Homologous recombination and non-homologous end-joining repair pathways in bovine embryos with different developmental competence

FGF18 impairs blastocyst viability, DNA double-strand breaks and maternal recognition of pregnancy genes

Embryonic mortality in cattle is high, reaching 10-40 % in vivo and 60-70 % in vitro. Death of embryos involves reduced expression of genes related to embryonic viability, inhibition of DNA repair and increased DNA damage. In follicular granulosa cells, FGF18 from the theca layer increases apoptosis and DNA damage, so we hypothesized that FGF18 may also affect the oocyte and contribute to early embryonic death. The aims of this study were to identify the effects of FGF18 on cumulus expansion, oocyte maturation and embryo development from cleavage to blastocyst stage using a conventional bovine in vitro embryo production system using ovaries of abattoir origin. Addition of FGF18 during in-vitro maturation did not affect FSH-induced cumulus expansion or rates of nuclear maturation. When FGF18 was present in the culture system, rates of cleavage were not affected however, blastocyst and expanded blastocyst development was substantially inhibited (P < 0.05), indicating a delay of blastulation. The number of phosphorylated histone H2AFX foci per nucleus, a marker of DNA damage, was higher in cleavage-stage embryos cultured with FGF18 than in those from control group (P < 0.05). Furthermore, FGF18 decreased accumulation of PTGS2 and IFNT2 mRNA in blastocysts. In conclusion, these novel findings suggest that FGF18 plays a role in the regulation of embryonic death during the early stages of development by impairing DNA double-strand break repair and expression of genes associated with embryo viability and maternal recognition of pregnancy during the progression from oocyte to expanded blastocysts.

Analysis of nuclear maturation, DNA damage and repair gene expression of bovine oocyte and cumulus cells submitted to ionizing radiation

Radiotherapy causes destruction of tumor cells, but also threatens the integrity and survival of surrounding normal cells. Then, woman submitted to irradiation for cancer treatment may present permanent ovary damage, resulting in impaired fertility. The objective of this study was to investigate the effects of therapeutic doses of ionizing radiation (IR), used for ovarian cancer treatment in humans, on bovine cumulus-oocyte complexes (COCs) as experimental model. Bovine ovaries were exposed to 0.9 Gy, 1.8 Gy, 3.6 Gy or 18.6 Gy IR, and then COCs were collected and used to evaluate: (a) oocyte nuclear maturation; (b) presence of phosphorylated H2A.X (γH2AX), as an indicator of DNA double-strand breaks (DSBs); and (c) expression of genes involved in DNA repair (TP53BP1, RAD52, ATM, XRCC6 and XRCC5) and apoptosis (BAX). The radiation doses tested in this study had no detrimental effects on nuclear maturation and did not increase γH2AX in the oocytes. However, IR treatment altered the mRNA abundance of RAD52 (RAD52 homolog, DNA repair protein) and BAX (BCL2-associated X protein). We conclude that although IR doses had no apparent effect on oocyte nuclear maturation and DNA damage, molecular pathways involved in DNA repair and apoptosis were affected by IR exposure in cumulus cells.

Expression profile of key genes involved in DNA repair mechanisms in bovine cumulus cells cultured with bovine serum albumin or fetal calf serum

Cumulus cells from cumulus-oocyte complexes (COC) matured in vitro in serum-free medium show high incidence of apoptosis and DNA double-strand breaks (DSB). This study aimed to characterize the transcript expression profile of selected genes involved in DNA repair mechanisms in bovine cumulus cells cultured with bovine serum albumin (BSA) or fetal calf serum (FCS). Briefly, bovine cumulus-oocyte complexes were in vitro matured with either, 0.4% BSA or 10% FCS for 3, 6, 12 or 24 h. The total RNA of cumulus cells was used for real-time PCR analysis. Transcript abundance of XRCC6, XRCC5, DNAPK, GAAD45B, TP53BP1, RAD50, RAD52, ATM and BRCA2 target genes changed as the IVM proceeded (P < 0.05). However, an interaction between protein source (FCS or BSA) and time was not detected (P ≥ 0.05). Cumulus cells from COCs matured with BSA presented higher mRNA expression of two genes compared to FCS group: TP53BP1 at 6 h and BRCA1 at 3, 6, 12 and 24 h (P < 0.05). In summary, our results showed for the first time the expression profile of the key genes involved in DSB repair mechanisms in cumulus cells obtained from bovine COCs matured with FCS or BSA. The higher mRNA expression of BRCA1 and TP53BP1 and lower mRNA expression of TNFAIP6 suggests an increase in apoptosis rate and DNA damage in cumulus cells cultured in BSA-supplemented medium and may explain, at least to some extent, the reduced developmental potential of bovine oocytes matured in serum-free medium.

DNA Damage Induction Alters the Expression of Ubiquitin and SUMO Regulators in Preimplantation Stage Pig Embryos

DNA damage in early-stage embryos impacts development and is a risk factor for segregation of altered genomes. DNA damage response (DDR) encompasses a sophisticated network of proteins involved in sensing, signaling, and repairing damage. DDR is regulated by reversible post-translational modifications including acetylation, methylation, phosphorylation, ubiquitylation, and SUMOylation. While important regulators of these processes have been characterized in somatic cells, their roles in early-stage embryos remain broadly unknown. The objective of this study was to explore how ubiquitylation and SUMOylation are involved in the regulation of early development in porcine embryos by assessing the mRNA profile of genes encoding ubiquitination (UBs), deubiquitination (DUBs), SUMOylation (SUMOs) or deSUMOylation (deSUMOs) enzymes in oocyte and embryos at different stages of development, and to evaluate if the induction of DNA damage at different stages of embryo development would alter the mRNA abundance of these genes. Pig embryos were produced by in vitro fertilization and DNA damage was induced by ultraviolet (UV) light exposure for 10 s on days 2, 4 or 7 of development. The relative mRNA abundance of most UBs, DUBs, SUMOs, and deSUMOs was higher in oocytes and early-stage embryos than in blastocysts. Transcript levels for UBs (RNF20, RNF40, RNF114, RNF169, CUL5, DCAF2, DECAF13, and DDB1), DUBs (USP16), and SUMOs (CBX4, UBA2 and UBC9), were upregulated in early-stage embryos (D2 and/or D4) compared to oocytes and blastocysts. In response to UV-induced DNA damage, transcript levels of several UBs, DUBs, SUMOs, and deSUMOs decreased in D2 and D4 embryos, but increased in blastocysts. These findings revealed that transcript levels of genes encoding for important UBs, DUBs, SUMOs, and deSUMOs are regulated during early embryo development and are modulated in response to induced DNA damage. This study has also identified candidate genes controlling post-translational modifications that may have relevant roles in the regulation of normal embryo development, repair of damaged DNA, and preservation of genome stability in the pig embryo.

Cushioned centrifugation during sperm selection increases the fertilization and cleavage rates of cattle embryos produced in vitro

This study was conducted to evaluate the effect of utilization of an iodixanol-based solution as a cushioning method during the sperm selection utilizing discontinuous Percoll gradient centrifugation in in vitro production (IVP) of cattle embryos. In Experiment I, all aliquots of thawed semen were subjected to sperm selection using the same discontinuous Percoll® gradients, except for the following four conditions: presence of cushioning solution (Cushion Fluid, Minitube) during the first centrifugation process (C1), presence of cushioning solution during the second centrifugation process (C2), inclusion of cushioning solution in both centrifugation steps (C1-2), and no addiction of cushioning solution (C; control group). Recovery rates, sperm kinetics, and reactive oxygen species (ROS) production were evaluated. In Experiment II, sperm cells were processed using sperm selection conditions C and C1, and fertilization rates and embryonic development kinetics were compared between experimental groups. With use of condition C1, there was improvement in fertilization and cleavage rates when compared to use of condition C (56.4% compared with 45.5% and 80.0% compared 64.7%, respectively). In conclusion, results indicate the use of a cushioning solution during sperm selection positively affects the developmental potential of embryos.

In vitro development of IVF-derived bovine embryos following cytoplasmic microinjection for the episomal expression of the IGF2 gene

Important genomic imprinting changes usually occur following the in vitro production (IVP) of bovine embryos, especially in the imprinting pattern of components of the IGF system. This study aimed to evaluate the effects of a transient episomal overexpression of the IGF2 gene in bovine IVP embryos following embryo cytoplasmic microinjection (CMI) at the 1-cell stage on embryo survival, early and late developmental kinetics and morphological quality up to Day 7 of development. Selected cumulus-oocyte complexes (COCs) were matured and fertilized in vitro and subsequently segregated into six experimental groups: non-CMI control group and five CMI groups at increasing doses (0, 10, 20, 40 and 80 ng/μl) of a GFP vector built for the episomal expression of bovine IGF2. Zygote CMI was effective in delivering the expression vector into the ooplasm, irrespective of the groups, with 58% of positive GFP fluorescence in Day 7 blastocysts. Considering developmental rates and late embryo kinetics, the 10-ng/μl CMI vector dose promoted a lower blastocyst rate (10.4%), but for blastocysts at more advanced stages of development (93.0% blastocysts and expanded blastocysts), and higher number of cells (116.0 ± 3.0) than non-CMI controls (23.3%, 75.0% and 75.0 ± 6.8 were obtained, respectively). In conclusion, CMI at the 1-cell stage did not compromise subsequent in vitro development of surviving embryos, with the 10-ng/μl group demonstrating a possible growth-promoting effect of the IGF2 gene on embryo development, from the 1-cell to the blastocyst stage.

Altered expression of BRG1 and histone demethylases, and aberrant H3K4 methylation in less developmentally competent embryos at the time of embryonic genome activation

Epigenetics is a fundamental regulator underlying many biological functions, such as development and cell differentiation. Epigenetic modifications affect key chromatin regulation, including transcription and DNA repair, which are critical for normal embryo development. In this study, we profiled the expression of epigenetic modifiers and patterns of epigenetic changes in porcine embryos around the period of embryonic genome activation (EGA). We observed that Brahma-related gene 1 (BRG1) and Lysine demethylase 1A (KDM1A), which can alter the methylation status of lysine 4 in histone 3 (H3K4), localize to the nucleus at Day 3-4 of development. We then compared the abundance of epigenetic modifiers between early- and late-cleaving embryos, which were classified based on the time to the first cell cleavage, to investigate if their nuclear localization contributes to developmental competence. The mRNA abundance of BRG1, KDM1A, as well as other lysine demethylases (KDM1B, KDM5A, KDM5B, and KDM5C), were significantly higher in late- compared to early-cleaving embryos near the EGA period, although these difference disappeared at the blastocyst stage. The abundance of H3K4 mono- (H3K4me) and di-methylation (H3K4me2) during the EGA period was reduced in late-cleaving and less developmentally competent embryos. By contrast, BRG1, KDM1A, and H3K4me2 abundance was greater in embryos with more than eight cells at Day 3-4 of development compared to those with fewer than four cells. These findings suggest that altered epigenetic modifications of H3K4 around the EGA period may affect the developmental capacity of porcine embryos to reach the blastocyst stage. Mol. Reprod. Dev. 84: 19-29, 2017. © 2016 Wiley Periodicals, Inc.

Melatonin inhibits paraquat-induced cell death in bovine preimplantation embryos

Preimplantation embryos are sensitive to oxidative stress-induced damage that can be caused by reactive oxygen species (ROS) originating from normal embryonic metabolism and/or the external surroundings. Paraquat (PQ), a commonly used pesticide and potent ROS generator, can induce embryotoxicity. The present study aimed to investigate the effects of melatonin on PQ-induced damage during embryonic development in bovine preimplantation embryos. PQ treatment significantly reduced the ability of bovine embryos to develop to the blastocyst stage, and the addition of melatonin markedly reversed the developmental failure caused by PQ (20.9% versus 14.3%). Apoptotic assay showed that melatonin pretreatment did not change the total cell number in blastocysts, but the incidence of apoptotic nuclei and the release of cytochrome c were significantly decreased. Using real-time quantitative polymerase chain reaction analysis, we found that melatonin pre-incubation significantly altered the expression levels of genes associated with redox signaling, particularly by attenuating the transcript level of Txnip and reinforcing the expression of Trx. Furthermore, melatonin pretreatment significantly reduced the expression of the pro-apoptotic caspase-3 and Bax, while the expression of the anti-apoptotic Bcl-2 and XIAP was unaffected. Western blot analysis showed that melatonin protected bovine embryos from PQ-induced damage in a p38-dependent manner, but extracellular signal-regulated kinase (ERK) and c-JUN N-terminal kinase (JNK) did not appear to be involved. Together, these results identify an underlying mechanism by which melatonin enhances the developmental potential of bovine preimplantation embryos under oxidative stress conditions.

The Incidence of DNA Double-Strand Breaks Is Higher in Late-Cleaving and Less Developmentally Competent Porcine Embryos

Studies in different species, including human, mice, bovine, and swine, demonstrated that early-cleaving embryos have higher capacity to develop to the blastocyst stage and produce better quality embryos with superior capacity to establish pregnancy than late-cleaving embryos. It has also been shown that experimentally induced DNA damage delays embryo cleavage kinetics and reduces blastocyst formation. To gain additional insights into the effects of genome damage on embryo cleavage kinetics and development, the present study compared the occurrence of DNA double-strand breaks (DSBs) with the expression profile of genes involved in DNA repair and cell cycle control between early- and late-cleaving embryos. Porcine oocytes matured in vitro were activated, and then early-cleaving (before 24 h) and late-cleaving (between 24 and 48 h) embryos were identified and cultured separately. Developing embryos, on Days 3, 5, and 7, were used to evaluate the total cell number and presence of DSBs (by counting the number of immunofluorescent foci for phosphorylated histone H2A.x [H2AX139ph] and RAD51 proteins) and to quantify transcripts of genes involved in DNA repair and cell cycle control by quantitative RT-PCR. Early-cleaving embryos had fewer DSBs, lower transcript levels for genes encoding DNA repair and cell cycle checkpoint proteins, and more cells than late-cleaving embryos. Interestingly, at the blastocyst stage, embryos that developed from early- and late-cleaving groups had similar number of DSBs as well as transcript levels of genes induced by DNA damage. This indicates that only embryos with less DNA damage and/or superior capacity for DNA repair are able to progress to the blastocyst stage. Collectively, findings in this study revealed a negative correlation between the occurrence of DSBs and embryo cleavage kinetics and embryo developmental capacity to the blastocyst stage.

Inhibition of histone deacetylases enhances DNA damage repair in SCNT embryos

Recent studies have shown that DNA damage affects embryo development and also somatic cell reprogramming into induced pluripotent stem (iPS) cells. It has been also shown that treatment with histone deacetylase inhibitors (HDACi) improves development of embryos produced by somatic cell nuclear transfer (SCNT) and enhances somatic cell reprogramming. There is evidence that increasing histone acetylation at the sites of DNA double-strand breaks (DSBs) is critical for DNA damage repair. Therefore, we hypothesized that HDACi treatment enhances cell programming and embryo development by facilitating DNA damage repair. To test this hypothesis, we first established a DNA damage model wherein exposure of nuclear donor cells to ultraviolet (UV) light prior to nuclear transfer reduced the development of SCNT embryos proportional to the length of UV exposure. Detection of phosphorylated histone H2A.x (H2AX139ph) foci confirmed that exposure of nuclear donor cells to UV light for 10 s was sufficient to increase DSBs in SCNT embryos. Treatment with HDACi during embryo culture increased development and reduced DSBs in SCNT embryos produced from UV-treated cells. Transcript abundance of genes involved in either the homologous recombination (HR) or nonhomologous end-joining (NHEJ) pathways for DSBs repair was reduced by HDACi treatment in developing embryos at day 5 after SCNT. Interestingly, expression of HR and NHEJ genes was similar between HDACi-treated and control SCNT embryos that developed to the blastocyst stage. This suggested that the increased number of embryos that could achieve the blastocyst stage in response to HDACi treatment have repaired DNA damage. These results demonstrate that DNA damage in nuclear donor cells is an important component affecting development of SCNT embryos, and that HDACi treatment after nuclear transfer enhances DSBs repair and development of SCNT embryos.

Clinical significance of expression of RAD52 in gastric cancer

AIM: To investigate the expression of RAD52 in human gastric cancer (GC) and adjacent gastric tissues, and to explore the correlation between expression of RAD52 and clinicopathological characteristics of GC.

METHODS: Immunohistochemistry and Western blot were employed to examine the expression of RAD52 in GC and adjacent non-cancerous tissues obtained from surgical specimens of GC patients who underwent gastric resections at our hospital. The correlation between expression of RAD52 and clinicopathologic features of GC was analyzed.

RESULTS: RAD52 was mainly located in the nucleus, and the positive rate of RAD52 expression was significantly higher in GC tissues than in adjacent non-cancerous tissues (76.67% vs 6.67%, P < 0.01). Similar results were obtained in Western blot analysis. RAD52 expression was significantly correlated with clinical stage, but not with gender, age, lymph node metastasis or tumor size (P > 0.05 for all). The positive rate of RAD52 expression in stage I-II GC was significantly lower than that in stage III-ⅣGC (50% vs 85%, P < 0.05).

CONCLUSION: RAD52 may play a critical role in tumor genesis of GC. RAD52 may be a potential marker for clinical diagnosis and treatment of GC.

Phosphorylated histone H2A.x in porcine embryos produced by IVF and somatic cell nuclear transfer

Phosphorylated histone H2A.x (H2AX139ph) is a key factor for the repair of DNA double-strand breaks (DSBs) and the presence of H2AX139ph foci indicates the sites of DSBs. In this study, we characterized the presence of H2AX139ph during in vitro development of porcine embryos produced by IVF and somatic cell nuclear transfer (SCNT). Pronuclear stage embryos produced by IVF had, on average, 9.2 H2AX139ph foci per pronucleus. The number of H2AX139ph foci was higher in the 2-cell-stage embryos than in the 4-cell-stage embryos fixed at 48 h post-fertilization. The percentage of H2AX139ph-positive nuclei was higher in SCNT embryos that were activated with ionomycin (ION) alone than in those activated with ION and strontium chloride (ION+Sr(2+)). A negative correlation was found between the percentage of H2AX139ph-positive cells and the total number of cells per embryo in day 7 blastocysts produced by IVF or SCNT. Based on the detection of H2AX139ph foci, the findings of this study indicate that DSBs occur in a high proportion of porcine embryos produced by either IVF or SCNT; fast-cleaving embryos have fewer DSBs than slow-cleaving embryos; the oocyte activation protocol can affect DNA integrity in SCNT embryos; and better-quality blastocysts have fewer DSBs. We propose that the presence of H2AX139ph foci can be a useful marker of embryo quality.