Axon elongation: Effect of nerve growth factor on microtubule protein

Nerve growth factor (NGF) causes a rapid outgrowth of axons from dorsal root ganglia in vitro. Abundant microtubules are found in such axons, as well as in axons of control ganglia not treated with NGF. Using the colchicine-binding assay for microtubule protein, it was found that NGF treatment does not cause an increased accumulation of microtubule protein over that seen in non-NGF controls. Similarly, total protein synthesis in control and NGF-treated ganglia is identical during the critical early phases of axonal outgrowth. Thus, NGF does not appear to elicit axon outgrowth by causing increased rates of overall protein synthesis, or by differential accumulation of microtubule protein. Instead, NGF may act by stimulating “growth cone” activity.