New perspective on conceptus estrogens in maternal recognition and pregnancy establishment in the pig

The proposed signal for maternal recognition of pregnancy in pigs is estrogen (E2), produced by the elongating conceptuses between days 11 to 12 of pregnancy with a more sustained increase during conceptus attachment and placental development on days 15 to 30. To understand the role of E2 in porcine conceptus elongation and pregnancy establishment, a loss-of-function study was conducted by editing aromatase (CYP19A1) using CRISPR/Cas9 technology. Wild-type (CYP19A1+/+) and (CYP19A1–/–) fibroblast cells were used to create embryos through somatic cell nuclear transfer, which were transferred into recipient gilts. Elongated and attaching conceptuses were recovered from gilts containing CYP19A1+/+ or CYP19A1–/– embryos on day 14 and 17 of pregnancy. Total E2 in the uterine flushings of gilts with CYP19A1–/– embryos was lower than recipients containing CYP19A1+/+ embryos with no difference in testosterone, PGF2α, or PGE2 on either day 14 or 17. Despite the loss of conceptus E2 production, CYP19A1–/– conceptuses were capable of maintaining the corpora lutea. However, gilts gestating CYP19A1–/– embryos aborted between days 27 and 31 of gestation. Attempts to rescue the pregnancy of CYP19A1–/– gestating gilts with exogenous E2 failed to maintain pregnancy. However, CYP19A1–/– embryos could be rescued when co-transferred with embryos derived by in vitro fertilization. Endometrial transcriptome analysis revealed that ablation of conceptus E2 resulted in disruption of a number biological pathways. Results demonstrate that intrinsic E2 conceptus production is not essential for pre-implantation development, conceptus elongation, and early CL maintenance, but is essential for maintenance of pregnancy beyond 30 days . Summary Sentence Ablation of pig conceptus estrogen production does not affect early maternal recognition of pregnancy and conceptus development but causes a ripple effect in conceptus/endometrial programming resulting in failure to maintain pregnancy beyond 30 days of gestation.