Ablation of conceptus PTGS2 provides a new understanding of early pregnancy events in the pig
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Pig conceptuses produce and secrete estrogens (E), interleukin 1 beta 2 (IL1B2), and prostaglandins (PGs) during the period of rapid trophoblast elongation and establishment of pregnancy. Previous studies established that IL1B2 is essential for rapid conceptus elongation (Whyte et al., Proc Natl Acad Sci USA 2018), whereas E is not essential for conceptus elongation or early maintenance of the corpora lutea (CL) (Meyer et al., 2019). Prostaglandin synthase 2 (PTGS2) expression increases during early pig conceptus development along with production of PGs. Blastocysts express PTGS2 but not prostaglandin synthase 1 (PTGS1) during early development. To evaluate the role of conceptus PTGS2-derived PGs in early pregnancy, CRISPR/Cas9 gene editing was used to create a deletion in exon 1 of the PTGS2 gene. Both PTGS2[+/+] and PTGS2[-/-] embryos were generated using edited fibroblast cells and somatic cell nuclear transfer. Culture media from PTGS2[+/+] and PTGS2[-/-] blastocysts was collected at day 7. Total PG was substantially lower (P < 0.0001) in the culture media of PTGS2[-/-] compared to PTGS2[+/+] blastocysts. PTGS2 was detectable by immunolocalization in PTGS2[+/+] but absent in PTGS2[-/-] blastocysts. Next, PTGS2[+/+] and PTGS2[-/-] blastocysts were transferred into the uterus of surrogate gilts, and the reproductive tract was collected on either day 14 or 17 of pregnancy. Elongating and filamentous type conceptuses were recovered from the uterine lumen by flushing. The conceptuses were cultured for 3 hours to determine overall PG production. Total PG was lower (P < 0.0001) in media of PTGS2[-/-] conceptuses compared to PTGS2[+/+] conceptuses. However, total content of prostaglandin E (PGE) and prostaglandin F[2alpha] (PGF[2alpha]) in the flushings of the uterine lumen containing either PTGS2[-/-] or PTGS2[+/+] conceptuses were not different (P = 0.99 and P = 0.15, respectively). Next, PTGS2[-/-] blastocysts were transferred into surrogate gilts to assess pregnancy establishment beyond 17 days. Of note, pregnancy was maintained beyond day 30 in gilts gestating PTGS2[-/-] embryos. Thus, conceptus-derived PGs do not have a biological role in early pregnancy in terms of conceptus elongation and pregnancy establishment.
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