Endogenous Retroviral Gene Elements ( and ), -τ, and Are Differentially Expressed in Maternal and Fetal Tissues During the First 50 Days of Gestation in Beef Heifers

We hypothesized that the endogenous retroviruses [ERV: and ()], and pregnancy hormones [-τ (-τ), and ()] would be differentially expressed whereas progesterone and insulin concentrations in maternal blood would remain steady during early gestation. To test this hypothesis Angus crossbred heifers ( = 46; ∼15 mo of age; BW = 363 ± 35 kg) were fed native grass hay, supplemented with cracked corn to gain 0.3 kg/d, and given ad libitum access to water. All heifers were subjected to a 5-d CO-Synch + CIDR estrous synchronization protocol and AI (breeding = d 0). Ovariohysterectomies were performed on d 16, 22, 28, 34, 40, and 50 of gestation and at d 16 of the estrous cycle for non-pregnant (NP) controls. Utero-placental tissues [maternal caruncle (CAR); maternal intercaruncular endometrium (ICAR); and fetal membranes, (FM, chorion on d 16, chorioallantois on d 22 to 50)] were collected from the uterine horn ipsilateral to the corpus luteum (CL). Tissues were flash frozen and stored at -80°C. Expression of mRNA was evaluated using qPCR. In CAR, expression was greater ( < 0.01) on d 50 (81.5-fold) compared with NP controls or any other day of early pregnancy. In contrast, expression in I-CAR only tended ( = 0.09) to change across days of early pregnancy and did not differ ( = 0.27) in FM tissues. In CAR, the expression of was not different ( > 0.79) at d 16 and 22, was intermediate at d 28, 34, and 40, and was greatest on d 50 (108-fold increase compared with NP). Expression of in FM was increased ( < 0.01) on d 28, 34, and 50 compared with NP controls, but at d 40 did not differ from NP controls. The mRNA expression of -τ in FM at d 22 was greater ( < 0.01) than all other days of gestation. In CAR, expression of increased ( < 0.001) dramatically on d 40 (20,000-fold) and d 50 (86,000-fold) compared with NP heifers ( < 0.01). In ICAR, expression of was greater ( < 0.05) on d 28 and 40 (fold increases of 113 and 102, respectively, compared with NP). Insulin concentrations were not different ( = 0.53) but progesterone was greater ( < 0.01) on d 16, 22, 28, 34, and 40 compared with d 50 of gestation. These data confirm differential ERV, -τ, and gene expression during critical time points of early gestation in utero-placental tissues.