Dissecting the first transcriptional divergence during human embryonic development

Ectopic expression of DNMT3L in human trophoblast stem cells restores features of the placental methylome

The placental DNA methylation landscape is unique, with widespread partially methylated domains (PMDs). The placental "methylome" is conserved across mammals, a shared feature of many cancers, and extensively studied for links with pregnancy complications. Human trophoblast stem cells (hTSCs) offer exciting potential for functional studies to better understand this epigenetic feature; however, whether the hTSC epigenome recapitulates primary trophoblast remains unclear. We find that hTSCs exhibit an atypical methylome compared with trophectoderm and 1st trimester cytotrophoblast. Regardless of cell origin, oxygen levels, or culture conditions, hTSCs show localized DNA methylation within transcribed gene bodies and a complete loss of PMDs. Unlike early human trophoblasts, hTSCs display a notable absence of DNMT3L expression, which is necessary for PMD establishment in mouse trophoblasts. Remarkably, we demonstrate that ectopic expression of DNMT3L in hTSCs restores placental PMDs, supporting a conserved role for DNMT3L in de novo methylation in trophoblast development in human embryogenesis.

Transcription factor AP-2 gamma affects porcine early embryo development by regulating epigenetic modification

RESEARCH QUESTION

What is the role and mechanism of action of transcription factor AP-2 gamma (TFAP2C) in porcine early embryo development?

DESIGN

TFAP2C siRNA were injected into porcine oocytes, which subsequently underwent IVF. Different stages of embryos were collected for RNA sequencing, quantitative polymerase chain reaction, immunofluorescence staining to explore the affects in gene expression and epigenetic modification. Porcine fetal fibroblasts were transfected with siRNA, and cells were collected for chromatin immunoprecipitation and dual luciferase reporter assays.

RESULTS

The deficiency of TFAP2C led to disorders in early embryonic development; 1208 genes were downregulated and 792 genes were upregulated in TFAP2C knockdown (TFAP2C-KD) embryos. The expression of epigenetic modification enzymes KDM5B, SETD2 were significantly elevated in the TFAP2C-KD group (P < 0.001). Meanwhile, the modification levels of H3K4me3 and H3K4me2 were significantly decreased (P = 0.0021, P = 0.0029), and H3K36me3 and DNA methylation were significantly increased in TFAP2C-KD group (P = 0.0045, P = 0.0025). DNMT1 was mainly expressed in nuclei in the TFAP2C-KD group (P = 0.0103). In addition, TFAP2C could bind to the promoter region of SETD2, and the mutation of the TFAP2C binding site resulted in increased activity of SETD2 promoter (P < 0.001).

CONCLUSIONS

The knockdown of TFAP2C affects early embryonic development by regulating histone modification and DNA methylation.

Discovery of Pathogenic Variants Associated with Idiopathic Recurrent Pregnancy Loss Using Whole-Exome Sequencing

Idiopathic recurrent pregnancy loss (RPL) is defined as at least two pregnancy losses before 20 weeks of gestation. Approximately 5% of pregnant couples experience idiopathic RPL, which is a heterogeneous disease with various causes including hormonal, chromosomal, and intrauterine abnormalities. Although how pregnancy loss occurs is still unknown, numerous biological factors are associated with the incidence of pregnancy loss, including genetic variants. Whole-exome sequencing (WES) was conducted on blood samples from 56 Korean patients with RPL and 40 healthy controls. The WES data were aligned by means of bioinformatic analysis, and the detected variants were annotated using machine learning tools to predict the pathogenicity of protein alterations. Each indicated variant was confirmed using Sanger sequencing. A replication study was also conducted in 112 patients and 114 controls. The Variant Effect Scoring Tool, Combined Annotation Dependent Depletion tool, Sorting Intolerant from Tolerant annotation tool, and various databases detected 10 potential variants previously associated with spontaneous abortion genes in patients by means of a bioinformatic analysis of WES data. Several variants were detected in more than one patient. Interestingly, several of the detected genes were functionally clustered, including some with a secretory function (mucin 4; MUC4; rs200737893 G>A and hyaluronan-binding protein 2; HABP2; rs542838125 G>T), in which growth arrest-specific 2 Like 2 (GAS2L2; rs140842796 C>T) and dynamin 2 (DNM2; rs763894364 G>A) are functionally associated with cell protrusion and the cytoskeleton. ATP Binding Cassette Subfamily C Member 6 (ABCC6) was the only gene with two variants. HABP2 (rs542838125 G>T), MUC4 (rs200737893 G>A), and GAS2L2 (rs140842796 C>T) were detected in only the patient group in the replication study. The combination of WES and machine learning tools is a useful method to detect potential variants associated with RPL. Using bioinformatic tools, we found 10 potential variants in 9 genes. WES data from patients are needed to better understand the causes of RPL.

VGLL1 cooperates with TEAD4 to control human trophectoderm lineage specification

In contrast to rodents, the mechanisms underlying human trophectoderm and early placenta specification are understudied due to ethical barriers and the scarcity of embryos. Recent reports have shown that human pluripotent stem cells (PSCs) can differentiate into trophectoderm (TE)-like cells (TELCs) and trophoblast stem cells (TSCs), offering a valuable in vitro model to study early placenta specification. Here, we demonstrate that the VGLL1 (vestigial-like family member 1), which is highly expressed during human and non-human primate TE specification in vivo but is negligibly expressed in mouse, is a critical regulator of cell fate determination and self-renewal in human TELCs and TSCs derived from naïve PSCs. Mechanistically, VGLL1 partners with the transcription factor TEAD4 (TEA domain transcription factor 4) to regulate chromatin accessibility at target gene loci through histone acetylation and acts in cooperation with GATA3 and TFAP2C. Our work is relevant to understand primate early embryogenesis and how it differs from other mammalian species.

Development of a human iPSC-derived placental barrier-on-chip model

Although recently developed placenta-on-chip systems opened promising perspectives for placental barrier modeling, they still lack physiologically relevant trophoblasts and are poorly amenable to high-throughput studies. We aimed to implement human-induced pluripotent stem cells (hiPSC)-derived trophoblasts into a multi-well microfluidic device to develop a physiologically relevant and scalable placental barrier model. When cultured in a perfused micro-channel against a collagen-based matrix, hiPSC-derived trophoblasts self-arranged into a 3D structure showing invasive behavior, fusogenic and endocrine activities, structural integrity, and expressing placental transporters. RNA-seq analysis revealed that the microfluidic 3D environment boosted expression of genes related to early placental structural development, mainly involved in mechanosensing and cell surface receptor signaling. These results demonstrated the feasibility of generating a differentiated primitive syncytium from hiPSC in a microfluidic platform. Besides expanding hiPSC-derived trophoblast scope of applications, this study constitutes an important resource to improve placental barrier models and boost research and therapeutics evaluation in pregnancy.

Biology of Cancer-Testis Antigens and Their Therapeutic Implications in Cancer

Tumour-specific antigens have been an area of interest in cancer therapy since their discovery in the middle of the 20th century. In the era of immune-based cancer therapeutics, redirecting our immune cells to target these tumour-specific antigens has become even more relevant. Cancer-testis antigens (CTAs) are a class of antigens with an expression specific to the testis and cancer cells. CTAs have also been demonstrated to be expressed in a wide variety of cancers. Due to their frequency and specificity of expression in a multitude of cancers, CTAs have been particularly attractive as cancer-specific therapeutic targets. There is now a rapid expansion of CTAs being identified and many studies have been conducted to correlate CTA expression with cancer and therapy-resistant phenotypes. Furthermore, there is an increasing number of clinical trials involving using some of these CTAs as molecular targets in pharmacological and immune-targeted therapeutics for various cancers. This review will summarise the current knowledge of the biology of known CTAs in tumorigenesis and the regulation of CTA genes. CTAs as molecular targets and the therapeutic implications of these CTA-targeted anticancer strategies will also be discussed.

Single-cell multi-omics of human preimplantation embryos shows susceptibility to glucocorticoids

The preconceptual, intrauterine, and early life environments can have a profound and long-lasting impact on the developmental trajectories and health outcomes of the offspring. Given the relatively low success rates of assisted reproductive technologies (ART; ∼25%), additives and adjuvants, such as glucocorticoids, are used to improve the success rate. Considering the dynamic developmental events that occur during this window, these exposures may alter blastocyst formation at a molecular level, and as such, affect not only the viability of the embryo and the ability of the blastocyst to implant, but also the developmental trajectory of the first three cell lineages, ultimately influencing the physiology of the embryo. In this study, we present a comprehensive single-cell transcriptome, methylome, and small RNA atlas in the day 7 human embryo. We show that, despite no change in morphology and developmental features, preimplantation glucocorticoid exposure reprograms the molecular profile of the trophectoderm (TE) lineage, and these changes are associated with an altered metabolic and inflammatory response. Our data also suggest that glucocorticoids can precociously mature the TE sublineages, supported by the presence of extravillous trophoblast markers in the polar sublineage and presence of X Chromosome dosage compensation. Further, we have elucidated that epigenetic regulation-DNA methylation and microRNAs (miRNAs)-likely underlies the transcriptional changes observed. This study suggests that exposures to exogenous compounds during preimplantation may unintentionally reprogram the human embryo, possibly leading to suboptimal development and longer-term health outcomes.

The microRNA cluster C19MC confers differentiation potential into trophoblast lineages upon human pluripotent stem cells

The first cell fate commitment during mammalian development is the specification of the inner cell mass and trophectoderm. This irreversible cell fate commitment should be epigenetically regulated, but the precise mechanism is largely unknown in humans. Here, we show that naïve human embryonic stem (hES) cells can transdifferentiate into trophoblast stem (hTS) cells, but primed hES cells cannot. Our transcriptome and methylome analyses reveal that a primate-specific miRNA cluster on chromosome 19 (C19MC) is active in naïve hES cells but epigenetically silenced in primed ones. Moreover, genome and epigenome editing using CRISPR/Cas systems demonstrate that C19MC is essential for hTS cell maintenance and C19MC-reactivated primed hES cells can give rise to hTS cells. Thus, we reveal that C19MC activation confers differentiation potential into trophoblast lineages on hES cells. Our findings are fundamental to understanding the epigenetic regulation of human early development and pluripotency.

Little is known about the epigenetic mechanisms of the first cell fate commitment in humans. Here, the authors show that activation of the miRNA cluster C19MC confers differentiation potential into trophoblast lineages on human embryonic stem cells.

Polycomb repressive complex 2 shields naïve human pluripotent cells from trophectoderm differentiation

The first lineage choice in human embryo development separates trophectoderm from the inner cell mass. Naïve human embryonic stem cells are derived from the inner cell mass and offer possibilities to explore how lineage integrity is maintained. Here, we discover that polycomb repressive complex 2 (PRC2) maintains naïve pluripotency and restricts differentiation to trophectoderm and mesoderm lineages. Through quantitative epigenome profiling, we found that a broad gain of histone H3 lysine 27 trimethylation (H3K27me3) is a distinct feature of naïve pluripotency. We define shared and naïve-specific bivalent promoters featuring PRC2-mediated H3K27me3 concomitant with H3K4me3. Naïve bivalency maintains key trophectoderm and mesoderm transcription factors in a transcriptionally poised state. Inhibition of PRC2 forces naïve human embryonic stem cells into an 'activated' state, characterized by co-expression of pluripotency and lineage-specific transcription factors, followed by differentiation into either trophectoderm or mesoderm lineages. In summary, PRC2-mediated repression provides a highly adaptive mechanism to restrict lineage potential during early human development.

BMP-treated human embryonic stem cells transcriptionally resemble amnion cells in the monkey embryo

Human embryonic stem cells (hESCs) possess an immense potential to generate clinically relevant cell types and unveil mechanisms underlying early human development. However, using hESCs for discovery or translation requires accurately identifying differentiated cell types through comparison with their in vivo counterparts. Here, we set out to determine the identity of much debated BMP-treated hESCs by comparing their transcriptome to recently published single cell transcriptomic data from early human embryos ( Xiang et al., 2020). Our analyses reveal several discrepancies in the published human embryo dataset, including misclassification of putative amnion, intermediate and inner cell mass cells. These misclassifications primarily resulted from similarities in pseudogene expression, highlighting the need to carefully consider gene lists when making comparisons between cell types. In the absence of a relevant human dataset, we utilized the recently published single cell transcriptome of the early post implantation monkey embryo to discern the identity of BMP-treated hESCs. Our results suggest that BMP-treated hESCs are transcriptionally more similar to amnion cells than trophectoderm cells in the monkey embryo. Together with prior studies, this result indicates that hESCs possess a unique ability to form mature trophectoderm subtypes via an amnion-like transcriptional state.

This article has an associated First Person interview with the first author of the paper.

Summary: We show that BMP-treated human embryonic stem cells (hESCs) are more likely to represent an amnion rather than a trophectoderm cell type.

Placental DNA methylation signatures of maternal smoking during pregnancy and potential impacts on fetal growth

Maternal smoking during pregnancy (MSDP) contributes to poor birth outcomes, in part through disrupted placental functions, which may be reflected in the placental epigenome. Here we present a meta-analysis of the associations between MSDP and placental DNA methylation (DNAm) and between DNAm and birth outcomes within the Pregnancy And Childhood Epigenetics (PACE) consortium (N = 1700, 344 with MSDP). We identify 443 CpGs that are associated with MSDP, of which 142 associated with birth outcomes, 40 associated with gene expression, and 13 CpGs are associated with all three. Only two CpGs have consistent associations from a prior meta-analysis of cord blood DNAm, demonstrating substantial tissue-specific responses to MSDP. The placental MSDP-associated CpGs are enriched for environmental response genes, growth-factor signaling, and inflammation, which play important roles in placental function. We demonstrate links between placental DNAm, MSDP and poor birth outcomes, which may better inform the mechanisms through which MSDP impacts placental function and fetal growth.

Side-Population Trophoblasts Exhibit the Differentiation Potential of a Trophoblast Stem Cell Population, Persist to Term, and are Reduced in Fetal Growth Restriction

BACKGROUND

Fetal growth restriction often results from poor placental function and is a major cause of stillbirth. Clinically, fetal growth restriction is difficult to diagnose and currently has no effective treatment. Trophoblasts are unique placental cells that form the feto-maternal interface and facilitate nutrient and gas exchange. Fetal growth restriction is linked to inadequate trophoblast function. However, our understanding of the mechanisms underlying this dysfunction are poor, in part because of our inability to isolate and study the trophoblast stem cells from which mature trophoblasts arise in pathologic pregnancies.

METHODS

Cells isolated from first-trimester placentae using the Hoechst side-population technique were propagated or differentiated into mature trophoblasts. Side-population trophoblasts were isolated from normal third-trimester and growth restricted placentae using the same technique. First and third-trimester side-population trophoblasts were compared by microarray analysis.

RESULTS

First-trimester side-population trophoblasts could be propagated in an undifferentiated state or differentiated, via intermediate cytotrophoblasts, into syncytiotrophoblast or extravillous trophoblasts. Using the same technique, side-population trophoblasts could be isolated from term placentae for the first time, demonstrating that while they were present at consistent levels throughout gestation (~3·5%), side-population trophoblasts were significantly depleted in growth restricted pregnancies (0·32%).

CONCLUSIONS

Our novel method of isolating a population of human trophoblast stem cell-like cells directly from human placental tissue throughout gestation provides the first insights into trophoblast dysfunction in pregnancy pathologies. The depletion of side-population trophoblasts in growth restricted placentae may contribute to poor placental function.

Genomics-Guided Drawing of Molecular and Pathophysiological Components of Malignant Regulatory Signatures Reveals a Pivotal Role in Human Diseases of Stem Cell-Associated Retroviral Sequences and Functionally-Active hESC Enhancers

Repetitive DNA sequences (repeats) colonized two-third of human genome and a majority of repeats comprised of transposable genetic elements (TE). Evolutionary distinct categories of TE represent nucleic acid sequences that are repeatedly copied from and pasted into chromosomes at multiple genomic locations and acquired a multitude of regulatory functions. Here, genomics-guided maps of stemness regulatory signatures were drawn to dissect the contribution of TE to clinical manifestations of malignant phenotypes of human cancers. From patients’ and physicians’ perspectives, the clinical definition of a tumor’s malignant phenotype could be restricted to the early diagnosis of sub-types of malignancies with the increased risk of existing therapy failure and high likelihood of death from cancer. It is the viewpoint from which the understanding of stemness and malignant regulatory signatures is considered in this contribution. Genomics-guided analyses of experimental and clinical observations revealed the pivotal role of human stem cell-associated retroviral sequences (SCARS) in the origin and pathophysiology of clinically-lethal malignancies. SCARS were defined as the evolutionary- and biologically-related family of genomic regulatory sequences, the principal physiological function of which is to create and maintain the stemness phenotype during human preimplantation embryogenesis. For cell differentiation to occur, SCARS expression must be silenced and SCARS activity remains repressed in most terminally-differentiated human cells which are destined to perform specialized functions in the human body. Epigenetic reprogramming, de-repression, and sustained activity of SCARS results in various differentiation-defective phenotypes. One of the most prominent tissue- and organ-specific clinical manifestations of sustained SCARS activities is diagnosed as a pathological condition defined by a consensus of morphological, molecular, and genetic examinations as the malignant growth. Here, contemporary evidence are acquired, analyzed, and reported defining both novel diagnostic tools and druggable molecular targets readily amenable for diagnosis and efficient therapeutic management of clinically-lethal malignancies. These diagnostic and therapeutic approaches are based on monitoring of high-fidelity molecular signals of continuing SCARS activities in conjunction with genomic regulatory networks of thousands’ functionally-active embryonic enhancers affecting down-stream phenotype-altering genetic loci. Collectively, reported herein observations support a model of SCARS-activation triggered singular source code facilitating the intracellular propagation and intercellular (systemic) dissemination of disease states in the human body.

Cross-species single-cell transcriptomic analysis reveals pre-gastrulation developmental differences among pigs, monkeys, and humans

Interspecies blastocyst complementation enables organ-specific enrichment of xenogeneic pluripotent stem cell (PSC) derivatives, which raises an intriguing possibility to generate functional human tissues/organs in an animal host. However, differences in embryo development between human and host species may constitute the barrier for efficient chimera formation. Here, to understand these differences we constructed a complete single-cell landscape of early embryonic development of pig, which is considered one of the best host species for human organ generation, and systematically compared its epiblast development with that of human and monkey. Our results identified a developmental coordinate of pluripotency spectrum among pigs, humans and monkeys, and revealed species-specific differences in: (1) pluripotency progression; (2) metabolic transition; (3) epigenetic and transcriptional regulations of pluripotency; (4) cell surface proteins; and (5) trophectoderm development. These differences may prevent proper recognition and communication between donor human cells and host pig embryos, resulting in low integration and survival of human cells. These results offer new insights into evolutionary conserved and divergent processes during mammalian development and may be helpful for developing effective strategies to overcome low human-pig chimerism, thereby enabling the generation of functional human organs in pigs in the future.

Impact of AHR Ligand TCDD on Human Embryonic Stem Cells and Early Differentiation

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, which mediates the effects of a variety of environmental stimuli in multiple tissues. Recent advances in AHR biology have underlined its importance in cells with high developmental potency, including pluripotent stem cells. Nonetheless, there is little data on AHR expression and its role during the initial stages of stem cell differentiation. The purpose of this study was to investigate the temporal pattern of AHR expression during directed differentiation of human embryonic stem cells (hESC) into neural progenitor, early mesoderm and definitive endoderm cells. Additionally, we investigated the effect of the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the gene expression profile in hESCs and differentiated cells by RNA-seq, accompanied by identification of AHR binding sites by ChIP-seq and epigenetic landscape analysis by ATAC-seq. We showed that AHR is differentially regulated in distinct lineages. We provided evidence that TCDD alters gene expression patterns in hESCs and during early differentiation. Additionally, we identified novel potential AHR target genes, which expand our understanding on the role of this protein in different cell types.

The unknown human trophectoderm: implication for biopsy at the blastocyst stage

Trophectoderm biopsy is increasingly performed for pre-implantation genetic testing of aneuploidies and considered a safe procedure on short-term clinical outcome, without strong assessment of long-term consequences. Poor biological information on human trophectoderm is available due to ethical restrictions. Therefore, most studies have been conducted in vitro (choriocarcinoma cell lines, embryonic and pluripotent stem cells) and on murine models that nevertheless poorly reflect the human counterpart. Polarization, compaction, and blastomere differentiation (e.g., the basis to ascertain trophectoderm origin) are poorly known in humans. In addition, the trophectoderm function is poorly known from a biological point of view, although a panoply of questionable and controversial microarray studies suggest that important genes overexpressed in trophectoderm are involved in pluripotency, metabolism, cell cycle, endocrine function, and implantation. The intercellular communication system between the trophectoderm cells and the inner cell mass, modulated by cell junctions and filopodia in the murine model, is obscure in humans. For the purpose of this paper, data mainly on primary cells from human and murine embryos has been reviewed. This review suggests that the trophectoderm origin and functions have been insufficiently ascertained in humans so far. Therefore, trophectoderm biopsy should be considered an experimental procedure to be undertaken only under approved rigorous experimental protocols in academic contexts.

Modeling human trophoblast, the placental epithelium at the maternal fetal interface

Appropriate human trophoblast lineage specification and differentiation is crucial for the establishment of normal placentation and maintenance of pregnancy. However, due to the lack of proper modeling systems, the molecular mechanisms of these processes are still largely unknown. Much of the early studies in this area have been based on animal models and tumor-derived trophoblast cell lines, both of which are suboptimal for modeling this unique human organ. Recent advances in regenerative and stem cell biology methods have led to development of novel in vitro model systems for studying human trophoblast. These include derivation of human embryonic and induced pluripotent stem cells and establishment of methods for the differentiation of these cells into trophoblast, as well as the more recent derivation of human trophoblast stem cells. In addition, advances in culture conditions, from traditional two-dimensional monolayer culture to 3D culturing systems, have led to development of trophoblast organoid and placenta-on-a-chip model, enabling us to study human trophoblast function in context of more physiologically accurate environment. In this review, we will discuss these various model systems, with a focus on human trophoblast, and their ability to help elucidate the key mechanisms underlying placental development and function. This review focuses on model systems of human trophoblast differentiation, including advantages and limitations of stem cell-based culture, trophoblast organoid, and organ-on-a-chip methods and their applications in understanding placental development and disease.

Placenta-Specific Genes, Their Regulation During Villous Trophoblast Differentiation and Dysregulation in Preterm Preeclampsia

The human placenta maintains pregnancy and supports the developing fetus by providing nutrition, gas-waste exchange, hormonal regulation, and an immunological barrier from the maternal immune system. The villous syncytiotrophoblast carries most of these functions and provides the interface between the maternal and fetal circulatory systems. The syncytiotrophoblast is generated by the biochemical and morphological differentiation of underlying cytotrophoblast progenitor cells. The dysfunction of the villous trophoblast development is implicated in placenta-mediated pregnancy complications. Herein, we describe gene modules and clusters involved in the dynamic differentiation of villous cytotrophoblasts into the syncytiotrophoblast. During this process, the immune defense functions are first established, followed by structural and metabolic changes, and then by peptide hormone synthesis. We describe key transcription regulatory molecules that regulate gene modules involved in placental functions. Based on transcriptomic evidence, we infer how villous trophoblast differentiation and functions are dysregulated in preterm preeclampsia, a life-threatening placenta-mediated obstetrical syndrome for the mother and fetus. In the conclusion, we uncover the blueprint for villous trophoblast development and its impairment in preterm preeclampsia, which may aid in the future development of non-invasive biomarkers for placental functions and early identification of women at risk for preterm preeclampsia as well as other placenta-mediated pregnancy complications.

An integrated genome-wide multi-omics analysis of gene expression dynamics in the preimplantation mouse embryo

Early mouse embryos have an atypical translational machinery that consists of cytoplasmic lattices and is poorly competent for translation. Hence, the impact of transcriptomic changes on the operational level of proteins is predicted to be relatively modest. To investigate this, we performed liquid chromatography–tandem mass spectrometry and mRNA sequencing at seven developmental stages, from the mature oocyte to the blastocyst, and independently validated our data by immunofluorescence and qPCR. We detected and quantified 6,550 proteins and 20,535 protein-coding transcripts. In contrast to the transcriptome – where changes occur early, mostly at the 2-cell stage – our data indicate that the most substantial changes in the proteome take place towards later stages, between the morula and blastocyst. We also found little to no concordance between the changes in protein and transcript levels, especially for early stages, but observed that the concordance increased towards the morula and blastocyst, as did the number of free ribosomes. These results are consistent with the cytoplasmic lattice-to-free ribosome transition being a key mediator of developmental regulation. Finally, we show how these data can be used to appraise the strengths and limitations of mRNA-based studies of pre-implantation development and expand on the list of known developmental markers.

Human placenta and trophoblast development: key molecular mechanisms and model systems

Abnormal placentation is considered as an underlying cause of various pregnancy complications such as miscarriage, preeclampsia and intrauterine growth restriction, the latter increasing the risk for the development of severe disorders in later life such as cardiovascular disease and type 2 diabetes. Despite their importance, the molecular mechanisms governing human placental formation and trophoblast cell lineage specification and differentiation have been poorly unravelled, mostly due to the lack of appropriate cellular model systems. However, over the past few years major progress has been made by establishing self-renewing human trophoblast stem cells and 3-dimensional organoids from human blastocysts and early placental tissues opening the path for detailed molecular investigations. Herein, we summarize the present knowledge about human placental development, its stem cells, progenitors and differentiated cell types in the trophoblast epithelium and the villous core. Anatomy of the early placenta, current model systems, and critical key regulatory factors and signalling cascades governing placentation will be elucidated. In this context, we will discuss the role of the developmental pathways Wingless and Notch, controlling trophoblast stemness/differentiation and formation of invasive trophoblast progenitors, respectively.

Transcriptional landscape changes during human embryonic stem cell derivation

STUDY QUESTION

What are the transcriptional changes occurring during the human embryonic stem cell (hESC) derivation process, from the inner cell mass (ICM) to post-ICM intermediate stage (PICMI) to hESC stage, that have downstream effects on pluripotency states and differentiation?

SUMMARY ANSWER

We reveal that although the PICMI is transcriptionally similar to the hESC profile and distinct from ICM, it exhibits upregulation of primordial germ cell (PGC) markers, dependence on leukemia inhibitory factor (LIF) signaling, upregulation of naïve pluripotency-specific signaling networks and appears to be an intermediate switching point from naïve to primed pluripotency.

WHAT IS KNOWN ALREADY

It is currently known that the PICMI exhibits markers of early and late-epiblast stage. It is suggested that hESCs acquire primed pluripotency features due to the upregulation of post-implantation genes in the PICMI which renders them predisposed towards differentiation cues. Despite this current knowledge, the transcriptional landscape changes during hESC derivation from ICM to hESC and the effect of PICMI on pluripotent state is still not well defined.

STUDY DESIGN, SIZE, DURATION

To gain insight into the signaling mechanisms that may govern the ICM to PICMI to hESC transition, comparative RNA sequencing (RNA-seq) analysis was performed on preimplantation ICMs, PICMIs and hESCs in biological and technical triplicates (n = 3).

PARTICIPANTS/MATERIALS, SETTING, AND METHODS

Primed hESCs (XX) were maintained in feeder-free culture conditions on Matrigel for two passages and approximately 50 cells were collected in biological and technical triplicates (n = 3). For ICM sample collection, Day 3, frozen-thawed human embryos were cultured up to day five blastocyst stage and only good quality blastocysts were subjected to laser-assisted micromanipulation for ICM collection (n = 3). Next, day six expanded blastocysts were cultured on mouse embryonic fibroblasts and manual dissection was performed on the PICMI outgrowths between post-plating Day 6 and Day 10 (n = 3). Sequencing of these samples was performed on NextSeq500 and statistical analysis was performed using edgeR (false discovery rate (FDR) < 0.05).

MAIN RESULTS AND THE ROLE OF CHANCE

Comparative RNA-seq data analysis revealed that 634 and 560 protein-coding genes were significantly up and downregulated in hESCs compared to ICM (FDR < 0.05), respectively. Upon ICM to PICMI transition, 471 genes were expressed significantly higher in the PICMI compared to ICM, while 296 genes were elevated in the ICM alone (FDR < 0.05). Principle component analysis showed that the ICM was completely distinct from the PICMI and hESCs while the latter two clustered in close proximity to each other. Increased expression of E-CADHERIN1 (CDH1) in ICM and intermediate levels in the PICMI was observed, while CDH2 was higher in hESCs, suggesting a role of extracellular matrix components in facilitating pluripotency transition during hESC derivation. The PICMI also showed regulation of naïve-specific LIF and bone morphogenetic protein signaling, differential regulation of primed pluripotency-specific fibroblast growth factor and NODAL signaling pathway components, upregulation of phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway (PI3K/AKT/mTORC), as well as predisposition towards the germ cell lineage, further confirmed by gene ontology analysis. Hence, the data suggest that the PICMI may serve as an intermediate pluripotency stage which, when subjected to an appropriate culture niche, could aid in enhancing naïve hESC derivation and germ cell differentiation efficiency.

LARGE-SCALE DATA

Gene Expression Omnibus (GEO) Accession number GSE119378.

LIMITATIONS, REASONS FOR CAUTION

Owing to the limitation in sample availability, the sex of ICM and PICMI have not been taken into consideration. Obtaining cells from the ICM and maintaining them in culture is not feasible as it will hamper the formation of PICMI and hESC derivation. Single-cell quantitative real-time PCR on low ICM and PICMI cell numbers, although challenging due to limited availability of human embryos, will be advantageous to further corroborate the RNA-seq data on transcriptional changes during hESC derivation process.

WIDER IMPLICATIONS OF THE FINDINGS

We elucidate the dynamics of transcriptional network changes from the naïve ICM to the intermediate PICMI stage and finally the primed hESC lines. We provide an in-depth understanding of the PICMI and its role in conferring the type of pluripotent state which may have important downstream effects on differentiation, specifically towards the PGC lineage. This knowledge contributes to our limited understanding of the true nature of the human pluripotent state in vitro.

STUDY FUNDING/COMPETING INTEREST(S)

This research is supported by the Concerted Research Actions funding from Bijzonder Onderzoeksfonds University Ghent (BOF GOA 01G01112).The authors declare no conflict of interest.

The Effect of Genetic Variation on the Placental Transcriptome in Humans

The knowledge of genetic variants shaping human placental transcriptome is limited and they are not cataloged in the Genotype-Tissue Expression project. So far, only one whole genome analysis of placental expression quantitative trait loci (eQTLs) has been published by Peng et al. (2017) with no external independent validation. We report the second study on the landscape of placental eQTLs. The study aimed to generate a high-confidence list of placental cis-eQTLs and to investigate their potential functional implications. Analysis of cis-eQTLs (±100 kbp from the gene) utilized 40 placental RNA sequencing and respective whole genome genotyping datasets. The identified 199 placental cis-eSNPs represented 88 independent eQTL signals (FDR < 5%). The most significant placental eQTLs (FDR < 10-5) modulated the expression of ribosomal protein RPL9, transcription factor ZSCAN9 and aminopeptidase ERAP2. The analysis confirmed 50 eSNP-eGenes pairs reported by Peng et al. (2017) and thus, can be claimed as robust placental eQTL signals. The study identified also 13 novel placental eGenes. Among these, ZSCAN9 is modulated by several eSNPs (experimentally validated: rs1150707) that have been also shown to affect the methylation level of genes variably escaping X-chromosomal inactivation. The identified 63 placental eGenes exhibited mostly mixed or ubiquitous expression. Functional enrichment analysis highlighted 35 Gene Ontology categories with the top ranking pathways "ruffle membrane" (FDR = 1.81 × 10-2) contributing to the formation of motile cell surface and "ATPase activity, coupled" (FDR = 2.88 × 10-2), critical for the membrane transport. Placental eGenes were also significantly enriched in pathways implicated in development, signaling and immune function. However, this study was not able to confirm a significant overrepresentation of genome-wide association studies top hits among the placental eSNP and eGenes, reported by Peng et al. (2017). The identified eSNPs were further analyzed in association with newborn and pregnancy traits. In the discovery step, a suggestive association was detected between the eQTL of ALPG (rs11678251) and reduced placental, newborn's and infant's weight. Meta-analysis across REPROMETA, HAPPY PREGNANCY, ALSPAC cohorts (n = 6830) did not replicate these findings. In summary, the study emphasizes the role of genetic variation in driving the transcriptome profile of the human placenta and the importance to explore further its functional implications.

Expression dynamics of Mage family genes during self-renewal and differentiation of mouse pluripotent stem and teratocarcinoma cells

The biological roles of cancer-testis antigens of the Melanoma antigen (Mage) family in mammalian development, stem cell differentiation and carcinogenesis are largely unknown. In order to understand the involvement of the Mage family genes in maintenance of normal and cancer stem cells, the expression patterns of Mage-a, Mage-b, Mage-d, Mage-e, Mage-h and Mage-l gene subfamilies were analyzed during the self-renewal and differentiation of mouse pluripotent stem and teratocarcinoma cells. Clustering analysis based on the gene expression profiles of undifferentiated and differentiating cell populations revealed strong correlations between Mage expression patterns and differentiation and malignant states. Gene co-expression analysis disclosed the potential contributions of Mage family members in self-renewal and differentiation of pluripotent stem and teratocarcinoma cells. Two gene clusters including Mage-a4 and Mage-a8, Mageb1, Mage-d1, Mage-d2, Mage-e1, Mage-l2 were identified as functional antagonists with opposing roles in the regulation of proliferation and differentiation of mouse pluripotent stem and teratocarcinoma cells. The identified aberrant expression patterns of Mage-a2, Mage-a6, Mage-b4, Mageb-16 and Mage-h1 in teratocarcinoma cells can be considered as specific teratocarcinoma biomarkers promoted the malignant phenotype. Our study first provides a model for the involvement of Mage family members in regulatory networks during the self-renewal and early differentiation of normal and cancerous stem cells for further research of the predicted functional modules and the development of new cancer treatment strategies.

Placenta Transcriptome Profiling in Intrauterine Growth Restriction (IUGR)

Intrauterine growth restriction (IUGR) is a serious pathological complication associated with compromised fetal development during pregnancy. The aim of the study was to broaden knowledge about the transcriptomic complexity of the human placenta by identifying genes potentially involved in IUGR pathophysiology. RNA-Seq data were used to profile protein-coding genes, detect alternative splicing events (AS), single nucleotide variant (SNV) calling, and RNA editing sites prediction in IUGR-affected placental transcriptome. The applied methodology enabled detection of 37,501 transcriptionally active regions and the selection of 28 differentially-expressed genes (DEGs), among them 10 were upregulated and 18 downregulated in IUGR-affected placentas. Functional enrichment annotation indicated that most of the DEGs were implicated in the processes of inflammation and immune disorders related to IUGR and preeclampsia. Additionally, we revealed that some genes (S100A13, GPR126, CTRP1, and TFPI) involved in the alternation of splicing events were mainly implicated in angiogenic-related processes. Significant SNVs were overlapped with 6533 transcripts and assigned to 2386 coding sequence (CDS), 1528 introns, 345 5' untranslated region (UTR), 1260 3'UTR, 918 non-coding RNA (ncRNA), and 10 intergenic regions. Within CDS regions, 543 missense substitutions with functional effects were recognized. Two known mutations (rs4575, synonymous; rs3817, on the downstream region) were detected within the range of AS and DEG candidates: PA28β and PINLYP, respectively. Novel genes that are dysregulated in IUGR were detected in the current research. Investigating genes underlying the IUGR is crucial for identification of mechanisms regulating placental development during a complicated pregnancy.

Single cell expression analysis of primate-specific retroviruses-derived HPAT lincRNAs in viable human blastocysts identifies embryonic cells co-expressing genetic markers of multiple lineages

Chromosome instability and aneuploidies occur very frequently in human embryos, impairing proper embryogenesis and leading to cell cycle arrest, loss of cell viability, and developmental failures in 50–80% of cleavage-stage embryos. This high frequency of cellular extinction events represents a significant experimental obstacle challenging analyses of individual cells isolated from human preimplantation embryos. We carried out single cell expression profiling of 241 individual cells recovered from 32 human embryos during the early and late stages of viable human blastocyst (VHB) differentiation. Classification of embryonic cells was performed solely based on expression patterns of human pluripotency-associated transcripts (HPAT), which represent a family of primate-specific transposable element-derived lincRNAs highly expressed in human embryonic stem cells and regulating nuclear reprogramming and pluripotency induction. We then validated our findings by analyzing transcriptomes of 1,708 individual cells recovered from more than 100 human embryos and 259 mouse cells from more than 40 mouse embryos at different stages of preimplantation embryogenesis. HPAT's expression-guided spatiotemporal reconstruction of human embryonic development inferred from single-cell expression analysis of VHB differentiation enabled identification of telomerase-positive embryonic cells co-expressing key pluripotency regulatory genes and genetic markers of three major lineages. Follow-up validation analyses confirmed the emergence in human embryos prior to lineage segregation of telomerase-positive cells co-expressing genetic markers of multiple lineages. Observations reported in this contribution support the hypothesis of a developmental pathway of creation embryonic lineages and extraembryonic tissues from telomerase-positive pre-lineage cells manifesting multi-lineage precursor phenotype.

The accessible chromatin landscape during conversion of human embryonic stem cells to trophoblast by bone morphogenetic protein 4

Human embryonic stem cells (hESCs) exposed to the growth factor bone morphogenetic protein 4 (BMP4) in the absence of FGF2 have been used as a model to study the development of placental development. However, little is known about the cis-regulatory mechanisms underlying this important process. In this study, we used the public available chromatin accessibility data of hESC H1 cells and BMP4-induced trophoblast (TB) cell lines to identify DNase I hypersensitive sites (DHSs) in the two cell lines, as well as the transcription factor (TF) binding sites within the DHSs. By comparing read profiles in H1 and TB, we identified 17 472 TB-specific DHSs. The TB-specific DHSs are enriched in terms of "blood vessel" and "trophectoderm," consisting of TF motifs family: Leucine Zipper, Helix-Loop-Helix, GATA, and ETS. To validate differential expression of the TFs binding to these motifs, we analyzed public available RNA-seq and microarray data in the same context. Finally, by integrating the protein-protein interaction data, we constructed a TF network for placenta development and identified top 20 key TFs through centrality analysis in the network. Our results indicate BMP4-induced TB system provided an invaluable model for the study of TB development and highlighted novel candidate genes in placenta development in human.

GATA2/3-TFAP2A/C transcription factor network couples human pluripotent stem cell differentiation to trophectoderm with repression of pluripotency

To elucidate the molecular basis of BMP4-induced differentiation of human pluripotent stem cells (PSCs) toward progeny with trophectoderm characteristics, we produced transcriptome, epigenome H3K4me3, H3K27me3, and CpG methylation maps of trophoblast progenitors, purified using the surface marker APA. We combined them with the temporally resolved transcriptome of the preprogenitor phase and of single APA+ cells. This revealed a circuit of bivalent TFAP2A, TFAP2C, GATA2, and GATA3 transcription factors, coined collectively the "trophectoderm four" (TEtra), which are also present in human trophectoderm in vivo. At the onset of differentiation, the TEtra factors occupy multiple sites in epigenetically inactive placental genes and in OCT4 Functional manipulation of GATA3 and TFAP2A indicated that they directly couple trophoblast-specific gene induction with suppression of pluripotency. In accordance, knocking down GATA3 in primate embryos resulted in a failure to form trophectoderm. The discovery of the TEtra circuit indicates how trophectoderm commitment is regulated in human embryogenesis.

Hypothesis about Transdifferentiation As Backbone of Malignancy

Background

Cancer is mainly watched through the prism of random mutations and related corruption of signaling pathways. However, it would seem puzzling to explain the tumor organization, pugnacity and steady evolution of the tumorous disease and, moreover, a systematic ascendancy over the healthy tissues, only through stochastic genomic alterations.

Malignancy specific properties

Considering the core characteristics of cancer cells, it appears that two major sets of properties are emerging, corresponding to well-identified physiological phenotypes, i.e., (1) the trophoblastic logistical functions for cell survival, protection, expansion, migration, and host-tissue conditioning for angiogenesis and immune tolerance and (2) the sexual functions for genome maintenance. To explain the resurgence of these trophoblastic and sexual phenotypes, a particular cell reprogramming, to be called “malignant transdifferentiation” in view of its key role in the precancer-to-cancer shift, appears to be a convincing hypothesis.

Perspectives

The concept of malignant transdifferentiation, in addition to oncogenic mutations, would determine a more rational approach of oncogenesis and would open so far unexplored ways of therapeutic actions. Indeed, the trophoblastic phenotype would be a good candidate for therapeutic purposes because, on the one hand, it covers numerous properties that all are vital for the tumor, and on the other hand, it can be targeted with potentially no risk of affecting the healthy tissues as it is not expressed there after birth.

DNA methylation signature of long noncoding RNA genes during human pre-implantation embryonic development

DNA methylation have crucial roles in regulating the expression of developmental genes during mammalian pre-implantation embryonic development (PED). However, the DNA methylation dynamic pattern of long noncoding RNA (lncRNA) genes, one type of epigenetic regulators, in human PED have not yet been demonstrated. Here, we performed a comprehensive analysis of lncRNA genes in human PED based on public reduced representation bisulphite sequencing (RRBS) data. We observed that both lncRNA and protein-coding genes complete the major demethylation wave at the 2-cell stage, whereas the promoters of lncRNA genes show higher methylation level than protein-coding genes during PED. Similar methylation distribution was observed across the transcription start sites (TSS) of lncRNA and protein-coding genes, contrary to previous observations in tissues. Besides, not only the gamete-specific differentially methylated regions (G-DMRs) but also the embryonic developmental-specific DMRs (D-DMRs) showed more paternal bias, especially in promoter regions in lncRNA genes. Moreover, coding-non-coding gene co-expression network analysis of genes containing D-DMRs suggested that lncRNA genes involved in PED are associated with gene expression regulation through several means, such as mRNA splicing, translational regulation and mRNA catabolic. This firstly provides study provides the methylation profiles of lncRNA genes in human PED and improves the understanding of lncRNA genes involvement in human PED.

Comprehensive chromosome screening and gene expression analysis from the same biopsy in human preimplantation embryos

STUDY QUESTION

Can simultaneous comprehensive chromosome screening (CCS) and gene expression analysis be performed on the same biopsy of preimplantation human embryos?

SUMMARY ANSWER

For the first time, CCS and reliable gene expression analysis have been performed on the same human preimplantation embryo biopsy.

WHAT IS KNOWN ALREADY

A single trophectoderm (TE) biopsy is routinely used for many IVF programs offering CCS for selection of only chromosomally normal embryos for transfer. Although the gene expression profiling of human preimplantation embryos has been described, to date no protocol allows for simultaneous CCS and gene expression profiling from a single TE biopsy.

STUDY DESIGN, SIZE AND DURATION

This is a proof of concept and validation study structured in two phases. In Phase 1, cell lines were subjected to a novel protocol for combined CCS and gene expression analysis so as to validate the accuracy and reliability of the proposed protocol. In Phase 2, 20 donated human blastocysts were biopsied and processed with the proposed protocol in order to obtain an accurate CCS result and characterize their gene expression profiles using the same starting material.

PARTICIPANTS/MATERIALS, SETTING AND METHOD

A novel protocol coupling quantitative real-time PCR-based CCS and gene expression analysis using RT-PCR was designed for this study. Phase 1: six-cell aliquots of well-characterized fibroblast cell lines (GM00323, 46,XY and GM04435, 48,XY,+16,+21) were subjected to the proposed protocol. CCS results were compared with the known karyotypes for consistency, and gene expression levels were compared with levels of purified RNA from same cell lines for validation of reliable gene expression profiling. Phase 2: four biopsies were performed on 20 frozen human blastocysts previously diagnosed as trisomy 21 (10 embryos) and monosomy 21 (10 embryos) by CCS. All samples were processed with the proposed protocol and re-evaluated for concordance with the original CCS result. Their gene expression profiles were characterized and differential gene expression among embryos and early embryonic cell lineages was also evaluated.

MAIN RESULTS AND THE ROLE OF CHANCE

CCS results from cell lines showed 100% consistency with their known karyotypes. ΔΔCt values of differential gene expression of four selected target genes from the cell lines GM4435 and GM0323 were comparable between six-cell aliquots and purified RNA (Collagen type I alpha-1 (COL1A1), P = 0.54; Fibroblast growth factor-5 (FGF5), P = 0.11; Laminin subunit beta-1 (LAMB1), P = 1.00 and Atlastin-1 (ATL1), P = 0.23). With respect to human blastocysts, 92% consistency was reported after comparing embryonic CCS results with previous diagnosis. A total of 30 genes from a human stem cell pluripotency panel were selected to evaluate gene expression in human embryos. Correlation coefficients of expression profiles from biopsies of the same embryo (r = 0.96 ± 0.03 (standard deviation), n = 45) were significantly higher than when biopsies from unrelated embryos were evaluated (r = 0.93 ± 0.03, n = 945) (P < 0.0001). Growth differentiation factor 3 (GDF3) was found to be significantly up-regulated in the inner cell mass (ICM), whereas Caudal type homebox protein-2 (CDX2), Laminin subunit alpha-1 (LAMA1) and DNA methyltransferase 3-beta (DNMT3B) showed down-regulation in ICM compared with TE. Trisomy 21 embryos showed significant up-regulation of markers of cell differentiation (Cadherin-5 (CDH5) and Laminin subunit gamma-1 (LAMC1)), whereas monosomy 21 blastocysts showed higher expression of genes reported to be expressed in undifferentiated cells (Gamma-Aminobutyric Acid Type-A Receptor Beta3 Subunit (GABRB3) and GDF3).

LARGE SCALE DATA

N/A

LIMITATIONS, REASONS FOR CAUTION

Gene expression profiles of chromosomally normal embryos were not assessed due to restrictive access to euploid embryos for research. Nonetheless, the profile of blastocysts with single aneuploidies was characterized and compared. Only 30 target genes were analyzed for gene expression in this study. Increasing the number of target genes will provide a more comprehensive transcriptomic signature and reveal potential pathways paramount for embryonic competence and correct development.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first time that CCS and gene expression analysis have been performed on the same human preimplantation embryo biopsy. Further optimization of this protocol with other CCS platforms and inclusion of more target genes will provide innumerable research and clinical applications, such as discovery of biomarkers for embryonic reproductive potential and characterization of the transcriptomic signatures of embryos, potentially allowing for further embryo selection prior to embryo transfer and therefore improving outcomes.

STUDY FUNDING AND COMPETING INTERESTS

This study was funded by the Foundation for Embryonic Competence, Basking Ridge, NJ, USA. No conflicts of interests declared.

Identification and functional analysis of long intergenic noncoding RNA genes in porcine pre-implantation embryonic development

Genome-wide transcriptome studies have identified thousands of long intergenic noncoding RNAs (lincRNAs), some of which play important roles in pre-implantation embryonic development (PED). Pig is an ideal model for reproduction, however, porcine lincRNAs are still poorly characterized and it is unknown if they are associated with porcine PED. Here we reconstructed 195,531 transcripts in 122,007 loci, and identified 7,618 novel lincRNAs from 4,776 loci based on published RNA-seq data. These lincRNAs show low exon number, short length, low expression level, tissue-specific expression and cis-acting, which is consistent with previous reports in other species. By weighted co-expression network analysis, we identified 5 developmental stages specific co-expression modules. Gene ontology enrichment analysis of these specific co-expression modules suggested that many lincRNAs are associated with cell cycle regulation, transcription and metabolism to regulate the process of zygotic genome activation. Futhermore, we identified hub lincRNAs in each co-expression modules, and found two lincRNAs TCONS_00166370 and TCONS_00020255 may play a vital role in porcine PED. This study systematically analyze lincRNAs in pig and provides the first catalog of lincRNAs that might function as gene regulatory factors of porcine PED.

Stem cell insights into human trophoblast lineage differentiation

BACKGROUND

The human placenta is vital for fetal development, yet little is understood about how it forms successfully to ensure a healthy pregnancy or why this process is inadequate in 1 in 10 pregnancies, leading to miscarriage, intrauterine growth restriction or preeclampsia. Trophoblasts are placenta-specific epithelial cells that maximize nutrient exchange. All trophoblast lineages are thought to arise from a population of trophoblast stem cells (TSCs). However, whilst the isolation of murine TSC has led to an explosion in understanding murine placentation, the isolation of an analogous human TSC has proved more difficult. Consequently, alternative methods of studying human trophoblast lineage development have been employed, including human embryonic stem cells (hESCs), induced pluripotent stem cells (iPS) and transformed cell lines; but what do these proxy models tell us about what is happening during early placental development?

OBJECTIVE AND RATIONALE

In this systematic review, we evaluate current approaches to understanding human trophoblast lineage development in order to collate and refine these models and inform future approaches aimed at establishing human TSC lines.

SEARCH METHODS

To ensure all relevant articles were analysed, an unfiltered search of Pubmed, Embase, Scopus and Web of Science was conducted for 25 key terms on the 13th May 2016. In total, 47 313 articles were retrieved and manually filtered based on non-human, non-English, non-full text, non-original article and off-topic subject matter. This resulted in a total of 71 articles deemed relevant for review in this article.

OUTCOMES

Candidate human TSC populations have been identified in, and isolated from, both the chorionic membrane and villous tissue of the placenta, but further investigation is required to validate these as 'true' human TSCs. Isolating human TSCs from blastocyst trophectoderm has not been successful in humans as it was in mice, although recently the first reported TSC line (USFB6) was isolated from an eight-cell morula. In lieu of human TSC lines, trophoblast-like cells have been induced to differentiate from hESCs and iPS. However, differentiation in these model systems is difficult to control, culture conditions employed are highly variable, and the extent to which they accurately convey the biology of 'true' human TSCs remains unclear, particularly as a consensus has not been met among the scientific community regarding which characteristics a human TSC must possess.

WIDER IMPLICATIONS

Human TSC models have the potential to revolutionize our understanding of trophoblast differentiation, allowing us to make significant gains in understanding the underlying pathology of pregnancy disorders and to test potential therapeutic interventions on cell function in vitro. In order to do this, a collaborative effort is required to establish the criteria that define a human TSC to confirm the presence of human TSCs in both primary isolates and to determine how accurately trophoblast-like cells derived from current model systems reflect trophoblast from primary tissue. The in vitro systems currently used to model early trophoblast lineage formation have provided insights into early human placental formation but it is unclear whether these trophoblast-like cells are truly representative of primary human trophoblast. Consequently, continued refinement of current models, and standardization of culture protocols is essential to aid our ability to identify, isolate and propagate 'true' human TSCs from primary tissue.

Noncoding RNA-regulated gain-of-function of STOX2 in Finnish pre-eclamptic families

The familial forms of early onset pre-eclampsia and related syndromes (HELLP) present with hypertension and proteinuria in the mother and growth restriction of the fetus. Genetically, these clinically similar entities are caused by different founder-dependent, placentally-expressed paralogous genes. All susceptibility genes (STOX1, lincHELLP, INO80B) identified so far are master control genes that regulate an essential trophoblast differentiation pathway, but act at different entry points. Many genes remain to be identified. Here we demonstrate that a long non-coding RNA (lncRNA) within intron 3 of the STOX2 gene on 4q35.1 acts as a permissive cis-acting regulator of alternative splicing of STOX2. When this lncRNA is mutated or absent, an alternative exon (3B) of STOX2 is included. This introduces a stop codon resulting in the deletion of a highly conserved domain of 64 amino acids in the C-terminal of the STOX2 protein. A mutation present within a regulatory region within intron 1 of STOX2 has the same effect after blocking with CRISPR technology: transcripts with exon 3B are upregulated. This proces appears related to transcriptional control by a chromatin-splicing adaptor complex as described for FGFR2. For STOX2, CHD5, coding for a chromodomain helicase DNA binding protein, qualifies as the chromatin modifier in this process.

Molecular Criteria for Defining the Naive Human Pluripotent State

Recent studies have aimed to convert cultured human pluripotent cells to a naive state, but it remains unclear to what extent the resulting cells recapitulate in vivo naive pluripotency. Here we propose a set of molecular criteria for evaluating the naive human pluripotent state by comparing it to the human embryo. We show that transcription of transposable elements provides a sensitive measure of the concordance between pluripotent stem cells and early human development. We also show that induction of the naive state is accompanied by genome-wide DNA hypomethylation, which is reversible except at imprinted genes, and that the X chromosome status resembles that of the human preimplantation embryo. However, we did not see efficient incorporation of naive human cells into mouse embryos. Overall, the different naive conditions we tested showed varied relationships to human embryonic states based on molecular criteria, providing a backdrop for future analysis of naive human pluripotency.

•

Naive human ESCs share a unique transposon signature with cleavage-stage embryos

•

Global DNA demethylation in naive human ESCs is reversible except at imprinted loci

•

The X chromosome status of naive human ESCs resembles the preimplantation embryo

•

Naive human ESCs incorporate into the mouse morula or blastocyst very inefficiently

Human pluripotent stem cells as a model of trophoblast differentiation in both normal development and disease

Trophoblast is the primary epithelial cell type in the placenta, a transient organ required for proper fetal growth and development. Different trophoblast subtypes are responsible for gas/nutrient exchange (syncytiotrophoblasts, STBs) and invasion and maternal vascular remodeling (extravillous trophoblasts, EVTs). Studies of early human placental development are severely hampered by the lack of a representative trophoblast stem cell (TSC) model with the capacity for self-renewal and the ability to differentiate into both STBs and EVTs. Primary cytotrophoblasts (CTBs) isolated from early-gestation (6-8 wk) human placentas are bipotential, a phenotype that is lost with increasing gestational age. We have identified a CDX2(+)/p63(+) CTB subpopulation in the early postimplantation human placenta that is significantly reduced later in gestation. We describe a reproducible protocol, using defined medium containing bone morphogenetic protein 4 by which human pluripotent stem cells (hPSCs) can be differentiated into CDX2(+)/p63(+) CTB stem-like cells. These cells can be replated and further differentiated into STB- and EVT-like cells, based on marker expression, hormone secretion, and invasive ability. As in primary CTBs, differentiation of hPSC-derived CTBs in low oxygen leads to reduced human chorionic gonadotropin secretion and STB-associated gene expression, instead promoting differentiation into HLA-G(+) EVTs in an hypoxia-inducible, factor-dependent manner. To validate further the utility of hPSC-derived CTBs, we demonstrated that differentiation of trisomy 21 (T21) hPSCs recapitulates the delayed CTB maturation and blunted STB differentiation seen in T21 placentae. Collectively, our data suggest that hPSCs are a valuable model of human placental development, enabling us to recapitulate processes that result in both normal and diseased pregnancies.

Human induced pluripotent stem cells: A disruptive innovation

This year (2016) will mark the 10th anniversary of the discovery of induced pluripotent stem cells (iPSCs). The finding that the transient expression of four transcription factors can radically remodel the epigenome, transcriptome and metabolome of differentiated cells and reprogram them into pluripotent stem cells has been a major and groundbreaking technological innovation. In this review, we discuss the major applications of this technology that we have grouped in nine categories: a model to study cell fate control; a model to study pluripotency; a model to study human development; a model to study human tissue and organ physiology; a model to study genetic diseases in a dish; a tool for cell rejuvenation; a source of cells for drug screening; a source of cells for regenerative medicine; a tool for the production of human organs in animals.

The peroxisome proliferator-activated receptors under epigenetic control in placental metabolism and fetal development

The placental metabolism can adapt to the environment throughout pregnancy to both the demands of the fetus and the signals from the mother. Such adaption processes include epigenetic mechanisms, which alter gene expression and may influence the offspring's health. These mechanisms are linked to the diversity of prenatal environmental exposures, including maternal under- or overnutrition or gestational diabetes. The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that contribute to the developmental plasticity of the placenta by regulating lipid and glucose metabolism pathways, including lipogenesis, steroidogenesis, glucose transporters, and placental signaling pathways, thus representing a link between energy metabolism and reproduction. Among the PPAR isoforms, PPARγ appears to be the main modulator of mammalian placentation. Certain fatty acids and lipid-derived moieties are the natural activating PPAR ligands. By controlling the amounts of maternal nutrients that go across to the fetus, the PPARs play an important regulatory role in placenta metabolism, thereby adapting to the maternal nutritional status. As demonstrated in animal studies, maternal nutrition during gestation can exert long-term influences on the PPAR methylation pattern in offspring organs. This review underlines the current state of knowledge on the relationship between environmental factors and the epigenetic regulation of the PPARs in placenta metabolism and offspring development.

Oncogenic cancer/testis antigens: prime candidates for immunotherapy

Recent developments have set the stage for immunotherapy as a supplement to conventional cancer treatment. Consequently, a significant effort is required to further improve efficacy and specificity, particularly the identification of optimal therapeutic targets for clinical testing. Cancer/testis antigens are immunogenic, highly cancer-specific, and frequently expressed in various types of cancer, which make them promising candidate targets for cancer immunotherapy, including cancer vaccination and adoptive T-cell transfer with chimeric T-cell receptors. Our current understanding of tumor immunology and immune escape suggests that targeting oncogenic antigens may be beneficial, meaning that identification of cancer/testis antigens with oncogenic properties is of high priority. Recent work from our lab and others provide evidence that many cancer/testis antigens, in fact, have oncogenic functions, including support of growth, survival and metastasis. This novel insight into the function of cancer/testis antigens has the potential to deliver more effective cancer vaccines. Moreover, immune targeting of oncogenic cancer/testis antigens in combination with conventional cytotoxic therapies or novel immunotherapies such as checkpoint blockade or adoptive transfer, represents a highly synergistic approach with the potential to improve patient survival.

Comparison of syncytiotrophoblast generated from human embryonic stem cells and from term placentas

Human embryonic stem cells (ESCs) readily commit to the trophoblast lineage after exposure to bone morphogenetic protein-4 (BMP-4) and two small compounds, an activin A signaling inhibitor and a FGF2 signaling inhibitor (BMP4/A83-01/PD173074; BAP treatment). During differentiation, areas emerge within the colonies with the biochemical and morphological features of syncytiotrophoblast (STB). Relatively pure fractions of mononucleated cytotrophoblast (CTB) and larger syncytial sheets displaying the expected markers of STB can be obtained by differential filtration of dispersed colonies through nylon strainers. RNA-seq analysis of these fractions has allowed them to be compared with cytotrophoblasts isolated from term placentas before and after such cells had formed syncytia. Although it is clear from extensive gene marker analysis that both ESC- and placenta-derived syncytial cells are trophoblast, each with the potential to transport a wide range of solutes and synthesize placental hormones, their transcriptome profiles are sufficiently dissimilar to suggest that the two cell types have distinct pedigrees and represent functionally different kinds of STB. We propose that the STB generated from human ESCs represents the primitive syncytium encountered in early pregnancy soon after the human trophoblast invades into the uterine wall.

MSX2 Induces Trophoblast Invasion in Human Placenta

Normal implantation depends on appropriate trophoblast growth and invasion. Inadequate trophoblast invasion results in pregnancy-related disorders, such as early miscarriage and pre-eclampsia, which are dangerous to both the mother and fetus. Msh Homeobox 2 (MSX2), a member of the MSX family of homeobox proteins, plays a significant role in the proliferation and differentiation of various cells and tissues, including ectodermal organs, teeth, and chondrocytes. Recently, MSX2 was found to play important roles in the invasion of cancer cells into adjacent tissues via the epithelial-mesenchymal transition (EMT). However, the role of MSX2 in trophoblastic invasion during placental development has yet to be explored. In the present study, we detected MSX2 expression in cytotrophoblast, syncytiotrophoblast, and extravillous cytotrophoblast cells of first or third trimester human placentas via immunohistochemistry analysis. Furthermore, we found that the in vitro invasive ability of HTR8/SVneo cells was enhanced by exogenous overexpression of MSX2, and that this effect was accompanied by increased protein expression of matrix metalloproteinase-2 (MMP-2), vimentin, and β-catenin. Conversely, treatment of HTR8/SVneo cells with MSX2-specific siRNAs resulted in decreased protein expression of MMP-2, vimentin, and β-catenin, and reduced invasion levels in a Matrigel invasion test. Notably, however, treatment with the MSX2 overexpression plasmid and the MSX2 siRNAs had no effect on the mRNA expression levels of β-catenin. Meanwhile, overexpression of MSX2 and treatment with the MSX2-specific siRNA resulted in decreased and increased E-cadherin expression, respectively, in JEG-3 cells. Lastly, the protein expression levels of MSX2 were significantly lower in human pre-eclamptic placental villi than in the matched control placentas. Collectively, our results suggest that MSX2 may induce human trophoblast cell invasion, and dysregulation of MSX2 expression may be associated with pre-eclampsia.

The role of GAGE cancer/testis antigen in metastasis: the jury is still out

Background

GAGE cancer/testis antigens are frequently expressed in various types of malignancies and represent attractive targets for immunotherapy, however their role in cancer initiation and progression has remained elusive. GAGE proteins are expressed in normal cells during early development with migratory and invasive properties and were found to be upregulated in cancer cells with metastasizing potential in a gastric cancer model.

Methods

We have addressed the direct role of GAGE proteins in supporting metastasis using an isogenic metastasis model of human cancer, consisting of 4 isogenic cell lines, which are equally tumorigenic in immunodeficient mice, but differ with their ability to generate metastases in the lungs and lymph nodes.

Results

Although GAGE proteins were strongly upregulated in the highly metastatic clone (CL16) compared to non-metastatic (NM2C5), weakly metastatic (M4A4) and moderately metastatic clones (LM3), stable downregulation of GAGE expression did not affect the ability of CL16 cells to establish primary tumors and form metastasis in the lungs of immunodeficient mice.

Conclusions

These results suggest that GAGE proteins per se do not support metastasis and that further studies are needed to clarify the contribution of GAGE proteins to the metastatic potential of different types of cancer cells.

Factors affecting the gene expression of in vitro cultured human preimplantation embryos

STUDY QUESTION

What is the relative effect of common environmental and biological factors on transcriptome changes during human preimplantation development?

SUMMARY ANSWER

Developmental stage and maternal age had a larger effect on the global gene expression profile of human preimplantation embryos than the culture medium or oxygen concentration used in in vitro culture.

WHAT IS KNOWN ALREADY

Studies on mouse and bovine embryos have shown that different conditions in the in vitro culture of embryos can lead to changes in transcriptome profiles. For humans, an effect of developmental stage on the transcriptome profile of embryos has been demonstrated, but studies on the effect of maternal age or culture conditions are lacking.

STUDY DESIGN, SIZE, DURATION

Donated, good quality, day 4 cryopreserved human preimplantation embryos (N = 89) were randomized to be cultured in one of two culture media (G5 medium or HTF medium) and one of two oxygen concentrations (5% or 20%), with stratification for maternal age. Next to these variables, developmental stage after culture was taken into account in the analysis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Embryos that developed to morula or blastocyst stage during these 2 days whose amplified mRNA passed our quality control criteria for microarray hybridization were individually examined for genome-wide gene expression (N = 37).

MAIN RESULTS AND THE ROLE OF CHANCE

Based on the number of differentially expressed genes (DEGs), developmental stage (3519 DEGs) and maternal age (1258 DEGs) had a larger effect on the global gene expression profile of human preimplantation embryos than either tested culture medium (596 DEGs) or oxygen concentration (492 DEGs) used during in vitro culture. Interactions between the factors were found, indicating that culture conditions might have a different effect depending on the developmental stage or the maternal age of the embryos. Affected pathways included metabolism, cell cycle processes and oxidative phosphorylation.

LIMITATIONS, REASONS FOR CAUTION

Culture of embryos for only 2 days might have limited the effect on global gene expression by the investigated culture conditions. Earlier stages of development (Day 0 until Day 4) were not analyzed and these embryos might respond differently to the experimental conditions. The freezing and thawing procedures might have had an effect on gene expression. RT-PCR validation was not performed due to scarcity of the material.

WIDER IMPLICATIONS OF THE FINDINGS

Our results show that when studying gene expression in single human preimplantation embryos under various experimental conditions, one should take into account the confounding effect of biological variables, such as developmental stage and maternal age. This makes these experiments different from gene expression experiments where these variables can be tightly controlled, for example when using cell lines.

STUDY FUNDING/COMPETING INTERESTS

This study received no external funding and there were no competing interests.

Transcriptomic Features of Bovine Blastocysts Derived by Somatic Cell Nuclear Transfer

Reprogramming incompletely occurs in most somatic cell nuclear transfer (SCNT) embryos, which results in misregulation of developmentally important genes and subsequent embryonic malfunction and lethality. Here we examined transcriptome profiles in single bovine blastocysts derived by in vitro fertilization (IVF) and SCNT. Different types of donor cells, cumulus cell and ear-skin fibroblast, were used to derive cSCNT and fSCNT blastocysts, respectively. SCNT blastocysts expressed 13,606 genes on average, similar to IVF (13,542). Correlation analysis found that both cSCNT and fSCNT blastocyst groups had transcriptomic features distinctive from the IVF group, with the cSCNT transcriptomes closer to the IVF ones than the fSCNT. Gene expression analysis identified 56 underrepresented and 78 overrepresented differentially expressed genes in both SCNT groups. A 400-kb locus harboring zinc-finger protein family genes in chromosome 18 were found coordinately down-regulated in fSCNT blastocysts, showing a feature of reprogramming-resistant regions. Probing into different categories of genes important for blastocyst development revealed that genes involved in trophectoderm development frequently were underrepresented, and those encoding epigenetic modifiers tended to be overrepresented in SCNT blastocysts. Our effort to identify reprogramming-resistant, differentially expressed genes can help map reprogramming error-prone loci onto the genome and elucidate how to handle the stochastic events of reprogramming to improve cloning efficiency.

Dynamic expression of DNA methyltransferases (DNMTs) in oocytes and early embryos

Epigenetic mechanisms play critical roles in oogenesis and early embryo development in mammals. One of these epigenetic mechanisms, DNA methylation is accomplished through the activities of DNA methyltransferases (DNMTs), which are responsible for adding a methyl group to the fifth carbon atom of the cytosine residues within cytosine-phosphate-guanine (CpG) and non-CpG dinuclotide sites. Five DNMT enzymes have been identified in mammals including DNMT1, DNMT2, DNMT3A, DNMT3B, and DNMT3L. They function in two different methylation processes: maintenance and de novo. For maintenance methylation, DNMT1 preferentially transfers methyl groups to the hemi-methylated DNA strands following DNA replication. However, for de novo methylation activities both DNMT3A and DNMT3B function in the methylation of the unmodified cytosine residues. Although DNMT3L indirectly contributes to de novo methylation process, DNMT2 enables the methylation of the cytosine 38 in the anticodon loop of aspartic acid transfer RNA and does not methylate DNA. In this review article, we have evaluated and discussed the existing published studies to characterize the spatial and temporal expression patterns of the DNMTs in mouse, bovine and human oocytes and early embryos. We have also reviewed the effects of in vitro culture conditions (serum abundance and glucose concentration), aging, superovulation, vitrification, and somatic cell nuclear transfer technology on the dynamics of DNMTs.

Exploring the function of long non-coding RNA in the development of bovine early embryos

Now recognised as part of the cellular transcriptome, the function of long non-coding (lnc) RNA remains unclear. Previously, we found that some lncRNA molecules in bovine embryos are highly responsive to culture conditions. In view of a recent demonstration that lncRNA may play a role in regulating important functions, such as maintenance of pluripotency, modification of epigenetic marks and activation of transcription, we sought evidence of its involvement in embryogenesis. Among the numerous catalogued lncRNA molecules found in oocytes and early embryos of cattle, three candidates chosen for further characterisation were found unexpectedly in the cytoplasmic compartment rather than in the nucleus. Transcriptomic survey of subcellular fractions found these candidates also associated with polyribosomes and one of them spanning transzonal projections between cumulus cells and the oocyte. Knocking down this transcript in matured oocytes increased developmental rates, leading to larger blastocysts. Transcriptome and methylome analyses of these blastocysts showed concordant data for a subset of four genes, including at least one known to be important for blastocyst survival. Functional characterisation of the roles played by lncRNA in supporting early development remains elusive. Our results suggest that some lncRNAs play a role in translation control of target mRNA. This would be important for managing the maternal reserves within which is embedded the embryonic program, especially before embryonic genome activation.

Cultured Cells from the Human Oocyte Cumulus Niche Are Efficient Feeders to Propagate Pluripotent Stem Cells

Pluripotency is at the crossroads of stem cell research and biology of reproduction. The mature metaphase II oocyte contains the key factors for pluripotency induction and maintenance as assessed by its capacity to reprogram somatic nuclei. The cumulus cells (CCs) niche that surrounds the oocyte is crucial for its maturation and presumably for the oocyte to acquire its competence to confer pluripotency. In this study, we examined whether cells cultured from the human mature metaphase II oocyte CC niche (hCC) could be used as feeders for the propagation of human induced pluripotent stem cells. The induced pluripotent (iPS) cells cultured on hCC (hCC-iPS) were assessed for their pluripotency potential by their expression of pluripotency-associated genes such as Oct4, Nanog, and TRA1-60 and their competence to differentiate into the three germ layers in vitro (embryoid bodies) as well as in vivo (teratoma formation). We show that not only the hCC-iPS cells maintained their pluripotency potential, but they also exhibited much better self-renewal performance in terms of proliferation rate compared to the same cells cultured on human foreskin fibroblast (hFF) feeders (hFF-iPS). A comparative gene expression profile study of hCC and hFF revealed significant differences (P < 0.05) in expression of cellular matrix components and an upregulation in hCC of genes known to be important players in cell proliferation such as interleukin 6 gene (IL6).

KLF5 regulates infection- and inflammation-induced pro-labour mediators in human myometrium

The transcription factor Kruppel-like factor 5 (KLF5) has been shown to associate with nuclear factor kappa B (NFκB) to regulate genes involved in inflammation. However, there are no studies on the expression and regulation of KLF5 in the processes of human labour and delivery. Thus, the aims of this study were to determine the effect of i) human labour on KLF5 expression in both foetal membranes and myometrium; ii) the pro-inflammatory cytokine interleukin 1 beta (IL1β), bacterial product flagellin and the viral dsRNA analogue poly(I:C) on KLF5 expression and iii) KLF5 knockdown by siRNA in human myometrial primary cells on pro-inflammatory and pro-labour mediators. In foetal membranes, there was no effect of term or preterm labour on KLF5 expression. In myometrium, the term labour was associated with an increase in nuclear KLF5 protein expression. Moreover, KLF5 expression was also increased in myometrial cells treated with IL1β, flagellin or poly(IC), likely factors contributing to preterm birth. KLF5 silencing in myometrial cells significantly decreased IL1β-induced cytokine expression (IL6 and IL8 mRNA expression and release), COX2 mRNA expression, and subsequent release of prostaglandins PGE2 and PGF2α. KLF5 silencing also significantly reduced flagellin- and poly(I:C)-induced IL6 and IL8 mRNA expression. Lastly, IL1β-, flagellin- and poly(I:C)-stimulated NFκB transcriptional activity was significantly suppressed in KLF5-knockout myometrial cells. In conclusion, this study describes novel data in which KLF5 is increased in labouring myometrium, and KLF5 silencing decreased inflammation- and infection-induced pro-labour mediators.

Deoxyribonucleic acid methylation profiling of single human blastocysts by methylated CpG-island amplification coupled with CpG-island microarray

Objective

To study whether methylated CpG-island (CGI) amplification coupled with microarray (MCAM) can be used to generate DNA (deoxyribonucleic acid) methylation profiles from single human blastocysts.

Design

A pilot microarray study with methylated CpG-island amplification applied to human blastocyst genomic DNA and hybridized on CpG-island microarrays.

Setting

University research laboratory.

Patient(s)

Five cryopreserved sibling 2-pronuclear zygotes that were surplus to requirements for clinical treatment by in vitro fertilization were donated with informed consent from a patient attending Bourn Hall Clinic, Cambridge, United Kingdom.

Intervention(s)

None.

Main Outcome Measure(s)

Successful generation of genome-wide DNA methylation profiles at CpG islands from individual human blastocysts, with common genomic regions of DNA methylation identified between embryos.

Result(s)

Between 472 and 734 CpG islands were methylated in each blastocyst, with 121 CpG islands being commonly methylated in all 5 blastocysts. A further 159 CGIs were commonly methylated in 4 of the 5 tested blastocysts. Methylation was observed at a number of CGIs within imprinted-gene, differentially methylated regions (DMRs), including placental and preimplantation-specific DMRs.

Conclusion(s)

The MCAM method is capable of providing comprehensive DNA methylation data in individual human blastocysts.

Heightened potency of human pluripotent stem cell lines created by transient BMP4 exposure

Human pluripotent stem cells (PSCs) show epiblast-type pluripotency that is maintained with ACTIVIN/FGF2 signaling. Here, we report the acquisition of a unique stem cell phenotype by both human ES cells (hESCs) and induced pluripotent stem cells (iPSCs) in response to transient (24-36 h) exposure to bone morphogenetic protein 4 (BMP4) plus inhibitors of ACTIVIN signaling (A83-01) and FGF2 (PD173074), followed by trypsin dissociation and recovery of colonies capable of growing on a gelatin substratum in standard medium for human PSCs at low but not high FGF2 concentrations. The self-renewing cell lines stain weakly for CDX2 and strongly for NANOG, can be propagated clonally on either Matrigel or gelatin, and are morphologically distinct from human PSC progenitors on either substratum but still meet standard in vitro criteria for pluripotency. They form well-differentiated teratomas in immune-compromised mice that secrete human chorionic gonadotropin (hCG) into the host mouse and include small areas of trophoblast-like cells. The cells have a distinct transcriptome profile from the human PSCs from which they were derived (including higher expression of NANOG, LEFTY1, and LEFTY2). In nonconditioned medium lacking FGF2, the colonies spontaneously differentiated along multiple lineages, including trophoblast. They responded to PD173074 in the absence of both FGF2 and BMP4 by conversion to trophoblast, and especially syncytiotrophoblast, whereas an A83-01/PD173074 combination favored increased expression of HLA-G, a marker of extravillous trophoblast. Together, these data suggest that the cell lines exhibit totipotent potential and that BMP4 can prime human PSCs to a self-renewing alternative state permissive for trophoblast development. The results may have implications for regulation of lineage decisions in the early embryo.