Effects of epidermal growth factor and transforming growth factor alpha on the mouse trophoblast outgrowth in vitro

In order to analyze the involvement of growth factors in the implantation mechanism, we examined the direct effects of epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha) on trophoblast outgrowth of the mouse blastocyst in vitro. ICR mouse blastocysts were cultured for 4 days on a culture plate in medium containing EGF or TGF-alpha or conditioned medium obtained from cultured endometrial epithelial cells. Blastocysts were also co-cultured with endometrial epithelial cells. The trophoblast outgrowth of these cultured blastocysts was observed daily and the percentage of outgrowing embryos was calculated and analyzed statistically by the chi-squared test. Analysis for the specific binding of 125I-EGF in outgrown trophoblasts was carried out by autoradiography. The co-culture (days 3 and 4) and the presence of EGF (10 ng/ml, day 4), TGF-alpha (1 ng/ml, day 3; 10 ng/ml, days 2 and 3; 50 ng/ml, days 2-4) or conditioned medium (days 3 and 4) significantly stimulated the rate of trophoblast outgrowth. Preincubation of the conditioned medium with monoclonal anti-EGF or anti-TGF-alpha antibody suppressed the stimulatory effect of the conditioned medium on trophoblast outgrowth. The specific 125I-EGF binding in outgrown trophoblasts was demonstrated by autoradiography. These results suggest that EGF and TGF-alpha play an important role in the implantation process by directly stimulating trophoblast development.