Origins of growth factors: NGF and EGF.

This presentation describes the events that led to the sequential discoveries of nerve growth factor (NGF) and epidermal growth factor (EGF). Each was isolated during attempts to understand the biochemical basis for unexpected biological observations. The in vivo stimulation of the growth of specific nerve fibers following the transplantation of a mouse sarcoma into a chick embryo eventually resulted in the finding of NGF, not only in the transplanted tumor but also in snake venom and in the mouse salivary gland. Unexpectedly, treatment of newborn animals with extracts of the mouse salivary gland resulted not only in enhancement of nerve growth but also in precocious eyelid opening and tooth eruption. The latter observations led to the isolation of both EGF and its tyrosine kinase-active receptor.