Activin receptor expression and induction of apoptosis in rat blastocysts in vitro.

BACKGROUND Apoptosis, a process of normal embryonic development, is enhanced in blastocyst from diabetic rats. Nevertheless, glucose seems not to be the only factor involved. Activin A, a TGF-beta family member, is also increased in maternal serum from diabetic pregnancy. METHODS Flushing medium, blastocysts and uterine cells were obtained from 5 day old pregnant rats. The presence of activin A in flushing medium was investigated by western blotting. RT-PCR was used to test for the presence of activin betaA subunit mRNA in cultured uterine cells. Blastocysts were stained by immunohistochemistry for activin receptor types IIA and IIB, and chromatin degradation (apoptosis) was investigated by terminal transferase-mediated dUTP nick end labelling in blastocysts exposed in vitro to activin. RESULTS In this study, we demonstrate the presence of activin A protein in fluid from rat uterine horns at day 5 of pregnancy, as well as the presence of activin A receptors type IIB in the trophectoderm and inner cell mass and activin A receptor type IIA in trophectoderm cells only. Activin A increases the chromatin degradation level in vitro. CONCLUSIONS Activin A protein was found in fluid from uterine horns, and mRNA expression of betaA activin subunit in cultured uterine cells suggests probable secretion from decidual cells. Moreover, activin A increases specifically the apoptosis level in rat blastocyst in vitro.