Live-cell imaging of nuclear-chromosomal dynamics in bovine in vitro fertilised embryos

Effect of ovarian stimulation on developmental speed of preimplantation embryo in a mouse model

Ovarian stimulation protocols are widely used to collect oocytes in assisted reproductive technologies (ARTs). Although the influence of ovarian stimulation on embryo quality has been described, this issue remains controversial. Here, we analyzed the influence of ovarian stimulation on developmental speed and chromosome segregation using live cell imaging. Female mice at the proestrus stage were separated by the appearance of the vagina as the non-stimulation (-) group, and other mice were administered pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) as the stimulation (+) groups. The cumulus-oocyte complexes from both groups were inseminated with sperm suspensions from the same male mice. Fertilization rates and developmental capacities were examined, and the developmental speed and frequency of chromosome segregation errors were measured by live-cell imaging using a Histone H2B-mCherry probe. The number of fertilized oocytes obtained was 1.4-fold more frequent in the stimulation (+) group. The developmental rate and chromosome stability did not differ between the groups. Image analysis showed that the mean speed of development in the stimulation (+) group was slightly higher than that in the non-stimulation (-) group. This increase in speed seemed to arise from the slight shortening of the 2- and 4-cell stages and third division lengths and consequent synchronization of cleavage timing in each embryo, not from the emergence of an extremely rapidly developing subpopulation of embryos. In conclusion, ovarian stimulation does not necessarily affect embryo quality but rather increases the chances of obtaining high-quality oocytes in mice.

Three-dimensional morphology of bovine blastocysts hatched against lipopolysaccharide exposure in vitro

Embryo transfer in cattle is globally becoming more ubiquitous, but the pregnancy rate is lower than that of artificial insemination. The uterus contains its own bacteria, and concentrations of lipopolysaccharides (LPS) from gram-negative bacteria are higher in uteri affected by endometritis than in healthy uteri and they suppress embryogenesis. The purpose of this study was to investigate the morphological characteristics of bovine embryos with a higher viability and implantability, by analyzing the morphology of bovine blastocysts that successfully hatched under challenge of LPS, using an optical coherence tomography (OCT) system. Developing embryos produced by in vitro fertilization that had reached the blastocyst stage on Day 7 were three-dimensionally scanned using an OCT system, then were continued to culture with or without LPS until Day 9, when the presence or absence of hatching was determined. The OCT-captured three-dimensional images were used to quantify 20 different metrics, including inner cell mass (ICM), trophectoderm, blastocoel, and total embryo volume; each of the parameters was compared between the hatched and unhatched embryos. Under the LPS challenge, hatched embryos had higher ICM thickness and volume, and lower trophectoderm thickness than unhatched embryos. Furthermore, hatched embryos under LPS challenge had higher ICM thickness and ICM volume than hatched embryos without LPS challenge. The present results suggest the possibility that ICM thickness and ICM volume calculated by OCT system could be indices for good quality bovine embryos.

Serum-free spontaneously immortalized bovine oviduct epithelial cell conditioned medium promotes the early development of bovine in vitro fertilized embryos

Embryonic transfer of bovine blastocysts produced using in vitro fertilization (IVF) is widely used, although the challenge of compromised conception rates remains. Using bovine oviduct epithelial cells (BOEC) to improve embryo culture conditions has attracted attention, particularly since the recent discovery of extracellular vesicles from BOEC. The selection of embryos for transfer has also been the subject of various studies, and a set of evaluation criteria to predict pregnancy success has been suggested, in which the embryos are judged by their kinetics and morphology at the early stages. In the present study, we established a spontaneously immortalized BOEC line (SI-BOEC) and examined the effects of conditioned medium on IVF embryos, focusing on the results of the recommended criteria. A modified KSOM (mKSOM) was used to prepare conditioned media. Presumptive zygotes were cultured in mKSOM (control), SI-BOEC-conditioned medium, mKSOM supplemented with sediment (pellet) collected after the ultracentrifugation of the conditioned medium (mKSOM/sediment), and the supernatant. A significantly higher percentage of embryos satisfied the recommended criteria when grown in the conditioned medium than in the mKSOM. A higher proportion of embryos developed into blastocysts after achieving the four criteria. A similar tendency was observed when grown in mKSOM/sediment compared to mKSOM; however, this was not observed in the supernatant. Vesicles with a size similar to that of exosomes were observed in the sediment. In conclusion, the culture medium conditioned by SI-BOEC promoted the production of bovine blastocysts that satisfied the four evaluation criteria recommended for embryo selection.

Insights into embryonic chromosomal instability: mechanisms of DNA elimination during mammalian preimplantation development

Mammalian preimplantation embryos often contend with aneuploidy that arose either by the inheritance of meiotic errors from the gametes, or from mitotic mis-segregation events that occurred following fertilization. Regardless of the origin, mis-segregated chromosomes become encapsulated in micronuclei (MN) that are spatially isolated from the main nucleus. Much of our knowledge of MN formation comes from dividing somatic cells during tumorigenesis, but the error-prone cleavage-stage of early embryogenesis is fundamentally different. One unique aspect is that cellular fragmentation (CF), whereby small subcellular bodies pinch off embryonic blastomeres, is frequently observed. CF has been detected in both in vitro and in vivo-derived embryos and likely represents a response to chromosome mis-segregation since it only appears after MN formation. There are multiple fates for MN, including sequestration into CFs, but the molecular mechanism(s) by which this occurs remains unclear. Due to nuclear envelope rupture, the chromosomal material contained within MN and CFs becomes susceptible to double stranded-DNA breaks. Despite this damage, embryos may still progress to the blastocyst stage and exclude chromosome-containing CFs, as well as non-dividing aneuploid blastomeres, from participating in further development. Whether these are attempts to rectify MN formation or eliminate embryos with poor implantation potential is unknown and this review will discuss the potential implications of DNA removal by CF/blastomere exclusion. We will also extrapolate what is known about the intracellular pathways mediating MN formation and rupture in somatic cells to preimplantation embryogenesis and how nuclear budding and DNA release into the cytoplasm may impact overall development.

Hatchability evaluation of bovine IVF embryos using OCT-based 3D image analysis

Although embryo transfer is widely applied in cattle, many of the transferred embryos do not result in pregnancy. To determine a new parameter for bovine embryo evaluation, we investigated the relationships between in vitro hatchability and embryo morphological parameters using optical coherence tomography (OCT) that we established recently. Bovine embryos were obtained from Japanese Black cattle by in vitro fertilization (IVF). The quality of the blastocysts was examined under an inverted microscope and confirmed as Codes 1-3 according to the IETS standards for embryo evaluation. The OCT images of the embryos were captured on Day 7 after IVF, and the embryos were cultured until Day 9 to determine their hatchability. During OCT, the embryos were irradiated with near-infrared light for a few minutes to obtain three-dimensional images. In total, 22 parameters were assessed for each of the 42 embryos, of which 25 hatched (H embryos) and 17 did not (NH embryos). The thickness of the trophectoderm (TE) and TE+zona pellucida (ZP) was lesser, and the volumes of the TE, ZP, blastocoel, and whole embryo and blastocoel diameter were greater in the H embryos than in the NH embryos. PCA identified that the increase in the blastocoel-related value along with the decrease in the thickness-related value of the TE and/or ZP could be indicators for evaluating the hatchability of bovine IVF embryos. These results support the idea that OCT-captured structural data of blastocyst-stage embryos can be used as a potential model to predict the quality of bovine embryos.

Pre-Implantation Bovine Embryo Evaluation-From Optics to Omics and Beyond

Approximately 80% of the ~1.5 million bovine embryos transferred in 2021 were in vitro produced. However, only ~27% of the transferred IVP embryos will result in live births. The ~73% pregnancy failures are partly due to transferring poor-quality embryos, a result of erroneous stereomicroscopy-based morphological evaluation, the current method of choice for pre-transfer embryo evaluation. Numerous microscopic (e.g., differential interference contrast, electron, fluorescent, time-lapse, and artificial-intelligence-based microscopy) and non-microscopic (e.g., genomics, transcriptomics, epigenomics, proteomics, metabolomics, and nuclear magnetic resonance) methodologies have been tested to find an embryo evaluation technique that is superior to morphologic evaluation. Many of these research tools can accurately determine embryo quality/viability; however, most are invasive, expensive, laborious, technically sophisticated, and/or time-consuming, making them futile in the context of in-field embryo evaluation. However accurate they may be, using complex methods, such as RNA sequencing, SNP chips, mass spectrometry, and multiphoton microscopy, at thousands of embryo production/collection facilities is impractical. Therefore, future research is warranted to innovate field-friendly, simple benchtop tests using findings already available, particularly from omics-based research methodologies. Time-lapse monitoring and artificial-intelligence-based automated image analysis also have the potential for accurate embryo evaluation; however, further research is warranted to innovate economically feasible options for in-field applications.

Direct cleavage during the first mitosis is a sign of abnormal fertilization in cattle

Direct cleavage, a type of abnormal cleavage in which one zygote divides into three or more blastomeres, has been reported in mammals. The incidence of direct cleavage increases in zygotes with three or more pronuclei (multi-PN) and those showing abnormal pronuclei migration. However, there are few reports on the relationship between pronuclei and direct cleavage, and the effects of these relationships on subsequent embryogenesis have not been clarified. It is difficult to observe pronuclei under visible light, especially in bovine zygotes, because of abundant dark lipid droplets in the cytoplasm. We visualized pronuclei by removing lipid droplets from bovine zygotes and analyzed the relationship between the number of pronuclei and direct cleavage using time-lapse cinematography. The direct cleavage rate of multi-PN zygotes was 78.6%, which was significantly higher than that of zygotes with one pronucleus (1 PN, 0.0%) and two pronuclei (2 PN, 8.2%). Observation of pronuclei migration in 2 PN zygotes showed that 3.1% of 2 PN zygotes had non-apposed pronuclei. The direct cleavage rate of zygotes with non-apposed pronuclei was 66.7%, which was significantly higher than that of zygotes with apposed pronuclei (6.4%). Among multi-PN zygotes, the proportions of zygotes with apposed pronuclei and non-apposed pronuclei were 37.5% and 64.3%, respectively. The direct cleavage rate of multi-PN zygotes with non-apposed pronuclei was 100.0%, which was significantly higher than that of zygotes with apposed pronuclei (40.0%). Three-dimensional live-cell imaging of bovine zygotes injected with the mRNA-encoding histone H2B-mCherry showed that the direct cleavage rates of 2 PN and multi-PN zygotes bypassing syngamy were 63.2% and 75.5%, respectively. These rates were significantly higher than that of 2 PN and multi-PN zygotes that underwent syngamy (5.6% and 20.0%, respectively). Regardless of the number of pronuclei, a high frequency of direct cleavage was observed in zygotes in which the pronuclei did not migrate inward the cytoplasm and bypassed syngamy. These results suggest that abnormal fertilization such as multi-PN and migration error of pronuclei in cattle is the primary reason for direct cleavage during the first mitosis. Assessment of direct cleavage during the first mitosis allows exclusion of embryos with abnormal fertilization and may contribute to in vitro produced embryo transfer success.

Micronucleus formation during early cleavage division is a potential hallmark of preimplantation embryonic loss in cattle

In assisted reproductive technology (ART)-derived embryos of non-rodent mammals, including humans and cattle, chromosome segregation errors are highly likely to occur during early cleavage division, resulting in aneuploidy, including mosaicism. However, the relationship between chromosomal segregation errors during early cleavage and subsequent embryonic development has not been detailed in these mammals. In the present study, we developed non-invasive live-cell imaging of chromosome segregation dynamics using a histone H2B-mCherry mRNA probe in bovine preimplantation embryos. Chromosome segregation errors in early cleavage affected blastocyst formation. Especially, embryos that underwent abnormal chromosome segregation (ACS) with multiple or large micronucleus formation rarely developed into blastocysts. Embryos with the severe ACS had prolonged cell cycle duration. After transfer of blastocysts with live-cell imaging of chromosome segregation to ten cows, six became pregnant and four of them gave full-term offspring. Interestingly, two of them were derived from blastocysts with ACS. Hence, chromosomal segregation errors with micronucleus formation during early cleavage can be a fatal hallmark of preimplantation embryogenesis in cattle. This technique has shown potential for understanding the relationship between chromosome segregation error and subsequent embryo development, and for selecting viable ART-derived embryos for medical and livestock production.

Asynchronous division at 4–8-cell stage of preimplantation embryos affects live birth through ICM/TE differentiation

To improve the performance of assisted reproductive technology, it is necessary to find an indicator that can identify and select embryos that will be born or be aborted. We searched for indicators of embryo selection by comparing born/abort mouse embryos. We found that asynchronous embryos during the 4–8-cell stage were predisposed to be aborted. In asynchronous mouse embryos, the nuclear translocation of YAP1 in some blastomeres and compaction were delayed, and the number of ICMs was reduced. Hence, it is possible that asynchronous embryos have abnormal differentiation. When the synchrony of human embryos was observed, it was confirmed that embryos that did not reach clinical pregnancy had asynchrony as in mice. This could make synchrony a universal indicator common to all animal species.

Molecular contribution to embryonic aneuploidy and karyotypic complexity in initial cleavage divisions of mammalian development

Embryonic aneuploidy is highly complex, often leading to developmental arrest, implantation failure or spontaneous miscarriage in both natural and assisted reproduction. Despite our knowledge of mitotic mis-segregation in somatic cells, the molecular pathways regulating chromosome fidelity during the error-prone cleavage-stage of mammalian embryogenesis remain largely undefined. Using bovine embryos and live-cell fluorescent imaging, we observed frequent micro-/multi-nucleation of mis-segregated chromosomes in initial mitotic divisions that underwent unilateral inheritance, re-fused with the primary nucleus or formed a chromatin bridge with neighboring cells. A correlation between a lack of syngamy, multipolar divisions and asymmetric genome partitioning was also revealed, and single-cell DNA-seq showed propagation of primarily non-reciprocal mitotic errors. Depletion of the mitotic checkpoint protein BUB1B (also known as BUBR1) resulted in similarly abnormal nuclear structures and cell divisions, as well as chaotic aneuploidy and dysregulation of the kinase-substrate network that mediates mitotic progression, all before zygotic genome activation. This demonstrates that embryonic micronuclei sustain multiple fates, provides an explanation for blastomeres with uniparental origins, and substantiates defective checkpoints and likely other maternally derived factors as major contributors to the karyotypic complexity afflicting mammalian preimplantation development.

Mechanism of spindle pole organization and instability in human oocytes

Human oocytes are prone to assembling meiotic spindles with unstable poles, which can favor aneuploidy in human eggs. The underlying causes of spindle instability are unknown. We found that NUMA (nuclear mitotic apparatus protein)-mediated clustering of microtubule minus ends focused the spindle poles in human, bovine, and porcine oocytes and in mouse oocytes depleted of acentriolar microtubule-organizing centers (aMTOCs). However, unlike human oocytes, bovine, porcine, and aMTOC-free mouse oocytes have stable spindles. We identified the molecular motor KIFC1 (kinesin superfamily protein C1) as a spindle-stabilizing protein that is deficient in human oocytes. Depletion of KIFC1 recapitulated spindle instability in bovine and aMTOC-free mouse oocytes, and the introduction of exogenous KIFC1 rescued spindle instability in human oocytes. Thus, the deficiency of KIFC1 contributes to spindle instability in human oocytes.

Chromosome counting in the mouse zygote using low-invasive super-resolution live-cell imaging

In preimplantation embryos, an abnormal chromosome number causes developmental failure and a reduction in the pregnancy rate. Conventional chromosome testing methods requiring biopsy reduce the risk of associated genetic diseases; nevertheless, the reduction in cell number also reduces the pregnancy rate. Therefore, we attempted to count the chromosomes in mouse embryos using super-resolution live-cell imaging as a new method of chromosome counting that does not reduce the cell number or viability. We counted the forty chromosomes at the first mitosis by injecting embryos with histone H2B-mCherry mRNA under conditions by which pups could be obtained; however, the results were often an underestimation of chromosome number and varied by embryo and time point. Therefore, we developed a method to count the chromosomes via CRISPR/dCas-mediated live-cell fluorescence in situ hybridization targeting the sequence of the centromere region, enabling us to count the chromosomes more accurately in mouse embryos. The methodology presented here may provide useful information for assisted reproductive technologies, such as those used in livestock animals/humans, as a technique for assessing the chromosomal integrity of embryos prior to transfer.

Parameters to identify good quality oocytes and embryos in cattle

Oocyte/embryo selection methodologies are either invasive or noninvasive and can be applied at various stages of development from the oocyte to cleaved embryos and up to the blastocyst stage. Morphology and the proportion of embryos developing to the blastocyst stage are important criteria to assess developmental competence. Evaluation of morphology remains the method of choice for selecting viable oocytes for IVP or embryos prior to transfer. Although non-invasive approaches are improving, invasive ones have been extremely helpful in finding candidate genes to determine oocyte/embryo quality. There is still a strong need for further refinement of existing oocyte and embryo selection methods and quality parameters. The development of novel, robust and non-invasive procedures will ensure that only embryos with the highest developmental potential are chosen for transfer. In the present review, various methods for assessing the quality of oocytes and preimplantation embryos, particularly in cattle, are considered. These methods include assessment of morphology including different staining procedures, transcriptomic and proteomic analyses, metabolic profiling, as well as the use of artificial intelligence technologies.

Sperm migration, selection, survival, and fertilizing ability in the mammalian oviduct†

In vitro fertilization (IVF) gives rise to embryos in a number of mammalian species and is currently widely used for assisted reproduction in humans and for genetic purposes in cattle. However, the rate of polyspermy is generally higher in vitro than in vivo and IVF remains ineffective in some domestic species like pigs and horses, highlighting the importance of the female reproductive tract for gamete quality and fertilization. In this review, the way the female environment modulates sperm selective migration, survival, and acquisition of fertilizing ability in the oviduct is being considered under six aspects: (1) the utero-tubal junction that selects a sperm sub-population entering the oviduct; (2) the presence of sperm binding sites on luminal epithelial cells in the oviduct, which prolong sperm viability and plays a role in limiting polyspermic fertilization; (3) the contractions of the oviduct, which promote sperm migration toward the site of fertilization in the ampulla; (4) the regions of the oviduct, which play different roles in regulating sperm physiology and interactions with oviduct epithelial cells; (5) the time of ovulation, and (6) the steroid hormonal environment which regulates sperm release from the luminal epithelial cells and facilitates capacitation in a finely orchestrated manner.

Abnormal cleavage is involved in the self-correction of bovine preimplantation embryos

Chromosome instability leading to aneuploidy during early cleavage is well known in humans and cattle. Partial compaction (PC), which occurs only in some blastomeres, is suggested as a self-correction mechanism through which human embryos avoid aneuploid mosaicism. Partially compacted embryos show abnormal cleavages more frequently during early development; however, the mechanism by which blastomeres are excluded has not been elucidated. Here, we confirmed PC in approximately half of the tested bovine embryos, similar to that in human embryos. DNA sequencing of single-cell and intact embryos revealed that the morulae that excluded some blastomeres had euploidy, but many of the excluded blastomeres had aneuploidy. Time-lapse imaging of zygotes without the zona pellucida revealed that the excluded blastomeres underwent reverse and direct cleavages, which are abnormal cleavages, more frequently than the blastomeres involved in compaction. These results suggest the potential role of abnormal cleavage in the self-correction mechanism during the development of mammalian preimplantation embryos.

Three-Dimensional Live Imaging of Bovine Preimplantation Embryos: A New Method for IVF Embryo Evaluation

Conception rates for transferred bovine embryos are lower than those for artificial insemination. Embryo transfer (ET) is widely used in cattle but many of the transferred embryos fail to develop, thus, a more effective method for selecting bovine embryos suitable for ET is required. To evaluate the developmental potential of bovine preimplantation embryos (2-cell stage embryos and blastocysts), we have used the non-invasive method of optical coherence tomography (OCT) to obtain live images. The images were used to evaluate 22 parameters of blastocysts, such as the volume of the inner cell mass and the thicknesses of the trophectoderm (TE). Bovine embryos were obtained by in vitro fertilization (IVF) of the cumulus-oocyte complexes aspirated by ovum pick-up from Japanese Black cattle. The quality of the blastocysts was examined under an inverted microscope and all were confirmed to be Code1 according to the International Embryo Transfer Society standards for embryo evaluation. The OCT images of embryos were taken at the 2-cell and blastocyst stages prior to the transfer. In OCT, the embryos were irradiated with near-infrared light for a few minutes to capture three-dimensional images. Nuclei of the 2-cell stage embryos were clearly observed by OCT, and polynuclear cells at the 2-cell stage were also clearly found. With OCT, we were able to observe embryos at the blastocyst stage and evaluate their parameters. The conception rate following OCT (15/30; 50%) is typical for ETs and no newborn calves showed neonatal overgrowth or died, indicating that the OCT did not adversely affect the ET. A principal components analysis was unable to identify the parameters associated with successful pregnancy, while by using hierarchical clustering analysis, TE volume has been suggested to be one of the parameters for the evaluation of bovine embryo. The present results show that OCT imaging can be used to investigate time-dependent changes of IVF embryos. With further improvements, it should be useful for selecting high-quality embryos for transfer.

A New Toolbox in Experimental Embryology-Alternative Model Organisms for Studying Preimplantation Development

Preimplantation development is well conserved across mammalian species, but major differences in developmental kinetics, regulation of early lineage differentiation and implantation require studies in different model organisms, especially to better understand human development. Large domestic species, such as cattle and pig, resemble human development in many different aspects, i.e., the timing of zygotic genome activation, mechanisms of early lineage differentiations and the period until blastocyst formation. In this article, we give an overview of different assisted reproductive technologies, which are well established in cattle and pig and make them easily accessible to study early embryonic development. We outline the available technologies to create genetically modified models and to modulate lineage differentiation as well as recent methodological developments in genome sequencing and imaging, which form an immense toolbox for research. Finally, we compare the most recent findings in regulation of the first lineage differentiations across species and show how alternative models enhance our understanding of preimplantation development.

Morphokinetic analysis of pronuclei using time-lapse cinematography in bovine zygotes

The morphokinetics of pronuclei (PN) are considered crucial factors affecting embryogenesis in mammals. Whereas, since bovine zygotes contain a large number of cytosolic lipid droplets, detailed observation of PN has not been performed. In this study, we visualized PN using time-lapse cinematography (TLC) with light microscopy for the first time in delipidated bovine zygotes. The proportions of 0 PN, 1PN, 2PN, and multi-PN in delipidated bovine zygotes were 10.1%, 6.5%, 72.7%, and 10.8%, respectively. Abnormal fertilization, including 1 PN and multi-PN, was observed in 15.6% of blastocysts. The times from IVF to PN appearance, PN fading, and first cleavage in 2 PN bovine zygotes that developed into blastocysts were 10.4, 25.5, and 27.6 h, respectively, which were similar to PN morphokinetics in humans. The 2 PN zygotes showed that the prolonged time from IVF to the appearance of PN and from the fading of PN to the first cleavage negatively affected blastocyst formation. The time from appearance to fading of PN in multi-PN zygotes that developed into blastocysts was longer than that in multi-PN zygotes that did not develop into blastocysts. Besides, among zygotes that developed into blastocysts, the time from appearance to fading of PN in multi-PN zygotes was longer than that in 2 PN and 1 PN zygotes. These results suggest that PN morphokinetic abnormalities are associated with subsequent embryonic development. Observation of PN in bovine zygotes by using non-invasive visible light TLC by delipidation could be a powerful tool to clarify the relationship between PN morphokinetics and developmental competence.

Three-dimensional live imaging of bovine embryos by optical coherence tomography

While embryo transfer (ET) is widely practiced, many of the transferred embryos fail to develop in cattle. To establish a more effective method for selecting bovine embryos for ET, here we quantified morphological parameters of living embryos using three-dimensional (3D) images non-invasively captured by optical coherence tomography (OCT). Seven Japanese Black embryos produced by in vitro fertilization that had reached the expanded blastocyst stage after 7 days of culture were transferred after imaged by OCT. Twenty-two parameters, including thickness and volumes of the inner cell mass, trophectoderm, and zona pellucida, and volumes of blastocoel and whole embryo, were quantified from 3D images. Four of the seven recipients became pregnant. We suggest that these 22 parameters can be potentially employed to evaluate the quality of bovine embryos before ET.

Chromosome segregation error during early cleavage in mouse pre-implantation embryo does not necessarily cause developmental failure after blastocyst stage

In the pre-implantation embryo, aneuploidy resulting from chromosome segregation error is considered responsible for pregnancy loss. However, only a few studies have examined the relationship between chromosome segregation errors during early cleavage and development. Here, we evaluated this relationship by live-cell imaging using the histone H2B-mCherry probe and subsequent single blastocyst transfer using mouse embryos obtained by in vitro fertilization. We showed that some embryos exhibiting early chromosomal segregation error and formation of micronuclei retained their developmental potential; however, the error affected the blastocyst/arrest ratio. Further, single-cell sequencing after live-cell imaging revealed that all embryos exhibiting micronuclei formation during 1^st mitosis showed aneuploidy at the 2-cell stage. These results suggest that early chromosome segregation error causing micronuclei formation affects ploidy and development to blastocyst but does not necessarily cause developmental failure after the blastocyst stage. Our result suggests the importance of the selection of embryos that have reached blastocysts.