Novel insights into conceptus–maternal signaling during pregnancy establishment in pigs

Abstract

Pregnancy establishment in mammals, including pigs, requires coordinated communication between developing conceptuses (embryos with associated membranes) and the maternal organism. Porcine conceptuses signalize their presence by secreting multiple factors, of which estradiol‐17β (E2) is considered the major embryonic signal initiating the maternal recognition of pregnancy. During this time, a limited supply of prostaglandin (PGF2α) to the corpora lutea and an increased secretion of luteoprotective factors (e.g., E2 and prostaglandin E2 [PGE2]) lead to the corpus luteum's maintained function of secreting progesterone, which in turn primes the uterus for implantation. Further, embryo implantation is related to establishing an appropriate proinflammatory environment coordinated by the secretion of proinflammatory mediators including cytokines, growth factors, and lipid mediators of both endometrial and conceptus origin. The novel, dual role of PGF2α has been underlined. Recent studies involving high‐throughput technologies and sophisticated experimental models identified a number of novel factors and revealed complex relationships between these factors and those already established. Hence, it seems that early pregnancy should be regarded as a sequence of processes orchestrated by pleiotropic factors that are involved in redundancy and compensatory mechanisms that preserve the essential functions critical for implantation and placenta formation. Therefore, establishing the hierarchy between all molecules present at the embryo–maternal interface is now even more challenging

Integrated Analysis of DNA Methylation and Gene Expression in Porcine Placental Development

“…The placenta is a temporary organ that connects the developing fetus to the uterine wall through the umbilical cord to allow for nutrient absorption, thermal regulation, waste disposal, and gas exchange [ 1 , 2 , 34 , 35 ]. The fetal demand for nutrient uptake increases rapidly with the advancement of gestation; thus, the placenta undergoes remodeling to increase placental efficiency by: (1) developing placental folds to expand the maternal–fetal exchange surface area and (2) increasing capillary density and permeability [ 11 ].…”

“…The placenta is an organ formed during pregnancy that supports the intrauterine regulation of fetal growth. It plays critical roles in the exchange of nutrients, waste, and gas; maternal–fetal immune tolerance; and metabolic and endocrine functions via the mother’s blood supply during fetal development [ 1 , 2 ]. Normal placental function is essential to the growth of a healthy fetus.…”

“…Dysfunctional placental development is the main cause of fetal loss and reduced piglet birth weight, which are the primary factors associated with reproductive performance [ 6 , 7 , 8 ]. Unlike human placenta, pigs have a non-invasive, diffuse, epitheliochorial type of placenta, in which the porcine uterine epithelium remains intact instead of invading the uterine wall throughout gestation [ 1 , 2 , 9 , 10 ]. At around 15–20 gestation days in the pig, the trophoblast epithelial layer attaches to endometrial epithelial cells to form the epithelial bilayer [ 11 ].…”

Prokineticin 1 is a novel factor regulating porcine corpus luteum function

“…The lack of fertilization results in CL regression on days 14–16 post ovulation. During pregnancy, CL function is maintained by luteoprotective and luteotrophic factors such as estradiol-17β and prostaglandin E2 3 . Previous reports have indicated a high rate of embryo mortality in pigs during early pregnancy; however, the etiology of this phenomenon is not yet fully understood 4 .…”

Novel role for conceptus signals in mRNA expression regulation by DNA methylation in porcine endometrium during early pregnancy

“…Maternal recognition of pregnancy in pigs occurs between days 10 and 13 after fertilization, whereas implantation of embryos takes place between days 14 and 19 of pregnancy (reviewed in [ 6 ]). During the process of maternal recognition of pregnancy, the conceptuses, namely the embryos with associated membranes, signal their presence to the maternal organism by secreting multiple factors (steroids, prostaglandins, cytokines and others), allowing for maintained progesterone (P4) secretion by the ovaries and for preparation of the endometrium for embryonic implantation (reviewed in [ 7 ]). At the time of maternal recognition of pregnancy, porcine conceptuses secrete increased levels of estrogens, mainly estradiol-17β (E 2 ) on days 11–13.…”