A spatially resolved timeline of the human maternal-fetal interface.

Beginning in the first trimester, fetally derived extravillous trophoblasts (EVTs) invade the uterus and remodel its spiral arteries, transforming them into large, dilated blood vessels. Several mechanisms have been proposed to explain how EVTs coordinate with the maternal decidua to promote a tissue microenvironment conducive to spiral artery remodelling (SAR)1-3. However, it remains a matter of debate regarding which immune and stromal cells participate in these interactions and how this evolves with respect to gestational age. Here we used a multiomics approach, combining the strengths of spatial proteomics and transcriptomics, to construct a spatiotemporal atlas of the human maternal-fetal interface in the first half of pregnancy. We used multiplexed ion beam imaging by time-of-flight and a 37-plex antibody panel to analyse around 500,000 cells and 588 arteries within intact decidua from 66 individuals between 6 and 20 weeks of gestation, integrating this dataset with co-registered transcriptomics profiles. Gestational age substantially influenced the frequency of maternal immune and stromal cells, with tolerogenic subsets expressing CD206, CD163, TIM-3, galectin-9 and IDO-1 becoming increasingly enriched and colocalized at later time points. By contrast, SAR progression preferentially correlated with EVT invasion and was transcriptionally defined by 78 gene ontology pathways exhibiting distinct monotonic and biphasic trends. Last, we developed an integrated model of SAR whereby invasion is accompanied by the upregulation of pro-angiogenic, immunoregulatory EVT programmes that promote interactions with the vascular endothelium while avoiding the activation of maternal immune cells.

Spatial multiomics map of trophoblast development in early pregnancy.

The relationship between the human placenta-the extraembryonic organ made by the fetus, and the decidua-the mucosal layer of the uterus, is essential to nurture and protect the fetus during pregnancy. Extravillous trophoblast cells (EVTs) derived from placental villi infiltrate the decidua, transforming the maternal arteries into high-conductance vessels1. Defects in trophoblast invasion and arterial transformation established during early pregnancy underlie common pregnancy disorders such as pre-eclampsia2. Here we have generated a spatially resolved multiomics single-cell atlas of the entire human maternal-fetal interface including the myometrium, which enables us to resolve the full trajectory of trophoblast differentiation. We have used this cellular map to infer the possible transcription factors mediating EVT invasion and show that they are preserved in in vitro models of EVT differentiation from primary trophoblast organoids3,4 and trophoblast stem cells5. We define the transcriptomes of the final cell states of trophoblast invasion: placental bed giant cells (fused multinucleated EVTs) and endovascular EVTs (which form plugs inside the maternal arteries). We predict the cell-cell communication events contributing to trophoblast invasion and placental bed giant cell formation, and model the dual role of interstitial EVTs and endovascular EVTs in mediating arterial transformation during early pregnancy. Together, our data provide a comprehensive analysis of postimplantation trophoblast differentiation that can be used to inform the design of experimental models of the human placenta in early pregnancy.

Placenta: the forgotten organ.

The placenta sits at the interface between the maternal and fetal vascular beds where it mediates nutrient and waste exchange to enable in utero existence. Placental cells (trophoblasts) accomplish this via invading and remodeling the uterine vasculature. Amazingly, despite being of fetal origin, trophoblasts do not trigger a significant maternal immune response. Additionally, they maintain a highly reliable hemostasis in this extremely vascular interface. Decades of research into how the placenta differentiates itself from embryonic tissues to accomplish these and other feats have revealed a previously unappreciated level of complexity with respect to the placenta's cellular composition. Additionally, novel insights with respect to roles played by the placenta in guiding fetal development and metabolism have sparked a renewed interest in understanding the interrelationship between fetal and placental well-being. Here, we present an overview of emerging research in placental biology that highlights these themes and the importance of the placenta to fetal and adult health.

Mouse Trophoblast Cells Have Attenuated Responses to TNF-α and IFN-γ and Can Avoid Synergic Cytotoxicity of the Two Cytokines.

TNF-α and IFN-γ are two inflammatory cytokines that play critical roles in immune responses, but they can also negatively affect cell proliferation and viability. In particular, the combination of the two cytokines (TNF-α/IFN-γ) synergistically causes cytotoxicity in many cell types. We recently reported that mouse embryonic stem cells (ESCs) isolated from the blastocyst stage embryo do not respond to TNF-α and have limited response to IFN-γ, thereby avoiding TNF-α/IFN-γ cytotoxicity. The current study expanded our investigation to mouse trophoblast stem cells (TSCs) and their differentiated trophoblasts (TSC-TBs), the precursors and the differentiated cells of the placenta, respectively. In this study, we report that the combination of TNF-α/IFN-γ does not show the cytotoxicity to TSCs and TSC-TBs that otherwise effectively kills fibroblasts, similar to ESCs. Although ESCs, TSCs, and TSC-TBs are dramatically different in their growth rate, morphology, and physiological functions, they nevertheless share a similarity in being able to avoid TNF-α/IFN-γ cytotoxicity. We propose that this unique immune property may serve as a protective mechanism that limits cytokine cytotoxicity in the blastocyst. With molecular and cellular approaches and genome-wide transcriptomic analysis, we have demonstrated that the attenuated NF-κB and STAT1 transcription activation is a limiting factor that restricts the effect of TNF-α/IFN-γ on TSCs and TSC-TBs.

Endogenous retrovirus-derived enhancers confer the transcriptional regulation of human trophoblast syncytialization.

Endogenous retroviruses (ERVs) have been proposed as a driving force for the evolution of the mammalian placenta, however, the contribution of ERVs to placental development and the underlying regulatory mechanism remain largely elusive. A key process of placental development is the formation of multinucleated syncytiotrophoblasts (STBs) in direct contact with maternal blood, through which constitutes the maternal-fetal interface critical for nutrient allocation, hormone production and immunological modulation during pregnancy. We delineate that ERVs profoundly rewire the transcriptional program of trophoblast syncytialization. Here, we first determined the dynamic landscape of bivalent ERV-derived enhancers with dual occupancy of H3K27ac and H3K9me3 in human trophoblast stem cells (hTSCs). We further demonstrated that enhancers overlapping several ERV families tend to exhibit increased H3K27ac and reduced H3K9me3 occupancy in STBs relative to hTSCs. Particularly, bivalent enhancers derived from the Simiiformes-specific MER50 transposons were linked to a cluster of genes important for STB formation. Importantly, deletions of MER50 elements adjacent to several STB genes, including MFSD2A and TNFAIP2, significantly attenuated their expression concomitant to compromised syncytium formation. Together, we propose that ERV-derived enhancers, MER50 specifically, fine-tune the transcriptional networks accounting for human trophoblast syncytialization, which sheds light on a novel ERV-mediated regulatory mechanism underlying placental development.

Extracellular vesicles secreted by human uterine stromal cells regulate decidualization, angiogenesis, and trophoblast differentiation.

In humans, the uterus undergoes a dramatic transformation to form an endometrial stroma-derived secretory tissue, termed decidua, during early pregnancy. The decidua secretes various factors that act in an autocrine/paracrine manner to promote stromal differentiation, facilitate maternal angiogenesis, and influence trophoblast differentiation and development, which are critical for the formation of a functional placenta. Here, we investigated the mechanisms by which decidual cells communicate with each other and with other cell types within the uterine milieu. We discovered that primary human endometrial stromal cells (HESCs) secrete extracellular vesicles (EVs) during decidualization and that this process is controlled by a conserved HIF2α-RAB27B pathway. Mass spectrometry revealed that the decidual EVs harbor a variety of protein cargo, including cell signaling molecules, growth modulators, metabolic regulators, and factors controlling endothelial cell expansion and remodeling. We tested the hypothesis that EVs secreted by the decidual cells mediate functional communications between various cell types within the uterus. We demonstrated that the internalization of EVs, specifically those carrying the glucose transporter 1 (GLUT1), promotes glucose uptake in recipient HESCs, supporting and advancing the decidualization program. Additionally, delivery of HESC-derived EVs into human endothelial cells stimulated their proliferation and led to enhanced vascular network formation. Strikingly, stromal EVs also promoted the differentiation of trophoblast stem cells into the extravillous trophoblast lineage. Collectively, these findings provide a deeper understanding of the pleiotropic roles played by EVs secreted by the decidual cells to ensure coordination of endometrial differentiation and angiogenesis with trophoblast function during the progressive phases of decidualization and placentation.

Global proteomic analyses of human cytotrophoblast differentiation/invasion.

During human pregnancy, cytotrophoblasts (CTBs) from the placenta differentiate into specialized subpopulations that play crucial roles in proper fetal growth and development. A subset of these CTBs differentiate along an invasive pathway, penetrating the decidua and anchoring the placenta to the uterus. A crucial hurdle in pregnancy is the ability of these cells to migrate, invade and remodel spiral arteries, ensuring adequate blood flow to nourish the developing fetus. Although advances continue in describing the molecular features regulating the differentiation of these cells, assessment of their global proteomic changes at mid-gestation remain undefined. Here, using sequential window acquisition of all theoretical fragment-ion spectra (SWATH), which is a data-independent acquisition strategy, we characterized the protein repertoire of second trimester human CTBs during their differentiation towards an invasive phenotype. This mass spectrometry-based approach allowed identification of 3026 proteins across four culture time points corresponding to sequential stages of differentiation, confirming the expression dynamics of established molecules and offering new information into other pathways involved. The availability of a SWATH CTB global spectral library serves as a beneficial resource for hypothesis generation and as a foundation for further understanding CTB differentiation dynamics.

Establishment and comparison of human term placenta-derived trophoblast cells†.

Research on the biology of fetal-maternal barriers has been limited by access to physiologically relevant cells, including trophoblast cells. In this study, we describe the development of a human term placenta-derived cytotrophoblast immortalized cell line (hPTCCTB) derived from the basal plate. Human-term placenta-derived cytotrophoblast immortalized cell line cells are comparable to their primary cells of origin in terms of morphology, marker expression, and functional responses. We demonstrate that these can transform into syncytiotrophoblast and extravillous trophoblasts. We also compared the hPTCCTB cells to immortalized chorionic trophoblasts (hFM-CTC), trophoblasts of the chorionic plate, and BeWo cells, choriocarcinoma cell lines of conventional use. Human-term placenta-derived cytotrophoblast immortalized cell line and hFM-CTCs displayed more similarity to each other than to BeWos, but these differ in syncytialization ability. Overall, this study (1) demonstrates that the immortalized hPTCCTB generated are cells of higher physiological relevance and (2) provides a look into the distinction between the spatially distinct placental and fetal barrier trophoblasts cells, hPTCCTB and hFM-CTC, respectively.

Trophoblast organoids as a model for maternal-fetal interactions during human placentation.

The placenta is the extraembryonic organ that supports the fetus during intrauterine life. Although placental dysfunction results in major disorders of pregnancy with immediate and lifelong consequences for the mother and child, our knowledge of the human placenta is limited owing to a lack of functional experimental models1. After implantation, the trophectoderm of the blastocyst rapidly proliferates and generates the trophoblast, the unique cell type of the placenta. In vivo, proliferative villous cytotrophoblast cells differentiate into two main sub-populations: syncytiotrophoblast, the multinucleated epithelium of the villi responsible for nutrient exchange and hormone production, and extravillous trophoblast cells, which anchor the placenta to the maternal decidua and transform the maternal spiral arteries2. Here we describe the generation of long-term, genetically stable organoid cultures of trophoblast that can differentiate into both syncytiotrophoblast and extravillous trophoblast. We used human leukocyte antigen (HLA) typing to confirm that the organoids were derived from the fetus, and verified their identities against four trophoblast-specific criteria3. The cultures organize into villous-like structures, and we detected the secretion of placental-specific peptides and hormones, including human chorionic gonadotropin (hCG), growth differentiation factor 15 (GDF15) and pregnancy-specific glycoprotein (PSG) by mass spectrometry. The organoids also differentiate into HLA-G+ extravillous trophoblast cells, which vigorously invade in three-dimensional cultures. Analysis of the methylome reveals that the organoids closely resemble normal first trimester placentas. This organoid model will be transformative for studying human placental development and for investigating trophoblast interactions with the local and systemic maternal environment.

Disabling de novo DNA methylation in embryonic stem cells allows an illegitimate fate trajectory.

Genome remethylation is essential for mammalian development but specific reasons are unclear. Here we examined embryonic stem (ES) cell fate in the absence of de novo DNA methyltransferases. We observed that ES cells deficient for both Dnmt3a and Dnmt3b are rapidly eliminated from chimeras. On further investigation we found that in vivo and in vitro the formative pluripotency transition is derailed toward production of trophoblast. This aberrant trajectory is associated with failure to suppress activation of Ascl2Ascl2 encodes a bHLH transcription factor expressed in the placenta. Misexpression of Ascl2 in ES cells provokes transdifferentiation to trophoblast-like cells. Conversely, Ascl2 deletion rescues formative transition of Dnmt3a/b mutants and improves contribution to chimeric epiblast. Thus, de novo DNA methylation safeguards against ectopic activation of Ascl2 However, Dnmt3a/b-deficient cells remain defective in ongoing embryogenesis. We surmise that multiple developmental transitions may be secured by DNA methylation silencing potentially disruptive genes.

Intersection of regulatory pathways controlling hemostasis and hemochorial placentation.

Hemochorial placentation is characterized by the development of trophoblast cells specialized to interact with the uterine vascular bed. We utilized trophoblast stem (TS) cell and mutant rat models to investigate regulatory mechanisms controlling trophoblast cell development. TS cell differentiation was characterized by acquisition of transcript signatures indicative of an endothelial cell-like phenotype, which was highlighted by the expression of anticoagulation factors including tissue factor pathway inhibitor (TFPI). TFPI localized to invasive endovascular trophoblast cells of the rat placentation site. Disruption of TFPI in rat TS cells interfered with development of the endothelial cell-like endovascular trophoblast cell phenotype. Similarly, TFPI was expressed in human invasive/extravillous trophoblast (EVT) cells situated within first-trimester human placental tissues and following differentiation of human TS cells. TFPI was required for human TS cell differentiation to EVT cells. We next investigated the physiological relevance of TFPI at the placentation site. Genome-edited global TFPI loss-of-function rat models revealed critical roles for TFPI in embryonic development, resulting in homogeneous midgestation lethality prohibiting analysis of the role of TFPI as a regulator of the late-gestation wave of intrauterine trophoblast cell invasion. In vivo trophoblast-specific TFPI knockdown was compatible with pregnancy but had profound effects at the uterine-placental interface, including restriction of the depth of intrauterine trophoblast cell invasion while leading to the accumulation of natural killer cells and increased fibrin deposition. Collectively, the experimentation implicates TFPI as a conserved regulator of invasive/EVT cell development, uterine spiral artery remodeling, and hemostasis at the maternal-fetal interface.

Cannabinoid and planar cell polarity signaling converges to direct placentation.

Directed trophoblast migration toward the maternal mesometrial pole is critical for placentation and pregnancy success. Trophoblasts replace maternal arterial endothelial cells to increase blood supply to the placenta. Inferior trophoblast invasion results in pregnancy complications including preeclampsia, intrauterine growth restriction, miscarriage, and preterm delivery. The maternal chemotactic factors that direct trophoblast migration and the mechanism by which trophoblasts respond to these factors are not clearly understood. Here, we show that invasive trophoblasts deficient in Vangl2, a core planar cell polarity (PCP) component, fail to invade in maternal decidua, and this deficiency results in middle-gestational fetal demise. Previously, we have shown that tightly regulated endocannabinoids via G protein-coupled cannabinoid receptor CB1 are critical to the invasion of trophoblasts called spiral artery trophoblast giant cells (SpA-TGCs). We find that CB1 directly interacts with VANGL2. Trophoblast stem cells devoid of Cnr1 and/or Vangl2 show compromised cell migration. To study roles of VANGL2 and CB1 in trophoblast invasion in vivo, we conditionally deleted Cnr1 (coding CB1) and Vangl2 in progenitors of SpA-TGCs using trophoblast-specific protein alpha (Tpbpa)-Cre. We observed that signaling mediated by VANGL2 and CB1 restrains trophoblasts from random migration by keeping small GTPases quiescent. Our results show that organized PCP in trophoblasts is indispensable for their directed movement and that CB1 exerts its function by direct interaction with membrane proteins other than its canonical G protein-coupled receptor role.

Down-regulated Wnt7a and GPR124 in early-onset preeclampsia placentas reduce invasion and migration of trophoblast cells.

OBJECTIVES: Preeclampsia (PE) is a disease specific to pregnancy that causes 9-10 % of maternal deaths. Early-onset PE (<34 weeks' gestation) is the most dangerous category of PE. Wnt7a and GPR124 (G protein-coupled receptor 124) are widely expressed in the human reproductive process. Especially during embryogenesis and tumorigenesis, Wnt7a plays a crucial role. However, few studies have examined the association between Wnt7a-GPR124 and early-onset PE. The aim of this study was to examine the significance of Wnt7a and GPR124 in early-onset PE as well as Wnt7a's role in trophoblast cells. METHODS: Immunohistochemistry (IHC), real-time PCR, and western blotting (WB) were used to investigate Wnt7a and GPR124 expression in normal and early-onset PE placentas. Additionally, FACS, Transwell, and CCK-8 assays were used to diagnose Wnt7a involvement in migration, invasion, and proliferation. RESULTS: In the early-onset PE group, Wnt7a and GPR124 expression was significantly lower than in the normal group, especially in the area of syncytiotrophoblasts (STBs) and extravillous trophoblasts (EVTs). A negative correlation was found between Wnt7a RNA and GPR124 expression (r=-0.42, p<0.01). However, the Wnt7a RNA expression level was positive correlated with PE severity. In further cellular functional experiments, knockdown of Wnt7a inhibits HTR8/SVeno cells invasion and migration but has little effect on proliferation and apoptosis. CONCLUSIONS: Through the Wnt pathway, Wnt7a regulates trophoblast cell invasion and migration, and may contribute to early-onset preeclampsia pathogenesis. A molecular level study of Wnt7a will be needed to find downstream proteins and mechanisms of interaction.

Trophoblast stem cells, trophoblast invasion, and organoids - advancements in gynecology.

The human placenta serves as a vital barrier between the mother and the developing fetus during pregnancy. A defect in the early development of the placenta is associated with severe pregnancy disorders. Despite its complex development, various molecular processes control placental development, and the specialization of trophoblast cells is still not fully understood. One primary obstacle is the lack of suitable cell model systems. Traditional two-dimensional (2D) cell cultures fail to mimic in vivo conditions and do not capture the intricate intercellular interactions vital for studying placental development. However, three-dimensional (3D) organoid models derived from stem cells that replicate natural cell organization and architecture have greatly improved our understanding of trophoblast behavior and its medicinal applications. Organoids with relevant phenotypes provide a valuable platform to model both placental physiology and pathology, including the modeling of placental disorders. They hold great promise for personalized medicine, improved diagnostics, and the evaluation of pharmaceutical drug efficacy and safety. This article provides a concise overview of trophoblast stem cells, trophoblast invasion, and the evolving role of organoids in gynecology.

Resveratrol alleviates preeclampsia-like symptoms in rats through a mechanism involving the miR-363-3p/PEDF/VEGF axis.

Preeclampsia (PE) is a hypertension-associated disease, and resveratrol (RES) is a polyphenol recognized to present beneficial effects in cardiovascular disease including hypertension. Recently, attentions have come to the therapeutic effect of RES in PE, but the underlying molecular mechanisms remain largely unknown. This study sought to delineate the mechanistic basis regarding bioinformatically identified miR-363-3p/PEDF/VEGF axis for RES treatment in PE. PE-like symptoms were induced in vivo in Sprague-Dawley rats by intraperitoneal injection with Ng-nitro-L-arginine methyl ester (L-NAME), and hypoxia was induced in vitro in trophoblasts by CoCl2. Accordingly, RES was found to enhance viability, migration, angiogenesis, and to repress the apoptosis of hypoxic trophoblasts in vitro. Furthermore, in vivo experiments noted that RES alleviated placental injury and promoted angiogenesis in rats with PE-like symptoms in vivo by increasing VEGF via promoting miR-363-3p-mediated PEDF suppression. Collectively, RES ameliorates PE by upregulating VEGF through miR-363-3p-mediated PEDF downregulation, the mechanism of which may be of promising significance to augment RES efficacy in PE treatment.

Early steps of embryo implantation are regulated by exchange of extracellular vesicles between the embryo and the endometrium.

In early pregnancy, as the embryo arrives in the uterus, intensive communication between the embryo and uterus begins. Hundreds of molecules are known to be involved, but despite numerous findings, full understanding of the complexity of the embryo-maternal dialog remains elusive. Recently, extracellular vesicles, nanoparticles able to transfer functionally active cargo between cells, have emerged as important players in cell-cell communication, and as such, they have gained great attention over the past decade also in reproductive biology. Here, we use a domestic animal model (Sus scrofa) with an epitheliochorial, superficial type of placentation because of its advantage in studding uterine luminal fluid extracellular vesicles. We show that during early pregnancy, the uterine lumen is abundant with extracellular vesicles that carry a plethora of miRNAs able to target genes involved in embryonic and organismal development. These extracellular vesicles, upon the delivery to primary trophoblast cells, affect genes governing development as well as cell-to-cell signaling and interactions, consequently having an impact on trophoblast cell proliferation, migration, and invasion. We conclude that the exchange of a unique population of extracellular vesicles and their molecular cargo at the maternal-embryo interface is the key to the success of embryo implantation and pregnancy.

Origins of abnormal placentation: why maternal veins must not be forgotten.

The importance of uterine microvascular adaptations during placentation in pregnancy has been well established for decades. Inadequate dilatation of spiral arteries is associated with gestational complications, such as preeclampsia and/or intrauterine growth restriction. More recently, it has become clear that trophoblast cells invade and adapt decidual veins and lymphatic vessels 1 month before spiral arteries become patent and before intervillous space perfusion starts. Normal intervillous space hemodynamics is characterized by high volume flow at low velocity and pressure in the interseptal compartments surrounding the chorionic villi, hereby facilitating efficient maternal-fetal exchange. In case of shallow decidual vein dilatation, intervillous arterial supply exceeds venous drainage. This will cause congestion in the interseptal compartments with subsequently reduced perfusion and increased pressure. An efficient mechanism to counteract venous congestion and safeguard the viability of the conceptus is by reducing arterial inflow via shallow dilatation of the spiral arteries. This review made the case for intervillous space congestion as an unexplored trigger for inadequate spiral artery dilatation during the placentation process, eventually leading to abnormal systemic circulatory dysfunctions. An abnormal maternal venous function can result from an abnormal maternal immune response to paternal antigens with an imbalanced release of vasoactive mediators or can exist before conception. To get the full picture of abnormal placentation, maternal veins must not be forgotten.

Here and there a trophoblast, a transcriptional evaluation of trophoblast cell models.

A recent explosion of methods to produce human trophoblast and stem cells (hTSCs) is fuelling a renewed interest in this tissue. The trophoblast is critical to reproduction by facilitating implantation, maternal physiological adaptations to pregnancy and the growth of the fetus through transport of nutrients between the mother and fetus. More broadly, the trophoblast has phenotypic properties that make it of interest to other fields. Its angiogenic and invasive properties are similar to tumours and could identify novel drug targets, and its ability to regulate immunological tolerance of the allogenic fetus could lead to improvements in transplantations. Within this review, we integrate and assess transcriptomic data of cell-based models of hTSC alongside in vivo samples to identify the utility and applicability of these models. We also integrate single-cell RNA sequencing data sets of human blastoids, stem cells and embryos to identify how these models may recapitulate early trophoblast development.

Atypical protein kinase C iota (PKCλ/ι) ensures mammalian development by establishing the maternal-fetal exchange interface.

In utero mammalian development relies on the establishment of the maternal-fetal exchange interface, which ensures transportation of nutrients and gases between the mother and the fetus. This exchange interface is established via development of multinucleated syncytiotrophoblast cells (SynTs) during placentation. In mice, SynTs develop via differentiation of the trophoblast stem cell-like progenitor cells (TSPCs) of the placenta primordium, and in humans, SynTs are developed via differentiation of villous cytotrophoblast (CTB) progenitors. Despite the critical need in pregnancy progression, conserved signaling mechanisms that ensure SynT development are poorly understood. Herein, we show that atypical protein kinase C iota (PKCλ/ι) plays an essential role in establishing the SynT differentiation program in trophoblast progenitors. Loss of PKCλ/ι in the mouse TSPCs abrogates SynT development, leading to embryonic death at approximately embryonic day 9.0 (E9.0). We also show that PKCλ/ι-mediated priming of trophoblast progenitors for SynT differentiation is a conserved event during human placentation. PKCλ/ι is selectively expressed in the first-trimester CTBs of a developing human placenta. Furthermore, loss of PKCλ/ι in CTB-derived human trophoblast stem cells (human TSCs) impairs their SynT differentiation potential both in vitro and after transplantation in immunocompromised mice. Our mechanistic analyses indicate that PKCλ/ι signaling maintains expression of GCM1, GATA2, and PPARγ, which are key transcription factors to instigate SynT differentiation programs in both mouse and human trophoblast progenitors. Our study uncovers a conserved molecular mechanism, in which PKCλ/ι signaling regulates establishment of the maternal-fetal exchange surface by promoting trophoblast progenitor-to-SynT transition during placentation.

Development of the human placenta.

The placenta is essential for normal in utero development in mammals. In humans, defective placental formation underpins common pregnancy disorders such as pre-eclampsia and fetal growth restriction. The great variation in placental types across mammals means that animal models have been of limited use in understanding human placental development. However, new tools for studying human placental development, including 3D organoids, stem cell culture systems and single cell RNA sequencing, have brought new insights into this field. Here, we review the morphological, molecular and functional aspects of human placental formation, with a focus on the defining cell of the placenta - the trophoblast.