Placental development during early pregnancy in sheep: Effects of embryo origin on fetal and placental growth and global methylation

摘要

The origin of embryos including those created through assisted reproductive technologies (ART) may have profound effects on placental and fetal development, possibly leading to compromised pregnancies associated with poor placental development. To determine the effects of embryo origin on fetal size, and maternal and fetal placental cellular proliferation and global methylation, pregnancies were achieved through natural mating (NAT), or transfer of embryos generated through in vivo (NAT-ET), IVF, or in vitro activation (IVA). On Day 22 of pregnancy, fetuses were measured and placental tissues were collected to immunodetect Ki67 (a marker of proliferating cells) and 5-methyl cytosine (5mC) followed by image analysis, and determination of mRNA expression for three DNA methyltransferases (DNMT). Fetal length and labeling index (proportion of proliferating cells) in maternal caruncles (CAR; maternal placenta) and fetal membranes (FM; fetal placenta) were less (P < 0.001) in NAT-ET, IVF and IVA than in NAT. Expression of 5mC was greater (P < 0.02) in IVF and IVA than in NAT. In CAR, mRNA expression for DNMT1 was greater (P < 0.01) in IVA compared to the other groups, but DNMT3A expression was less (P < 0.04) in NAT-ET and IVA than NAT. In FM, expression of mRNA for DNMT3A was greater (P < 0.01) in IVA compared to the other groups, and was similar in NAT, NAT-ET and IVF groups. Thus, embryo origin may have specific effects on growth and function of ovine utero-placental and fetal tissues through regulation of tissue growth, DNA methylation and likely other mechanisms. These data provide a foundation for determining expression of specific factors regulating placental and fetal tissue growth and function in normal and compromised pregnancies, including those achieved with ART.