Chromosomal instability in mammalian pre-implantation embryos: potential causes, detection methods, and clinical consequences

Mechanism of chromosomal mosaicism in preimplantation embryos and its effect on embryo development

Aneuploidy is one of the main causes of miscarriage and in vitro fertilization failure. Mitotic abnormalities in preimplantation embryos are the main cause of mosaicism, which may be influenced by several endogenous factors such as relaxation of cell cycle control mechanisms, defects in chromosome cohesion, centrosome aberrations and abnormal spindle assembly, and DNA replication stress. In addition, incomplete trisomy rescue is a rare cause of mosaicism. However, there may be a self-correcting mechanism in mosaic embryos, which allows some mosaicisms to potentially develop into normal embryos. At present, it is difficult to accurately diagnose mosaicism using preimplantation genetic testing for aneuploidy. Therefore, in clinical practice, embryos diagnosed as mosaic should be considered comprehensively based on the specific situation of the patient.

Association of early cleavage, morula compaction and blastocysts ploidy of IVF embryos cultured in a time-lapse system and biopsied for genetic test for aneuploidy

IVF embryos have historically been evaluated by morphological characteristics. The time-lapse system (TLS) has become a promising tool, providing an uninterrupted evaluation of morphological and dynamic parameters of embryo development. Furthermore, TLS sheds light on unknown phenomena such as direct cleavage and incomplete morula compaction. We retrospectively analyzed the morphology (Gardner Score) and morphokinetics (KIDScore) of 835 blastocysts grown in a TLS incubator (Embryoscope+), which were biopsied for preimplantation genetic testing for aneuploidy (PGT-A). Only the embryos that reached the blastocyst stage were included in this study and time-lapse videos were retrospectively reanalysed. According to the pattern of initial cleavages and morula compaction, the embryos were classified as: normal (NC) or abnormal (AC) cleavage, and fully (FCM) or partially compacted (PCM) morulae. No difference was found in early cleavage types or morula compaction patterns between female age groups (< 38, 38-40 and > 40 yo). Most of NC embryos resulted in FCM (≅ 60%), while no embryos with AC resulted in FCM. Aneuploidy rate of AC-PCM group did not differ from that of NC-FCM group in women < 38 yo, but aneuploidy was significantly higher in AC-PCM compared to NC-FCM of women > 40 yo. However, the quality of embryos was lower in AC-PCM blastocysts in women of all age ranges. Morphological and morphokinetic scores declined with increasing age, in the NC-PCM and AC-PCM groups, compared to the NC-FCM. Similar aneuploidy rates among NC-FCM and AC-PCM groups support the hypothesis that PCM in anomalous-cleaved embryos can represent a potential correction mechanism, even though lower morphological/morphokinetic scores are seen on AC-PCM. Therefore, both morphological and morphokinetic assessment should consider these embryonic development phenomena.

Genetic mechanisms of fertilization failure and early embryonic arrest: a comprehensive review

BACKGROUND

Infertility and pregnancy loss are longstanding problems. Successful fertilization and high-quality embryos are prerequisites for an ongoing pregnancy. Studies have proven that every stage in the human reproductive process is regulated by multiple genes and any problem, at any step, may lead to fertilization failure (FF) or early embryonic arrest (EEA). Doctors can diagnose the pathogenic factors involved in FF and EEA by using genetic methods. With the progress in the development of new genetic technologies, such as single-cell RNA analysis and whole-exome sequencing, a new approach has opened up for us to directly study human germ cells and reproductive development. These findings will help us to identify the unique mechanism(s) that leads to FF and EEA in order to find potential treatments.

OBJECTIVE AND RATIONALE

The goal of this review is to compile current genetic knowledge related to FF and EEA, clarifying the mechanisms involved and providing clues for clinical diagnosis and treatment.

SEARCH METHODS

PubMed was used to search for relevant research articles and reviews, primarily focusing on English-language publications from January 1978 to June 2023. The search terms included fertilization failure, early embryonic arrest, genetic, epigenetic, whole-exome sequencing, DNA methylation, chromosome, non-coding RNA, and other related keywords. Additional studies were identified by searching reference lists. This review primarily focuses on research conducted in humans. However, it also incorporates relevant data from animal models when applicable. The results were presented descriptively, and individual study quality was not assessed.

OUTCOMES

A total of 233 relevant articles were included in the final review, from 3925 records identified initially. The review provides an overview of genetic factors and mechanisms involved in the human reproductive process. The genetic mutations and other genetic mechanisms of FF and EEA were systematically reviewed, for example, globozoospermia, oocyte activation failure, maternal effect gene mutations, zygotic genome activation abnormalities, chromosome abnormalities, and epigenetic abnormalities. Additionally, the review summarizes progress in treatments for different gene defects, offering new insights for clinical diagnosis and treatment.

WIDER IMPLICATIONS

The information provided in this review will facilitate the development of more accurate molecular screening tools for diagnosing infertility using genetic markers and networks in human reproductive development. The findings will also help guide clinical practice by identifying appropriate interventions based on specific gene mutations. For example, when an individual has obvious gene mutations related to FF, ICSI is recommended instead of IVF. However, in the case of genetic defects such as phospholipase C zeta1 (PLCZ1), actin-like7A (ACTL7A), actin-like 9 (ACTL9), and IQ motif-containing N (IQCN), ICSI may also fail to fertilize. We can consider artificial oocyte activation technology with ICSI to improve fertilization rate and reduce monetary and time costs. In the future, fertility is expected to be improved or restored by interfering with or supplementing the relevant genes.

Spatiotemporal view of malignant histogenesis and macroevolution via formation of polyploid giant cancer cells

To understand how malignant tumors develop, we tracked cell membrane, nuclear membrane, spindle, and cell cycle dynamics in polyploid giant cancer cells (PGCCs) during the formation of high-grade serous carcinoma organoids using long-term time-lapse imaging. Single cells underwent traditional mitosis to generate tissue with uniform nuclear size, while others formed PGCCs via asymmetric mitosis, endoreplication, multipolar endomitosis, nuclear fusion, and karyokinesis without cytokinesis. PGCCs underwent restitution multipolar endomitosis, nuclear fragmentation, and micronuclei formation to increase nuclear contents and heterogeneity. At the cellular level, the development of PGCCs was associated with forming transient intracellular cells, termed fecundity cells. The fecundity cells can be decellularized to facilitate nuclear fusion and synchronized with other nuclei for subsequent nuclear replication. PGCCs can undergo several rounds of entosis to form complex tissue structures, termed fecundity structures. The formation of PGCCs via multiple modes of nuclear replication in the absence of cytokinesis leads to an increase in the nuclear-to-cytoplasmic (N/C) ratio and intracellular cell reproduction, which is remarkably similar to the mode of nuclear division during pre-embryogenesis. Our data support that PGCCs may represent a central regulator in malignant histogenesis, intratumoral heterogeneity, immune escape, and macroevolution via the de-repression of suppressed pre-embryogenic program in somatic cells.

A Patient Diagnosed with Mosaic Trisomy 18 Presenting New Symptoms: Diaphragmatic Relaxation and Cyclic Vomiting Syndrome. Updated Review of Mosaic Trisomy 18 Cases

Although data on T18 are widespread, there is a lack of knowledge on mosaic trisomy 18 (mT18). A current review of mT18 symptomatology, long-term follow-up, and potential health risks is lacking for health care professionals. Our paper addresses these, emphasizing the importance of regular tumor screening as a key message for mT18 patient follow-up. We also present the case of a female patient with mT18 who presented with diaphragmatic relaxation and cyclic vomiting syndrome (CVS), which had previously not been reported in this genetic condition. On further investigating the etiology of CVS, we revealed a novel mitochondrial mutation in the MT-ND6 gene in heteroplasmic form. Based on the literature, we hypothesize that the mitochondrial mutation together with mT18 could result in CVS.

iPSC reprogramming-mediated aneuploidy correction in autosomal trisomy syndromes

Trisomy 21, 18, and 13 are the major autosomal aneuploidy disorders in humans. They are mostly derived from chromosome non-disjunction in maternal meiosis, and the extra trisomic chromosome can cause several congenital malformations. Various genes on the trisomic chromosomes are intricately involved in the development of disease, and fundamental treatments have not yet been established. However, chromosome therapy has been developed to correct the extra chromosome in cultured patient cells, and it was recently reported that during reprogramming into iPSCs, fibroblasts from a Down syndrome patient lost the extra chromosome 21 due to a phenomenon called trisomy-biased chromosome loss. To gain preliminary insights into the underlying mechanism of trisomy rescue during the early stages of reprogramming, we reprogrammed skin fibroblasts from patients with trisomy syndromes 21, 18, 13, and 9 to iPSC, and evaluated the genomes of the individual iPSC colonies by molecular cytogenetic techniques. We report the spontaneous correction from trisomy to disomy upon cell reprogramming in at least one cell line examined from each of the trisomy syndromes, and three possible combinations of chromosomes were selected in the isogenic trisomy-rescued iPSC clones. Single nucleotide polymorphism analysis showed that the trisomy-rescued clones exhibited either heterodisomy or segmental uniparental isodisomy, ruling out the possibility that two trisomic chromosomes were lost simultaneously and the remaining one was duplicated, suggesting instead that one trisomic chromosome was lost to generate disomic cells. These results demonstrated that trisomy rescue may be a phenomenon with random loss of the extra chromosome and subsequent selection for disomic iPSCs, which is analogous to the karyotype correction in early preimplantation embryos. Our finding is relevant for elucidating the mechanisms of autonomous karyotype correction and future application in basic and clinical research on aneuploidy disorders.

Haplotyping-based preimplantation genetic testing reveals parent-of-origin specific mechanisms of aneuploidy formation

Chromosome instability is inherent to human IVF embryos, but the full spectrum and developmental fate of chromosome anomalies remain uncharacterized. Using haplotyping-based preimplantation genetic testing for monogenic diseases (PGT-M), we mapped the parental and mechanistic origin of common and rare genomic abnormalities in 2300 cleavage stage and 361 trophectoderm biopsies. We show that while single whole chromosome aneuploidy arises due to chromosome-specific meiotic errors in the oocyte, segmental imbalances predominantly affect paternal chromosomes, implicating sperm DNA damage in segmental aneuploidy formation. We also show that postzygotic aneuploidy affects multiple chromosomes across the genome and does not discriminate between parental homologs. In addition, 6% of cleavage stage embryos demonstrated signatures of tripolar cell division with excessive chromosome loss, however hypodiploid blastomeres can be excluded from further embryo development. This observation supports the selective-pressure hypothesis in embryos. Finally, considering that ploidy violations may constitute a significant proportion of non-viable embryos, using haplotyping-based approach to map these events might further improve IVF success rate.

Molecular Drivers of Developmental Arrest in the Human Preimplantation Embryo: A Systematic Review and Critical Analysis Leading to Mapping Future Research

Developmental arrest of the preimplantation embryo is a multifactorial condition, characterized by lack of cellular division for at least 24 hours, hindering the in vitro fertilization cycle outcome. This systematic review aims to present the molecular drivers of developmental arrest, focusing on embryonic and parental factors. A systematic search in PubMed/Medline, Embase and Cochrane-Central-Database was performed in January 2021. A total of 76 studies were included. The identified embryonic factors associated with arrest included gene variations, mitochondrial DNA copy number, methylation patterns, chromosomal abnormalities, metabolic profile and morphological features. Parental factors included, gene variation, protein expression levels and infertility etiology. A valuable conclusion emerging through critical analysis indicated that genetic origins of developmental arrest analyzed from the perspective of parental infertility etiology and the embryo itself, share common ground. This is a unique and long-overdue contribution to literature that for the first time presents an all-inclusive methodological report on the molecular drivers leading to preimplantation embryos’ arrested development. The variety and heterogeneity of developmental arrest drivers, along with their inevitable intertwining relationships does not allow for prioritization on the factors playing a more definitive role in arrested development. This systematic review provides the basis for further research in the field.

Giant cells: Linking McClintock's heredity to early embryogenesis and tumor origin throughout millennia of evolution on Earth

The "life code" theory postulates that egg cells, which are giant, are the first cells in reproduction and that damaged or aged giant somatic cells are the first cells in tumorigenesis. However, the hereditary basis for giant cells remains undefined. Here I propose that stress-induced genomic reorganization proposed by Nobel Laureate Barbara McClintock may represent the underlying heredity for giant cells, referred to as McClintock's heredity. Increase in cell size may serve as a response to environmental stress via switching proliferative mitosis to intranuclear replication for reproduction. Intranuclear replication activates McClintock's heredity to reset the genome following fertilization for reproduction or restructures the somatic genome for neoplastic transformation via formation of polyploid giant cancer cells (PGCCs). The genome-based McClintock heredity functions together with gene-based Mendel's heredity to regulate the genomic stability at two different stages of life cycle or tumorigenesis. Thus, giant cells link McClintock's heredity to both early embryogenesis and tumor origin. Cycling change in cell size together with ploidy number switch may represent the most fundamental mechanism on how both germ and soma for coping with environmental stresses for the survival across the tree of life which evolved over millions of years on Earth.

Polyploid giant cancer cells and ovarian cancer: new insights into mitotic regulators and polyploidy†

Current first-line treatment of patients with high-grade serous ovarian cancer (HGSOC) involves the use of cytotoxic drugs that frequently lead to recurrent tumors exhibiting increased resistance to the drugs and poor patient survival. Strong evidence is accumulating to show that HGSOC tumors and cell lines contain a subset of cells called polyploidy giant cancer cells (PGCCs) that act as stem-like, self-renewing cells. These PGCCs appear to play a key role in tumor progression by generating drug-resistant progeny produced, in part, as a consequence of utilizing a modified form of mitosis known as endoreplication. Thus, developing drugs to target PGCCs and endoreplication may be an important approach for reducing the appearance of drug-resistant progeny. In the review, we discuss newly identified regulatory factors that impact mitosis and which may be altered or repurposed during endoreplication in PGCCs. We also review recent papers showing that a single PGCC can give rise to tumors in vivo and spheroids in culture. To illustrate some of the specific features of PGCCs and factors that may impact their function and endoreplication compared to mitosis, we have included immunofluorescent images co-localizing p53 and specific mitotic regulatory, phosphoproteins in xenografts derived from commonly used HGSOC cell lines.

Preimplantation loss of fertilized human ova: estimating the unobservable

STUDY QUESTION

What proportion of fertilized human ova are lost before implantation?

SUMMARY ANSWER

An estimated 40 to 50% of fertilized ova fail to implant.

WHAT IS KNOWN ALREADY

Preimplantation loss is not detectable with current technology. Published estimates of preimplantation loss range from 10 to 70%.

STUDY DESIGN, SIZE, DURATION

We combine data from epidemiologic, demographic, laboratory and in vitro fertilization studies to construct an empirical framework for the estimation of preimplantation loss. This framework is summarized in a user-friendly Excel file included in supplement.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We draw from multiple sources to generate plausible estimates of fecundability, sterility, transient anovulation, intercourse patterns and the proportion of ova fertilized in the presence of sperm. We combine these estimates to generate a summary estimate of preimplantation loss. This estimate can be considered an average for couples in their prime reproductive years.

MAIN RESULTS AND THE ROLE OF CHANCE

Under a plausible range of assumptions, we estimate that 40 to 50% of fertilized ova fail to implant.

LIMITATIONS, REASONS FOR CAUTION

A crucial factor in estimating preimplantation loss is the probability that an ovum will be fertilized when exposed to sperm. Human data are available only from in vitro fertilization (IVF), which may not accurately represent events in vivo. We therefore assume a range of in vivo fertilization rates, from 64% (human IVF data) to 90% (mouse data).

WIDER IMPLICATIONS OF THE FINDINGS

Our estimate of preimplantation loss takes into account the biological processes relevant to fertilization and loss. Using this empirical basis for estimation, we find support for the usual assumption that risk of loss is highest in the earliest days following fertilization. Furthermore, this framework can provide improved estimates as better reproductive data become available. To the extent that our estimates are accurate, more fertilized ova are apparently lost in vitro than in vivo, suggesting that further improvements in IVF success rates may be possible.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the Intramural Program of the National Institute of Environmental Health Sciences, NIH. Professor Adashi serves as Co-Chair of the Safety Advisory Board of Ohana Biosciences, Inc. The other authors have no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Chromosomal mosaicism: Origins and clinical implications in preimplantation and prenatal diagnosis

The diagnosis of chromosomal mosaicism in the preimplantation and prenatal stage is fraught with uncertainty and multiple factors need to be considered in order to gauge the likely impact. The clinical effects of chromosomal mosaicism are directly linked to the type of the imbalance (size, gene content, and copy number), the timing of the initial event leading to mosaicism during embryogenesis/fetal development, the distribution of the abnormal cells throughout the various tissues within the body as well as the ratio of normal/abnormal cells within each of those tissues. Additional factors such as assay noise and culture artifacts also have an impact on the significance and management of mosaic cases. Genetic counseling is an important part of educating patients about the likelihood of having a liveborn with a chromosome abnormality and these risks differ according to the time of ascertainment and the tissue where the mosaic cells were initially discovered. Each situation needs to be assessed on a case-by-case basis and counseled accordingly. This review will discuss the clinical impact of finding mosaicism through: embryo biopsy, chorionic villus sampling, amniocentesis, and noninvasive prenatal testing using cell-free DNA.

Uniparental disomy: Origin, frequency, and clinical significance

Uniparental disomy (UPD) is defined as two copies of a whole chromosome derived from the same parent. There can be multiple mechanisms that lead to UPD; these are reviewed in the context of contemporary views on the mechanism leading to aneuploidy. Recent studies indicate that UPD is rare in an apparently healthy population and also rare in spontaneous abortion tissues. The most common type of UPD is a maternal heterodisomy (both maternal allele sets present). Isodisomy (a duplicated single set of alleles) or segmental loss of heterozygosity is sometimes encountered in SNP-based microarray referrals. Decisions regarding the most appropriate follow-up testing should consider the possibility of consanguinity (that will generally involve multiple regions), an imprinted gene disorder (chromosomes 6, 7, 11, 14, 15, 20), expression of an autosomal recessive disorder, and an occult aneuploid cell line that may be confined to the placenta. Upd(16)mat, per se, does not appear to be associated with an abnormal phenotype. UPD provides an insight into the history of early chromosome segregation error and understanding the rates and fate of these events are of key importance in the provision of fertility management and prenatal healthcare.

A Rapid PCR-Free Next-Generation Sequencing Method for the Detection of Copy Number Variations in Prenatal Samples

Next-generation sequencing (NGS) is emerging as a new method for the detection of clinically significant copy number variants (CNVs). In this study, we developed and validated rapid CNV-sequencing (rCNV-seq) for clinical application in prenatal diagnosis. Low-pass whole-genome sequencing was performed on PCR libraries prepared from amniocyte genomic DNA. From 10-40 ng of input DNA, PCR-free libraries consistently produced sequencing data with high unique read mapping ratios, low read redundancy, low coefficient of variation for all chromosomes and high genomic coverage. In validation studies, reliable and accurate CNV detection using PCR-free-based rCNV-seq was demonstrated for a range of common trisomies and sex chromosome aneuploidies as well as microdeletion and duplication syndromes. In reproducibility studies, CNV copy number and genomic intervals closely matched those defined by chromosome microarray analysis. Clinical testing of genomic DNA samples from 217 women referred for prenatal diagnosis identified eight samples (3.7%) with known chromosome disorders. We conclude that PCR-free-based rCNV-seq is a sensitive, specific, reproducible and efficient method that can be used in any NGS-based diagnostic laboratory for detection of clinically significant CNVs.

Reanalysis of discarded blastocysts for autosomal aneuploidy after sex selection in cleavage-stage embryos

Objective

The goal of the present study was to investigate the rate of chromosomal aneuploidies in surplus embryos after sex determination at the cleavage stage. Then, the same chromosomal aneuploidies were evaluated in blastocysts after extended culture.

Methods

Sixty-eight surplus embryos were biopsied at the cleavage stage and incubated for an additional 3 days to allow them to reach the blastocyst stage. The embryos were reanalyzed via fluorescence in situ hybridization (FISH) to examine eight chromosomes (13, 15, 16, 18, 21, 22, X, and Y) in both cleavage-stage embryos and blastocysts.

Results

Although the total abnormality rate was lower in blastocysts (32.35%) than in cleavage-stage embryos (45.58%), the difference was not significant (p=0.113). However, when we restricted the analysis to autosomal abnormalities, we observed a significant difference in the abnormality rate between the cleavage-stage embryos (44.11%) and the blastocysts (17.64%, p=0.008). A higher rate of sex chromosomal abnormalities was also observed in cleavage-stage embryos (29.4%) than in blastocysts (14.70%, p=0.038).

Conclusion

The data indicated that embryo biopsy should be conducted at the blastocyst stage rather than the cleavage stage. The results also emphasized that examination of common chromosomal aneuploidies apart from sex selection cycles can be conducted in the blastocyst stage with the FISH method.

Cytokinesis-Block Micronucleus Cytome Assay Evolution into a More Comprehensive Method to Measure Chromosomal Instability

This review describes the cytokinesis-block micronucleus (CBMN) cytome assay and its evolution into a molecular cytogenetic method of chromosomal instability (CIN). Micronuclei (MNi) originate from whole chromosomes or chromosome fragments that fail to segregate to the poles of the cell during mitosis. These lagging chromosomes are excluded from the daughter nuclei and are enveloped in their own membrane to form MNi. The CBMN assay was developed to allow MNi to be scored exclusively in once-divided binucleated cells, which enables accurate measurement of chromosome breakage or loss without confounding by non-dividing cells that cannot express MNi. The CBMN assay can be applied to cell lines in vitro and cells such as lymphocytes that can be stimulated to divide ex vivo. In the CBMN assay, other CIN biomarkers such as nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs) are also measured. Use of centromere, telomere, and chromosome painting probes provides further insights into the mechanisms through which MNi, NPBs and NBUDs originate. Measurement of MNi is also important because entrapment within a micronucleus may cause chromosomes to shatter and, after nuclear reintegration, become rearranged. Additionally, leakage of DNA from MNi can stimulate inflammation via the cyclic GMP-AMP Synthase—Stimulator of Interferon Genes (cGAS-STING) DNA sensing mechanism of the innate immune system.

Improving the clinical outcomes by extended culture of day 3 embryos with low blastomere number to blastocyst stage following frozen-thawed embryo transfer

Purpose

This study aimed to investigate whether the extended culture of day 3 (D3) embryos with low blastomere number to blastocyst following frozen–thawed embryo transfer improved the clinical outcomes.

Methods

This was a retrospective study of clinical data of women undergoing in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles in the Tangdu Hospital. The patients were divided into groups with 4–5, 6, 7–9 and > 9 cells based on the blastomere number of D3 embryos. The clinical outcomes were compared.

Results

In fresh transfer cycles, the implantation and clinical pregnancy rates significantly decreased, while the abortion rate significantly increased in the groups with 4–5 and 6 cells compared with those with 7–9 and > 9 cells. In frozen–thawed transfer cycles, the clinical pregnancy and implantation rates for a single blastocyst transfer cycle showed no significant differences in the groups with 4–5 and 6 cells compared with those with 7–9 and > 9 cells. However, the abortion rate was significantly higher in the group with 4–5 cells than in that with 7–9 and > 9 cells. In the double blastocyst transfer cycle, the clinical pregnancy rate showed no significant differences among the groups with 4–5, 6, and 7–9 cells.

Conclusion

The implantation and clinical pregnancy rates of D3 embryos with 6 cells significantly decreased; these embryos were not considered as high-quality embryos. Extended culture of D3 embryos with ≤ 6 blastomeres to blastocysts, particularly 6-cell embryos, resulted in a similar clinical pregnancy rate as that of blastocysts derived from D3 embryos with ≥ 7 blastomeres.

Assessing equine embryo developmental competency by time-lapse image analysis

The timing of early mitotic events during preimplantation embryo development is important for subsequent embryogenesis in many mammalian species, including mouse and human, but, to date, no study has closely examined mitotic timing in equine embryos from oocytes obtained by ovum pick-up. Here, cumulus-oocyte complexes were collected by transvaginal follicular aspiration, matured invitro and fertilised via intracytoplasmic sperm injection. Each fertilised oocyte was cultured up to the blastocyst stage and monitored by time-lapse imaging for the measurement of cell cycle intervals and identification of morphological criteria indicative of developmental potential. Of the 56 fertilised oocytes, 35 initiated mitosis and 11 progressed to the blastocyst stage. Analysis of the first three mitotic divisions in embryos that formed blastocysts determined that typical blastocyst timing (median±IQR) is 30.0±17.5min, 8.8±1.7h and 0.6±1.4h respectively. Frequent cellular fragmentation, multipolar divisions and blastomere exclusion suggested that equine embryos likely contend with a high incidence of chromosomal missegregation. Indeed, chromosome-containing micronuclei and multinuclei with extensive DNA damage were observed throughout preimplantation embryogenesis. This indicates that time-lapse image analysis may be used as a non-invasive method to assess equine embryo quality in future studies.

Equine non-invasive time-lapse imaging and blastocyst development

In this study we examined the timeline of mitotic events of invitro-produced equine embryos that progressed to blastocyst stage using non-invasive time-lapse microscopy (TLM). Intracytoplasmic sperm injection (ICSI) embryos were cultured using a self-contained imaging incubator system (Miri®TL; Esco Technologies) that captured brightfield images at 5-min intervals that were then generated into video for retrospective analysis. For all embryos that progressed to the blastocyst stage, the initial event of extrusion of acellular debris preceded all first cleavages and occurred at mean (±s.e.m.) time of 20.0±1.1h after ICSI, whereas 19 of 24 embryos that did not reach the blastocyst stage demonstrated debris extrusion that occurred at 23.8±1.1h, on average 4h longer for this initial premitotic event (P<0.05). Embryos that failed to reach the blastocyst stage demonstrated a 4-h delay compared with those that reached the blastocyst stage to reach the 2-cell stage (P<0.05). All embryos that reached the blastocyst stage expressed pulsation of the blastocyst with visible expansion and contraction at approximate 10-min intervals, or five to six times per hour. Using a logit probability method, we determined that 2- and 8-cell stage embryos could reasonably predict which embryos progressed to the blastocyst stage. Together, the results indicate that TLM for equine embryo development is a dynamic tool with promise for predicting successful embryo development.

Aneuploidy and DNA Methylation as Mirrored Features of Early Human Embryo Development

Genome stability is an integral feature of all living organisms. Aneuploidy is the most common cause of fetal death in humans. The timing of bursts in increased aneuploidy frequency coincides with the waves of global epigenetic reprogramming in mammals. During gametogenesis and early embryogenesis, parental genomes undergo two waves of DNA methylation reprogramming. Failure of these processes can critically affect genome stability, including chromosome segregation during cell division. Abnormal methylation due to errors in the reprogramming process can potentially lead to aneuploidy. On the other hand, the presence of an entire additional chromosome, or chromosome loss, can affect the global genome methylation level. The associations of these two phenomena are well studied in the context of carcinogenesis, but here, we consider the relationship of DNA methylation and aneuploidy in early human and mammalian ontogenesis. In this review, we link these two phenomena and highlight the critical ontogenesis periods and genome regions that play a significant role in human reproduction and in the formation of pathological phenotypes in newborns with chromosomal aneuploidy.

Polyploid Giant Cancer Cells (PGCCs): The Evil Roots of Cancer

Polyploidy is associated with increased cell size and is commonly found in a subset of adult organs and blastomere stage of the human embryo. The polyploidy is formed through endoreplication or cell fusion to support the specific need of development including earliest embryogenesis. Recent data demonstrated that Polyploid Giant Cancer Cells (PGCCs) may have acquired an activated early embryonic-like program in response to oncogenic and therapeutic stress to generate reprogrammed cancer cells for drug resistance and metastasis. Targeting PGCCs may open up new opportunities for cancer therapy.

Single-cell analysis of human embryos reveals diverse patterns of aneuploidy and mosaicism

Less than half of human zygotes survive to birth, primarily due to aneuploidies of meiotic or mitotic origin. Mitotic errors generate chromosomal mosaicism, defined by multiple cell lineages with distinct chromosome complements. The incidence and impacts of mosaicism in human embryos remain controversial, with most previous studies based on bulk DNA assays or comparisons of multiple biopsies of few embryonic cells. Single-cell genomic data provide an opportunity to quantify mosaicism on an embryo-wide scale. To this end, we extended an approach to infer aneuploidies based on dosage-associated changes in gene expression by integrating signatures of allelic imbalance. We applied this method to published single-cell RNA sequencing data from 74 human embryos, spanning the morula to blastocyst stages. Our analysis revealed widespread mosaic aneuploidies, with 59 of 74 (80%) embryos harboring at least one putative aneuploid cell (1% FDR). By clustering copy number calls, we reconstructed histories of chromosome segregation, inferring that 55 (74%) embryos possessed mitotic aneuploidies and 23 (31%) embryos possessed meiotic aneuploidies. We found no significant enrichment of aneuploid cells in the trophectoderm compared to the inner cell mass, although we do detect such enrichment in data from later postimplantation stages. Finally, we observed that aneuploid cells up-regulate immune response genes and down-regulate genes involved in proliferation, metabolism, and protein processing, consistent with stress responses documented in other stages and systems. Together, our work provides a high-resolution view of aneuploidy in preimplantation embryos, and supports the conclusion that low-level mosaicism is a common feature of early human development.

The 2019 PGDIS position statement on transfer of mosaic embryos within a context of new information on PGT-A

BACKGROUND

A recently published Position Statement (PS) by the Preimplantation Genetics Diagnosis International Society (PGDIS) regarding utilization of preimplantation genetic testing for aneuploidy (PGT-A) in association with in vitro fertilization (IVF) contained inaccuracies and misrepresentations. Because opinions issued by the PGDIS have since 2016 determined worldwide IVF practice, corrections appear of importance.

METHODS

The International Do No Harm Group in IVF (IDNHG-IVF) is a spontaneously coalesced body of international investigators, concerned with increasing utilization of add-ons to IVF. It is responsible for the presented consensus statement, which as a final document was reached after review of the pertinent literature and again revised after the recent publication of the STAR trial and related commentaries.

RESULTS

In contrast to the PGDIA-PS, we recommend restrictions to the increasing, and by IVF centers now often even mandated, utilization of PGT-A in IVF cycles. While PGT-A has been proposed as a tool for achieving enhanced singleton livebirth outcomes through embryo selection, continued false-positive rates and increasing evidence for embryonic self-correction downstream from the testing stage, has led IDNHG-IVF to conclude that currently available data are insufficient to impose overreaching recommendations for PGT-A utilization.

DISCUSSION

Here presented consensus offers an alternative to the 2019 PGDIS position statement regarding utilization of preimplantation genetic testing for aneuploidy (PGT-A) in association with in vitro fertilization (IVF). Mindful of what appears to offer best outcomes for patients, and in full consideration of patient autonomy, here presented opinion is based on best available evidence, with the goal of improving safety and efficacy of IVF and minimizing wastage of embryos with potential for healthy births.

CONCLUSIONS

As the PGDIS never suggested restrictions on clinical utilization of PGT-A in IVF, here presented rebuttal represents an act of self-regulation by parts of the IVF community in attempts to control increasing utilization of different unproven recent add-ons to IVF.

Dynamic nature of somatic chromosomal mosaicism, genetic-environmental interactions and therapeutic opportunities in disease and aging

BACKGROUND

Somatic chromosomal mosaicism is the presence of cell populations differing with respect to the chromosome complements (e.g. normal and abnormal) in an individual. Chromosomal mosaicism is associated with a wide spectrum of disease conditions and aging. Studying somatic genome variations has indicated that amounts of chromosomally abnormal cells are likely to be unstable. As a result, dynamic changes of mosaicism rates occur through ontogeny. Additionally, a correlation between disease severity and mosaicism rates appears to exist. High mosaicism rates are usually associated with severe disease phenotypes, whereas low-level mosaicism is generally observed in milder disease phenotypes or in presumably unaffected individuals. Here, we hypothesize that dynamic nature of somatic chromosomal mosaicism may result from genetic-environmental interactions creating therapeutic opportunities in the associated diseases and aging.

CONCLUSION

Genetic-environmental interactions seem to contribute to the dynamic nature of somatic mosaicism. Accordingly, an external influence on cellular populations may shift the ratio of karyotypically normal and abnormal cells in favor of an increase in the amount of cells without chromosome rearrangements. Taking into account the role of somatic chromosomal mosaicism in health and disease, we have hypothesized that artificial changing of somatic mosaicism rates may be beneficial in individuals suffering from the associated diseases and/or behavioral or reproductive problems. In addition, such therapeutic procedures might be useful for anti-aging strategies (i.e. possible rejuvenation through a decrease in levels of chromosomal mosaicism) increasing the lifespan. Finally, the hypothesis appears to be applicable to any type of somatic mosacism.

Chromosomal mosaicism in human blastocysts: the ultimate diagnostic dilemma

BACKGROUND

Trophectoderm (TE) biopsy and next generation sequencing (NGS) are currently the preferred techniques for preimplantation genetic testing for aneuploidies (PGT-A). Although this approach delivered important improvements over previous testing strategies, increased sensitivity has also prompted a rise in diagnoses of uncertain clinical significance. This includes reports of chromosomal mosaicism, suggesting the presence of karyotypically distinct cells within a single TE biopsy. Given that PGT-A relies on the chromosomal constitution of the biopsied cells being representative of the entire embryo, the prevalence and clinical implications of blastocyst mosaicism continue to generate considerable controversy.

OBJECTIVE AND RATIONALE

The objective of this review was to evaluate existing scientific evidence regarding the prevalence and impact of chromosomal mosaicism in human blastocysts. We discuss insights from a biological, technical and clinical perspective to examine the implications of this diagnostic dilemma for PGT-A.

SEARCH METHODS

The PubMed and Google Scholar databases were used to search peer-reviewed publications using the following terms: ‘chromosomal mosaicism’, ‘human’, ‘embryo’, ‘blastocyst’, ‘implantation’, ‘next generation sequencing’ and ‘clinical management’ in combination with other keywords related to the subject area. Relevant articles in the English language, published until October 2019 were critically discussed.

OUTCOMES

Chromosomal mosaicism predominately results from errors in mitosis following fertilization. Although it appears to be less pervasive at later developmental stages, establishing the true prevalence of mosaicism in human blastocysts remains exceedingly challenging. In a clinical context, blastocyst mosaicism can only be reported based on a single TE biopsy and has been ascribed to 2–13% of embryos tested using NGS. Conversely, data from NGS studies disaggregating whole embryos suggests that mosaicism may be present in up to ~50% of blastocysts. However, differences in testing and reporting strategies, analysis platforms and the number of cells sampled inherently overshadow current data, while added uncertainties emanate from technical artefacts. Moreover, laboratory factors and aspects of in vitro culture generate further variability. Outcome data following the transfer of blastocysts diagnosed as mosaic remain limited. Current studies suggest that the transfer of putative mosaic embryos may lead to healthy live births, but also results in significantly reduced ongoing pregnancy rates compared to the transfer of euploid blastocysts. Observations that a subset of mosaic blastocysts has the capacity to develop normally have sparked discussions regarding the ability of embryos to self-correct. However, there is currently no direct evidence to support this assumption. Nevertheless, the exclusion of mosaic blastocysts results in fewer embryos available for transfer, which may inevitably compromise treatment outcomes.

WIDER IMPLICATIONS

Chromosomal mosaicism in human blastocysts remains a perpetual diagnostic and clinical dilemma in the context of PGT-A. This review offers an important scientific resource, informing about the challenges, risks and value of diagnosing mosaicism. Elucidating these uncertainties will ultimately pave the way towards improved clinical and patient management.

Homozygous mutations in REC114 cause female infertility characterised by multiple pronuclei formation and early embryonic arrest

BACKGROUND

Abnormal pronuclear formation during fertilisation and subsequent early embryonic arrest results in female infertility. In recent years, with the prevalence of assisted reproductive technology, a few genes have been identified that are involved in female infertility caused by abnormalities in oocyte development, fertilisation and embryonic development. However, the genetic factors responsible for multiple pronuclei formation during fertilisation and early embryonic arrest remain largely unknown.

OBJECTIVE

We aim to identify genetic factors responsible for multiple pronuclei formation during fertilisation or early embryonic arrest.

METHODS

Whole-exome sequencing was performed in a cohort of 580 patients with abnormal fertilisation and early embryonic arrest. Effects of mutations were investigated in HEK293T cells by western blotting and immunoprecipitation, as well as minigene assay.

RESULTS

We identified a novel homozygous missense mutation (c.397T>G, p.C133G) and a novel homozygous donor splice-site mutation (c.546+5G>A) in the meiotic gene REC114. REC114 is involved in the formation of double strand breaks (DSBs), which initiate homologous chromosome recombination. We demonstrated that the splice-site mutation affected the normal alternative splicing of REC114, while the missense mutation reduced the protein level of REC114 in vitro and resulted in the loss of its function to protect its partner protein MEI4 from degradation.

CONCLUSIONS

Our study has identified mutations in REC114 responsible for human multiple pronuclei formation and early embryonic arrest, and these findings expand our knowledge of genetic factors that are responsible for normal human female meiosis and fertility.

Aurora B prevents aneuploidy via MAD2 during the first mitotic cleavage in oxidatively damaged embryos

OBJECTIVES

A high rate of chromosome aneuploidy is exhibited in in vitro fertilization (IVF)-derived embryos. Our previous experiments suggested that reactive oxygen species (ROS) can activate Mad2, a key protein in the spindle assembly checkpoint (SAC), and delay the first mitotic, providing time to prevent the formation of embryonic aneuploidy. We aimed to determine whether mitotic kinase Aurora B was involved in the SAC function to prevent aneuploidy in IVF-derived embryos.

MATERIALS AND METHODS

We analysed aneuploidy formation and repair during embryo pre-implantation via 4',6-diamidino-2-phenylindole (DAPI) staining and karyotype analysis. We assessed Aurora B activation by immunofluorescence and investigated the effect of Aurora B inhibition on embryo injury-related variables, such as embryonic development, ROS levels, mitochondrial membrane potential and γH2AX-positive expression.

RESULTS

We observed the expression and phosphorylation of Thr232 in Aurora B in oxidative stress-induced zygotes. Moreover, inhibition of Aurora B caused chromosome mis-segregation, abnormal spindle structures, abnormal chromosome number and reduced expression of Mad2 in IVF embryos. Our results suggest that Aurora B causes mitotic arrest and participates in SAC via Mad2 and H3S10P, which is required for self-correction of aneuploidies.

CONCLUSIONS

We demonstrate here that oxidative stress-induced DNA damage triggers Aurora B-mediated activation of SAC, which prevents aneuploidy at the first mitotic cleavage in early mouse IVF embryos.

Sperm chromosomal abnormalities and their contribution to human embryo aneuploidy

In this work we reviewed 18 years of experience using fluorescence in situ hybridization (FISH) for sperm aneuploidy testing. We evaluated parameters associated with increased numerical sperm chromosome abnormalities and determined the male contribution to embryo aneploidies in terms of reproductive outcome by increased sperm aneuploidy. This retrospective study analyzed data from 2008 sperm samples of infertile males undergoing FISH analysis because of clinical history of repetitive implantation failure, recurrent miscarriage, impaired sperm parameters, or mixed causes. Sperm concentration was the only sperm parameter associated with FISH results—we observed a gradual increase of abnormal sperm FISH results in males with decreasing sperm concentration. However, a great proportion of normozoospermic males also showed increased sperm aneuploidies, suggesting that sperm parameters alone do not enable identification of a substantial proportion of infertile males at risk of sperm aneuploidies. Regarding reproductive outcomes, couples with normal sperm FISH results for the male had similar outcomes regardless of conventional in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), or preimplantation genetic testing for aneuploidies (PGT-A). However, couples with abnormal sperm FISH results for the male showed better clinical outcomes after PGT-A, suggesting a potential contribution of sperm to embryo aneuploidy. Moreover, PGT-A cycles showed better clinical outcomes when 24 chromosomes were analyzed by array comparative genome hybridization (aCGH) or next-generation sequencing (NGS) instead of only nine chromosomes analyzed by FISH. In conclusion, sperm FISH analysis offers clinical prognostic value to evaluate reproductive possibilities in infertile couples. Therefore, couples with abnormal sperm FISH results should be offered genetic counseling and presented with clinical options such as PGT-A.

Pig in vitro fertilization: Where are we and where do we go?

The pig is an important livestock animal. Biotechnological interest in this species has increased due to its use, among others, in the generation of transgenic animals for use in biomedicine based on its greater physiological proximity to the human species than other large domestic animals. This development has paralleled an improvement in Assisted Reproduction Techniques (ART) used for this species. However, the ability to generate animals from embryos produced entirely in vitro is still limited and a wide margin for improvement remains. Here we review the procedures, additives, and devices used during pig in vitro fertilization (IVF), focusing on the main points of each step that have offered the best results in terms of increased efficiency of the system. The lack of standardized protocols and consensus on the parameters to be assessed makes it difficult to compare results across different studies, but some conclusions are drawn from the literature. We anticipate that new physiological protocols will advance the field of swine IVF, including induction of prefertilization ZP hardening with oviductal fluid, sperm preparation by swim-up method, increased viscosity through the addition of inert molecules or reproductive biofluids, and the incorporation of 3D devices. Here we also reflect on the need to expand the variables on which the efficiency of pig IVF is based, providing new parameters that should be considered to supply more objective and quantitative assessment of IVF additives and protocols.

The model of "genetic compartments": a new insight into reproductive genetics

Currently, we are witnessing revolutionary advances in the analytical power of genetic tools. An enormous quantity of data can now be obtained from samples; however, the translation of genetic findings to the general status of individuals, or their offspring, should be done with caution. This is especially relevant in the reproductive context, where the concepts of "transmission" and "inheritability" of a trait are crucial. Against this background, we offer new insight based on a systemic view of genetic constitution in the compartmentalized organism, that is, the human body. This model considers the coexistence of "different" genomes in the same individual and the repercussion of this on reproductive efficacy and offspring. Herein, we review the major differences between somatic, germinal, embryonic, and fetal/placental genomes and their contribution to the next generation and its reproductive efficacy. The major novelty of our approach is the holistic interaction between microsystems within a macrosystem (i.e., the reproductive system). This panoramic model allows us to sketch the future implications of genetic results in function of the origin (compartment) of the sample: peripheral blood or other somatic tissues, gametes, zygotes, preimplantation embryos, fetus, or placenta. We believe this perspective can be of great use in the context of reproductive genetic counseling.

Potential Role of Chromothripsis in the Genesis of Complex Chromosomal Rearrangements in Human Gametes and Preimplantation Embryo

The discovery of a new class of massive chromosomal rearrangement, baptized chromothripsis, in different cancers and congenital disorders has deeply modified our understanding on the genesis of complex genomic rearrangements. Several mechanisms, involving abortive apoptosis, telomere erosion, mitotic errors, micronuclei formation, and p53 inactivation, might cause chromothripsis. The remarkable point is that all these plausible mechanisms have been identified in the field of human reproduction as causal factors for reproductive failures and chromosomal abnormality genesis. Specific features of gametogenesis and early embryonic development may contribute to the emergence of chromothripsis. Multiple lines of evidence support the assumption that chromothripsis may arise more frequently than previously thought in both gametogenesis and early human embryogenesis.

Deoxyribonucleic acid detection in blastocoelic fluid: a new predictor of embryo ploidy and viable pregnancy

OBJECTIVE

To investigate blastocysts, defined as euploid and aneuploid by trophectoderm (TE) cell analysis, for the presence of DNA in the blastocoelic fluid (BF) detected by whole-genomic amplification (WGA); and to correlate the presence of DNA in BF with the clinical outcome after the transfer of TE-euploid blastocysts.

DESIGN

Retrospective study.

SETTING

In vitro fertilization unit.

PATIENT(S)

This study included 91 patients performing preimplantation genetic testing for aneuploidy on TE cells from January 2015 to December 2017. In the case of ET, only single blastocyst transfers were performed.

INTERVENTION(S)

Blastocoelic fluids and TE cells were retrieved from 256 blastocysts before vitrification. All blastocysts were diagnosed by array-comparative genomic hybridization (a-CGH) on TE cells. Amplification and a-CGH of DNA from BFs was performed at a later time after TE biopsy and ET.

MAIN OUTCOME MEASURE(S)

Whole-genomic amplification of BFs, evaluation of the chromosome condition in BFs and TE cells, and correlation of BF results with the clinical outcome of TE-euploid transferred blastocysts.

RESULT(S)

The incidence of amplification after WGA was significantly lower in BFs from TE-euploid blastocysts (n = 32, 45%) when compared with the aneuploid ones (n = 150, 81%), resulting in 182 BFs with successful DNA amplification. When submitted to a-CGH, informative results were obtained from 172 BFs. Comparison of these results with those from the corresponding TE cells gave a ploidy concordance of 93.6% and a mean number of aneuploid events per sample that was higher in BFs than in TE cells (2.0 vs. 1.4, respectively). After the transfer of 53 TE-euploid blastocysts, the clinical pregnancy rate was 77% in the group with BF-failed amplification, and 37% after BF-successful amplification. The same trend was found for the ongoing pregnancy rate (68% vs. 31.5%, respectively).

CONCLUSION(S)

The presence of DNA in BFs detected by WGA is correlated with the blastocyst ploidy condition defined by TE cell biopsy and with the implantation potential of TE-euploid blastocysts. These findings could have a clinical implication for the selection of the most viable embryo for transfer because, after submitting BFs to WGA, priority would be given to TE-euploid blastocysts with BF-failed amplification. Similarly, BF-failed amplification could be an additional selection criterion to prioritize embryos for transfer even in conventional IVF cycles with blastocysts that were vitrified after BF aspiration.

The dualistic origin of human tumors

Life starts with a zygote, which is formed by the fusion of a haploid sperm and egg. The formation of a blastomere by cleavage division (nuclear division without an increase in cell size) is the first step in embryogenesis, after the formation of the zygote. Blastomeres are responsible for reprogramming the parental genome as a new embryonic genome for generation of the pluripotent stem cells which then differentiate by Waddington's epigenetic landscape to create a new life. Multiple authors over the past 150 years have proposed that tumors arises from development gone awry at a point within Waddington's landscape. Recent discoveries showing that differentiated somatic cells can be reprogrammed into induced pluripotent stem cells, and that somatic cell nuclear transfer can be used to successfully clone animals, have fundamentally reshaped our understanding of tumor development and origin. Differentiated somatic cells are plastic and can be induced to dedifferentiate into pluripotent stem cells. Here, I review the evidence that suggests somatic cells may have a previously overlooked endogenous embryonic program that can be activated to dedifferentiate somatic cells into stem cells of various potencies for tumor initiation. Polyploid giant cancer cells (PGCCs) have long been observed in cancer and were thought originally to be nondividing. Contrary to this belief, recent findings show that stress-induced PGCCs divide by endoreplication, which may recapitulate the pattern of cleavage-like division in blastomeres and lead to dedifferentiation of somatic cells by a programmed process known as "the giant cell cycle", which comprise four distinct but overlapping phases: initiation, self-renewal, termination and stability. Depending on the intensity and type of stress, different levels of dedifferentiation result in the formation of tumors of different grades of malignancy. Based on these results, I propose a unified dualistic model to demonstrate the origin of human tumors. The tenet of this model includes four points, as follows. 1. Tumors originate from a stem cell at a specific developmental hierarchy, which can be achieved by dualistic origin: dedifferentiation of the zygote formed by two haploid gametes (sexual reproduction) via the blastomere during normal development, or transformation from damaged or aged mature somatic cells via a blastomere-like embryonic program (asexual reproduction). 2. Initiation of the tumor begins with a stem cell that has uncoupled the differentiation from the proliferation program which results in stem cell maturation arrest. 3. The developmental hierarchy at which stem cells arrest determines the degree of malignancy: the more primitive the level at which stem cells arrest, the greater the likelihood of the tumor being malignant. 4. Environmental factors and intrinsic genetic or epigenetic alterations represent the risk factors or stressors that facilitate stem cell arrest and somatic cell dedifferentiation. However, they, per se, are not the driving force of tumorigenesis. Thus, the birth of a tumor can be viewed as a triad that originates from a stem cell via dedifferentiation through a blastomere or blastomere-like program, which then differentiates along Waddington's landscape, and arrests at a developmental hierarchy. Blocking the PGCC-mediated dedifferentiation process and inducing their differentiation may represent a novel alternative approach to eliminate the tumor occurrence and therapeutic resistance.

Murine embryos exposed to human endometrial MSCs-derived extracellular vesicles exhibit higher VEGF/PDGF AA release, increased blastomere count and hatching rates

Endometrial Mesenchymal Stromal Cells (endMSCs) are multipotent cells with immunomodulatory and pro-regenerative activity which is mainly mediated by a paracrine effect. The exosomes released by MSCs have become a promising therapeutic tool for the treatment of immune-mediated diseases. More specifically, extracellular vesicles derived from endMSCs (EV-endMSCs) have demonstrated a cardioprotective effect through the release of anti-apoptotic and pro-angiogenic factors. Here we hypothesize that EV-endMSCs may be used as a co-adjuvant to improve in vitro fertilization outcomes and embryo quality. Firstly, endMSCs and EV-endMSCs were isolated and phenotypically characterized for in vitro assays. Then, in vitro studies were performed on murine embryos co-cultured with EV-endMSCs at different concentrations. Our results firstly demonstrated a significant increase on the total blastomere count of expanded murine blastocysts. Moreover, EV-endMSCs triggered the release of pro-angiogenic molecules from embryos demonstrating an EV-endMSCs concentration-dependent increase of VEGF and PDGF-AA. The release of VEGF and PDGF-AA by the embryos may indicate that the beneficial effect of EV-endMSCs could be mediating not only an increase in the blastocyst’s total cell number, but also may promote endometrial angiogenesis, vascularization, differentiation and tissue remodeling. In summary, these results could be relevant for assisted reproduction being the first report describing the beneficial effect of human EV-endMSCs on embryo development.

Live imaging of cell division in 3D stem-cell organoid cultures

Examining cell behavior in its correct tissue context is a major challenge in cell biology. The recent development of mammalian stem cell-based organoid cultures offers exciting opportunities to visualize dynamic cellular events in a 3D tissue-like setting. We describe here an approach for live imaging of cell division processes in intestinal organoid cultures derived from human and mouse adult stem cells. These approaches can be extended to the analysis of cellular events in diseased tissue, such as patient-derived tumor organoids.

The Genomic Characteristics and Origin of Chromothripsis

In 2011 a phenomenon involving complex chromosomal rearrangements was discovered in cancer genomes. This phenomenon has been termed chromothripsis, on the basis of its chromosomal hallmarks, which point to an underlying process involving chromosome (chromo) shattering (thripsis). The prevailing hypothesis of cancer genome evolution as a gradual process of mutation and selection was challenged by the discovery of chromothripsis, because its patterns of chromosome rearrangement rather indicated an one-off catastrophic burst of genome rearrangement. The initial discovery of chromothripsis has led to many more examples of chromothripsis both in cancer genomes as well as in patients with congenital diseases and in the genomes of healthy individuals. Since then, a burning topic has been the study of the molecular mechanism that leads to chromothripsis. Cumulating evidence has shown that chromothripsis may result from lagging chromosomes encapsulated in micronuclei, as well as from telomere fusions followed by chromosome bridge formation. In this chapter, we will outline the genomic characteristics of chromothripsis, and we present genomic methodologies that enable the detection of chromothripsis. Furthermore, we will give an overview of recent insights into the mechanisms underlying chromothripsis.

Time-Lapse Imaging for the Detection of Chromosomal Abnormalities in Primate Preimplantation Embryos

The use of time-lapse microscopic imaging has proven to be a powerful tool for the study of mitotic divisions and other cellular processes across diverse species and cell types. Although time-lapse monitoring (TLM) of human preimplantation development was first introduced to the in vitro fertilization (IVF) community several decades ago, it was not until relatively recently that TLM systems were commercialized for clinical embryology purposes. Traditionally, human IVF embryos are assessed by successful progression and morphology under a stereomicroscope at distinct time points prior to selection for transfer. Due to the high frequency of aneuploidy, embryos may also be biopsied at the cleavage or blastocyst stage for preimplantation genetic screening (PGS) of whole and/or partial chromosomal abnormalities. However, embryo biopsy is invasive and can hinder subsequent development, and there are additional concerns over chromosomal mosaicism and resolution with PGS. Moreover, embryos are typically outside of the incubator in suboptimal culture conditions for extended periods of time during these procedures. With TLM systems, embryos remain in the stable microenvironment of an incubator and are simultaneously imaged for noninvasive embryo evaluation using a fraction of the light exposure as compared to a stereomicroscope. Each image is then compiled into a time-lapse movie, the information from which can be extrapolated to correlate morphological, spatial, and temporal parameters with embryo quality and copy number status. Here, we describe the various TLM systems available for clinical and/or research use in detail and provide step-by-step instructions on how the measurement of specific timing intervals and certain morphological criteria can be implemented into IVF protocols to enhance embryo assessment and avoid the selection of aneuploid embryos. We also discuss the biological significance of processes unique to mitotically dividing embryos and the likelihood that complex chromosomal events such as chromothripsis occur during preimplantation development in humans and other mammals, particularly nonhuman primates.

Mosaic autosomal aneuploidies are detectable from single-cell RNAseq data

BACKGROUND

Aneuploidies are copy number variants that affect entire chromosomes. They are seen commonly in cancer, embryonic stem cells, human embryos, and in various trisomic diseases. Aneuploidies frequently affect only a subset of cells in a sample; this is known as "mosaic" aneuploidy. A cell that harbours an aneuploidy exhibits disrupted gene expression patterns which can alter its behaviour. However, detection of aneuploidies using conventional single-cell DNA-sequencing protocols is slow and expensive.

METHODS

We have developed a method that uses chromosome-wide expression imbalances to identify aneuploidies from single-cell RNA-seq data. The method provides quantitative aneuploidy calls, and is integrated into an R software package available on GitHub and as an Additional file of this manuscript.

RESULTS

We validate our approach using data with known copy number, identifying the vast majority of aneuploidies with a low rate of false discovery. We show further support for the method's efficacy by exploiting allele-specific gene expression levels, and differential expression analyses.

CONCLUSIONS

The method is quick and easy to apply, straightforward to interpret, and represents a substantial cost saving compared to single-cell genome sequencing techniques. However, the method is less well suited to data where gene expression is highly variable. The results obtained from the method can be used to investigate the consequences of aneuploidy itself, or to exclude aneuploidy-affected expression values from conventional scRNA-seq data analysis.

AIRE is a critical spindle-associated protein in embryonic stem cells

Embryonic stem (ES) cells go though embryo-like cell cycles regulated by specialized molecular mechanisms. However, it is not known whether there are ES cell-specific mechanisms regulating mitotic fidelity. Here we showed that Autoimmune Regulator (Aire), a transcription coordinator involved in immune tolerance processes, is a critical spindle-associated protein in mouse ES(mES) cells. BioID analysis showed that AIRE associates with spindle-associated proteins in mES cells. Loss of function analysis revealed that Aire was important for centrosome number regulation and spindle pole integrity specifically in mES cells. We also identified the c-terminal LESLL motif as a critical motif for AIRE's mitotic function. Combined maternal and zygotic knockout further revealed Aire's critical functions for spindle assembly in preimplantation embryos. These results uncovered a previously unappreciated function for Aire and provide new insights into the biology of stem cell proliferation and potential new angles to understand fertility defects in humans carrying Aire mutations.

Revealing the secret life of pre-implantation embryos by time-lapse monitoring: A review

High implantation success following in vitro fertilization cycles are achieved via the transfer of embryos with the highest developmental competence. Multiple pregnancies as a result of the transfer of several embryos per cycle accompany with various complication. Thus, single-embryo transfer (SET) is the preferred practice in assisted reproductive technique (ART) treatment. In order to improve the pregnancy rate for SET, embryologists need reliable biomarkers to aid their selection of embryos with the highest developmental potential. Time-lapse technology is a noninvasive alternative conventional microscopic assessment. It provides uninterrupted and continues the survey of embryo development to transfer day. Today, there are four time-lapse systems that are commercially available for ART centers. In world and Iran, the first time lapse babies were born in 2010 and 2015, respectively, conceived by SET. Here, we review the use of time-lapse monitoring in the observation of embryogenesis as well as its role in SET. Although, the findings from our review support common use of time-lapse monitoring in ART centers; but, future large studies assessing this system in well-designed trials are necessary.

Maternal common variant rs2305957 spanning PLK4 is associated with blastocyst formation and early recurrent miscarriage

OBJECTIVE

To investigate whether the common variant rs2305957 spanning PLK4 (Polo-like kinase 4) confers risk to embryo development in Northern Chinese Han (CHN) women.

DESIGN

Genetic association study.

SETTING

University hospital.

PATIENT(S)

A total of 2,015 infertile women who underwent in vitro fertilization (IVF), 530 women with early recurrent miscarriage (ERM), and 600 fertile control women in the CHN population.

INTERVENTION(S)

Genotyping of rs2305957 was performed by means of high-resolution melting analysis.

MAIN OUTCOME MEASURE(S)

Blastocyst formation, implantation, early miscarriage, and live birth rates in infertile women; genotype distribution at rs2305957 in ERM case and control subjects.

RESULT(S)

In the first cohort of this study, infertile women with AA genotype had a lower blastocyst formation rate than those with AG or GG genotype. No significant differences were observed in implantation rate, early miscarriage rate, or live birth rate among AA, AG, and GG subgroups. In the second cohort, common variant rs2305957 was related to ERM. Genotype frequency differences were also significant in both additive model and dominant model.

CONCLUSION(S)

Common variant rs2305957 is associated with blastocyst formation and ERM in CHN women. Further investigations of PLK4 gene during embryo development could be worthwhile.

Early embryo mortality in natural human reproduction: What the data say

How many human embryos die between fertilisation and birth under natural conditions? It is widely accepted that natural human embryo mortality is high, particularly during the first weeks after fertilisation, with total prenatal losses of 70% and higher frequently claimed. However, the first external sign of pregnancy occurs two weeks after fertilisation with a missed menstrual period, and establishing the fate of embryos before this is challenging. Calculations are additionally hampered by a lack of data on the efficiency of fertilisation under natural conditions. Four distinct sources are used to justify quantitative claims regarding embryo loss: (i) a hypothesis published by Roberts & Lowe in TheLancet  is widely cited but has no practical quantitative value; (ii) life table analyses give consistent assessments of clinical pregnancy loss, but cannot illuminate losses at earlier stages of development; (iii) studies that measure human chorionic gonadotrophin (hCG) reveal losses in the second week of development and beyond, but not before; and (iv) the classic studies of Hertig and Rock offer the only direct insight into the fate of human embryos from fertilisation under natural conditions. Re-examination of Hertig's data demonstrates that his estimates for fertilisation rate and early embryo loss are highly imprecise and casts doubt on the validity of his numerical analysis. A recent re-analysis of hCG study data concluded that approximately 40-60% of embryos may be lost between fertilisation and birth, although this will vary substantially between individual women. In conclusion, natural human embryo mortality is lower than often claimed and widely accepted. Estimates for total prenatal mortality of 70% or higher are exaggerated and not supported by the available data.