Tauroursodeoxycholic acid improves pre-implantation development of porcine SCNT embryo by endoplasmic reticulum stress inhibition

Atractylenolide Ⅲ partially alleviates tunicamycin-induced damage in porcine oocytes during in vitro maturation by reducing oxidative stress

Assisted reproductive technology (ART) is widely used to address infertility and enhance reproductive outcomes in livestock. Among various ART techniques, in vitro maturation (IVM) is commonly used to obtain high-quality oocytes but is susceptible to oxidative stress. In traditional Chinese medicine, Rhizoma Atractylodis Macrocephalae (Bai Zhu) is used to enhance maternal and fetal health. Atractylenolide Ⅲ (AⅢ), a major component of Bai Zhu, has shown both antioxidant properties and oxidative stress induction, leading to controversy. This study used porcine oocytes as a model to investigate the effects of AⅢ under tunicamycin (TM)-induced oxidative stress. During IVM, oocytes were treated with various concentrations of AⅢ and a constant dose of TM. AⅢ promoted oocyte maturation and cumulus cell expansion, with the optimal concentration being 1 mg/L. AⅢ reduced reactive oxygen species (ROS) and malondialdehyde (MDA) levels, indicating reduced oxidative damage. Mitochondrial function and membrane potential (MMP) were preserved in AⅢ-treated oocytes. Additionally, AIII could alleviate TM-induced endoplasmic reticulum (ER) stress, as shown by decreased mRNA expression of ER stress markers. Following parthenogenetic activation (PA), AⅢ-treated oocytes exhibited increased cleavage and blastocyst formation rates with reduced apoptosis compared to the TM group. These findings suggest that AⅢ protects against oxidative stress, improving oocyte quality and developmental potential, with potential applications in ART.

Attenuation of endoplasmic reticulum stress improves invitro growth and subsequent maturation of bovine oocytes

Endoplasmic reticulum (ER) stress interferes with developmental processes in oocyte maturation and embryo development. Invitro growth (IVG) is associated with low developmental competence, and ER stress during IVG culture may play a role. Therefore, this study aimed to examine the effect of tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, on the IVG of bovine oocytes to understand the role of ER stress. Oocyte-granulosa cell complexes (OGCs) were collected from early antral follicles (1.5-1.8 mm) and allowed to grow in vitro for 5 days at 38.5 °C in a humidified atmosphere containing 5 % CO2. Basic growth culture medium was supplemented with TUDCA at various concentrations (0, 50, 100, 250, and 500 μM). After IVG, oocyte diameters were similar among groups, but the antrum formation rate tended to be higher in the TUDCA 100 μM group. The mRNA expression levels of ER stress-associated genes (PERK, ATF6, ATF4, CHOP, BAX, IRE1, and XBP1) in OGCs were downregulated in the TUDCA 100 μM group than those in the control group. Moreover, the TUDCA 100 μM group exhibited reduced ROS production with higher GSH levels and improved in vitro-grown oocyte maturation compared with those in the control group. In contrast, no difference in the developmental competence of embryos following invitro fertilization was observed between the control and TUDCA 100 μM groups. These results indicate that ER stress could impair IVG and subsequent maturation rate of bovine oocytes, and TUDCA could alleviate these detrimental effects. These outcomes might improve the quality of oocytes in IVG culture in assisted reproductive technology.

Schisandrin B enhances embryo competence and potentially mitigates endoplasmic reticulum stress during porcine preimplantation development

Endoplasmic reticulum (ER) stress induced by agents such as tunicamycin (TM) substantially impedes the developmental progression of porcine embryos. Lignan compounds such as Schisandrin B (Sch-B), may have the potential to mitigate this stress. However, there are few studies on the effects of Sch-B on embryo development. To address this research gap, this study evaluates the protective efficacy of Sch-B against TM-induced ER stress during pivotal stages of porcine embryogenesis. Notably, embryos treated with Sch-B exhibited pronounced resistance to TM-induced developmental arrest, particularly at the 4-cell stage, facilitating progression to the 8-cell stage and subsequent blastocyst formation. It was also observed that Sch-B effectively reduced reactive oxygen species (ROS) levels and improved mitochondrial membrane potential (MMP). Furthermore, Sch-B positively influenced the expression of several stress-related genes. These findings highlight the promising role of Sch-B in improving porcine embryo development and mitigating ER stress.

Ochratoxin A triggers endoplasmic reticulum stress through PERK/NRF2 signaling and DNA damage during early embryonic developmental competence in pigs

Ochratoxin A (OTA), a mycotoxin found in foods, has a deleterious effect on female reproduction owing to its endocrine-disrupting activity mediated through endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) production. However, the mechanisms of OTA-induced ER stress in pig embryos during in vitro culture (IVC) are not yet fully understood. In the present study, porcine embryos were cultured for two days in an IVC medium supplemented with 0.5, 1.0, and 5.0 μM OTA, which led to an OTA-induced reduction in the developmental rate of blastocysts. The mRNA-seq transcriptome analysis revealed that the reduced blastocyst development ability of OTA-exposed porcine embryos was caused by ER stress, ultimately resulting in the accumulation of ROS and the occurrence of apoptosis. The expression levels of some UPR/PERK signaling-related genes (DDIT3, EIF2AK3, EIF2S1, NFE2L2, ATF4, EIF2A, and KEAP1) were found to differ in OTA-exposed pig embryos. OTA induces DNA damage by triggering an increase in RAD51/γ-H2AX levels and suppressing p-NRF2 activity. This effect is mediated through intracellular ROS and superoxide accumulation in the nuclei of porcine embryos. The cytotoxicity of OTA increased the activation of the PERK signal pathways (p-PERK, PERK, p-eIF2α, eIF2α, ATF4, and CHOP) in porcine embryos, with abnormal distribution of the ER observed around the nucleus. Collectively, our findings indicate that ER stress is a major cause of decline in the development of porcine embryos exposed to OTA. Therefore, OTA exposure induces ER stress and DNA damage via oxidative stress by disrupting PERK/NRF2 signaling activity in the developmental competence of porcine embryos during IVC.

Tauroursodeoxycholic Acid Supplementation in In Vitro Culture of Indicine Bovine Embryos: Molecular and Cellular Effects on the In Vitro Cryotolerance

During embryo development, the endoplasmic reticulum (ER) acts as an important site for protein biosynthesis; however, in vitro culture (IVC) can negatively affect ER homeostasis. Therefore, the aim of our study was to evaluate the effects of the supplementation of tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, in the IVC of bovine embryos. Two experiments were carried out: Exp. 1: an evaluation of blastocyst rate, hatching kinetics, and gene expression of hatched embryos after being treated with different concentrations of TUDCA (50, 200, or 1000 μM) in the IVC; Exp. 2: an evaluation of the re-expansion, hatching, and gene expression of hatched embryos previously treated with 200 µM of TUDCA at IVC and submitted to vitrification. There was no increase in the blastocyst and hatched blastocyst rates treated with TUDCA in the IVC. However, embryos submitted to vitrification after treatment with 200 µM of TUDCA underwent an increased hatching rate post-warming together with a down-regulation in the expression of ER stress-related genes and the accumulation of lipids. In conclusion, this work showed that the addition of TUDCA during in vitro culture can improve the cryotolerance of the bovine blastocyst through the putative modulation of ER and oxidative stress.

Cadmium exposure impairs oocyte meiotic maturation by inducing endoplasmic reticulum stress in vitro maturation of porcine oocytes

Cadmium (Cd) is toxic metal that can induce various diseases, such as cardiovascular, nervous, and reproductive systems. This study investigated the effect of Cd exposure on porcine oocyte maturation and the underlying mechanism. Porcine cumulus-oocyte complexes were exposed various Cd concentration and tauroursodeoxycholic acid (TUDCA), an inhibitor of endoplasmic reticulum (ER) stress during in vitro maturation (IVM). After IVM, we evaluated meiotic maturation, ER stress, and oocyte quality by Cd exposure. Cd exposure inhibited cumulus cell expansion and meiotic maturation, increased oocyte degeneration, and induced ER stress. The levels of spliced XBP1 and ER stress-associated transcripts, markers of ER stress, were elevated in Cd-treated cumulus-oocyte complexes and denuded oocytes during IVM. Moreover, Cd-induced ER stress impaired oocyte quality by disrupting mitochondrial function and elevating intracellular reactive oxygen species levels while decreasing ER function. Interestingly, TUDCA supplementation significantly decreased the expression of ER stress-related genes and increased the quantity of ER compared with the Cd treatment. Additionally, TUDCA was also able to rescue excessive levels of ROS and restore normal mitochondrial function. Moreover, the addition of TUDCA under Cd exposure greatly ameliorated Cd-mediated detrimental effects on meiotic maturation and oocyte quality, including cumulus cell expansion and MII rate. These findings suggest that Cd exposure during IVM impairs the meiotic maturation of oocytes by inducing of ER stress.

Vitamin C enhances porcine cloned embryo development and improves the derivation of embryonic stem-like cells

Porcine cloning through somatic cell nuclear transfer (SCNT) has been widely used in biotechnology for generating animal disease models and genetically modified animals for xenotransplantation. Vitamin C is a multifunctional factor that reacts with several enzymes. In this study, we used porcine oocytes to investigate the effects of different concentrations of vitamin C on in vitro maturation (IVM), in vitro culture (IVC), and the derivation of nuclear transfer embryonic stem-like cells (NT-ESCs). We demonstrated that vitamin C promoted the cleavage and blastocyst rate of genetically modified cloned porcine embryos and improved the derivation of NT-ESCs. Vitamin C integrated into IVM and IVC enhanced cleavage and blastocyst formation (P < 0.05) in SCNT embryos. Glutathione level was increased, and reactive oxygen species levels were decreased (P < 0.05) due to vitamin C treatment. Vitamin C decreased the gene expression of apoptosis (BAX) and increased the expression of genes associated with nuclear reprogramming (NANOG, POU5F1, SOX2, c-Myc, Klf4, and TEAD4), antioxidation (SOD1), anti-apoptotic (Bcl2), and trophectoderm (CDX2). Moreover, vitamin C improved the attachment, derivation, and passaging of NT-ESCs, while the control group showed no outgrowths beyond the primary culture. In conclusion, supplementation of vitamin C at a dose of 50 µg/ml to the IVM and IVC culture media was appropriate to improve the outcomes of porcine IVM and IVC and for the derivation of NT-ESCs as a model to study the pre- and post-implantation embryonic development in cloned transgenic embryos. Therefore, we recommend the inclusion of vitamin C as a supplementary factor to IVM and IVC to improve porcine in vitro embryonic development.

Current Progress and Prospects in Rabbit Cloning

Somatic cell nuclear transfer (SCNT) shows great value in the generation of transgenic animals, protection of endangered animals, and stem cell therapy. The combination of SCNT and gene editing has produced a variety of genetically modified animals for life science and medical research. Rabbits have unique advantages as transgenic bioreactors and human disease models; however, the low SCNT efficiency severely impedes the application of this technology. The difficulty in SCNT may be attributable to the abnormal reprogramming of somatic cells in rabbits. This review focuses on the abnormal reprogramming of cloned mammalian embryos and evaluates the progress and prospects of rabbit somatic cell cloning.

Glycine Ameliorates Endoplasmic Reticulum Stress Induced by Thapsigargin in Porcine Oocytes

The endoplasmic reticulum (ER) is a multifunctional organelle in the cytoplasm that plays important roles in female mammalian reproduction. The endoplasmic reticulum and mitochondria interact to maintain the normal function of cells by maintaining intracellular calcium homeostasis. As proven by previous research, glycine (Gly) can regulate the intracellular free calcium concentration ([Ca²⁺]_i) and enhance mitochondrial function to improve oocyte maturation in vitro. The effect of Gly on ER function during oocyte in vitro maturation (IVM) is not clear. In this study, we induced an ER stress model with thapsigargin (TG) to explore whether Gly can reverse the ER stress induced by TG treatment and whether it is associated with calcium regulation. The results showed that the addition of Gly could improve the decrease in the average cumulus diameter, the first polar body excretion rate caused by TG-induced ER stress, the cleavage rate and the blastocyst rate. Gly supplementation could reduce the ER stress induced by TG by significantly improving the ER levels and significantly downregulating the expression of genes related to ER stress (Xbp1, ATF4, and ATF6). Moreover, Gly also significantly alleviated the increase in reactive oxygen species (ROS) levels and the decrease in mitochondrial membrane potential (ΔΨ m) to improve mitochondrial function in porcine oocytes exposed to TG. Furthermore, Gly reduced the [Ca²⁺]_i and mitochondrial Ca²⁺ ([Ca²⁺]_m) levels and restored the ER Ca²⁺ ([Ca²⁺]_ER) levels in TG-exposed porcine oocytes. Moreover, we found that the increase in [Ca²⁺]_i may be caused by changes in the distribution and expression of inositol 1,4,5-triphosphate receptor (IP₃R1) and voltage-dependent anion channel 1 (VDAC1), while Gly can restore the distribution and expression of IP₃R1 and VDAC1 to normal levels. Apoptosis-related indexes (Caspase 3 activity and Annexin-V) and gene expression Bax, Cyto C, and Caspase 3) were significantly increased in the TG group, but they could be restored by adding Gly. Our results suggest that Gly can ameliorate ER stress and apoptosis in TG-exposed porcine oocytes and can further enhance the developmental potential of porcine oocytes in vitro.

Porcine oviductal extracellular vesicles facilitate early embryonic development via relief of endoplasmic reticulum stress

The key to successful in vitro embryo production (IVEP) is to mimic the natural in vivo oviductal microenvironment. Although the chemically defined media in extensive use for the in vitro culture of mammalian embryos is based on the composition of oviductal fluid, the IVEP systems in current use must still bypass the oviduct to produce embryos in vitro. Extracellular vesicles (EVs) in the oviduct are versatile intercellular delivery vehicles for maternal-embryo communication, and a lack of them can be associated with failed early embryonic development under in vitro culture conditions. Herein, we isolated EVs from porcine oviduct fluid and confirmed that oviductal EV supplementation improves the embryonic development of parthenogenetically activated (PA) embryos in terms of blastocyst formation rates and total cell numbers. Our experiments also revealed that a beneficial effect of oviductal EVs on PA embryos was achievable, at least in part, by relieving endoplasmic reticulum stress. These results suggest that the maternal-embryo communication mediated by oviductal EVs benefits early embryonic development. Given the contribution of oviductal EVs to early embryonic development, these findings offer novel insights for the optimization of current IVEP systems.

Effects of changing culture medium on preimplantation embryo development in rabbit

Many studies have focused on the optimization of the composition of embryo culture medium; however, there are few studies involving the effect of a culture medium changing procedure on the preimplantation development of embryos. In this study, three groups were designed: a non-renewal group, a renewal group and a half-renewal group. The levels of reactive oxygen species (ROS), apoptotic index, blastocyst ratio and blastocyst total cell number were analyzed in each group. The results showed that the ROS level and the apoptotic index of blastocyst in the non-renewal group were significantly higher than in the renewal group and the half-renewal group (P < 0.05). The blastocyst ratio and blastocyst total cell number were significantly higher in the half-renewal group than that in non-renewal group and the renewal group (P < 0.05). These results demonstrated that the procedure of changing the culture medium influenced ROS level, apoptotic index, blastocyst ratio and total cell number of blastocysts. In addition, the result suggested that changing the culture medium may lead to a loss of important regulatory factors for embryos, while not changing the culture medium may lead to the accumulation of toxic substances. Half-renewal can alleviate the defects of both no renewal and renewal, and benefit embryo development. This study will be of high value as a reference for the optimization of embryo culture in vitro, and is very significant for assisted reproduction.

Tauroursodeoxycholic acid/TGR5 signaling promotes survival and early development of glucose-stressed porcine embryos†

Conditions of impaired energy and nutrient homeostasis, such as diabetes and obesity, are associated with infertility. Hyperglycemia increases endoplasmic reticulum stress as well as oxidative stress and reduces embryo development and quality. Oxidative stress also causes deoxyribonucleic acid damage, which impairs embryo quality and development. The natural bile acid tauroursodeoxycholic acid reduces endoplasmic reticulum stress and rescues developmentally incompetent late-cleaving embryos, as well as embryos subjected to nuclear stress, suggesting the endoplasmic reticulum stress response, or unfolded protein response, and the genome damage response are linked. Tauroursodeoxycholic acid acts via the Takeda-G-protein-receptor-5 to alleviate nuclear stress in embryos. To evaluate the role of tauroursodeoxycholic acid/Takeda-G-protein-receptor-5 signaling in embryo unfolded protein response, we used a model of glucose-induced endoplasmic reticulum stress. Embryo development was impaired by direct injection of tauroursodeoxycholic acid into parthenogenetically activated oocytes, whereas it was improved when tauroursodeoxycholic acid was added to the culture medium. Attenuation of the Takeda-G-protein-receptor-5 precluded the positive effect of tauroursodeoxycholic acid supplementation on development of parthenogenetically activated and fertilized embryos cultured under standard conditions and parthenogenetically activated embryos cultured with excess glucose. Moreover, attenuation of tauroursodeoxycholic acid/Takeda-G-protein-receptor-5 signaling induced endoplasmic reticulum stress, oxidative stress and cell survival genes, but decreased expression of pluripotency genes in parthenogenetically activated embryos cultured under excess glucose conditions. These data suggest that Takeda-G-protein-receptor-5 signaling pathways link the unfolded protein response and genome damage response. Furthermore, this study identifies Takeda-G-protein-receptor-5 signaling as a potential target for mitigating fertility issues caused by nutrient excess-associated blastomere stress and embryo death.

Pig Cloning Using Somatic Cell Nuclear Transfer

Porcine cloning technology can be used to produce progenies genetically identical to the donor cells from high-quality breeding pigs. In addition, genetically modified pigs have been produced by somatic cell nuclear transfer using genetically modified porcine fetal fibroblasts. The method of preparing genetically modified pigs is critical for establishing pig models for human diseases, and for generating donor animals for future xenotransplantation. This chapter describes detailed procedures for generating cloned pigs using fetal fibroblasts as nuclear donors.

Development of Porcine Somatic Cell Nuclear Transfer Embryos Following Treatment Time of Endoplasmic Reticulum Stress Inhibitor

We examine the effect of endoplasmic reticulum (ER) stress inhibitor treatment time on the in vitro development of porcine somatic cell nuclear transfer (SCNT) embryos. Porcine SCNT embryos were classified by four groups following treatment time of ER stress inhibitor, tauroursodeoxycholic acid (TUDCA; 100 μM); 1) non-treatment group (control), 2) treatment during micromanipulation process and for 3 h after fusion (NT+3 h group), 3) treatment only during in vitro culture after fusion (IVC group), and 4) treatment during micromanipulation process and in vitro culture (NT+IVC group). SCNT embryos were cultured for six days to examine the X-box binding protein 1 (Xbp1) splicing levels, the expression levels of ER stress-associated genes, oxidative stress-related genes, and apoptosis-related genes in blastocysts, and in vitro development. There was no significant difference in Xbp1 splicing level among all groups. Reduced expression of some ER stress-associated genes was observed in the treatment groups. The oxidative stress and apoptosis-related genes were significantly lower in all treatment groups than control (p<0.05). Although blastocyst development rates were not different among all groups (17.5% to 21.7%), the average cell number in blastocysts increased significantly in NT+3 h (48.5±2.3) and NT+IVC (47.7±2.4) groups compared to those of control and IVC groups (p<0.05). The result of this study suggests that the treatment of ER stress inhibitor on SCNT embryos from the micromanipulation process can improve the reprogramming efficiency of SCNT embryos by inhibiting the ER and oxidative stresses that may occur early in the SCNT process.

Adiponectin Improves In Vitro Development of Cloned Porcine Embryos by Reducing Endoplasmic Reticulum Stress and Apoptosis

Simple Summary

Successful attenuation of endoplasmic reticulum (ER) stress signaling has a beneficial outcome in in vitro embryonal improvement. We evaluated the effect of adiponectin during in vitro culture in porcine embryos derived from parthenogenetic activation and somatic cell nuclear transfer (SCNT). We found that 15 and 30 μg/mL adiponectin treatment significantly improved cleavage rates, blastocyst formation rates, and total cell number (TCN) of blastocysts derived from parthenogenetic activation and reduced the expression levels of XBP1. In SCNT embryos, the cleavage rate, blastocyst formation rate, and TCN of blastocysts were significantly improved by 15 μg/mL adiponectin treatment compared to the control. In addition, the 15 μg/mL adiponectin treatment reduced the levels of XBP1 expression and ER stress-related genes, increased expression levels of pluripotency-related genes, and decreased apoptosis-related gene expression. Comprehensively, treatment with 15 μg/mL adiponectin enhanced the in vitro developmental capacity of early-stage SCNT porcine embryos by reducing ER stress and apoptosis.

Abstract

The main factor of embryonic demise is endoplasmic reticulum (ER) stress. Successful attenuation of ER stress results in an improvement in embryo development. We studied the impact of adiponectin in the in vitro culture (IVC) of porcine embryos derived from parthenogenetic activation and somatic cell nuclear transfer (SCNT). The first experiment revealed that 15 and 30 μg/mL adiponectin treatments improved cleavage, blastocyst rates, and total cell number (TCN) of parthenogenetic embryos and reduced the expression of XBP1 compared to the 5 μg/mL adiponectin treatment and control groups (p < 0.05). The second experiment showed that cleavage rate, blastocyst formation rate, and TCN of blastocysts were improved in the 15 μg/mL adiponectin treatment group compared with the control group, with significantly reduced XBP1 expression in ≥4-cell stage SCNT embryos and blastocysts (p < 0.05). Treatment with 15 μg/mL adiponectin significantly improved the expression of XBP1 and reduced the expression of ER stress-related genes (uXBP1, sXBP1, PTPN1, and ATF4), increased the expression levels of pluripotency-related genes (Nanog and SOX2), and decreased apoptosis-related gene expression (Caspase-3). These results suggest that 15 μg/mL adiponectin enhanced the in vitro developmental capacity of early-stage SCNT porcine embryos by reducing ER stress and apoptosis.

Evaluating endoplasmic reticulum stress and unfolded protein response through the lens of ecology and evolution

Considerable progress has been made in understanding the physiological basis for variation in the life-history patterns of animals, particularly with regard to the roles of oxidative stress and hormonal regulation. However, an underappreciated and understudied area that could play a role in mediating inter- and intraspecific variation of life history is endoplasmic reticulum (ER) stress, and the resulting unfolded protein response (UPR^ER ). ER stress response and the UPR^ER maintain proteostasis in cells by reducing the intracellular load of secretory proteins and enhancing protein folding capacity or initiating apoptosis in cells that cannot recover. Proper modulation of the ER stress response and execution of the UPR^ER allow animals to respond to intracellular and extracellular stressors and adapt to constantly changing environments. ER stress responses are heritable and there is considerable individual variation in UPR^ER phenotype in animals, suggesting that ER stress and UPR^ER phenotype can be subjected to natural selection. The variation in UPR^ER phenotype presumably reflects the way animals respond to ER stress and environmental challenges. Most of what we know about ER stress and the UPR^ER in animals has either come from biomedical studies using cell culture or from experiments involving conventional laboratory or agriculturally important models that exhibit limited genetic diversity. Furthermore, these studies involve the assessment of experimentally induced qualitative changes in gene expression as opposed to the quantitative variations that occur in naturally existing populations. Almost all of these studies were conducted in controlled settings that are often quite different from the conditions animals experience in nature. Herein, we review studies that investigated ER stress and the UPR^ER in relation to key life-history traits including growth and development, reproduction, bioenergetics and physical performance, and ageing and senescence. We then ask if these studies can inform us about the role of ER stress and the UPR^ER in mediating the aforementioned life-history traits in free-living animals. We propose that there is a need to conduct experiments pertaining to ER stress and the UPR^ER in ecologically relevant settings, to characterize variation in ER stress and the UPR^ER in free-living animals, and to relate the observed variation to key life-history traits. We urge others to integrate multiple physiological systems and investigate how interactions between ER stress and oxidative stress shape life-history trade-offs in free-living animals.

Epigallocatechin-3-gallate (EGCG) protects the oocytes from methyl parathion-induced cytoplasmic deformities by suppressing oxidative and endoplasmic reticulum stress

Methyl parathion (MP) is a commonly used organophosphorus insecticide in commercial farming. It is well known that MP exposure can affect the function of nervous, respiratory, cardiovascular and reproductive systems. In our previous report we have demonstrated that MP exposure results in poor oocyte maturation and defective embryo development which is mainly mediated through oxidative stress. The present investigation was designed to explore whether using a potent free radical scavenger like Epigallocatechin-3-gallate (EGCG) can help in reducing the detrimental effects of MP on the oocytes. For the study, germinal vesicle (GV) stage oocytes collected from the ovaries of adult Swiss albino mice were subjected to in vitro maturation (IVM) in the presence or absence of MP (100 μg/mL) and/or EGCG (0.25 μM). MP significantly reduced the nuclear maturation rate, and resulted in poor cytoplasmic organization which was evident from the altered distribution pattern of mitochondria, endoplasmic reticulum and abnormal spindle organization. These changes were associated with significant elevation in oxidative stress and expression of ER stress markers such as 78 kDa Glucose regulated protein (GRP78) as well as X-box binding protein-1 (XBP1) in the oocytes. Further, the oocytes exposed to MP had lower activation rate and developmental potential. Supplementation of EGCG during IVM not only improved the nuclear maturation rate but also reduced the cytoplasmic abnormalities. These beneficial effects appear to be due to mitigation of oxidative and ER stress in oocytes. In conclusion, results of our study indicate that EGCG can help in alleviating MP-induced oocyte abnormalities.

Endoplasmic Reticulum (ER) Stress Inhibitor or Antioxidant Treatments during Micromanipulation Can Inhibit Both ER and Oxidative Stresses in Porcine SCNT Embryos

We investigated the effects of endoplasmic reticulum (ER) stress inhibitor and antioxidant treatments during the micromanipulation of somatic cell nuclear transfer (SCNT) on in vitro development of SCNT embryos. Tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor and vitamin C (Vit. C), an antioxidant, were treated by alone or in combination, then, the level of X-box binding protein 1 (Xbp1) splicing and the expressions of ER stress-associated genes, oxidative stress-related genes, and apoptotic genes were confirmed in the 1-cell and blastocyst stages. In the 1-cell stage, the levels of Xbp1 splicing were significantly decreased in TUDCA and Vit. C treatment groups compared to the control (p<0.05). In addition, the expression levels of most ER stress-associated genes and oxidative stress-related genes were significantly lower in all treatment groups than the control (p<0.05), and the transcript levels of apoptotic genes were also significantly lower in all treatment groups than the control (p<0.05). In the blastocyst stage, decreased expression of ER stress-, oxidative stress-, and apoptosis-related genes were observed only in some treatments. However, the blastocyst formation rates in TUDCA and Vit. C treatment groups (24.8% and 22.0%, respectively) and mean blastocyst cell number in all treatment groups (59.7±4.3 to 63.5±3.3) were significantly higher (p<0.05) than those of control. The results showed that the TUDCA or Vit. C treatment during micromanipulation inhibited both ER and oxidative stresses in the early stage of SCNT embryos, thereby reducing cell damage and promoting in vitro development.

CRISPR/Cas9-Mediated Biallelic Knockout of IRX3 Reduces the Production and Survival of Somatic Cell-Cloned Bama Minipigs

Bama minipigs are a local pig breed that is unique to China and has a high development and utilization value. However, its high fat content, low feed utilization rate, and slow growth rate have limited its popularity and utilization. Compared with the long breeding cycle and high cost of traditional genetic breeding of pigs, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) endonuclease 9 system (CRISPR/Cas9)-mediated gene editing can cost-effectively implement targeted mutations in animal genomes, thereby providing a powerful tool for rapid improvement of the economic traits of Bama minipigs. The iroquois homeobox 3 (IRX3) gene has been implicated in human obesity. Mouse experiments have shown that knocking out IRX3 significantly enhances basal metabolism, reduces fat content, and controls body mass and composition. This study aimed to knock out IRX3 using the CRISPR/Cas9 gene editing method to breed Bama minipigs with significantly reduced fat content. First, the CRISPR/Cas9 gene editing method was used to efficiently obtain IRX3-/- cells. Then, the gene-edited cells were used as donor cells to produce surviving IRX3-/- Bama minipigs using somatic cell cloning. The results show that the use of IRX3-/- cells as donor cells for the production of somatic cell-cloned pigs results in a significant decrease in the average live litter size and a significant increase in the average number of stillbirths. Moreover, the birth weight of surviving IRX3-/- somatic cell-cloned pigs is significantly lower, and viability is poor such that all piglets die shortly after birth. Therefore, the preliminary results of this study suggest that IRX3 may have important biological functions in pigs, and IRX3 should not be used as a gene editing target to reduce fat content in Bama minipigs. Moreover, this study shows that knocking out IRX3 does not favor the survival of pigs, and whether targeted regulation of IRX3 in the treatment of human obesity will also induce severe adverse consequences requires further investigation.

Embryo aggregation regulates in vitro stress conditions to promote developmental competence in pigs

Embryo aggregation is a useful method to produce blastocysts with high developmental competence to generate more offspring in various mammals, but the underlying mechanism(s) regarding the beneficial effects are largely unknown. In this study, we investigated the effects of embryo aggregation using 4-cell stage embryos in in vitro developmental competence and the relationship of stress conditions in porcine early embryogenesis. We conducted aggregation using the well of the well system and confirmed that aggregation using two or three embryos was useful for obtaining blastocysts. Aggregated embryos significantly improved developmental competence, including blastocyst formation rate, blastomere number, ICM/TE ratio, and cellular survival rate, compared to non-aggregated embryos. Investigation into the relationship between embryo aggregation and stress conditions revealed that mitochondrial function increased, and oxidative and endoplasmic reticulum (ER)-stress decreased compared to 1X (non-aggregated embryos) blastocysts. In addition, 3X (three-embryo aggregated) blastocysts increased the expression of pluripotency, anti-apoptosis, and implantation related genes, and decreased expression of pro-apoptosis related genes. Therefore, these findings indicate that embryo aggregation regulates in vitro stress conditions to increase developmental competence and contributes to the in vitro production of high-quality embryos and the large-scale production of transgenic and chimeric pigs.

Tauroursodeoxycholic acid (TUDCA) enhanced intracytoplasmic sperm injection (ICSI) embryo developmental competence by ameliorating endoplasmic reticulum (ER) stress and inhibiting apoptosis

PURPOSE

The objective of this study was to examine the effect of tauroursodeoxycholic acid (TUDCA) on intracytoplasmic sperm injection (ICSI) embryos by evaluating endoplasmic reticulum (ER) stress, apoptosis, and embryo developmental competence in vitro and in vivo.

METHODS

ER stress-associated genes and apoptosis-associated genes were measured and apoptosis index was analyzed. Embryo developmental competence was assessed in vitro and in vivo via the inner cell mass (ICM)/trophectoderm (TE) index, pregnancy and implantation rates, and birth rate.

RESULTS

The relative mRNA and protein expression of binding immunoglobulin protein (BIP) was significantly higher in the ICSI embryo group without TUDCA treatment (ICSI-C) than in the in vitro fertilization (IVF) group and in the ICSI embryo group with TUDCA treatment (200 μM) (ICSI-T), while TUDCA ameliorated ER stress in ICSI embryos. Embryos in the ICSI-C group showed a higher apoptosis index than those in the IVF group and ICSI-T group, and there was no significant difference between the IVF group and ICSI-T group. TUDCA can significantly improve ICSI embryo developmental competence in vitro and in vivo based on the ICM/TE index, pregnancy and implantation rates, and birth rate.

CONCLUSION

ICSI embryos manifested high ER stress and high apoptosis, while TUDCA ameliorated ER stress and reduced apoptosis in ICSI embryos. TUDCA can significantly improve the developmental competence of ICSI embryos in vitro and in vivo. This study provides a new idea for improving the efficiency of ICSI, and it will also have a positive effect on the development of assisted reproduction technologies for humans and other animals.

Tauroursodeoxycholic acid acts via TGR5 receptor to facilitate DNA damage repair and improve early porcine embryo development

DNA damage associated with assisted reproductive technologies is an important factor affecting gamete fertility and embryo development. Activation of the TGR5 receptor by tauroursodeoxycholic acid (TUDCA) has been shown to reduce endoplasmic reticulum (ER) stress in embryos; however, its effect on genome damage responses (GDR) activation to facilitate DNA damage repair has not been examined. This study aimed to investigate the effect of TUDCA on DNA damage repair and embryo development. In a porcine model of ultraviolet light (UV)-induced nuclear stress, TUDCA reduced DNA damage and ER stress in developing embryos, as measured by γH2AX and glucose-regulated protein 78 immunofluorescence, respectively. TUDCA was equally able to rescue early embryo development. No difference in total cell number, DNA damage, or percentage of apoptotic cells, measured by cleaved caspase 3 immunofluorescence, was noted in embryos that reached the blastocyst stage. Interestingly, Dicer-substrate short interfering RNA-mediated disruption of TGR5 signaling abrogated the beneficial effects of TUDCA on UV-treated embryos. Quantitative PCR analysis revealed activation of the GDR, through increased messenger RNA abundance of DNAPK, 53BP1, and DNA ligase IV, as well as the ER stress response, through increased spliced XBP1 and X-linked inhibitor of apoptosis. Results from this study demonstrated that TUDCA activates TGR5-mediated signaling to reduce DNA damage and improve embryo development after UV exposure.

Imperatorin improves in vitro porcine embryo development by reducing oxidative stress and autophagy

Imperatorin (IMP), a furanocoumarin derivative with many biological properties and pharmacological activities, is widely used as an antibacterial, anti-inflammatory, antiviral, anticancer, cardiovascular and neuroprotective agent. The purpose of this study was to explore the effects of IMP on early embryo development in pigs as well as the potential mechanisms. Our results showed that IMP can enhance the developmental competence of porcine early embryos. Supplementation of in vitro culture medium with 40 μM IMP significantly increased the blastocyst rate and total cell number. At the same time, apoptosis of blastocysts was also significantly decreased in the supplemented group compared with the control group, in accordance with the subsequent results of FAS and CASP3 gene expression analysis. Furthermore, IMP attenuated intracellular reactive oxygen species (ROS) generation, increased fluorescein diacetate (FDA) and glutathione (GSH) levels. Importantly, IMP not only improved the activity of mitochondria but also inhibited the occurrence of autophagy. In addition, pluripotency-related genes (OCT4, NANOG, and SOX2) and a growth and metabolism regulatory gene (mTOR) were upregulated after IMP supplementation on Day 7. These results demonstrate that IMP exerts a beneficial effect on preimplantation embryo development by reducing oxidative stress and autophagy.

Role of endoplasmic reticulum stress on developmental competency and cryo-tolerance in bovine embryos

Endoplasmic reticulum (ER) stress, a dysfunction in protein folding capacity of the ER, is involved in many physiological responses including mammalian reproductive systems. Studies have shown that ER stress interferes with the developmental process of in vitro oocyte maturation and embryo development; however, little is known about its effects on bovine preimplantation embryonic development. In this study, we examined the effects of ER stress during IVC on developmental competency and cryo-tolerance in bovine embryos. IVF-derived zygotes were cultured in CR1aa medium supplemented with tauroursodeoxycholic acid (TUDCA) and/or tunicamycin (TM), which are ER stress-inhibitory and stress-inducing agents, respectively, for 8 days. TM treatment decreased the blastocyst developmental rate and increased the percentage of apoptotic cells compared to that in the control group (10.2 ± 2.3% vs. 39.75 ± 1.3% and 17.8 ± 1.2% vs. 3.6 ± 1.1%, respectively; P < 0.01). However, the blastocyst developmental rate was increased and the percentage of apoptotic cells was decreased by addition of TUDCA in IVC medium compared to that in the control group (50.9 ± 0.9% vs. 39.75 ± 1.3% and 1.13 ± 1.0% vs. 3.6 ± 1.1%, respectively; P < 0.01). Importantly, in the group treated with TM plus TUDCA, the developmental rate and the percentage of apoptotic cells in blastocysts were similar to that in the control group, indicating that TUDCA ameliorates the adverse effects of TM alone on embryo development. In addition, TUDCA treatment significantly reduced the reactive oxygen species, expression of ER stress (GRP78, ATF4, ATF6, IER1, and sXBP1) and pro-apoptotic (CHOP and BAX) genes, while it increased anti-apoptotic BCL2 gene expression and glutathione levels. Moreover, TUDCA improved blastocyst cryo-tolerance as marked by a significantly increased hatching rate and decreased the number of apoptotic cells recorded at 48 h after a post-warming. Therefore, in concordance with a previous report in mice or pig, we showed that TUDCA supplementation during IVC increases the developmental competency of bovine in vitro-derived embryos. Additionally, we found that the presence of TUDCA in IVC medium improves the cryo-tolerance of bovine embryos. These results suggest that modulation of ER stress during IVC contributes to the production of high-quality bovine embryos in terms of cryo-tolerance.

Real-time PCR quantification of spliced X-box binding protein 1 (XBP1) using a universal primer method

X-box binding protein 1 (XBP1) mRNA processing plays a crucial role in the unfolded protein response (UPR), which is activated in response to endoplasmic reticulum (ER) stress. Upon accumulation of the UPR-converted XBP1 mRNA splicing from an unspliced (u) XBP1 (inactive) isoform to the spliced (s) XBP1 (active) isoform, inositol-requiring enzyme 1 α (IRE1α) removes a 26-nucleotide intron from uXBP1 mRNA. Recent studies have reported the assessment of ER stress by examining the ratio of sXBP1 to uXBP1 mRNA (s/uXBP1 ratio) via densitometric analysis of PCR bands relative to increased levels of sXBP1 to uXBP1 using a housekeeping gene for normalization. However, this measurement is visualized by gel electrophoresis, making it very difficult to quantify differences between the two XBP1 bands and complicating data interpretation. Moreover, most commonly used housekeeping genes display an unacceptably high variable expression pattern of the s/uXBP1 ratio under different experimental conditions, such as various phases of development and different cell types, limiting their use as internal controls. For a more quantitative determination of XBP1 splicing activity, we measured the expression levels of total XBP1 (tXBP1: common region of s/uXBP1) and sXBP1 via real-time PCR using specific primer sets. We also designed universal real-time PCR primer sets capable of amplifying a portion of each u/s/tXBP1 mRNA that is highly conserved in eukaryotes, including humans, monkeys, cows, pigs, and mice. Therefore, we provide a more convenient and easily approachable quantitative real-time PCR method that can be used in various research fields to assess ER stress.

N-glycosylation of uterine endometrium determines its receptivity

Glycosylation alters the molecular and functional features of glycoproteins, which is closely related with many physiological processes and diseases. During "window of implantation", uterine endometrium transforms into a receptive status to accept the embryo, thereby establishing successful embryo implantation. In this article, we aimed at investigating the role of N-glycosylation, a major modification type of glycoproteins, in the process of endometrial receptivity establishment. Results found that human uterine endometrial tissues at mid-secretory phase exhibited Lectin PHA-E+L (recognizes the branched N-glycans) positive N-glycans as measured by the Lectin fluorescent staining analysis. By utilizing in vitro implantation model, we found that de-N-glycosylation of human endometrial Ishikawa and RL95-2 cells by tunicamycin (inhibitor of N-glycosylation) and peptide-N-glycosidase F (PNGase F) impaired their receptive ability to human trophoblastic JAR cells. Meanwhile, N-glycosylation of integrin αvβ3 and leukemia inhibitory factor receptor (LIFR) are found to play key roles in regulating the ECM-dependent FAK/Paxillin and LIF-induced STAT3 signaling pathways, respectively, thus affecting the receptive potentials of endometrial cells. Furthermore, in vivo experiments and primary mouse endometrial cells-embryos coculture model further verified that N-glycosylation of mouse endometrial cells contributed to the successful implantation. Our results provide new evidence to show that N-glycosylation of uterine endometrium is essential for maintaining the receptive functions, which gives a better understanding of the glycobiology of implantation.

Effects of Endoplasmic Reticulum Stress Inhibitor Treatment during the Micromanipulation of Somatic Cell Nuclear Transfer in Porcine Oocytes

We examined the effects of endoplasmic reticulum (ER) stress inhibitor treatment during the micromanipulation of porcine somatic cell nuclear transfer (SCNT) on the in vitro development of SCNT embryos. ER stress inhibitors such as salubrinal (200 nM) and tauroursodeoxycholic acid (TUDCA; 100 μM) were added to the micromanipulation medium and holding medium. The expression of X-box binding protein 1 (Xbp1), ER-stress-associated genes, and apoptotic genes in SCNT embryos was confirmed at the one-cell and blastocyst stages. Levels of Xbp1 splicing and expression of ER-stress-associated genes in SCNT embryos at the one-cell stage decreased significantly with TUDCA treatment (p<0.05). The expression of ER-stress-associated genes also decreased slightly with the addition of both salubrinal and TUDCA (Sal+TUD). The expression levels of caspase-3 and Bcl2-associated Xprotein (Bax) mRNA were also significantly lower in the TUDCA and Sal+TUD treatments (p<0.05). At the blastocyst stage, there were no differences in levels of Xbp1 splicing, and transcription of ER-stress-associated genes and apoptosis genes between control and treatment groups. However, the blastocyst formation rate (20.2%) and mean blastocyst cell number (63.0±7.2) were significantly higher (p<0.05) for embryos in the TUDCA treatment compared with those for control (12.6% and 41.7±3.1, respectively). These results indicate that the addition of ER-stress inhibitors, especially TUDCA, during micromanipulation can inhibit cellular damage and enhance in vitro development of SCNT embryos by reducing stress levels in the ER.

Identifying Biomarkers of Autophagy and Apoptosis in Transfected Nuclear Donor Cells and Transgenic Cloned Pig Embryos

In this study, we first investigated the effects of 3-methyladenine (3-MA), an autophagy inhibitor, and the inducer – rapamycin (RAPA) on the incidence of programmed cell death (PCD) symptoms during in vitro development of porcine somatic cell nuclear transfer (SCNT)-derived embryos. The expression of autophagy inhibitor mTOR protein was decreased in porcine SCNT blastocysts treated with 3MA. The abundance of the autophagy marker LC3 increased in blastocysts following RAPA treatment. Exposure of porcine SCNT-derived embryos to 3-MA suppressed their developmental abilities to reach the blastocyst stage. No significant difference in the expression pattern of PCD-related proteins was found between non-transfected dermal cell and transfected dermal cell groups. Additionally, the pattern of PCD in SCNT-derived blastocysts generated using SC and TSC was not significantly different, and in terms of porcine SCNT-derived embryo development rates and total blastocyst cell numbers, there was no significant difference between non-transfected cells and transfected cells. In conclusion, regulation of autophagy affected the development of porcine SCNT embryos. Regardless of the type of nuclear donor cells (transfected or non-transfected dermal cells) used for SCNT, there was no difference in the developmental potential and quantitative profiles of autophagy/apoptosis biomarkers between porcine transgenic and non-transgenic cloned embryos. These results led us to conclude that PCD is important for controlling porcine SCNT-derived embryo development, and that transfected dermal cells can be utilized as a source of nuclear donors for the production of transgenic cloned progeny in pigs.

Endoplasmic Reticulum (ER) Stress and Unfolded Protein Response (UPR) in Mammalian Oocyte Maturation and Preimplantation Embryo Development

Mammalian oocytes and early embryos derived from in vitro production are highly susceptible to a variety of cellular stresses. During oocyte maturation and preimplantation embryo development, functional proteins must be folded properly in the endoplasmic reticulum (ER) to maintain oocyte and embryo development. However, some adverse factors negatively impact ER functions and protein synthesis, resulting in the activation of ER stress and unfolded protein response (UPR) signaling pathways. ER stress and UPR signaling have been identified in mammalian oocytes and embryos produced in vitro, suggesting that modulation of ER stress and UPR signaling play very important roles in oocyte maturation and the development of preimplantation embryos. In this review, we briefly describe the current state of knowledge regarding ER stress, UPR signaling pathways, and their roles and mechanisms in mammalian (excluding human) oocyte maturation and preimplantation embryo development.

Strategies for improvement of cloning by somatic cell nuclear transfer

Somatic cell nuclear transfer (SCNT) is a powerful tool that is being applied in a variety of fields as diverse as the cloning and production of transgenic animals, rescue of endangered species and regenerative medicine. However, cloning efficiency is still very low and SCNT embryos generally show poor developmental competency and many abnormalities. The low efficiency is probably due to incomplete reprogramming of the donor nucleus and most of the developmental problems are thought to be caused by epigenetic defects. Applications of SCNT will, therefore, depend on improvements in the efficiency of production of healthy clones. This review has summarised the progress and strategies that have been used to make improvements in various animal species, especially over the period 2010–2017, including strategies based on histone modification, embryo aggregation and mitochondrial function. There has been considerable investiagation into the mechanisms that underpin each strategy, helping us better understand the nature of genomic reprogramming and nucleus–cytoplasm interactions.

Melatonin supplementation during prolonged in vitro maturation improves the quality and development of poor-quality porcine oocytes via anti-oxidative and anti-apoptotic effects

Poor-quality oocytes (those with 1-2 layers of cumulus cells) typically possess low meiotic competence and development. Prolonging the duration of in vitro maturation (IVM; 52 hr) can enhance the maturation rate of poor-quality oocytes, but it does not improve subsequent embryonic development. This likely reflects the increased reactive oxygen species (ROS) production and apoptosis seen in these oocytes compared with the non-prolonged IVM (44 hr) group. Melatonin is a free radical scavenger, anti-oxidant and anti-apoptotic agent that reported to enhance the quality of embryos by inhibiting ROS generation and apoptosis. Therefore, we herein investigated whether melatonin combined with prolonged IVM (52 hr) could improve the quality and development of poor-quality oocytes. We supplemented IVM and/or in vitro culture (IVC) media with various concentrations (0, 10^-7 , 10^-6 , 10^-5  M) of melatonin, and estimated parameters related to oocyte quality and development. The addition of melatonin (10^-6  M) to a prolonged IVM system improved the oocyte quality and development compared with those of the melatonin-free poor-quality oocytes group, and that this was due to decreases in ROS generation, apoptosis, and DNA damage. When melatonin was added during both IVM (10^-6  M) and IVC (10^-6  M), we observed a cumulative positive influence on the embryonic development and quality; this treatment enhanced the expression level of Oct4 and decreased the levels of ROS, DNA damage, and apoptosis. Together, these findings suggest that the combination of melatonin plus prolonged IVM can improve the quality and development of poor-quality porcine oocytes via anti-oxidative and anti-apoptotic effects.

Tauroursodeoxycholic acid (TUDCA) alleviates endoplasmic reticulum stress of nuclear donor cells under serum starvation

Serum starvation is a routine protocol for synchronizing nuclear donor cells to G0/G1 phase during somatic cell nuclear transfer (SCNT). However, abrupt serum deprivation can cause serious stress to the cells cultured in vitro, which might result in endoplasmic reticulum (ER) stress, chromosome damage, and finally reduce the success rate of SCNT. In the present study, the effects of tauroursodeoxycholic acid (TUDCA), an effective ER stress-relieving drug, on the nuclear donor cells under serum deprivation condition as well as following SCNT procedures were first assessed in the bovine. The results showed that TUDCA significantly reduced ER stress and cell apoptosis in those nuclear donor cells. Moreover, it significantly decreased the expression of Hdac1 and Dnmt1, and increased the level of H3K9 acetylation in nuclear donor cells compared with control group. SCNT reconstructed embryos cloned from TUDCA-treated donor cells showed significantly higher fusion, cleavage, blastocyst formation rate, total cell number in day 7 blastocysts, and lower apoptotic index than that from control group. In addition, the expression of Hdac1, Dnmt1 and Bax was significantly lower in blastocysts derived from TUDCA-treated donor cells than that from control group. In conclusion, TUDCA significantly reduced the ER stress of nuclear donor cells under serum starvation condition, and significantly improved the developmental competence of following SCNT reconstructed embryos when these TUDCA-treated cells were used as the nuclear donors.

Dynamic changes of SETD2, a histone H3K36 methyltransferase, in porcine oocytes, IVF and SCNT embryos

SETD2 (SET domain containing protein 2) acts as a histone H3 lysine 36 (H3K36)-specific methyltransferase and may play important roles in active gene transcription in human cells. However, its expression and role in porcine oocytes and preimplantation embryos are not well understood. Here, we used immunofluorescence and laser scanning confocal microscopy to examine SETD2 expression in porcine fetal fibroblasts, oocytes, and preimplantation embryos derived from in vitro fertilization (IVF), parthenogenetic activation (PA), and somatic cell nuclear transfer (SCNT). In porcine fetal fibroblasts, SETD2 expression was detected in interphase cells, but not in M (mitotic)-phase cells. The SETD2 signal was observed in non-surrounded nucleolus (NSN)-stage oocytes, but not in surrounded nucleolus (SN)-, metaphase I (MI)-, or metaphase II (MII)-stage oocytes. The SETD2 signal was detectable in sperm, and undetectable immediately after fertilization, detectable at the 2-cell stage, and peaked at the 4-cell stage of IVF embryos in which porcine embryonic genome is activated. Similar to the pattern found in IVF embryos, the SETD2 signal was absent from PA embryos at the 1-cell stage, but it was detected at the 2-cell stage and thereafter maintained to the blastocyst stage. Interestingly, unlike the IVF and PA embryos, the SETD2 signal was detected throughout the development of SCNT embryos, including at the 1-cell stage. These data suggest that SETD2 may be functional for embryonic gene transcription in porcine preimplantation embryos. It is further speculated that the aberrant expression of SETD2 at the 1-cell stage of porcine SCNT embryos may be a factor in the low efficiency of cloning in pig.

Relief of endoplasmic reticulum stress enhances DNA damage repair and improves development of pre-implantation embryos

Early-cleaving embryos are known to have better capacity to reach the blastocyst stage and produce better quality embryos compared to late-cleaving embryos. To investigate the significance of endoplasmic reticulum (ER) stress on early embryo cleavage kinetics and development, porcine embryos produced in vitro were separated into early- and late-cleaving groups and then cultured in the absence or presence of the ER stress inhibitor tauroursodeoxycholic acid (TUDCA). Developing embryos were collected at days 3 to 7 of culture for assessment of ER stress status, incidence of DNA double-strand breaks (DSBs), development and total cell number. In the absence of TUDCA treatment, late-cleaving embryos exhibited ER stress, higher incidence of DNA DSBs, as well as reductions in development to the blastocyst stage and total embryo cell numbers. Treatment of late-cleaving embryos with TUDCA mitigated these effects and markedly improved embryo quality and development. These results demonstrate the importance of stress coping responses in early developing embryos, and that reduction of ER stress is a potential means to improve embryo quality and developmental competence.

Reduced glutathione alleviates tunicamycin-induced endoplasmic reticulum stress in mouse preimplantation embryos

Endoplasmic reticulum (ER) stress, a dysfunction in protein-folding capacity, is involved in many pathological and physiological responses, including embryonic development. This study aims to determine the developmental competence, apoptosis, and stress-induced gene expression in mouse preimplantation embryos grown in an in vitro culture medium supplemented with different concentrations of the ER stress inducer tunicamycin (TM) and the antioxidant glutathione (GSH). Treatment of zygotes with 0.5 µg/ml TM significantly decreased (P < 0.05) the rate of blastocyst formation, whereas 1 mM GSH supplementation improved the developmental rate of blastocysts. Furthermore, TM treatment significantly increased (P < 0.05) the apoptotic index and reduced the total number of cells, whereas GSH significantly increased the total number of cells and decreased the apoptotic index. The expression levels of ER chaperones, including immunoglobulin-binding protein, activating transcription factor 6, double-stranded activated protein kinase-like ER kinase, activating transcription factor 4, and C/EBP homologous protein were significantly increased (P < 0.05) by TM, but significantly decreased (P < 0.05) by GSH treatment. A similar pattern was observed in the case of the pro-apoptotic gene, B cell lymphoma-associated X protein. The expression level of the anti-apoptotic gene B cell lymphoma 2, was decreased by TM, but significantly increased after co-treatment with GSH. In conclusion, GSH improves the developmental potential of mouse embryos and significantly alleviates ER stress.