The majority of early embryonic mortality in pregnancy occurs during the peri-implantation stage, suggesting that this period is important for conceptus viability and the establishment of pregnancy. Successful establishment of preg-nancy in all mammalian species depends on the orchestrated molecular events that transpire at the conceptus- uterine interface during the peri-implantation period. This maternal-conceptus interaction is especially crucial in pigs because in them non-invasive epitheliochorial placentation occurs, in which the pre-implantation phase is prolonged. During the pre-implantation period, conceptus survival and the establishment of pregnancy are known to depend on the developing conceptus receiving an adequate supply of histotroph, which contains a wide range of nutrients and grow-th factors. Evidence links growth factors including epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), vascular endothelial growth factor (VEGF), and colony-stimulating factor 2 (CSF2) to embryogenesis or implantation in various mammalian species; however, in the case of pig, little is known about such functions of these growth factors, especially their regulatory mechanisms at the maternal-conceptus interface. Our research group has presented evidence for promising growth factors affecting cellular activities of primary porcine trophectoderm (pTr) cells, and we have identified potential intracellular signaling pathways responsible for the activities induced by these factors. Therefore, this review focuses on promising growth factors at the maternal-conceptus interface regulating the develop-ment of the porcine conceptus and playing pivotal roles in implantation events during early pregnancy in pigs.

Insulin-like growth factor 2 (Igf-2) and H19 genes are closely linked imprinted genes which have a pivotal role in embryogenesis and fetal development. Igf-2 and H19 are coexpressed in tissues of mesodermal, endodermal and neuroectodermal origin. Rat Igf-2 has a complex structure with three promoters and a complicate imprinting mechanism having an exception of biallelic expression in the choroid plexus, leptomeninges, and fetal tissues of neuroectodermal origin. To detect the expression of maternal and paternal alleles of Igf-2 and H19 during orofacial development, fetal and neonatal hybrid rats, obtained from Wistar and Fisher interstrain rat crosses were used. We also detected the promoter-specificity of Igf-2 transcripts by primers selected from P1, P2, and P3 of Igf-2 gene. RT-PCR analysis of Igf-2 and H19 showed the monoallelic expression of Igf-2 from the paternal allele and H19 from the maternal allele in E15.5 to E19.5 orofaciall structures including the maxilla, tongue, and salivary gland. P3 promoters were active in all tested samples, whereas transcripts derived from P2 promoter arised with approximately half of the tested cases and showed variable alternation. P1 promoter was not transcribed in all tested samples. These results suggest that Igf-2 and H19 may be involved in orofacial development and exhibit parent-of-origin monoallelic expression. On the other hand, in orofaciall development, P2 and P3 promoters except for P1 promoter are transcribed with variable alternative transcripts

The majority of early conceptus mortality in pregnancy occurs during the peri-implantation stage, suggesting that this period is important for conceptus viability and the establishment of pregnancy. Successful establishment of pregnancy in all mammalian species depends on the orchestrated molecular events that transpire at the conceptus-uterine interface during the peri-implantation phase. This maternal-conceptus interaction is especially crucial in pigs because in them non-invasive epitheliochorial placentation occurs, in which the pre-implantation phase is prolonged. During the pre-implantation period, conceptus survival and the establishment of pregnancy are known to depend on the developing conceptus receiving an adequate supply of histotroph, which contains a wide range of nutrients and growth factors. Evidence links epidermal growth factor (EGF), insulin- like growth factor-I (IGF-I), vascular endothelial growth factor (VEGF), and colony-stimulating factor 2 (CSF2) to embryogenesis or implantation in various mammalian species; however, in the case of pig, little is known about such functions of these growth factors, especially their regulatory mechanisms at the maternal-conceptus interface. Therefore, the objectives of this study were to determine: 1) the temporal and cell-specific expression of EGF, IGF-I, VEGF, and CSF2 signaling systems in the porcine endometrium during the estrous cycle and early pregnancy; 2) the potential intracellular signaling pathways responsible for the activities of these four factors in primary porcine trophectoderm (pTr) cells; and 3) the changes in cellular activities induced by these promising factors. First, the functional effect and cellular signaling cascades in pTr cells induced by EGF, which exhibits potential growth-promoting activities on the conceptus and endometrium, were investigated. EGFR mRNA and protein were abundant in endometrial luminal epithelia (LE) and glandular epithelia (GE), stratum compactum stroma, and conceptus trophectoderm on Days 13-14 of pregnancy, but not in any other cells of the uterus. EGF treatment of pTr cells increased the abundance of phosphorylated (p)-AKT1, p-ERK1/2 MAPK and p-P90RSK in the nucleus and/or cytoplasm when compared with the levels in control cells. Furthermore, EGF-stimulated phosphorylation of AKT1 and ERK1/2 MAPK were inhibited in pTr cells transfected with an EGFR siRNA, and compared with control siRNA- transfected pTr cells, the EGFR siRNA-transfected pTr cells exhibited an increase in the expression of gene encoding interferon (IFN)-δ and transforming growth factor (TGF) β-1; by contrast, no effect was detected on the expression of the gene encoding IFN-γ. Moreover, EGF stimulated the proliferation and migration of pTr cells, but these stimulatory effects were blocked by pharmacological inhibitors such as SB203580 (a p38 inhibitor), U0126 (a MAPK inhibitor), rapamycin (an MTOR inhibitor), and LY294002 (a PI3K inhibitor). Second, IGF-I was examined. IGF-1 is another promising growth factor that is known to play key roles in reproductive processes; however, little is known about IGF-I-induced functional effects and regulatory mechanisms during peri-implantation in pigs. In this study, endometrial type I IGF receptor (IGF-IR) mRNA was determined to increase substantially during early pregnancy relative to the level during the estrous cycle, and the mRNAs of both IGF-I and IGF-IR were abundant in endometrial LE and GE, stroma and conceptus trophectoderm on Day 12 of pregnancy. Moreover, IGF-I treatment potently increased the amounts of p-AKT1 and, ERK1/2 MAPK in the nucleus and cytoplasm and of RPS6 in the cytosol when compared with the amounts in untreated pTr cells, and IGF-I-induced activation of AKT1 and ERK1/2 was blocked by LY294002. Furthermore, IGF-I strongly stimulated both the proliferation and the migration of pTr cells, but these effects were inhibited by SB203580, U0126, rapamycin and LY294002. Third, this study focused on VEGF, which was identified as a potential mediator of the fetal-maternal dialog that regulates the development of the peri-implantation porcine conceptus. In addition to its known angiogenic effects, VEGF has been suggested to play roles in the development of the early embryo, but VEGF-induced effects on the peri-implantation conceptus remain unknown. Results of this study revealed that endometrial VEGF, VEGF receptor (VEGFR)-1, and VEGFR-2 mRNA levels in endometrial LE and GE, endothelial blood vessels, and scattered cells in the stroma were more abundant during the peri-implantation period of pregnancy than during the estrous cycle. Moreover, VEGF treatment of pTr cells increased the abundance of p-AKT1, p-ERK1/2, p-p70RSK, p-RPS6 and p-4EBP1, and the addition of LY294002 suppressed VEGF-induced phosphorylation of ERK1/2 and AKT1. Furthermore, VEGF potently stimulated both the proliferation and the migration of pTr cells, but these effects were inhibited in the presence of SB203580, U0126, rapamycin and LY294002. The fourth promising cytokine studied was CSF2, which is also known as granulocyte-macrophage colony-stimulating factor (GM-CSF). CSF2 plays a role in facilitating mammalian early embryonic development. In this study, endometrial CSF2 mRNA expression was determined to be increased during the peri-implantation period relative to the mRNA level during the estrous cycle. In pTr cells, CSF2 significantly induced the activation of AKT1, ERK1/2, MTOR, p70RSK, and RPS6, but not of STAT3, and the addition of LY294002 abolished CSF2-induced increases in p-ERK1/2, p-MTOR, and p-AKT1 levels. Furthermore, CSF2 strongly stimulated pTr cell proliferation, an effect that was blocked by U0126, rapamycin and LY294002. Collectively, these results provide new insights into the potential mediators that regulate the development of the peri-implantation conceptus at the fetal-maternal interface. These results indicate that endometrial- and/or conceptus derived EGF, IGF-I, VEGF, and CSF2 critically affect the growth and development of porcine trophectoderm cells, and that these stimulatory effects are coordinately regulated by multiple cellular signaling cascades including the PI3K-AKT and ERK1/2 MAPK pathways during early pregnancy in pigs.

DNA 메틸화 (DNA methylation)는 유전자의 발현을 조절하는 대표적인 후생학적 조절기작 (epigenetic regulation) 중에 하나이다. DNA 메틸화 양상은 생식세포 형성과정 및 배 발생단계에서 탈메틸화 (demethylation)와 de novo 메틸화의 드라마틱한 변화가 일어난다. 또한 이러한 DNA 메틸화는 배아줄기세포 (embryonic stem cells, ESCs)에서 특징적인 양상을 보이는 것으로 알려져 있다. 본 연구에서는 생쥐 수정란 유래 배아줄기세포와 체세포핵이식 배아줄기세포 (nuclear transplanted ESCs)를 이용해서 대표적 각인유전자 (imprinting genes)로 알려진 Snrpn, Igf2r, H19 유전자들에 대한 메틸화 양상을 알아보고자 하였다. 연구 결과 H19 유전자에 대해서는 DNA 메틸화 양상은 수정란 유래 배아줄기세포와 체세포핵이식 배아줄기세포에서 비슷한 경향을 보였으나, Snrpn과 Igf2r의 경우에는 체세포핵이식 배아줄기세포에서 과메틸화 (hypermethylation) 경향을 보였다.