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.