DNA repair signalling pathway genes are overexpressed in poor-quality pre-implantation human embryos with complex aneuploidy

Investigation of BAK, BAX and MAD2L1 gene expression in human aneuploid blastocysts

Maintaining genomic stability is crucial for normal development. At earlier stages of preimplantation development, as the embryonic genome activation is not fully completed, the embryos may be more prone to abnormalities. Aneuploidies are one of the most common genetic causes of implantation failure or first-trimester miscarriages. Apoptosis is a crucial mechanism to eliminate damaged or abnormal cells from the organism to enable healthy growth. Therefore, this study aimed to determine the relationship between the expression levels of genes involved in apoptosis in human aneuploid and euploid blastocysts. In total, 32 human embryos obtained from 21 patients were used for this study. Trophectoderm biopsies were performed and next-generation screening was carried out for aneuploidy screening. Total RNA was extracted from each blastocyst separately and cDNA was synthesized. Gene expression levels were evaluated using RT-PCR. The statistical analysis was performed to evaluate the gene expression level variations in the euploid and aneuploid embryos, respectively. The expression level of the BAX gene was significantly different between the aneuploid and euploid samples. BAX expression levels were found to be 1.5-fold lower in aneuploid cells. However, the expression levels of BAK and MAD2L1 genes were similar in each group. This study aimed to investigate the possible role of genes involved in apoptosis and aneuploidy mechanisms. The findings of this investigation revealed that the BAX gene was expressed significantly differently between aneuploid and euploid embryos. Therefore, it is possible that the genes involved in the apoptotic pathway have a role in the aneuploidy mechanism.

Checkpoint Kinase 1 Is a Key Signal Transducer of DNA Damage in the Early Mammalian Cleavage Embryo

After fertilization, remodeling of the oocyte and sperm genome is essential for the successful initiation of mitotic activity in the fertilized oocyte and subsequent proliferative activity of the early embryo. Despite the fact that the molecular mechanisms of cell cycle control in early mammalian embryos are in principle comparable to those in somatic cells, there are differences resulting from the specific nature of the gene totipotency of the blastomeres of early cleavage embryos. In this review, we focus on the Chk1 kinase as a key transduction factor in monitoring the integrity of DNA molecules during early embryogenesis.

Cleavage of Early Mouse Embryo with Damaged DNA

The preimplantation period of embryogenesis is crucial during mammalian ontogenesis. During this period, the mitotic cycles are initiated, the embryonic genome is activated, and the primary differentiation of embryonic cells occurs. All cellular abnormalities occurring in this period are the primary cause of fetal developmental disorders. DNA damage is a serious cause of developmental failure. In the context of DNA damage response on the cellular level, we analyzed the course of embryogenesis and phenotypic changes during the cleavage of a preimplantation embryo. Our results document that DNA damage induced before the resumption of DNA synthesis in a zygote can significantly affect the preimplantation development of the embryo. This developmental ability is related to the level of the DNA damage. We showed that one-cell embryos can correct the first cleavage cycle despite low DNA damage and incomplete replication. It seems that the phenomenon creates a predisposition to a segregation disorder of condensed chromatin that results in the formation of micronuclei in the developmental stages following the first cleavage. We conclude that zygote tolerates a certain degree of DNA damage and considers its priority to complete the first cleavage stage and continue embryogenesis as far as possible.

Glutamine as a Potential Noninvasive Biomarker for Human Embryo Selection

To determine whether glutamine consumption is associated with embryo quality and aneuploidy, a retrospective study was conducted in an in vitro fertilization center. Spent embryo culture media from patients undergoing assisted reproduction treatment and preimplantation genetic testing (PGT) were obtained on day 3 of in vitro culture. Embryo quality was assessed for cell number and fragmentation rate. PGT for aneuploidy was performed using whole genome amplification and DNA sequencing. Glutamine levels in spent embryo culture media were analyzed by gas chromatography–mass spectrometry. The results demonstrated that glutamine was a primary contributor to the classification of the good-quality and poor-quality embryos based on the orthogonal partial least-squares discriminant analysis model. Glutamine consumption in the poor-quality embryos was significantly higher than that in the good-quality embryos (P < 0.05). A significant increase in glutamine consumption was observed from aneuploid embryos compared with that from euploid embryos (P < 0.01). The Pearson correlation coefficients between embryo quality and glutamine consumption, and between aneuploidy and glutamine consumption, were 0.430 and 0.757, respectively. The area under the ROC curve was 0.938 (95% CI: 0.902–0.975) for identifying aneuploidy. Animal experiments demonstrate that increased glutamine consumption may be a compensatory mechanism to mitigate oxidative stress. Our data suggest that glutamine consumption is associated with embryo quality and aneuploidy. Glutamine may serve as a molecular indicator for embryo assessment and aneuploidy testing.

Coculture of porcine luteal cells during in vitro porcine oocyte maturation affects blastocyst gene expression and developmental potential

Oocyte maturation in culture is still the weakest part of in vitro fertilization (IVF) and coculture with somatic cells may be an alternative to improve suboptimal culture conditions, especially in the pig in which maturation takes more than 44 h. In the present study, we investigated the effect of a coculture system of porcine luteal cells (PLC) during in vitro maturation (IVM) on embryo development and gene expression. Cumulus-oocyte complexes were matured in vitro in TCM-199 with human menopausal gonadotrophin (control) and in coculture with PLC. IVF was performed with frozen-thawed boar semen in Tris-buffered medium. Presumptive zygotes were cultured in PZM for 7 days. The coculture with PLC significantly increased blastocysts rates. Gene expression changes were measured with a porcine embryo-specific microarray and confirmed by RT-qPCR. The global transcription pattern of embryos developing after PLC coculture exhibited overall downregulation of gene expression. Following global gene expression pattern analysis, genes associated with lipid metabolism, mitochondrial function, endoplasmic reticulum stress, and apoptosis were found downregulated, and genes associated with cell cycle and proliferation were found upregulated in the PLC coculture. Canonical pathway analysis by Ingenuity Pathway revealed that differential expression transcripts were associated with the sirtuin signaling pathway, oxidative phosphorylation pathway, cytokines and ephrin receptor signaling. To conclude, the coculture system of PLC during IVM has a lasting effect on the embryo until the blastocyst stage, modifying gene expression, with a positive effect on embryo development. Our model could be an alternative to replace the conventional maturation medium with gonadotrophins with higher rates of embryo development, a key issue in porcine in vitro embryo production.

Preserving Genome Integrity During the Early Embryonic DNA Replication Cycles

During the very early stages of embryonic development chromosome replication occurs under rather challenging conditions, including a very short cell cycle, absence of transcription, a relaxed DNA damage response and, in certain animal species, a highly contracted S-phase. This raises the puzzling question of how the genome can be faithfully replicated in such a peculiar metabolic context. Recent studies have provided new insights into this issue, and unveiled that embryos are prone to accumulate genetic and genomic alterations, most likely due to restricted cellular functions, in particular reduced DNA synthesis quality control. These findings may explain the low rate of successful development in mammals and the occurrence of diseases, such as abnormal developmental features and cancer. In this review, we will discuss recent findings in this field and put forward perspectives to further study this fascinating question.

Effect of Sperm DNA Fragmentation on Embryo Quality in Normal Responder Women in In Vitro Fertilization and Intracytoplasmic Sperm Injection

PURPOSE

To investigate the associations between sperm DNA fragmentation (SDF) and embryo formation rate in normal responder women to in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI).

MATERIALS AND METHODS

Fifty-three consecutive, fresh IVF/ICSI cycles performed from 2014 to 2017 were selected. All women were normal responders (4 to 14 mature oocytes were retrieved) and at least one normally fertilized oocyte with two pronuclei was obtained in all cycles. Semen was collected on the day of oocyte retrieval, and SDF levels were measured by sperm chromatin dispersion test (Halosperm assay). At day 3 after insemination, embryo quality was evaluated by morphologic criteria and categorized as A/B/C/D. Top quality embryo were defined as grade A embryos with seven cells or more.

RESULTS

SDF levels showed a positive linear correlation with the male's age (r=0.307, p=0.025) and a negative linear correlation with sperm motility (r=-0.491, p<0.0001). To achieve top-quality or a grade A embryo formation rate >70%, the cut-off value SDF was <30.7% for each. Among individuals with SDF <30.7%, the median top-quality or grade A embryo formation rate was significantly higher than that among individuals with SDF ≥30.7% (38.1% vs. 20.0%, p=0.038; 50% vs. 25.0%, p=0.017).

CONCLUSION

In normal responder women, high SDF level resulted in low day 3 embryo formation rates. Our results suggest a paternal effect on embryo quality in IVF/ICSI cycles.

Early blastocyst expansion in euploid and aneuploid human embryos: evidence for a non-invasive and quantitative marker for embryo selection

RESEARCH QUESTION

How can the kinetics of human blastocyst expansion be used to evaluate an embryo's ploidy identified using preimplantation genetic testing for aneuploidy (PGT-A)?

DESIGN

This was a retrospective observational study of 188 autologous blastocysts from 34 sequential treatment cycles using PGT-A and blastocyst biopsy. Using time-lapse imaging, blastocyst expansion was evaluated using a quantitative standardized expansion assay (qSEA). Trophectoderm cell division was examined in selected, unbiopsied embryos (n = 7) to evaluate the contribution of mitosis to the expansion rate.

RESULTS

The averaged euploid blastocyst expansion rate was significantly (52.8%) faster than in aneuploid blastocysts (P = 0.0041). Scatterplots, representing 'expansion maps', revealed that both populations showed a similarly overlapping distribution of blastocyst formation times at 80-140 h from fertilization. Euploidy and aneuploidy were better distinguished in regions of higher and lower expansion, respectively, in expansion maps. Based upon the expansion slopes, rank-ordering of individual embryos within cohorts resulted in more than 90% euploid embryos in the first two ranks in patients less than 35 years of age. Additional detailed time-lapse image analysis provided evidence that rapid expansion was associated with robust, integrative cellular mitosis in trophectoderm cells.

CONCLUSIONS

The kinetics of human blastocyst expansion are related to an embryo's ploidy. These preliminary observations describe a new quantitative, non-invasive approach to embryo assessment that may be useful to identify single blastocysts for transfer, particularly in younger patient groups. However, this approach may also be useful for euploid embryo selection after PGT-A. The results support the hypothesis that aneuploidy universally impairs general cellular processes, including cell division, in differentiated cells.

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.

Origins of Intraindividual Genetic Variation in Human Fetuses

BACKGROUND

Intraindividual copy number variation (CNV) origin is largely unknown. They might be due to aging and/or common genome instability at the preimplantation stage while contribution of preimplantation in human intraindividual CNVs occurrence is unknown. To address this question, we investigated mosaicism and its origin in the fetuses of natural conception.

METHODS

We studied normal fetuses following therapeutic abortion due to maternal indications. We analyzed the genome of 22 tissues of each fetus by array comparative genomic hybridization for intraindividual CNVs. Each tissue was studied in 2 microarray experiments; the reciprocal aberrations larger than 40 Kb, identified by comparing tissues of each fetus, were subsequently validated using quantitative polymerase chain reaction.

RESULTS

Through intraindividual comparison, frequency of reciprocal events varied from 2 to 9. According to the distribution pattern of the frequent CNV in derivatives of different germ layers, we found that its origin is early development including preimplantation, whereas CNVs with low frequency have occurred in later stages. Shared CNVs in both fetuses were belonged to thymus and related to the functional role of genes located in these CNVs.

CONCLUSIONS

The origin of some of fetal CNVs is preimplantation stage. Each organ might inherit CNVs with an unpredictable pattern due to the extensive cell mixing/migration in embryonic development.

Effect of ghost pepper on cell proliferation, apoptosis, senescence and global proteomic profile in human renal adenocarcinoma cells

Chili peppers are an important constituent of many foods and contain medicinally valuable compounds, such as capsaicin and dihydrocapsaicin. As various dietary botanicals have anticancer properties, this study was aimed to examine the effect of Ghost pepper (Bhut Jolokia), one of the hottest chili peppers in the world, on cell proliferation, apoptosis, senescence and the global proteomic profile in human renal cell adenocarcinoma in vitro. 769-P human renal adenocarcinoma cells were cultured on RPMI-1640 media supplemented with fetal bovine serum (10%) and antibiotic-antimycotic solution (1%). Treatment stock solutions were prepared in ethanol. Cell proliferation was tested with phenol red-free media with capsaicin (0-400 μM), dihydrocapsaicin (0-400 μM), capsaicin + dihydrocapsaicin (5:1), and dry Ghost peppers (0-3 g L-1) for 24, 48 and 72 h. Polycaspase and senescence associated-beta-galactosidase (SA-beta-gal) activities were tested with capsaicin (400 μM), dihydrocapsaicin (400 μM), capsaicin (400 μM) + dihydrocapsaicin (80 μM), and ghost pepper (3 g L-1) treatments. Global proteomic profile of cells in control and ghost pepper treatment (3 g L-1) was analyzed after 6 h by a shotgun proteomic approach using tandem mass spectrometry. At 24 h after treatment (24 HAT), relative to control, cell proportion with capsaicin (400 μM), dihydrocapsaicin (400 μM), capsaicin (400 μM) + dihydrocapsaicin (80 μM), and ghost pepper (3 g L-1) treatments was reduced to 36%, 18%, 33% and 20%, respectively, and further reduced at 48 and 72 HAT. All treatments triggered an early polycaspase response. SA-beta-gal activity was normal or suppressed with all treatments. About 68,220 protein isoforms were identified by shotgun proteomic approach. Among these, about 8.2% were significantly affected by ghost pepper. Ghost pepper regulated various proteins involved in intrinsic and extrinsic apoptotic pathways, Ras, Rb/E2F, p53, TGF-beta, WNT-beta catenin, and calcium induced cell death pathways. Ghost pepper also induced changes in proteins related to methylation, acetylation, genome stability, cell cycle check points, carbohydrate, protein and other metabolism and cellular mechanisms. Ghost pepper exhibited antiproliferation activity by inducing apoptosis through a complex network of proteins in human renal cell adenocarcinoma in vitro.

A speculative outlook on embryonic aneuploidy: Can molecular pathways be involved?

The journey of embryonic development starts at oocyte fertilization, which triggers a complex cascade of events and cellular pathways that guide early embryogenesis. Recent technological advances have greatly expanded our knowledge of cleavage-stage embryo development, which is characterized by an increased rate of whole-chromosome losses and gains, mixoploidy, and atypical cleavage morphokinetics. Embryonic aneuploidy significantly contributes to implantation failure, spontaneous miscarriage, stillbirth or congenital birth defects in both natural and assisted human reproduction. Essentially, early embryo development is strongly determined by maternal factors. Owing to considerable limitations associated with human oocyte and embryo research, the use of animal models is inevitable. However, cellular and molecular mechanisms driving the error-prone early stages of development are still poorly described. In this review, we describe known events that lead to aneuploidy in mammalian oocytes and preimplantation embryos. As the processes of oocyte and embryo development are rigorously regulated by multiple signal-transduction pathways, we explore the putative role of signaling pathways in genomic integrity maintenance. Based on the existing evidence from human and animal data, we investigate whether critical early developmental pathways, like Wnt, Hippo and MAPK, together with distinct DNA damage response and DNA repair pathways can be associated with embryo genomic instability, a question that has, so far, remained largely unexplored.

Comprehensive chromosome screening and gene expression analysis from the same biopsy in human preimplantation embryos

STUDY QUESTION

Can simultaneous comprehensive chromosome screening (CCS) and gene expression analysis be performed on the same biopsy of preimplantation human embryos?

SUMMARY ANSWER

For the first time, CCS and reliable gene expression analysis have been performed on the same human preimplantation embryo biopsy.

WHAT IS KNOWN ALREADY

A single trophectoderm (TE) biopsy is routinely used for many IVF programs offering CCS for selection of only chromosomally normal embryos for transfer. Although the gene expression profiling of human preimplantation embryos has been described, to date no protocol allows for simultaneous CCS and gene expression profiling from a single TE biopsy.

STUDY DESIGN, SIZE AND DURATION

This is a proof of concept and validation study structured in two phases. In Phase 1, cell lines were subjected to a novel protocol for combined CCS and gene expression analysis so as to validate the accuracy and reliability of the proposed protocol. In Phase 2, 20 donated human blastocysts were biopsied and processed with the proposed protocol in order to obtain an accurate CCS result and characterize their gene expression profiles using the same starting material.

PARTICIPANTS/MATERIALS, SETTING AND METHOD

A novel protocol coupling quantitative real-time PCR-based CCS and gene expression analysis using RT-PCR was designed for this study. Phase 1: six-cell aliquots of well-characterized fibroblast cell lines (GM00323, 46,XY and GM04435, 48,XY,+16,+21) were subjected to the proposed protocol. CCS results were compared with the known karyotypes for consistency, and gene expression levels were compared with levels of purified RNA from same cell lines for validation of reliable gene expression profiling. Phase 2: four biopsies were performed on 20 frozen human blastocysts previously diagnosed as trisomy 21 (10 embryos) and monosomy 21 (10 embryos) by CCS. All samples were processed with the proposed protocol and re-evaluated for concordance with the original CCS result. Their gene expression profiles were characterized and differential gene expression among embryos and early embryonic cell lineages was also evaluated.

MAIN RESULTS AND THE ROLE OF CHANCE

CCS results from cell lines showed 100% consistency with their known karyotypes. ΔΔCt values of differential gene expression of four selected target genes from the cell lines GM4435 and GM0323 were comparable between six-cell aliquots and purified RNA (Collagen type I alpha-1 (COL1A1), P = 0.54; Fibroblast growth factor-5 (FGF5), P = 0.11; Laminin subunit beta-1 (LAMB1), P = 1.00 and Atlastin-1 (ATL1), P = 0.23). With respect to human blastocysts, 92% consistency was reported after comparing embryonic CCS results with previous diagnosis. A total of 30 genes from a human stem cell pluripotency panel were selected to evaluate gene expression in human embryos. Correlation coefficients of expression profiles from biopsies of the same embryo (r = 0.96 ± 0.03 (standard deviation), n = 45) were significantly higher than when biopsies from unrelated embryos were evaluated (r = 0.93 ± 0.03, n = 945) (P < 0.0001). Growth differentiation factor 3 (GDF3) was found to be significantly up-regulated in the inner cell mass (ICM), whereas Caudal type homebox protein-2 (CDX2), Laminin subunit alpha-1 (LAMA1) and DNA methyltransferase 3-beta (DNMT3B) showed down-regulation in ICM compared with TE. Trisomy 21 embryos showed significant up-regulation of markers of cell differentiation (Cadherin-5 (CDH5) and Laminin subunit gamma-1 (LAMC1)), whereas monosomy 21 blastocysts showed higher expression of genes reported to be expressed in undifferentiated cells (Gamma-Aminobutyric Acid Type-A Receptor Beta3 Subunit (GABRB3) and GDF3).

LARGE SCALE DATA

N/A

LIMITATIONS, REASONS FOR CAUTION

Gene expression profiles of chromosomally normal embryos were not assessed due to restrictive access to euploid embryos for research. Nonetheless, the profile of blastocysts with single aneuploidies was characterized and compared. Only 30 target genes were analyzed for gene expression in this study. Increasing the number of target genes will provide a more comprehensive transcriptomic signature and reveal potential pathways paramount for embryonic competence and correct development.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first time that CCS and gene expression analysis have been performed on the same human preimplantation embryo biopsy. Further optimization of this protocol with other CCS platforms and inclusion of more target genes will provide innumerable research and clinical applications, such as discovery of biomarkers for embryonic reproductive potential and characterization of the transcriptomic signatures of embryos, potentially allowing for further embryo selection prior to embryo transfer and therefore improving outcomes.

STUDY FUNDING AND COMPETING INTERESTS

This study was funded by the Foundation for Embryonic Competence, Basking Ridge, NJ, USA. No conflicts of interests declared.

In vitro developmental ability of ovine oocytes following intracytoplasmic injection with freeze-dried spermatozoa

Freeze-drying (FD) is a new and alternative method to preserve spermatozoa in refrigeration or at room temperature. Suitable protection is required to maintain the sperm DNA integrity during the whole process and storage. The aim of this study was to examine the effect of rosmarinic acid and storage temperature on the DNA integrity of freeze-dried ram sperm. In addition, we evaluated the in vitro developmental ability to the blastocyst stage of oocytes injected with freeze-dried sperm. Ram sperm was freeze-dried in basic medium and in this medium supplemented with 105 µM rosmarinic acid. The vials were stored for 1 year at 4 °C and at room temperature. Frozen sperm was used as control. After rehydration, sperm DNA damage was evaluated, observing that the percentage of spermatozoa with DNA damage decreased significantly in the presence of rosmarinic acid, without differences between the two storage temperatures. Moreover, no differences were observed between the freeze-dried group and the frozen-thawed group in terms of blastocyst formation rate. We proved for the first time that ovine spermatozoa can be lyophilized effectively, stored at room temperature for long term, reconstituted and further injected into oocytes with initial embryo development.

Topology of chromosome centromeres in human sperm nuclei with high levels of DNA damage

Several studies have shown that the 'poor' sperm DNA quality appears to be an important factor affecting male reproductive ability. In the case of sperm cells from males with the correct somatic karyotype but with deficient spermatogenesis, resulting in a high degree of sperm DNA fragmentation, we observed changes in the preferential topology of the chromosome 7, 9, 15, 18, X and Y centromeres. The changes occurred in radial localization and may have been directly linked to the sperm chromatin damage. This conclusion is mainly based on a comparison of FISH signals that were observed simultaneously in the TUNEL-positive and TUNEL-negative sperm cells. The analyzed cells originated from the same ejaculated sample and FISH was performed on the same slides, after in situ TUNEL reaction. Based on the observed changes and previous data, it appears that the sperm nucleus architecture can be disrupted by a variety of factors and has a negative influence on spermatogenesis at the same time. Often, these factors coexist (e.g. chromosomal translocations, aneuploidies, a higher DNA fragmentation, abnormal seminology), but no direct correlations between the factors were observed.

The Effect of Prolonged Culture of Chromosomally Abnormal Human Embryos on The Rate of Diploid Cells

Background

A decrease in aneuploidy rate following a prolonged co-culture of human blastocysts has been reported. As co-culture is not routinely used in assisted reproductive technology, the present study aimed to evaluate the effect of the prolonged single culture on the rate of diploid cells in human embryos with aneuploidies.

Materials and Methods

In this cohort study, we used fluorescence in situ hybridi- zation (FISH) to reanalyze surplus blastocysts undergoing preimplantation genetic diagnosis (PGD) on day 3 postfertilization. They were randomly studied on days 6 or 7 following fertilization.

Results

Of the 30 analyzed blastocysts, mosaicism was observed in 26(86.6%), while 2(6.7%) were diploid, and 2(6.7%) were triploid. Of those with mosaicism, 23(88.5%) were determined to be diploid-aneuploid and 3(11.5%) were aneuploid mosaic. The total frequency of embryos with more than 50% diploid cells was 33.3% that was lower on day 7 in comparison with the related value on day 6 (P<0.05); however, there were no differences when the embryos were classified according to maternal age, blastocyst developmental stage, total cell number on day 3, and embryo quality.

Conclusion

Although mosaicism is frequently observed in blastocysts, the prolonged single culture of blastocysts does not seem to increase the rate of normal cells.

Prediction model for aneuploidy in early human embryo development revealed by single-cell analysis

Aneuploidies are prevalent in the human embryo and impair proper development, leading to cell cycle arrest. Recent advances in imaging and molecular and genetic analyses are postulated as promising strategies to unveil the mechanisms involved in aneuploidy generation. Here we combine time-lapse, complete chromosomal assessment and single-cell RT-qPCR to simultaneously obtain information from all cells that compose a human embryo until the approximately eight-cell stage (n=85). Our data indicate that the chromosomal status of aneuploid embryos (n=26), including those that are mosaic (n=3), correlates with significant differences in the duration of the first mitotic phase when compared with euploid embryos (n=28). Moreover, gene expression profiling suggests that a subset of genes is differentially expressed in aneuploid embryos during the first 30 h of development. Thus, we propose that the chromosomal fate of an embryo is likely determined as early as the pronuclear stage and may be predicted by a 12-gene transcriptomic signature.

A high incidence of chromosome abnormalities in two-cell stage porcine IVP embryos

In pigs, in vitro production is difficult with a high occurrence of polyspermy and low blastocyst formation rates. To test the hypothesis that this may, at least in part, be due to chromosomal errors, we employed whole genome amplification and comparative genomic hybridization, performing comprehensive chromosome analysis to assess both cells of the two-cell stage in vitro porcine embryos. We thus described the incidence, nature and origin of chromosome abnormalities, i.e. whether they derived from incorrect meiotic division during gametogenesis or aberrant mitotic division in the zygote. We observed that 19 out of 51 (37%) of two-cell stage early pig IVP embryos had a chromosome abnormality, mostly originating from an abnormal division in the zygote. Moreover, we frequently encountered multiple aneuploidies and segmental chromosome aberrations. These results indicate that the pig may be particularly sensitive to in vitro production, which may, in turn, be due to incorrect chromosome segregations during meiosis and early cleavage divisions. We thus accept our hypothesis that chromosome abnormality could explain poor IVP outcomes in pigs.

Why we should not select the faster embryo: lessons from mice and cattle

Many studies have shown that in vitro culture can negatively impact preimplantation development. This necessitates some selection criteria for identifying the best-suited embryos for transfer. That said, embryo selection after in vitro culture remains a subjective process in most mammalian species, including cows, mice and humans. General consensus in the field is that embryos that develop in a timely manner have the highest developmental competence and viability after transfer. Herein lies the key question: what is a timely manner? With emerging data in bovine and mouse supporting increased developmental competency in embryos with moderate rates of development, it is time to question whether the fastest developing embryos are the best embryos for transfer in the human clinic. This is especially relevant to epigenetic gene regulation, including genomic imprinting, where faster developing embryos exhibit loss of imprinted methylation, as well as to sex selection bias, where faster developmental rates of male embryos may lead to biased embryo transfer and, in turn, biased sex ratios. In this review, we explore evidence surrounding the question of developmental timing as it relates to bovine embryo quality, mouse embryo quality and genomic imprint maintenance, and embryo sex.

Paternal influence of sperm DNA integrity on early embryonic development

STUDY QUESTION

Does sperm DNA damage affect early embryonic development?

SUMMARY ANSWER

Increased sperm DNA damage adversely affects embryo quality starting at Day 2 of early embryonic development and continuing after embryo transfer, resulting in reduced implantation rates and pregnancy outcomes.

WHAT IS KNOWN ALREADY

Abnormalities in the sperm DNA in the form of single and double strand breaks can be assessed by an alkaline Comet assay. Some prior studies have shown a strong paternal effect of sperm DNA damage on IVF outcome, including reduced fertilization, reduced embryo quality and cleavage rates, reduced numbers of embryos developing into blastocysts, increased percentage of embryos undergoing developmental arrest, and reduced implantation and pregnancy rates.

STUDY DESIGN, SIZE, DURATION

A cross-sectional study of 215 men from infertile couples undergoing assisted reproduction techniques at the University of Utah Center for Reproductive Medicine.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm from men undergoing ART were analyzed for DNA damage using an alkaline Comet assay and classified into three groups: 'low damage' (0-30%), 'intermediate damage' (31-70%) and 'high damage' (71-100%). The cause of couples' infertility was categorized into one of the three types (male, female or unexplained). Each embryo was categorized as 'good', 'fair' or 'poor' quality, based on the number and grade of blastomeres. The influence of sperm DNA damage on early embryonic development was observed and classified into four stages: peri-fertilization effect (fertilization rate), early paternal effect (embryonic days 1-2), late paternal effect (embryonic days 3-5) and implantation stage effect.

MAIN RESULTS AND THE ROLE OF CHANCE

The paternal effect of sperm DNA damage was observed at each stage of early embryonic development. The peri-fertilization effect was higher in oocytes from patients with female infertility (20.85%) compared with male (8.22%; P < 0.001) and unexplained (7.30%; P < 0.001) infertility factors. In both the early and late paternal effect stages, the low DNA damage group had a higher percentage of good quality embryos (P < 0.05) and lower percentage of poor quality embryos (P < 0.05) compared with the high DNA damage group. Implantation was lower in the high DNA damage (33.33%) compared with intermediate DNA damage (55.26%; P < 0.001) and low DNA damage (65.00%; P < 0.001) groups. The implantation rate was higher following blastocyst transfer (58.33%), when compared with early stage blastocyst (53.85%; P = 0.554) and cavitating morula transfers (34.40%; P < 0.001). Implantation was higher when the female partner age was ≤35 years when compared with >35 year age group (52.75 versus 35.44%; P = 0.008).

LIMITATIONS, REASONS FOR CAUTION

A potential limitation of this study is that it is cross-sectional. Generally in such studies more than one variable could affect the outcome. Analyzing sperm is one part of the equation but a number of environmental and female factors also have the potential to influence embryo development and implantation. Furthermore, the selection of morphologically normal and physiologically motile sperm may result in isolation of sperm with reduced DNA damage. Therefore, selecting the best available sperm for ICSI may lead to experimental bias, as the selected sperm do not represent the overall sperm population in which the DNA damage is measured. Similar studies on selected sperm and with a larger sample size are now required.

WIDER IMPLICATIONS OF THE FINDINGS

The paternal influence of damaged chromatin is more prominent after zygotic transcriptional activation. A prolonged paternal effect on the developing embryo may be due to the active repair mechanism present in oocytes that tends to overcome the damaged paternal chromatin. The probability of eliminating an embryo fertilized by a sperm with damaged DNA is higher at the blastocyst stage than the cleavage stage; therefore blastocyst transfer could be recommended for better implantation success. Finally, we recommend ICSI treatment for patients with a higher percentage of sperm with DNA damage as well as additional studies with a larger sample size aimed at assessing DNA damage analysis as a diagnostic tool for IVF.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the University of Utah internal funds. The authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.