Conceptus Estrogen and prostaglandins provide the maternal recognition of pregnancy signal to prevent Luteolysis during early pregnancy in the pig†.

Conceptus estrogens and prostaglandins have long been considered the primary signals for maternal recognition of pregnancy (MRP) in the pig. However, loss-of-function studies targeting conceptus aromatase genes (CYP19A1 and CYP19A2) and prostaglandin-endoperoxide synthase 2 (PTGS2) indicated that conceptuses can not only signal MRP without estrogens or prostaglandins but can maintain early pregnancy. However, complete loss of estrogen production leads to abortion after day 25 of gestation. Although neither conceptus estrogens nor prostaglandins had a significant effect on early maintenance of CL function alone, the two conceptus factors have a biological relationship. To investigate the role that both conceptus estrogens and prostaglandins have on MRP and maintenance of pregnancy, a triple loss-of function model (TKO) was generated for conceptus CYP19A1, CYP19A2 and PTGS2. In addition, a conceptus CYP19A2-/- model (A2KO) was established to determine the role of placental estrogen during later pregnancy. Estrogen and prostaglandin synthesis were greatly reduced in TKO conceptuses which resulted in a failure to inhibit luteolysis after day 15 of pregnancy despite the presence of conceptuses in the uterine lumen. However, A2KO placentae not only maintained functional CL but were able to maintain pregnancy to day 32 of gestation. Despite the loss of placental CYP19A2 expression, the allantois fluid content of estrogen was not affected as the placenta compensated by expressing CYP19A1 and CYP19A3, which are normally absent in controls. Results suggest conceptuses can signal MRP through production of conceptus PGE or stimulating PGE synthesis from the endometrium through conceptus estrogen. Failure of conceptuses to produce both factors results in failure of MRP and loss of pregnancy.

Porcine-specific expression of the three functional CYP19 paralogs in early conceptus, placenta, and gonads.

In brief: Aromatase catalyzes the synthesis of estrogens and has been shown to have an important role during the establishment of pregnancy in the pig. This study confirmed the differential expression of the three aromatase isoforms. Abstract: Although three porcine aromatase isoforms have been identified, their gene expression profiles in reproduction are still poorly understood. Here, we identified by Sanger sequencing unique nucleotide signatures for the three paralogous copies of Cyp19 and analyzed by RT-PCR the occurrence of the Cyp19 and Cyp17a1 transcripts at different tissues and stages of conceptus and fetal-placental development. Cyp19a1 and Cyp19a3 expressions were detected in conceptuses and gonads, respectively. Cyp19a2 transcripts were identified on both the conceptuses and the placenta samples. Transcripts for Cyp17a1 were detected predominantly in conceptus and gonads. In the endometrium of day 21 pregnant females, as well as days 12 and 17 pseudopregnant females, we did not detect the expression of Cyp19a1, Cyp19a2, or Cyp19a3. In our study, we have demonstrated distinct transcriptional regulation for the three functional Cyp19 paralogs and a potential role for Cyp17a1 in controlling the secretion of estrogen from the conceptus and the placenta.

Gene editing provides a tool to investigate genes involved in reproduction of pigs.

CRISPR-Cas9 gene editing technology provides a method to generate loss-of-function studies to investigate, in vivo, the specific role of specific genes in regulation of reproduction. With proper design and selection of guide RNAs (gRNA) designed to specifically target genes, CRISPR-Cas9 gene editing allows investigation of factors proposed to regulate biological pathways involved with establishment and maintenance of pregnancy. The advantages and disadvantages of using the current gene editing technology in a large farm species is discussed. CRISPR-Cas9 gene editing of porcine conceptuses has generated new perspectives for the regulation of endometrial function during the establishment of pregnancy. The delicate orchestration of conceptus factors facilitates an endometrial proinflammatory response while regulating maternal immune cell migration and expansion at the implantation site is essential for establishment and maintenance of pregnancy. Recent developments and use of endometrial epithelial "organoids" to study endometrial function in vitro provides a future method to screen and target specific endometrial genes as an alternative to generating a gene edited animal model. With continuing improvements in gene editing technology, future researchers will be able to design studies to enhance our knowledge of mechanisms essential for early development and survival of the conceptus.