Weikert T, Rathjen F G, Layer P G
Max-Planck-Institut für Entwicklungsbiologie, Tübingen, F.R.G.
J Neurochem. 1994 Apr;62(4):1570-7. doi: 10.1046/j.1471-4159.1994.62041570.x.
The G4 glycoprotein is found on the earliest developing neurite tracts of the chick embryo. An ELISA is introduced here to quantify the amount of G4-expressing neurites in the picogram range. In this double-sandwich assay, an anti-G4 monoclonal antibody fixes the G4 antigen to the plastic surface, which then is detected by a polyclonal antiserum; nonspecific background is decreased by competitive displacement. The sensitivity of the assay allows us to follow quantitatively the very first 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 from the same homogenates, our earlier histochemical findings are verified now on a quantitative basis, again showing that AChE consistently precedes G4 antigen. Moreover, as an in vitro example, the G4 ELISA is applied to the nerve growth factor (NGF) standard bioassay on dorsal root ganglia; the half-maximal response is reached at approximately 10 ng/ml of NGF for G4-based neurite growth and at approximately 1 ng/ml of NGF for AChE expression, respectively.
G4糖蛋白存在于鸡胚最早发育的神经突束上。本文介绍了一种酶联免疫吸附测定法（ELISA），用于定量皮克范围内表达G4的神经突数量。在这种双夹心测定法中，抗G4单克隆抗体将G4抗原固定在塑料表面，然后用多克隆抗血清进行检测；通过竞争性置换降低非特异性背景。该测定法的灵敏度使我们能够定量跟踪胚胎头部、躯干、视网膜和大脑中最早的神经突生长。结果表明，基于G4的神经突生长在头部比在躯干中更早出现；到胚胎第8天，大脑中的G4表达量比视网膜中高近10倍。通过测定同一匀浆中的乙酰胆碱酯酶（AChE）活性，我们早期的组织化学研究结果现在在定量基础上得到了验证，再次表明AChE始终先于G4抗原出现。此外，作为一个体外实例，G4 ELISA被应用于背根神经节的神经生长因子（NGF）标准生物测定；对于基于G4的神经突生长，在约10 ng/ml的NGF时达到半数最大反应，对于AChE表达，在约1 ng/ml的NGF时达到半数最大反应。
