Time-Lapse Videomicrographic Analyses of Contractions in Mouse Blastocysts

The first lineage determination in mammals

This review describes in detail the morphological, cytoskeletal and gene expression events leading to the gene regulatory network bifurcation point of trophoblast and inner cell mass cells in a variety of mammalian preimplantation embryos. The interrelated processes of compaction and polarity establishment are discussed in terms of how they affect YAP/WWTR activity and the location and fate of cells. Comparisons between mouse, human, cattle, pig and rabbit embryos suggest a conserved role for YAP/WWTR signalling in trophoblast induction in eutherian animals though the mechanisms for, and timing of, YAP/WWTR activation differs among species. Downstream targets show further differences, with the trophoblast marker GATA3 being a direct target in all examined mammals, while CDX2-positive and SOX2-negative regulation varies.

Exploring the benefit of different methods to perform assisted hatching in the ART laboratory: A narrative review

In the last decades, to enhance success rates in assisted reproductive technology (ART) cycles, scientists have continually tried to optimize embryo culture and selection to increase clinical outcomes. In this scenario, the application of laser technology has increased considerably worldwide and is currently applied across ART in several ways: for assisted hatching (AH) or thinning of the zona pellucida (ZP), embryo biopsy, to immobilize and select the sperm during intracytoplasmic sperm injection, as well as to induce artificial blastocyst shrinkage before cryopreservation. Laser-AH has been suggested as a procedure to improve embryo implantation: the concept is that drilling holes through or thinning of the ZP could improve the hatching process and implantation. The artificial disruption of the ZP can be performed by different approaches: mechanically, chemically and with the laser, which is one of the most favourable and easy methods to remove part of the ZP and to augment the possibilities of implantation in patients defined as having a poor prognosis of success, or when the ZP is too thick. However, in the current literature, there is not sufficient evidence about the potential risk or impairment that laser utilization might induce on embryo development; therefore, the main aim of the current review is to provide an overview of the existing knowledge on the ZP and the mechanisms of manipulating it to improve the effectiveness of ART. Also, it emphasizes the positive aspect of laser application as a powerful tool that might increase the chance of pregnancy for infertile couples undergoing ART cycles.

Effective mechanical potential of cell-cell interaction in tissues harboring cavity and in cell sheet toward morphogenesis

Measuring mechanical forces of cell-cell interactions is important for studying morphogenesis in multicellular organisms. We previously reported an image-based statistical method for inferring effective mechanical potentials of pairwise cell-cell interactions by fitting cell tracking data with a theoretical model. However, whether this method is applicable to tissues with non-cellular components such as cavities remains elusive. Here we evaluated the applicability of the method to cavity-harboring tissues. Using synthetic data generated by simulations, we found that the effect of expanding cavities was added to the pregiven potentials used in the simulations, resulting in the inferred effective potentials having an additional repulsive component derived from the expanding cavities. Interestingly, simulations by using the effective potentials reproduced the cavity-harboring structures. Then, we applied our method to the mouse blastocysts, and found that the inferred effective potentials can reproduce the cavity-harboring structures. Pairwise potentials with additional repulsive components were also detected in two-dimensional cell sheets, by which curved sheets including tubes and cups were simulated. We conclude that our inference method is applicable to tissues harboring cavities and cell sheets, and the resultant effective potentials are useful to simulate the morphologies.

Multiple collapses of blastocysts after full blastocyst formation is an independent risk factor for aneuploidy - a study based on AI and manual validation

BACKGROUND

The occurrence of blastocyst collapse may become an indicator of preimplantation embryo quality assessment. It has been reported that collapsing blastocysts can lead to higher rates of aneuploidy and poorer clinical outcomes, but more large-scale studies are needed to explore this relationship. This study explored the characteristics of blastocyst collapse identified and quantified by artificial intelligence and explored the associations between blastocyst collapse and embryo ploidy, morphological quality, and clinical outcomes.

METHODS

This observational study included data from 3288 biopsied blastocysts in 1071 time-lapse preimplantation genetic testing cycles performed between January 2019 and February 2023 at a single academic fertility center. All transferred blastocysts are euploid blastocysts. The artificial intelligence recognized blastocyst collapse in time-lapse microscopy videos and then registered the collapsing times, and the start time, the recovery duration, the shrinkage percentage of each collapse. The effects of blastocyst collapse and embryo ploidy, pregnancy, live birth, miscarriage, and embryo quality were studied using available data from 1196 euploid embryos and 1300 aneuploid embryos.

RESULTS

5.6% of blastocysts collapsed at least once only before the full blastocyst formation (tB), 19.4% collapsed at least once only after tB, and 3.1% collapsed both before and after tB. Multiple collapses of blastocysts after tB (times ≥ 2) are associated with higher aneuploid rates (54.6%, P > 0.05; 70.5%, P < 0.001; 72.5%, P = 0.004; and 71.4%, P = 0.049 in blastocysts collapsed 1, 2, 3 or ≥ 4 times), which remained significant after adjustment for confounders (OR = 2.597, 95% CI 1.464-4.607, P = 0.001). Analysis of the aneuploid embryos showed a higher ratio of collapses and multiple collapses after tB in monosomies and embryos with subchromosomal deletion of segmental nature (P < 0.001). Blastocyst collapse was associated with delayed embryonic development and declined blastocyst quality. There is no significant difference in pregnancy and live birth rates between collapsing and non-collapsing blastocysts.

CONCLUSIONS

Blastocyst collapse is common during blastocyst development. This study underlined that multiple blastocyst collapses after tB may be an independent risk factor for aneuploidy which should be taken into account by clinicians and embryologists when selecting blastocysts for transfer.

How great thou ART: biomechanical properties of oocytes and embryos as indicators of quality in assisted reproductive technologies

Assisted Reproductive Technologies (ART) have revolutionized infertility treatment and animal breeding, but their success largely depends on selecting high-quality oocytes for fertilization and embryos for transfer. During preimplantation development, embryos undergo complex morphogenetic processes, such as compaction and cavitation, driven by cellular forces dependent on cytoskeletal dynamics and cell-cell interactions. These processes are pivotal in dictating an embryo's capacity to implant and progress to full-term development. Hence, a comprehensive grasp of the biomechanical attributes characterizing healthy oocytes and embryos is essential for selecting those with higher developmental potential. Various noninvasive techniques have emerged as valuable tools for assessing biomechanical properties without disturbing the oocyte or embryo physiological state, including morphokinetics, analysis of cytoplasmic movement velocity, or quantification of cortical tension and elasticity using microaspiration. By shedding light on the cytoskeletal processes involved in chromosome segregation, cytokinesis, cellular trafficking, and cell adhesion, underlying oogenesis, and embryonic development, this review explores the significance of embryo biomechanics in ART and its potential implications for improving clinical IVF outcomes, offering valuable insights and research directions to enhance oocyte and embryo selection procedures.

Spontaneously hatching human blastocyst is associated with high development potential and live birth rate in vitrified-warmed single blastocyst transfer: A retrospective cohort study

OBJECTIVE

To investigate the effect of hatching status on predicting pregnancy outcomes in single vitrified-warmed blastocyst transfer (SVBT) by objectively subdividing pre-implantation blastocysts according to hatching status.

METHODS

This retrospective study included 817 SVBT cycles performed between January 2016 and December 2017. Transferred embryos were categorized according to their hatching status as follows: group I (n = 147), non-hatching blastocysts; group II (n = 484), hatching blastocysts; and group III (n = 186), completely hatched blastocysts. Hatching blastocysts (group II) were then classified based on the ratio of the blastocystic diameter outside and inside the zona pellucida into early (n = 185), mid- (n = 103), and late (n = 196) hatching stages. Implantation rate (IR), clinical pregnancy rate (CPR), live birth rate (LBR), multiple pregnancy rate (MPR), miscarriage rate, and neonatal outcomes were evaluated.

RESULTS

For groups I, II, and III, respectively, the results were as follows: IR (28.6%, 43.6%, and 53.8%; P < 0.001), CPR (27.9%, 42.8%, and 53.2%; P < 0.001), and LBR (23.1%, 32.0%, and 42.5%; P < 0.001). Group III had better IR, CPR, and LBR. Among hatching blastocysts, late-hatching blastocysts had the highest IR (33.5%, 46.6%, and 51.5% for early, mid-, and late hatching, respectively; P = 0.002) and CPR (33.0%, 45.6%, and 50.5%; P = 0.002), with a tendency for a higher rate of LBR. Neonatal outcomes were not influenced by the hatching status.

CONCLUSION

Advanced hatching status is positively associated with a higher rate of clinical pregnancy and live birth with no negative effects on neonatal outcomes. Additionally, the quantitative classification of hatching status was found to be predictive of pregnancy outcomes.

Spontaneous collapse as a prognostic marker for human blastocysts: a systematic review and meta-analysis

STUDY QUESTION

Is spontaneous collapse (SC) by human blastocysts a prognostic factor in IVF treatment?

SUMMARY ANSWER

SC in human blastocyst is associated with reduced euploid embryo and pregnancy rates.

WHAT IS KNOWN ALREADY

SC of the human blastocyst is a phenomenon that was revealed relatively recently following the clinical application of time-lapse monitoring in IVF laboratories. The ploidy and clinical prognosis of affected blastocysts are still poorly understood, with inconsistent reports. Systematic reviews and meta-analyses on this topic are currently absent in the literature but its potential as a marker of embryo viability holds great clinical value. In this study, we aimed to comprehensively evaluate the potential of SC as a prognostic factor in regard to ploidy status, and pregnancy, live birth and miscarriage rates.

STUDY DESIGN, SIZE, DURATION

A systematic review and meta-analysis were performed according to PRISMA guidelines, with a protocol registered with PROSPERO (CRD42022373749). A search of MEDLINE, EMBASE, and the Cochrane Library for relevant studies was carried out on 10 October 2022, using key words relevant to 'blastocyst collapse' and 'time-lapse imaging'.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two independent reviewers systematically screened and evaluated each study in terms of participants, exposure, comparator, and outcomes (PECO). The Quality In Prognosis Studies tool was used for quality assessment. Data were extracted according to Cochrane methods. Pregnancy, live birth, ploidy, or miscarriage data were summarized by risk ratios (RRs) or odds ratios and their 95% CIs. All meta-analyses were performed with random-effects models.

MAIN RESULTS AND THE ROLE OF CHANCE

Following removal of duplicates, a total of 196 records were identified by the initial search. After screening according to PECO, 19 articles were included for further eligibility assessment. For meta-analysis, seven retrospective cohort studies were eventually included. After data pooling, the incidence of blastocyst SC was 37.0% (2516/6801) among seven studies (ranging from 17.4% to 56.2%). SC was associated with significantly lower clinical pregnancy rates (two studies, n = 736; RR = 0.77, 95% CI = 0.62-0.95; I2 = 30%), ongoing pregnancy rates (five studies, n = 2503; RR = 0.66, 95% CI = 0.53-0.83; I2 = 60%), and reduced euploidy rates (three studies, n = 3569; RR = 0.70, 95% CI = 0.59-0.83; I2 = 69%). Nevertheless, live birth rates (two studies, n = 816; RR = 0.76, 95% CI = 0.55-1.04; I2 = 56%) and miscarriage rate (four studies, n = 1358; RR = 1.31, 95% CI = 0.95-1.80; I2 = 0%) did not differ between blastocysts with or without SC. There was, however, significant heterogeneity between the studies included for evaluation of ongoing pregnancy rates (I2 = 60%, P = 0.04), live birth rates (I2 = 56%, P = 0.13), and ploidy rates (I2 = 69%, P = 0.04). Subgroup analyses were conducted according to different definitions of SC, number of collapse events, and whether the transferred blastocyst had undergone preimplantation genetic testing for aneuploidy; with inconclusive findings across subgroups.

LIMITATIONS, REASONS FOR CAUTION

All studies in the meta-analysis were retrospective with varying levels of heterogeneity for different outcomes. Not all studies had accounted for potential confounding factors, therefore only unadjusted data could be used in the main meta-analysis. Studies employed slightly different strategies when defining blastocyst SC. Standardization in the definition for SC is needed to improve comparability between future studies.

WIDER IMPLICATIONS OF THE FINDINGS

Our results indicate that blastocyst SC has negative implications for a pregnancy. Such blastocysts should be given a low ranking when selecting from a cohort for intrauterine transfer. Blastocyst SC should be considered as a contributing variable when building blastocyst algorithms to predict pregnancy or live birth.

STUDY FUNDING/COMPETING INTEREST(S)

There is no external funding to report. All authors report no conflict of interest.

REGISTRATION NUMBER

PROSPERO 2022 CRD42022373749.

Liquid storage of porcine in vitro-produced blastocysts; a practical approach for short storage

Commercial application of embryo transfer in pig breeding is dependent on the storage of embryos. The aim of this study was to assess the embryo quality of in vitro-produced blastocysts after 3 h liquid storage at 37°C in CO2-free medium by evaluating morphology, in vitro developmental capacity and apoptosis. Blastocysts at days 5 and 6 post-fertilization were randomly allocated to the storage group (HEPES-buffered NCSU-23 medium including bovine serum albumin in a portable embryo transport incubator at 37°C) or a control group (porcine blastocyst medium in a conventional culture incubator). Thereafter, blastocysts were evaluated for morphology and stained to assess apoptosis straight after the 3 h storage period or after a further 24 h conventional incubation. There was no significant difference between the storage and control group after 3 h storage and the further 24 h conventional incubation for any of the parameters, nor for apoptosis straight after the 3 h storage. Embryos that reached the blastocyst stage at day 5 showed less apoptosis (6.6% vs 10.9%, P = 0.01) and a trend for a higher rate of developmental capacity (70.6% vs 51.5%, P = 0.089) than embryos reaching the blastocyst stage on day 6. In conclusion, in vitro-produced porcine blastocysts can be stored for 3 h at physiological temperature in transportable incubators using a CO2-independent medium without compromising quality.

Embryo Pulsing: Repeated Expansion and Contraction of In Vivo and In Vitro Equine Blastocysts

Morphokinetic evaluation of embryo development has allowed the discovery of events occurring during blastulation. Here, we describe equine embryo pulsing, determined as continued expansion and contraction of both in vivo and in vitro produced blastocysts. Using time-lapse imaging, we demonstrated that pulsing starts during early blastocyst development of in vitro-produced embryos in horses. The median time for a complete contraction was 0.22h (0.08h-2h; min-max) where embryos reduced their sizes around 12.0% (median; 2.3%-27.0%) and the median time for an expansion was 3.3h (0.75-9.0h) where embryo re-expanded around 16.9% (3.2%-42.8%). We also found that pulsing can be observed in in vivo-produced embryos obtained from mares 6.5 days after ovulation and continues during the expansion of the blastocysts. Even though its exact mechanism remains unknown, studies in human IVF suggest that the pulsing of embryos is associated with embryo quality and implantation rates. Thus, further investigations regarding this event in equine in vitro production procedures are warranted. Additionally, the pulsing in the in vivo-produced embryos could explain the diverse morphology occasionally observed in the collected or shipped embryos. Future studies are necessary to understand the underlying mechanism of pulsing and its association with embryo quality and embryo transfer outcome.

Impact of mono(2-ethylhexyl) phthalate (MEHP) on the development of mouse embryo in vitro

Mono(2-ethylhexyl) phthalate (MEHP) is the most studied metabolite of di(2-ethylhexyl) phthalate (DEHP), a phthalate found in cosmetics, flooring, paints, and plastics products, including toys and medical tubing. Humans are frequently exposed to this compound due to its ubiquitous presence in our environment. DEHP and MEHP are known to be endocrine-disrupting chemicals and exposure levels have been associated to decreased reproductive success. However, few studies have focused on the direct effects of MEHP on embryos. The present study investigated effects of MEHP (0.1, 1, 10, 100 and 1000 µM) on mice preimplantation embryonic development, evaluating percentage of blastocyst formation, hatching from zona pellucida, methylation-related genes, cell lineage commitment, micronucleation, and adherens junction marker at different stages of development during in vitro culture for 6 days. We show MEHP negatively impacts embryo competence by reducing blastocyst formation and hatching at 100 and 1000 µM. In addition, 100 µM MEHP increases the expression of Tet3 gene in blastocysts, which is related to a reduction of DNA methylation, an important mechanism regulating gene expression. Exposed embryos that completed the hatching process in groups 0.1, 1 and 10 µM MEHP had similar number of inner cell mass and trophectoderm cells compared to the control, while micronucleation occurrence and E-cadherin expression was not affected in exposed morulae by MEHP at 10 or 100 µM. Our results showed that high concentrations of MEHP can negatively impact embryo development. New studies unveiling the mechanism of toxicity involved and encompassing further developmental stages are warranted for further understanding.

Trophectoderm formation: regulation of morphogenesis and gene expressions by RHO, ROCK, cell polarity, and HIPPO signaling

In brief

Trophectoderm is the first tissue to differentiate in the early mammalian embryo and is essential for hatching, implantation, and placentation. This review article discusses the roles of Ras homolog family members (RHO) and RHO-associated coiled-coil containing protein kinases (ROCK) in the molecular and cellular regulation of trophectoderm formation.

Abstract

The trophectoderm (TE) is the first tissue to differentiate during the preimplantation development of placental mammals. It constitutes the outer epithelial layer of the blastocyst and is responsible for hatching, uterine attachment, and placentation. Thus, its formation is the key initial step that enables the viviparity of mammals. Here, we first describe the general features of TE formation at the morphological and molecular levels. Prospective TE cells form an epithelial layer enclosing an expanding fluid-filled cavity by establishing the apical-basal cell polarity, intercellular junctions, microlumen, and osmotic gradient. A unique set of genes is expressed in TE that encode the transcription factors essential for the development of trophoblasts of the placenta upon implantation. TE-specific gene expressions are driven by the inhibition of HIPPO signaling, which is dependent on the prior establishment of the apical-basal polarity. We then discuss the specific roles of RHO and ROCK as essential regulators of TE formation. RHO and ROCK modulate the actomyosin cytoskeleton, apical-basal polarity, intercellular junctions, and HIPPO signaling, thereby orchestrating the epithelialization and gene expressions in TE. Knowledge of the molecular mechanisms underlying TE formation is crucial for assisted reproductive technologies in human and farm animals, as it provides foundation to help improve procedures for embryo handling and selection to achieve better reproductive outcomes.

Morphological and morphokinetic associations with aneuploidy: a systematic review and meta-analysis

BACKGROUND

A time lapse system (TLS) is utilized in some fertility clinics with the aim of predicting embryo viability and chance of live birth during IVF. It has been hypothesized that aneuploid embryos display altered morphokinetics as a consequence of their abnormal chromosome complement. Since aneuploidy is one of the fundamental reasons for IVF failure and miscarriage, attention has focused on utilizing morphokinetics to develop models to non-invasively risk stratify embryos for ploidy status. This could avoid or reduce the costs associated with pre-implantation genetic testing for aneuploidy (PGT-A). Furthermore, TLS have provided an understanding of the true prevalence of other dysmorphisms. Hypothetically, the incorporation of morphological features into a model could act synergistically, improving a model's discriminative ability to predict ploidy status.

OBJECTIVE AND RATIONALE

The aim of this systematic review and meta-analysis was to investigate associations between ploidy status and morphokinetic or morphological features commonly denoted on a TLS. This will determine the feasibility of a prediction model for euploidy and summarize the most useful prognostic markers to be included in model development.

SEARCH METHODS

Five separate searches were conducted in Medline, Embase, PubMed and Cinahl from inception to 1 July 2021. Search terms and word variants included, among others, PGT-A, ploidy, morphokinetics and time lapse, and the latter were successively substituted for the following morphological parameters: fragmentation, multinucleation, abnormal cleavage and contraction. Studies were limited to human studies.

OUTCOMES

Overall, 58 studies were included incorporating over 40 000 embryos. All except one study had a moderate risk of bias in at least one domain when assessed by the quality in prognostic studies tool. Ten morphokinetic variables were significantly delayed in aneuploid embryos. When excluding studies using less reliable genetic technologies, the most notable variables were: time to eight cells (t8, 1.13 h, 95% CI: 0.21-2.05; three studies; n = 742; I2 = 0%), t9 (2.27 h, 95% CI: 0.5-4.03; two studies; n = 671; I2 = 33%), time to formation of a full blastocyst (tB, 1.99 h, 95% CI 0.15-3.81; four studies; n = 1640; I2 = 76%) and time to expanded blastocyst (tEB, 2.35 h, 95% CI: 0.06-4.63; four studies; n = 1640; I2 = 83%). There is potentially some prognostic potential in the degree of fragmentation, multinucleation persisting to the four-cell stage and frequency of embryo contractions. Reverse cleavage was associated with euploidy in this meta-analysis; however, this article argues that these are likely spurious results requiring further investigation. There was no association with direct unequal cleavage in an embryo that progressed to a blastocyst, or with multinucleation assessed on Day 2 or at the two-cell stage. However, owing to heterogeneous results and poor-quality evidence, associations between these morphological components needs to be investigated further before conclusions can be reliably drawn.

WIDER IMPLICATIONS

This first systematic review and meta-analysis of morphological and morphokinetic associations with ploidy status demonstrates the most useful morphokinetic variables, namely t8, t9 and tEB to be included in future model development. There is considerable variability within aneuploid and euploid embryos making definitively classifying them impossible; however, it is feasible that embryos could be prioritized for biopsy. Furthermore, these results support the mechanism by which algorithms for live birth may have predictive ability, suggesting aneuploidy causes delayed cytokinesis. We highlight significant heterogeneity in our results secondary to local conditions and diverse patient populations, therefore calling for future models to be robustly developed and tested in-house. If successful, such a model would constitute a meaningful breakthrough when accessing PGT-A is unsuitable for couples.

The morphokinetics algorithm based on data from day 5 blastocyst transfer (KIDScoreD5 version 3) is also useful for embryo selection in day 6 blastocyst transfer

Purpose

To analyze whether the morphokinetics algorithm based on data from day 5 blastocyst transfer (KIDScoreD5 version 3) can predict the pregnancy rate of both day 5 and day 6 blastocyst transfers.

Methods

The relationship between KIDScoreD5 and clinical pregnancy rate was evaluated using the Cochran-Armitage test and receiver-operating characteristic (ROC) curve analysis.

Results

A positive correlation was observed between the KIDScoreD5 value and clinical pregnancy rate for both day 5 (p = 0.0003) and day 6 blastocysts (p = 0.0019) using the Cochrane-Armitage test. ROC curve analysis showed that the area under the curve (AUC) of KIDScoreD5 for clinical pregnancy was 0.627 (0.575-0.677, p < 0.0001) for day 5 blastocysts and 0.685 (0.571-0.780, p = 0.0009) for day 6 blastocysts. The combined analysis of both day 5 and day 6 blastocysts also showed an AUC of 0.680 (0.636-0.720, p < 0.0001), suggesting that it is possible to select embryos that are more likely to result in pregnancy.

Conclusions

KIDScoreD5 could predict pregnancy not only in day 5 blastocysts but also in day 6 blastocysts. When both day 5 and day 6 blastocysts are vitrified, embryo selection by KIDScoreD5 is possible with a high prediction ability of pregnancy.

Arrdc4-dependent extracellular vesicle biogenesis is required for sperm maturation

Extracellular vesicles (EVs) are important players in cell to cell communication in reproductive systems. Notably, EVs have been found and characterized in the male reproductive tract, however, direct functional evidence for their importance in mediating sperm function is lacking. We have previously demonstrated that Arrdc4, a member of the α-arrestin protein family, is involved in extracellular vesicle biogenesis and release. Here we show that Arrdc4-mediated extracellular vesicle biogenesis is required for proper sperm function. Sperm from Arrdc4-/- mice develop normally through the testis but fail to acquire adequate motility and fertilization capabilities through the epididymis, as observed by reduced motility, premature acrosome reaction, reduction in zona pellucida binding and two-cell embryo production. We found a significant reduction in extracellular vesicle production by Arrdc4-/- epididymal epithelial cells, and further, supplementation of Arrdc4-/- sperm with additional vesicles dampened the acrosome reaction defect and restored zona pellucida binding. These results indicate that Arrdc4 is important for proper sperm maturation through the control of extracellular vesicle biogenesis.

Blastocyst-like structures generated from human pluripotent stem cells

Limited access to embryos has hampered the study of human embryogenesis and disorders that occur during early pregnancy. Human pluripotent stem cells provide an alternative means to study human development in a dish^1-7. Recent advances in partial embryo models derived from human pluripotent stem cells have enabled human development to be examined at early post-implantation stages^8-14. However, models of the pre-implantation human blastocyst are lacking. Starting from naive human pluripotent stem cells, here we developed an effective three-dimensional culture strategy with successive lineage differentiation and self-organization to generate blastocyst-like structures in vitro. These structures-which we term 'human blastoids'-resemble human blastocysts in terms of their morphology, size, cell number, and composition and allocation of different cell lineages. Single-cell RNA-sequencing analyses also reveal the transcriptomic similarity of blastoids to blastocysts. Human blastoids are amenable to embryonic and extra-embryonic stem cell derivation and can further develop into peri-implantation embryo-like structures in vitro. Using chemical perturbations, we show that specific isozymes of protein kinase C have a critical function in the formation of the blastoid cavity. Human blastoids provide a readily accessible, scalable, versatile and perturbable alternative to blastocysts for studying early human development, understanding early pregnancy loss and gaining insights into early developmental defects.

Live visualisation of electrolytes during mouse embryonic development using electrolyte indicators

Studies have shown that some electrolytes, including Na+ and K+, play important roles in embryonic development. However, these studies evaluated these electrolytes by using inhibitors or knockout mice, with no mention on the changes in the intracellular electrolyte concentrations during embryogenesis. In this study, we used the electrolyte indicators CoroNa Green AM and ION Potassium Green-2 AM to directly visualise intracellular concentrations of Na+ and K+, respectively, at each embryonic developmental stage in mouse embryos. We directly observed intracellular electrolyte concentrations at the morula, blastocyst, and hatching stages. Our results revealed dynamic changes in intracellular electrolyte concentrations; we found that the intracellular Na+ concentration decreased, while K+ concentration increased during blastocoel formation. The degree of change in intensity in response to ouabain, an inhibitor of Na+/K+ ATPase, was considered to correspond to the degree of Na+/K+ ATPase activity at each developmental stage. Additionally, after the blastocyst stage, trophectoderm cells in direct contact with the blastocoel showed higher K+ concentrations than in direct contact with inner cell mass, indicating that Na+/K+ ATPase activity differs depending on the location in the trophectoderm. This is the first study to use CoroNa Green AM and ION Potassium Green-2 AM in mouse embryos and visualise electrolytes during embryonic development. The changes in electrolyte concentration observed in this study were consistent with the activity of Na+/K+ ATPase reported previously, and it was possible to image more detailed electrolyte behaviour in embryo cells. This method can be used to improve the understanding of cell physiology and is useful for future embryonic development studies.

Clinical pregnancy is significantly associated with the blastocyst width and area: a time-lapse study

In order to maintain pregnancy rates following single embryo transfer, optimisation of embryo culture and selection is vital. Time-lapse monitoring (TLM) has the potential to play a crucial role by providing sequential images of embryo development and minimal disturbance. Therefore, in this study morphometric assessment of blastocyst area and maximum width was performed in order to evaluate if these parameters are associated with pregnancy outcomes in IVF/ICSI cycles. This is a retrospective study of 664 patients who had elective single blastocyst transfer (eSBT). The EmbryoScope drawing tools were used to measure specific variables such as the maximum blastocyst width and blastocyst area. Our results show that women who were pregnant had significantly (P < 0.01) larger blastocyst width [median (range) μm] 184 (125-239) versus non-pregnant, 160 (120-230)] and area [median (range) μm²] 26099 (12101-45,280) versus non-pregnant women, 22,251 (10992-37,931)]. A univariate logistic regression performed showed that blastocyst width [(OR = 1.026, 95% CI = (1.019, 1.033)] was significant (P < 0.01) and for every μm increase of blastocyst width, the odds of clinical pregnancy increase by 2.6%. A univariate logistic regression performed showed that blastocyst area [(OR = 1.00008, 95% CI = (1.00006, 1.00011)] was significant with P < 0.01. For every μm² increase of blastocyst area, our data showed the odds of clinical pregnancy increase by 0.008%. Hosmer-Lemeshow tests of calibrations were performed to verify calibration. Although our findings show a clear correlation between blastocyst dimensions and the clinical pregnancy rate, further studies are necessary to confirm these observations.

Risk Factors for Monozygotic Twins in IVF-ICSI Cycles: a Case-Control Study

In vitro fertilization (IVF) is associated with a higher incidence of monozygotic twin pregnancies, which are known to be burdened by a higher risk of main obstetric complications. The reasons behind this association are still unclear. In the present study, we therefore investigate the risk factors for monozygotic twinning in pregnancies achieved by IVF. We conducted a multicenter retrospective case-control study. All IVF cycles performed between 2014 and 2019 at the infertility units of two Italian academic institutes were retrospectively reviewed. Only pregnancies obtained with single embryo transfer were eligible. A total of 50 monozygotic twin pregnancies (cases) were identified and matched in a 1:5 ratio to 250 singleton pregnancies (controls) by study center and study period. Monozygotic twin pregnancies were diagnosed by ultrasound. Women experiencing miscarriage could be included provided that the pregnancy loss occurred after a definitive diagnosis of monozygotic twin pregnancy. Demographic, clinical, and embryological characteristics were retrieved from patients' charts. Overall, the incidence of monozygotic twin pregnancies was 1.2% (50 out of 4016 single embryo transfers). At univariate analyses, statistically significant differences emerged for BMI, peripheral levels of estradiol and progesterone at the time of hCG administration, total number of retrieved suitable oocytes, freezing-thawing cycles, and assisted hatching. After performing a multivariate logistic analysis, only assisted hatching remained significantly associated with monozygotic twinning (adjusted odds ratio 2.32, 95%CI 1.03-5.25). Blastomere separation during the passage through this artificial hole or interference with the signaling pathway within the embryo could be the mechanisms involved.

Common principles of early mammalian embryo self-organisation

Pre-implantation mammalian development unites extreme plasticity with a robust outcome: the formation of a blastocyst, an organised multi-layered structure ready for implantation. The process of blastocyst formation is one of the best-known examples of self-organisation. The first three cell lineages in mammalian development specify and arrange themselves during the morphogenic process based on cell-cell interactions. Despite decades of research, the unifying principles driving early mammalian development are still not fully defined. Here, we discuss the role of physical forces, and molecular and cellular mechanisms, in driving self-organisation and lineage formation that are shared between eutherian mammals.

Blastocyst contractions are strongly related with aneuploidy, lower implantation rates, and slow-cleaving embryos: a time lapse study

OBJECTIVES

This study aimed to identify human blastocyst contraction patterns and their correlations with ploidy status (PGT-A analysis), the time it took for embryos to reach the blastocyst stage, and pregnancy rates.

METHODS

The study included 912 embryos from 270 patients seen in our center. All embryos were cultivated in an Embryoscope incubator. An NGS platform was used to test 778 of the 912 embryos initially included in the study for aneuploidy at a reference laboratory. Blastocyst contractions were evaluated using the embryo drawing tool to compute percent contraction. A total of 182 single-embryo transfers were performed. The mean age of the included patients was 30.44 years (24-39 years).

RESULTS

The embryos were divided into two groups, the first with embryos that contracted (CT group) and the second with embryos that did not contract, herein referred to as expanding-only embryos or solo expanding (SE group). In terms of ploidy status, 58.33% of the embryos in the SE group were euploid, while 53.58% of embryos in the CT group were aneuploid. The difference between the groups was statistically significant (p=0.029), showing that embryos that do not contract have a higher chance of being euploid than embryos that contract. Pregnancy rates were also significantly higher among embryos in the SE group than in the CT group (63.10% vs. 46.67%; p=0.012). Finally, we saw that embryos in the CT group took significantly longer to reach the blastocyst stage compared to embryos in the SE group (p=0.004). Patient age was not significantly different between the CT and SE groups, indicating that age might not be a factor in embryo contraction.

CONCLUSION

Two of the traits for which the embryos included in this study were compared were statistically different. Embryos in the CT group had lower implantation rates, took longer to reach the blastocyst stage, and had a higher chance of being aneuploid, regardless of maternal age. Therefore, embryo contraction might be a useful parameter in the selection of embryos for transfer.

Spontaneous blastocyst collapse as an embryo marker of low pregnancy outcome: A Time-Lapse study

OBJECTIVE

In this study we investigate the correlation between spontaneous blastocyst collapse and pregnancy outcome.

METHODS

This is a retrospective study performed at Edinburgh Assisted Conception Programme, EFREC, Royal Infirmary of Edinburgh, UK. Embryos were cultured individually in 6.0% CO2, 5.0% O2, 89.0% N2, using single step medium (GTL™ Vitrolife, Göteborg, Sweden) and selected for transfer using standard morphological criteria. Using the EmbryoScope™ time-lapse monitoring (TLM), blastocysts collapse was analyzed by measuring the maximum volume reduction and defined as having collapsed if there was >50% volume reduction. Couples undergoing IVF/ICSI treatment and having an elective single embryo transfer (eSET) at blastocyst stage were included in this study. After the embryo transfer, retrospectively, each blastocyst was allocated to one of two groups (collapsed or not collapsed). 62 blastocysts collapsed once or more during development (17.4%), the remaining 294 showed no collapse (82.6%).

RESULTS

A significantly higher implantation rate (IR) of 61.2% and ongoing pregnancy rate (OPR) of 53.7% was observed when blastocysts which had not collapsed were replaced compared to cycles in which collapsed blastocysts were replaced (IR rate 22.6% and OPR 17.7%).

CONCLUSION

This study demonstrated that human blastocysts which collapse spontaneously during in vitro development are less likely to implant and generate a pregnancy compared with embryos which do not. Although this is a retrospective study, the results establish the utility of collapse episodes as new marker of embryo selection following eSET at blastocyst stage.

Blastocyst collapse as an embryo marker of low implantation potential: a time-lapse multicentre study

Spontaneous blastocyst collapse during in vitro embryo development has been suggested as a novel marker of embryo quality. Therefore, the aim of this multicentre study was to carry out a retrospective multicentre analysis to investigate the correlation between blastocyst collapse and pregnancy outcome. Here, 1297 intracytoplasmic sperm injection (ICSI)/in vitro fertilization (IVF) fresh cycles, with an elective single blastocyst transfer (eSET) were included in this study. Embryos were cultured individually in 6.0% CO2, 5.0% O2, 89.0% N2, using single step medium (GTLTM VitroLife, Sweden) or sequential medium (CookTM, Cook Medical, Australia) and selected for transfer using standard morphological criteria. With the use of time-lapse monitoring (TLM), blastocysts were analyzed by measuring the maximum volume reduction and defined as having collapsed, if there was ≥ 50% volume reduction from the expanded blastocyst and the collapse event. Following embryo replacement, each blastocyst was retrospectively allocated to one of two groups (collapsed or not collapsed). Here, 259 blastocysts collapsed once or more during development (19.9%) and the remaining 1038 either contracted minimally or not collapsed (80.1%). A significantly higher ongoing pregnancy rate (OPR) of 51.9% (95% CI 48.9-59.9%) was observed when blastocysts that had not collapsed were replaced compared with cycles in which collapsed blastocysts were transferred 37.5% (95% CI 31.6-43.4%). This study suggests that human blastocysts that collapse spontaneously during development are less likely to implant and generate a pregnancy compared with embryos that do not. Although this is a retrospective study, the results demonstrated the utility of collapse episodes as new marker of embryo selection following eSET at blastocyst stage.

Hydraulic control of mammalian embryo size and cell fate

Size control is fundamental in tissue development and homeostasis^1,2. Although the role of cell proliferation in these processes has been widely studied, the mechanisms that control embryo size-and how these mechanisms affect cell fate-remain unknown. Here we use the mouse blastocyst as a model to unravel a key role of fluid-filled lumen in the control of embryo size and specification of cell fate. We find that there is a twofold increase in lumenal pressure during blastocyst development, which translates into a concomitant increase in cell cortical tension and tissue stiffness of the trophectoderm that lines the lumen. Increased cortical tension leads to vinculin mechanosensing and maturation of functional tight junctions, which establishes a positive feedback loop to accommodate lumen growth. When the cortical tension reaches a critical threshold, cell-cell adhesion cannot be sustained during mitotic entry, which leads to trophectoderm rupture and blastocyst collapse. A simple theory of hydraulically gated oscillations recapitulates the observed dynamics of size oscillations, and predicts the scaling of embryo size with tissue volume. This theory further predicts that disrupted tight junctions or increased tissue stiffness lead to a smaller embryo size, which we verified by biophysical, embryological, pharmacological and genetic perturbations. Changes in lumenal pressure and size can influence the cell division pattern of the trophectoderm, and thereby affect cell allocation and fate. Our study reveals how lumenal pressure and tissue mechanics control embryo size at the tissue scale, which is coupled to cell position and fate at the cellular scale.

Human frozen-thawed blastocyst morphokinetics observed using time-lapse cinematography reflects the number of trophectoderm cells

Recent studies reported morphokinetic indices for optimal selection of embryos in assisted reproductive technology (ART). The morphokinetics in blastocyst stage include the collapse and re-expansion rates after thawing. However, evaluation methods using these morphokinetics have not been established, mainly because the underlying molecular mechanisms remain unclarified. In this study, we focused on the relationship between these morphokinetic observation of the blastocyst behaviour and the number of cells constituting the blastocyst. We evaluated 38 surplus human frozen-thawed blastocysts using time-lapse cinematography and recorded their expansion, contraction, and hatching. A total of 28 blastocysts expanded in culture (cross-sectional area ≥ 5,000 π μm²). In comparison to the ones that did not, the expanded group presented significantly more number of inner cell mass (ICM) and trophectoderm (TE) cells, which eventually develop into the fetus and placenta, respectively (ICM: Expanded 10.2 ± 6.3 vs. Non-Expanded 6.0 ± 12.3, p < 0.05; TE: Expanded 165.7 ± 74.8 vs. Non-Expanded 57.0 ± 29.4, p < 0.05). Moreover, a positive correlation was found between the expansion rate (up to 4 h) and the number of TE cells (r = 0.558, p = 0.0021). Additionally, blastocysts that hatched had a significantly higher number of TE cells than those that did not (hatching 225.2 ± 61.2 vs. no hatching 121.1 ± 48.6, p < 0.0001). The number of TE cells per unit of cross-sectional area correlated negatively with the contraction time (r = –0.601, p = 0.0007). No correlation between the number of ICM cells and these morphokinetics was detected. In conclusion, our study demonstrates that different morphokinetics of frozen-thawed blastocysts reflect the number of TE cells. The differentiation of blastocysts containing sufficient TE cells would be beneficial for implantation and prognosis of a subsequent pregnancy. Thus, evaluation of these morphokinetics can be an effective method to screen good embryos for ART.

Artificial blastocyst collapse prior to vitrification significantly improves Na+/K+-ATPase-dependent post-warming blastocoel re-expansion kinetics without inducing endoplasmic reticulum stress gene expression in the mouse

Blastocoel expansion during embryo development is known to be reliant on the Na+/K+-ATPase pump, but little is known about the relative contribution of active (Na+/K+-ATPase pump) and facilitated diffusion (aquaporins) water transport during blastocoel re-expansion after vitrification. The aims of this study were to examine potential effects of artificial blastocoel collapse (ABC) on markers of embryo stress and the contribution of active and facilitated diffusion water transport mechanisms to blastocoel re-expansion. Day 5 mouse embryos were vitrified using either a standard protocol, laser pulse ABC, a hyperosmotic sucrose ABC protocol or both laser pulse and sucrose. Using real-time polymerase chain reaction, no differences were found in the gene expression of the endoplasmic reticulum (ER) stress markers activating transcription factor 4 (Atf4) or heat shock protein 90-alpha (Hsp90α) 2h after warming. Similarly, expression of the Na+/K+-ATPase pump gene, ATPase, Na+/K+ transporting, beta 1 polypeptide (Atp1b1) and protein did not differ between groups. Aquaporin 8 (Aqp8) gene expression was significantly lower in the laser+sucrose ABC group than in fresh controls, and aquaporin 3 (Aqp3) expression significantly higher in standard vitrified embryos compared with all other groups. Ouabain, a potent and specific Na+/K+-ATPase pump inhibitor, inhibited blastocoel re-expansion in both standard protocol- and laser ABC-vitrified embryos, reducing both groups to the same rate of re-expansion 3h after warming. These results demonstrate that ABC before vitrification does not alter mRNA or protein expression of Na+/K+-ATPase, or mRNA levels of ER stress genes Atf4 and Hsp90α. Activity of the pump may be increased in ABC embryos, with potential compensation by AQP3 when it is compromised.

The profiling of pre- and post-warming DNA in mouse embryos with microsatellite method

Aims:

This research aimed to identify the deoxyribonucleic acid (DNA) profile and changes of post-warming embryo after being frozen with vitrification method using microsatellite method.

Materials and Methods:

This research examined the mouse embryo blastocysts that were divided into four groups: Post-warming living blastocyst, post-warming living blastocyst with half fragmented cell, post-warming dead blastocyst, and pre-freezing living blastocyst. The isolation sample applied phenol-chloroform method. After obtaining polymerase chain reaction results, all the samples of pre-freezing fresh embryo, post-warming living embryo, dead embryo, and degenerated embryo were then examined by single-strand conformation polymorphism (SSCP).

Results:

The amplification with D18mit14 primer was 100 bp and 150bp with D18mit87 primer, 150bp with D7mit22, and 300bp with D7mit25. The result of SSCP with D18mit14 primer showed that the blastocysts were fragmented and dead after warming process and formed into two DNA strand fragments, while the fresh embryos which passed freezing process did not form any fragment. D18mit87 primer SSCP indicated different fragments for each treatment. The result of SSCP using D7mit22 formed two different fragments for each treatment. While using D7mit25, the SSCP result formed some different fragments for each sample. Post-warming living embryo had similar ribbon to pre-freezing fresh embryo.

Conclusion:

D7mit222, D7mit25, and D18mit87 primers could be used as the aneuploidy marker on mouse embryos that were induced by post-warming process. The profile of living blastocyst, dead blastocyst, and post-warming fragmented blastocyst had different DNA tapes.

Contraction behaviour reduces embryo competence in high-quality euploid blastocysts

PURPOSE

The aim of the study is to investigate how blastocyst contraction behaviour affects the reproductive competence in high-quality euploid embryos.

METHODS

Eight hundred ninety-six high-quality blastocysts derived from 190 patients (mean age 38.05 (SD = 2.9) years) who underwent preimplantation genetic testing for aneuploidies (PGT-A) from January 2016 to October 2017 were included in this study. PGT-A results were reported as euploid or aneuploid. Aneuploid embryos were sub-classified into three categories: monosomy, trisomy and complex aneuploid. Retrospective studies of time-lapse monitoring (TLM) of those embryos were analysed and reproductive outcome of transferred embryos was collected.

RESULTS

A total of 234/896 were euploid (26.1%) whilst 662/896 (73.9%) blastocysts were proven to be aneuploid from which 116 (17.6%) presented monosomies, 136 (20.5%) trisomies and 410 (61.9%) were complex aneuploid. The most frequent chromosomal complements were trisomies affecting chromosome 21 and monosomies involving chromosomes 16 and 22. Data analysis showed a statistical difference in the number of contractions being reported greater in aneuploid when compared to euploid embryos (0.6 vs 1.57; p < 0.001). Analysis of the aneuploid embryos showed that monosomies present less number of contractions when compared to embryos affected with trisomies or complex aneuploidies (1.23 vs 1.53 and 1.40; p < 0.05). No difference was observed when comparing the latter two groups. Euploid embryos presenting at least one contraction resulted in lower implantation and clinical pregnancy rates when compared to blastocysts that do not display this event (47.6 vs 78.5% and 40.0 vs 59.0% respectively).

CONCLUSIONS

Most aneuploid blastocysts diagnosed by PGT-A have complex aneuploidies, showing that aneuploid embryos can develop after genomic activation and reaching high morphological scores. It becomes clear that embryo contraction, despite being a physiological feature during blastulation, is conditioned by the ploidy status of the embryo. Furthermore, the presence of contractions may compromise implantation rates.

Revisiting embryo assisted hatching approaches: a systematic review of the current protocols

Zona pellucida (ZP) manipulation, termed "assisted hatching" (AH), has been introduced in order to favor embryo hatching and ultimately improve assisted reproductive technology success but with poor proofs of safety and biological plausibility. We herein provide a systematic review of clinical outcomes following the application of different methods of ZP manipulation on fresh or frozen/thawed embryos at different developmental stages in different groups of patients. Out of the 69 papers that compared the clinical outcomes deriving from hatched versus non-hatched embryos, only 11 considered blastocysts while the rest referred to cleavage stage embryos. The ZP thinning of fresh embryos either by chemical or laser approach was shown to provide very limited benefit in terms of clinical outcomes. Better results were observed with procedures implying a higher degree of zona manipulation, including zona removal. Studies comparing the mechanical or chemical procedures to those laser-mediated consistently reported a superiority of the latter ones over the former. Literature is consistent for a benefit of ZP breaching in thawed blastocysts. This review provides the current knowledge on the AH procedure in order to improve its efficacy in the appropriate context. Embryologists might benefit from the approaches presented herein in order to improve Assisted Reproduction Technologies (ART) outcomes.

Evaluation of an ovary-on-a-chip in large mammalian models: Species specificity and influence of follicle isolation status

The ability to grow oocytes from immature ovarian follicles in vitro has significant potential for fertility preservation; yet, it has proved challenging in large mammalian species due to the complex metabolic needs and long-term culture requirements. Currently, follicular incubations are based on a "static" system with manual exchange of medium. Despite the numerous advantages of conventional culturing approaches, recapitulating the native microenvironment and supporting the survival of ovarian follicles from large mammalian species still represent challenges. In this study, we utilized an innovative, dynamic microfluidic system to support the in vitro survival of domestic cat and dog follicles enclosed within the ovarian cortex or isolated from ovarian cortex. Results indicate both species-specific and tissue type-specific differences in response to microfluidic culture. Domestic cat but not dog ovarian cortical tissues maintained viability under flow similar to conventional agarose gel controls. Preantral stage isolated follicles from both species that grew most favourably in conventional alginate bead culture, but overall, there was no influence of culture system on expression of follicle development or oocyte health markers. This system represents an important exploration toward the development of an improved ovarian in vitro culture system of large mammalian species (e.g., cats and dogs), which has potential applications for fertility preservation, reproductive toxicology, and endangered mammal conservation efforts.

Organ size control via hydraulically gated oscillations

Hollow vesicular tissues of various sizes and shapes arise in biological organs such as ears, guts, hearts, brains and even entire organisms. Regulating their size and shape is crucial for their function. Although chemical signaling has been thought to play a role in the regulation of cellular processes that feed into larger scales, it is increasingly recognized that mechanical forces are involved in the modulation of size and shape at larger length scales. Motivated by a variety of examples of tissue cyst formation and size control that show simultaneous growth and size oscillations, we create a minimal theoretical framework for the growth and dynamics of a soft, fluid-permeable, spherical shell. We show that these shells can relieve internal pressure by bursting intermittently, shrinking and re-growing, providing a simple mechanism by which hydraulically gated oscillations can regulate size. To test our theory, we develop an in vitro experimental set-up to monitor the growth and oscillations of a hollow tissue spheroid growing freely or when confined. A simple generalization of our theory to account for irreversible deformations allows us to explain the time scales and the amplitudes of oscillations in terms of the geometry and mechanical properties of the tissue shells. Taken together, our theory and experimental observations show how soft hydraulics can regulate the size of growing tissue shells.

Artificial blastocoel collapse of human blastocysts before vitrification and its effect on re-expansion after warming - a prospective observational study using time-lapse microscopy

Vitrified human blastocysts show varied re-expansion capacity after warming. This prospective observational study compared behaviour of artificially collapsed blastocysts (study group patients, n = 69) to that of blastocysts that were vitrified without artificial collapse (control group patients, n = 72). Warmed blastocysts were monitored by time-lapse microscopy and blastocoel re-expansion speed and growth patterns compared between study and control groups. These parameters were also retrospectively compared between blastocysts that resulted in live birth and those that failed. Artificially collapsed blastocysts re-expanded on average 15.01 µm²/min faster than control blastocysts (P = 0.0013). Warmed blastocysts expressed four different patterns of blastocoel growth. The pattern showing contractions at the end of culture was observed to have a lower prevalence in control blastocysts, which coincided with the lower incidence of hatching in this group. Re-expansion speed and prevalence of growth patterns were comparable between blastocysts that did and did not result in a live birth. This was seen in the study and control groups. Despite faster re-expansion and different growth patterns of artificially collapsed blastocysts, live birth rate did not differ between groups. However, this result should be interpreted with caution due to the small sample size and high risk of bias.

The location of "8"-shaped hatching influences inner cell mass formation in mouse blastocysts

The hatching of a blastocyst where the blastocyst portions on the inside and the outside of the zona pellucida feature a figure-of-eight shape is termed “8”-shaped hatching; this type of hatching has been reported to affect the proper presentation of the inner cell mass (ICM) in both human and mouse embryos. Here, our aim was to investigate the factors that affect ICM presentation during “8”-shaped hatching. We performed IVF by using B6D2F1 female mice and ICR male mice, and used the 104 captured blastocysts. Embryos were maintained in KSOM at 37°C in a 5% CO₂, 5% O₂, and 90% N₂ environment, and their growth behavior was monitored individually and continuously using time-lapse cinematography. At 120 h after insemination, embryos were immunostained and examined under a confocal microscope. We used the hatching form to identify “8”-shaped hatching, and we classified the “8”-shaped-hatching blastocysts into two groups, one in which the hatching site was near the ICM center, and the other in which the hatching site was far from the ICM center. We measured each group for ICM size and the number of Oct3/4-positive cells. Of the 95 hatching or hatched embryos, 74 were “8”-shaped-hatching blastocysts, and in these embryos, the ICM was significantly wider when the hatching site was near the ICM than when the hatching site was far from the ICM (P = 0.0091). Moreover, in the “8”-shaped-hatching blastocysts in which the ICM was included in the blastocyst portion outside the zona pellucida―the portion defined as the “outside blastocyst”―after the collapse of this outside blastocyst, the ICM adhered to the trophectoderm of the outside blastocyst, opposite the hatching site. Our results indicate that in “8”-shaped-hatching blastocysts, the hatching site and the collapse of outside blastocyst affect ICM formation. Thus, the assessment of “8”-shaped hatching behaviors could yield indices for accurately evaluating embryo quality.

Prediction of blastocyst development and implantation potential in utero based on the third cleavage and compaction times in mouse pre-implantation embryos

Cytokinesis and cell division during pre-implantation embryonic development occur as an orchestrated spatiotemporal program. Cleavage, compaction, and blastulation in pre-implantation embryos are essential for successful implantation and pregnancy. Their alteration is associated with chromosomal imbalance and loss of developmental competence. In this study, we evaluated the time of cleavage and compaction as predictors for in vitro pre- and peri-implantation development and in utero implantation potential by time-lapse monitoring. Mouse 2-cell embryos were collected on 1.5 days post coitum (dpc) and were individually cultured to the outgrowth (OG) stage (7.5 dpc). Developmental stages were classified as 3-cell, 4-cell, 8-cell, morula, blastocyst, and OG. Cut-off times for successful blastocyst development were determined by receiver operating characteristic curve analysis. When cut-off times were set as 9 h for the third cleavage from the 2- to 4-cell stage, and 40 h for compaction from the 2-cell to morula stage, blastocyst and OG development rates, respectively, were significantly higher (P < 0.0001). Embryos were grouped according to the above cut-off time and transferred to the contralateral uterine horn on 3.5 dpc. Implantation rates in utero on 5.5 dpc were significantly higher in early third cleaved (≤ 9 h from 2- to 4-cell) and early compacted embryos (≤ 40 h from 2-cell to morula) than those in delayed embryos (P < 0.05). Therefore, the time of the third cleavage from 2- to the 4-cell stage and compaction from 2-cell to morula stage may be a useful morphokinetic parameter for predicting developmental potential, including successful implantation and pregnancy in human in vitro fertilization-embryo transfer programs.

Time-lapse monitoring reveals that vitrification increases the frequency of contraction during the pre-hatching stage in mouse embryos

Contraction during the blastocyst stage is observed during embryonic development of various mammals, including humans, but the physiological role of this process is not well understood. Using time-lapse monitoring (TLM), we studied the influence of vitrification and contractions on embryonic development in mice. Mouse embryos were cultured at the 2-cell stage. At the 8-cell stage, embryos were randomly divided into a fresh group (FG) and vitrified group (VG) and observed for up to 144 h. Strong contractions (i.e., contractions causing a decrease in volume of more than 20% and expansion of the perivitelline space) occurred significantly more often in unhatched embryos than hatching embryos in both groups. Regarding hatching embryos, contractions in the pre-hatching stage were significantly more frequent in the VG than the FG. Furthermore, mRNA expression levels of genes related to contractions were determined at three time points, the 8-cell stage, early blastocyst stage, and 20 h after blastocoel formation, with quantitative reverse transcription-polymerase chain reaction. There was no significant difference in Hspa1a expression between the FG and VG, but Hspa1a overexpression was observed just after thawing and tended to decrease gradually thereafter in some blastocysts. Furthermore, in the VG, Atp1a1 tended to show higher expression in the strong contraction group than in the weak contraction group. Overall, vitrification is an excellent method for cryopreservation but could increase contractions in the pre-hatching stage and may increase energy demands of the embryo. Observation of contraction by TLM may improve the evaluation of embryo quality.

Collapse of blastocysts is strongly related to lower implantation success: a time-lapse study

STUDY QUESTION

Is there an association between blastocyst collapse patterns and implantation potential?

SUMMARY ANSWER

Embryos that exhibit collapse are as likely to hatch as those that do not, but are less likely to implant and should not be replaced if alternatives are available.

WHAT IS KNOWN ALREADY

Studies of blastocyst collapse in different species of mammals have found that most blastocysts, that experience consecutive weak contractions, hatch successfully whereas those that exhibit strong contractions or collapse, fail to hatch.

STUDY DESIGN, SIZE, DURATION

Retrospective cohort study. Seven hundred and fifteen transferred blastocysts were analyzed from July 2012 to May 2013.

PARTICIPANTS/MATERIALS, SETTING, METHODS

University-affiliated infertility center. Participant patients were recipients of oocyte donation and autologous IVF cycles (n = 460). Embryo development was analyzed with a time-lapse imaging system. Variables studied included blastocyst collapse (defined as the separation of ≥50% of the surface of the trophectoderm of the blastocyst from the zona pellucida), kinetic variables, embryo morphology, implantation and clinical pregnancy rates.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 139 blastocysts presented collapse (19.4%), of these 8 presented 2 collapses and 2 presented 3 collapses. The timings of embryo cleavages and the time taken to reach the morula stage and blastulation were significantly shorter in embryos with collapse than in those without. Implantation rates were compared in cycles where either all or none of the embryos replaced, implanted so that implantation data were known for every embryo. Among 408 embryos without collapse and 94 embryos with at least one collapse (94) the implantation rates were 48.5% (95% confidence intervals (CI) 46.7-53.4%) and 35% (95% CI 25.3-44.9%), respectively. The percentage of embryos that hatched was similar in both groups 28.7 and 31%, respectively.

LIMITATIONS, REASONS FOR CAUTION

The retrospective nature of the study limits its potential value.

WIDER IMPLICATIONS OF THE FINDINGS

Study the collapse pattern of the blastocyst, may assist selection of the blastocysts most likely to implant and increase IVF/ICSI success rates.

Dysfunction in gap junction intercellular communication induces aberrant behavior of the inner cell mass and frequent collapses of expanded blastocysts in mouse embryos

PURPOSE

We investigated the role of gap junctions (GJs) in embryological differentiation, and observed the morphological behavior of the inner cell mass (ICM) by time-lapse movie observation (TLM) with gap junction inhibitors (GJis).

METHODS

ICR mouse embryos were exposed to two types of GJis in CZB medium: oleamide (0 to 50 μM) and 1-heptanol (0 to 10 mM). We compared the rate of blastocyst formation at embryonic day 4.5 (E4.5) with E5.5. We also observed and evaluated the times from the second cleavage to each embryonic developing stage by TLM. We investigated embryonic distribution of DNA, Nanog protein, and Connexin 43 protein with immunofluorescent staining.

RESULTS

In the comparison of E4.5 with E5.5, inhibition of gap junction intercellular communication (GJIC) delayed embryonic blastocyst formation. The times from the second cleavage to blastocyst formation were significantly extended in the GJi-treated embryos (control vs with oleamide, 2224 ± 179 min vs 2354 ± 278 min, p = 0.013). Morphological differences were traced in control versus GJi-treated embryos until the hatching stage. Oleamide induced frequent severe collapses of expanded blastocysts (77.4 % versus 26.3 %, p = 0.0001) and aberrant ICM divisions connected to sticky strands (74.3 % versus 5.3 %, p = 0.0001). Immunofluorescent staining indicated Nanog-positive cells were distributed in each divided ICM.

CONCLUSIONS

GJIC plays an important role in blastocyst formation, collapses of expanded blastocysts, and the ICM construction in mouse embryos.

Microwells support high-resolution time-lapse imaging and development of preimplanted mouse embryos

A vital aspect affecting the success rate of in vitro fertilization is the culture environment of the embryo. However, what is not yet comprehensively understood is the affect the biochemical, physical, and genetic requirements have over the dynamic development of human or mouse preimplantation embryos. The conventional microdrop technique often cultures embryos in groups, which limits the investigation of the microenvironment of embryos. We report an open microwell platform, which enables micropipette manipulation and culture of embryos in defined sub-microliter volumes without valves. The fluidic environment of each microwell is secluded from others by layering oil on top, allowing for non-invasive, high-resolution time-lapse microscopy, and data collection from each individual embryo without confounding factors. We have successfully cultured mouse embryos from the two-cell stage to completely hatched blastocysts inside microwells with an 89% success rate (n = 64), which is comparable to the success rate of the contemporary practice. Development timings of mouse embryos that developed into blastocysts are statistically different to those of embryos that failed to form blastocysts (p-value < 10(-10), two-tailed Student's t-test) and are robust indicators of the competence of the embryo to form a blastocyst in vitro with 94% sensitivity and 100% specificity. Embryos at the cleavage- or blastocyst-stage following the normal development timings were selected and transferred to the uteri of surrogate female mice. Fifteen of twenty-two (68%) blastocysts and four of ten (40%) embryos successfully developed into normal baby mice following embryo transfer. This microwell platform, which supports the development of preimplanted embryos and is low-cost, easy to fabricate and operate, we believe, opens opportunities for a wide range of applications in reproductive medicine and cell biology.

Possible selection of viable human blastocysts after vitrification by monitoring morphological changes

PURPOSE

Morphological assessment of human blastocysts has been effective for selecting embryos with high potential. However, they often show repeated shrinkage and expansion toward their hatching. Here we assessed whether capturing morphological changes over time of vitrified-warmed blastocysts could lead to a better selection of viable embryos from shrunken blastocysts.

METHODS

The implantation rates of vitrified-warmed blastocysts that were shrunken or expanded (developing) at the time of loading for transfer were compared among 2,729 cycles that were subjected to single blastocyst transfer. Vitrified (107) and fresh blastocysts (17) were donated for the experimental study. To assess the relationship between morphology (expanded vs. shrunken) and the mitochondrial respiration of blastocysts, the oxygen consumption rate (OCR) was analyzed for 55 specimens using an uncoupler of oxidative phosphorylation. The remaining 69 blastocysts were used for recording morphological changes every 15 min for 48 h after warming.

RESULTS

Because there were no surplus embryos, 7 % of the vitrified-warmed blastocysts were shrunken and transferred. The shrunken embryos had sufficient implantation ability (40 %). The OCR of the shrunken embryos was significantly lower than that of their expanded counterparts. Upon exposure to the uncoupler, the OCR of some shrunken embryos increased to levels similar to the expanded specimens. Time-lapse images revealed some shrunken embryos which formed blastocoel by 5 h following warming exhibited developmental competence to the hatched stage.

CONCLUSIONS

Data of the present study suggest a group of shrunken blastocysts contains many viable and clinically available embryos and time-lapse observation of vitrified-warmed blastocysts is a potential method to distinguish viable embryos from shrunken blastocysts.

Time-lapse observations to analyze the effects of assisted hatching

Purpose

Assisted hatching (AH) is an artificial disruption of the zona pellucida with the aim of facilitating embryo implantation. We used time-lapse observations of mouse embryos to examine the effect of AH in mouse blastocysts.

Methods

AH techniques were performed with acid Tyrode's solution. We compared the rates of blastocyst formation and blastocyst attachment to Ishikawa cells between the control (n = 28) and the AH group (n = 24). To analyze the effects of AH, 8-cell mice embryos were cultured under time-lapse observations (every 15 min). The time required for hatching, the hatching rates, the frequency of contraction, and the contraction rates in the blastocysts were analyzed.

Results

There were no significant differences between the two groups in hatching rate or attachment rate. The times required for hatching were 286 ± 22 min in the AH group and 990 ± 437 min in the control group (P = 0.018). The contraction frequencies in blastocysts were 3.5 ± 0.7 times in the AH group and 7.5 ± 2.5 times in the control group (P = 0.020).

Conclusions

From the time-lapse observations we found that the time required for hatching and the frequency of contraction in blastocysts were both reduced by AH, although blastocyst formation and attachment were not affected.

The timing of monozygotic twinning: a criticism of the common model

In the dominant model, monozygotic (MZ) twinning is universally accepted as a post-fertilization event resulting from splitting of the embryo along its first 2 weeks of development. The stage at which splitting occurs determines chorionicity and amnionicity. A short history on how the model was built is presented, stressing the role played by some embryologists, in particular George Corner, in its completion and final success. Strikingly, for more than 60 years no deep criticisms have been raised against the model, which, in virtue of its rational and plausible character, enjoys the status of undisputed truth. At close examination, the embryological support of the model shows some important weak points, particularly when dealing with late splitting. In the author's view, the model not only has contributed to 'suspend' our knowledge on the timing of MZ twinning, but seems indefensible and claims to be substituted. That factor could imply relevant consequences for embryology and bioethics. As an alternative to the model, a new theory to explain the timing of MZ twinning is proposed. It is based on two premises. First, MZ twinning would be a fertilization event. In that case, due to an alteration of the zygote-blastomere transition, the first zygotic division, instead of producing two blastomeres, generates twin zygotes. Second, monochorionicity and monoamnionicity would not depend on embryo splitting, but on fusion of membranes. Some support for this theory can be found in recent embryological advances and also in some explanations of old.

Hatching and distribution of actin filaments in mouse blastocysts whose activities of protein kinase A were suppressed by H-89

The role of actin filaments and contractions in hatching was determined in mouse blastocysts whose actin filament bundling abilities had been suppressed by H-89, an inhibitor of protein kinase A. The hatching rate of blastocysts developed from morulae in a medium containing H-89 at a concentration of 4.0 microM was 17.2%, which was significantly lower than the 76.7% of the control blastocysts developed from morulae in a medium without H-89. The rates of blastocysts starting hatching and forming a slit in the zona pellucida were significantly lower in H-89-treated blastocysts (84.4 and 21.9%) than in control blastocysts (100.0 and 90.6%). The lengths of time needed for slit formation in the zona pellucida and for completion of hatching were significantly longer in the H-89-treated blastocysts (27.4 and 43.3 h) than in the control blastocysts (6.5 and 18.8 h). Over the course of 32 h after blastocoel formation, the number of strong contractions was similar in the H-89-treated and control blastocysts, but the number of weak contractions was significantly fewer in the H-89-treated blastocysts (2.41 times) than in the control blastocysts (4.19 times). Although the distribution of actin filaments was similar in the H-89-treated and control blastocysts in the pre-hatching, hatching and post-hatching periods, the rate of H-89-treated blastocysts in which most trophectoderm cells possessed the fluorescence of actin filaments (12.7%) was significantly lower than the 95.0% of the control blastocysts in the pre-hatching period. These results suggest that actin filament-mediated movements of trophectoderm cells contribute to hatching by facilitating the protrusion of trophectoderm cells from a small hole in the zona pellucida and by enlarging the protrusion. We also suggest that the low hatching ability of the treated blastocysts is related to weak contractions with a low frequency and to strong contractions requiring a longer time for re-expansion.

A physiological role of contractions in hatched mouse blastocysts

Purpose

Using mouse blastocysts with implantation delayed for 7 days (dormant blastocysts) and time-lapse videomicrography, we examined the physiological role of contractions in hatched blastocysts.

Methods

The degree and number of contractions in dormant blastocysts were analyzed in images recorded for 48 h of culture, and compared with those in dormant blastocysts in which implantation was induced (activated blastocysts), and dormant blastocysts cultured with estrogen or progesterone.

Results

Activated blastocysts exhibited a significantly smaller number of weak contractions and a significantly larger number of strong contractions, compared with dormant blastocysts. Furthermore, the numbers of weak and strong contractions in dormant blastocysts cultured with estradiol-17β were significantly less frequent or more frequent than those in dormant blastocysts cultured with progesterone and those cultured without steroids. Expression of estrogen receptor mRNA was also detected in dormant blastocysts by the method of reverse transcription-polymerase chain reaction.

Conclusion

These results suggested that activated blastocysts enhance the contractions as a preparation for the implantation, and that the enhanced contractions in those serve as a physical stimulation for maternal recognition of pregnancy.

Identification and expression analysis of genes associated with bovine blastocyst formation

BACKGROUND

Normal preimplantation embryo development encompasses a series of events including first cleavage division, activation of the embryonic genome, compaction and blastocyst formation. First lineage differentiation starts at the blastocyst stage with the formation of the trophectoderm and the inner cell mass. The main objective of this study was the detection, identification and expression analysis of genes associated with blastocyst formation in order to help us better understand this process. This information could lead to improvements of in vitro embryo production procedures.

RESULTS

A subtractive cDNA library was constructed enriched for transcripts preferentially expressed at the blastocyst stage compared to the 2-cell and 8-cell stage. Sequence information was obtained for 65 randomly selected clones. The RNA expression levels of 12 candidate genes were determined throughout 3 stages of preimplantation embryo development (2-cell, 8-cell and blastocyst) and compared with the RNA expression levels of in vivo "golden standard" embryos using real-time PCR. The RNA expression profiles of 9 (75%) transcripts (KRT18, FN1, MYL6, ATP1B3, FTH1, HINT1, SLC25A5, ATP6V0B, RPL10) were in agreement with the subtractive cDNA cloning approach, whereas for the remaining 3 (25%) (ACTN1, COPE, EEF1A1) the RNA expression level was equal or even higher at the earlier developmental stages compared to the blastocyst stage. Moreover, significant differences in RNA expression levels were observed between in vitro and in vivo produced embryos. By immunofluorescent labelling, the protein expression of KRT18, FN1 and MYL6 was determined throughout bovine preimplantation embryo development and showed the same pattern as the RNA expression analyses.

CONCLUSION

By subtractive cDNA cloning, candidate genes involved in blastocyst formation were identified. For several candidate genes, important differences in gene expression were observed between in vivo and in vitro produced embryos, reflecting the influence of the in vitro culture system on the embryonic gene expression. Both RNA and protein expression analysis demonstrated that KRT18, FN1 and MYL6 are differentially expressed during preimplantation embryo development and those genes can be considered as markers for bovine blastocyst formation.