Mouse embryos contain polypeptide growth factor(s) capable of inducing a reversible neoplastic phenotype in nontransformed cells in culture.

A growth-factor-like substance capable of inducing nontransformed mouse AKR-2B, rat NRK, and EGF-receptorless mouse NR6 cells to form progressively growing colonies in soft agar was identified in acid/ethanol extracts of 17-day mouse embryos. This "mouse embryo factor" (MEF) is similar to previously described transforming growth factors in that it is capable of stimulating DNA synthesis and conferring a reversible transformed morphology on nontransformed cells in vitro. Passage of crude embryo extracts over a Bio-Gel P-60 column gave a major peak of soft agar growth-stimulating activity in the 15,000 molecular weight range with a minor peak at about 22,000. This biological activity was sensitive to treatment with either trypsin or dithiothreitol, but was unaffected by heat (56 degrees C for 30 minutes or 100 degrees C for 3 minutes), indicating that the activity is due to a heat-stable polypeptide(s) with disulfide bonds. Separation of these polypeptide(s) by chromatography on carboxymethyl cellulose revealed two peaks of soft agar growth-stimulating activity which did not cochromatograph with a peak of epidermal growth factor receptor-competing activity. The similarities of this mouse embryo-derived growth factor to previously identified transforming growth factors suggest that both fetal development and neoplastic transformation may be affected by similar mechanisms.