Complex aneuploidy triggers autophagy and p53-mediated apoptosis and impairs the second lineage segregation in human preimplantation embryos.

About 70% of human cleavage stage embryos show chromosomal mosaicism, falling to 20% in blastocysts. Chromosomally mosaic human blastocysts can implant and lead to healthy new-borns with normal karyotypes. Studies in mouse embryos and human gastruloids showed that aneuploid cells are eliminated from the epiblast by p53-mediated apoptosis while being tolerated in the trophectoderm.

Clinical pregnancy rates after blastocyst culture at a stable temperature of 36.6°C versus 37.1°C: a prospective randomized controlled trial.

Study Question: Is there a difference in clinical pregnancy rates (CPRs) in good prognosis patients after single embryo transfer (SET) on Day 5, in case of stable culture at 36.6°C or 37.1°C?

Summary Answer: CPR (with heartbeat at 7 weeks) after blastocyst transfer do not differ after culturing at 36.

Screening embryos for polygenic disease risk: a review of epidemiological, clinical, and ethical considerations.

Background: The genetic composition of embryos generated by in vitro fertilization (IVF) can be examined with preimplantation genetic testing (PGT). Until recently, PGT was limited to detecting single-gene, high-risk pathogenic variants, large structural variants, and aneuploidy. Recent advances have made genome-wide genotyping of IVF embryos feasible and affordable, raising the possibility of screening embryos for their risk of polygenic diseases such as breast cancer, hypertension, diabetes, or schizophrenia.

Children born after assisted reproduction more commonly carry a mitochondrial genotype associating with low birthweight.

Children conceived through assisted reproductive technologies (ART) have an elevated risk of lower birthweight, yet the underlying cause remains unclear. Our study explores mitochondrial DNA (mtDNA) variants as contributors to birthweight differences by impacting mitochondrial function during prenatal development. We deep-sequenced the mtDNA of 451 ART and spontaneously conceived (SC) individuals, 157 mother-child pairs and 113 individual oocytes from either natural menstrual cycles or after ovarian stimulation (OS) and find that ART individuals carried a different mtDNA genotype than SC individuals, with more de novo non-synonymous variants.

An update on human pre- and peri-implantation development: a blueprint for blastoids.

Despite over 40 years following the first birth from medically assisted reproduction (MAR) technologies, mechanisms underlying the key developmental events during the first 7 days of human development, such as signaling pathway contribution, are remaining a mystery. An in-depth mechanistic understanding of how the human preimplantation embryo develops would support the optimization of embryo quality assessment methods and culturing conditions, thereby increasing the success rate of MAR. However, the limited availability of human embryos, legitimate ethical concerns, and regulations still present an obstacle toward our advancement of knowledge.

Electronic witnessing in the medically assisted reproduction laboratory: insights and considerations after 10 years of use.

Study Question: What have we learnt after 10 years of electronic witnessing?

Summary Answer: When applied correctly, an electronic witnessing system can replace manual witnessing in the medically assisted reproduction lab to prevent sample mix-up.

What Is Known Already: Electronic witnessing systems have been implemented to improve the correct identification, processing, and traceability of biological materials. When non-matching samples are simultaneously present in a single workstation, a mismatch event is generated to prevent sample mix-up.

Lineage segregation in human pre-implantation embryos is specified by YAP1 and TEAD1.

Study Question: Which processes and transcription factors specify the first and second lineage segregation events during human preimplantation development?

Summary Answer: Differentiation into trophectoderm (TE) cells can be initiated independently of polarity; moreover, TEAD1 and YAP1 co-localize in (precursor) TE and primitive endoderm (PrE) cells, suggesting a role in both the first and the second lineage segregation events.

What Is Known Already: We know that polarity, YAP1/GATA3 signalling and phospholipase C signalling play a key role in TE initiation in compacted human embryos, however, little is known about the TEAD family of transcription factors that become activated by YAP1 and, especially, whether they play a role during epiblast (EPI) and PrE formation. In mouse embryos, polarized outer cells show nuclear TEAD4/YAP1 activity that upregulates Cdx2 and Gata3 expression while inner cells exclude YAP1 which upregulates Sox2 expression.

A conserved role of the Hippo signalling pathway in initiation of the first lineage specification event across mammals.

Our understanding of the molecular events driving cell specification in early mammalian development relies mainly on mouse studies, and it remains unclear whether these mechanisms are conserved across mammals, including humans. We have shown that the establishment of cell polarity via aPKC is a conserved event in the initiation of the trophectoderm (TE) placental programme in mouse, cow and human embryos. However, the mechanisms transducing cell polarity into cell fate in cow and human embryos are unknown.

Mitochondrial DNA variants segregate during human preimplantation development into genetically different cell lineages that are maintained postnatally.

Humans present remarkable diversity in their mitochondrial DNA (mtDNA) in terms of variants across individuals as well as across tissues and even cells within one person. We have investigated the timing of the first appearance of this variant-driven mosaicism. For this, we deep-sequenced the mtDNA of 254 oocytes from 85 donors, 158 single blastomeres of 25 day-3 embryos, 17 inner cell mass and trophectoderm samples of 7 day-5 blastocysts, 142 bulk DNA and 68 single cells of different adult tissues.

Podocalyxin inhibits human embryo implantation in vitro and luminal podocalyxin in putative receptive endometrium is associated with implantation failure in fertility treatment.

Objective: To study whether endometrial epithelial podocalyxin (PCX) inhibits implantation of human embryos in vitro and in patients undergoing in vitro fertilization (IVF).

Design: We have recently identified PCX as a key negative regulator of endometrial epithelial receptivity. Podocalyxin is expressed in all epithelial cells in the nonreceptive endometrium, but is selectively downregulated in the luminal epithelium (LE) for receptivity.

Initiation of a conserved trophectoderm program in human, cow and mouse embryos.

Current understandings of cell specification in early mammalian pre-implantation development are based mainly on mouse studies. The first lineage differentiation event occurs at the morula stage, with outer cells initiating a trophectoderm (TE) placental progenitor program. The inner cell mass arises from inner cells during subsequent developmental stages and comprises precursor cells of the embryo proper and yolk sac.

SARS-CoV-2 host receptors ACE2 and CD147 (BSG) are present on human oocytes and blastocysts.

Purpose: To visualize SARS-CoV-2 host receptors ACE2 and CD147 on human oocytes and blastocysts.

Methods: Immunohistochemistry and confocal microscopy on human primary oocytes and pre (5 days post fertilization (dpf5) and (dpf6))- and peri (dpf7)-implantation blastocysts donated to research.

Results: SARS-CoV-2 host receptors ACE2 and CD147 are present on the membrane of trophectoderm, epiblast and hypoblast cells in human blastocysts.

The effect of different temperature conditions on human embryosin vitro: two sibling studies.

Research Question: What temperature is optimal for human embryo development up to day 5 or 6?

Design: Two prospective sibling oocyte studies on culture temperature were conducted in a university-based tertiary referral centre. Eligibility critera for both studies: Study 1: 50 cycles between August and October 2015, with culture at a stable temperature (37.0°C ± 0.

Random Mutagenesis, Clonal Events, and Embryonic or Somatic Origin Determine the mtDNA Variant Type and Load in Human Pluripotent Stem Cells.

In this study, we deep-sequenced the mtDNA of human embryonic and induced pluripotent stem cells (hESCs and hiPSCs) and their source cells and found that the majority of variants pre-existed in the cells used to establish the lines. Early-passage hESCs carried few and low-load heteroplasmic variants, similar to those identified in oocytes and inner cell masses. The number and heteroplasmic loads of these variants increased with prolonged cell culture.

Obstetric and neonatal outcome following ICSI with assisted oocyte activation by calcium ionophore treatment.

Purpose: Calcium ionophore treatment is being used in assisted reproductive technology (ART) for cases with previous low fertilization rate or total absence of fertilization after insemination by intracytoplasmic sperm injection or when a specific indication such as globozoospermia is present. As this technique is more invasive and differs from the physiological process of fertilization, a thorough investigation of the health of the children born following this procedure is required. We intent to report the medical outcome of all children conceived following calcium ionophore treatment in our IVF center.

Birthweight of singletons born after cleavage-stage or blastocyst transfer in fresh and warming cycles.

Study Question: Does extended culture to the blastocyst stage affect singleton birthweight after either fresh or vitrified-warmed embryo transfer?

Summary Answer: Singleton birthweight z-scores did not vary significantly after a fresh blastocyst transfer, whereas the additional effect of vitrification remains inconclusive.

What Is Known Already: Observational studies have associated extended culture with an increased risk of preterm birth and low birthweight. On the contrary, in terms of birthweight and gestational age, singletons born after vitrification have been associated with a better perinatal outcome when compared to those born following a fresh transfer.

Deregulation of the endometrial stromal cell secretome precedes embryo implantation failure.

Study Question: Is implantation failure following ART associated with a perturbed decidual response in endometrial stromal cells (EnSCs)?

Summary Answer: Dynamic changes in the secretome of decidualizing EnSCs underpin the transition of a hostile to a supportive endometrial microenvironment for embryo implantation; perturbation in this transitional pathway prior to ART is associated with implantation failure.

What Is Known Already: Implantation is the rate-limiting step in ART, although the contribution of an aberrant endometrial microenvironment in IVF failure remains ill defined.

Study Design, Size, Duration: In vitro characterization of the temporal changes in the decidual response of primary EnSCs isolated prior to a successful or failed ART cycle.

Cumulative live birth rates after fresh and vitrified cleavage-stage versus blastocyst-stage embryo transfer in the first treatment cycle.

Study Question: Do cumulative live birth rates differ between single cleavage-stage Day 3 transfer and single blastocyst-stage Day 5 transfer?

Summary Answer: Cumulative live birth rates after Day 3 and 5 transfers were similar in young patients when the vitrified embryo transfers were also taken into account.

What Is Known Already: Previous evidence has shown that the probability of live birth following IVF with a fresh embryo transfer is significantly higher after blastocyst-stage Day 5 transfer. However, because the introduction of vitrification has enhanced the survival of cryopreserved embryos and improved pregnancy rates, the optimal outcome measure for this comparison should now be cumulative live birth rates, as these include the eventual contribution of vitrified-warmed embryos.

Similar kinetics for 5-methylcytosine and 5-hydroxymethylcytosine during human preimplantation development in vitro.

After fertilization, the mammalian embryo undergoes epigenetic reprogramming with genome-wide DNA demethylation and subsequent remethylation. Oxidation of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC) was suggested to be an intermediate step in the DNA demethylation pathway. Other evidence, such as the stability of 5hmC in specific tissues, suggests that 5hmC constitutes a new epigenetic modification with its own biological function.

DAZL regulates Tet1 translation in murine embryonic stem cells.

Embryonic stem cell (ESC) cultures display a heterogeneous gene expression profile, ranging from a pristine naïve pluripotent state to a primed epiblast state. Addition of inhibitors of GSK3β and MEK (so-called 2i conditions) pushes ESC cultures toward a more homogeneous naïve pluripotent state, but the molecular underpinnings of this naïve transition are not completely understood. Here, we demonstrate that DAZL, an RNA-binding protein known to play a key role in germ-cell development, marks a subpopulation of ESCs that is actively transitioning toward naïve pluripotency.

Dynamic regulation of DNA methyltransferases in human oocytes and preimplantation embryos after assisted reproductive technologies.

DNA methylation is a key epigenetic modification which is essential for normal embryonic development. Major epigenetic reprogramming takes place during gametogenesis and in the early embryo; the complex DNA methylation patterns are established and maintained by DNA methyltransferases (DNMTs). However, the influence of assisted reproductive technologies (ART) on DNA methylation reprogramming enzymes has predominantly been studied in mice and less so in human oocytes and embryos.

Human trophectoderm cells are not yet committed.

Study Question: Are human trophectoderm (TE) cells committed or still able to develop into inner cell mass (ICM) cells?

Summary Answer: Human full blastocyst TE cells still have the capacity to develop into ICM cells expressing the pluripotency marker NANOG, thus they are not yet committed.

What Is Known Already: Human Day 5 full blastocyst TE cells express the pluripotency markers POU5F1, SOX2 and SALL4 as well as the TE markers HLA-G and KRT18 but not yet CDX2, therefore their developmental direction may not yet be definite.

Study Design, Size, Duration: The potency of human blastocyst TE cells was investigated by determining their in vitro capacity to develop into a blastocyst with ICM cells expressing NANOG; TE cells were isolated either by aspiration under visual control or after labeling with fluorescent 594-wheat germ agglutinin.

Establishment of hESC lines from the inner cell mass of blastocyst-stage embryos and single blastomeres of 4-cell stage embryos.

More than 600 human embryonic stem cell (hESC) lines have been reported today at the human European Embryonic Stem Cell Registry ( http://www.hescreg.eu/ ).