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

Non-invasive evaluation of embryo quality for the selection of transferable embryos in human in vitro fertilization-embryo transfer

The ultimate goal of human assisted reproductive technology is to achieve a healthy pregnancy and birth, ideally from the selection and transfer of a single competent embryo. Recently, techniques for efficiently evaluating the state and quality of preimplantation embryos using time-lapse imaging systems have been applied. Artificial intelligence programs based on deep learning technology and big data analysis of time-lapse monitoring system during in vitro culture of preimplantation embryos have also been rapidly developed. In addition, several molecular markers of the secretome have been successfully analyzed in spent embryo culture media, which could easily be obtained during in vitro embryo culture. It is also possible to analyze small amounts of cell-free nucleic acids, mitochondrial nucleic acids, miRNA, and long non-coding RNA derived from embryos using real-time polymerase chain reaction (PCR) or digital PCR, as well as next-generation sequencing. Various efforts are being made to use non-invasive evaluation of embryo quality (NiEEQ) to select the embryo with the best developmental competence. However, each NiEEQ method has some limitations that should be evaluated case by case. Therefore, an integrated analysis strategy fusing several NiEEQ methods should be urgently developed and confirmed by proper clinical trials.

Effects of oxygen tension and humidity on the preimplantation development of mouse embryos produced by <i>in vitro</i> fertilization: analysis using a non-humidifying incubator with time-lapse cinematography

To examine the effects of oxygen tension and humidity on early embryonic development, the preimplantation development of mouse embryos produced by in vitro fertilization was assessed by time-lapse cinematography to evaluate morphokinetic development with higher precision. Zygotes were produced from spermatozoa and oocytes from ICR mice and cultured in KSOM under low or high oxygen tension in a non-humidified incubator with time-lapse cinematography (CCM-iBIS). The developmental rates of embryos to the 4-cell and blastocyst stages under lower oxygen tension in CCM-iBIS were significantly higher than those under higher oxygen tension in CCM-iBIS. Ninety-six hours after insemination, a large number of embryos cultured under low oxygen tension developed to the hatching blastocyst stage. Embryonic development was more synchronized under lower oxygen tension. Non-humidified cultures did not affect embryonic development. On average, mouse embryos cultured at lower oxygen tension reached 2-cell at 18 h, 3-cell at 39 h, 4-cell at 40 h, initiation of compaction at 58 h, morula at 69 h, and blastocyst at 82 h after insemination. In conclusion, lower oxygen tension better supports preimplantation development of mouse embryos fertilized in vitro, and non-humidified culture conditions do not influence the embryonic development in vitro.

Effect of nucleocytoplasmic ratio on the in vitro porcine embryo development after in vitro fertilization or parthenogenetic activation

This study was conducted to examine whether the nuclear to cytoplasmic (N/C) ratio had any influence on the timing of embryo compaction and blastocoel formation, as well as formation rate and quality of blastocyst. First, we produced embryos with increased N/C ratio by removal of approximately one-third of the cytoplasm and with decreased N/C ratio by doubling the oocyte cytoplasm with an enucleated oocyte. The initiation of compaction and cavitation in reduced cytoplasm group was significantly earlier (P < 0.05) compared with the control and doubled cytoplasm groups. The rate of blastocysts in the reduced cytoplasm and doubled cytoplasm groups was significantly lower (P < 0.05) compared with the control group. Blastocyst quality in terms of total cell number in the reduced cytoplasm group was significantly lower (P < 0.05) compared with the doubled cytoplasm group, but not different from the control group. Next, we produced embryos with various N/C ratios by oocyte fusion combined with cytochalasin D treatment. The onset of compaction and cavitation in the 2N/2C group (decreased N/C ratio) was significantly delayed (P < 0.05) or had the tendency to be delayed (P = 0.064), respectively, compared with the control group (2N/1C). A significantly higher rate of blastocyst was observed in the 4N/2C group compared with the 1N/1C group (P < 0.05) but not different from the remaining groups. These results demonstrated that an increase in N/C ratio caused an earlier occurrence of morula compaction and blastocyst formation in both in vitro fertilization (IVF) and parthenogenetically activated pig embryos.

Probing morphological, genetic and metabolomic changes of in vitro embryo development in a microfluidic device

Assisted reproduction technologies for clinical and research purposes rely on a brief in vitro embryo culture which, despite decades of progress, remain suboptimal in comparison to the physiological environment. One promising tool to improve this technique is the development of bespoke microfluidic chambers. Here we present and validate a new microfluidic device in polydimethylsiloxane (PDMS) for the culture of early mouse embryos. Device material and design resulted embryo compatible and elicit minimal stress. Blastocyst formation, hatching, attachment and outgrowth formation on fibronectin-coated devices were similar to traditional microdrop methods. Total blastocyst cell number and allocation to the trophectoderm and inner cell mass lineages were unaffected. The devices were designed for culture of 10-12 embryos. Development rates, mitochondrial polarization and metabolic turnover of key energy substrates glucose, pyruvate and lactate were consistent with groups of 10 embryos in microdrop controls. Increasing group size to 40 embryos per device was associated with increased variation in development rates and altered metabolism. Device culture did not perturb blastocyst gene expression but did elicit changes in embryo metabolome, which can be ascribed to substrate leaching from PDMS and warrant further investigation.

Mechanisms of human embryo development: from cell fate to tissue shape and back

Gene regulatory networks and tissue morphogenetic events drive the emergence of shape and function: the pillars of embryo development. Although model systems offer a window into the molecular biology of cell fate and tissue shape, mechanistic studies of our own development have so far been technically and ethically challenging. However, recent technical developments provide the tools to describe, manipulate and mimic human embryos in a dish, thus opening a new avenue to exploring human development. Here, I discuss the evidence that supports a role for the crosstalk between cell fate and tissue shape during early human embryogenesis. This is a critical developmental period, when the body plan is laid out and many pregnancies fail. Dissecting the basic mechanisms that coordinate cell fate and tissue shape will generate an integrated understanding of early embryogenesis and new strategies for therapeutic intervention in early pregnancy loss.

Advantages of the outgrowth model for evaluating the implantation competence of blastocysts

The implantation process is highly complex and difficult to mimic in vitro, and a reliable experimental model of implantation has yet to be established. Many researchers have used embryo transfer (ET) to assess implantation potential; however, ET with pseudopregnant mice requires expert surgical skills and numerous sacrificial animals. To overcome those economic and ethical problems, several researchers have tried to use outgrowth models to evaluate the implantation potential of embryos. Many previous studies, as well as our experiments, have found significant correlations between blastocyst outgrowth in vitro and implantation in utero by ET. This review proposes the blastocyst outgrowth model as a possible alternative to animal experimentation involving ET in utero. In particular, the outgrowth model might be a cost- and time-effective alternative method to ET for evaluating the effectiveness of culture conditions or treatments. An advanced outgrowth model and further culture of outgrowth embryos could provide a subtle research model of peri- and postimplantation development, excluding maternal effects, and thereby could facilitate progress in assisted reproductive technologies. Recently, we found that outgrowth embryos secreted extracellular vesicles containing specific microRNAs. The function of microRNAs from outgrowth embryos should be elucidated in further researches.

Effects of dynamic oxygen concentrations on the development of mouse pre- and peri-implantation embryos using a double-channel gas supply incubator system

Objective

We aimed to evaluate the effects of different oxygen conditions (20% [high O₂], 5% [low O₂] and 5% decreased to 2% [dynamic O₂]) on mouse pre- and peri-implantation development using a novel double-channel gas supply (DCGS) incubator (CNC Biotech Inc.) to alter the oxygen concentration during in vitro culture.

Methods

The high-O₂ and low-O₂ groups were cultured from the one-cell to the blastocyst stage under 20% and 5% oxygen concentrations, respectively. In the dynamic-O₂ group, mouse embryos were cultured from the one-cell to the morula stage under 5% O₂ for 3 days, followed by culture under 2% O₂ to the blastocyst stage. To evaluate peri-implantation development, the blastocysts from the three groups were individually transferred to a fibronectin-coated dish and cultured to the outgrowth stage in droplets.

Results

The blastocyst formation rate was significantly higher in the low-O₂ and dynamic-O₂ groups than in the high-O₂ group. The total cell number was significantly higher in the dynamic-O₂ group than in the low-O₂ and high-O₂ groups. Additionally, the apoptotic index was significantly lower in the low-O₂ and dynamic-O₂ groups than in the high-O₂ group. The trophoblast outgrowth rate and spread area were significantly higher in the low-O₂ and dynamic-O₂ groups than in the high-O₂ group.

Conclusion

Our results showed that a dynamic oxygen concentration (decreasing from 5% to 2%) had beneficial effects on mouse pre- and peri-implantation development. Optimized, dynamic changing of oxygen concentrations using the novel DCGS incubator could improve the developmental competence of in vitro cultured embryos in a human in vitro fertilization and embryo transfer program.

Are cleavage anomalies, multinucleation, or specific cell cycle kinetics observed with time-lapse imaging predictive of embryo developmental capacity or ploidy?

OBJECTIVE

To determine whether cleavage anomalies, multinucleation, and specific cellular kinetic parameters available from time-lapse imaging are predictive of developmental capacity or blastocyst chromosomal status.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

Single academic center.

PATIENT(S)

A total of 1,478 zygotes from patients with blastocysts biopsied for preimplantation genetic screening were cultured in the EmbryoScope.

INTERVENTION(S)

Trophectoderm biopsy.

MAIN OUTCOME MEASURE(S)

Embryo dysmorphisms, developmental kinetics, and euploidy.

RESULT(S)

Of the 767 biopsied blastocysts, 41.6% (95% confidence interval [CI], 38%-45%) were diagnosed as euploid. Individual dysmorphisms such as multinucleation, reverse cleavage, irregular chaotic division, or direct uneven cleavage were not associated with aneuploidy. Direct uneven cleavage and irregular chaotic division embryos did, however, exhibit lower developmental potential. The presence of two or more dysmorphisms was associated with an overall lower euploidy rate, 27.6% (95% CI 19%-39%). Early embryo kinetics were predictive of blastocyst development but not ploidy status. In contrast, chromosomal status correlated significantly with start time of blastulation (tSB), expansion (tEB), and the tEB-tSB interval. A lower euploidy rate, 36.6% (95% CI 33%-42%) was observed with tSB ≥ 96.2 hours, compared with 48.2% with tSB < 96.2 (95% CI 42%-54%). A drop in euploidy rate to 30% (95% CI 25%-37%) was observed in blastocysts with delayed expansion (tEB > 116). The proportion of euploid blastocysts was increased with tEB-tSB intervals of ≤13 hours. A logistic regression model to enhance the probability of selecting a euploid blastocyst was constructed.

CONCLUSION(S)

Morphokinetics may aid in selection of euploid embryos from a cohort of day 5/6 blastocysts.