN TO QUANTITATE NEURITE OUTGROWTH IN THE CHICK BOTH IN-VIVO AND IN-VITRO

The G4 glycoprotein is found on the earliest developing neurite tracts of the chick embryo. An ELISA is introduced here to quantify the amou nt of G4-expressing neurites in the picogram range. In this double-san dwich assay, an anti-G4 monoclonal antibody fixes the G4 antigen to th e plastic surface, which then is detected by a polyclonal antiserum; n onspecific background is decreased by competitive displacement. The se nsitivity of the assay allows us to follow quantitatively the very fir st neurite growth in embryonic heads, trunks, retinae, and brains. G4- based neurite growth is shown to occur earlier in heads than in trunks ; in brain it is nearly 10-fold higher than in the retina by embryonic day 8. By determination of acetylcholinesterase (AChE) activities fro m the same homogenates, our earlier histochemical findings are verifie d now on a quantitative basis, again showing that AChE consistently pr ecedes G4 antigen. Moreover, as an in vitro example, the G4 ELISA is a pplied to the nerve growth factor (NGF) standard bioassay on dorsal ro ot ganglia; the half-maximal response is reached at approximately 10 n g/ml of NGF for G4-based neurite growth and at approximately 1 ng/ml o f NGF for AChE expression, respectively.