Genes governing placental development

The interaction of ER stress and autophagy in trophoblasts: navigating pregnancy outcome†

The endoplasmic reticulum is a complex and dynamic organelle that initiates unfolded protein response and endoplasmic reticulum stress in response to the accumulation of unfolded or misfolded proteins within its lumen. Autophagy is a paramount intracellular degradation system that facilitates the transportation of proteins, cytoplasmic components, and organelles to lysosomes for degradation and recycling. Preeclampsia and intrauterine growth retardation are two common complications of pregnancy associated with abnormal trophoblast differentiation and placental dysfunctions and have a major impact on fetal development and maternal health. The intricate interplay between endoplasmic reticulum stress, and autophagy and their impact on pregnancy outcomes, through mediating trophoblast differentiation and placental development, has been highlighted in various reports. Autophagy controls trophoblast regulation through a variety of gene expressions and signaling pathways while excessive endoplasmic reticulum stress triggers downstream apoptotic signaling, culminating in trophoblast apoptosis. This comprehensive review delves into the intricacies of placental development and explores the underlying mechanisms of preeclampsia and intrauterine growth retardation. In addition, this review will elucidate the molecular mechanisms of endoplasmic reticulum stress and autophagy, both individually and in their interplay, in mediating placental development and trophoblast differentiation, particularly highlighting their roles in preeclampsia and intrauterine growth retardation development. This research seeks to the interplay between endoplasmic reticulum stress and impaired autophagy in the placental trophoderm, offering novel insights into their contribution to pregnancy complications.

Homeobox genes in the human placenta: Twists and turns on the path to find novel targets

Fetal growth restriction (FGR) is a clinically important human pregnancy disorder that is thought to originate early in pregnancy and while its aetiology is not well understood, the disorder is associated with placental insufficiency. Currently treatment for FGR is limited by increased surveillance using ultrasound monitoring and premature delivery, or corticosteroid medication in the third trimester to prolong pregnancy. There is a pressing need for novel strategies to detect and treat FGR at its early stage. Homeobox genes are well established as master regulators of early embryonic development and increasing evidence suggests they are also important in regulating early placental development. Most important is that specific homeobox genes are abnormally expressed in human FGR. This review focusses on identifying the molecular pathways controlled by homeobox genes in the normal and FGR-affected placenta. This information will begin to address the knowledge gap in the molecular aetiology of FGR and lay the foundation for identifying potential diagnostic and therapeutic targets.

Underlying Mechanisms and Treatment of Cellular Senescence-Induced Biological Barrier Interruption and Related Diseases

Given its increasing prevalence, aging is of great concern to researchers worldwide. Cellular senescence is a physiological or pathological cellular state caused by aging and a prominent risk factor for the interruption of the integrity and functionality of human biological barriers. Health barriers play an important role in maintaining microenvironmental homeostasis within the body. The senescence of barrier cells leads to barrier dysfunction and age-related diseases. Cellular senescence has been reported to be a key target for the prevention of age-related barrier diseases, including Alzheimer's disease, Parkinson's disease, age-related macular degeneration, diabetic retinopathy, and preeclampsia. Drugs such as metformin, dasatinib, quercetin, BCL-2 inhibitors, and rapamycin have been shown to intervene in cellular senescence and age-related diseases. In this review, we conclude that cellular senescence is involved in age-related biological barrier impairment. We further outline the cellular pathways and mechanisms underlying barrier impairment caused by cellular senescence and describe age-related barrier diseases associated with senescent cells. Finally, we summarize the currently used anti-senescence pharmacological interventions and discuss their therapeutic potential for preventing age-related barrier diseases.

Shared developmental pathways of the placenta and fetal heart

Congenital heart defects (CHD) remain the most common class of birth defect worldwide, affecting 1 in every 110 live births. A host of clinical and morphological indicators of placental dysfunction are observed in pregnancies complicated by fetal CHD and, with the recent emergence of single-cell sequencing capabilities, the molecular and physiological associations between the embryonic heart and developing placenta are increasingly evident. In CHD pregnancies, a hostile intrauterine environment may negatively influence and alter fetal development. Placental maldevelopment and dysfunction creates this hostile in-utero environment and may manifest in the development of various subtypes of CHD, with downstream perfusion and flow-related alterations leading to yet further disruption in placental structure and function. The adverse in-utero environment of CHD-complicated pregnancies is well studied, however the specific etiological role that the placenta plays in CHD development remains unclear. Many mouse and rat models have been used to characterize the relationship between CHD and placental dysfunction, but these paradigms present substantial limitations in the assessment of both the heart and placenta. Improvements in non-invasive placental assessment can mitigate these limitations and drive human-specific investigation in relation to fetal and placental development. Here, we review the clinical, structural, and molecular relationships between CHD and placental dysfunction, the CHD subtype-dependence of these changes, and the future of Placenta-Heart axis modeling and investigation.

A differentiation roadmap of murine placentation at single-cell resolution

The placenta is one of the most important yet least understood organs. Due to the limitations of conventional research approaches, we are still far from a comprehensive understanding of mouse placentation, especially regarding the differentiation of trophoblast lineages at the early developmental stage. To decipher cell compositions and developmental processes, we systematically profile the single-cell transcriptomes of trophoblast cells from extraembryonic tissues (embryonic day 7.5 (E7.5) and E8.5) and placentae (E9.5-E14.5) at one-day intervals. We identify distinct trophoblast cell types during mouse placentation, including unreported progenitor cells and intermediate precursor cells. An updated differentiation roadmap of mouse trophoblast lineages is presented following systematic transcriptome analyses. Based on transcriptomic regulatory network inference, we specify transcription factors responsible for the regulation of dynamic developmental processes during lineage diversification. We map lineage differentiation trajectories and find that sinusoid trophoblast giant cells arise from the subpopulation of ectoplacental cone cells. We provide a comprehensive single-cell data resource to shed light on future mechanistic studies of the gene regulatory networks governing hemochorial placentation.

Identifying novel regulators of placental development using time-series transcriptome data

The placenta serves as a connection between the mother and the fetus during pregnancy, providing the fetus with oxygen, nutrients, and growth hormones. However, the regulatory mechanisms and dynamic gene interaction networks underlying early placental development are understudied. Here, we generated RNA-sequencing data from mouse fetal placenta at embryonic days 7.5, 8.5, and 9.5 to identify genes with timepoint-specific expression, then inferred gene interaction networks to analyze highly connected network modules. We determined that timepoint-specific gene network modules were associated with distinct developmental processes, and with similar expression profiles to specific human placental cell populations. From each module, we identified hub genes and their direct neighboring genes, which were predicted to govern placental functions. We confirmed that four novel candidate regulators identified through our analyses regulate cell migration in the HTR-8/SVneo cell line. Overall, we predicted several novel regulators of placental development expressed in specific placental cell types using network analysis of bulk RNA-sequencing data. Our findings and analysis approaches will be valuable for future studies investigating the transcriptional landscape of early development.

Abnormal growth and morphogenesis of placenta at term is linked to adverse fetal development after perigestational alcohol consumption up to early gestation in mouse

BACKGROUND

Gestation alcohol consumption produces fetal growth restriction and malformations by affecting the embryo-fetal development. Recently a relationship between abnormal placentation and fetal malformation and intrauterine growth retardation has been suggested. However, the effects of perigestational alcohol ingestion up to early pregnancy on the placenta at term and its association with fetal abnormalities are little known.

METHODS

In female mice, ethanol 10% in water was administered for 15 days previous and up to days 4 (D4), 8 (D8), or 10 (D10) of gestation (TF), and gestation continues without ethanol exposure. Control females (CF) received ethanol-free water. At day 18, feto-placental units and implantation sites were studied.

RESULTS

TF had increased resorptions and only fetuses from D8-TF and D10-TF had significantly increased weights versus CF. D4 and D10-TF-placentas had significantly reduced weights. All TF had increased junctional zone (JZ) and reduced labyrinth (Lab) areas (PAS-histology and morphometry) compared with CF. Fetuses with mainly with craniofacial abnormalities and skeletal defects (Alizarin red staining), significantly increase; while the fetal bone density (alizarin color intensity, ImageJ) was reduced in D4, D8 and D10-TF versus CF. Although all TF-placentas were histo-structural affected, TF-abnormal fetuses had the most severe placental anomalies, with junctional abundant glycogenic cells into the labyrinth, disorganized labyrinthine vascularization with signs of leukocyte infiltrates and feto-maternal blood mix.

CONCLUSIONS

Perigestational alcohol consumption up to early gestation induces at term fetal growth alterations, dysmorphology and defective skeleton, linked to deficient growth and abnormal morphogenesis of placenta, highlighting insight into the prenatal etiology of FASD.

Analysis of commonly expressed genes between first trimester fetal heart and placenta cell types in the context of congenital heart disease

Congenital heart disease (CHD) is often associated with fetal growth abnormalities. During the first trimester of pregnancy, the heart and placenta develop concurrently, and share key developmental pathways. It is hypothesized that defective morphogenesis of either organ is synergistically linked. However, many studies determined to understand the mechanisms behind CHD overlook the contribution of the placenta. In this study, we aimed to identify commonly expressed genes between first trimester heart and placenta cells using two publicly available single cell sequencing databases. Using a systematic computational approach, we identified 328 commonly expressed genes between heart and placenta endothelial cells and enrichment in pathways including Vasculature Development (GO:0001944, FDR 2.90E−30), and Angiogenesis (GO:0001525, FDR 1.18E−27). We also found, in comparison with fetal heart endothelial cells, 197 commonly expressed genes with placenta extravillous trophoblasts, 128 with cytotrophoblasts and 80 with syncytiotrophoblasts, and included genes such as FLT1, GATA2, ENG and CDH5. Finally, comparison of first trimester cardiomyocytes and placenta cytotrophoblasts revealed 53 commonly expressed genes and enrichment in biological processes integral to cellular function including Cellular Respiration (GO:0045333; FDR 5.05E−08), Ion Transport (GO:0006811; FDR 2.08E−02), and Oxidation–Reduction Process (GO:0055114; FDR 1.58E−07). Overall, our results identify specific genes and cellular pathways common between first trimester fetal heart and placenta cells which if disrupted may concurrently contribute to the developmental perturbations resulting in CHD.

Molecular regulation of trophoblast stem cell self-renewal and giant cell differentiation by the Hippo components YAP and LATS1

Background

Trophoblast stem cells (TSCs), the precursors of trophoblast cells of placenta, possess the potential to differentiate into various trophoblastic subtypes in vitro. Establishment of extraembryonic trophoblastic lineage is preceded by the “outside versus inside” positional information in preimplantation embryos, critically synchronized by the Hippo components. Abundant expression of Hippo effector YAP in TSCs and differentiated cells with paucity of information on Hippo regulation of TSC proliferation/differentiation led us test the hypothesis that Hippo dynamics is one of the regulators of  TSC proliferation/differentiation.

Methods

Blastocyst-derived murine TSCs were used. Dynamics of Hippo components were analyzed using immunofluorescence, western blotting, immunoprecipitation, qRT-PCR. Interaction studies were performed using full-length and deletion constructs. BrdU incorporation assay, flow cytometry-based polyploidy analysis and confocal microscopy were used to decipher the underlying mechanism.

Results

YAP translocates to the nucleus in TSCs and utilizes its WW₂ domain to interact with the PPQY motif of the stemness factor, CDX2. YAP limits TSC proliferation with associated effect on CDX2 target CyclinD1. Trophoblast giant cells (TGC) differentiation is associated with cytoplasmic retention of YAP, heightened pYAP^Ser127, decrease in the level of the core Hippo component, LATS1, which thereby impedes LATS1-LIMK2 association. Decreased LATS1-LIMK2 complex formation in TGCs was associated with elevated pLIMK2^Thr505 as well as its target pCOFILIN^Ser3. Precocious overexpression of LATS1 during trophoblast differentiation decreased TGC marker, Prl2c2, diminished pLIMK2^Thr505 and inactive COFILIN (pCOFILIN^Ser3) while COFILIN-phosphatase, CHRONOPHIN remained unchanged. LATS1 overexpression inhibited trophoblast endoreduplication with smaller-sized TGC-nuclei, lower ploidy level and disintegrated actin filaments. Inhibition of LIMK2 activity recapitulated the effects of LATS1 overexpression in trophoblast cells.

Conclusion

These results unveil a multilayered regulation of trophoblast self-renewal and differentiation by the Hippo components.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02844-w.

Maternal B cell signaling orchestrates fetal development in mice

B cell participation in early embryo/fetal development and the underlying molecular pathways have not been explored. To understand whether maternal B cell absence or impaired signaling interferes with placental and fetal growth, we paired CD19-deficient (CD19-/-) mice, females with B cell-specific MyD88 (BMyD88-/-) or IL10 (BIL10-/-) deficiency as well as wild-type and MyD88-/- controls on C57Bl/6 background with BALB/c males. Pregnancies were followed by ultrasound and Doppler measurements. Implantation number was reduced in BMyD88-/- and MyD88-/- mice. Loss of MyD88 or B cell-specific deletion of MyD88 or IL10 resulted in decreased implantation areas at gestational day (gd) 5, gd8 and gd10, accompanied by reduced placental thickness, diameter and areas at gd10. Uterine artery resistance was enhanced in BIL10-/- dams at gd10. Challenge with 0.4 mg lipopolysaccharide/kg bodyweight at gd16 revealed that BMyD88-/-, BIL10-/- and CD19-/- mothers delivered preterm, whereas controls maintained their pregnancy. B cell-specific MyD88 and IL10 expression is essential for appropriate in utero development. IL10+B cells are involved in uterine blood flow regulation during pregnancy. Finally, B cell-specific CD19, MyD88 and IL10 expression influences susceptibility towards preterm birth.

The role of cellular senescence in female reproductive aging and the potential for senotherapeutic interventions

BACKGROUND

Advanced maternal age is associated with decreased oocyte quantity and quality as well as uterine and placental dysfunctions. These changes lead to infertility, pregnancy complications and birth defects in the offspring. As the mean age of giving birth is increasing worldwide, prevention of age-associated infertility and pregnancy complications, along with the more frequent use of ART, become extremely important. Currently, significant research is being conducted to unravel the mechanisms underlying female reproductive aging. Among the potential mechanisms involved, recent evidence has suggested a contributing role for cellular senescence, a cellular state of irreversible growth arrest characterized by a hypersecretory and pro-inflammatory phenotype. Elucidating the role of senescence in female reproductive aging holds the potential for developing novel and less invasive therapeutic measures to prevent or even reverse female reproductive aging and increase offspring wellbeing.

OBJECTIVE AND RATIONALE

The review will summarize the positive and negative implications of cellular senescence in the pathophysiology of the female reproductive organs during aging and critically explore the use of novel senotherapeutics aiming to reverse and/or eliminate their detrimental effects. The focus will be on major senescence mechanisms of the ovaries, the uterus, and the placenta, as well as the potential and risks of using senotherapies that have been discovered in recent years.

SEARCH METHODS

Data for this review were identified by searches of MEDLINE, PubMed and Google Scholar. References from relevant articles using the search terms 'Cellular Senescence', 'Aging', 'Gestational age', 'Maternal Age', 'Anti-aging', 'Uterus', 'Pregnancy', 'Fertility', 'Infertility', 'Reproduction', 'Implant', 'Senolytic', 'Senostatic', 'Senotherapy' and 'Senotherapeutic' where selected. A total of 182 articles published in English between 2005 and 2020 were included, 27 of which focus on potential senotherapies for reproductive aging. Exclusion criteria were inclusion of the terms 'male' and 'plants'.

OUTCOMES

Aging is a major determinant of reproductive wellbeing. Cellular senescence is a basic aging mechanism, which can be exploited for therapeutic interventions. Within the last decade, several new strategies for the development and repurposing of drugs targeting senescent cells have emerged, such as modulators of the anti-inflammatory response, oxidative stress, DNA damage, and mitochondria and protein dysfunctions. Several studies of female reproductive aging and senotherapies have been discussed that show promising results for future interventions.

WIDER IMPLICATIONS

In most countries of the Organization for Economic Co-operation and Development, the average age at which women give birth is above 30 years. Currently, in countries such as the Netherlands, Australia, Spain, Finland, Germany and the UK, birth rates among 30- to 34-year-olds are now higher than in any other age groups. This review will provide new knowledge and scientific advancement on the senescence mechanisms during female reproductive aging, and benefit fundamental and clinical scientists and professionals in the areas of reproduction, cancer, immunobiology and fibrosis.

Disruption of Folate Metabolism Causes Poor Alignment and Spacing of Mouse Conceptuses for Multiple Generations

Abnormal uptake or metabolism of folate increases risk of human pregnancy complications, though the mechanism is unclear. Here, we explore how defective folate metabolism influences early development by analysing mice with the hypomorphic Mtrr^gt mutation. MTRR is necessary for methyl group utilisation from folate metabolism, and the Mtrr^gt allele disrupts this process. We show that the spectrum of phenotypes previously observed in Mtrr^gt/gt conceptuses at embryonic day (E) 10.5 is apparent from E8.5 including developmental delay, congenital malformations, and placental phenotypes. Notably, we report misalignment of some Mtrr^gt conceptuses within their implantation sites from E6.5. The degree of misorientation occurs across a continuum, with the most severe form visible upon gross dissection. Additionally, some Mtrr^gt/gt conceptuses display twinning. Therefore, we implicate folate metabolism in blastocyst orientation and spacing at implantation. Skewed growth likely influences embryo development since developmental delay and heart malformations (but not defects in neural tube closure or trophoblast differentiation) associate with severe misalignment of Mtrr^gt/gt conceptuses. Typically, the uterus is thought to guide conceptus orientation. To investigate a uterine effect of the Mtrr^gt allele, we manipulate the maternal Mtrr genotype. Misaligned conceptuses were observed in litters of Mtrr^+/+, Mtrr^+/gt, and Mtrr^gt/gt mothers. While progesterone and/or BMP2 signalling might be disrupted, normal decidual morphology, patterning, and blood perfusion are evident at E6.5 regardless of conceptus orientation. These observations argue against a post-implantation uterine defect as a cause of conceptus misalignment. Since litters of Mtrr^+/+ mothers display conceptus misalignment, a grandparental effect is explored. Multigenerational phenotype inheritance is characteristic of the Mtrr^gt model, though the mechanism remains unclear. Genetic pedigree analysis reveals that severe conceptus skewing associates with the Mtrr genotype of either maternal grandparent. Moreover, the presence of conceptus skewing after embryo transfer into a control uterus indicates that misalignment is independent of the peri- and/or post-implantation uterus and instead is likely attributed to an embryonic mechanism that is epigenetically inherited. Overall, our data indicates that abnormal folate metabolism influences conceptus orientation over multiple generations with implications for subsequent development. This study casts light on the complex role of folate metabolism during development beyond a direct maternal effect.

Placental and fetal characteristics of the Ohia mouse line recapitulate outcomes in human hypoplastic left heart syndrome

Congenital heart defects (CHDs) are the most common birth defect worldwide. The morbidity and mortality associated with these defects is compounded by increased frequency of fetal growth abnormalities. In the Ohia mouse model of hypoplastic left heart syndrome (HLHS), the double homozygous genotype is embryonically lethal at mid-pregnancy; a time in which optimal establishment of the placenta is crucial to fetal survival. We aimed to characterize placental and fetal growth and development in the double heterozygous genotype (Sap130^m/+Pcdha9^m/+). There was a shift in frequency of fetuses with reduced weight near term in the Sap130^m/+Pcdha9^m/+ fetuses compared to wildtype, driven by lower fetal weight in male fetuses compared to female. This shift in fetal weight distribution in the Sap130^m/+Pcdha9^m/+ fetuses was associated with reduced labyrinth region area (P < 0.001) and reduced fetal capillary density (P < 0.001) in the placentas, the latter being significantly lower in male Sap130^m/+Pcdha9^m/+ placentas compared to female. mRNA expression of several nutrient transporters was also lower in placentas from males compared to placentas from females, irrespective of genotype. Overall, this data shows that whilst the double heterozygous fetuses do not carry heart defects, placental development and function is impaired, particularly in males. Such differences are similar to findings in studies of human placentas and highlights the importance of this mouse model in continuing to understand the developmental links and disruptions to the heart-placenta axis.

Adhesion G protein-coupled receptor Gpr126/Adgrg6 is essential for placental development

Mutations in the G protein–coupled receptor GPR126/ADGRG6 cause human diseases, including defective peripheral nervous system (PNS) myelination. To study GPR126 function, we generated new genetic mice and zebrafish models. Murine Gpr126 is expressed in developing heart endocardium, and global Gpr126 inactivation is embryonically lethal, with mutants having thin-walled ventricles but unaffected heart patterning or maturation. Endocardial-specific Gpr126 deletion does not affect heart development or function, and transgenic endocardial GPR126 expression fails to rescue lethality in Gpr126-null mice. Zebrafish gpr126 mutants display unaffected heart development. Gpr126 is also expressed in placental trophoblast giant cells. Gpr126-null mice with a heterozygous placenta survive but exhibit GPR126-defective PNS phenotype. In contrast, Gpr126-null embryos with homozygous mutant placenta die but are rescued by placental GPR126 expression. Gpr126-deficient placentas display down-regulation of preeclampsia markers Mmp9, Cts7, and Cts8. We propose that the placenta-heart axis accounts for heart abnormalities secondary to placental defects in Gpr126 mutants.

Transcription Factor PLAGL1 Is Associated with Angiogenic Gene Expression in the Placenta

During pregnancy, the placenta is important for transporting nutrients and waste between the maternal and fetal blood supply, secreting hormones, and serving as a protective barrier. To better understand placental development, we must understand how placental gene expression is regulated. We used RNA-seq data and ChIP-seq data for the enhancer associated mark, H3k27ac, to study gene regulation in the mouse placenta at embryonic day (e) 9.5, when the placenta is developing a complex network of blood vessels. We identified several upregulated transcription factors with enriched binding sites in e9.5-specific enhancers. The most enriched transcription factor, PLAGL1 had a predicted motif in 233 regions that were significantly associated with vasculature development and response to insulin stimulus genes. We then performed several experiments using mouse placenta and a human trophoblast cell line to understand the role of PLAGL1 in placental development. In the mouse placenta, Plagl1 is expressed in endothelial cells of the labyrinth layer and is differentially expressed in placentas from mice with gestational diabetes compared to placentas from control mice in a sex-specific manner. In human trophoblast cells, siRNA knockdown significantly decreased expression of genes associated with placental vasculature development terms. In a tube assay, decreased PLAGL1 expression led to reduced cord formation. These results suggest that Plagl1 regulates overlapping gene networks in placental trophoblast and endothelial cells, and may play a critical role in placental development in normal and complicated pregnancies.

Perigestational alcohol consumption induces altered early placentation and organogenic embryo growth restriction by disruption of trophoblast angiogenic factors

RESEARCH QUESTION

Maternal alcohol consumption produces fetal retardation and malformations, probably associated with placental defects. Does perigestational alcohol consumption up to organogenesis lead to abnormal placentation and embryo growth restriction by disrupting the vascular endothelial growth factor (VEGF) system in embryo-placental development?

DESIGN

Female mice were treated with 10% ethanol in drinking water before and up to day 10 of gestation. Control mice received ethanol-free water. After treatment, the trophoblastic tissue, embryo growth and the angiogenic VEGF pathway were analysed.

RESULTS

Female mice who had received treatment had resorbed and delayed implantation sites with poor ectoplacental cone development. Reduced trophoblastic area tissue from female mice who had received treatment had abnormal junctional zone and diminished labyrinthine vascularization. After treatment, the labyrinth had increased chorionic trophoblast proliferation, hypoxia inducible factor-1α immunoexpression but reduced apoptosis. The embryo growth was reduced concomitantly with low VEGF immunostaining but high endothelial nitric oxide synthase (eNOS) expression. In junctional and labyrinth of treated female mice, gene and protein immunoexpression of VEGF was reduced and the protein expression of FLT-1 increased compared with controls. Increased activation of kinase insert domain receptor receptor (phosphorylated KDR) and expression of eNOS were observed in placenta of treated female mice. Immunoexpression of metalloproteinase-9, however, was reduced in junctional zone but increased in labyrinth, compared with controls.

CONCLUSIONS

These data reveal inadequate expression of VEGF/receptors and angiogenic eNOS and metalloproteinase factors related to abnormal early placentation after perigestational alcohol ingestion, providing insight into aetiological factors underlying early placentopathy associated with intrauterine growth restriction caused by maternal alcohol consumption.

Hyperactivated Wnt-β-catenin signaling in the absence of sFRP1 and sFRP5 disrupts trophoblast differentiation through repression of Ascl2

Background

Wnt signaling is a critical determinant for the maintenance and differentiation of stem/progenitor cells, including trophoblast stem cells during placental development. Hyperactivation of Wnt signaling has been shown to be associated with human trophoblast diseases. However, little is known about the impact and underlying mechanisms of excessive Wnt signaling during placental trophoblast development.

Results

In the present work, we observed that two inhibitors of Wnt signaling, secreted frizzled-related proteins 1 and 5 (Sfrp1 and Sfrp5), are highly expressed in the extraembryonic trophoblast suggesting possible roles in early placental development. Sfrp1 and Sfrp5 double knockout mice exhibited disturbed trophoblast differentiation in the placental ectoplacental cone (EPC), which contains the precursors of trophoblast giant cells (TGCs) and spongiotrophoblast cells. In addition, we employed mouse models expressing a truncated β-catenin with exon 3 deletion globally and trophoblast-specifically, as well as trophoblast stem cell lines, and unraveled that hyperactivation of canonical Wnt pathway exhausted the trophoblast precursor cells in the EPC, resulting in the overabundance of giant cells at the expense of spongiotrophoblast cells. Further examination uncovered that hyperactivation of canonical Wnt pathway disturbed trophoblast differentiation in the EPC via repressing Ascl2 expression.

Conclusions

Our investigations provide new insights that the homeostasis of canonical Wnt-β-catenin signaling is essential for EPC trophoblast differentiation during placental development, which is of high clinical relevance, since aberrant Wnt signaling is often associated with trophoblast-related diseases.

Advances in imaging feto-placental vasculature: new tools to elucidate the early life origins of health and disease

Optimal placental function is critical for fetal development, and therefore a crucial consideration for understanding the developmental origins of health and disease (DOHaD). The structure of the fetal side of the placental vasculature is an important determinant of fetal growth and cardiovascular development. There are several imaging modalities for assessing feto-placental structure including stereology, electron microscopy, confocal microscopy, micro-computed tomography, light-sheet microscopy, ultrasonography and magnetic resonance imaging. In this review, we present current methodologies for imaging feto-placental vasculature morphology ex vivo and in vivo in human and experimental models, their advantages and limitations and how these provide insight into placental function and fetal outcomes. These imaging approaches add important perspective to our understanding of placental biology and have potential to be new tools to elucidate a deeper understanding of DOHaD.

Harnessing Autophagic Network Is Essential for Trophoblast Stem Cell Differentiation

Differentiation of trophoblast stem (TS) cells into various cell lineages of the placenta during mammalian development is accompanied by dynamic changes in its proteome for exerting the highly specialized functions of various cell subtypes. In the present study, we demonstrate that the autophagic machinery, which includes proteins for initiation, vesicle nucleation, and autophagosome maturation are robustly upregulated during differentiation of TS cells. Interestingly, basal levels of autophagy were detectable in the developing mouse placenta as well as TS cells. However, autophagic flux was actively triggered by induction of differentiation evident from LC3 maturation. Formation of Beclin1, Vps34, and PIK3R4 ternary complex at the phagophore assembly site that is typically known to induce autophagy was also enhanced during differentiation. Degradation of the p62/SQSTM1 cargo protein and its colocalization with LC3, a mature autophagosome marker, was most prevalent in the trophoblast giant cells (TGCs) and negligible in other trophoblast cells at day 6 of differentiation. Furthermore, disruption of autophagy by impairing lysosomal fusion in TS cells before induction of differentiation led to a decrease in the giant cell and spongiotrophoblast cell markers Prl3d1, Prl2c2, Prl4a1, and Tpbpα upon differentiation. In addition, inhibition of autophagy was associated with a decrease in nuclear size of TGCs. Taken together, these data highlight that autophagy is a necessary prelude in commitment of trophoblast differentiation from the multipotent TS cells probably by regulating protein turnover at the onset of differentiation.

Expression of Retinoid Acid Receptor-Responsive Genes in Rodent Models of Placental Pathology

In humans, retinoic acid receptor responders (RARRES) have been shown to be altered in third trimester placentas complicated by the pathologies preeclampsia (PE) and PE with intrauterine growth restriction (IUGR). Currently, little is known about the role of placental Rarres in rodents. Therefore, we examined the localization and expression of Rarres1 and 2 in placentas obtained from a Wistar rat model of isocaloric maternal protein restriction (E18.5, IUGR-like features) and from an eNOS-knockout mouse model (E15 and E18.5, PE-like features). In both rodent models, Rarres1 and 2 were mainly localized in the placental spongiotrophoblast and giant cells. Their placental expression, as well as the expression of the Rarres2 receptor chemokine-like receptor 1 (CmklR1), was largely unaltered at the examined gestational ages in both animal models. Our results have shown that RARRES1 and 2 may have different expression and roles in human and rodent placentas, thereby underlining immanent limitations of comparative interspecies placentology. Further functional studies are required to elucidate the potential involvement of these proteins in early placentogenesis.

DNA methylation of the Rtl1 promoter in the placentas with fetal growth restriction

BACKGROUND

Small for gestational age (SGA) babies experience fetal growth restriction because of placental insufficiency, and aberrant fetal growth has been linked to DNA methylation in the placenta. An imprinted gene encoding retrotransposon-like protein 1 (RTL1) is regulated by DNA methylation in the promoter region and plays a key role in placental development. We therefore investigated the DNA methylation status of RTL1 in the placenta of infants with severe SGA.

METHODS

We extracted DNA from the placenta of appropriate for gestational age (AGA; gestational age 35 ± 6 weeks, birthweight 2292 ± 1006 g; n = 12), SGA (birthweight z-score ≤-2 SD, 33 ± 5 weeks, 1373 ± 580 g; n = 11), and severe SGA (birthweight z-score ≤-3 SD, 33 ± 4 weeks, 1145 g ± 423 g; n = 7) infants, and we determined the methylation rates of five CpG sites in the CG4 (82,275,427-82,275,737 in NT_026437 sequence, NCBI database) region of the RTL1 promoter by pyrosequencing. We defined hypermethylation (>75.5%) and hypomethylation (<45.6%) based on the average methylation rate exceeding ± two standard deviations (SD) in the AGA group, respectively, and compared these among groups.

RESULTS

There was no significant difference in the average methylation of CpG1-5 (control 59%, SGA 60%, severe SGA 63%), but abnormal methylation (hyper-/hypo-methylation) in CpG1 differed significantly among the groups (control 0%, SGA 36%, severe SGA 71%).

CONCLUSION

Infants with severe SGA have abnormal placental DNA methylation of CpG1 in the CG4 region of RTL1, suggesting the existence of disturbed epigenetic control in utero.

Human-specific LAIR2 contributes to the high invasiveness of human extravillous trophoblast cells

The placenta is a temporary vital organ for intra-uterine development and growth. The anatomical structure of the placenta has evolved substantially, resulting in broad inter-species diversity. In particular, human placental extravillous trophoblast cells (EVTs) have evolved aggressive features, although the mechanism underlying this aggressiveness remains elusive. In the present study, we compared the human and mouse homologous gene databases and obtained 2272 human-specific genes, 807 of which are expressed in the placenta according to the UniGene database. Using the human trophoblast cell line HTR8/SVneo, we further verified the expression and function of one of these genes, the leukocyte-associated immunoglobulin-like receptor 2 (LAIR2). This gene shows increased expression during pregnancy and its reduced expression is associated with pregnancy complications. Although LAIR2 was expressed in the human placenta villus and decidua in the first trimester of pregnancy, it was not expressed in mouse tissues. Knockdown of LAIR2 markedly improved cell viability and inhibited the invasive ability of HTR8/SVneo cells. These data suggest that species-specific genes are pivotal to the evolution of a more aggressive human placenta to match the physiological demands of human development. Further investigation is required to obtain evidence on the function of LAIR2 and other specific genes in the placenta, providing insight on the mechanism, properties, and possible applications of this in humans.

Secondary Placental Defects in Cxadr Mutant Mice

The Coxsackie virus and adenovirus receptor (CXADR) is an adhesion molecule known for its role in virus-cell interactions, epithelial integrity, and organogenesis. Loss of Cxadr causes numerous embryonic defects in mice, notably abnormal development of the cardiovascular system, and embryonic lethality. While CXADR expression has been reported in the placenta, the precise cellular localization and function within this tissue are unknown. Since impairments in placental development and function can cause secondary cardiovascular abnormalities, a phenomenon referred to as the placenta-heart axis, it is possible placental phenotypes in Cxadr mutant embryos may underlie the reported cardiovascular defects and embryonic lethality. In the current study, we determine the cellular localization of placental Cxadr expression and whether there are placental abnormalities in the absence of Cxadr. In the placenta, CXADR is expressed specifically by trophoblast labyrinth progenitors as well as cells of the visceral yolk sac (YS). In the absence of Cxadr, we observed altered expression of angiogenic factors coupled with poor expansion of trophoblast and fetal endothelial cell subpopulations, plus diminished placental transport. Unexpectedly, preserving endogenous trophoblast Cxadr expression revealed the placental defects to be secondary to primary embryonic and/or YS phenotypes. Moreover, further tissue-restricted deletions of Cxadr suggest that the secondary placental defects are likely influenced by embryonic lineages such as the fetal endothelium or those within the extraembryonic YS vascular plexus.

Gestational exposure to acrylamide inhibits mouse placental development in vivo

Acrylamide, a carcinogen and neurotoxic substance, recently has been discovered in various heat-treated carbohydrate-rich foods. The aim of this study was to investigate the effects of acrylamide exposure on placental development. Pregnant mice received acrylamide by gavage at dosages of 0, 10, and 50 mg/kg/day from gestational days (GD) 3 until GD 8 or GD 13. The results showed that acrylamide feeding significantly decreased the numbers of viable embryos and increased the numbers of resorbed embryos on GD 13. Acrylamide exposure reduced the absolute and relative weight of placentas and embryos, and inhibited the development of ectoplacental cone (EPC) and placenta, as shown by the atrophy of EPC and reduced placental area. Acrylamide markedly reduced the numbers of labyrinth vessels. Expression levels of most placental key genes such as Esx1, Hand1, and Hand2 mRNA dramatically decreased in acrylamide-treated placentas. Furthermore, acrylamide treatment inhibited proliferation and induced apoptosis of placentas, as shown by decreased Ki67-positive cells and Bcl-2 protein, and increased the expression of Bax, cleaved-caspase-3, and cleaved-caspase-8 proteins. In conclusion, our results indicated that gestational exposure to acrylamide inhibits placental development through dysregulation of placental key gene expression and labyrinth vessels, suppression of proliferation, and apoptosis induction in mice.

Down-regulation of DKK1 and Wnt1/β-catenin pathway by increased homeobox B7 resulted in cell differentiation suppression of intrauterine fetal growth retardation in human placenta

OBJECTIVE

This study aimed to test the influence of homeobox B7 (HoxB7) on the proliferation, invasion, and migration of human trophoblast cells and to reveal the down-regulation of HoxB7 on the transcriptional suppression of Dick Kopf-related protein1 (DKK1) and of Cysteine-rich glycosylated wingless protein 1 (Wnt1)/β-catenin in intrauterine fetal growth retardation (FGR).

METHODS

Quantitative measurement of HoxB7, DKK1, Wnt1, and β-catenin was performed in human placentas collected from normal pregnancies and from FGR with quantitative real time PCR (qRT-PCR). Cultured HTR-8/SVneo cells, transfected with a lentiviral plasmid that in-frame expresses human HoxB7 gene, were applied to functional assessment to study the biological impact of HoxB7 gene on DKK1, Wnt1, and β-catenin. Counting Kit-8, Transwell invasion assays, and flow cytometry were applied for the functional measurements.

RESULTS

The expression of HoxB7 was significantly increased, and of DKK1, Wnt1, and β-catenin was decreased, in FGR placenta tissues and in HTR-8/SVneo cells. Function studies revealed that overexpression of HoxB7 inhibited proliferation, migration, and invasion in HTR-8/SVneo cells. DKK1, Wnt1, and β-catenin were down-regulated in HTR-8/SVneo cells, inversely correlated with HoxB7 expression. Overexpression of HoxB7 showed a suppressive effect on proliferation, migration, and invasion in the HTR-8/SVneo cells.

CONCLUSIONS

Our results indicate that HoxB7 inhibited human trophoblast cell differentiation by down-regulating DKK1 expression and that it may affect transcription of Wnt1/β-catenin. The activation of HoxB7 might suppress the cell differentiation in HTR-8/SVneo cell cultures. The Wnt/β-catenin signaling pathway may play a significant role in the pathogenesis of FGR by regulating the invasion and proliferation of trophoblasts.

NOSTRIN: A novel modulator of trophoblast giant cell differentiation

Differentiation-dependent expression of NOSTRIN in murine trophoblast cells prompted investigation on NOSTRIN's function in trophoblast differentiation. We show here that NOSTRIN levels increased in both mouse and rat placenta during gestation. NOSTRIN expression was not co-related to expression of eNOS precluding its eNOS mediated function. NOSTRIN transcripts were identified in trophoblast cells of the placenta, predominantly in trophoblast giant cells (TGC). Precocious over-expression of NOSTRIN during differentiation of trophoblast stem cells led to up-regulation of genetic markers associated with invasion (Prl4a1, Prl2a1) and TGC formation (Prl2c2, Prl3d1, Prl3b1). The functional consequence of NOSTRIN over-expression was increased TGC formation and trophoblast cell invasion. Furthermore, number of polyploid TGCs that arise by endoreduplication, were higher in presence of NOSTRIN. Early induction of NOSTRIN was associated with substantial decrease in G/F actin ratio and augmentation of N-WASP-Dynamin-NOSTRIN ternary complex formation that might be partially responsible for nucleation of actin filaments. NOSTRIN also formed a complex with Cdk1 and increased phosphorylation of T14 and Y15 residues that inhibits cytokinesis. Interestingly, SH3 domain deleted NOSTRIN was ineffective in eliciting NOSTRIN's function in differentiating trophoblast cells. These findings demonstrate that NOSTRIN potentiates trophoblast differentiation towards TGC trajectory that is critical for hemochorial placentation.

Cultured bovine embryo biopsy conserves methylation marks from original embryo

A major limitation of embryo epigenotyping by chromatin immunoprecipitation analysis is the reduced amount of sample available from an embryo biopsy. We developed an in vitro system to expand trophectoderm cells from an embryo biopsy to overcome this limitation. This work analyzes whether expanded trophectoderm (EX) is representative of the trophectoderm (TE) methylation or adaptation to culture has altered its epigenome. We took a small biopsy from the trophectoderm (30-40 cells) of in vitro produced bovine-hatched blastocysts and cultured it on fibronectin-treated plates until we obtained ∼4 × 104 cells. The rest of the embryo was allowed to recover its spherical shape and, subsequently, TE and inner cell mass were separated. We examined whether there were DNA methylation differences between TE and EX of three bovine embryos using whole-genome bisulfite sequencing. As a consequence of adaptation to culture, global methylation, including transposable elements, was higher in EX, with 5.3% of quantified regions showing significant methylation differences between TE and EX. Analysis of individual embryos indicated that TE methylation is more similar to its EX counterpart than to TE from other embryos. Interestingly, these similarly methylated regions are enriched in CpG islands, promoters and transcription units near genes involved in biological processes important for embryo development. Our results indicate that EX is representative of the embryo in terms of DNA methylation, thus providing an informative proxy for embryo epigenotyping.

Recent Advances in Placenta-Heart Interactions

Congenital heart defects (CHD) occur in ∼1 in every 100 live births. In addition, an estimated 10% of fetal loss is due to severe forms of CHD. This makes heart defects the most frequently occurring birth defect and single cause of in utero fatality in humans. There is considerable evidence that CHD is heritable, indicating a strong contribution from genetic risk factors. There are also known external environmental exposures that are significantly associated with risk for CHD. Hence, the majority of CHD cases have long been considered to be multifactorial, or generally caused by the confluence of several risk factors potentially from genetic, epigenetic, and environmental sources. Consequently, a specific cause can be very difficult to ascertain, although patterns of associations are very important to prevention. While highly protective of the fetus, the in utero environment is not immune to insult. As the conduit between the mother and fetus, the placenta plays an essential role in maintaining fetal health. Since it is not a fully-formed organ at the onset of pregnancy, the development of the placenta must keep pace with the growth of the fetus in order to fulfill its critical role during pregnancy. In fact, the placenta and the fetal heart actually develop in parallel, a phenomenon known as the placenta–heart axis. This leaves the developing heart particularly vulnerable to early placental insufficiency. Both organs share several developmental pathways, so they also share a common vulnerability to genetic defects. In this article we explore the coordinated development of the placenta and fetal heart and the implications for placental involvement in the etiology and pathogenesis of CHD.

Regulation of Placental Development and Its Impact on Fetal Growth-New Insights From Mouse Models

The placenta is the chief regulator of nutrient supply to the growing embryo during gestation. As such, adequate placental function is instrumental for developmental progression throughout intrauterine development. One of the most common complications during pregnancy is insufficient growth of the fetus, a problem termed intrauterine growth restriction (IUGR) that is most frequently rooted in a malfunctional placenta. Together with conventional gene targeting approaches, recent advances in screening mouse mutants for placental defects, combined with the ability to rapidly induce mutations in vitro and in vivo by CRISPR-Cas9 technology, has provided new insights into the contribution of the genome to normal placental development. Most importantly, these data have demonstrated that far more genes are required for normal placentation than previously appreciated. Here, we provide a summary of common types of placental defects in established mouse mutants, which will help us gain a better understanding of the genes impacting on human placentation. Based on a recent mouse mutant screen, we then provide examples on how these data can be mined to identify novel molecular hubs that may be critical for placental development. Given the close association between placental defects and abnormal cardiovascular and brain development, these functional nodes may also shed light onto the etiology of birth defects that co-occur with placental malformations. Taken together, recent insights into the regulation of mouse placental development have opened up new avenues for research that will promote the study of human pregnancy conditions, notably those based on defects in placentation that underlie the most common pregnancy pathologies such as IUGR and pre-eclampsia.

Expression of Homeobox Gene HLX and its Downstream Target Genes are Altered in Placentae From Discordant Twin Pregnancies

A discordant twin gestation, in which one fetus is significantly growth restricted, compared to the other normal twin, is a unique model that can be used to elucidate the mechanism(s) by which the intrauterine environment affects fetal growth. In many model systems, placental transcription factor genes regulate fetal growth. Transcription factors regulate growth through their activation or repression of downstream target genes that mediate important cell functions. The objective of this study was to determine the expression of the placental HLX homeobox gene transcription factor and its downstream target genes in dizygotic twins with growth discordance. In this cross-sectional study, HLX and its downstream target genes' retinoblastoma 1 (RB1) and cyclin kinase D (CDKN1C) expression levels were determined in placentae obtained from dichorionic diamniotic twin pregnancies (n = 23) where one of the twins was growth restricted. Fetal growth restriction (FGR) was defined as small for gestational age with abnormal umbilical artery Doppler indices when compared with the normal control co-twin. Homeobox gene HLX expression was significantly decreased at both the mRNA and protein levels in FGR twin placentae compared with the normal control co-twin placentae (p < .05). Downstream target genes CDKN1C and RB1 were also significantly decreased and increased, respectively, at both the mRNA and protein levels in FGR twin placentae compared with normal control co-twin placentae (p < .05). Together, these observations suggest an important association between HLX transcription factor expression and abnormal human placental development in discordant twin pregnancies.

Decidualisation and placentation defects are a major cause of age-related reproductive decline

Mammalian reproductive performance declines rapidly with advanced maternal age. This effect is largely attributed to the exponential increase in chromosome segregation errors in the oocyte with age. Yet many pregnancy complications and birth defects that become more frequent in older mothers, in both humans and mice, occur in the absence of karyotypic abnormalities. Here, we report that abnormal embryonic development in aged female mice is associated with severe placentation defects, which result from major deficits in the decidualisation response of the uterine stroma. This problem is rooted in a blunted hormonal responsiveness of the ageing uterus. Importantly, a young uterine environment can restore normal placental as well as embryonic development. Our data highlight the pivotal, albeit under-appreciated, impact of maternal age on uterine adaptability to pregnancy as major contributor to the decline in reproductive success in older females.Advanced maternal age has been associated with lower reproductive success and higher risk of pregnancy complications. Here the authors show that maternal ageing-related embryonic abnormalities in mouse are caused by decidualisation and placentation defects that can be rescued by transferring the embryo from an old to a young uterus.

The depletion of MARVELD1 leads to murine placenta accreta via integrin β4-dependent trophoblast cell invasion

The placenta is a remarkable organ, it serves as the interface between the mother and the fetus. Proper invasion of trophoblast cells is required for a successful pregnancy. Previous studies have found that the adhesion molecule integrin β4 plays important roles during trophoblast cell invasion. Here, we found that the overall birth rate of the MARVELD1 knockout mouse is much lower than that of the wild-type mouse (p < 0.001). In E18.5 MARVELD1 knockout mice, we observed an over-invasion of trophoblast cells, and indeed, the pregnant mice had a partial placenta accreta phenotype. The HTR8/SVneo cell line was used as an in vitro model to elucidate the underlying mechanisms of MARVELD1-mediated trophoblast invasion. We detected a diminished expression of integrin β4 upon the downregulation of MARVELD1 and enhanced migrate and invasive abilities of trophoblast cells both in vivo and in vitro. The integrin β4 rescue assay also supported the results. In conclusion, this study found that MARVELD1 mediated the invasion of trophoblast cells via regulating the expression of integrin β4 during placenta development.

Dynamic maternal and fetal Notch activity and expression in placentation

INTRODUCTION

Murine placentation requires trophoblast Notch2, while the Notch ligand, JAGGED1, is reduced in invasive trophoblasts from women with preeclampsia. However, the placental cells with active Notch signaling and expression of other Notch proteins and ligands in placentation have yet to be defined. We sought to identify endothelial cell and trophoblast subtypes with canonical Notch signaling in the decidua and placenta and correlate this to expression of Notch proteins and ligands.

METHODS

Notch reporter transgenic mice were used to define canonical Notch activity and immunofluorescence staining performed to characterize expression of Notch1, 2, 3, 4 and ligands, Delta-like 4 (Dll4) and Jagged1 (Jag1) during early placentation and in the mature placenta.

RESULTS

Notch signaling is active in maternal and fetal endothelial cells and trophoblasts during early placentation and in the mature placenta. Dll4, Jag1, Notch1, and Notch4 are expressed in maternal vasculature in the decidua. Dll4, Jag1 and Notch1 are expressed in fetal vasculature in the labyrinth. Dll4, Notch2 and Notch4 are co-expressed in the ectoplacental cone. Notch2 and Notch4 are expressed in parietal-trophoblast giant cells and junctional zone trophoblasts with active canonical Notch signaling and in labyrinthine syncytiotrophoblasts and sinusoidal-trophoblast giant cells.

DISCUSSION

Canonical Notch activity and distinct expression patterns for Notch proteins and ligands was evident in endothelium and trophoblasts, suggesting Notch1, Notch2, Notch4, Dll4, and Jag1 have distinct and overlapping functions in placentation. Characterization of Notch signaling defects in existing mouse models of preeclampsia may shed light on the role of Notch in developing the preeclampsia phenotype.

Gene networks for total number born in pigs across divergent environments

For reproductive traits such as total number born (TNB), variance due to different environments is highly relevant in animal breeding. In this study, we aimed to perform a gene-network analysis for TNB in pigs across different environments using genomic reaction norm models. Thus, based on relevant single-nucleotide polymorphisms and linkage disequilibrium blocks across environments obtained from GWAS, different sets of candidate genes having biological roles linked to TNB were identified. Network analysis across environment levels resulted in gene interactions consistent with known mammal's fertility biology, captured relevant transcription factors for TNB biology and pointing out different sets of candidate genes for TNB in different environments. These findings may have important implication for animal production, as optimal breeding may vary depending on later environments. Based on these results, genomic diversity was identified and inferred across environments highlighting differential genetic control in each scenario.

Integrin α8 Is Abundant in Human, Rat, and Mouse Trophoblasts

OBJECTIVE

Integrins exert regulatory functions in placentogenesis. Null mutation of certain integrin α subunits leads to placental defects with subsequent fetal growth restriction or embryonic lethality in mice. So far, the placental role of α8 integrin remains to be determined.

METHODS

Localization of α8 integrin and its ligands, fibronectin (FN) and osteopontin (OPN), was studied by immunohistochemistry in human, rat, and mouse placenta. The vascularization of the placental labyrinth layer of α8 integrin-deficient mice was determined by CD31 staining. In humans, α8 integrin expression was assessed via real-time polymerase chain reaction in healthy placentas, in the placental pathologies such as intrauterine growth restriction (IUGR), preeclampsia, and HELLP-syndrome (hemolysis, elevated liver enzymes, low platelet count), as well as in primary extravillous trophoblasts (EVT) and villous trophoblasts.

RESULTS

In humans, α8 integrin was detected in first and third trimester syncytiotrophoblast and EVT. Although OPN showed the same localization, FN was observed in EVT only. No expressional changes in α8 integrin were detected in the placental pathologies studied. Rodent placenta showed α8 integrin expression in giant cells and in the labyrinth layer. The localization of OPN and FN, however, showed species-specific differences. Knockout of α8 integrin in mice did not cause IUGR, despite some reduction in labyrinth layer vascularization.

CONCLUSION

α8 Integrin is expressed in functional placental compartments among its ligands, OPN and/or FN, across species. Although this may point to a regulatory role in trophoblast function, our data from α8 integrin-deficient mice indicated only mild placental pathology. Thus, the lack of placental α8 integrin seems to be largely compensated for.

Id2 Mediates Differentiation of Labyrinthine Placental Progenitor Cell Line, SM10

The placenta is an organ that is formed transiently during pregnancy, and appropriate placental development is necessary for fetal survival and growth. Proper differentiation of the labyrinthine layer of the placenta is especially crucial, as it establishes the fetal-maternal interface that is involved in physiological exchange processes. Although previous studies have indicated the importance of inhibitor of differentiation/inhibitor of DNA binding-2 (Id2) helix-loop-helix transcriptional regulator in mediating cell differentiation, the ability of Id2 to regulate differentiation toward the labyrinthine (transport) lineage of the placenta has yet to be determined. In the current study, we have generated labyrinthine trophoblast progenitor cells with increased (SM10-Id2) or decreased (SM10-Id2-shRNA) Id2 expression and determined the effect on TGF-β-induced differentiation. Our Id2 overexpression and knockdown analyses indicate that Id2 mediates TGF-β-induced morphological differentiation of labyrinthine trophoblast cells, as Id2 overexpression prevents differentiation and Id2 knockdown results in differentiation. Thus, our data indicate that Id2 is an important molecular mediator of labyrinthine trophoblast differentiation. An understanding of the regulators of trophoblast progenitor differentiation toward the labyrinthine lineage may offer insights into events governing pregnancy-associated disorders, such as placental insufficiency, fetal growth restriction, and preeclampsia.

Plet1 is an epigenetically regulated cell surface protein that provides essential cues to direct trophoblast stem cell differentiation

Gene loci that are hypermethylated and repressed in embryonic (ESCs) but hypomethylated and expressed in trophoblast (TSCs) stem cells are very rare and may have particularly important roles in early developmental cell fate decisions, as previously shown for Elf5. Here, we assessed another member of this small group of genes, Placenta Expressed Transcript 1 (Plet1), for its function in establishing trophoblast lineage identity and modulating trophoblast differentiation. We find that Plet1 is tightly repressed by DNA methylation in ESCs but expressed on the cell surface of TSCs and trophoblast giant cells. In hypomethylated ESCs that are prone to acquire some trophoblast characteristics, Plet1 is required to confer a trophoblast-specific gene expression pattern, including up-regulation of Elf5. Plet1 displays an unusual biphasic expression profile during TSC differentiation and thus may be pivotal in balancing trophoblast self-renewal and differentiation. Furthermore, overexpression and CRISPR/Cas9-mediated knockout in TSCs showed that high Plet1 levels favour differentiation towards the trophoblast giant cell lineage, whereas lack of Plet1 preferentially induces syncytiotrophoblast formation. Thus, the endogenous dynamics of Plet1 expression establish important patterning cues within the trophoblast compartment by promoting differentiation towards the syncytiotrophoblast or giant cell pathway in Plet1-low and Plet1-high cells, respectively.

Dynamic integrated analysis of DNA methylation and gene expression profiles in in vivo and in vitro fertilized mouse post-implantation extraembryonic and placental tissues

STUDY HYPOTHESIS

How does in vitro fertilization (IVF) alter promoter DNA methylation patterns and its subsequent effects on gene expression profiles during placentation in mice?

STUDY FINDING

IVF-induced alterations in promoter DNA methylation might have functional consequences in a number of biological processes and functions during IVF placentation, including actin cytoskeleton organization, hematopoiesis, vasculogenesis, energy metabolism and nutrient transport.

WHAT IS KNOWN ALREADY

During post-implantation embryonic development, both embryonic and extraembryonic tissues undergo de novo DNA methylation, thereby establishing a global DNA methylation pattern, and influencing gene expression profiles. Embryonic and placental tissues of IVF conceptuses can have aberrant morphology and functions, resulting in adverse pregnancy outcomes such as pregnancy loss, low birthweight, and long-term health effects. To date, the IVF-induced global profiling of DNA methylation alterations, and their functional consequences on aberrant gene expression profiles in IVF placentas have not been systematically studied.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Institute for Cancer Research mice (6 week-old females and 8-9 week-old males) were used to generate in vivo fertilization (IVO) and IVF blastocysts. After either IVO and development (IVO group as control) or in vitro fertilization and culture (IVF group), blastocysts were collected and transferred to pseudo-pregnant recipient mice. Extraembryonic (ectoplacental cone and extraembryonic ectoderm) and placental tissues from both groups were sampled at embryonic day (E) 7.5 (IVO, n = 822; IVF, n = 795) and E10.5 (IVO, n = 324; IVF, n = 278), respectively. The collected extraembryonic (E7.5) and placental tissues (E10.5) were then used for high-throughput RNA sequencing (RNA-seq) and methylated DNA immunoprecipitation sequencing (MeDIP-seq). The main dysfunctions indicated by bioinformatic analyses were further validated using molecular detection, and morphometric and phenotypic analyses.

MAIN RESULTS AND THE ROLE OF CHANCE

Dynamic functional profiling of high-throughput data, together with molecular detection, and morphometric and phenotypic analyses, showed that differentially expressed genes dysregulated by DNA methylation were functionally involved in: (i) actin cytoskeleton disorganization in IVF extraembryonic tissues, which may impair allantois or chorion formation, and chorioallantoic fusion; (ii) disturbed hematopoiesis and vasculogenesis, which may lead to abnormal placenta labyrinth formation and thereby impairing nutrition transport in IVF placentas; (iii) dysregulated energy and amino acid metabolism, which may cause placental dysfunctions, leading to delayed embryonic development or even lethality; (iv) disrupted genetic information processing, which can further influence gene transcriptional and translational processes.

LIMITATIONS, REASONS FOR CAUTION

Findings in mouse placental tissues may not be fully representative of human placentas. Further studies are necessary to confirm these findings and determine their clinical significance.

WIDER IMPLICATIONS OF THE FINDINGS

Our study is the first to provide the genome-wide analysis of gene expression dysregulation caused by DNA methylation during IVF placentation. Systematic understanding of the molecular mechanisms implicated in IVF placentation can be useful for the improvement of existing assisted conception systems to prevent these IVF-associated safety concerns.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by grants from the National Natural Science Foundation of China (No. 31472092), and the National High-Tech R&D Program (Nos. 2011|AA100303, 2013AA102506). There was no conflict of interest.

Intrauterine trophoblast migration: A comparative view of humans and rodents

Trophoblast migration and invasion through the decidua and maternal uterine spiral arteries are crucial events in placentation. During this process, invasive trophoblast replace vascular endothelial cells as the uterine arteries are remodeled to form more permissive vessels that facilitate adequate blood flow to the growing fetus. Placentation failures resulting from either extensive or shallow trophoblastic invasion can cause pregnancy complications such as preeclampsia, intrauterine growth restriction, placenta creta, gestational trophoblastic disease and even maternal or fetal death. Consequently, the use of experimental animal models such as rats and mice has led to great progress in recent years with regards to the identification of mechanisms and factors that control trophoblast migration kinetics. This review aims to perform a comparative analysis of placentation and the mechanisms and factors that coordinate intrauterine trophoblast migration in humans, rats and mice under physiological and pathological conditions.

Changes in the enhancer landscape during early placental development uncover a trophoblast invasion gene-enhancer network

INTRODUCTION

Trophoblast invasion establishes adequate blood flow between mother and fetus in early placental development. However, little is known about the cis-regulatory mechanisms underlying this important process. We aimed to identify enhancer elements that are active during trophoblast invasion, and build a trophoblast invasion gene-enhancer network.

METHODS

We carried out ChIP-Seq for an enhancer-associated mark (H3k27Ac) at two time points during early placental development in mouse. One time point when invasion is at its peak (e7.5) and another time point shortly afterwards (e9.5). We use computational analysis to identify putative enhancers, as well as the transcription factor binding sites within them, that are specific to the time point of trophoblast invasion.

RESULTS

We compared read profiles at e7.5 and e9.5 to identify 1,977 e7.5-specific enhancers. Within a subset of e7.5-specific enhancers, we discovered a cell migration associated regulatory code, consisting of three transcription factor motifs: AP1, Ets, and Tcfap2. To validate differential expression of the transcription factors that bind these motifs, we performed RNA-Seq in the same context. Finally, we integrated these data with publicly available protein-protein interaction data and constructed a trophoblast invasion gene-enhancer network.

DISCUSSION

The data we generated and analysis we carried out improves our understanding of the regulatory mechanisms of trophoblast invasion, by suggesting a transcriptional code exists in the enhancers of cell migration genes. Furthermore, the network we constructed highlights novel candidate genes that may be critical for trophoblast invasion.

Determination of PCNA, cyclin D3, p27, p57 and apoptosis rate in normal and dexamethasone-induced intrauterine growth restricted rat placentas

Intrauterine growth restriction (IUGR) is a major clinical problem, which causes perinatal morbidity and mortality. One of the reasons for IUGR is abnormal placentation. In rats, fetal-placental exposure to maternally administered glucocorticoids decreases birth weight and placental weight. Proper placental development depends on the proliferation and differentiation of trophoblasts. Our knowledge about the mitotic regulators that play key roles in synchronizing these events is limited. Also the mechanisms underlying the placental growth inhibitory effects of glucocorticoids have not been elucidated. The aim of this study was to investigate the immunolocalization, mRNA and protein levels of proliferating cell nuclear antigen (PCNA), cyclin D3, p27 and p57 in normal and dexamethasone-induced IUGR Wistar rat placentas by reverse transcriptase polymerase chain reaction (RT-PCR), immunohistochemistry and Western blot. We also compared apoptotic cell numbers at the light microscopic level via terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) and transmission electron microscopy. Glucocorticoid levels were higher in IUGR rats than in control rats after 60 and 120min of injection. We showed reduced gene and protein expressions of PCNA and cyclin D3 and increased expressions of p27 and p57 in IUGR placentas compared to control placentas. Apoptotic cell number was higher in the placentas of the IUGR group. In brief we found that maternal dexamethasone treatment led to a shift from cell proliferation to apoptosis in IUGR placentas. Dexamethasone induced placental and embryonal abnormalities which could be associated with reduced expressions of PCNA and cyclin D3, increased expressions of p27 and p57 and increased rate of apoptosis in IUGR placentas.

Expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and peroxiredoxin 6 (Prdx6) proteins in healthy and pathologic placentas of human and rat

A relationship has been shown between preeclampsia (PE) and intrauterine growth restriction (IUGR) and oxidative stress (OS). Since such pregnancies experience OS, we aimed to detect the distribution pattern and expression levels of a transcription factor, Nuclear factor erythroid 2-related factor-2 (Nrf2) that has a role in the regulation of antioxidant enzymes, and peroxiredoxin 6 (Prdx6) an antioxidant enzyme, in human healthy, IUGR, PE and in groups of rat healthy and IUGR placentas using immunohistochemistry and Western blotting. Both Nrf2 and Prdx6 immunoreactivities were weaker in human and rat IUGR group placentas compared to human and rat control group placentas, respectively. Nrf2 and Prdx6 were immunostained in labyrinth trophoblasts, decidua, giant, glycogen and fetal vessel endothelial cells in rat control and IUGR group placentas. Nrf2 and Prdx6 immunoreactivities were seen in the decidua, syncytiotrophoblasts, villous stromal cells, and vascular endothelium in human control, IUGR and PE group placentas. Results of Nrf2 and Prdx6 Western blotting applied for rat and human placentas were compatible with the results of Nrf2 and Prdx6 immunohistochemical observations with regard to rat and human placentas. Down-regulation of Nrf2 and Prdx6 proteins in human and rat IUGR group placentas may have led to the formation of OS which may have impaired proliferation and invasion of cytotrophoblasts.

Major mouse placental compartments revealed by diffusion-weighted MRI, contrast-enhanced MRI, and fluorescence imaging

Mammalian models, and mouse studies in particular, play a central role in our understanding of placental development. Magnetic resonance imaging (MRI) could be a valuable tool to further these studies, providing both structural and functional information. As fluid dynamics throughout the placenta are driven by a variety of flow and diffusion processes, diffusion-weighted MRI could enhance our understanding of the exchange properties of maternal and fetal blood pools--and thereby of placental function. These studies, however, have so far been hindered by the small sizes, the unavoidable motions, and the challenging air/water/fat heterogeneities, associated with mouse placental environments. The present study demonstrates that emerging methods based on the spatiotemporal encoding (SPEN) of the MRI information can robustly overcome these obstacles. Using SPEN MRI in combination with albumin-based contrast agents, we analyzed the diffusion behavior of developing placentas in a cohort of mice. These studies successfully discriminated the maternal from the fetal blood flows; the two orders of magnitude differences measured in these fluids' apparent diffusion coefficients suggest a nearly free diffusion behavior for the former and a strong flow-based component for the latter. An intermediate behavior was observed by these methods for a third compartment that, based on maternal albumin endocytosis, was associated with trophoblastic cells in the interphase labyrinth. Structural features associated with these dynamic measurements were consistent with independent intravital and ex vivo fluorescence microscopy studies and are discussed within the context of the anatomy of developing mouse placentas.

Essential role of the ERK/MAPK pathway in blood-placental barrier formation

The mammalian genome contains two ERK/MAP kinase kinase genes, Map2k1 and Map2k2, which encode dual-specificity kinases responsible for ERK activation. Loss of Map2k1 function in mouse causes embryonic lethality due to placental defects, whereas Map2k2 mutants have a normal lifespan. The majority of Map2k1(+/-) Map2k2(+/-) embryos die during gestation from the underdevelopment of the placenta labyrinth, demonstrating that both kinases are involved in placenta formation. Map2k1(+/-) Map2k2(+/-) mutants show reduced vascularization of the labyrinth and defective formation of syncytiotrophoblast layer II (SynT-II) leading to the accumulation of multinucleated trophoblast giant cells (MTGs). To define the cell type-specific contribution of the ERK/MAPK pathway to placenta development, we performed deletions of Map2k1 function in different Map2k1 Map2k2 allelic backgrounds. Loss of MAP kinase kinase activity in pericytes or in allantois-derived tissues worsens the MTG phenotype. These results define the contribution of the ERK/MAPK pathway in specific embryonic and extraembryonic cell populations for normal placentation. Our data also indicate that MTGs could result from the aberrant fusion of SynT-I and -II. Using mouse genetics, we demonstrate that the normal development of SynT-I into a thin layer of multinucleated cells depends on the presence of SynT-II. Lastly, the combined mutations of Map2k1 and Map2k2 alter the expression of several genes involved in cell fate specification, cell fusion and cell polarity. Thus, appropriate ERK/MAPK signaling in defined cell types is required for the proper growth, differentiation and morphogenesis of the placenta.

A novel combination of homeobox genes is expressed in mesenchymal chorionic stem/stromal cells in first trimester and term pregnancies

Human chorionic mesenchymal stem/stromal cells (CMSCs) derived from the placenta are similar to adult tissue-derived MSCs. The aim of this study was to investigate the role of these cells in normal placental development. Transcription factors, particularly members of the homeobox gene family, play crucial roles in maintaining stem cell proliferation and lineage specification in embryonic tissues. In adult tissues and organs, stem cells proliferate at low levels in their niche until they receive cues from the microenvironment to differentiate. The homeobox genes that are expressed in the CMSC niche in placental tissues have not been identified. We used the novel strategy of laser capture microdissection to isolate the stromal component of first trimester villi and excluded the cytotrophoblast and syncytiotrophoblast layers that comprise the outer layer of the chorionic villi. Microarray analysis was then used to screen for homeobox genes in the microdissected tissue. Candidate homeobox genes were selected for further RNA analysis. Immunohistochemistry of candidate genes in first trimester placental villous stromal tissue revealed homeobox genes Meis1, myeloid ectropic viral integration site 1 homolog 2 (MEIS2), H2.0-like Drosophila (HLX), transforming growth factor β-induced factor (TGIF), and distal-less homeobox 5 (DLX5) were expressed in the vascular niche where CMSCs have been shown to reside. Expression of MEIS2, HLX, TGIF, and DLX5 was also detected in scattered stromal cells. Real-time polymerase chain reaction and immunocytochemistry verified expression of MEIS2, HLX, TGIF, and DLX5 homeobox genes in first trimester and term CMSCs. These data suggest a combination of regulatory homeobox genes is expressed in CMSCs from early placental development to term, which may be required for stem cell proliferation and differentiation.

Mst1 and mst2 are essential regulators of trophoblast differentiation and placenta morphogenesis

The placenta is essential for survival and growth of the fetus because it promotes the delivery of nutrients and oxygen from the maternal circulation as well as fetal waste disposal. Mst1 and Mst2 (Mst1/2), key components of the mammalian hpo/Mst signaling pathway, encode two highly conserved Ser/Thr kinases and play important roles in the prevention of tumorigenesis and autoimmunity, control of T cell development and trafficking, and embryonic development. However, their functions in placental development are not fully understood, and the underlying cellular and molecular mechanisms remain elusive. Here, we investigated the functions of Mst1/2 in mouse placental development using both conventional and conditional (endothelial) Mst1/2 double knockout mice. We found that the number of trophoblast giant cells dramatically increased while spongiotrophoblast cells almost completely disappeared in Mst1/2 deficient placentas. We showed that Mst1/2 deficiency down regulated the expression of Mash2, which is required for suppressing the differentiation of trophoblast giant cells. Furthermore, we demonstrated that endothelial-specific deletion of Mst1/2 led to impaired placental labyrinthine vasculature and embryonic lethality at E11.5, but neither affected vasculature in yolk sac and embryo proper nor endocardium development. Collectively, our findings suggest that Mst1/2 regulate placental development by control of trophoblast cell differentiation and labyrinthine vasculature at midgestation and Mst1/2 control labyrinth morphogenesis in trophoblast- and fetal endothelial-dependent manners. Thus, our studies have defined novel roles of Mst1/2 in mouse placental development.

The nexus of prematurity, birth defects, and intrauterine growth restriction: a role for plac1-regulated pathways

Epidemiological studies have demonstrated an increased prevalence of birth defects and intrauterine growth restriction (IUGR) among infants born prematurely suggesting they share common biological determinants. The identification of key regulatory pathways contributing to this nexus is essential to ongoing efforts to develop effective intervention strategies. Plac1 is a paternally imprinted and X-linked gene that conforms to this paradigm. Examination of a mutant mouse model has confirmed that Plac1 is essential for normal placental development and function. Moreover, it is expressed throughout the developing embryo indicating that it also has broad relevance to embryogenesis. Most notably, its absence in the developing embryo is associated with abnormal brain development and an increased risk of lethal, postnatal hydrocephalus identifying it as a novel, X-linked determinant of brain development. The essential and non-redundant roles of Plac1 in placental and neurological development represent a novel regulatory paradigm for embryonic growth and pregnancy maintenance. Regulatory pathways influenced, in part, by Plac1 are likely to contribute to the observed nexus of IUGR, prematurity, and birth defects.

Review: placental homeobox genes and their role in regulating human fetal growth

The regulation of fetal growth is multifactorial and complex. Normal fetal growth is determined by the genetically predetermined growth potential and further modulated by maternal, fetal, placental, and environmental factors. The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface is controlled by several growth factors, cytokines and transcription factors including homeobox genes. This review summarizes our current knowledge regarding homeobox genes in the human placenta and their differential expression and functions in human idiopathic fetal growth restriction (FGR). The review also describes the research strategies that were used for the identification of homeobox genes, their expression in FGR, functional role and target genes of homeobox genes in the trophoblasts and the hormonal regulators of homeobox gene expression in vitro. A better understanding of molecular pathways driven by placental homeobox genes and further elucidation of signaling pathways underlying the hormone-mediated homeobox gene developmental programs may offer novel strategies of targeted therapy for improving feto-placental growth in idiopathic FGR pregnancies.

Environmental origins of congenital heart disease: the heart-placenta connection

Although the mammalian embryo is well protected in the uterus, environmental chemicals, drugs, and maternal nutritional imbalances can interfere with regulatory pathways directing placental and embryonic development early in gestation. Embryonic cells are most susceptible to environmental influences during cellular specification and differentiation stages. Because biochemical differentiation precedes morphological outcome often by days, the period of susceptibility to environmental chemicals expectedly precedes visible morphogenic effects. The cellular mechanisms by which drugs and other environmental factors disrupt embryonic development and induce cardiac abnormalities have remained undefined.