Impact of a controlled culture temperature gradient on mouse embryo development and morphokinetics

Metabolic regulation of preimplantation embryo development in vivo and in vitro: Molecular mechanisms and insights

Understanding of embryonic development has led to the clinical application of Assisted Reproductive technologies (ART), with the resulting birth of millions of children. Recent developments in metabolomics, proteomics, and transcriptomics have brought to light new insights into embryonic growth dynamics, with implications spanning reproductive medicine, stem cell research, and regenerative medicine. The review explores the key metabolic processes and molecular pathways active during preimplantation embryo development, including PI3K-Akt, mTOR, AMPK, Wnt/β-catenin, TGF-β, Notch and Jak-Stat signaling pathways. We focused on analyzing the differences occurring in vitro as opposed to in vivo development and we discussed significant physiological and clinical implications.

Machine learning in time-lapse imaging to differentiate embryos from young vs old mice†

Time-lapse microscopy for embryos is a non-invasive technology used to characterize early embryo development. This study employs time-lapse microscopy and machine learning to elucidate changes in embryonic growth kinetics with maternal aging. We analyzed morphokinetic parameters of embryos from young and aged C57BL6/NJ mice via continuous imaging. Our findings show that aged embryos accelerated through cleavage stages (from 5-cells) to morula compared to younger counterparts, with no significant differences observed in later stages of blastulation. Unsupervised machine learning identified two distinct clusters comprising of embryos from aged or young donors. Moreover, in supervised learning, the extreme gradient boosting algorithm successfully predicted the age-related phenotype with 0.78 accuracy, 0.81 precision, and 0.83 recall following hyperparameter tuning. These results highlight two main scientific insights: maternal aging affects embryonic development pace, and artificial intelligence can differentiate between embryos from aged and young maternal mice by a non-invasive approach. Thus, machine learning can be used to identify morphokinetics phenotypes for further studies. This study has potential for future applications in selecting human embryos for embryo transfer, without or in complement with preimplantation genetic testing.

Temperature fluctuations during embryo transfer can be mitigated by optimizing transfer protocol

RESEARCH QUESTION

What impact do variations in embryo transfer catheter loading and movement procedures have on temperature and pH fluctuations during embryo transfer?

DESIGN

Mock embryo transfers were conducted to test the impact of air flow/movement, use of catheter coverings, and the type of workstation used for catheter loading on catheter temperature. A thermocouple probe inserted into the tip of the outer catheter or taped to the exterior of the inner catheter recorded temperature within the catheter every 5 s from time of mock embryo loading (TL) to 60 s (TL + 60 s) or from the start of transit (TT). Fluctuations in culture medium pH in embryo transfer dishes were monitored.

RESULTS

The rate of cooling during transit was faster (all P < 0.05) when catheters were uncovered compared with all covering methods tested. This resulted in a lower catheter temperature at TL + 20 s (28.43 ± 0.30 °C) compared with catheters covered by plastic tubing (31.4 ± 0.30 °C), paper (31.0 ± 0.26 °C) or paper + thumb (31.1 ± 0.78 °C; all P ≤ 0.05). Temperature was maintained more effectively when catheters were loaded in a crib compared with a heated stage, until initiation of transit, when the rate of temperature decrease was similar. Culture medium pH increased more rapidly when embryo transfer dishes remained on a heated stage during the procedure compared with in an open crib.

CONCLUSIONS

Temperature loss during the embryo transfer procedure can be mitigated by reducing the transit time and using catheter coverings. Use of a crib for catheter loading only improved temperature stability while the catheter remained in the crib, not during transit, and reduced pH fluctuations during the procedure.

A feedback-driven IoT microfluidic, electrophysiology, and imaging platform for brain organoid studies

The analysis of tissue cultures, particularly brain organoids, takes a high degree of coordination, measurement, and monitoring. We have developed an automated research platform enabling independent devices to achieve collaborative objectives for feedback-driven cell culture studies. Unified by an Internet of Things (IoT) architecture, our approach enables continuous, communicative interactions among various sensing and actuation devices, achieving precisely timed control of in vitro biological experiments. The framework integrates microfluidics, electrophysiology, and imaging devices to maintain cerebral cortex organoids and monitor their neuronal activity. The organoids are cultured in custom, 3D-printed chambers attached to commercial microelectrode arrays for electrophysiology monitoring. Periodic feeding is achieved using programmable microfluidic pumps. We developed computer vision fluid volume estimations of aspirated media, achieving high accuracy, and used feedback to rectify deviations in microfluidic perfusion during media feeding/aspiration cycles. We validated the system with a 7-day study of mouse cerebral cortex organoids, comparing manual and automated protocols. The automated experimental samples maintained robust neural activity throughout the experiment, comparable with the control samples. The automated system enabled hourly electrophysiology recordings that revealed dramatic temporal changes in neuron firing rates not observed in once-a-day recordings.

The Clockwork Embryo: Mechanisms Regulating Developmental Rate

Organismal development requires the reproducible unfolding of an ordered sequence of discrete steps (cell fate determination, migration, tissue folding, etc.) in both time and space. Here, we review the mechanisms that grant temporal specificity to developmental steps, including molecular clocks and timers. Individual timing mechanisms must be coordinated with each other to maintain the overall developmental sequence. However, phenotypic novelties can also arise through the modification of temporal patterns over the course of evolution. Two main types of variation in temporal patterning characterize interspecies differences in developmental time: allochrony, where the overall developmental sequence is either accelerated or slowed down while maintaining the relative duration of individual steps, and heterochrony, where the duration of specific developmental steps is altered relative to the rest. New advances in in vitro modeling of mammalian development using stem cells have recently enabled the revival of mechanistic studies of allochrony and heterochrony. In both cases, differences in the rate of basic cellular functions such as splicing, translation, protein degradation, and metabolism seem to underlie differences in developmental time. In the coming years, these studies should identify the genetic differences that drive divergence in developmental time between species.

The effect of discrete wavelengths of visible light on the developing murine embryo

PURPOSE

A current focus of the IVF field is non-invasive imaging of the embryo to quantify developmental potential. Such approaches use varying wavelengths to gain maximum biological information. The impact of irradiating the developing embryo with discrete wavelengths of light is not fully understood. Here, we assess the impact of a range of wavelengths on the developing embryo.

METHODS

Murine preimplantation embryos were exposed daily to wavelengths within the blue, green, yellow, and red spectral bands and compared to an unexposed control group. Development to blastocyst, DNA damage, and cell number/allocation to blastocyst cell lineages were assessed. For the longer wavelengths (yellow and red), pregnancy/fetal outcomes and the abundance of intracellular lipid were investigated.

RESULTS

Significantly fewer embryos developed to the blastocyst stage when exposed to the yellow wavelength. Elevated DNA damage was observed within embryos exposed to blue, green, or red wavelengths. There was no effect on blastocyst cell number/lineage allocation for all wavelengths except red, where there was a significant decrease in total cell number. Pregnancy rate was significantly reduced when embryos were irradiated with the red wavelength. Weight at weaning was significantly higher when embryos were exposed to yellow or red wavelengths. Lipid abundance was significantly elevated following exposure to the yellow wavelength.

CONCLUSION

Our results demonstrate that the impact of light is wavelength-specific, with longer wavelengths also impacting the embryo. We also show that effects are energy-dependent. This data shows that damage is multifaceted and developmental rate alone may not fully reflect the impact of light exposure.

The effects of temperature variation treatments on embryonic development: a mouse study

Since the development of ART, embryos have been cultured at 37 °C in an attempt to mimic the in vivo conditions and the average body temperature of an adult. However, a gradient of temperatures within the reproductive tract has been demonstrated in humans and several other mammalian species. Therefore, the aim of this study was to evaluate the effects of temperature variation treatments on mouse embryo quality through morphokinetic events, blastocyst morphology, the relative gene expression of Igf2, Bax, Bcl2 and Apaf1 and the metabolomics of individual culture media. Study groups consisted of 2 circadian treatments, T1 with embryos being cultured at 37 °C during the day and 35.5 °C during the night, T2 with 38.5 °C during the day and 37 °C during the night and a control group with constant 37 °C. Our main findings are that the lower-temperature group (T1) showed a consistent negative effect on mouse embryo development with “slow” cleaving embryos, poor-quality blastocysts, a higher expression of the apoptotic gene Apaf1, and a significantly different set of amino acids representing a more stressed metabolism. On the other hand, our higher-temperature group (T2) showed similar results to the control group, with no adverse effects on blastocyst viability.

Optimised CO2-containing medium for in vitro culture and transportation of mouse preimplantation embryos without CO2 incubator

Conventional in vitro culture and manipulation of mouse embryos require a CO₂ incubator, which not only increases the cost of performing experiments but also hampers the transport of embryos to the other laboratories. In this study, we established and tested a new CO₂ incubator-free embryo culture system and transported embryos using this system. Using an Anaero pouch, which is a CO₂ gas-generating agent, to increase the CO₂ partial pressure of CZB medium to 4%–5%, 2-cell embryos were cultured to the blastocyst stage in a sealed tube without a CO₂ incubator at 37°C. Further, the developmental rate to blastocyst and full-term development after embryo transfer were comparable with those of usual culture method using a CO₂ incubator (blastocyst rate: 97% versus 95%, respectively; offspring rate: 30% versus 35%, respectively). Furthermore, using a thermal bottle, embryos were reliably cultured using this system for up to 2 days at room temperature, and live offspring were obtained from embryos transported in this simple and very low-cost manner without reducing the offspring rate (thermal bottle: 26.2% versus CO₂ incubator: 34.3%). This study demonstrates that CO₂ incubators are not essential for embryo culture and transportation and that this system provides a useful, low-cost alternative for mouse embryo culture and manipulation.

Focus on time-lapse analysis: blastocyst collapse and morphometric assessment as new features of embryo viability

The main goal of assisted reproductive technology (ART) is to achieve a healthy singleton live birth after the transfer of one embryo. A major objective of IVF scientists has always been to use adequate criteria for selecting the embryo for transfer according to its implantation potential. Indeed, embryo quality is usually assessed by evaluating visual morphology, which relies on the removal of the embryo from the incubator and might include inter- and intra-evaluator variation among embryologists. Recently, an advancement in embryo culture has taken place with the introduction of a new type of incubator with an integrated time-lapse monitoring system, which enables embryologists to analyse the dynamic events of embryo development from fertilization to blastocyst formation. This novel practice is rapidly growing and has been used in many IVF centres worldwide. Therefore, the main aim of this review is to present the benefits of time-lapse monitoring in a modern embryology laboratory; in particular, we discuss blastocyst collapse and morphometric blastocyst assessment, and analyse their association with embryo viability and implantation potential. In addition, we highlight preliminary studies involving artificial intelligence and machine learning models as non-invasive markers of clinical pregnancy.

Electrofusion Stimulation Is an Independent Factor of Chromosome Abnormality in Mice Oocytes Reconstructed via Spindle Transfer

Oocytes reconstructed by spindle transfer (ST) are prone to chromosome abnormality, which is speculated to be caused by mechanical interference or premature activation, the mechanism is controversial. In this study, C57BL/6N oocytes were used as the model, and electrofusion ST was performed under normal conditions, Ca²⁺ free, and at room temperature, respectively. The effect of enucleation and electrofusion stimulation on MPF activity, spindle morphology, γ-tubulin localization and chromosome arrangement was compared. We found that electrofusion stimulation could induce premature chromosome separation and abnormal spindle morphology and assembly by decreasing the MPF activity, leading to premature activation, and thus resulting in chromosome abnormality in oocytes reconstructed via ST. Electrofusion stimulation was an independent factor of chromosome abnormality in oocytes reconstructed via ST, and was not related to enucleation, fusion status, temperature, or Ca²⁺. The electrofusion stimulation number should be minimized, with no more than 2 times being appropriate. As the electrofusion stimulation number increased, several typical abnormalities in chromosome arrangement and spindle assembly occurred. Although blastocyst culture could eliminate embryos with chromosomal abnormalities, it would significantly decrease the number of normal embryos and reduce the availability of embryos. The optimum operating condition for electrofusion ST was the 37°C group without Ca²⁺.

Blastulation rates of sibling oocytes in two IVF culture media: an evidence-based workflow to implement newly commercialized products

RESEARCH QUESTION

An evidence-based novel commercially available continuous IVF culture medium in compliance with an efficient quality-management system is proposed.

DESIGN

Non-interventional study on sibling oocytes. Intracytoplasmic sperm injection cycles among women aged 42 years or younger that used ejaculated spermatozoa and retrieved four to eight oocytes were included. Sibling oocytes were randomized for culture in the novel Geri-medium or continuous single culture medium (CSCM). Primary outcome measure was blastulation rate per cohort of inseminated oocytes; 1182 oocytes were required to outline down to a 7% difference (power = 80%).

RESULTS

A total of 181 cohorts of sibling oocytes were included. Geri-medium (n = 631 oocytes) and CSCM (n = 643 oocytes) resulted in similar blastulation rates (mean ± SD: 42.8% ± 30.1% versus 43.1% ± 29.0%; Wilcoxon signed rank test = 0.77). Blastocysts cultured in the former (n = 275 versus n = 277) showed longer timings during preimplantation development (P < 0.01) and were poorer quality (26% versus 18%; P = 0.03). Euploidy rate was no different in cycles that underwent preimplantation genetic testing for aneuploidy (n = 113) (117/237 [49%] versus 117/249 blastocysts [47%]; P = 0.6). Ongoing implantation rate was comparable in the study arms after euploid (29/47 [63%] versus 14/ 34 [41%]; P = 0.1) or untested (12/31 [39%] versus 7/18 [39%]; P = 0.3) transfers.

CONCLUSION

Blastulation rate among cohorts of sibling oocytes cultured in the same incubator is a fast, reliable and comprehensive performance indicator to validate novel commercially available culture medium. The media tested were considered similarly efficient. The differences in blastocyst morphology and developmental timings warrant further investigation, although euploidy and ongoing implantation rates were similar.

Assessment of embryo implantation potential with a cloud-based automatic software

RESEARCH QUESTION

Is embryo selection by Dana (automatic software for embryo evaluation) associated with a higher implantation rate in IVF treatments?

DESIGN

A three-phase study for Dana system's validation: creation of a data-cloud of known implantation data (KID) embryos from 1676 transferred embryos; embryo evaluation by Dana considering manual annotations and embryo development videos (389 transferred embryos); and validation of Dana automatic selection, without embryologist's intervention (147 transferred embryos); RESULTS: The implantation rate of the 1021 KID embryos from phase 1 served to set four grades of embryos referring to implantation rate: A = 34%, B = 25%, C = 24%, and D = 19%. Phase 2: a classification ranking according to the unit average distance (UAD) and implantation potential was established: top (UAD ≤0.50), high (UAD = 0.51-0.66), medium (UAD = 0.67-1.03) and low (UAD >1.03). Pregnancy rates were 59%, 46%, 36% and 28%, respectively (P < 0.001). Phase 3: embryos were automatically categorized according to Dana's classification ranking. Most implanted embryos were found in groups top, high and medium (UAD ≤1.03), whereas the implantation rate in group low (UAD >1.03) was significantly lower: 46% versus 25%, respectively (P = 0.037). The twin gestation rate was higher when number of top embryos (UAD ≤0.5) transferred were two (52%) versus one (25%) (P < 0.001).

CONCLUSIONS

Embryo selection based on Dana ranking increases the success of IVF treatments at least in oocyte donation programmes. The multicentre nature of the study supports its applicability at different clinics, standardizing the embryo development's interpretation. Dana's innovation is that the system increases its accuracy as the database grows.