Human Preimplantation Embryos Research Articles

Global, Survival, and Apoptotic Transcriptome during Mouse and Human Early Embryonic Development.

Survival and cell death signals are crucial for mammalian embryo preimplantation development. However, the knowledge on the molecular mechanisms underlying their regulation is still limited. Mouse studies are widely used to understand preimplantation embryo development, but extrapolation of these results to humans is questionable. Therefore, we wanted to analyse the global expression profiles during early mouse and human development with a special focus on genes involved in the regulation of the apoptotic and survival pathways. We used DNA microarray technology to analyse the global gene expression profiles of preimplantation human and mouse embryos (metaphase II oocytes, embryos at the embryonic genome activation stage, and blastocysts). Components of the major apoptotic and survival signalling pathways were expressed during early human and mouse embryonic development; however, most expression profiles were species-specific. Particularly, the expression of genes encoding components and regulators of the apoptotic machinery were extremely stable in mouse embryos at all analysed stages, while it was more stage-specific in human embryos. CASP3, CASP9, and AIF were the only apoptosis-related genes expressed in both species and at all studied stages. Moreover, numerous transcripts related to the apoptotic and survival pathway were reported for the first time such as CASP6 and IL1RAPL1 that were specific to MII oocytes; CASP2, ENDOG, and GFER to blastocysts in human. These findings open new perspectives for the characterization and understanding of the survival and apoptotic signalling pathways that control early human and mouse embryonic development.

Human blastocysts of normal and abnormal karyotypes display distinct transcriptome profiles

Unveiling the transcriptome of human blastocysts can provide a wealth of important information regarding early embryonic ontology. Comparing the mRNA production of embryos with normal and abnormal karyotypes allows for a deeper understanding of the protein pathways leading to viability and aberrant fetal development. In addition, identifying transcripts specific for normal or abnormal chromosome copy number could aid in the search for secreted substances that could be used to non-invasively identify embryos best suited for IVF embryo transfer. Using RNA-seq, we characterized the transcriptome of 71 normally developing human blastocysts that were karyotypically normal vs. trisomic or monosomic. Every monosomy and trisomy of the autosomal and sex chromosomes were evaluated, mostly in duplicate. We first mapped the transcriptome of three normal embryos and found that a common core of more than 3,000 genes is expressed in all embryos. These genes represent pathways related to actively dividing cells, such as ribosome biogenesis and function, spliceosome, oxidative phosphorylation, cell cycle and metabolic pathways. We then compared transcriptome profiles of aneuploid embryos to those of normal embryos. We observed that non-viable embryos had a large number of dysregulated genes, some showing a hundred-fold difference in expression. On the contrary, sex chromosome abnormalities, XO and XXX displayed transcriptomes more closely mimicking those embryos with 23 normal chromosome pairs. Intriguingly, we identified a set of commonly deregulated genes in the majority of both trisomies and monosomies. This is the first paper demonstrating a comprehensive transcriptome delineation of karyotypic abnormalities found in the human pre-implantation embryo. We believe that this information will contribute to the development of new pre-implantation genetic screening methods as well as a better understanding of the underlying developmental abnormalities of abnormal embryos, fetuses and children.

Dynamics of alternative polyadenylation in human preimplantation embryos

Alternative polyadenylation (APA) affects the length of the 3′ untranslated region (3′-UTR) and the regulation of microRNAs. Previous studies have shown that cancer cells tend to have shorter 3′-UTRs than normal cells. A plausible explanation for this is that it enables cancer cells to escape the regulation of microRNAs. Here, we extend this concept to an opposing context: changes in 3′-UTR length in the development of the human preimplantation embryo. Unlike cancer cells, during early development 3′-UTRs tended to become longer, and gene expression was negatively correlated with 3′-UTR length. Moreover, our functional enrichment results showed that length changes are part of the development mechanism. We also investigated the analogy of 3′-UTR length variation with respect to lncRNAs and found that, similarly, lncRNA length tended to increase during embryo development.

Understanding the scope and significance of mosaicism in human preimplantation embryos

Understanding the scope and significance of mosaicism in human preimplantation embryos

MiR-21 in extracellular vesicles contributes to the growth of fertilized eggs and embryo development in mice.

Human preimplantation embryo development is susceptible to high rates of early embryo wastage. We determined the miR-21 expression of extracellular vesicles (EVs) in fertilized eggs and embryos of varying stages and their response to miR-21 microinjection. Sexually mature female and male mice were mated. Next, the expression and immunohistochemistry intensity of surface markers (CD9 and CD63) of EVs were detected in pregnant and non-pregnant mice. Exosomes were co-cultured with embryos for detection of blastocyst formation rate, and embryo apoptosis. Moreover, the expressions of Bcl-2 associated X protein (Bax), B cell lymphoma 2 (Bcl-2), and octamer-binding transcription factor-4 (Oct4) were determined. Finally, we detected miR-21 expression in EVs of uterus in pregnant mice, in embryos after embryo implantation and after embryo co-cultured with exosomes in uterine luminal fluid. MiR-21 was up-regulated in EVs of uterus, and higher immunohistochemistry intensity of CD9 and CD63, suggesting more EVs secreted in uterine luminal fluid in pregnant mice. After microinjection, miR-21 inhibitor suppresses embryo development of mice. Moreover, embryos co-cultured with exosomes display higher blastocyst formation rate, reduced apoptotic rate of embryos in pregnant mice. In addition, miR-21 was down-regulated with the development of embryos after embryo implantation, while miR-21 expression in embryos was up-regulated by exosomes in uterine luminal fluid in the pregnant mice. Increased miR-21 expression in EVs of uterus and increased miR-21 expression after implantation, which indicate the key role in the growth of fertilized eggs and embryo development in mice.

PH stability of human preimplantation embryo culture media: effects of culture and batches.

How stable is the pH of human preimplantation embryo culture media during IVF culture and is there variation in pH between batches of culture media? To evaluate pH stability, three batches of three culture media were incubated in triplicate without embryos (sham culture) at CO2 levels recommended by the manufacturers (5% or 6%) for 4 days. To evaluate differences in pH between batches, the pH of three batches of five culture media was measured in triplicate during 1 day of sham culture. Linear mixed models were used for the analysis. An increase in pH during 4 days of culture was found in all three culture media, but the observed increased values were within the generally accepted range for clinical practice (pH 7.2-7.4). One medium was pH 7.1 in the first 2 days, but this was within the range provided by the manufacturer for that medium. Three out of five analysed media showed batch variation in pH that exceeded the generally accepted range for clinical practice. A relevant difference in pH was found between batches of human preimplantation embryo culture media. This suggests that the CO2 level of incubators may need to be adjusted for new batches of culture medium based on measured pH, to anticipate batch variability and safely accommodate limited pH increase over time. This study was unable to identify the cause of the differences in pH between batches, and further investigation on a larger number of batches and other media seems warranted.

Expression of endogenous retroviruses in pre‐implantation stages of bovine embryo

Endogenous retroviruses (ERVs) are involved in cellular proliferation, pluripotency, tissue-specific remodelling and regulation of developmental processes. These elements are transcriptionally active in mouse and human pre-implantation embryos. Empirical evidence indicates that regulatory networks involved with ERV transcripts are responsible for pluripotency and totipotency at certain stages of mouse and human pre-implantation development. Yet, the expression in pre-implantation bovine embryo remains unidentified. To determine whether two members of bovine endogenous retroviruses, BERV-K1 and BERV-K2, are expressed in the pre-implantation bovine embryo, each embryonic stage developed in vitro and was subjected to RNA release, reverse transcription and quantitative PCR. We found that BERV-K1 and BERV-K2 are expressed throughout different stages of pre-implantation development. The higher level of expression was detected in embryonic blastomeres with totipotent/pluripotent status (two-cell to 16-cell stages), while the more differentiated blastocyst stage showed significantly lower levels of ERVs expression. These findings suggest a possible role for endogenous retroviruses in the establishment of totipotent and pluripotent states in pre-implantation bovine embryo, similar to functions which have been suggested for these elements in human and mouse embryos.

Epigenetic Symmetry of DLGAP2: Pre-Implantation Maternal Methylation Switches to a Random Monoallelic Profile in Somatic Tissues

- Background Symmetric DNA methylation profiles of autosomal genes is associated with equal expression from both alleles. Genes with an allelic imbalance or monoallelic expression are associated with discrete intervals of allele-specific methylation (ASM), as highlighted by genomic imprinting, X-chromosome inactivation and genotype-driven ASM. However, a more complex pattern has been described in which random monoallelic methylation provides cells a unique mechanism for modulating allelic dosage. - Methods We combined direct interrogation of genome-wide methyl-seq datasets with locus-specific methylation and expression analysis to characterize the epigenetic profile of a CpG island associated with the DLGAP2 gene. The random nature of the ASM was confirmed using both bisulphite PCR in tissues and single-cell derived clonal analysis. - Results We identify an interval of oocyte-derived methylation that manifests as a maternally-methylated differentially methylated region (DMR) in human blastocysts and placenta which switches to a random ASM profile by week 16 of a gestation. Characterization using 5’RACE revealed that the ERICH1-AS1 transcript is linked to DLGAP2 presenting an alternative transcript start site. Quantitative RT-PCR of DLGAP2 suggests a highly restricted expression profile limited to testis and brain, with allelic RT-PCR demonstrating robust biallelic expression. - Conclusions While many intervals subject to transient maternal methylation in the human pre-implantation embryo resolve to a fully unmethylated state in somatic tissues, we describe the first example of a CpG island reverting to random ASM. This profile has unique parallels with X-chromosome inactivation (XCI) in female mice in which XCI is initially imprinted during pre-implantation development and maintained in the placenta, whilst derivatives of the inner cell mass are subject to random XCI. Since DLGAP2 has been associated with many neurological disorders, a potential role of allele-specific expression and random ASM may influence the presentation of the phenotypes.

Single-cell RNA sequencing reveals distinct gene expression patterns in glucose metabolism of human preimplantation embryos.

Precise regulation of glucose metabolism-related genes is essential for early embryonic development. Although previous research has yielded detailed information on the biochemical processes, little is yet known of the dynamic gene expression profiles in glucose metabolism of preimplantation embryos at a single-cell resolution. In the present study, we performed integrated analysis of single-cell RNA sequencing (scRNA-seq) data of human preimplantation embryos that had been cultured in sequential medium. Different cells in the same embryo have similar gene expression patterns in glucose metabolism. During the switch from the cleavage to morula stage, the expression of glycolysis-related genes, such as glucose transporter genes (solute carrier family 2 (facilitated glucose transporter), member 1 (SLC2A1) and solute carrier family 2 (facilitated glucose transporter), member 3 (SLC2A3) and genes encoding hexokinase, phosphofructokinase, pyruvate kinase and lactate dehydrogenase, is increased. The genes involved in the pentose phosphate pathway are highly expressed at the cleavage stage, generating the reducing power to balance oxidative stress derived from biosynthesis. Expression of the genes involved in the biosynthesis of glycerophospholipids is increased after the morula stage. Nevertheless, the expression of tricarboxylic acid-related genes remains relatively unchanged during the preimplantation stages. In conclusion, we discovered that the gene expression profiles are dynamic according to glucose utilisation in the embryos at different stages, which contributes to our understanding of regulatory mechanisms of glucose metabolism-related genes in human preimplantation embryos.

Low Cell-Matrix Adhesion Reveals Two Subtypes of Human Pluripotent Stem Cells

SummaryWe show that a human pluripotent stem cell (hPSC) population cultured on a low-adhesion substrate developed two hPSC subtypes with different colony morphologies: flat and domed. Notably, the dome-like cells showed higher active proliferation capacity and increased several pluripotent genes’ expression compared with the flat monolayer cells. We further demonstrated that cell-matrix adhesion mediates the interaction between cell morphology and expression of KLF4 and KLF5 through a serum response factor (SRF)-based regulatory double loop. Our results provide a mechanistic view on the coupling among adhesion, stem cell morphology, and pluripotency, shedding light on the critical role of cell-matrix adhesion in the induction and maintenance of hPSC.

Time-lapse imaging algorithms rank human preimplantation embryos according to the probability of live birth.

Can blastocysts leading to live births be ranked according to morphokinetic-based algorithms? Retrospective analysis of 781 single blastocyst embryo transfers, including all patient clinical factors that might be potential confounders for the primary outcome measure of live birth, was weighed using separate multi-variable logistic regression models. There was strong evidence of effect of embryo rank on odds of live birth. Embryos were classified A, B, C or D according to calculated variables; time to start (tSB) and duration (dB{tB - tSB}) of blastulation. Embryos of rank D were less likely to result in live birth than embryos of rank A (odds ratio [OR] 0.3046; 95% confidence interval [CI] 0.129, 0.660; P<0.005). Embryos ranked B were less likely to result in live birth than those ranked A (OR 0.7114; 95% Cl 0.505, 1.001; P<0.01), and embryos ranked C were less likely to result in live birth than those ranked A (OR 0.6501, 95% Cl 0.373, 1.118; P<0.01). Overall, the LRT (Likelihood Ratio Test) p-value for embryo rank shows that there is strong evidence that embryo rank is informative as a whole in discriminating between live birth and no live birth outcomes (p= 0.0101). The incidence of live birth was 52.5% from rank A, 39.2% from rank B, 31.4% from rank C and 13.2% from rank D. Time-lapse imaging morphokinetic-based algorithms for blastocysts can provide objective hierarchical ranking of embryos for predicting live birth and may have greater discriminating power than conventional blastocyst morphology assessment.

A single-cell chromatin map of human embryos.

The transition from a fertilized egg to a pluripotent and transcriptionally independent embryo requires multi-layered chromatin regulation. A study now provides simultaneous profiling of chromatin accessibility and DNA methylation in human preimplantation embryos at single-cell resolution.

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.

Extracellular vesicles: a promising tool for assessment of embryonic competence.

Extracellular vesicles have recently emerged as a promising field of research due to their pivotal roles in intercellular communication and potential to serve as biomarkers. This review focuses on extracellular vesicles secreted by the human preimplantation embryo. The most recent findings on embryo-derived extracellular vesicles are described and discussed, as well as current technical challenges to study them. So far, only a few studies have addressed extracellular vesicles of embryonic origin and explored their potential as biomarkers for embryo selection. Two main hypotheses have driven interest in studying extracellular vesicles in IVF embryo-conditioned culture media. On the one hand, the potential roles of extracellular vesicles in mediating the embryo-endometrial crosstalk for proper implantation. On the other hand, the profile of secreted extracellular vesicles as an indicator of embryonic fitness irrespective of any involvement or communication with the endometrium. Embryo-derived extracellular vesicles have already been investigated to design diagnostic tests for embryo viability, however with small sample sizes or without extensive technology validation. Extracellular vesicles offer indeed a novel means to assess embryonic fitness. Further validation studies, technology development and more complex study designs are certainly required to implement the profiling of embryonic extracellular vesicles as a diagnostic test for embryo selection.

Randomized controlled trial of low (5%) versus ultralow (2%) oxygen for extended culture using bipronucleate and tripronucleate human preimplantation embryos

To determine whether [1] exposure of embryos to 5% oxygen (O2) from day 1 (D1) to D3, and then to 2% O2 from D3 to D5, improves total blastocyst yield, as compared with continuous exposure to 5% O2; and [2] extended culture in 2% O2 alters key metabolic processes and O2-regulated gene expression in human preimplantation embryos. Randomized controlled trial. Academic medical center. Bipronucleate and tripronucleate embryos donated for research. On D1, sibling zygotes were randomized to culture in 5% O2 from D1 to D5 (n = 102; "5% group") or 5% O2 from D1 to D3, then 2% O2 from D3 to D5 (n = 101, "2% group"). Developmental stage and grade; D5 total cell counts; mass spectrometry of spent media; quantitative polymerase chain reaction of 21 genes in inner cell mass and trophectoderm. Among cleaved embryos (n = 176, 87%), those in the 2% group were less likely to arrest at the cleavage stage on D5 (34 of 87, 39.1%) compared with the 5% group (52 of 89, 58.4%) (adjusted odds ratio 0.38, 95% confidence interval 0.18-0.80). Those in the 2% group were more likely to blastulate (35 of 87, 40.2%) than those in the 5% group (20 of 89, 22.5%) (adjusted odds ratio 2.55, 95% confidence interval 1.27-5.12). Culture in 2% O2 was associated with significantly fewer cells in early and advanced blastocysts, alteration in relative abundances of anabolic amino acids and metabolites involved in redox homeostasis, and differential expression of MUC1 in trophectoderm. These findings provide foundational evidence for future investigation of 2% O2 as the preferred O2 tension for extended culture of human embryos.

Editorial introductions

Current Opinion in Obstetrics and Gynecology was launched in 1989. It is one of a successful series of review journals whose unique format is designed to provide a systematic and critical assessment of the literature as presented in the many primary journals. The field of obstetrics and gynecology is divided into nine sections that are reviewed once a year. Each section is assigned a Section Editor, a leading authority in the area, who identifies the most important topics at that time. Here we are pleased to introduce the Journal's Section Editors for this issue. SECTION EDITORS Emre SeliEmre SeliDr Seli received his medical degree from the Istanbul Medical School in Turkey and completed his Residency in Obstetrics and Gynecology at Yale University. His postdoctoral training included a fellowship in Reproductive Endocrinology and Infertility as well as a research fellowship in molecular biology, both at Yale University. He is currently Professor of Obstetrics, Gynecology, and Reproductive Sciences at Yale School of Medicine. Dr Seli is the recipient of many National Institutes of Health and pharmaceutical industry-sponsored research grants and has trained more than 50 pre- and post-doctoral fellows. His research focuses on infertility, egg donation and gestational surrogacy, assessment of embryo viability and oocyte and pre-implantation embryo development. He is a current or past member of the editorial boards of Molecular Human Reproduction, Frontiers in Bioscience, Reproductive Sciences, and Journal of Assisted Reproduction and Genetics, and serves as a reviewer for more than 20 scientific journals including New England Journal of Medicine, Science, The Lancet, Human Reproduction, Fertility and Sterility, Molecular Endocrinology, Endocrinology, Journal of Clinical Endocrinology and Metabolism, and Journal of Clinical Investigation. He has published more than 100 scientific articles, and edited four books: Non-invasive Management of Gynecologic Disorders, Infertility, Fertility Preservation, and Human Gametes and Pre-implantation Embryos: Assessment and Diagnosis. Dr Seli is the recipient of multiple awards for teaching, clinical excellence, and research, including: American College of Obstetricians and Gynecologists Fellowship Award for Research in Endocrinology of the Postreproductive Woman, Yale University “Resident of Excellence Award” for research, Society for Reproductive Investigation (SRI) President's Presenter Award, the American Society for Reproductive Medicine (ASRM) Ira and Ester Rosenwaks New Investigator Award, and Association of Professors of Gynecology and Obstetrics (APGO)-Yale Excellence in Teaching Award. He is also an active member of numerous professional societies including SRI, Society at the Study of Reproduction (SSR), European Society for Human Reproduction and Embryology (ESHRE) and ASRM, and a frequent invited speaker who has presented at national and international medical and scientific symposia. Juan A. García-VelascoJuan A. García-VelascoProfessor Juan A. García-Velasco is Director of IVI RMA-Madrid, Spain. He gained his degree in medicine at Complutense University, Madrid in 1990, before going on to train as a specialist in obstetrics and gynecology at La Paz Hospital, Madrid between 1992 and 1995. Professor García Velasco gained his PhD in medicine and surgery at Autónoma University, Madrid in 1995. He then became a sub-specialist in reproductive endocrinology and infertility at Yale University, USA in 1998. Professor García Velasco has published 122 scientific articles in impact journals along with 22 chapters and 4 books. He is the Principal Investigator of projects funded by the Ministry of Education and the Ministry of Health. He is a member of the Editorial Committee of Fertility & Sterility and Reproductive Biomedicine Online and SGI, ESHRE, ASRM, SEGO and SEF.

Prevalence of XXY karyotypes in human blastocysts: multicentre data from 7549 trophectoderm biopsies obtained during preimplantation genetic testing cycles in IVF.

Which is the prevalence of a 47,XXY karyotype in human blastocysts biopsied during preimplantation genetic testing for aneuploidies (PGT-A) cycles? The prevalence of a 47,XXY karyotype amongst male blastocysts without autosomal aneuploides is ~1%. The prevalence of Klinefelter syndrome is estimated as 0.1-0.2% in male newborns. However, the KS phenotype is extremely variable and there are men with a 47,XXY karyotype and less evident signs, who may go undetected. No risk factor for the 47,XXY karyotype in products of conception has been yet clearly defined, and no data are available regarding the prevalence of this karyotype among human preimplantation embryos. This multicentre cohort study involved 7549 blastocysts obtained during 2826 PGT-A cycles performed between April 2013 and September 2017 at six IVF clinics in Italy. During 2826 PGT-A cycles, 7549 blastocysts underwent trophectoderm biopsy and quantitative-PCR-based comprehensive chromosomal testing to predict the karyotype of the corresponding embryos. The results were also presented according to ranges of maternal and paternal age at oocyte retrieval as well as sperm factor and blastocyst quality. Univariate and multivariate logistic regression analyses were conducted to investigate the correlation of possible confounding factors with the prevalence of 47,XXY karyotype. Overall, 62 blastocysts were 47,XXY or had an XXY karyotype associated with autosomal aneuploidies. After exclusion of the latter, the prevalence of a 47,XXY karyotype among male blastocysts without autosomal aneuploidies was 0.9% (n = 17/1794). A significant correlation was only found for maternal age and blastocyst quality (OR: 1.20, 95% CI: 1.01-1.42; P = 0.04 and OR: 1.6, 95% CI: 1.13-2.45; P = 0.01). These retrospective data have been produced based on a population of infertile couples undergoing IVF and PGT-A, and the women were mainly of advanced maternal age. Moreover, the qPCR technique is validated only to detect full-chromosome uniform aneuploidies in trophectoderm biopsies. The 0.9% prevalence of the 47,XXY karyotype among male blastocysts, when compared with the 0.1-0.2% prevalence reported in the prenatal and postnatal periods, suggests four possible scenarios that require further investigations: (i) the latter prevalence is underestimated; (ii) 47,XXY blastocysts result in a lower implantation rate than euploid embryos (estimated to be ≈50%); (iii) 47,XXY blastocysts result in a higher early miscarriage rate than euploid embryos (estimated to be ≈10%); or (iv) infertile patients of advanced maternal age and referred to IVF/PGT-A produce a higher rate of 47,XXY blastocysts. None. N/A.

Biallelic PADI6 variants linking infertility, miscarriages, and hydatidiform moles.

Recurrent hydatidiform moles (RHM) are aberrant human pregnancies characterized by absence of, or abnormal, embryonic development, hydropic degeneration of chorionic villi, and hyperproliferation of the trophoblast. Biallelic mutations in two maternal-effect genes, NLRP7 and KHDC3L, underlie the causation of RHM in 60% of patients. We performed exome sequencing on a patient with six pregnancy losses, two miscarriages and four HM, and found no variants that affect the functions of the known genes. We found biallelic missense variants that affect conserved amino acids in PADI6 and segregate with the disease phenotype in the family. PADI6 is another maternal-effect gene and a member of the subcortical maternal complex that has been shown to have recessive variants that affect the gene function in four unrelated women with infertility who also experienced early embryonic arrest during preimplantation development after IVF. We demonstrated that PADI6 co-localizes with NLRP7 in human oocytes and preimplantation embryos and reviewed the morphology and genotypes of four products of conception from our patient. Our data expand the involvement of PADI6 to other forms of reproductive loss and highlight the commonality between infertility, miscarriages, and molar pregnancies, in some cases.

Tripolar chromosome segregation drives the association between maternal genotype at variants spanning PLK4 and aneuploidy in human preimplantation embryos.

Aneuploidy is prevalent in human embryos and is the leading cause of pregnancy loss. Many aneuploidies arise during oogenesis, increasing with maternal age. Superimposed on these meiotic aneuploidies are frequent errors occurring during early mitotic divisions, contributing to widespread chromosomal mosaicism. Here we reanalyzed a published dataset comprising preimplantation genetic testing for aneuploidy in 24653 blastomere biopsies from day-3 cleavage-stage embryos, as well as 17051 trophectoderm biopsies from day-5 blastocysts. We focused on complex abnormalities that affected multiple chromosomes simultaneously, seeking insights into their formation. In addition to well-described patterns such as triploidy and haploidy, we identified 4.7% of blastomeres possessing characteristic hypodiploid karyotypes. We inferred this signature to have arisen from tripolar chromosome segregation in normally fertilized diploid zygotes or their descendant diploid cells. This could occur via segregation on a tripolar mitotic spindle or by rapid sequential bipolar mitoses without an intervening S-phase. Both models are consistent with time-lapse data from an intersecting set of 77 cleavage-stage embryos, which were enriched for the tripolar signature among embryos exhibiting abnormal cleavage. The tripolar signature was strongly associated with common maternal genetic variants spanning the centrosomal regulator PLK4, driving the association we previously reported with overall mitotic errors. Our findings are consistent with the known capacity of PLK4 to induce tripolar mitosis or precocious M-phase upon dysregulation. Together, our data support tripolar chromosome segregation as a key mechanism generating complex aneuploidy in cleavage-stage embryos and implicate maternal genotype at a quantitative trait locus spanning PLK4 as a factor influencing its occurrence.

The temperature and type of intracellular ice formation in preimplantation human embryos

The temperature and type of intracellular ice formation in preimplantation human embryos