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Equine placental development is a long process with unique features. Implantation occurs around 40 days of gestation (dpo) with the presence of a transient invasive placenta from 25–35 to 100–120 dpo. The definitive, non-invasive placenta remains until term (330 days). This definitive placenta is diffuse and epitheliochorial, exchanging nutrients, gas and waste with the endometrium through microvilli, called microcotyledons. These are lined by an external layer of haemotrophic trophoblast. Moreover, histotrophic exchange remains active through the histotrophic trophoblast located along the areolae. Placental development is dependent on the maternal environment that can be affected by several factors (e.g. nutrition, metabolism, age, embryo technologies, pathologies) that may affect fetal development as well as long-term offspring health. The first section of the review focuses on normal placental development as well as definitive placental structure. Differences between the various regions of the placenta are also highlighted. The latter sections provide an overview of the effects of the maternal environment and reproductive pathologies, respectively, on trophoblast/placental gene expression and structure. So far, only pre-implantation and late gestation/term data are available, which demonstrate important placental plasticity in response to environmental variation, with genes involved in oxidative stress and tissue differentiation mostly involved in the pre-implantation period, whereas genes involved in feto-placental growth and nutrient transfers are mostly perturbed at term.

Polycomb repressive complex 2 (PRC2) catalyses the repressive epigenetic modification of histone 3 lysine 27 tri-methylation (H3K27me3) and functions as a key epigenetic regulator during embryonic development. PRC2 is known to regulate the development of a range of tissues by transcriptional silencing of genes that control cell differentiation, but its roles in female germline and ovarian development remain unknown. Using a mouse model with hypomorphic embryonic ectoderm development (EED) function that reduced H3K27me3 in somatic and germ cells, we found that PRC2 was required for survival, with more than 95% of female animals dying before birth. Although surviving adult EED hypomorphic females appeared morphologically similar to controls and were fertile, Eed^hypo/hypo adult ovaries were abnormal, with altered morphology characterised by abnormal follicles. Early Eed^hypo/hypo and control fetal ovaries were morphologically similar, and germ cells entered meiosis normally. Immunofluorescent analyses of somatic and germline markers indicated that ovarian development in Eed^hypo/hypo ovaries was similar to heterozygous and WT controls. However, TUNEL analyses revealed higher rates of apoptosis in the ovarian surface epithelium, and transcriptional analyses revealed changes in genes regulating epithelial and steroidogenic cell differentiation, possibly foreshadowing the defects observed in adult ovaries of hypomorphic females. While it was possible to analyse early-mid fetal ovarian development, postnatal stages were inaccessible due to the high level of lethality during late fetal stages. Despite this limitation, the data we were able to obtain reveal a novel role for EED in the ovary that is likely to alter ovarian development and ovarian function in adult animals.

Embryo implantation, a critical step during the mammalian reproductive process, requires normal developing blastocysts and a receptive endometrium. Endometriosis, a common pathologically benign gynecological condition, is associated with decreased fertility and reduced endometrial receptivity. The oncoprotein, Gankyrin, has been associated with endometriosis and endometrial cancer. Here, we examined the role of Gankyrin during the process of embryo implantation and found that Gankyrin expression levels were significantly increased during the mid-secretory phase, but unaffected during the proliferative phase in the human endometrium. Using an in vitro cell adhesion assay to examine the cell adhesion rate of BeWo trophoblast spheroids to Gankyrin knockdown or overexpressing human endometrial carcinoma RL95-2 cells, we demonstrated that the adhesion rate was significantly reduced in Gankyrin-knockdown RL95-2 cells, while overexpression of Gankyrin promoted cell adhesion. Furthermore, we found that the downregulation of Gankyrin inhibited STAT3 activation and subsequent matrix metalloproteinase 2 (MMP2) expression, while overexpression led to STAT3 activation and MMP2 expression. In vivo, we found that Gankyrin expression was increased in the endometrium after conception but decreased with the prolongation of gestation time in female mice. siRNA-mediated knockdown of Gankyrin in the uterine horn led to a significant reduction in the number of implanted embryos 9 days post-gestation, which was associated with a decrease in p-STAT3 expression and MMP2 transcription. Taken together, our findings indicate that Gankryin has a potential role in embryo implantation via STAT3 activation.

Development and the subsequent function of the fetal membranes of the equine placenta require both complex and precise regulation of gene expression. Advancements in recent years in bioinformatic techniques have allowed more extensive analyses into gene expression than ever before. This review starts by combining publically available transcriptomic data sets obtained from a range of embryonic, placental and maternal tissues, with previous knowledge of equine placental development and physiology, to gain insights into key gene families relevant to placentation in the horse. Covering the whole of pregnancy, the review covers trophectoderm, yolk sac, chorionic girdle cells, allantoamnion and allantochorion. In particular, 182 predicted ‘early high impact’ genes were identified (>100 transcripts per million (TPM) and >100 fold-change) that distinguish between progenitor trophectoderm, chorionic girdle tissue and allantochorion. Furthermore, 71 genes were identified as enriched in placental tissues (placental TPM > 10, with minimal expression in 12 non-placental TPM < 1), including excellent candidates for functional studies such as IGF1, apolipoproteins, VGLL1, GCM1, CDX2 and FABP4. It is pertinent that future studies should focus on single-cell transcriptomic approaches in order to determine how these changes in gene expression relate to tissue composition and start to better define trophoblast subpopulations in the equine placenta. Future functional characterisation of these genes and pathways will also be key not only to understanding normal placental development and fetal health but also their potential role in pathologies of pregnancy.

Recent data suggest that the DNA damage response (DDR) is altered in the eutopic endometrium (EE) of women with endometriosis and this probably ensues in response to higher DNA damage encountered by the EE in endometriosis. DDR operates in a tissue-specific manner and involves different pathways depending on the type of DNA lesions. Among these pathways, the non-homologous end joining (NHEJ) pathway plays a critical role in the repair of dsDNA breaks. The present study was undertaken to explore whether NHEJ is affected in the EE of women with endometriosis. Toward this, we focused on the X-ray repair cross-complementing 4 (XRCC4) protein, one of the core components of the NHEJ pathway. Endometrial XRCC4 protein levels in the mid-proliferative phase were found significantly (P  < 0.05) downregulated in women with endometriosis, compared to control women. Investigation of a microarray-based largest dataset in the Gene Expression Omnibus database (GSE51981) revealed a similar trend at the transcript level in the EE of women with endometriosis, compared to control women. Further in vitro studies were undertaken to explore the effects of H₂O₂-induced oxidative stress on DNA damage, as assessed by γ-H2AX and 8-hydroxy-2’-deoxyguanosine (8-OHdG) immunolocalization, and XRCC4 protein levels in endometrial stromal (hTERT immortalized human endometrial stromal cell line (ThESCs)) and epithelial (Ishikawa) cells. A significant decrease in XRCC4 protein levels and significantly higher localization of γ-H2AX and 8-OHdG were evident in ThESCs and Ishikawa cells experiencing oxidative stress. Overall, the study demonstrates that the endometrial XRCC4 expression is dysregulated in women with endometriosis and this could be due to higher oxidative stress in endometriosis.

Recurrent implantation failure (RIF) is a challenge in the field of reproductive medicine, but mechanisms for its occurrence remain still unclear. Long non-coding RNAs (lncRNAs) have been found to play a vital role in many different diseases. In recent years, the differentially expressed lncRNAs have been reported in endometrial tissues. Here, we profiled dysregulated lncRNAs and mRNAs in the endometrial tissues of RIF patients and performed correlation analysis. We found that LINC02190 was upregulated in RIF endometrium and was bound to the integrin αD (ITGAD) mRNA promoter. Immunofluorescence assays were used to detect the location of ITGAD in the Ishikawa cell line and patients’ endometrial biopsies. Overexpressed LINC02190 could decrease the expression of ITGAD and the adhesion rate of Ishikawa and JAR cells. Knockdown of the expression of LINC02190 significantly increased the ITGAD level, as well as the adhesion rate of Ishikawa and JAR cells. Furthermore, we demonstrated that the 150–250 bps of LINC02190 were the cis-elements involved in the regulation of ITGAD promoter activities. In conclusion, the results demonstrated that LINC02190 plays an important role in the occurrence of RIF, and the molecular mechanism may be associated with the embryo–endometrial attachment mediated by ITGAD. This study emphasizes the importance of lncRNAs in the occurrence of RIF and provides a potential new biomarker for diagnosis and therapies.

Implantation-related events are crucial for pregnancy success. In particular, defects in vascular remodeling at the maternal–fetal interface are associated with spontaneous miscarriage and recurrent pregnancy loss. Physical activity and therapies oriented to reduce stress improve pregnancy outcomes. In animal models, environmental stimulation and enrichment are associated with enhanced well-being, cognitive function and stress resilience. Here, we studied whether the exposure of BALB/c mice to an enriched environment (EE) regulates crucial events during early gestation at the maternal–fetal interface. Pregnant BALB/c mice were exposed to the EE that combines non-invasive stimuli from the sensory pathway with voluntary physical activity. The pregnancy rate was evaluated. Implantation sites were investigated microscopically and macroscopically. Vascular adaptation parameters at the maternal–fetal interface were analyzed. We found that exposure to the EE prevented pregnancy loss between gestational days 7 and 15. Also, it increased the diameter of the uterine artery and decreased the wall:lumen ratio of the mesometrial decidual vessels, suggesting that EE exposure promotes vascular remodeling. Moreover, it increased nitric oxide synthase activity and inducible nitric oxide synthase expression, as well as prostaglandin F_2a production and endoglin expression in the implantation sites. Exposure of pregnant females to the EE regulates uterine physiology, promoting vascular remodeling during early gestation. These adaptations might contribute to preventing embryo loss. Our results highlight the importance of the maternal environment for pregnancy success. The design of an ‘EE-like’ protocol for humans could be considered as a new non-pharmacologic strategy to prevent implantation failure and recurrent miscarriage.

Exposure of the fetal testis to numerous individual environmental chemicals (ECs) is frequently associated with dysregulated development, leading to impaired adult reproductive competence. However, ‘real-life’ exposure involves complex mixtures of ECs. Here we test the consequences, for the male fetus, of exposing pregnant ewes to EC mixtures derived from pastures treated with biosolids fertiliser (processed human sewage). Fetal testes from continuously exposed ewes were either unaffected at day 80 or exhibited a reduced area of testis immunostained for CYP17A1 protein at day 140. Fetal testes from day 140 pregnant ewes that were exposed transiently for 80-day periods during early (0–80 days), mid (30–110 days), or late (60–140 days) pregnancy had fewer Sertoli cells and reduced testicular area stained for CYP17A1. Male fetuses from ewes exposed during late pregnancy also exhibited reduced fetal body, adrenal and testis mass, anogenital distance, and lowered testosterone; collectively indicative of an anti-androgenic effect. Exposure limited to early gestation induced more testis transcriptome changes than observed for continuously exposed day 140 fetuses. These data suggest that a short period of EC exposure does not allow sufficient time for the testis to adapt. Consequently, testicular transcriptomic changes induced during the first 80 days of gestation may equate with phenotypic effects observed at day 140. In contrast, relatively fewer changes in the testis transcriptome in fetuses exposed continuously to ECs throughout gestation are associated with less severe consequences. Unless corrected by or during puberty, these differential effects would predictably have adverse outcomes for adult testicular function and fertility.

Pregnancy-specific glycoproteins (PSGs) are members of the immunoglobulin superfamily and are closely related to the predominantly membrane-bound CEACAM proteins. PSGs are produced by placental trophoblasts and secreted into the maternal bloodstream at high levels where they may regulate maternal immune and vascular functions through receptor binding and modulation of cytokine and chemokine expression and activity. PSGs may have autocrine and paracrine functions in the placental bed, and PSGs can activate soluble and extracellular matrix bound TGF-β, with potentially diverse effects on multiple cell types. PSGs are also found at high levels in the maternal circulation, at least in human, where they may have endocrine functions. In a non-reproductive context, PSGs are expressed in the gastrointestinal tract and their deregulation may be associated with colorectal cancer and other diseases. Like many placental hormones, PSGs are encoded by multigene families and they have an unusual phylogenetic distribution, being found predominantly in species with hemochorial placentation, with the notable exception of the horse in which PSG-like proteins are expressed in the endometrial cups of the epitheliochorial placenta. The evolution and expansion of PSG gene families appear to be a highly active process, with significant changes in gene numbers and protein domain structures in different mammalian lineages and reports of extensive copy number variation at the human locus. Against this apparent diversification, the available evidence indicates extensive conservation of PSG functions in multiple species. These observations are consistent with maternal–fetal conflict underpinning the evolution of PSGs.