Assessment of DNA damage in individual hamster embryos by comet assay

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.

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.

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.

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.

Genome stabilization by RAD51-stimulatory compound 1 enhances efficiency of somatic cell nuclear transfer-mediated reprogramming and full-term development of cloned mouse embryos

OBJECTIVES

The genetic instability and DNA damage arise during transcription factor-mediated reprogramming of somatic cells, and its efficiency may be reduced due to abnormal chromatin remodelling. The efficiency in somatic cell nuclear transfer (SCNT)-mediated reprogramming is also very low, and it is caused by development arrest of most reconstituted embryos.

MATERIALS AND METHODS

Whether the repair of genetic instability or double-strand breaks (DSBs) during SCNT reprogramming may play an important role in embryonic development, we observed and analysed the effect of Rad 51, a key modulator of DNA damage response (DDR) in SCNT-derived embryos.

RESULTS

Here, we observed that the activity of Rad 51 is lower in SCNT eggs than in conventional IVF and found a significantly lower level of DSBs in SCNT embryos during reprogramming. To address this difference, supplementation with RS-1, an activator of Rad51, during the activation of SCNT embryos can increase RAD51 expression and DSB foci and thereby increased the efficiency of SCNT reprogramming. Through subsequent single-cell RNA-seq analysis, we observed the reactivation of a large number of genes that were not expressed in SCNT-2-cell embryos by the upregulation of DDR, which may be related to overcoming the developmental block. Additionally, there may be an independent pathway involving histone demethylase that can reduce reprograming-resistance regions.

CONCLUSIONS

This technology can contribute to the production of comparable cell sources for regenerative medicine.

Bifenthrin induces DNA damage and autophagy in Spodoptera frugiperda (Sf9) insect cells

Bifenthrin is one of the most commonly used synthetic pyrethroid insecticides. It targets the nervous system of insects, mainly acting on sodium channels in nerve cell membranes. The high use of bifrenthrin may lead to an increase in pest insect resistance. Additionally, there are only a few studies describing its cytotoxic action. A series of bioassays were carried out, and the results showed that bifenthrin has a significant ability to induce DNA damage and the inhibition of viability in Spodoptera frugiperda (Sf9) cells. Monodansylcadaverine staining and transmission electron microscope assays were used to observe significant levels of autophagosomes and mitochondrial dysfunction in the cytoplasm. Additionally, western blot analysis showed an upregulation in LC3-II and beclin-1 protein expression and a downregulation in p62 expression, which contributed to the cytotoxic effect of bifenthrin on Sf9 cells. Overall, bifenthrin significantly impacts the viability of Sf9 cells by inducing DNA damage and autophagy. These results provide a theoretical basis for understanding bifrenthin's mechanism of cytotoxicity.

The role of Trp53 in the mouse embryonic response to DNA damage

Apoptosis occurs primarily in the blastocyst inner cell mass, cells of which go on to form the foetus. Apoptosis is likely to play a role in ensuring the genetic integrity of the foetus, yet little is known about its regulation. In this study, the role of the mouse gene, transformation-related protein 53 (Trp53) in the response of embryos to in vitro culture and environmentally induced DNA damage was investigated using embryos from a Trp53 knockout mouse model. In vivo-derived blastocysts were compared to control embryos X-irradiated at the two-cell stage and cultured to Day 5. An analysis of DNA by comet assay demonstrated that 1.5 Gy X-irradiation directly induced damage in cultured two-cell mouse embryos; this was correlated with retarded development to blastocyst stage and increased apoptosis at the blastocyst stage but not prior to this. Trp53 null embryos developed to blastocysts at a higher frequency and with higher cell numbers than wild-type embryos. Trp53 also mediates apoptosis in conditions of low levels of DNA damage, in vivo or in vitro in the absence of irradiation. However, following DNA damage induced by X-irradiation, apoptosis is induced by Trp53 independent as well as dependent mechanisms. These data suggest that Trp53 and apoptosis play important roles in normal mouse embryonic development both in vitro and in vivo and in response to DNA damage. Therefore, clinical ART practices that alter apoptosis in human embryos and/or select embryos for transfer, which potentially lack a functional Trp53 gene, need to be carefully considered.

Comet assay on one- and two-cell mouse embryos

DNA damage quantified as the comet tail length was assessed using in vitro and in vivo comet assay on one- and two-cell mouse embryos obtained by natural mating. The use of a protocol with three layers of agarose reduces the embryo loss and makes it possible to study a small number of embryos. A significantly lower level of basal, but not induced DNA damage was found in embryos with cleaved zona pellucida compared to embryos with intact zona pellucida. There were no significant differences in the length of the comet's tail between embryos lysed in different lysis solutions, both in cases of basal and induced DNA damage. A significant increase in the comet tail length was detected in one-cell embryos of mice treated with methyl methanesulfonate and etoposide compared to the control. The data show that DNA damage induced in maternal germ cells persists, which can be detected in embryos using the comet assay.

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.

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.

Embryotropic effects of vascular endothelial growth factor on porcine embryos produced by in vitro fertilization

Current research suggests that supplementing in vitro culture (IVC) media with vascular endothelial growth factor (VEGF) may have beneficial effects on the development of porcine embryos in vitro. However, the molecular signaling mechanisms underlying this effect are unclear. Therefore, we aimed to investigate the effects of VEGF on molecular signaling events during in vitro embryonic development of porcine embryos. Porcine oocytes matured in vitro were fertilized, and the resultant zygotes were cultured with 5 ng/mL of VEGF supplemented with or without fetal bovine serum from day 4 till day 7. Without VEGF and/or FBS served as the control group. Real-time quantitative PCR was used to detect expression patterns of apoptosis- and oxidative stress-related genes in day 7 blastocysts (BLs). Early-stage apoptosis was detected by annexin-V assays in day 2 and day 7 embryos. We found that the addition of VEGF throughout the culture period with or without FBS supplementation significantly improved embryo survival and development. Supplementation with VEGF in the IVC medium significantly increased early BL formation (p < 0.05), although addition of FBS on day 4 significantly increased hatched BL formation (p < 0.05) regardless of VEGF supplementation. However, supplementation of media with both VEGF and FBS increased the formation of expanded BLs synergistically. The average total cell numbers per BL were significantly (p < 0.05) higher in embryos supplemented with VEGF and FBS than in those supplemented with either VEGF or FBS alone. We also found that accumulation of reactive oxygen species in VEGF-treated embryos was significantly lower (p < 0.05) than that in untreated embryos. The mRNA levels of caspase-3 were significantly lower (p < 0.05), and those of Bcl-2 and Nrf-2 were significantly higher (p < 0.05) in embryos grown in VEGF-supplemented media than in embryos grown in non-supplemented media. Furthermore, on day 2, the numbers of viable embryos (44.06 ± 3.94%) and blastomeres (67.18 ± 3.60%) were significantly higher (p < 0.05), and the numbers of early apoptotic embryos (55.94 ± 3.94) and blastomeres (23.23 ± 4.22) were significantly lower (p < 0.05) in VEGF-treated BLs than in controls. Furthermore, the numbers of early apoptotic cells in BLs on day 7 were also significantly lower (p < 0.05) in VEGF-treated BLs than in controls. Overall, our results indicate that supplementing IVC media with VEGF during in vitro culture of porcine embryos increases their developmental potential.

Peroxiredoxin as a functional endogenous antioxidant enzyme in pronuclei of mouse zygotes

Antioxidant mechanisms to adequately moderate levels of endogenous reactive oxygen species (ROS) are important for oocytes and embryos to obtain and maintain developmental competence, respectively. Immediately after fertilization, ROS levels in zygotes are elevated but the antioxidant mechanisms during the maternal-to-zygotic transition (MZT) are not well understood. First, we identified peroxiredoxin 1 (PRDX1) and PRDX2 by proteomics analysis as two of the most abundant endogenous antioxidant enzymes eliminating hydrogen peroxide (H₂O₂). We here report the cellular localization of hyperoxidized PRDX and its involvement in the antioxidant mechanisms of freshly fertilized oocytes. Treatment of zygotes at the pronuclear stage with H₂O₂ enhanced pronuclear localization of hyperoxidized PRDX in zygotes and concurrently impaired the generation of 5-hydroxymethylcytosine (5hmC) on the male genome, which is an epigenetic reprogramming event that occurs at the pronuclear stage. Thus, our results suggest that endogenous PRDX is involved in antioxidant mechanisms and epigenetic reprogramming during MZT.

Comet assay on thawed embryos: An optimized technique to evaluate DNA damage in mouse embryos

Our objective was to optimize the CA technique on mammal embryos.

MATERIALS AND METHODS

1000 frozen 2-cell embryos from B6CBA mice were used. Based on a literature review, and after checking post-thaw embryo viability, the main outcome measures included: 1) comparison of the embryo recovery rate between 2 CA protocols (2 agarose layers and 3 agarose layers); 2) comparison of DNA damage by the CA on embryos with (ZP+) and without (ZP-) zona pellucida; and 3) comparison of DNA damage in embryos exposed to 2 genotoxic agents (H₂O₂ and simulated sunlight irradiation (SSI)). DNA damage was quantified by the % tail DNA.

RESULTS

1) The recovery rate was 3,3% (n=5/150) with the 2 agarose layers protocol and 71,3% (n=266/371) with the 3 agarose layers protocol. 2) DNA damage did not differ statistically significantly between ZP- and ZP+ embryos (12.60±2.53% Tail DNA vs 11.04±1.50 (p=0.583) for the control group and 49.23±4.16 vs 41.13±4.31 (p=0.182) for the H₂O₂ group); 3) H₂O₂ and SSI induced a statistically significant increase in DNA damage compared with the control group (41.13±4.31% Tail DNA, 36.33±3.02 and 11.04±1.50 (p<0.0001)). The CA on mammal embryos was optimized by using thawed embryos, by avoiding ZP removal and by the adjunction of a third agarose layer.

Selection of porcine oocytes in vitro through brilliant cresyl blue staining in distinct incubation media

Staining with brilliant cresyl blue (BCB) may be used for oocyte selection, but BCB staining itself and the most commonly used selection medium (DMPBS) may compromise the development of porcine oocytes in vitro. This study evaluated DNA fragmentation, nuclear maturation, the area of migration of cortical granules (CG) and embryo development for stained (BCB+) and unstained (BCB-) oocytes incubated in DMPBS and in a modified medium (ReproPel) tested for the first time. Unexposed (UN), BCB+ and BCB- oocytes were incubated composing six groups: DMPBS/UN; DMPBS/BCB+; DMPBS/BCB-; ReproPel/UN; ReproPel/BCB+; and ReproPel/BCB-. There were more BCB+ oocytes in ReproPel than in DMPBS (P < 0.05). The DNA fragmentation was evaluated for oocytes in DMPBS/BCB+, DMPBS/BCB-, ReproPel/BCB+, ReproPel/BCB- and in porcine follicular fluid (control). The frequency of oocytes with no DNA fragmentation was greatest (64.6%) in DMPBS/BCB+ and lowest in ReproPel/BCB+ and ReproPel/BCB- (26.8 and 34.1%, respectively) (P < 0.05). Nuclear maturation rates were greater (P < 0.05) for DMPBS/BCB+ (63.1%), ReproPel/UN (55.1%) and ReproPel/BCB+ (50.2%) than for DMPBS/UN (40.8%) and ReproPel/BCB- (35.5%). The area of CG was greater (P < 0.05) for ReproPel/BCB- (80.7%) and DMPBS/UN (77.6%) than for ReproPel/UN (34.7%). Cleavage rates for DMPBS/BCB+ and ReproPel/BCB+ were greater than for DMPBS/UN (P < 0.05). Blastocyst development rates were greatest (P < 0.05) for ReproPel/UN and ReproPel/BCB+. In both media, BCB staining was apparently unable to select competent oocytes, which likely occurred due to toxicity. Despite the similar nuclear maturation and area of CG compared with DMPBS, oocytes selected in ReproPel presented impaired DNA integrity.

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.

Markers of cellular senescence are elevated in murine blastocysts cultured in vitro: molecular consequences of culture in atmospheric oxygen

PURPOSE

We aimed to determine whether embryo culture induces markers of cellular senescence and whether these effects were dependent on culture conditions.

METHODS

Murine blastocysts were derived in vitro and in vivo and assessed for 2 primary markers of senescence: senescence-associated β-galactosidase (SA-β-gal) and phosphorylated H2A.X (γ-H2A.X), the latter being a mark of DNA oxidative damage. Expression of senescence-associated genes p21, p16, and interleukin 6 (IL6) were also assessed.

RESULTS

Compared with in vivo-derived blastocysts, in vitro embryos had high levels of SA-β-gal, nuclear γ-H2A.X, and p21 mRNA expression, indicating that a senescence-like phenotype is induced by in vitro culture. To determine the role of culture conditions, we studied the effect of oxygen (5 % vs 20 %) and protein supplementation on senescence markers. Blastocysts in reduced oxygen (5 %) had low levels of both SA-β-gal and γ-H2A.X compared with blastocysts cultured in ambient oxygen. Senescence markers also were reduced in the presence of protein, suggesting that antioxidant properties of protein reduce oxidative DNA damage in vitro.

CONCLUSION

Elevated SA-β-gal, γ-H2A.X, and p21 suggest that in vitro stress can induce a senescence-like phenotype. Reduced oxygen during embryo culture minimizes these effects, providing further evidence for potential adverse effects of culturing embryos at ambient oxygen concentrations.

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.

The influence of reduced glutathione in fertilization medium on the fertility of in vitro-matured C57BL/6 mouse oocytes

It is well known that IVM oocytes show a decreased potential for fertility and development compared with in vivo-matured oocytes. In this study, we added reduced glutathione (GSH) to the fertilization medium during IVF to investigate its effect on the fertility and early embryo development of IVM oocytes. The fertilization rate for IVM oocytes and fresh sperm increased with the addition of GSH (0, 1.0, and 2.0 mM: 51%, 76%, and 70%). Moreover, the addition of GSH to the fertilization medium also improved the developmental potential compared with the control sample (0 mM). In addition, we performed IVF using IVM oocytes and frozen/thawed sperm that had been cryopreserved in a mouse bank. Results indicated a marked increase in the fertilization rate when 1.0 mM GSH was added to the fertilization medium compared with when no GSM was used (0.0 mM GSH: 2% (3/195); 1.0 mM GSH: 33% (156/468)). Furthermore, the fertilization rate improved dramatically via zona drilling using laser equipment (52%: 267/516), whereas normal offspring were obtainsed after transferring embryos created via IVF using IVM oocytes and frozen/thawed sperm. This is the first report in which offspring have been obtained via IVF using IVM oocytes and frozen/thawed sperm.

Could time-lapse embryo imaging reduce the need for biopsy and PGS?

PURPOSE

To review relevant studies examining the relationship between embryo morpho-kinetics and aneuploidy.

METHODS

Search of Pubmed and Medline using relevant keywords pertaining to morphology, morphokinetics and embryonic aneuploidy, as well as examination of various reference lists and conference proceedings.

RESULTS

An abundance of publications, both preliminary and peer-reviewed, have emerged regarding the usefulness of time-lapse imaging in tracking embryo development and improving embryo selection. Recently, these publications have explored ability to not only predict blastocyst formation and implantation, but also the ability to detect embryonic chromosomal aneuploidy. Of the two peer-reviewed retrospective studies on morpho-kinetics and embryonic aneuploidy, one demonstrates that early cleavage timings can indicate chromosomal complement, while the other demonstrates that key events following the maternal-zygotic transition can be markers of aneuploidy. A recent paper also demonstrates improved outcomes following IVF using a selection algorithm to identify embryos at "low risk" of chromosomal abnormalities. However, the predictive nature of these events and timings is far from ideal. Additionally, results may be dependent upon the day of biopsy and method utilized for chromosomal assessment.

CONCLUSION

With continued effort, the combination of multiple morphologic endpoint assessments and developmental timings and refinement of modeling systems may improve the predictive ability to determine embryonic aneuploidy. This may help select a subset of embryos that are less likely to carry chromosomal abnormalities and improve assisted reproductive outcomes. However, embryo biopsy, followed by preimplantation genetic screening/comprehensive chromosomal screening still remains the most reliable method to assess chromosomal complement of preimplantation embryos.

Mitochondrial and DNA damage in bovine somatic cell nuclear transfer embryos

The generation of reactive oxygen species (ROS) and subsequent mitochondrial and DNA damage in bovine somatic cell nuclear transfer (SCNT) embryos were examined. Bovine enucleated oocytes were electrofused with donor cells and then activated by a combination of Ca-ionophore and 6-dimethylaminopurine culture. The H2O2 and ˙OH radical levels, mitochondrial morphology and membrane potential (ΔΨ), and DNA fragmentation of SCNT and in vitro fertilized (IVF) embryos at the zygote stage were analyzed. The H2O2 (35.6 ± 1.1 pixels/embryo) and ˙OH radical levels (44.6 ± 1.2 pixels/embryo) of SCNT embryos were significantly higher than those of IVF embryos (19.2 ± 1.5 and 23.8 ± 1.8 pixels/embryo, respectively, p < 0.05). The mitochondria morphology of SCNT embryos was diffused within the cytoplasm. The ΔΨ of SCNT embryos was significantly lower (p < 0.05) than that of IVF embryos (0.95 ± 0.04 vs. 1.21 ± 0.06, red/green). Moreover, the comet tail length of SCNT embryos was longer than that of IVF embryos (515.5 ± 26.4 μm vs. 425.6 ± 25.0 μm, p < 0.05). These results indicate that mitochondrial and DNA damage increased in bovine SCNT embryos, which may have been induced by increased ROS levels.

Oxidative stress and redox regulation on in vitro development of mammalian embryos

Many factors affect development of mammalian preimplantation embryos in vitro. It is well known that in vitro development of bovine embryos is highly affected by culture condition including energy source, growth factors, pH or gas environment. Many efforts have been made towards the suitable environments which can successfully support embryo development in vitro. For a rapid growth and differentiation, embryo requires energy by utilizing ATP, NADPH with oxygen molecules. These energy substrates are produced from the electron transport chain in the mitochondria. In addition to energy production, reactive oxygen species (ROS) are also generated as by-product of such energy production system. ROS production is sensitively controlled by the balance of oxidizing and reducing status and affected by several antioxidant enzymes such as superoxide dismutase (SOD), Catalase, glutathione peroxidase (GPx) or low molecular weight thiols such as glutathione (GSH). Imbalance of oxidation and reduction causes production of excess ROS, which causes the developmental arrest, physical DNA damage, apoptosis induction or lipid peroxidation. Environmental oxygen condition during embryo culture also highly affects embryo development as well as intracellular redox balance. Several studies have revealed that regulation of intra- and extra- cellular reducing environment by reducing excess ROS by using antioxidants, reducing oxygen concentration are effective for improving embryo development. Also, recent studies have demonstrated the difference in gene expression affected by oxidative stress. This review briefly summarizes the effects of ROS and the role of redox balance on preimplantation embryos for improving the efficiency of in vitro production of mammalian embryos.

Fundamental study of the radiation monitoring system based on evaluation of DNA lesions

The biological dosemeter that measures biological responses to ionising radiation is useful for radiation protection. This paper presents the development and characterisation of a gamma ray irradiation dosimetry system based on real-time PCR (polymerase chain reaction) methodology. Real-time PCR is used to amplify and simultaneously quantify a targeted DNA molecule. If there are no limitations due to limiting substrates or reagents, at each extension step, the amount of DNA target is doubled, leading to exponential (geometric) amplification of the specific DNA fragment. The essential point of this assay is that DNA lesions caused by ionising radiation block DNA synthesis by DNA polymerase, resulting in a decrease in the amplification of a damaged DNA template compared with that of non-damaged DNA templates.

Assessment of DNA damage during in vitro development of buffalo (Bubalus bubalis) embryos: effect of cysteamine

Comet assay was used in the present study to examine DNA damage to buffalo oocytes and embryos during in vitro culture. Embryos were produced in vitro from oocytes obtained from slaughterhouse ovaries in presence of cysteamine (IVM and IVC media supplemented with 50 and 100 μM, respectively) or in its absence (controls). Compared to controls, cysteamine supplementation increased (p < 0.01) cleavage rate and proportion of oocytes that developed to 8- to 16-cell stage. The incidence of DNA damage was lower (p < 0.01) in cysteamine group than that in controls at 8- to 16- (19.3 ± 4.24 vs 72.0 ± 5.22%) but not in 2-cell stage embryos (11.7 ± 5.63 vs 20.8 ± 5.49%) or in mature oocytes (5.3 ± 3.43 vs 10.3 ± 4.73%). The tail length, which indicates magnitude of DNA damage, was shorter (p < 0.01) in cysteamine group than in controls in mature oocytes (25.5 ± 0.5 vs 36.0 ± 0.71 pixels) and 8- to 16-cell stage (49.2 ± 1.64 vs 152.7 ± 1.28 pixels) but not in 2-cell stage embryos (36.3 ± 1.54 vs 36.4 ± 0.75 pixels). Also, exposure of oocytes/embryos to UV radiation or H2O2 caused extensive DNA damage. In conclusion, these results suggest that oocytes/embryos suffer from DNA damage during progress of in vitro culture, which can be partly ameliorated by cysteamine supplementation of culture media.

Fragmentation of embryos is associated with both necrosis and apoptosis

OBJECTIVE

To explore the association between embryo fragmentation and necrosis and apoptosis.

DESIGN

A prospective study.

SETTING

Mizmedi Hospital.

PATIENT(S)

None.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Staining with annexin V (a marker of apoptosis) and propidium iodide (PI, a marker of necrosis), DNA integrity and mitochondrial distribution, and a beneficial effect of fragment removal in human fragmented embryos.

RESULT(S)

Most of the mouse and human fragmented embryos were stained with PI but not with annexin V. The comet assay revealed severe DNA fragmentation of the fragmented human embryos but not of the unfragmented embryos. Fewer mitochondria were observed in the fragmented compared with the normal blastomeres, indicating a rapid depletion of ATP in the fragmented embryos. Microsurgical fragment removal from the embryos had a beneficial effect on their subsequent development.

CONCLUSION(S)

Fragments of human embryos exhibited various characteristics of necrosis, such as staining with PI, DNA fragmentation, rapid depletion of ATP, and harmful effects on neighboring blastomeres. We suggest that the fragmentation of embryos is closely associated with both necrosis and apoptosis. Whether this fragmentation is associated with primary or secondary necrosis remains to be elucidated.

Quality Management Issues in the Assisted Reproduction Laboratory

In the United States, the Clinical Laboratory Improvement Act (CLIA) of 1988 describes requirements and guidelines for implementing a quality control/quality assurance (QC/QA) program for moderate and high complexity laboratories. These requirements and guidelines apply to Assisted Reproductive Technology (ART) laboratories as well. The general topic of QC and QA as it pertains to in vitro fertilization (IVF) and embryo transfer (ET) is extensively reviewed. This review summarizes many of the QC and QA events that contribute to the advancement of knowledge in this biotechnological field. These events include control of the culture environment inside and outside of the incubator, as well as factors that affect culture media. This review also discusses, in considerable detail, the QC and the QA that pertain to equipment used within the laboratory and how to control for potential contaminants, which reside within the laboratory. This review provides evidence to indicate the need for laboratory personnel to monitor quality improvement issues on a continuous basis. Personnel must be willing to change as improvements in technology occur in order to meet the ever-evolving demands of a more difficult patient population. Suggestions for meeting these demands are offered.

Effect of embryonic fibroblast cell co-culture on development of mouse embryos following exposure to visible light

PURPOSE

To determine the effects of visible light on development of mouse embryos and the potential of fibroblast cells to overcome deleterious effects of visible light on mouse preimplantation stage embryos.

METHODS

Two-cell mouse embryos were randomly allocated to un-exposed group (control) and exposed group receiving 1600 lx visible light for various time lengths. Both exposed and un-exposed embryos were co-cultured with either Mouse Embryonic Fibroblast (MEF) or Human Embryonic Fibroblast (HEF). Developmental rate of embryos at day 3 (morula), 4 (expanded blastocyst) and 5 (hatching or hatched blastocyst) was evaluated.

RESULTS

Exposure of embryos to visible light for 30 min decreased developmental rate significantly (P<0.01). Developmental rate of exposed embryos co-cultured with MEF (58%; p<0.05 both at day 4 and 5) and HEF (67%; P<0.01 both at day 4 and 5) was higher than control.

CONCLUSIONS

Visible light adversely affects embryo development in a time-dependent manner. Feeder cells may enhance embryo development particularly when suboptimal conditions are involved.

DNA damage and metabolic activity in the preimplantation embryo

BACKGROUND

Embryos with greater viability have a lower or 'quieter' amino acid metabolism than those which arrest. We have hypothesized this is due to non-viable embryos possessing greater cellular/molecular damage and consuming more nutrients, such as amino acids for repair processes. We have tested this proposition by measuring physical damage to DNA in bovine, porcine and human embryos at the blastocyst stage and relating the data to amino acid profiles during embryo development.

METHODS

Amino acid profiles of in vitro-derived porcine and bovine blastocysts were measured by high-performance liquid chromatography and the data related retrospectively to DNA damage in each individual blastomere using a modified alkaline comet assay. Amino acid profiles of spare human embryos on Day 2-3 were related to DNA damage at the blastocyst stage.

RESULTS

A positive correlation between amino acid turnover and DNA damage was apparent when each embryo was examined individually; a relationship exhibited by all three species. There was no relationship between DNA damage and embryo grade.

CONCLUSIONS

Amino acid profiling of single embryos can provide a non-invasive marker of DNA damage at the blastocyst stage. The data are consistent with the quiet embryo hypothesis with viable embryos (lowest DNA damage) having the lowest amino acid turnover. Moreover, these data support the notion that metabolic profiling, in terms of amino acids, might be used to select single embryos for transfer in clinical IVF.

Heat shock-derived reactive oxygen species induce embryonic mortality in in vitro early stage bovine embryos

Heat shock is known to increase the mortality of early stage embryos, but the exact mechanism is unclear. In the present study, we investigated the possibility that the increased mortality is caused by heat shock-generated reactive oxygen species (ROS). The level of ROS was controlled by using beta-mercaptoethanol (beta-ME), a scavenger of ROS. In vitro-produced 8-cell stage embryos were cultured at 38.5 C or heat-shocked by exposure to 41 C for 6 h with 0, 10 and 50 microM beta-ME. Intracellular ROS levels were measured by a fluorescent dye, 2',7'-dichlorodihydrofluorescein diacetate (DCHFDA), and intracellular reduced form of glutathione (GSH) contents were estimated by another fluorescent dye, 4-chloromethyl-6,8-difluoro-7-hydroxycoumarin. Total glutathione content was estimated by the glutathione recycling assay. On day 8 after insemination, heat shock decreased the percentage of embryos that developed to the blastocyst stage and increased intracellular ROS levels, but there was no significant effect on the GSH and total glutathione contents. In contrast, beta-ME significantly decreased ROS levels in heat-shocked embryos and increased the GSH and total glutathione concentrations. Ten microM beta-ME significantly improved the viability of heat-shocked embryos. beta-ME caused no detrimental effects when it was added at normal culture temperature (38.5 C). These results indicate that ROS is the primary cause of increased embryonic mortality in heat-shocked early stage embryos.

DL-alpha-tocopherol acetate mitigates maternal hyperthermia-induced pre-implantation embryonic death accompanied by a reduction of physiological oxidative stress in mice

Maternal hyperthermia induces pre-implantation embryo death, which is accompanied by enhanced physiological oxidative stress. We evaluated whether the administration of DL-alpha-tocopherol acetate (TA) to hyperthermic mothers mitigated pre-implantation embryo death. Mice were exposed to heat stress (35 degrees C, 60% relative humidity) for 12 h or not heated (25 degrees C) on the day of mating. Twelve hours before the beginning of temperature treatment, TA was injected intraperitoneally at a dose of 1 g/kg body weight. After the treatment, zygotes were recovered and the developmental abilities and intracellular glutathione (GSH) levels were evaluated. Another set of mice, with or without TA treatment, was exposed to heat stress for 12, 24 and 36 h, and the urinary levels of the oxidative stress marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) were measured. Heat stress significantly decreased the blastocyst development rate and the GSH content in zygotes, as compared with the non-heat-stressed embryos, while TA administration significantly mitigated the deleterious effects of heat stress with regard to both parameters. Moreover, although the urinary levels of 8-OHdG gradually increased according to the duration of heat exposure, with or without TA administration, the levels were lower in the TA-administered group than in the placebo-injected mice. These results suggest that heat stress enhances physiological oxidative stress, and that TA administration alleviates the hyperthermia-induced death of pre-implantation embryos by reducing physiological oxidative stress.

Bacterial endotoxin (LPS)-induced DNA damage in preimplanting embryonic and uterine cells inhibits implantation

OBJECTIVE

To investigate lipopolysaccharide (LPS)-induced DNA damage in preimplanting embryonic and uterine cells during preimplantation period of pregnancy that may ultimately inhibit the process of implantation in mouse.

DESIGN

Animal study.

SETTING

Academic research environment.

ANIMAL(S)

Sixty four Park strain female mice.

INTERVENTION(S)

The "minimum dose" (MD) of LPS was injected intraperitoneally in the pregnant females on day 0.5 of pregnancy, and individual embryos and uterine cells were assessed by comet assay on days 1.5, 2.5, 3.5, and 4.375 of the preimplantation period of pregnancy.

MAIN OUTCOME MEASURE(S)

Percentage of embryos and uterine cells with tail, mean comet tail length, percentage of fragmented DNA in tail.

RESULT(S)

Significantly higher numbers of embryos with higher mean comet tail length and percentage of fragmented DNA in tail were observed in the LPS-treated compared with control animals as the period of pregnancy approaches the stage of implantation. At the same time, DNA damage was also significantly higher in the uterine cells of LPS-treated compared with control animals.

CONCLUSION(S)

The MD of LPS can induce DNA damage in the preimplantation-stage embryos and uterine cells, which causes poor embryonic development and improper preparation of uterine horns during the preimplantation period of pregnancy, which may ultimately inhibit the process of implantation in mouse.

Endotoxin-induced silencing of mesoderm induction and functional differentiation: role of HMGB1 in pluripotency and infection

OBJECTIVES

Mechanisms underpinning Gram-negative bacterial vaginosis-induced birth anomalies are obscure. Ethical issues limit such studies on peri-implantation-stage human embryos. Here we have used embryoid bodies (EBs) as an in vitro model to examine the effect of Gram-negative bacterial endotoxins/lipopolysaccharides (LPS) on the faithful induction of germ lineages during embryogenesis. The role of LPS-inducible cytokine and pluripotency-related DNA-binding protein HMGB1 was also studied in these EBs.

METHODS

EBs derived from the human embryonic stem cell line HUES9 were exposed to 12.5 pg/ml of LPS for 48 h. The expression profile of the ectoderm, endoderm, mesoderm and trophectoderm lineage markers, such as beta III-tubulin, GATA4, BMP2, Brachury and beta-hCG, were studied, by RT-PCR and immunofluorescence. Inhibition of mesoderm induction was confirmed by RT-PCR analysis for hANP, cTnT, ABCG2, GATA2, BMP4 and HAND1. Osteoblast differentiation was induced in the EBs, and confirmed by von Kosa and Alizarin red staining. A comet assay was also carried out to assess the degree of apoptosis in these EBs.

RESULTS AND CONCLUSIONS

We found that the LPS-treated EBs were selectively silenced for mesoderm markers and failed to differentiate into functional osteoblasts. HMGB1 expression was absent in the normal EBs and was found to be localized in the cytoplasm of the LPS-treated EBs. Overall, our data indicate that endotoxin-induced HMGB1 expression in the peri-implantation-stage embryos can bring about severe birth defects of, for example, the bone and heart. This study also indicates that HMGB1 could be involved in maintenance of pluripotency in the human embryonic stem cells by impeding their differentiation.

Light exposure of the ovum and preimplantation embryo during ART procedures

Exposure to visible light (400-700 nm wavelengths) is an unnatural stress factor to preimplantation embryos cultured in vitro. This study investigated the spectral composition and intensity of light during IVF procedures, and calculated radiation doses reaching the embryo during handling and manipulation. The study shows that normal IVF procedure may result in stressing radiation doses, unless filters are applied. This is at present not sufficiently recognised. No Danish IVF clinics use filters to protect embryos against visible light. 95% of the radiation was from microscopes. Ambient light, in contrast, was not a significant contributor to light stress and the use of dark laboratories is not justified.

Effect of polyvinylpyrrolidone on bovine oocyte maturation in vitro and subsequent fertilization and embryonic development

The exact role of polyvinylpyrrolidone (PVP) in culture medium for oocyte maturation is still largely unknown. Bovine cumulus-oocyte complexes (COC) were cultured in in-vitro maturation (IVM) medium supplemented with 10% fetal bovine serum (FBS), 0.3% PVP (K-90) or 10% serum substitute supplement (SSS) respectively. The rates of oocyte maturation, fertilization and early embryonic development were evaluated. In addition, the status of DNA fragmentation in the oocytes was determined by comet assay, and the ratio of trophectoderm (TE) cells and inner cell mass (ICM) in blastocysts was determined by differential staining. Furthermore, the percentage of apoptotic cells in the blastocysts was examined by TUNEL assay. The results indicated that the effect of PVP in IVM medium was similar to FBS in terms of oocyte maturation and subsequent embryonic development. However, the addition of SSS in IVM medium retarded further embryonic development and resulted in more oocyte DNA fragmentation and a higher ratio of TE cells and ICM in the blastocysts. However, the number of apoptotic cells in blastocysts was similar among the three groups. These results suggest for the first time that the addition of PVP in oocyte maturation medium is not only a suitable substitute for serum but is also beneficial to in-vitro oocyte maturation.

Effect of gonadotrophin stimulation on mouse oocyte quality and subsequent embryonic development in vitro

In-vivo-matured oocytes were collected from naturally ovulated and superovulated [pregnant mare's serum gonadotrophin (PMSG) + human chorionic gonadotrophin (HCG)] mice. Immature oocytes were retrieved from naturally cycling mice and from mice primed with PMSG. The percentages of cleavage and blastocyst formation were significantly different (P < 0.05) between in-vivo- and in-vitro-matured oocytes. Blastocyst formation rate was significantly higher (P < 0.05) in immature oocytes derived from PMSG-primed mice, and the percentages of oocytes with comet tails, and their length, were significantly higher and longer respectively in in-vitro-matured oocytes. Total cell numbers of blastocysts were also significantly different (P < 0.05) between in-vivo- and in-vitro-matured oocytes, but there were also no differences in ratio of trophectoderm (TE)/inner cell mass (ICM). In conclusion, in-vivo-matured mouse oocytes were more competent than those matured in-vitro, perhaps due to a lesser degree of DNA damage. Embryonic development capacity of in-vivo-matured oocytes is not promoted by ovarian stimulation. Gonadotrophin priming prior to immature mouse oocyte retrieval is beneficial to subsequent embryonic development.

Addition of glutathione or thioredoxin to culture medium reduces intracellular redox status of porcine IVM/IVF embryos, resulting in improved development to the blastocyst stage

The present series of experiments investigated the effect of a reducing environment created by addition of reduced glutathione (GSH) or thioredoxin (TRX) to in vitro culture medium on the developmental competence of in vitro produced porcine embryos, and their intracellular redox status. Porcine cumulus-oocyte complexes were collected from ovaries matured and fertilized in vitro. The putative zygotes were then cultured for 6 days in modified NCSU-37 medium with or without (control) GSH or TRX, and their developmental competence was evaluated. In addition, the intracellular redox status of the cultured embryos was compared quantitatively using an index based on the ratio of the intracellular GSH content relative to the intracellular H(2)O(2) level. The proportion of embryos that developed to the blastocyst stage was significantly increased when 0.5 or 1.0 microM GSH (29.6% or 30.4%, P < 0.05 or 0.01, respectively) or 1.0 mg/ml TRX (30.6%, P < 0.01) was added to the medium compared to that without any supplementation (control; 20.1%). The intracellular redox status of embryos at the 8- to 12-cell stage or the blastocyst stage in the group cultured in the presence of GSH or TRX was significantly reduced in comparison with the control (P < 0.05 to 0.001). Furthermore, administration of GSH or TRX enhanced the total cell number (from 48.3 to 49.2) and lowered the proportion of apoptotic cells (from 6.2% to 7.0%) in blastocysts compared with the control (cell number 39.3; apoptosis rate 11.1%, P < 0.05). These results suggest that GSH or TRX can improve the in vitro development of porcine embryos, while maintaining an intracellular reductive status.

Effects of oxygen concentration and antioxidants on the in vitro developmental ability, production of reactive oxygen species (ROS), and DNA fragmentation in porcine embryos

After in vitro maturation and fertilization of porcine oocytes, the fertilized embryos were cultured under 5 or 20% oxygen (O2) for 7 days. In embryos cultured under 5% O2 versus 20% O2, development to the blastocyst stage was higher (36.3% versus 22.5%, P < 0.05); the hydrogen peroxide (H2O2) content as a reactive oxygen species was lower (92 pixels versus 111 pixels, P < 0.05); and fragmentation of DNA in 8- to 16-cell stage embryos (estimated by the comet assay) resulted in a shorter (P < 0.05) DNA tail (36 microm versus 141 microm). Antioxidants such as beta-mercaptoethanol (beta-ME) and Vitamin-E (Vit-E) suppressed oxidative damage in the embryos and improved their developmental ability. For embryos cultured under 20% O2, there were the following differences (P < 0.05) between embryos exposed to 0 microM versus 50 microM beta-ME: 28% versus 57% developed to the blastocyst stage; 125 pixels versus 98 pixels per embryo in H2O2 content; and a DNA tail of 209 microm versus 105 microm. In addition, for embryos cultured under 20% O2, there were also differences (P < 0.05) between those exposed to 0 microM versus 50 microM of Vit-E: 28% versus 40% rate of development to the blastocyst stage; 28.9 cells versus 35.9 cells in the expanded blastocyst; 122 pixels versus 95 pixels per embryo (H2O2 content); and 215 microm versus 97 microm length of the DNA tail. Therefore, a low O2 concentration during in vitro culture of porcine embryos decreased the H2O2 content and, as a consequence, reduced DNA fragmentation, and, thereby, improved developmental ability.

Developmental regulation and in vitro culture effects on expression of DNA repair and cell cycle checkpoint control genes in rhesus monkey oocytes and embryos

DNA repair is essential for maintaining genomic integrity, and may be required in the early embryo to correct damage inherited via the gametes, damage that arises during DNA replication, or damage that arises in response to exposure to genotoxic agents. The capacity of preimplantation stage mammalian embryos to repair damaged DNA has not been well characterized, particularly in primate embryos. In this study, we examined the expression of 48 mRNAs related to sensing different kinds of DNA damage, repairing that DNA damage, and controlling the cell cycle to provide an opportunity for DNA repair. The expression data reveal dynamic temporal changes, indicating a changing ability of the rhesus embryo to detect and repair different kinds of DNA damage. Low expression or overexpression of specific DNA repair genes may limit the ability of the embryo to respond to DNA damage at certain stages. Additionally, our data reveal that in vitro culture may lead to dysregulation of many such genes and a potentially impaired ability to repair DNA damage, thus affecting cellular viability and long-term embryo viability via effects on genome integrity. This effect of in vitro culture on nonhuman primate embryos may be relevant to assessing the potential advantages and disadvantages of prolonged in vitro culture of human embryos.

Effects of heat stress on the redox status in the oviduct and early embryonic development in mice

This study examined the association between redox status in the oviduct and early embryonic death in heat-stressed mice. In Experiment 1, non-pregnant mice were heat-stressed at 35 C with 60% relative humidity for 12, 24, or 36 h, and the maternal redox status was verified by measuring the levels of reactive oxygen species (ROS) and free radical scavenging activity (FRSA) in the oviduct, and thiobarbituric acid reactive substances (TBARS) and glutathione peroxidase (GSH-Px) activity in the liver. In Experiment 2, zygotes were collected from mice heat-stressed for 12 h on the day of pregnancy, and their developmental abilities were assessed in vitro, along with the intensity of DNA damage at the 2-cell stage. The TBARS value and GSH-Px activity in the liver, and ROS level in the oviduct were significantly higher in heat-stressed mice, and this increase appeared to depend on the duration of the heat stress. Maternal heat stress significantly reduced the percentage of zygotes that developed to the morula and blastocyst and the total cell number in the blastocyst. In addition, DNA damage at the 2-cell stage was significantly higher in maternally heat-stressed embryos. These results suggest that heat stress induces systemic changes in redox status in the maternal body, and the resultant increase in oxidative stress in the oviduct is possibly involved in heat stress-induced early embryonic death .

Redox status of the oviduct and CDC2 activity in 2-cell stage embryos in heat-stressed mice

Mammalian preimplantation embryos are vulnerable to heat stress. However, the mechanisms by which maternal heat stress compromises embryonic development are unclear. We hypothesized that the loss of developmental competence in maternally heat-stressed embryos results from enhanced oxidative stress in the oviducts. In experiment 1, oviducts and zygotes were collected from mice that were heat-stressed at 35 degrees C and 60% relative humidity for 12 h on the day of pregnancy as well as from control mice. The zygotes were cultured for 84 h to assess their development, and the H(2)O(2) level, glutathione concentration, and free radical scavenging activity (FRSA) were measured in the oviduct. In experiment 2, zygotes were cultured for 22 h to reach the late G(2) phase in the 2-cell stage, and Cdc2 activity was assessed using immunoblotting. A high percentage (87.6%) of control embryos developed to morulae or blastocysts, whereas the majority (67.4%) of the heat-stressed group arrested at the 2-cell stage. Although heat stress did not alter the FRSA or glutathione concentration in the oviducts, the H(2)O(2) level (P < 0.01) and its ratio to the FRSA (P < 0.05) significantly increased in the heat-stressed group. The Cdc2 activation at the 2-cell stage, as shown by the ratio of the dephosphorylated form to the phosphorylated form, was evident in control embryos but absent in heat-stressed embryos, and the level was similar to that in embryos blocked at the 2-cell stage (positive control). These results indicate that maternal heat stress enhances oxidative stress in the oviducts and that loss of developmental competence in maternally heat-stressed embryos correlates with a defect in Cdc2 activity at the 2-cell stage.

Detection of DNA damage in bovine metaphase II oocytes resulting from cryopreservation

Developmental competence of mammalian oocytes is compromised by currently available oocyte cryopreservation protocols. Experiments were designed to examine the effect of three cryopreservation protocols on the integrity of bovine oocyte DNA. In vitro matured bovine oocytes were cryopreserved either by slow cooling, vitrification in 0.25 ml straws, or in open pulled straws. After thawing/warming, recovered oocytes were immediately subjected to morphological evaluation. Morphologically intact oocytes underwent comet assay to detect cryoinjury at DNA level. All cryopreservation protocols resulted in significant morphological damage as well as DNA damage compared to unfrozen control. Among the morphologically intact oocytes, there was no difference among protocols in the number of oocytes displaying DNA damage. However, oocytes that had been cryopreserved by slow cooling or by vitrification in open pulled straws exhibited more damage than those vitrified in 0.25 ml straws in the extent of DNA damage. If we combine the number of oocytes with morphological damage and oocytes with DNA damage, oocytes cooled by slow cooling resulted in the most damage. This experiment demonstrated that oocyte DNA is a target of cryoinjury and different protocols result in different degrees of damage.

Checkpoint for DNA integrity at the first mitosis after oocyte activation

Activation of oocytes, arrested at the meiosis II (MII) in mammals, initiates meiotic release, mitotic divisions, and development. Unlike most somatic cell types, MII arrested female germ cells lack an efficient DNA integrity checkpoint control. Here we present evidence showing a unique checkpoint for DNA integrity at first mitosis after oocyte activation. Mouse oocytes carrying intact DNA cleaved normally after meiotic release, whereas 50% of oocytes harboring damaged DNA manifested cytofragmentation, a morphological hallmark of apoptosis. If not activated, DNA-damaged MII oocytes did not show apoptotic fragmentation. Further, activated, enucleated oocytes or enucleated fertilized oocytes also underwent cytofragmentation, implicating cytoplasmic coordination of the fragmentation process, independent of the nucleus. Depolymerization of either actin filaments or microtubules induced no cytofragmentation, but inhibited fragmentation upon oocyte activation. During the process of fragmentation, microtubule networks formed, then microtubule asters congregated at discrete locations, around which fragmented cellular bodies formed. Mitotic spindles, however, were not formed inactivated oocytes with damaged or absent DNA; in contrast, normal mitotic spindles were formed in activated oocytes with intact DNA. These results demonstrate that damaged DNA or absence of DNA leads to cytofragmentation after oocyte activation. Further, we found a mechanism of cytoskeletal involvement in the process of cytofragmentation. In addition, possible implication of the present findings in somatic cell cloning and human clinical embryology is discussed.