BMP4 signaling stimulates terminal differentiation of chorionic girdle trophoblast cells and induces equine chorionic gonadotropin (eCG) secretion

Abstract

The chorionic girdle (CG) of the equine conceptus is a transient structure that gives rise to the endometrial cups. CG development is tightly controlled with the rapidly proliferating CG trophoblast differentiating into eCGsecreting binucleate cells beginning at around day 32 of pregnancy. The factors that regulate differentiation of CG trophoblast are not known. The objective of this study was to investigate the functional role of bone morphogenetic protein 4 (BMP4) in terminal differentiation of CG trophoblast cells. Normal conceptuses were obtained by nonsurgical uterine lavage at days 27, 30, 31 and 34 of pregnancy corresponding to stages of equine pregnancy prior to, during and following the terminal differentiation of CG trophoblast. CG and adjacent conceptus tissues (as controls) were used for RT-PCR, QRT-PCR or western blotting. Pure populations of day 30, 31 and 34 CG trophoblast were cultured with 1-100 ng/ml human BMP4 and differentiation status was determined following dual-labelling of the cells with CellTrace BODIPY TR methyl ester and Hoeschst. CG preferentially express mRNA for the following Type I, Type II and accessory receptors that can bind BMP4: ALK3, BMPRII, Dragon and Bambi but not ALK6 (n 1⁄4 12). ALK1, ALK5, ActRIIB, endoglin and betaglycan mRNAwas not detected in the CG. BMP4 mRNA expression in day 31 CG was 7.5 fold higher than day 34 CG. However, BMP4 mRNA expression in adjacent chorion, allantochorion and yolk sac was significantly higher compared to CG suggesting BMP4