Conceptus interferon gamma is essential for pregnancy maintenance in the pig
Authors:   , Johns Destiny Nicole 
Published: August 2021

Establishment and maintenance of pregnancy in the pig is a complex process that relies on adequate communication between the conceptus and maternal uterine endometrium. During the peri-implantation period, the conceptuses produce and secrete estrogens, interleukin 1 beta 2, prostaglandins and other biological factors into the uterine lumen that change the uterine epithelium to become receptive to the attaching conceptuses as well as promote proper conceptus development. Following elongation, beginning on day 12 of pregnancy, the conceptus is known to secrete two different types of interferons. The pig conceptus secretes both type I (interferon delta, IFND) and type II (interferon gamma, IFNG) interferons during this time. CRISPR/Cas9 gene editing and somatic cell nuclear transfer (SCNT) technologies were used to create an IFNG loss-of-function study in pigs. Blastocyst stage embryos that were IFNG[superscript +/+] or IFNG[superscript -/-] were transferred into recipient gilts and their reproductive tracts were collected on days 15 and 17 of pregnancy. Elongated conceptuses were flushed from recipient gilts on day 15 IFNG[superscript +/+] (4/4) and IFNG[superscript -/-] (4/4) recipient gilts. On day 17 of pregnancy, all IFNG[superscript +/+] recipient gilts (4/4) contained elongated viable conceptuses; however, conceptuses were only recovered from 2 of 8 IFNG[superscript -/-] embryo recipient gilts. In all IFNG[superscript -/-] pregnancies, the conceptuses were thin and fragmented compared to IFNG+/+ conceptuses. Additionally, the reproductive tracts that received IFNG[superscript -/-] conceptuses which were not pregnant on day 17 appeared hyperemic, inflamed and edematous. IFNG was localized to the trophectoderm of IFNG[superscript +/+] conceptuses on both day 15 and 17 of pregnancy. However, IFNG expression was not detected in IFNG[superscript -/-] conceptuses on either day 15 or day 17 of pregnancy. Conceptus IFNG mRNA expression was significantly affected by genotype (P [equals] 0.0006) and day (P [less than] 0.0001). Total IFNG was significantly lower (P [equals] 0.0018) in ULF of IFNG[superscript -/-] embryo recipient gilts compared to IFNG[superscript +/+] embryo recipient gilts. IFNG[superscript +/+] conceptuses induced endometrial folding and recruited large numbers of immune cells to the endometrial stroma beneath the site of conceptus attachment compared to less endometrial folding and presence of immune cells in IFNG[superscript -/-] pregnancies on day 15. An additional group of recipient gilts received either IFNG[superscript +/+] embryos (n [equals] 6) or both IFNG[superscript -/-] and IFNG[superscript +/+] embryos (n [equals] 5) to determine if the presence of IFNG producing conceptuses could rescue the IFNG-/- embryos beyond day 17 of pregnancy. On day 30 of pregnancy, 3/6 of IFNG[superscript +/+] embryo recipient gilts contained 3-4 viable embryos, however, only 1 of 5 IFNG[superscript -/-] and IFNG[superscript +/+] cotransferred recipient gilts maintained pregnancy to day 30. Genotyping indicated that all five (1 healthy, 4 degenerating) embryos were IFNG[superscript +/+]. These results indicate conceptus IFNG production is not essential for early conceptus development, rapid elongation or establishment of pregnancy. However, conceptus IFNG production does appear to be necessary for survival during the period of placental attachment beyond day 15.