Expression of tripartite motif family-like protein 1 and 2 in early conceptus development and placentation in the pig.

Abstract: The eutherian placenta is highly complex, evolving to regulate the inflammatory phase of pregnancy during conceptus attachment and placental tissue development. Tripartite motif family-like (TRIMLs) proteins are implicated in downregulating inflammation. In mammals, TRIML1 and TRIML2 show preferential expression in gonads, preimplantation embryos and placenta. TRIML1 domains differ between eutherians and marsupials, while TRIML2 is absent in marsupials, suggesting it may play a unique role in regulating the inflammatory phase during conceptus attachment, critical for establishing and maintaining pregnancy to term. This study aimed to investigate the expression pattern of TRIML1 and TRIML2 in various tissues, as well as during embryo development, conceptus attachment, and placental formation in pigs. Transcripts for TRIML2 were detected in embryos, conceptuses, extraembryonic membranes, ovary and testis but not in any of the other tissues examined. In contrast, TRIML1 expression was only observed in testis. In situ hybridization of TRIML1 and TRIML2 confirmed these results. The specific expression of TRIML2 in immune privileged sites is consistent with it serving as an anti-inflammatory factor to provide immunological protection of the eutherian placenta. To further investigate the role of TRIML2, CRISPR/Cas9 gene editing was employed to knock out either TRIML1 (control) or TRIML2. TRIML1 -/- and TRIML2 -/- porcine fetal fibroblasts were used for somatic cell nuclear transfer, and the resulting embryos were transferred into surrogate gilts. Early conceptus and placental development were not affected by the loss of conceptus TRIML2. Although a tissue-specific expression pattern was found, TRIML1 or TRIML2 are not required for pregnancy establishment in the pig. Lay summary: This study investigates the expression and possible roles of two specific proteins in pigs. These proteins are implicated in regulating inflammation and are thought to be important for the proper development of the placenta, which is essential for a successful pregnancy. TRIML2 was found in embryos and certain tissues, including ovary, testis and placenta, while TRIML1 appears only in the testis. We further used gene-editing techniques to generate pig embryos lacking these proteins to test whether their absence would affect early pregnancy and placental development. Lack of either TRIML1 or TRIML2 did not disrupt the early stages of pregnancy or placental formation, indicating that these proteins may not be critical for these processes in pigs.