The Nerve Growth Factor: 35 Years Later (Nobel Lecture)^†

Growth factors—for nerves and for epidermal tissue—are the areas of research of last year's recipients of the Nobel Prizes for Medicine. The growth of nerves and of epidermal tissue requires a chemical stimulant. Nerve growth factor (NGF) proved to be a freely diffusing protein that is essential for the normal development of embryos, but which, in excess, results in major disruption of neurogenic processes. NGF has been isolated from several sources, including the salivary glands of mice. Crude extracts of NGF had unexpected side effects, the systematic investigation of which led to the discovery of epidermal growth factor (EGF). EGF, like NGF, is a protein, whose sequence has been determined. The primary signal mediated by EGF is thought, at present, to involve the tyrosine kinase activity of its receptor.