Modeling Trophoblast Cell-Guided Uterine Spiral Artery Transformation in the Rat

Cited2 is a key regulator of placental development and plasticity

The biology of trophoblast cell lineage development and placentation is characterized by the involvement of several known transcription factors. Central to the action of a subset of these transcriptional regulators is CBP-p300 interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2). CITED2 acts as a coregulator modulating transcription factor activities and affecting placental development and adaptations to physiological stressors. These actions of CITED2 on the trophoblast cell lineage and placentation are conserved across the mouse, rat, and human. Thus, aspects of CITED2 biology in hemochorial placentation can be effectively modeled in the mouse and rat. In this review, we present information on the conserved role of CITED2 in the biology of placentation and discuss the use of CITED2 as a tool to discover new insights into regulatory mechanisms controlling placental development.

IL1β-NFκβ-Myocardin signaling axis governs trophoblast-directed plasticity of vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) plasticity is fundamental in uterine spiral artery remodeling during placentation in Eutherian mammals. Our previous work showed that the invasion of trophoblast cells into uterine myometrium coincides with a phenotypic change of VSMCs. Here, we elucidate the mechanism by which trophoblast cells confer VSMC plasticity. Analysis of genetic markers on E13.5, E16.5, and E19.5 in the rat metrial gland, the entry point of uterine arteries, revealed that trophoblast invasion is associated with downregulation of MYOCARDIN, α-smooth muscle actin, and calponin1, and concomitant upregulation of Smemb in VSMCs. Myocardin overexpression or knockdown in VSMCs led to upregulation or downregulation of contractile markers, respectively. Co-culture of trophoblast cells with VSMCs decreased MYOCARDIN expression along with compromised expression of contractile markers in VSMCs. However, co-culture of trophoblast cells with VSMCs overexpressing MYOCARDIN inhibited their change in phenotype, whereas, overexpression of transactivation domain deleted MYOCARDIN failed to elicit this response. Furthermore, the co-culture of trophoblast cells with VSMCs led to the activation of NFκβ signaling. Interestingly, despite producing IL-1β, trophoblast cells possess only the decoy receptor, whereas, VSMCs possess the IL-1β signaling receptor. Treatment of VSMCs with exogenous IL-1β led to a decrease in MYOCARDIN and an increase in phosphorylation of NFκβ. The effect of trophoblast cells in the downregulation of MYOCARDIN in VSMCs was reversed by blocking NFκβ translocation to the nucleus. Together, these data highlight that trophoblast cells direct VSMC plasticity, and trophoblast-derived IL-1β is a key player in downregulating MYOCARDIN via the NFκβ signaling pathway.

NOTUM-MEDIATED WNT SILENCING DRIVES EXTRAVILLOUS TROPHOBLAST CELL LINEAGE DEVELOPMENT

Trophoblast stem (TS) cells have the unique capacity to differentiate into specialized cell types, including extravillous trophoblast (EVT) cells. EVT cells invade into and transform the uterus where they act to remodel the vasculature facilitating the redirection of maternal nutrients to the developing fetus. Disruptions in EVT cell development and function are at the core of pregnancy-related disease. WNT-activated signal transduction is a conserved regulator of morphogenesis of many organ systems, including the placenta. In human TS cells, activation of canonical WNT signaling is critical for maintenance of the TS cell stem state and its downregulation accompanies EVT cell differentiation. We show that aberrant WNT signaling undermines EVT cell differentiation. Notum, palmitoleoyl-protein carboxylesterase (NOTUM), a negative regulator of canonical WNT signaling, was prominently expressed in first trimester EVT cells developing in situ and upregulated in EVT cells derived from human TS cells. Furthermore, NOTUM was required for human TS cell differentiation to EVT cells. Activation of NOTUM in EVT cells is driven, at least in part, by endothelial PAS domain 1 (also called hypoxia-inducible factor 2 alpha). Collectively, our findings indicate that canonical WNT signaling is essential for maintenance of human trophoblast cell stemness and prevention of human TS cell differentiation. Downregulation of canonical WNT signaling via the actions of NOTUM is required for EVT cell differentiation.

Human uterine natural killer cells regulate differentiation of extravillous trophoblast early in pregnancy

In humans, balanced invasion of trophoblast cells into the uterine mucosa, the decidua, is critical for successful pregnancy. Evidence suggests that this process is regulated by uterine natural killer (uNK) cells, but how they influence reproductive outcomes is unclear. Here, we used our trophoblast organoids and primary tissue samples to determine how uNK cells affect placentation. By locating potential interaction axes between trophoblast and uNK cells using single-cell transcriptomics and in vitro modeling of these interactions in organoids, we identify a uNK cell-derived cytokine signal that promotes trophoblast differentiation at the late stage of the invasive pathway. Moreover, it affects transcriptional programs involved in regulating blood flow, nutrients, and inflammatory and adaptive immune responses, as well as gene signatures associated with disorders of pregnancy such as pre-eclampsia. Our findings suggest mechanisms on how optimal immunological interactions between uNK cells and trophoblast enhance reproductive success.

Conditionally mutant animal model for investigating the invasive trophoblast cell lineage

Placental development involves coordinated expansion and differentiation of trophoblast cell lineages possessing specialized functions. Among the differentiated trophoblast cell lineages are invasive trophoblast cells, which exit the placenta and invade the uterus, where they restructure the uterine parenchyma and facilitate remodeling of uterine spiral arteries. The rat exhibits deep intrauterine trophoblast cell invasion, a feature shared with human placentation, and is also amenable to gene manipulation using genome-editing techniques. In this investigation, we generated a conditional rat model targeting the invasive trophoblast cell lineage. Prolactin family 7, subfamily b, member 1 (Prl7b1) is uniquely and abundantly expressed in the rat invasive trophoblast cell lineage. Disruption of Prl7b1 did not adversely affect placental development. We demonstrated that the Prl7b1 locus could be effectively used to drive the expression of Cre recombinase in invasive trophoblast cells. Our rat model represents a new tool for investigating candidate genes contributing to the regulation of invasive trophoblast cells and their roles in trophoblast-guided uterine spiral artery remodeling.

Modeling aging and retinal degeneration with mitochondrial DNA mutation burden

Somatic mitochondrial DNA (mtDNA) mutation accumulation has been observed in individuals with retinal degenerative disorders. To study the effects of aging and mtDNA mutation accumulation in the retina, a Polymerase gamma (POLG) deficiency model, the POLGD257A mutator mice (PolgD257A), was used. POLG is an enzyme responsible for regulating mtDNA replication and repair. Retinas of young and older mice with this mutation were analyzed in vivo and ex vivo to provide new insights into the contribution of age-related mitochondrial dysfunction due to mtDNA damage. Optical coherence tomography (OCT) image analysis revealed a decrease in retinal and photoreceptor thickness starting at 6 months of age in mice with the POLGD257A mutation compared to wild-type (WT) mice. Electroretinography (ERG) testing showed a significant decrease in all recorded responses at 6 months of age. Sections labeled with markers of different types of retinal cells, including cones, rods, and bipolar cells, exhibited decreased labeling starting at 6 months. However, electron microscopy analysis revealed differences in retinal pigment epithelium (RPE) mitochondria morphology beginning at 3 months. Interestingly, there was no increase in oxidative stress observed in the retina or RPE of POLGD257A mice. Additionally, POLGD257A RPE exhibited an accelerated rate of autofluorescence cytoplasmic granule formation and accumulation. Mitochondrial markers displayed decreased abundance in protein lysates obtained from retina and RPE samples. These findings suggest that the accumulation of mitochondrial DNA mutations leads to impaired mitochondrial function and accelerated aging, resulting in retinal degeneration.

Characterization of cannabinoid plasma concentration, maternal health, and cytokine levels in a rat model of prenatal Cannabis smoke exposure

Cannabis sativa has gained popularity as a "natural substance", leading many to falsely assume that it is not harmful. This assumption has been documented amongst pregnant mothers, many of whom consider Cannabis use during pregnancy as benign. The purpose of this study was to validate a Cannabis smoke exposure model in pregnant rats by determining the plasma levels of cannabinoids and associated metabolites in the dams after exposure to either Cannabis smoke or injected cannabinoids. Maternal and fetal cytokine and chemokine profiles were also assessed after exposure. Pregnant Sprague-Dawley rats were treated daily from gestational day 6-20 with either room air, i.p. vehicle, inhaled high-Δ9-tetrahydrocannabinol (THC) (18% THC, 0.1% cannabidiol [CBD]) smoke, inhaled high-CBD (0.7% THC, 13% CBD) smoke, 3 mg/kg i.p. THC, or 10 mg/kg i.p. CBD. Our data reveal that THC and CBD, but not their metabolites, accumulate in maternal plasma after repeated exposures. Injection of THC or CBD was associated with fewer offspring and increased uterine reabsorption events. For cytokines and chemokines, injection of THC or CBD up-regulated several pro-inflammatory cytokines compared to control or high-THC smoke or high-CBD smoke in placental and fetal brain tissue, whereas smoke exposure was generally associated with reduced cytokine and chemokine concentrations in placental and fetal brain tissue compared to controls. These results support existing, but limited, knowledge on how different routes of administration contribute to inconsistent manifestations of cannabinoid-mediated effects on pregnancy. Smoked Cannabis is still the most common means of human consumption, and more preclinical investigation is needed to determine the effects of smoke inhalation on developmental and behavioural trajectories.

CONDITIONALLY MUTANT ANIMAL MODEL FOR INVESTIGATING THE INVASIVE TROPHOBLAST CELL LINEAGE

Placental development involves coordinated expansion and differentiation of trophoblast cell lineages possessing specialized functions. Among the differentiated trophoblast cell lineages are invasive trophoblast cells, which exit the placenta and invade into the uterus where they restructure the uterine parenchyma and facilitate remodeling of uterine spiral arteries. The rat exhibits deep intrauterine trophoblast cell invasion, a feature shared with human placentation, and is also amenable to gene manipulation using genome editing techniques. In this investigation, we generated a conditional rat model targeting the invasive trophoblast cell lineage. Prolactin family 7, subfamily b, member 1 ( Prl7b1 ) is uniquely and abundantly expressed in the rat invasive trophoblast cell lineage. Disruption of Prl7b1 did not adversely affect placental development. We demonstrated that the Prl7b1 locus could be effectively used to drive the expression of Cre recombinase in invasive trophoblast cells. Our rat model represents a new tool for investigating candidate genes contributing to the regulation of invasive trophoblast cells and their contributions to trophoblast-guided uterine spiral artery remodeling.

Core conserved transcriptional regulatory networks define the invasive trophoblast cell lineage

The invasive trophoblast cell lineages in rat and human share crucial responsibilities in establishing the uterine-placental interface of the hemochorial placenta. These observations have led to the rat becoming an especially useful animal model for studying hemochorial placentation. However, our understanding of similarities or differences between regulatory mechanisms governing rat and human invasive trophoblast cell populations is limited. In this study, we generated single-nucleus ATAC-seq data from gestation day 15.5 and 19.5 rat uterine-placental interface tissues, and integrated the data with single-cell RNA-seq data generated at the same stages. We determined the chromatin accessibility profiles of invasive trophoblast, natural killer, macrophage, endothelial and smooth muscle cells, and compared invasive trophoblast chromatin accessibility with extravillous trophoblast cell accessibility. In comparing chromatin accessibility profiles between species, we found similarities in patterns of gene regulation and groups of motifs enriched in accessible regions. Finally, we identified a conserved gene regulatory network in invasive trophoblast cells. Our data, findings and analysis will facilitate future studies investigating regulatory mechanisms essential for the invasive trophoblast cell lineage.

Effects of cyclophosphamide on rat placental development

We examined the morphological effects of cyclophosphamide (CPA) on placental development in pregnant rats. CPA was administered as a single dose to pregnant rats intraperitoneally at 0 mg/kg (the control group), 25 mg/kg on gestation day (GD) 12 (the CPA GD 12-treated group), and 25 mg/kg on GD 14 (the CPA GD 14-treated group). The fetal and placental weight decreased in the CPA-treated groups, complete fetal resorption from GD 17 onwards in the CPA GD 12-treated group, and external malformations in the CPA GD 14-treated group. Histopathologically, CPA induced apoptosis and/or cell proliferation inhibition in each part of the placenta. In the labyrinth zone, syncytiotrophoblasts were selectively reduced, resulting in a small placenta. In the basal zone, the number of spongiotrophoblasts was reduced, resulting in hypoplasia of glycogen cell islands. In addition, a small number of interstitial trophoblasts invaded the metrial gland from the basal zone on GD 15. The severity of these lesions was higher in the CPA GD 12-treated group than in the CPA GD 14-treated group. In the metrial gland, although the number of uterine natural killer cells was reduced, metrial gland development was not affected.

Mitochondrial ROS Accumulation Contributes to Maternal Hypertension and Impaired Remodeling of Spiral Artery but Not IUGR in a Rat PE Model Caused by Maternal Glucocorticoid Exposure

Increased maternal glucocorticoid levels have been implicated as a risk factor for preeclampsia (PE) development. We found that pregnant rats exposed to dexamethasone (DEX) showed hallmarks of PE features, impaired spiral artery (SA) remodeling, and elevated circulatory levels of sFlt1, sEng IL-1β, and TNFα. Abnormal mitochondrial morphology and mitochondrial dysfunction in placentas occurred in DEX rats. Omics showed that a large spectrum of placental signaling pathways, including oxidative phosphorylation (OXPHOS), energy metabolism, inflammation, and insulin-like growth factor (IGF) system were affected in DEX rats. MitoTEMPO, a mitochondria-targeted antioxidant, alleviated maternal hypertension and renal damage, and improved SA remodeling, uteroplacental blood flow, and the placental vasculature network. It reversed several pathways, including OXPHOS and glutathione pathways. Moreover, DEX-induced impaired functions of human extravillous trophoblasts were associated with excess ROS caused by mitochondrial dysfunction. However, scavenging excess ROS did not improve intrauterine growth retardation (IUGR), and elevated circulatory sFlt1, sEng, IL-1β, and TNFα levels in DEX rats. Our data indicate that excess mitochondrial ROS contributes to trophoblast dysfunction, impaired SA remodeling, reduced uteroplacental blood flow, and maternal hypertension in the DEX-induced PE model, while increased sFlt1 and sEng levels and IUGR might be associated with inflammation and an impaired energy metabolism and IGF system.

CORE CONSERVED TRANSCRIPTIONAL REGULATORY NETWORKS DEFINE THE INVASIVE TROPHOBLAST CELL LINEAGE

The invasive trophoblast cell lineage in rat and human share crucial responsibilities in establishing the uterine-placental interface of the hemochorial placenta. These observations have led to the rat becoming an especially useful animal model to study hemochorial placentation. However, our understanding of similarities or differences between regulatory mechanisms governing rat and human invasive trophoblast cell populations is limited. In this study, we generated single-nucleus (sn) ATAC-seq data from gestation day (gd) 15.5 and 19.5 rat uterine-placental interface tissues and integrated the data with single-cell RNA-seq data generated at the same stages. We determined the chromatin accessibility profiles of invasive trophoblast, natural killer, macrophage, endothelial, and smooth muscle cells, and compared invasive trophoblast chromatin accessibility to extravillous trophoblast (EVT) cell accessibility. In comparing chromatin accessibility profiles between species, we found similarities in patterns of gene regulation and groups of motifs enriched in accessible regions. Finally, we identified a conserved gene regulatory network in invasive trophoblast cells. Our data, findings and analysis will facilitate future studies investigating regulatory mechanisms essential for the invasive trophoblast cell lineage.

Trans-differentiation of trophoblast stem cells: implications in placental biology

Trophoblast invasion is a hallmark of hemochorial placentation. Invasive trophoblast cells replace the endothelial cells of uterine spiral arteries. The mechanism by which the invasive trophoblast cells acquire this phenotype is unknown. Here, we demonstrate that, during differentiation, a small population of trophoblast stem (TS) cells trans-differentiate into a hybrid cell type expressing markers of both trophoblast (TC) and endothelial (EC) cells. In addition, a compendium of EC-specific genes was found to be associated with TS cell differentiation. Using functional annotation, these genes were categorized into angiogenesis, cell adhesion molecules, and apoptosis-related genes. HES1 repressed transcription of EC genes in TS cells. Interestingly, differentiated TCs secrete TRAIL, but its receptor DR4 is expressed only in ECs and not in TCs. TRAIL induced apoptosis in EC but not in TC. Co-culture of ECs with TC induced apoptosis in ECs via extrinsic apoptotic pathway. These results highlight that (a) TS cells possess the potential to trans-differentiate into "trophendothelial" phenotype, regulated by HES1 and (b) trophoblast differentiation-induced TRAIL secretion directs preferential demise of ECs located in their vicinity.

Molecular Mechanisms of Pregnancy-Related Vascular Remodeling and Pregnancy Complications

The purpose of this editorial is to highlight the various observations made in this Special Issue in the International Journal of Molecular Sciences [...].

CITED2 is a conserved regulator of the uterine-placental interface

Establishment of the hemochorial uterine-placental interface requires exodus of trophoblast cells from the placenta and their transformative actions on the uterus, which represent processes critical for a successful pregnancy, but are poorly understood. We examined the involvement of CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2) in rat and human trophoblast cell development. The rat and human exhibit deep hemochorial placentation. CITED2 was distinctively expressed in the junctional zone (JZ) and invasive trophoblast cells of the rat. Homozygous Cited2 gene deletion resulted in placental and fetal growth restriction. Small Cited2 null placentas were characterized by disruptions in the JZ, delays in intrauterine trophoblast cell invasion, and compromised plasticity. In the human placentation site, CITED2 was uniquely expressed in the extravillous trophoblast (EVT) cell column and importantly contributed to the development of the EVT cell lineage. We conclude that CITED2 is a conserved regulator of deep hemochorial placentation.

The AKT1-FOXO4 axis reciprocally regulates hemochorial placentation

Hemochorial placentation involves the differentiation of invasive trophoblast cells, specialized cells that possess the capacity to exit the placenta and invade into the uterus where they restructure the vasculature. Invasive trophoblast cells arise from a well-defined compartment within the placenta, referred to as the junctional zone in rat and the extravillous trophoblast cell column in human. In this study, we investigated roles for AKT1, a serine/threonine kinase, in placental development using a genome-edited/loss-of-function rat model. Disruption of AKT1 resulted in placental, fetal and postnatal growth restriction. Forkhead box O4 (Foxo4), which encodes a transcription factor and known AKT substrate, was abundantly expressed in the junctional zone and in invasive trophoblast cells of the rat placentation site. Foxo4 gene disruption using genome editing resulted in placentomegaly, including an enlarged junctional zone. AKT1 and FOXO4 regulate the expression of many of the same transcripts expressed by trophoblast cells, but in opposite directions. In summary, we have identified AKT1 and FOXO4 as part of a regulatory network that reciprocally controls critical indices of hemochorial placenta development.

Hyperglycemia disturbs trophoblast functions and subsequently leads to failure of uterine spiral artery remodeling

Uterine spiral artery remodeling is necessary for fetal growth and development as well as pregnancy outcomes. During remodeling, trophoblasts invade the arteries, replace the endothelium and disrupt the vascular smooth muscle, and are strictly regulated by the local microenvironment. Elevated glucose levels at the fetal-maternal interface are associated with disorganized placental villi and poor placental blood flow. Hyperglycemia disturbs trophoblast proliferation and invasion via inhibiting the epithelial-mesenchymal transition, altering the protein expression of related proteases (MMP9, MMP2, and uPA) and angiogenic factors (VEGF, PIGF). Besides, hyperglycemia influences the cellular crosstalk between immune cells, trophoblast, and vascular cells, leading to the failure of spiral artery remodeling. This review provides insight into molecular mechanisms and signaling pathways of hyperglycemia that influence trophoblast functions and uterine spiral artery remodeling.

Reliability of Rodent and Rabbit Models in Preeclampsia Research

In vivo studies on the pathology of gestation, including preeclampsia, often use small mammals such as rabbits or rodents, i.e., mice, rats, hamsters, and guinea pigs. The key advantage of these animals is their short reproductive cycle; in addition, similar to humans, they also develop a haemochorial placenta and present a similar transformation of maternal spiral arteries. Interestingly, pregnant dams also demonstrate a similar reaction to inflammatory factors and placentally derived antiangiogenic factors, i.e., soluble fms-like tyrosine kinase 1 (sFlt-1) or soluble endoglin-1 (sEng), as preeclamptic women: all animals present an increase in blood pressure and usually proteinuria. These constitute the classical duet that allows for the recognition of preeclampsia. However, the time of initiation of maternal vessel remodelling and the depth of trophoblast invasion differs between rabbits, rodents, and humans. Unfortunately, at present, no known animal replicates a human pregnancy exactly, and hence, the use of rabbit and rodent models is restricted to the investigation of individual aspects of human gestation only. This article compares the process of placentation in rodents, rabbits, and humans, which should be considered when planning experiments on preeclampsia; these aspects might determine the success, or failure, of the study. The report also reviews the rodent and rabbit models used to investigate certain aspects of the pathomechanism of human preeclampsia, especially those related to incorrect trophoblast invasion, placental hypoxia, inflammation, or maternal endothelial dysfunction.

Conservation at the uterine-placental interface

The hemochorial placentation site is characterized by a dynamic interplay between trophoblast cells and maternal cells. These cells cooperate to establish an interface required for nutrient delivery to promote fetal growth. In the human, trophoblast cells penetrate deep into the uterus. This is not a consistent feature of hemochorial placentation and has hindered the establishment of suitable animal models. The rat represents an intriguing model for investigating hemochorial placentation with deep trophoblast cell invasion. In this study, we used single-cell RNA sequencing to characterize the transcriptome of the invasive trophoblast cell lineage, as well as other cell populations within the rat uterine-placental interface during early (gestation day [gd] 15.5) and late (gd 19.5) stages of intrauterine trophoblast cell invasion. We identified a robust set of transcripts that define invasive trophoblast cells, as well as transcripts that distinguished endothelial, smooth muscle, natural killer, and macrophage cells. Invasive trophoblast, immune, and endothelial cell populations exhibited distinct spatial relationships within the uterine-placental interface. Furthermore, the maturation stage of invasive trophoblast cell development could be determined by assessing gestation stage-dependent changes in transcript expression. Finally, and most importantly, expression of a prominent subset of rat invasive trophoblast cell transcripts is conserved in the invasive extravillous trophoblast cell lineage of the human placenta. These findings provide foundational data to identify and interrogate key conserved regulatory mechanisms essential for the development and function of an important compartment within the hemochorial placentation site that is essential for a healthy pregnancy.

The role of extravillous trophoblasts and uterine NK cells in vascular remodeling during pregnancy

Successful embryo implantation requires both a receptive endometrium and competent blastocysts. After implantation, the maternal decidua undergoes a series of changes, including uterine spiral artery (SA) remodeling to accommodate the fetus and provide nutrients and oxygen for the fetus to survive. Uterine spiral arteries transform from small-diameter, high-resistance arteries to large-diameter and low-resistance arteries during pregnancy. This transformation includes many changes, such as increased permeability and dilation of vessels, phenotypic switching and migration of vascular smooth muscle cells (VSMCs), transient loss of endothelial cells (ECs), endovascular invasion of extravillous trophoblasts (EVTs), and presence of intramural EVT, which are regulated by uterine NK (uNK) cells and EVTs. In this review, we mainly focus on the separate and combined roles of uNK cells and EVTs in uterine SA remodeling in establishing and maintaining pregnancy. New insight into related mechanisms will help us better understand the pathogenesis of pregnancy complications such as recurrent pregnancy loss (RPL) and preeclampsia (PE).

Stem Cell-Based Trophoblast Models to Unravel the Genetic Causes of Human Miscarriages

Miscarriage affects approximately 15% of clinically recognized pregnancies, and 1-3% of couples experience pregnancy loss recurrently. Approximately 50-60% of miscarriages result from chromosomal abnormalities, whereas up to 60% of euploid recurrent abortions harbor variants in candidate genes. The growing number of detected genetic variants requires an investigation into their role in adverse pregnancy outcomes. Since placental defects are the main cause of first-trimester miscarriages, the purpose of this review is to provide a survey of state-of-the-art human in vitro trophoblast models that can be used for the functional assessment of specific abnormalities/variants implicated in pregnancy loss. Since 2018, when primary human trophoblast stem cells were first derived, there has been rapid growth in models of trophoblast lineage. It has been found that a proper balance between self-renewal and differentiation in trophoblast progenitors is crucial for the maintenance of pregnancy. Different responses to aneuploidy have been shown in human embryonic and extra-embryonic lineages. Stem cell-based models provide a powerful tool to explore the effect of a specific aneuploidy/variant on the fetus through placental development, which is important, from a clinical point of view, for deciding on the suitability of embryos for transfer after preimplantation genetic testing for aneuploidy.