Light intensity and wavelength during embryo manipulation are important factors for maintaining viability of preimplantation embryos in vitro

Shedding light on the ART laboratory

This commentary examines the impact of light conditions in the assisted reproductive technology (ART) laboratory, specifically considering gametes and embryo culture. While these processes traditionally occur in the absence of light within the female reproductive tract, laboratory conditions often involve exposure to varying wavelengths, intensities and light sources. Although literature reports describe potential detrimental effects of certain wavelengths of light on biological material, these findings are often based on experiments that might not reflect actual laboratory conditions. Current ART laboratory practices aim to minimize light exposure; however, some procedures necessitate light exposure, typically involving microscopy. Results from the authors' cross-sectional survey on light-intensity practices in ART laboratories revealed the frequent use of inadequate lighting, leading to errors and impacting staff well-being. A failure mode and effects analysis was used to identify potential failure modes and their impacts due to poor lighting. Overall, this manuscript stresses the importance of maintaining proper ambient lighting in the ART laboratory, balancing the potentially detrimental effects of light on gametes and embryos against the need for proper lighting for accurate procedures and staff well-being. Adequate lighting not only ensures the safety of reproductive cells, but also improves process management and the operators' psychological conditions.

Clinical Benefits of Decreased Photo-Oxidative Stress on Human Embryo Development

OBJECTIVE

Early embryonic development is characterized by rapid cell division and gene activation, making the embryo extremely sensitive to environmental influences. Light exposure can affect embryonic development through a direct toxic effect on the embryo via the generation of reactive oxygen species. In a previous study, we demonstrated the positive effect of improved light-protected embryo culture conditions implemented in our laboratory. This study aimed to investigate the changes in human embryo development under light protection during the conventional in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI).

MATERIALS AND METHODS

We tested the potential beneficial effect of light filters to reduce the risk of toxic effects of light. IVF outcomes were compared between two experimental conditions, light protection with red light filters versus no light protection as a control.

RESULTS

Blastocyst development rate in IVF was significantly higher in the light-protected group than in the group treated under conventional conditions (46.6 vs. 26.7%). In the case of ICSI, we obtained a similar result (44.5 vs. 31.6%). The rate of cryopreservation with at least one embryo was higher in the light-protected phase (32.8%) than in the conventionally manipulated phase (26.8%). The abortion rate was also significantly lower during the light-protected period in IVF, resulting in a higher live birth rate.

CONCLUSIONS

The implementation of light protection to reduce the embryotoxic wavelengths of light in IVF centers may improve the blastocyst development rate and embryo quality while maintaining embryo safety.

An Overview of Reactive Oxygen Species Damage Occurring during In Vitro Bovine Oocyte and Embryo Development and the Efficacy of Antioxidant Use to Limit These Adverse Effects

The in vitro production (IVP) of bovine embryos has gained popularity worldwide and in recent years and its use for producing embryos from genetically elite heifers and cows has surpassed the use of conventional superovulation-based embryo production schemes. There are, however, several issues with the IVP of embryos that remain unresolved. One limitation of special concern is the low efficiency of the IVP of embryos. Exposure to reactive oxygen species (ROS) is one reason why the production of embryos with IVP is diminished. These highly reactive molecules are generated in small amounts through normal cellular metabolism, but their abundances increase in embryo culture because of oocyte and embryo exposure to temperature fluctuations, light exposure, pH changes, atmospheric oxygen tension, suboptimal culture media formulations, and cryopreservation. When uncontrolled, ROS produce detrimental effects on the structure and function of genomic and mitochondrial DNA, alter DNA methylation, increase lipid membrane damage, and modify protein activity. Several intrinsic enzymatic pathways control ROS abundance and damage, and antioxidants react with and reduce the reactive potential of ROS. This review will focus on exploring the efficiency of supplementing several of these antioxidant molecules on oocyte maturation, sperm viability, fertilization, and embryo culture.

The Task Matters: A Comprehensive Review and Proposed Literature Score of the Effects of Chemical and Physical Parameters on Embryo Developmental Competence

To explore the effects of chemical and physical parameters on embryo developmental competence, we conducted a systematic search on PubMed for peer-reviewed original papers using specific keywords and medical subject heading terms. Studies of interest were selected from an initial cohort of 4141 potentially relevant records retrieved. The most relevant publications were critically evaluated to identify the effect of these parameters on embryo development. Moreover, we generated a literature score (LS) using the following procedure: (i) the number of studies favoring a reference group was expressed as a fraction of all analyzed papers; (ii) the obtained fraction was multiplied by 10 and converted into a decimal number. We identified and discussed six parameters (oxygen, temperature, humidity, oil overlay, light, pH). Moreover, we generated a LS according to five different comparisons (37 °C vs. <37 °C; 5% vs. 20% oxygen; 5-2% vs. 5% oxygen; humidity conditions vs. dry conditions; light exposure vs. reduced/protected light exposure). Only two comparisons (37 °C vs. <37 °C and 5% vs. 20% oxygen) yielded a medium-high LS (8.3 and 7, respectively), suggesting a prevalence of studies in favor of the reference group (37 °C and 5% oxygen). In summary, this review and LS methodology offer semi-quantitative information on studies investigating the effects of chemical and physical parameters on embryo developmental competence.

Long-Term Effects of ART on the Health of the Offspring

Assisted reproductive technologies (ART) significantly increase the chance of successful pregnancy and live birth in infertile couples. The different procedures for ART, including in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), intrauterine insemination (IUI), and gamete intrafallopian tube transfer (GIFT), are widely used to overcome infertility-related problems. In spite of its inarguable usefulness, concerns about the health consequences of ART-conceived babies have been raised. There are reports about the association of ART with birth defects and health complications, e.g., malignancies, high blood pressure, generalized vascular functional disorders, asthma and metabolic disorders in later life. It has been suggested that hormonal treatment of the mother, and the artificial environment during the manipulation of gametes and embryos may cause genomic and epigenetic alterations and subsequent complications in the health status of ART-conceived babies. In the current study, we aimed to review the possible long-term consequences of different ART procedures on the subsequent health status of ART-conceived offspring, considering the confounding factors that might account for/contribute to the long-term consequences.

Comparison of cattle derived from in vitro fertilization, multiple ovulation embryo transfer, and artificial insemination for milk production and fertility traits

The use of assisted-reproduction technologies such as in vitro fertilization (IVF) is increasing, particularly in dairy cattle. The question of consequences in later life has not yet been directly addressed by studies on large animal populations. Studies on rodents and early data from humans and cattle suggest that in vitro manipulation of gametes and embryos could result in long-term alteration of metabolism, growth, and fertility. Our goal was to better describe these presumed consequences in the population of dairy cows produced by IVF in Québec (Canada) and to compare them to animals conceived by artificial insemination (AI) or multiple ovulation embryo transfer (MOET). To do so, we leveraged a large phenotypic database (2.5 million animals and 4.5 million lactations) from milk records in Québec aggregated by Lactanet (Sainte-Anne-de-Bellevue, QC, Canada) and spanning 2012 to 2019. We identified 304,163, 12,993, and 732 cows conceived by AI, MOET, and IVF, respectively, for a total of 317,888 Holstein animals from which we retrieved information for 576,448, 24,192, and 1,299 lactations (total = 601,939), respectively. Genetic energy-corrected milk yield (GECM) and Lifetime Performance Index (LPI) of the parents of cows were used to normalize for genetic potential across animals. When compared with the general Holstein population, MOET and IVF cows outperformed AI cows. However, when comparing those same MOET and IVF cows with only herdmates and accounting for their higher GECM in the models, we found no statistical difference between the conception methods for milk production across the first 3 lactations. We also found that the rate of Lifetime Performance Index improvement of the IVF population during the 2012 to 2019 period was less than the rate observed in the AI population. Fertility analysis revealed that MOET and IVF cows also scored 1 point lower than their parents on the daughter fertility index and had a longer interval from first service to conception, with an average of 35.52 d compared with 32.45 for MOET and 31.87 for AI animals. These results highlight the challenges of elite genetic improvement while attesting to the progress the industry has made in minimizing epigenetic disturbance during embryo production. Nonetheless, additional work is required to ensure that IVF animals can maintain their performance and fertility potential.

Melatonin protects against visible light-induced oxidative stress and promotes the implantation potential of mouse blastocyst in vitro

Improvement of embryo culture media using antioxidant agents could help to improve embryo quality against environmental factors such as visible light and could overcome implantation failures. The usefulness of the melatonin against the effect of light on the expression of the primary implantation receptors, ErbB1 and ErbB4 on pre-implantation mouse embryo was investigated. Two-cell mouse embryos were exposed to the 1600 LUX light for 30 min then randomly divided into 3 groups including: Melatonin-Treated; Luzindole Treated and Simple media as a Control group. After 72-96  The expanded blastocysts were examined for morphological quality of the embryos by Hoechst and propidium iodide staining and for the expression of ErbB1 and ErbB4 by Real-time PCR and immunocytochemistry. The expression of the Sirt3 gene was also assayed. Furthermore, intracellular reactive oxygen species (ROS) levels and the total antioxidant capacity (TAC) were examined by DCFH-DA fluorescence intensity and radical cation respectively. The number of cells in the inner cell mass (ICM) and outer cell mass (OCM) were elevated significantly in the Melatonin-treated group suggesting increased viability and proliferation. Furthermore, we found that melatonin significantly increased the expression levels of ErbB1, ErbB4, and Sirt3 genes, and the protein expression of ErbB1, ErbB4 correlated with intracellular ROS levels and TAC significantly increased after melatonin treatment. Together, these results demonstrate that melatonin could be helpful to improve preimplantation embryos through its effects in decreasing ROS levels and increasing expression of implantation-related genes.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: Reactive oxygen species in the mammalian pre-implantation embryo

In brief

Reactive oxygen species are generated throughout the pre-implantation period and are necessary for normal embryo formation. However, at pathological levels, they result in reduced embryo viability which can be mediated through factors delivered by sperm and eggs at conception or from the external environment.

Abstract

Reactive oxygen species (ROS) occur naturally in pre-implantation embryos as a by-product of ATP generation through oxidative phosphorylation and enzymes such as NADPH oxidase and xanthine oxidase. Biological concentrations of ROS are required for crucial embryonic events such as pronuclear formation, first cleavage and cell proliferation. However, high concentrations of ROS are detrimental to embryo development, resulting in embryo arrest, increased DNA damage and modification of gene expression leading to aberrant fetal growth and health. In vivo embryos are protected against oxidative stress by oxygen scavengers present in follicular and oviductal fluids, while in vitro, embryos rely on their own antioxidant defence mechanisms to protect against oxidative damage, including superoxide dismutase, catalase, glutathione and glutamylcysteine synthestase. Pre-implantation embryonic ROS originate from eggs, sperm and embryos themselves or from the external environment (i.e. in vitro culture system, obesity and ageing). This review examines the biological and pathological roles of ROS in the pre-implantation embryo, maternal and paternal origins of embryonic ROS, and from a clinical perspective, we comment on the growing interest in combating increased oxidative damage in the pre-implantation embryo through the addition of antioxidants.

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.

Mysteries and unsolved problems of mammalian fertilization and related topics

Mammalian fertilization is a fascinating process that leads to the formation of a new individual. Eggs and sperm are complex cells that must meet at the appropriate time and position within the female reproductive tract for successful fertilization. I have been studying various aspects of mammalian fertilization over 60 years. In this review, I discuss many different aspects of mammalian fertilization, some of my laboratory's contribution to the field, and discuss enigmas and mysteries that remain to be solved.

Interplay of Oxidants and Antioxidants in Mammalian Embryo Culture System

One principal purpose of assisted reproductive technology (ART) is to produce viable and good quality embryos. However, a variety of environmental factors may induce epigenetic changes in the embryo. Moreover, laboratory conditions including the culture media may also affect embryo development. Therefore, media change is an important factor in maintaining proper oxidant/antioxidant balance during embryo culture. Alterations in the oxidant/antioxidant balance are related to various cellular responses such as an increase in the level of reactive oxygen species (ROS) and consequent lipid peroxidation (LPO), DNA damage, and apoptosis. The current study focuses on the role of external factors on embryo culture and the ability of antioxidants to enhance in vitro fertilization (IVF) outcomes. Indeed, an optimization of media culture by the addition of enzymatic and nonenzymatic antioxidants in animal models and human embryos in ART has been updated in this study, with an emphasis on comparing the available results and their possible reasons.

Non-invasive, label-free optical analysis to detect aneuploidy within the inner cell mass of the preimplantation embryo

STUDY QUESTION

Can label-free, non-invasive optical imaging by hyperspectral autofluorescence microscopy discern between euploid and aneuploid cells within the inner cell mass (ICM) of the mouse preimplantation embryo?

SUMMARY ANSWER

Hyperspectral autofluorescence microscopy enables discrimination between euploid and aneuploid ICM in mouse embryos.

WHAT IS KNOWN ALREADY

Euploid/aneuploid mosaicism affects up to 17.3% of human blastocyst embryos with trophectoderm biopsy or spent media currently utilized to diagnose aneuploidy and mosaicism in clinical in vitro fertilization. Based on their design, these approaches will fail to diagnose the presence or proportion of aneuploid cells within the foetal lineage ICM of some blastocyst embryos.

STUDY DESIGN, SIZE, DURATION

The impact of aneuploidy on cellular autofluorescence and metabolism of primary human fibroblast cells and mouse embryos was assessed using a fluorescence microscope adapted for imaging with multiple spectral channels (hyperspectral imaging). Primary human fibroblast cells with known ploidy were subjected to hyperspectral imaging to record native cell fluorescence (4-6 independent replicates, euploid n = 467; aneuploid n = 969). For mouse embryos, blastomeres from the eight-cell stage (five independent replicates: control n = 39; reversine n = 44) and chimeric blastocysts (eight independent replicates: control n = 34; reversine n = 34; 1:1 (control:reversine) n = 30 and 1:3 (control:reversine) n = 37) were utilized for hyperspectral imaging. The ICM from control and reversine-treated embryos were mechanically dissected and their karyotype confirmed by whole genome sequencing (n = 13 euploid and n = 9 aneuploid).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two models were employed: (i) primary human fibroblasts with known karyotype and (ii) a mouse model of embryo aneuploidy where mouse embryos were treated with reversine, a reversible spindle assembly checkpoint inhibitor, during the four- to eight-cell division. Individual blastomeres were dissociated from control and reversine-treated eight-cell embryos and either imaged directly or used to generate chimeric blastocysts with differing ratios of control:reversine-treated cells. Individual blastomeres and embryos were interrogated by hyperspectral imaging. Changes in cellular metabolism were determined by quantification of metabolic co-factors (inferred from their autofluorescence signature): NAD(P)H and flavins with the subsequent calculation of the optical redox ratio (ORR: flavins/[NAD(P)H + flavins]). Autofluorescence signals obtained from hyperspectral imaging were examined mathematically to extract features from each cell/blastomere/ICM. This was used to discriminate between different cell populations.

MAIN RESULTS AND THE ROLE OF CHANCE

An increase in the relative abundance of NAD(P)H and decrease in flavins led to a significant reduction in the ORR for aneuploid cells in primary human fibroblasts and reversine-treated mouse blastomeres (P < 0.05). Mathematical analysis of endogenous cell autofluorescence achieved separation between (i) euploid and aneuploid primary human fibroblast cells, (ii) control and reversine-treated mouse blastomeres cells, (iii) control and reversine-treated chimeric blastocysts, (iv) 1:1 and 1:3 chimeric blastocysts and (v) confirmed euploid and aneuploid ICM from mouse blastocysts. The accuracy of these separations was supported by receiver operating characteristic curves with areas under the curve of 0.97, 0.99, 0.87, 0.88 and 0.93, respectively. We believe that the role of chance is low as mathematical features separated euploid from aneuploid in both human fibroblasts and ICM of mouse blastocysts.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although we were able to discriminate between euploid and aneuploid ICM in mouse blastocysts, confirmation of this approach in human embryos is required. While we show this approach is safe in mouse, further validation is required in large animal species prior to implementation in a clinical setting.

WIDER IMPLICATIONS OF THE FINDINGS

We have developed an original, accurate and non-invasive optical approach to assess aneuploidy within the ICM of mouse embryos in the absence of fluorescent tags. Hyperspectral autofluorescence imaging was able to discriminate between euploid and aneuploid human fibroblast and mouse blastocysts (ICM). This approach may potentially lead to a new diagnostic for embryo analysis.

STUDY FUNDING/COMPETING INTEREST(S)

K.R.D. is supported by a Mid-Career Fellowship from the Hospital Research Foundation (C-MCF-58-2019). This study was funded by the Australian Research Council Centre of Excellence for Nanoscale Biophotonics (CE140100003) and the National Health and Medical Research Council (APP2003786). The authors declare that there is no conflict of interest.

Toxic effect of light on oocyte and pre-implantation embryo: a systematic review

In the female reproductive tract, oocytes and embryos are in a dark environment, while during the in vitro fertilization (IVF) they are exposed to various visible and invisible lights such as daylight, microscope, and laminar hood fluorescent lights. Studies have shown that light could damage cellular compartments of oocytes and embryos and consequently decrease rates of fertilization, development, and blastocyst formation. However, due to the lack of consensus about the effects of light on the embryos, and subsequently the inability to make definitive decisions regarding the light exposure management to improve IVF results, in the present study, we systematically reviewed the effect of light with different wavelengths and intensities on pre-implantation embryos. The toxic impact of light depends on the wavelength, intensity, and duration of light exposure and also the stage of embryo. Therefore, reducing the observation time of embryos out of the incubator and also using light filters can alleviate the detrimental effect of light in IVF labs.

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

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

Oxidative Stress in Oocytes and Embryo Development: Implications for In Vitro Systems

Significance: To improve the outcomes of in vitro culture of human oocytes and embryos, the dynamic balance and roles of reactive oxygen species (ROS) in folliculogenesis and embryo development merit further consideration. Recent Advances: ROS have been demonstrated to participate in various signaling processes and act as mediators in various physiological events in germ cells. An imbalance between pro-oxidants and antioxidants seems to explain the high failure rate of assisted reproduction. Critical Issues: Oxidative stress induced by excessive ROS or insufficient antioxidant protection can cause detrimental effects on both male and female reproduction. In this study, oxidative stress in folliculogenesis and embryo development are summarized and the multiple modifiable factors of in vitro culture systems in relation to ROS are discussed. Future Directions: More studies are needed to establish an optimal redox state in in vitro culture systems for human oocytes and embryos.

Elimination of stress factors by continuous embryo culture and its influence on in vitro fertilization outcomes

Recently, infertility has become one of the most important endemic conditions, affecting approximately 15-20 % of couples worldwide. Among others, the careerist lifestyle, the increasing maternal age and the parallel increment in the aneuploidy rate of embryos play a crucial role in this phenomenon. In this study, embryological parameters and pregnancy outcomes were investigated in IVF cycles using either sequential embryo culture or a single step culture system. By sequential media, oocytes/embryos are needlessly exposed to the potentially negative effects of light exposure, temperature decrement and altered oxygen tension. In comparison with sequential media, single step media induced 1.28, 1.21 and 1.21-fold increments in implantation, biochemical pregnancy and clinical pregnancy rates, respectively. Pregnancy outcomes showed strong maternal age-dependency, so the difference between the two investigated culture systems was equalized by the increasing maternal ages (35-44 years) and the supposed incidence of embryo aneuploidy. Nevertheless, the significant enlargements in the outcomes of the younger ages (25-34) induced by the single step cultures suggest that, beside the resultant maternal aneuploidy, aneuploidy (reduced pregnancy rates) may evolve from exposure to the mentioned environmental stress factors.

Reducing time to pregnancy and facilitating the birth of healthy children through functional analysis of embryo physiology†

An ever-increasing number of couples rely on assisted reproductive technologies (ART) in order to conceive a child. Although advances in embryo culture have led to increases in the success rates of clinical ART, it often takes more than one treatment cycle to conceive a child. Ensuring patients conceive as soon as possible with a healthy embryo is a priority for reproductive medicine. Currently, selection of embryos for transfer relies predominantly on the morphological assessment of the preimplantation embryo; however, morphology is not an absolute link to embryo physiology, nor the health of the resulting child. Non-invasive quantitation of individual embryo physiology, a key regulator of both embryo viability and health, could provide valuable information to assist in the selection of the most viable embryo for transfer, hence reducing the time to pregnancy. Further, according to the Barker Hypothesis, the environment to which a fetus is exposed to during gestation affects subsequent offspring health. If the environment of the preimplantation period is capable of affecting metabolism, which in turn will affect gene expression through the metaboloepigenetic link, then assessment of embryo metabolism should represent an indirect measure of future offspring health. Previously, the term viable embryo has been used in association with the potential of an embryo to establish a pregnancy. Here, we propose the term healthy embryo to reflect the capacity of that embryo to lead to a healthy child and adult.

A biophotonic approach to measure pH in small volumes in vitro: Quantifiable differences in metabolic flux around the cumulus-oocyte-complex (COC)

Unfertilised eggs (oocytes) release chemical biomarkers into the medium surrounding them. This provides an opportunity to monitor cell health and development during assisted reproductive processes if detected in a non-invasive manner. Here we report the measurement of pH using an optical fibre probe, OFP1, in 5 μL drops of culture medium containing single mouse cumulus oocyte complexes (COCs). This allowed for the detection of statistically significant differences in pH between COCs in culture medium with no additives and those incubated with either a chemical (cobalt chloride) or hormonal treatment (follicle stimulating hormone); both of which serve to induce the release of lactic acid into the medium immediately surrounding the COC. Importantly, OFP1 was shown to be cell-safe with no inherent cell toxicity or light-induced phototoxicity indicated by negative DNA damage staining. Pre-measurement photobleaching of the probe reduced fluorescence signal variability, providing improved measurement precision (0.01-0.05 pH units) compared to previous studies. This optical technology presents a promising platform for the measurement of pH and the detection of other extracellular biomarkers to assess cell health during assisted reproduction.

Oocyte and embryo evaluation by AI and multi-spectral auto-fluorescence imaging: Livestock embryology needs to catch-up to clinical practice

A highly accurate 'non-invasive quantitative embryo assessment for pregnancy' (NQEAP) technique that determines embryo quality has been an elusive goal. If developed, NQEAP would transform the selection of embryos from both Multiple Ovulation and Embryo Transfer (MOET), and even more so, in vitro produced (IVP) embryos for livestock breeding. The area where this concept is already having impact is in the field of clinical embryology, where great strides have been taken in the application of morphokinetics and artificial intelligence (AI); while both are already in practice, rigorous and robust evidence of efficacy is still required. Even the translation of advances in the qualitative scoring of human IVF embryos have yet to be translated to the livestock IVP industry, which remains dependent on the MOET-standardised 3-point scoring system. Furthermore, there are new ways to interrogate the biochemistry of individual embryonic cells by using new, light-based methodologies, such as FLIM and hyperspectral microscopy. Combinations of these technologies, in particular combining new imaging systems with AI, will lead to very accurate NQEAP predictive tools, improving embryo selection and recipient pregnancy success.

How to Reduce the Potential Harmful Effects of Light on Blastocyst Development during IVF

PURPOSE

Earlier findings revealed the damaging effect of visible light on zygotes and gametes. The aim of our study is to eliminate or significantly reduce the potentially harmful effects of light exposure during in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) and to investigate the effect of light protection on embryo development and implantation.

MATERIALS AND METHODS

To protect sperm cells, oocytes, and embryos from the potential harmful effects of light exposure during laboratory procedures, we created a dark environment for the cells and applied red filters on laboratory lamps and UV or infrared filters in the microscopes in order to eliminate white light exposure of the cells throughout all work stages.

RESULTS

The fertilization rate was significantly (p = 0.011) higher in light-protected ICSI cycles. Blastocyst development rates (blastocyst/embryo) were significantly (p < 0.001) higher in light-protected embryos than in those manipulated in conventional light conditions both in IVF (20.9% difference) and ICSI (38.6% difference). Numbers of clinical pregnancies/transfers of ICSI fertilized day 5 blastocysts were also significantly (p = 0.040) higher in light-protected conditions.

CONCLUSIONS

These data show that light protection has a positive effect on fertilization rate and increases the blastocyst development as well as the number of clinical pregnancies/transfers. Implementation of this light protection method in IVF centers may improve the success rate while maintaining maximal embryo safety.

Light-induced injury in mouse embryos revealed by single-cell RNA sequencing

Background

Light exposure is a common stress factor in in vitro manipulation of embryos in the reproductive center. Many studies have shown the deleterious effects of high-intensity light exposure in different animal embryos. However, no transcriptomic studies have explored the light-induced injury and response in preimplantation embryos.

Results

Here, we adopt different time-courses and illumination intensities to treat mouse embryos at the 2-cell stage and evaluate their effects on blastulation. Meanwhile, single-cell transcriptomes from the 2-cell to blastocyst stage were analyzed after high-intensity light exposure. These data show that cells at each embryonic stage can be categorized into different light conditions. Further analyses of differentially expressed genes and GO terms revealed the light-induced injury as well as the potential repair response after high-intensity lighting. Maternal-to-zygote transition is also affected by the failure to remove maternal RNAs and deactivate zygotic genome expression.

Conclusion

Our work revealed an integrated response to high-intensity lighting, involving morphological changes, long-lasting injury effects, and intracellular damage repair mechanisms.

White LED Light Exposure Inhibits the Development and Xanthophore Pigmentation of Zebrafish Embryo

Circadian rhythm in all living organisms is disturbed continuously by artificial light sources and artificial lighting has become a hazard for public health. Circadian rhythm of melatonin maintains high levels of melatonin during the night and low levels during the day. N-acetyltransferase (arylalkylamine N-acetyltransferase, AANAT) is one of the four enzymes required for melatonin synthesis and mtnr1ba is a melatonin receptor-encoding mRNA that is expressed widely in the embryonic brain. Pax7 has important roles during neural crest development and especially xanthophore pigmentation. Due to its diurnal nature, zebrafish provide a special opportunity for research on circadian rhythms that are regulated by melatonin. Here in this study, we showed that when compared with the white light control group, white LED light exposure resulted in loss of yellow pigmentation, decreased body length and locomotor activity, oxidant-antioxidant imbalance and decreased expressions of aanat2, mtnr1ba, and pax7 in zebrafish embryos. Histological analysis of this group revealed disorganization of the spaces among photoreceptor cells, decreased total retinal thickness and photoreceptor cell layer thickness compared with the control group. Artificial lighting pollution has the potential to become an important risk factor for different diseases including cancer especially for industrialized countries, therefore, more studies should be performed and necessary regulations should be made regarding this risk factor.

The effect of light exposure on the cleavage rate and implantation capacity of preimplantation murine embryos

During assisted reproduction the embryos are subjected to light. We investigated the relationship between light exposure and the developmental- and implantation capacity of mouse embryos. In vitro cultured embryos were exposed to white or red filtered light, then transferred to the uteri of pseudo-pregnant females. The mice were sacrificed on day 8.5 and implantation sites were counted. The number of nucleic acid containing (PI+) extracellular vesicles (EVs) in culture media of light-exposed and control embryos, as well as, the effect of the EVs on IL-10 production of CD8+ spleen cells was determined by flow cytometry. DNA fragmentation in control and light exposed embryos was detected in a TUNEL assay. The effect of light on the expression of apoptosis-related molecules was assessed in an apoptosis array. Light exposure significantly reduced the implantation capacity of the embryos. The harmful effect was related to the wavelength, rather than to the brightness of the light. Culture media of light exposed groups contained significantly higher number of PI + EVs than those of the control embryos, and failed to induce IL-10 production of spleen cells. The number of nuclei with fragmented DNA, was significantly higher in embryos treated with white light, than in the other two groups. In conclusion exposure to white light impairs the implantation potential of in vitro cultured mouse embryos. These effects are partly corrected by using a red filter. Since there is no information on the light sensitivity of human embryos, embryo manipulation during IVF and ICSI should be performed with caution.

Influence of wideband visible light with an padding red component on the functional state of mice embryos and embryonic stem cells

It is known that visible light, including sunlight and laboratory lighting, adversely affect the development of embryos in vitro. In with article we present a technology for the synthesis of composite screens, capable to photoconvert UV and a part of the blue spectrum into red light with the maximum ~630 nm. It is established that the application of such transformed light with an evident red component raises the chances of embryos to survive and protects embryonic stem cells. To create photoconversion screens, the CdZn/Se quantum dots were obtained, the average size being about 7 nm. When the quantum dots are excited by electromagnetic waves of the UV and blue spectral range, photoluminescence is observed. The average photon energy for photoluminescence is of the order of 2 eV. On the basis of CdZn/Se quantum dots and methylphenylsiloxane polymer, light-transforming composite screens were made. In case of the light-transforming composite screen, the UV component disappeared from the energy spectrum, and the intensity of the blue region of the spectrum was reduced. On the contrary, in the red region (λ_max = 630 nm) one can see a little more than two-fold increase of intensity. It is shown that when exposed to 2-cell embryos by transformed light, the proportion of normally developing embryos increases by 20%, the number of dead embryos decreases twice, and number of dead and apoptotic cells was lower in blastocysts, what's decreased by 70%, as compared to the control group. When blastocysts are transferred to the feeder substrate, colonies of embryonic stem cells are formed. Cells obtained from blastocysts irradiated with transformed visible light are in a normal state in 90% of cases and did not change expression levels, biochemistry and morphology for at least 20 passages. It is assumed that the data obtained can be used for the design of systems of efficient cultivation of embryonic cells for tissue engineering and cell therapy.

Comparison of the development of human embryos cultured in either an EmbryoScope or benchtop incubator

PURPOSE

In this current study, our main goal was to establish that EmbryoScope incubation environment is comparable to standard incubation.

METHODS

The development of sibling human zygotes was compared after culture in either a benchtop incubator (SI) or an EmbryoScope time-lapse incubator (ES). Between May 2015 to April 2016, a total of 581 normally fertilized 2PN, pronuclear-stage embryos, from 47 patients were allocated to culture in either a benchtop incubator (SI) or an EmbryoScope incubator (ES).

RESULTS

The development of embryos to cleavage (up to day 3) and blastocyst stages (day 5/6) was compared between the two different incubators. The proportion of good quality embryos was higher in the ES group compared to the SI on day 2 (66.8 vs. 50.5%, P = 0.014) and on day 3 (75.1 vs. 56.0%, P = 0.006). Those differences were statistically significant. A higher proportion of embryos developed to good quality blastocysts when cultured in the EmbryoScope compared to the benchtop (49.4 vs. 42.0%, P = 0.24), but this was not significant. Finally, no significant differences were noted with the proportion of blastocysts chosen for cryopreservation on day 5/6 in the two incubators.

CONCLUSIONS

The findings support the view that the EmbryoScope incubator supports at least equivalent in vitro development of human embryos compared to other standard incubation methods and may promote improved development during early cleavage stages.

Impact of the IVF laboratory environment on human preimplantation embryo phenotype

The phenotype of the human embryo conceived through in vitro fertilization (IVF), that is its morphology, developmental kinetics, physiology and metabolism, can be affected by numerous components of the laboratory and embryo culture system (which comprise the laboratory environment). The culture media formulation is important in determining embryo phenotype, but this exists within a culture system that includes oxygen, temperature, pH and whether an embryo is cultured individually or in a group, all of which can influence embryo development. Significantly, exposure of an embryo to one suboptimal component of the culture system of laboratory typically predisposes the embryo to become more vulnerable to a second stressor, as has been well documented for atmospheric oxygen and individual culture, as well as for oxygen and ammonium. Furthermore, the inherent viability of the human embryo is derived from the quality of the gametes from which it is created. Patient age, aetiology, genetics, lifestyle (as well as ovarian stimulation in women) are all known to affect the developmental potential of gametes and hence the embryo. Thus, as well as considering the impact of the IVF laboratory environment, one needs to be aware of the status of the infertile couple, as this impacts how their gametes and embryos will respond to an in vitro environment. Although far from straight forward, analysing the interactions that exist between the human embryo and its environment will facilitate the creation of more effective and safer treatments for the infertile couple.

The effects of chemical and physical factors on mammalian embryo culture and their importance for the practice of assisted human reproduction

BACKGROUND

Although laboratory procedures, along with culture media formulations, have improved over the past two decades, the issue remains that human IVF is performed in vitro (literally 'in glass').

METHODS

Using PubMed, electronic searches were performed using keywords from a list of chemical and physical factors with no limits placed on time. Examples of keywords include oxygen, ammonium, volatile organics, temperature, pH, oil overlays and incubation volume/embryo density. Available clinical and scientific evidence surrounding physical and chemical factors have been assessed and presented here.

RESULTS AND CONCLUSIONS

Development of the embryo outside the body means that it is constantly exposed to stresses that it would not experience in vivo. Sources of stress on the human embryo include identified factors such as pH and temperature shifts, exposure to atmospheric (20%) oxygen and the build-up of toxins in the media due to the static nature of culture. However, there are other sources of stress not typically considered, such as the act of pipetting itself, or the release of organic compounds from the very tissue culture ware upon which the embryo develops. Further, when more than one stress is present in the laboratory, there is evidence that negative synergies can result, culminating in significant trauma to the developing embryo. It is evident that embryos are sensitive to both chemical and physical signals within their microenvironment, and that these factors play a significant role in influencing development and events post transfer. From the viewpoint of assisted human reproduction, a major concern with chemical and physical factors lies in their adverse effects on the viability of embryos, and their long-term effects on the fetus, even as a result of a relatively brief exposure. This review presents data on the adverse effects of chemical and physical factors on mammalian embryos and the importance of identifying, and thereby minimizing, them in the practice of human IVF. Hence, optimizing the in vitro environment involves far more than improving culture media formulations.

Utility of antioxidants during assisted reproductive techniques: an evidence based review

Assisted reproductive technology (ART) is a common treatment of choice for many couples facing infertility issues, be it due to male or female factor, or idiopathic. Employment of ART techniques, however, come with its own challenges as the in vitro environment is not nearly as ideal as the in vivo environment, where reactive oxygen species (ROS) build-up leading to oxidative stress is kept in check by the endogenous antioxidants system. While physiological amounts of ROS are necessary for normal reproductive function in vivo, in vitro manipulation of gametes and embryos exposes these cells to excessive ROS production either by endogenous or exogenous environmental factors. In this review, we discuss the sources of ROS in an in vitro clinical setting and the influence of oxidative stress on gamete/embryo quality and the outcome of IVF/ICSI. Sources of ROS and different strategies of overcoming the excessive generation of ROS in vitro are also highlighted. Endogenously, the gametes and the developing embryo become sources of ROS. Multiple exogenous factors act as potential sources of ROS, including exposure to visible light, composition of culture media, pH and temperature, oxygen concentration, centrifugation during spermatozoa preparation, ART technique involving handling of gamete/embryo and cryopreservation technique (freeze/thawing process). Finally, the use of antioxidants as agents to minimize ROS generation in the in vitro environment and as oral therapy is highlighted. Both enzymatic and non-enzymatic antioxidants are discussed and the outcome of studies using these antioxidants as oral therapy in the male or female or its use in vitro in media is presented. While results of studies using certain antioxidant agents are promising, the current body of evidence as a whole suggests the need for further well-designed and larger scale randomized controlled studies, as well as research to minimize oxidative stress conditions in the clinical ART setting.

Analysis of the effects of blue light on morphofunctional status of in vitro cultured blastocysts from mice carrying gene of enhanced green fluorescent protein (EGFP)

We studied the effect of blue light (440-490 nm) on the development of late blastocysts of mice carrying the gene of enhanced green fluorescent protein (EGFP). Exposure to blue light for 20 min reduced adhesive properties of blastocysts and their capacity to form primary colonies consisting of the cells of inner cell mass, trophoblast, and extraembryonic endoderm. The negative effects of blue light manifested in morphological changes in the primary colonies and impairment of differentiation and migration of cells of the trophoblast and extraembryonic endoderm. The problems of cell-cell interaction and inductive influences of the inner cell mass on other cell subpopulations are discussed. EGFP blastocysts were proposed as the model for evaluation of the mechanisms underlying the effects of blue light as the major negative factor of visible light used in in vitro experiments on mammalian embryos.

Effect of red light on the development and quality of mammalian embryos

PURPOSE

To assess irradiance and total energy dose from different microscopes during the in-vitro embryonic developmental cycle in mouse and pig and to evaluate its effect on embryonic development and quality in pig.

METHOD

Spectral scalar irradiance (380-1050 nm) was measured by a fiber-optic microsensor in the focal plane of a dissection microscope, an inverted microscope and a time-lapse incubation system. Furthermore, the effect of three different red light levels was tested in the time-lapse system on mouse zygotes for 5 days, and on porcine zona-intact and zona-free parthenogenetically activated (PA) embryos for 6 days.

RESULTS

The time-lapse system used red light centered at 625 nm and with a lower irradiance level as compared to the white light irradiance levels on the dissection and inverted microscopes, which included more energetic radiation <550 nm. Even after 1000 times higher total energy dose of red light exposure in the time-lapse system, no significant difference was found neither in blastocyst development of mouse zygotes nor in blastocyst rates and total cell number of blastocysts of porcine PA embryos.

CONCLUSIONS

Our results indicate that red light (625 nm, 0.34 W/m(2)) used in the time-lapse incubation system does not decrease the development and quality of blastocysts in both mouse zygotes and porcine PA embryos (both zona-intact and zona-free).

Effect of ambient light exposure of media and embryos on development and quality of porcine parthenogenetically activated embryos

Light exposure is a common stress factor during in vitro handling of oocytes and embryos that originates from both microscope and ambient light. In the current study, the effect of two types of ambient light (daylight and laboratory light) on porcine parthenogenetically activated (PA) embryos was tested in two experiments: (1) ambient light on medium subsequently used for embryo in vitro development; and (2) ambient light exposure on activated oocytes before in vitro development. The results from Experiment 1 showed that exposure of culture medium to both types of ambient light decreased the percentage of blastocysts that showed good morphology, only after 24 h exposure. The results from Experiment 2 revealed a reduction in both blastocyst formation and quality when activated oocytes were exposed to both types of ambient light. This effect was seen after only 1 h exposure and increased with time. In conclusion, exposure to ambient light can be harmful to embryo development, both when medium is exposed for a long period of time and, to a greater extent, when the embryo itself is exposed for >1 h. In practice, it is therefore recommended to protect both culture medium and porcine embryos against ambient light during in vitro handling in the laboratory.

Altered cleavage patterns in human tripronuclear embryos and their association to fertilization method: a time-lapse study

PURPOSE

To analyze the cleavage patterns in dipronuclear (2PN) and tripronuclear (3PN) embryos in relation to fertilization method.

METHOD

Time-lapse analysis.

RESULTS

Compared to 2PN, more 3PN IVF embryos displayed early cleavage into 3 cells (p < 0.001), displayed longer duration of the 3-cell stage (p < 0.001), and arrested development from the compaction stage and onwards (p < 0.001). For the IVF embryos, the 2nd and 3rd cleavage cycles were completed within the expected time frame. However, timing of the cell divisions within the cleavage cycles differed between the two groups. In contrast, the completion of the 1st, 2nd, and 3rd cleavage cycle was delayed, but with a similar division pattern for 3PN ICSI compared with the 2PN ICSI embryos. 3PN, more often than 2PN ICSI embryos, displayed early cleavage into 3 cells (p = 0.03) and arrested development from the compaction stage and onwards (p = 0.001). More 3PN IVF than ICSI embryos displayed early cleavage into 3 cells (p < 0.001).

CONCLUSIONS

This study reports differences in cleavage patterns between 2PN and 3PN embryos and for the first time demonstrates differences in the cleavage pattern between 3PN IVF and ICSI embryos.

The Effect of Light on Embryos and Embryo Culture

In oviparous animals, the egg hatches outside of the body and is exposed to light; in some cases throughout the development of the fetus. In mammals, fertilization and the growth of embryos in vivo occurs in the dark but in human IVF, these embryos are exposed to variable light sources and intensities. Light can affect embryonic development in some species via either a direct toxic effect on the embryo, or indirectly via photo-oxidation of components in the media or oil. Although data regarding the effect of light on human embryos is lacking, it is prudent to take appropriate steps to minimize the potential harmful effects of both ambient and microscopic light on embryos.

The clinical benefit and safety of current and future assisted reproductive technology

Since the first birth by IVF was achieved in 1978, the techniques involved in assisted reproductive technology have grown at an enormous rate. However, new technology has rarely been robustly validated before clinical use and developing scientific understanding of the available techniques has done little to alter their use. Furthermore, there are inconsistencies in the available clinical studies and endpoints. The benefits of some technologies already established for routine use are currently dubious and there are clear ethical concerns with providing them to patients when their scientific basis is not clear. As the uptake of assisted reproductive technology increases and newer technologies continue to push the boundaries of science, it is important to consider the clinical benefits and safety of all assisted reproductive technologies. This review will discuss aspects of some of the more recent techniques, including sperm DNA-damage tests, intracytoplasmic morphologically selected sperm injection, amino acid and metabolomics profiling, preimplantation genetic screening and time-lapse imaging, and those that may have substantial impacts on the field of reproductive medicine in the future including artificial gametes, ovarian transplantation and gene therapy.

Full in vitro fertilization laboratory mechanization: toward robotic assisted reproduction?

OBJECTIVE

To describe the current efforts made to standardize different steps of assisted reproductive technology processes by the introduction of new technologies for the nonsubjective sperm selection process, oocyte denudation by mechanical removal of cumulus cells, oocyte positioning, sperm motility screening, fertilization, embryo culture, media replacement by microfluidics, and monitoring of embryo development by time-lapse photography, embryo secretions, and/or O(2) consumption. These technologies could be integrated in a unique and fully automated device.

DESIGN

Pubmed database and research and development data from authors.

SETTING

University-affiliated private center.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASUREMENT(S)

None.

RESULT(S)

Several technologies would be useful for: 1) selection of sperm based on viability; 2) manipulation and removal of the cumulus cells' narrow channel regions combined with microfluidics; 3) advances in oocyte positioning precision through the use of joystick-controlled micromanipulators; 4) microfluidics allowing the gradual change of a culture medium, which might result in better embryo development as well as reduce the amount of embryo manipulation; 5) time-lapse, proteomic, and metabolic scoring of the developing embryo, allowing multiple and optimized selection of the embryos. The technologies described in this review have not yet reported reliable clinical proofs.

CONCLUSION(S)

We already have available some of the technologies described, but we envisage an integrated device, i.e., an IVF lab-on-a-chip, by which oocyte and sperm would be processed to achieve a perfect embryo ready to be delivered into the uterus. With such a device, sample preparation, chemical or biologic reactions, and data collection would be integrated.

A randomized clinical trial comparing embryo culture in a conventional incubator with a time-lapse incubator

PURPOSE

Time-lapse monitoring allows for a flexible embryo evaluation and potentially provides new dynamic markers of embryo competence. Before introducing time-lapse monitoring in a clinical setting, the safety of the instrument must be properly documented. Accordingly, the aim of this study was to evaluate the safety of a commercially available time-lapse incubator.

METHODS

In a two center, randomized, controlled, clinical trial 676 oocytes from 59 patients in their 2nd or third treatment cycle, age <38 years and ≥ 8 oocytes retrieved were cultured in the time-lapse incubator or in a conventional incubator. The primary outcome was proportion of 4-cell embryos on day 2. Secondary outcomes were proportion of 7-8 cell embryos on day 3 and proportion of blastocysts on day 5. Implantation pregnancy rates were registered based on presence of fetal heart activity visualized by ultrasound 8 weeks after embryo transfer.

RESULTS

No significant difference was found between the time-lapse incubator (TLI) and conventional incubator (COI) in proportion of 4-cell embryos on day 2 irrespective of whether data was analyzed according to ITT (RR(TLI/COI): 0.81 (0.65; 1.02)) or PP (RR(TLI/COI): 0.80 (0.63; 1.01)). Nor were any significant differences detected in the secondary endpoints; i.e. proportion of 7-8-cell embryos on day three ITT (RR(TLI/COI): 0.96 (0.73; 1.26)); PP (RR(TLI/COI): 0.95 (0.72; 1.26)) and proportion of blastocysts on day five ITT (RR(TLI/COI): 1.09 (0.84; 1.41)); PP (RR(TLI/COI): 1.09 (0.83: 1.41)). We found no differences in clinical pregnancy rate or implantation rate.

CONCLUSION

Culture in the time-lapse incubator supports embryonic development equally to a conventional incubator.

Alterations in mouse embryo intracellular pH by DMO during culture impair implantation and fetal growth

The preimplantation embryo is highly susceptible to in-vitro stress, and although this does not necessarily perturb blastocyst development, it can significantly affect embryo physiology and the ability to form a viable pregnancy. This study determined that the preimplantation mouse embryo is highly sensitive to a small decrease in intracellular pH (<0.2 pH units). Embryos cultured in media containing a weak acid (5,5-dimethyl-2,4-oxazolidinedione; DMO) formed blastocysts with decreased cell number and inner cell mass number, as well as increased apoptosis, even though blastocyst development and morphology were unchanged. Interestingly, the effects were similar regardless of whether the pH stress was present for a short-term 'acute' exposure (during the zygote to 2-cell, or 2-cell to 8-cell division) or an extended 'chronic' period of time (continually from the zygote to the blastocyst stage). Exposure to DMO during the first cleavage division did not alter implantation; however, fetal weight and crown-rump length were significantly decreased (P<0.05). In contrast, continuous exposure to DMO throughout preimplantation development reduced not only implantation but also fetal weight and crown-rump length. This study highlights the importance of correct intracellular pH and demonstrates that slight deviations can significantly impact embryo development and viability.

Embryo culture: can we perform better than nature?

Culture of preimplantation-stage embryos has always been a key element of laboratory embryology and has contributed substantially to the success of many assisted reproduction procedures. During the past decade, its importance has increased as extended in-vitro embryo culture and single blastocyst transfer have become indispensable parts of the approach to decreasing the chance of multiple pregnancy while preserving the overall efficiency of the treatment. However, in spite of the scientific and commercial challenge stimulating research worldwide to optimize embryo culture conditions, a consensus is missing even in the basic principles, including composition and exchange of media, the required physical and biological environment and even the temperature of incubation. This review attempts to summarize the controversies, demonstrate the fragility of some widely accepted dogmas and generate an open-minded debate towards rapid and efficient optimization. New approaches expanding the traditional frames of mammalian embryo culture are also discussed. Although some researchers suppose that the efficiency of the presently applied in-vitro culture systems have already approached the biological limits, authors are confident that substantial improvement may be achieved that may expand considerably the possibilities of future assisted reproduction in humans.

Mitogen-activated protein kinase (MAPK) pathways mediate embryonic responses to culture medium osmolarity by regulating Aquaporin 3 and 9 expression and localization, as well as embryonic apoptosis

BACKGROUND

In order to advance the development of culture conditions and increase the potential for supporting normal preimplantation embryo development in vitro, it is critical to define the mechanisms that early embryos utilize to survive in culture. We investigated the mechanisms that embryos employ in response to culture medium osmolarity. We hypothesized that mitogen-activated protein kinase (MAPK) pathways mediate responses to hyperosmotic stress by regulating Aquaporin (AQP) 3 and 9 expression as well as embryonic apoptosis.

METHODS

Real-time reverse transcription and polymerase chain reaction and whole-mount immunofluorescence were used to determine the relative mRNA levels and protein localization patterns of AQP 3 and 9 after hyperosmotic medium treatment.

RESULTS

At 6 and 24 h, a significant increase in Aqp 3 and 9 mRNA was observed in the sucrose hyperosmotic treatment compared with standard medium and glycerol controls. Blockade of MAPK14/11 negated the increase in Aqp 3 and 9 mRNA levels, whereas culture in a MAPK8 blocker did not. Hyperosmotic sucrose treatment significantly increased embryonic apoptosis which was negated in the presence of MAPK8 blocker, but not MAPK14/11 blocker.

CONCLUSIONS

MAPK14/11 activation is a component of the rapid adaptive stress response mechanism that includes the effects of AQP mRNA expression and protein localization, whereas the MAPK8 pathway is a regulator of apoptosis.

Effect of retinoic acid on apoptosis and expression of Fas proteins in mouse blastocysts cultured in vitro

Mouse blastocysts were exposed to doses of 0, 1 and 10 micromol/L retinoic acid (RA) for 24 h and the cytotoxic effect of RA on the mouse blastocysts in vitro was observed. FITC-labeled terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL-FITC) assay was employed to stain apoptotic cells and immunohistochemical S-P staining method was used to detect the expression of Fas protein in mouse blastocysts in vitro. The results showed that RA could induce apoptosis and increase the expression of Fas proteins of trophectoderm (TE) and inner cell mass (ICM) cells in blastocysts. Compared with the findings for the control blastocysts, exposure to RA (10 micromol/L) resulted in a more significant apoptosis and higher expression level of Fas proteins (P<0.01). It was concluded that RA could induce apoptosis, which may result in a significant reduction in the average number of total cells and the trophectoderm/inner cell mass in blastocysts and an increased expression of Fas protein, suggesting that RA had a cytotoxic effect on the growth and development of early embryos in mice.