DNA repair in mammalian embryos

XRCC1 Polymorphisms p.Arg194Trp, p.Arg280His, and p.Arg399Gln, Polycyclic Aromatic Hydrocarbons, and Infertility: A Case-Control and In Silico Study

XRCC1 is involved in repair of single-strand breaks generated by mutagenic exposure. Polymorphisms within XRCC1 affect its ability to efficiently repair DNA damage. Polycyclic aromatic hydrocarbons or PAHs are genotoxic compounds which form bulky DNA adducts that are linked with infertility. Few reports suggest combined role of XRCC1 polymorphisms and PAHs in infertility. Present study investigates association of three XRCC1 polymorphisms (p.Arg194Trp, p.Arg280His, p.Arg399Gln) with male and female infertility in a North-West Indian population using case-control approach. Additionally, in silico approach has been used to predict whether XRCC1 polymorphisms effect interaction of XRCC1 with different PAHs. For case-control study, XRCC1 polymorphisms were screened in peripheral blood samples of age- and gender-matched 201 infertile cases (♂-100, ♀-101) and 201 fertile controls (♂-100, ♀-101) using PCR-RFLP method. For in silico study, AutoDock v4.2.6 was used for molecular docking of B[a]P, BPDE-I, ( ±)-anti-BPDE, DB[a,l]P, 1-N, 2-N, 1-OHP, 2-OHF with XRCC1 and assess effect of XRCC1 polymorphisms on their interaction. In case-control study, statistical analysis showed association of XRCC1 p.Arg280His GA genotype (p = 0.027), A allele (p = 0.019) with reduced risk of male infertility. XRCC1 p.Arg399Gln AA genotype (p = 0.021), A allele (p = 0.014) were associated with reduced risk for female primary infertility. XRCC1 p.Arg194Trp T allele was associated with increased risk for female infertility (p = 0.035). In silico analysis showed XRCC1-PAH interaction with non-significant effect of XRCC1 polymorphisms on predicted binding. Therefore, present study concludes that XRCC1 polymorphism-modified risk for male and female infertility in North-West Indians without significant effect on predicted XRCC1-PAH interactions. This is the first report on XRCC1 in female infertility.

Non-coding RNAs in oral cancer: Emerging biomarkers and therapeutic frontier

Around the world, oral cancer (OC) is a major public health problem, resulting in a significant number of deaths each year. Early detection and treatment are crucial for improving patient outcomes. Recent progress in DNA sequencing and transcriptome profiling has revealed extensive non-coding RNAs (ncRNAs) transcription, underscoring their regulatory importance. NcRNAs influence genomic transcription and translation and molecular signaling pathways, making them valuable for various clinical applications. Combining spatial transcriptomics (ST) and spatial metabolomics (SM) with single-cell RNA sequencing provides deeper insights into tumor microenvironments, enhancing diagnostic and therapeutic precision for OC. Additionally, the exploration of salivary biomarkers offers a non-invasive diagnostic avenue. This article explores the potential of ncRNAs as diagnostic and therapeutic tools for OC.

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.

Oocyte Vitrification Reduces its Capability to Repair Sperm DNA Fragmentation and Impairs Embryonic Development

Oocytes play a crucial role in repairing sperm DNA damage, which can affect the next generation; however, certain factors can impair this ability. This study examined whether oocyte vitrification, a widely used method for fertility preservation, negatively affects repair ability. Male DBA/2 mice (n = 28) were injected with 101.60 µmol/100 g body weight of tert-Butyl hydroperoxide (tBHP) for 14 days to induce sperm DNA damage. Histological changes, sperm functions, and DNA fragmentation were assessed using the TUNEL assay. Cumulus-oocyte-complexes (COCs) of superovulated female DBA/2 mice (n = 28) were vitrified using the Cryotop method. Fresh and vitrified oocytes were then fertilized by tBHP-treated and untreated sperms, and subsequent embryonic development was monitored. Additionally, the expression of Mre11a, Rad51, Brca1, and Xrcc4 was assessed in resulting zygotes and blastocysts using real-time PCR. The sperm tBHP treatment reduced differentiated spermatogenic cells in the testicular tissue, sperm concentration, and motility, while increasing DNA fragmentation (P < 0.05). The fertilization rate was decreased in the tBHP-treated sperm-vitrified oocyte group (P < 0.05), and the two-cell rate diminished in tBHP-treated sperm-fresh and vitrified oocyte groups (P < 0.05). The four-cell to blastocyst rate decreased in the untreated sperm-vitrified oocyte and the tBHP-treated sperm-fresh and vitrified oocyte groups (P < 0.05), and the tBHP-treated sperm-vitrified oocyte groups had the lowest blastocyst rate. In zygotes, Brca1 was upregulated in the tBHP-treated sperm-vitrified oocyte group (P < 0.05). Also, in blastocysts, Rad51, Brca1, and Xrcc4 were significantly upregulated in the untreated sperm-vitrified oocytes group (P < 0.05). Damages to the oocyte due to vitrification can disrupt the repair of sperm DNA fragmentation and consequently impair the embryo development.

Investigation of BAK, BAX and MAD2L1 gene expression in human aneuploid blastocysts

Maintaining genomic stability is crucial for normal development. At earlier stages of preimplantation development, as the embryonic genome activation is not fully completed, the embryos may be more prone to abnormalities. Aneuploidies are one of the most common genetic causes of implantation failure or first-trimester miscarriages. Apoptosis is a crucial mechanism to eliminate damaged or abnormal cells from the organism to enable healthy growth. Therefore, this study aimed to determine the relationship between the expression levels of genes involved in apoptosis in human aneuploid and euploid blastocysts. In total, 32 human embryos obtained from 21 patients were used for this study. Trophectoderm biopsies were performed and next-generation screening was carried out for aneuploidy screening. Total RNA was extracted from each blastocyst separately and cDNA was synthesized. Gene expression levels were evaluated using RT-PCR. The statistical analysis was performed to evaluate the gene expression level variations in the euploid and aneuploid embryos, respectively. The expression level of the BAX gene was significantly different between the aneuploid and euploid samples. BAX expression levels were found to be 1.5-fold lower in aneuploid cells. However, the expression levels of BAK and MAD2L1 genes were similar in each group. This study aimed to investigate the possible role of genes involved in apoptosis and aneuploidy mechanisms. The findings of this investigation revealed that the BAX gene was expressed significantly differently between aneuploid and euploid embryos. Therefore, it is possible that the genes involved in the apoptotic pathway have a role in the aneuploidy mechanism.

Melatonin improves the vitrification of sheep morulae by modulating transcriptome

Embryo vitrification technology is widely used in livestock production, but freezing injury has been a key factor hindering the efficiency of embryo production. There is an urgent need to further analyze the molecular mechanism of embryo damage by the vitrification process. In the study, morulae were collected from Hu sheep uterine horns after superovulation and sperm transfusion. Morulae were Cryotop vitrified and warmed. Nine morulae were in the vitrified control group (frozen), and seven morulae were vitrified and warmed with 10-5 M melatonin (melatonin). Eleven non-frozen morulae were used as controls (fresh). After warming, each embryo was sequenced separately for library construction and gene expression analysis. p < 0.05 was used to differentiate differentially expressed genes (DEG). The results showed that differentiated differentially expressed genes (DEG) in vitrified morulae were mainly enriched in protein kinase activity, adhesion processes, calcium signaling pathways and Wnt, PI3K/AKT, Ras, ErbB, and MAPK signaling pathways compared to controls. Importantly, melatonin treatment upregulated the expression of key pathways that increase the resistance of morulae against vitrification induced damage. These pathways include kinase activity pathway, ErbB, and PI3K/Akt signaling pathway. It is worth mentioning that melatonin upregulates the expression of XPA, which is a key transcription factor for DNA repair. In conclusion, vitrification affected the transcriptome of in vivo-derived Hu sheep morulae, and melatonin had a protective effect on the vitrification process. For the first time, the transcriptome profiles caused by vitrification and melatonin in sheep morulae were analyzed in single embryo level. These data obtained from the single embryo level provide an important molecular mechanism for further optimizing the cryopreservation of embryos or other cells.

Genetic variants underlying spermatogenic arrests in men with non-obstructive azoospermia

Spermatogenic arrest is a severe form of non-obstructive azoospermia (NOA), which occurs in 10-15% of infertile men. Interruption in spermatogenic progression at premeiotic, meiotic, or postmeiotic stage can lead to arrest in men with NOA. Recent studies have intensively focused on defining genetic variants underlying these spermatogenic arrests by making genome/exome sequencing. A number of variants were discovered in the genes involving in mitosis, meiosis, germline differentiation and other basic cellular events. Herein, defined variants in NOA cases with spermatogenic arrests and created knockout mouse models for the related genes are comprehensively reviewed. Also, importance of gene panel-based screening for NOA cases was discussed. Screening common variants in these infertile men with spermatogenic arrests may contribute to elucidating the molecular background and designing novel treatment strategies.

Transcriptome and Proteome Analyses Reveal Stage-Specific DNA Damage Response in Embryos of Sturgeon (Acipenser ruthenus)

DNA damage during early life stages may have a negative effect on embryo development, inducing mortality and malformations that have long-lasting effects during adult life. Therefore, in the current study, we analyzed the effect of DNA damage induced by genotoxicants (camptothecin (CPT) and olaparib) at different stages of embryo development. The survival, DNA fragmentation, transcriptome, and proteome of the endangered sturgeon Acipenser ruthenus were analyzed. Sturgeons are non-model fish species that can provide new insights into the DNA damage response and embryo development. The transcriptomic and proteomic patterns changed significantly after exposure to genotoxicants in a stage-dependent manner. The results of this study indicate a correlation between phenotype formation and changes in transcriptomic and proteomic profiles. CPT and olaparib downregulated oxidative phosphorylation and metabolic pathways, and upregulated pathways involved in nucleotide excision repair, base excision repair, and homologous recombination. We observed the upregulated expression of zona pellucida sperm-binding proteins in all treatment groups, as well as the upregulation of several glycolytic enzymes. The analysis of gene expression revealed several markers of DNA damage response and adaptive stress response, which could be applied in toxicological studies on fish embryos. This study is the first complex analysis of the DNA damage response in endangered sturgeons.

Theranostic Interpolation of Genomic Instability in Breast Cancer

Breast cancer is a diverse disease caused by mutations in multiple genes accompanying epigenetic aberrations of hazardous genes and protein pathways, which distress tumor-suppressor genes and the expression of oncogenes. Alteration in any of the several physiological mechanisms such as cell cycle checkpoints, DNA repair machinery, mitotic checkpoints, and telomere maintenance results in genomic instability. Theranostic has the potential to foretell and estimate therapy response, contributing a valuable opportunity to modify the ongoing treatments and has developed new treatment strategies in a personalized manner. “Omics” technologies play a key role while studying genomic instability in breast cancer, and broadly include various aspects of proteomics, genomics, metabolomics, and tumor grading. Certain computational techniques have been designed to facilitate the early diagnosis of cancer and predict disease-specific therapies, which can produce many effective results. Several diverse tools are used to investigate genomic instability and underlying mechanisms. The current review aimed to explore the genomic landscape, tumor heterogeneity, and possible mechanisms of genomic instability involved in initiating breast cancer. We also discuss the implications of computational biology regarding mutational and pathway analyses, identification of prognostic markers, and the development of strategies for precision medicine. We also review different technologies required for the investigation of genomic instability in breast cancer cells, including recent therapeutic and preventive advances in breast cancer.

DNA damage in preimplantation embryos and gametes: specification, clinical relevance and repair strategies

BACKGROUND

DNA damage is a hazard that affects all cells of the body. DNA-damage repair (DDR) mechanisms are in place to repair damage and restore cellular function, as are other damage-induced processes such as apoptosis, autophagy and senescence. The resilience of germ cells and embryos in response to DNA damage is less well studied compared with other cell types. Given that recent studies have described links between embryonic handling techniques and an increased likelihood of disease in post-natal life, an update is needed to summarize the sources of DNA damage in embryos and their capacity to repair it. In addition, numerous recent publications have detailed novel techniques for detecting and repairing DNA damage in embryos. This information is of interest to medical or scientific personnel who wish to obtain undamaged embryos for use in offspring generation by ART.

OBJECTIVE AND RATIONALE

This review aims to thoroughly discuss sources of DNA damage in male and female gametes and preimplantation embryos. Special consideration is given to current knowledge and limits in DNA damage detection and screening strategies. Finally, obstacles and future perspectives in clinical diagnosis and treatment (repair) of DNA damaged embryos are discussed.

SEARCH METHODS

Using PubMed and Google Scholar until May 2021, a comprehensive search for peer-reviewed original English-language articles was carried out using keywords relevant to the topic with no limits placed on time. Keywords included ‘DNA damage repair’, ‘gametes’, ‘sperm’, ‘oocyte’, ‘zygote’, ‘blastocyst’ and ‘embryo’. References from retrieved articles were also used to obtain additional articles. Literature on the sources and consequences of DNA damage on germ cells and embryos was also searched. Additional papers cited by primary references were included. Results from our own studies were included where relevant.

OUTCOMES

DNA damage in gametes and embryos can differ greatly based on the source and severity. This damage affects the development of the embryo and can lead to long-term health effects on offspring. DDR mechanisms can repair damage to a certain extent, but the factors that play a role in this process are numerous and altogether not well characterized. In this review, we describe the multifactorial origin of DNA damage in male and female gametes and in the embryo, and suggest screening strategies for the selection of healthy gametes and embryos. Furthermore, possible therapeutic solutions to decrease the frequency of DNA damaged gametes and embryos and eventually to repair DNA and increase mitochondrial quality in embryos before their implantation is discussed.

WIDER IMPLICATIONS

Understanding DNA damage in gametes and embryos is essential for the improvement of techniques that could enhance embryo implantation and pregnancy success. While our knowledge about DNA damage factors and regulatory mechanisms in cells has advanced greatly, the number of feasible practical techniques to avoid or repair damaged embryos remains scarce. Our intention is therefore to focus on strategies to obtain embryos with as little DNA damage as possible, which will impact reproductive biology research with particular significance for reproductive clinicians and embryologists.

Oogenesis Arrest Prior to Birth: A Trade-off between Possible Evolutionary Advantages and Age-Related Oocyte Dysfunction?

Oogenesis in mammalian females, including humans, is arrested prior to birth. Females, therefore, are born with a limited number of primary oocytes. This is in direct contrast to males in whom spermatogenesis continues during the entire lifespan following puberty. Here, we discuss possible evolutionary advantages that this confers and contrast this with age-related decline in oocyte quality that results in diminished fertility with advancing maternal age. We believe that a better understanding of these processes would be helpful in developing strategies to preserve fertility as maternal age increases, especially in the context of the current demographic shift with more and more women seeking fertility treatment at advanced age.

Genome maintenance during embryogenesis

Genome maintenance during embryogenesis is critical, because defects during this period can be perpetuated and thus have a long-term impact on individual's health and longevity. Nevertheless, genome instability is normal during certain aspects of embryonic development, indicating that there is a balance between the exigencies of timely cell proliferation and mutation prevention. In particular, early embryos possess unique cellular and molecular features that underscore the challenge of having an appropriate balance. Here, we discuss genome instability during embryonic development, the mechanisms used in various cell compartments to manage genomic stress and address outstanding questions regarding the balance between genome maintenance mechanisms in key cell types that are important for adulthood and progeny.

Association of Assisted Reproductive Technology Treatments with Imprinting Disorders

Assisted reproductive technology (ART) is a broad field in infertility that encompasses different types of treatments. These revolutionary treatment methods aimed to aid infertile or subfertile couples. Treatment was expanded exponentially, as 1 to 3% of the births worldwide takes place with ART procedures. However, treatment is not flawless. Gametes and embryos are exposed to different chemicals and stress through treatment, which leads to disturbance in proper embryo development and results in prenatal and congenital anomalies. When compared with in-vivo development of gametes and preimplantation embryos in mice, in-vitro conditions during ART treatments have been suggested to disturb the gene expression levels, especially imprinted genes. Therefore, ART has been suggested to be associated with increased incidences of different imprinting disorders such as Beckwith–Wiedemann syndrome, Angelman syndrome, and Silver–Russell syndrome, as proved by different case reports and studies. This literature review aims to explain the association of imprinting disorders with this revolutionary treatment procedure.

Effects of Vitrification on the Blastocyst Gene Expression Profile in a Porcine Model

This study was designed to investigate the impact of vitrification on the transcriptome profile of blastocysts using a porcine (Sus scrofa) model and a microarray approach. Blastocysts were collected from weaned sows (n = 13). A total of 60 blastocysts were vitrified (treatment group). After warming, vitrified embryos were cultured in vitro for 24 h. Non-vitrified blastocysts (n = 40) were used as controls. After the in vitro culture period, the embryo viability was morphologically assessed. A total of 30 viable embryos per group (three pools of 10 from 4 different donors each) were subjected to gene expression analysis. A fold change cut-off of ±1.5 and a restrictive threshold at p-value < 0.05 were used to distinguish differentially expressed genes (DEGs). The survival rates of vitrified/warmed blastocysts were similar to those of the control (nearly 100%, n.s.). A total of 205 (112 upregulated and 93 downregulated) were identified in the vitrified blastocysts compared to the control group. The vitrification/warming impact was moderate, and it was mainly related to the pathways of cell cycle, cellular senescence, gap junction, and signaling for TFGβ, p53, Fox, and MAPK. In conclusion, vitrification modified the transcriptome of in vivo-derived porcine blastocysts, resulting in minor gene expression changes.

Ancient Sturgeons Possess Effective DNA Repair Mechanisms: Influence of Model Genotoxicants on Embryo Development of Sterlet, Acipenser ruthenus

DNA damage caused by exogenous or endogenous factors is a common challenge for developing fish embryos. DNA damage repair (DDR) pathways help organisms minimize adverse effects of DNA alterations. In terms of DNA repair mechanisms, sturgeons represent a particularly interesting model due to their exceptional genome plasticity. Sterlet (Acipenser ruthenus) is a relatively small species of sturgeon. The goal of this study was to assess the sensitivity of sterlet embryos to model genotoxicants (camptothecin, etoposide, and benzo[a]pyrene), and to assess DDR responses. We assessed the effects of genotoxicants on embryo survival, hatching rate, DNA fragmentation, gene expression, and phosphorylation of H2AX and ATM kinase. Exposure of sterlet embryos to 1 µM benzo[a]pyrene induced low levels of DNA damage accompanied by ATM phosphorylation and xpc gene expression. Conversely, 20 µM etoposide exposure induced DNA damage without activation of known DDR pathways. Effects of 10 nM camptothecin on embryo development were stage-specific, with early stages, before gastrulation, being most sensitive. Overall, this study provides foundational information for future investigation of sterlet DDR pathways.

Features of DNA Repair in the Early Stages of Mammalian Embryonic Development

Cell repair machinery is responsible for protecting the genome from endogenous and exogenous effects that induce DNA damage. Mutations that occur in somatic cells lead to dysfunction in certain tissues or organs, while a violation of genomic integrity during the embryonic period often leads to death. A mammalian embryo’s ability to respond to damaged DNA and repair it, as well as its sensitivity to specific lesions, is still not well understood. In this review, we combine disparate data on repair processes in the early stages of preimplantation development in mammalian embryos.

Relationship between nutrition and reproduction

BACKGROUND

Recently, the relationship between nutrition and reproduction is being studied. In particular, when older women receive reproductive treatment, egg aging causes greater problems than organic factors.

METHODS

This study investigated the relationship between nutrition and reproduction with a focus on factors that cause aging, including oxidation, glycation, and chronic inflammation. A large volume of data concerning each nutrient's relationship with reproductive medicine was collected from a number of observational studies.

MAIN FINDINGS

The results showed that refined carbohydrates should be avoided and care should be taken to achieve proper intake of omega-3 fatty acids. Folic acid and vitamin D were also effective. For men, antioxidant measures are especially effective. The effects of antioxidants are related to insulin resistance, which causes chronic inflammation.

CONCLUSION

Recent research has shown that rather than meal content, meal intervals are more important for improving insulin resistance. Future research should examine lifestyle-related nutrition factors and their relationships to reproductive treatment.

Early prepubertal cyclophosphamide exposure in mice results in long-term loss of ovarian reserve, and impaired embryonic development and blastocyst quality

Background

Due to improved treatment, there is an increasing focus on the reproductive potential of survivors of childhood cancer. Cytotoxic chemotherapy accelerates the decline in the number of primordial follicles within the mammalian ovary at all ages, but effects on the developmental potential of remaining oocytes following prepubertal cancer treatment are unclear.

Objectives

To investigate whether cyclophosphamide (CY) exposure in the prepubertal period in female mice influences ovarian function and the functional competence of oocytes in adulthood.

Methods

This study used Swiss albino mice as the experimental model. Female mice were treated with 200 mg/kg CY on either postnatal day 14 (CY14), 21 (CY21) or 28 (CY28) i.e at a prepubertal and 2 young postpubertal ages. At 14 weeks of life, ovarian function, functional competence of oocytes, and embryo quality were assessed.

Results

The number of primordial follicles decreased significantly in CY14 and CY21 groups compared to control (p < 0.01). The number of oocytes from superovulated was 8.5 ± 1.4, 24.1 ± 2.9 and 26.8 ± 2.1 in CY14, CY21 and CY28 respectively which was significantly lower than control (50.2 ± 3.2; p < 0.001). In vitro culture of CY14 embryos demonstrated only 55.4% blastocyst formation (p < 0.0001) and reduced ability of inner cell mass (ICM) to proliferate in vitro (p < 0.05) at 120 and 216 h post insemination respectively. On the other hand, ICM proliferation was unaltered in 2 young postpubertal ages.

Conclusion

Our results indicate long-term effects on the developmental competence of oocytes exposed to CY in early but not adult life. These data provide a mechanism whereby long-term fertility can be impaired after chemotherapy exposure, despite the continuing presence of follicles within the ovary, and support the need for fertility preservation in prepubertal girls before alkylating agent exposure.

Apoptosis triggers the release of microRNA miR-294 in spent culture media of blastocysts

Purpose

To study whether members of the miR-290-295 cluster in spent culture medium (SCM) of embryos are correlated with morphokinetics and apoptosis.

Methods

Cryopreserved 1-cell stage mouse embryos were cultured to the blastocyst stage, development was monitored by time-lapse, 59 SCM were collected, and miR-291a and miR-294 were detected with polymerase chain reaction (PCR). Blastocysts were immuno-stained for sexing (H2AK119ub) and for apoptosis (TUNEL). Each embryo and SCM were individually processed. Correlations were run between the miRNAs and developmental events (t2, t3, t4, t5, t8, tSB, tB, ECC2, ECC3, s2, s3, dB) and apoptosis (apoptotic cells/total cell number %). MiR-294 SCM and cell levels were compared in 40 blastocysts. Apoptosis was induced in 15 blastocysts with UV radiation and SCM samples were analyzed for miR-294.

Results

MiR-291a and miR-294 are released in variable levels by mouse blastocysts. Their release is similar between male and female embryos. No significant correlations were found between these miRNAs and development. MiR-294 was significantly positively correlated with apoptosis (r = 0.560, p < 0.001). Cellular expression was lower in blastocysts that released miR-294 in high levels compared with null, low, and medium release embryos (p < 0.01). UV radiation caused apoptosis which triggered higher secretion of miR-294 in 15 blastocysts versus 13 control embryos (p < 0.01).

Conclusion(s)

MicroRNAs are important regulators of preimplantation development. Apoptosis triggers the release of miR-294 by blastocysts which possibly serves a secretory role for embryo-maternal communication. SCM miRNA analysis is possible for individually cultured embryos and future studies can investigate miRNAs as noninvasive markers of embryo quality.

Electronic supplementary material

The online version of this article (10.1007/s10815-020-01796-5) contains supplementary material, which is available to authorized users.

Genetic and epigenetic alterations induced by bisphenol A exposure during different periods of spermatogenesis: from spermatozoa to the progeny

Exposure to bisphenol A (BPA) has been related to male reproductive disorders. Since this endocrine disruptor also displays genotoxic and epigenotoxic effects, it likely alters the spermatogenesis, a process in which both hormones and chromatin remodeling play crucial roles. The hypothesis of this work is that BPA impairs early embryo development by modifying the spermatic genetic and epigenetic information. Zebrafish males were exposed to 100 and 2000 μg/L BPA during early spermatogenesis and during the whole process. Genotoxic and epigenotoxic effects on spermatozoa (comet assay and immunocytochemistry) as well as progeny development (mortality, DNA repairing activity, apoptosis and epigenetic profile) were evaluated. Exposure to 100 µg/L BPA during mitosis slightly increased sperm chromatin fragmentation, enhancing DNA repairing activity in embryos. The rest of treatments promoted high levels of sperm DNA damage, triggering apoptosis in early embryo and severely impairing survival. Regarding epigenetics, histone acetylation (H3K9Ac and H3K27Ac) was similarly enhanced in spermatozoa and embryos from males exposed to all the treatments. Therefore, BPA male exposure jeopardizes embryonic survival and development due to the transmission of a paternal damaged genome and of a hyper-acetylated histone profile, both alterations depending on the dose of the toxicant and the temporal window of exposure.

Preserving Genome Integrity During the Early Embryonic DNA Replication Cycles

During the very early stages of embryonic development chromosome replication occurs under rather challenging conditions, including a very short cell cycle, absence of transcription, a relaxed DNA damage response and, in certain animal species, a highly contracted S-phase. This raises the puzzling question of how the genome can be faithfully replicated in such a peculiar metabolic context. Recent studies have provided new insights into this issue, and unveiled that embryos are prone to accumulate genetic and genomic alterations, most likely due to restricted cellular functions, in particular reduced DNA synthesis quality control. These findings may explain the low rate of successful development in mammals and the occurrence of diseases, such as abnormal developmental features and cancer. In this review, we will discuss recent findings in this field and put forward perspectives to further study this fascinating question.

Chromoanasynthesis: another way for the formation of complex chromosomal abnormalities in human reproduction

Chromoanasynthesis has been described as a novel cause of massive constitutional chromosomal rearrangements. Based on DNA replication machinery defects, chromoanasynthesis is characterized by the presence of chromosomal duplications and triplications locally clustered on one single chromosome, or a few chromosomes, associated with various other types of structural rearrangements. Two distinct mechanisms have been described for the formation of these chaotic genomic disorders, i.e. the fork stalling and template switching and the microhomology-mediated break-induced replication. Micronucleus-based processes have been evidenced as a causative mechanism, thus, highlighting the close connection between segregation errors and structural rearrangements. Accumulating data indicate that chromoanasynthesis is operating in human germline cells and during early embryonic development. The development of new tools for quantifying chromoanasynthesis events should provide further insight into the impact of this catastrophic cellular phenomenon in human reproduction.

Diet and female fertility: doctor, what should I eat?

Fecundity is the capacity to produce offspring. Identifying dietary factors that influence human fecundity is of major clinical and public health significance. This review focuses on the evidence from epidemiologic literature for the relationships between key nutritional factors and female reproductive potential. According to existing data, women trying to achieve pregnancy are encouraged to increase consumption of whole grains, omega-3 fatty acids, fish, and soy and to reduce consumption of trans fats and red meat. In addition, a daily multivitamin that contains folic acid before and during pregnancy may not only prevent birth defects, but also improve the chance of achieving and maintaining a pregnancy. In contrast, there is limited evidence supporting an association between vitamin D and human fecundity outcomes despite promising evidence from nonhuman studies. Questions for future research included the roles of other types of fat (especially omega-6 and monounsaturated fats) and protein (especially white meat and seafood) on female fertility; particular attention should also be paid to exposure to environmental contaminants in foods. Although much work remains, this review accrued best available evidence to provide practical dietary recommendations for women trying to conceive.

Spent embryo culture medium metabolites are related to the in vitro attachment ability of blastocysts

The metabolomic profile of an embryo culture medium can aid in the advanced prediction of embryonic developmental potential and genetic integrity. But it is not known if this technology can be used to determine the in vitro potential of inner cell mass (ICM) in adherence and proliferation. Here, we investigated the developmental potential of mouse 2-cell embryos carrying cisplatin-induced DNA lesions (IDL), beyond blastocyst stage using ICM outgrowth assay. The genetic integrity of ICM cells was determined by comet assay. The metabolic signatures of spent medium were recorded 84 hours post injection of hCG (hpi-hCG), and after 96 hours of extended in vitro culture (Ex 96) by NMR spectroscopy. We observed that blastocysts that lack the ability to adhere in vitro had an increased requirement of pyruvate (p < 0.01), lactate (p < 0.01), and were accompanied by a significant reduction of pyruvate-alanine ratio in the culture medium. We propose that the aforementioned metabolites from 84 hpi-hCG spent medium be further explored using appropriate experimental models, to prove their potential as biomarkers in the prediction of implantation ability of in vitro derived human embryos in clinical settings.

FIGO analysis of research priorities in hyperglycemia in pregnancy

Hyperglycemia in pregnancy (HIP) is recognized as a major underlying cause of pregnancy complications and a contributing cause to health risks throughout the subsequent life of both mothers and babies, with amplification of the global epidemic of non-communicable diseases. Although some aspects of these associations are well described, detailed understanding of basic pathophysiologic mechanisms is lacking. Improved fundamental scientific knowledge must be developed to allow logical strategies for prevention and treatment. During pregnancy, much work is required to replace current empirical approaches to diagnosis and treatment of HIP with evidence based protocols, pragmatically adapted to differing health care and health economic contexts. Further, a life cycle approach to HIP, the risk of immediate pregnancy complications and later health risks to mother and baby must be developed and implemented across a wide range of health care environments. This document aims to outline key focus areas for further basic, epidemiologic, clinical and implementation research in this important area.

Tolerance to paternal genotoxic damage promotes survival during embryo development in zebrafish (Danio rerio)

Spermatozoa carry DNA damage that must be repaired by the oocyte machinery upon fertilization. Different strategies could be adopted by different vertebrates to face the paternal genotoxic damage. Mammals have strong sperm selection mechanisms and activate a zygotic DNA damage response (DDR) (including cell cycle arrest, DNA repair and alternative apoptosis) in order to guarantee the genomic conformity of the reduced progeny. However, external fertilizers, with different reproductive strategies, seem to proceed distinctively. Previous results from our group showed a downregulation of apoptotic activity in trout embryos with a defective DNA repairing ability, suggesting that mechanisms of tolerance to damaged DNA could be activated in fish to maintain cell survival and to progress with development. In this work, zebrafish embryos were obtained from control or UV-irradiated sperm (carrying more than 10% of fragmented DNA but still preserving fertilization ability). DNA repair (γH2AX and 53BP1 foci), apoptotic activity, expression of genes related to DDR and malformation rates were analyzed throughout development. Results showed in the progeny from damaged sperm, an enhanced repairing activity at the mid-blastula transition stage that returned to its basal level at later stages, rendering at hatching a very high rate of multimalformed larvae. The study of transcriptional and post-translational activity of tp53 (ZDF-GENE-990415-270) revealed the activation of an intense DDR in those progenies. However, the downstream pro-apoptotic factor noxa (ZDF-GENE-070119-3) showed a significant downregulation, whereas the anti-apoptotic gene bcl2 (ZDF-GENE-051015-1) was upregulated, triggering a repressive apoptotic scenario in spite of a clear genomic instability. This repression can be explained by the observed upregulation of p53 isoform Δ113p53, which is known to enhance bcl2 transcription. Our results showed that tp53 is involved in DNA damage tolerance (DDT) pathways, allowing the embryo survival regardless of the paternal DNA damage. DDT could be an evolutionary mechanism in fish: tolerance to unrepaired sperm DNA could introduce new mutations, some of them potentially advantageous to face a changing environment.

Summary: In fish embryos, genomic instability generated by fertilization with DNA damaged sperm activates mechanisms of DNA damage tolerance, which seems to be mediated by Δ113p53 expression, promoting survival.

A speculative outlook on embryonic aneuploidy: Can molecular pathways be involved?

The journey of embryonic development starts at oocyte fertilization, which triggers a complex cascade of events and cellular pathways that guide early embryogenesis. Recent technological advances have greatly expanded our knowledge of cleavage-stage embryo development, which is characterized by an increased rate of whole-chromosome losses and gains, mixoploidy, and atypical cleavage morphokinetics. Embryonic aneuploidy significantly contributes to implantation failure, spontaneous miscarriage, stillbirth or congenital birth defects in both natural and assisted human reproduction. Essentially, early embryo development is strongly determined by maternal factors. Owing to considerable limitations associated with human oocyte and embryo research, the use of animal models is inevitable. However, cellular and molecular mechanisms driving the error-prone early stages of development are still poorly described. In this review, we describe known events that lead to aneuploidy in mammalian oocytes and preimplantation embryos. As the processes of oocyte and embryo development are rigorously regulated by multiple signal-transduction pathways, we explore the putative role of signaling pathways in genomic integrity maintenance. Based on the existing evidence from human and animal data, we investigate whether critical early developmental pathways, like Wnt, Hippo and MAPK, together with distinct DNA damage response and DNA repair pathways can be associated with embryo genomic instability, a question that has, so far, remained largely unexplored.

Negative effects of oxidative stress in bovine spermatozoa on in vitro development and DNA integrity of embryos

Oxidative stress in spermatozoa has effects on subsequent embryo development. The aim of the present study was to elucidate whether sperm oxidative stress results in increased DNA damage in the embryo. To this end, bovine spermatozoa were incubated for 1 h at 37°C without or with 100 µM H2O2, resulting in non-oxidised (NOX-S) and oxidised (OX-S) spermatozoa respectively. Non-incubated spermatozoa served as the control group (CON-S). After IVF, developmental rates 30, 46 and 60 h and 7 days after IVF were assessed. DNA damage was analysed in embryos using the comet assay and a DNA damage marker (γH2AX immunostaining); the apoptotic index was determined in blastocysts. Exposure of spermatozoa to H2O2 induced a significant amount of sperm chromatin damage. The use of OX-S in IVF resulted in significantly reduced cleavage and blastocyst rates compared with the use of CON-S and NOX-S. Furthermore, in embryos resulting from the use of OX-S, a developmental delay was evident 30 and 46 h after IVF. γH2AX immunostaining was lower in blastocysts than in early embryos. In blastocysts, the comet and apoptotic indices were significantly higher in embryos resulting from the use of OX-S than CON-S and NOX-S. In conclusion, oxidative stress in spermatozoa induces developmental abnormalities and is a source of DNA damage in the resulting embryos.

FSH treatment in infertile males candidate to assisted reproduction improved sperm DNA fragmentation and pregnancy rate

The purpose of this study is to evaluate whether follicle-stimulating hormone treatment improves sperm DNA parameters and pregnancy outcome in infertile male candidates to in-vitro fertilization.Observational study in 166 infertile male partners of couples undergoing in-vitro fertilization. Eighty-four patients were receiving follicle-stimulating hormone treatment (cases) and 82 refused treatment (controls). Semen parameters, sexual hormones, and sperm nucleus (fluorescence in-situ hybridization, acridine orange, TUNEL, and γH2AX) were evaluated at baseline (T0) and after 3 months (T1), when all subjects underwent assisted reproduction techniques. Statistical analysis was performed by analysis of variance.Compared to baseline, cases showed significant improvements in seminal parameters and DNA fragmentation indexes after follicle-stimulating hormone therapy (all P < 0.05), whereas no changes were observed in controls. Within cases, follicle-stimulating hormone treatment allowed to perform intrauterine insemination in 35 patients with a pregnancy rate of 23.2 %. Intracytoplasmic sperm injection was performed in all controls and in 49 patients from cases, with pregnancy rates of 23.2 and 40.8 %, respectively (P < 0.05). After 3 months (T0 vs. T1) of follicle-stimulating hormone therapy, cases with positive outcome had reduced DNA fragmentation index and lower double strand breaks (P < 0.05 and P < 0.001 vs. negative outcome, respectively).In this observational study, we showed that follicle-stimulating hormone treatment improves sperm DNA fragmentation, which in turn leads to increased pregnancy rates in infertile males undergoing in-vitro fertilization. In particular, double strand breaks (measured with γH2AX test) emerged as the most sensible parameter to follicle-stimulating hormone treatment in predicting reproductive outcome.

Assessment of DNA damage in goat preantral follicles after vitrification of the ovarian cortex

Effective methods for gamete preservation should have low impact on DNA integrity. The present study investigated the effects of vitrification of goat ovarian tissues on the occurrence of DNA fragmentation and DNA double-stand breaks using the terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL) assay and detection of phosphorylated histone H2AX (γH2AX), respectively. Goat ovaries were collected at a local abattoir and 12 tissue fragments were prepared from each ovarian pair. Tissue fragments were used as fresh control samples or were cultured in vitro, vitrified or vitrified and cultured. Vitrification was performed using the Ovarian Tissue Cryosystem. Fragments from all groups (control and treatments) were processed for histology, transmission electron microscopy, TUNEL assay and immunofluorescence. Compared with fresh control samples, a lower percentage of morphologically normal follicles was detected in the vitrification followed by culture treatment group (P<0.05). Normal follicular ultrastructure was observed in all groups. Immunofluorescence revealed the presence of γH2AX foci in few oocytes and ovarian stromal cells. TUNEL-positive follicles were found in samples without significant differences among groups (P>0.05). In conclusion, the vitrification protocol used in the present study did not increase DNA damage in preantral follicles enclosed in goat ovarian tissues.

Transcriptome analyses of rhesus monkey preimplantation embryos reveal a reduced capacity for DNA double-strand break repair in primate oocytes and early embryos

Preimplantation embryogenesis encompasses several critical events including genome reprogramming, zygotic genome activation (ZGA), and cell-fate commitment. The molecular basis of these processes remains obscure in primates in which there is a high rate of embryo wastage. Thus, understanding the factors involved in genome reprogramming and ZGA might help reproductive success during this susceptible period of early development and generate induced pluripotent stem cells with greater efficiency. Moreover, explaining the molecular basis responsible for embryo wastage in primates will greatly expand our knowledge of species evolution. By using RNA-seq in single and pooled oocytes and embryos, we defined the transcriptome throughout preimplantation development in rhesus monkey. In comparison to archival human and mouse data, we found that the transcriptome dynamics of monkey oocytes and embryos were very similar to those of human but very different from those of mouse. We identified several classes of maternal and zygotic genes, whose expression peaks were highly correlated with the time frames of genome reprogramming, ZGA, and cell-fate commitment, respectively. Importantly, comparison of the ZGA-related network modules among the three species revealed less robust surveillance of genomic instability in primate oocytes and embryos than in rodents, particularly in the pathways of DNA damage signaling and homology-directed DNA double-strand break repair. This study highlights the utility of monkey models to better understand the molecular basis for genome reprogramming, ZGA, and genomic stability surveillance in human early embryogenesis and may provide insights for improved homologous recombination-mediated gene editing in monkey.

An essential developmental function for murine phosphoglycolate phosphatase in safeguarding cell proliferation

Mammalian phosphoglycolate phosphatase (PGP) is thought to target phosphoglycolate, a 2-deoxyribose fragment derived from the repair of oxidative DNA lesions. However, the physiological role of this activity and the biological function of the DNA damage product phosphoglycolate is unknown. We now show that knockin replacement of murine Pgp with its phosphatase-inactive Pgp^D34N mutant is embryonically lethal due to intrauterine growth arrest and developmental delay in midgestation. PGP inactivation attenuated triosephosphate isomerase activity, increased triglyceride levels at the expense of the cellular phosphatidylcholine content, and inhibited cell proliferation. These effects were prevented under hypoxic conditions or by blocking phosphoglycolate release from damaged DNA. Thus, PGP is essential to sustain cell proliferation in the presence of oxygen. Collectively, our findings reveal a previously unknown mechanism coupling a DNA damage repair product to the control of intermediary metabolism and cell proliferation.

Hyaluronic Acid Binding Sperm Selection for assisted reproduction treatment (HABSelect): study protocol for a multicentre randomised controlled trial

INTRODUCTION

The selection of a sperm with good genomic integrity is an important consideration for improving intracytoplasmic sperm injection (ICSI) outcome. Current convention selects sperm by vigour and morphology, but preliminary evidence suggests selection based on hyaluronic acid binding may be beneficial. The aim of the Hyaluronic Acid Binding Sperm Selection (HABSelect) trial is to determine the efficacy of hyaluronic acid (HA)-selection of sperm versus conventionally selected sperm prior to ICSI on live birth rate (LBR). The mechanistic aim is to assess whether and how the chromatin state of HA-selected sperm corresponds with clinical outcomes-clinical pregnancy rate (CPR), LBR and pregnancy loss (PL).

METHODS AND ANALYSIS

Couples attending UK Centres will be approached, eligibility screening performed and informed consent sought. Randomisation will occur within 24 hours prior to ICSI treatment. Participants will be randomly allocated 1:1 to the intervention arm (physiological intracytoplasmic sperm injection, PICSI) versus the control arm using conventional methods (ICSI). The primary clinical outcome is LBR ≥37 weeks' gestation with the mechanistic study determining LBR's relationship with sperm DNA integrity. Secondary outcomes will determine this for CPR and PL. Only embryologists performing the procedure will be aware of the treatment allocation. Steps will be taken to militate against biases arising from embryologists being non-blinded. Randomisation will use a minimisation algorithm to balance for key prognostic variables. The trial is powered to detect a 5% difference (24-29%: p=0.05) in LBR ≥37 weeks' gestation. Selected residual sperm samples will be tested by one or more assays of DNA integrity.

ETHICS AND DISSEMINATION

HABSelect is a UK NIHR-EME funded study (reg no 11/14/34; IRAS REF. 13/YH/0162). The trial was designed in partnership with patient and public involvement to help maximise patient benefits. Trial findings will be reported as per CONSORT guidelines and will be made available in lay language via the trial web site (http://www.habselect.org.uk/).

TRIAL REGISTRATION NUMBER

ISRCTN99214271; Pre-results.

Functional assessment for elimination of mismatches in nuclear and whole cell extracts obtained from mouse and human blastocysts

Preimplantation embryos may have an increased risk of having mismatches due to the rates of cell proliferation and DNA replication. Elimination of mismatches in human gametes and embryos has not been investigated. In this study we developed a sensitive functional assay to examine the repair or elimination of mismatches in both commercially available cell extracts and extracts obtained from preimplantation embryos. Heteroduplex molecules were constructed using synthetic oligonucleotides. Efficiency of the repair of mismatches was semi-quantitatively analysed by exposure to nuclear/whole cell extracts (as little as 2.5 µg) and extracts obtained from pooled mouse and human blastocysts to investigate the repair capacity in human embryos. A cell free in vitro assay was successfully developed to analyze the repair of mismatches using heteroduplex complexes. The assay was further optimized to analyze repair of mismatches in cell extracts obtained from oocytes and blastocysts using minute amounts of protein. The efficiency of mismatch repair was examined in both mouse and human blastocysts (2.5 µg). The blastocysts were observed to have a lower repair efficiency compared to commercially available nuclear and whole cell extracts. In conclusion, a sensitive, easy, and fast in vitro technique was developed to detect the repair of mismatch efficiency in embryos.

Mutation of DNA Polymerase β R137Q Results in Retarded Embryo Development Due to Impaired DNA Base Excision Repair in Mice

DNA polymerase β (Pol β), a key enzyme in the DNA base excision repair (BER) pathway, is pivotal in maintaining the integrity and stability of genomes. One Pol β mutation that has been identified in tumors, R137Q (arginine to glutamine substitution), has been shown to lower polymerase activity, and impair its DNA repair capacity. However, the exact functional deficiency associated with this polymorphism in living organisms is still unknown. Here, we constructed Pol β R137Q knock-in mice, and found that homozygous knock-in mouse embryos were typically small in size and had a high mortality rate (21%). These embryonic abnormalities were caused by slow cell proliferation and increased apoptosis. In R137Q knock-in mouse embryos, the BER efficiency was severely impaired, which subsequently resulted in double-strand breaks (DSBs) and chromosomal aberrations. Furthermore, R137Q mouse embryo fibroblasts (MEFs) were more sensitive to DNA-damaging reagents, such as methyl methanesulfonate (MMS) and H2O2. They displayed a higher percentage of DSBs, and were more likely to undergo apoptosis. Our results indicate that R137 is a key amino acid site that is essential for proper Pol β functioning in maintaining genomic stability and embryo development.

Expression of DNA repair genes in porcine oocytes before and after fertilization by ICSI using freeze-dried sperm

Boar sperm freeze-dried with trehalose showed a protective effect against sperm DNA fragmentation. However, normal fertilization and embryonic development were not improved. Damaged sperm may activate maternal DNA repair genes when injected into oocytes. Therefore, we investigated the expression profile of some DNA repair genes in porcine oocytes after intra-cytoplasmic sperm injection. First, the expression levels of MGMT, UDG, XPC, MSH2, XRCC6 and RAD51 genes that are concerned with different types of DNA repair were examined in in vitro mature (IVM) oocytes injected with ejaculated sperm, or freeze-dried sperm with or without trehalose. Quantitative reverse transcription polymerase chain reaction revealed that expression of six DNA repair genes in the oocytes at 4 h after injection did not differ among the four groups. Next, we investigated the gene expression levels of these genes at different stages of maturation. The relative expression levels of UDG and XPC were significantly up-regulated in mature oocytes compared with earlier stages. Furthermore, there was an increased tendency in relative expression of MSH2 and RAD51. These results suggested two possible mechanisms that messenger RNA of DNA repair genes are either accumulated during IVM to be ready for fertilization or increased expression levels of DNA repair genes in oocytes caused by suboptimal IVM conditions.

Association between serum folate and vitamin B-12 and outcomes of assisted reproductive technologies

BACKGROUND

Preconceptional folate and vitamin B-12 have been linked to beneficial reproductive outcomes in both natural pregnancies and those after assisted reproductive technology (ART) treatment.

OBJECTIVE

The objective of the study was to evaluate the associations of serum folate and vitamin B-12 with ART outcomes.

DESIGN

This analysis included a random sample of 100 women (154 ART cycles) participating in a prospective cohort study [Environment and Reproductive Health (EARTH)] at the Massachusetts General Hospital Fertility Center (2007-2013). Serum folate and vitamin B-12 were measured in blood samples collected between days 3 and 9 of treatment. Generalized estimating equations with adjustment for age, BMI, and race were used to evaluate the association of serum folate and vitamin B-12 with ART outcomes.

RESULTS

Women in the highest quartile of serum folate (>26.3 ng/mL) had 1.62 (95% CI: 0.99, 2.65) times the probability of live birth compared with women in the lowest quartile (<16.6 ng/mL). Women in the highest quartile of serum vitamin B-12 (>701 pg/mL) had 2.04 (95% CI: 1.14, 3.62) times the probability of live birth compared with women in the lowest quartile (<439 pg/mL). Suggestive evidence of an interaction was observed; women with serum folate and vitamin B-12 concentrations greater than the median had 1.92 (95% CI: 1.12, 3.29) times the probability of live birth compared with women with folate and vitamin B-12 concentrations less than or equal to the median. This translated into an adjusted difference in live birth rates of 26% (95% CI: 10%, 48%; P = 0.02).

CONCLUSION

Higher serum concentrations of folate and vitamin B-12 before ART treatment were associated with higher live birth rates among a population exposed to folic acid fortification. This trial was registered at clinicaltrials.gov as NCT00011713.

Prediction model for aneuploidy in early human embryo development revealed by single-cell analysis

Aneuploidies are prevalent in the human embryo and impair proper development, leading to cell cycle arrest. Recent advances in imaging and molecular and genetic analyses are postulated as promising strategies to unveil the mechanisms involved in aneuploidy generation. Here we combine time-lapse, complete chromosomal assessment and single-cell RT-qPCR to simultaneously obtain information from all cells that compose a human embryo until the approximately eight-cell stage (n=85). Our data indicate that the chromosomal status of aneuploid embryos (n=26), including those that are mosaic (n=3), correlates with significant differences in the duration of the first mitotic phase when compared with euploid embryos (n=28). Moreover, gene expression profiling suggests that a subset of genes is differentially expressed in aneuploid embryos during the first 30 h of development. Thus, we propose that the chromosomal fate of an embryo is likely determined as early as the pronuclear stage and may be predicted by a 12-gene transcriptomic signature.

Thyroid hormones alter the transcriptome of in vitro-produced bovine blastocysts

Thyroid hormones (THs) have been shown to improve in vitro embryo production in cattle by increasing blastocyst formation rate, and the average cell number of blastocysts and by significantly decreasing apoptosis rate. To better understand those genetic aspects that may underlie enhanced early embryo development in the presence of THs, we characterized the bovine embryonic transcriptome at the blastocyst stage, and examined differential gene expression profiles using a bovine-specific microarray. We found that 1212 genes were differentially expressed in TH-treated embryos when compared with non-treated controls (>1.5-fold at P < 0.05). In addition 23 and eight genes were expressed uniquely in control and treated embryos, respectively. The expression of genes specifically associated with metabolism, mitochondrial function, cell differentiation and development were elevated. However, TH-related genes, including those encoding TH receptors and deiodinases, were not differentially expressed in treated embryos. Furthermore, the over-expression of 52 X-chromosome linked genes in treated embryos suggested a delay or escape from X-inactivation. This study highlights the significant impact of THs on differential gene expression in the early embryo; the identification of TH-responsive genes provides an insight into those regulatory pathways activated during development.

Inhibition of zygotic DNA repair: transcriptome analysis of the offspring in trout (Oncorhynchus mykiss)

Zygotic repair of the paternal genome is a key event after fertilization. Spermatozoa accumulate DNA strand breaks during spermatogenesis and can suffer additional damage by different factors, including cryopreservation. Fertilization with DNA-damaged spermatozoa (DDS) is considered to promote implantation failures and abortions, but also long-term effects on the progeny that could be related with a defective repair. Base excision repair (BER) pathway is considered the most active in zygotic DNA repair, but healthy oocytes contain enzymes for all repairing pathways. In this study, the effects of the inhibition of the BER pathway in the zygote were analyzed on the progeny obtained after fertilization with differentially DDS. Massive gene expression (GE; 61 657 unique probes) was analyzed after hatching using microarrays. Trout oocytes are easily fertilized with DDS and the high prolificacy allows live progeny to be obtained even with a high rate of abortions. Nevertheless, the zygotic inhibition of Poly (ADP-ribose) polymerase, upstream of BER pathway, resulted in 810 differentially expressed genes (DEGs) after hatching. DEGs are related with DNA repair, apoptosis, telomere maintenance, or growth and development, revealing a scenario of impaired DNA damage signalization and repair. Downregulation of the apoptotic cascade was noticed, suggesting a selection of embryos tolerant to residual DNA damage during embryo development. Our results reveal changes in the progeny from defective repairing zygotes including higher malformations rate, weight gain, longer telomeres, and lower caspase 3/7 activity, whose long-term consequences should be analyzed in depth.

Tissue-specific effects of valproic acid on DNA repair genes and apoptosis in postimplantation mouse embryos

Exposure to the anticonvulsant drug valproic acid (VPA) is associated with an increased risk of congenital malformations. Although the mechanisms contributing to its teratogenicity are poorly understood, VPA has been shown to induce DNA double strand breaks (DSB) and to increase homologous recombination in vitro. The objective of the present study was to determine whether in utero exposure to VPA alters the frequency of intrachromosomal recombination and the expression of several genes involved in DSB repair in pKZ1 mouse embryos. Pregnant pKZ1 transgenic mice (GD 9.0) were administered VPA (500 mg/kg s.c.) and embryos were extracted and microdissected into the head, heart, and trunk regions 1, 3, 6, and 24 h after injection. Quantitative PCR was used to measure the tissue-specific expression of lacZ, a surrogate measure of recombination, Xrcc4, Rad51, Brca1, and Brca2, with Western blotting used to quantify Rad51, cleaved caspase-3 and cleaved-PARP protein. Increased recombination was only observed in the embryonic head following 6-h VPA exposure. VPA had no effect on Xrcc4 expression. Rad51, Brca1, and Brca2 expression rapidly decreased in head and trunk tissues after 1-h VPA exposure, followed by a subsequent increase in all tissues, although it was generally attenuated in the head and not due to differences in endogenous levels. Cleaved caspase-3 and cleaved-PARP expression was increased in all tissues 3 h following VPA exposure. This study indicates that the tissue-specific expression of several genes involved in DSB repair is altered following exposure to VPA and may be contributing to increased apoptosis.

Phospho-Cdc25 correlates with activating G2/M checkpoint in mouse zygotes fertilized with hydrogen peroxide-treated mouse sperm

The presence of oxidative stress in sperm cryopreservation induces sperm DNA damage. Our previous study has discovered that γH2AX, the DNA-damaged marker, was activated in the early mouse embryos fertilized with hydrogen peroxide (H2O2)-treated sperm. Furthermore, we found that checkpoint proteins ATM and Chk1 were phosphorylated and activated in the early mouse embryos. On the basis of previous researches, we examined the effects of sperm DNA damage on cell cycle arrest in mouse zygotes fertilized with H2O2-treated sperm. Development of fertilized eggs arrested at the PN disappearance stage. At 19 and 24 hours post-insemination (hpi), the percentage of zygotes at the PN disappearance stage was higher in H2O2-treated group compared to the control group. Immunofluorescence staining revealed Phospho-Cdc25C (Ser216) and Phospho-Cdc25B (Ser323) in or surrounding a single pronucleus, following insemination with H2O2-treated sperm. Our study suggests that fertilization with DNA-damaged sperm results in cell cycle arrest mediated by G2/M checkpoint activation in one of the pronuclei in mouse zygotes fertilized with H2O2-treated sperm; Phospho-Cdc25C and Phospho-Cdc25B correlate with activating G2/M checkpoint in zygotes fertilized with H2O2-treated sperm.

Nuclear reprogramming by interphase cytoplasm of two-cell mouse embryos

Successful mammalian cloning using somatic cell nuclear transfer (SCNT) into unfertilized, metaphase II (MII)-arrested oocytes attests to the cytoplasmic presence of reprogramming factors capable of inducing totipotency in somatic cell nuclei. However, these poorly defined maternal factors presumably decline sharply after fertilization, as the cytoplasm of pronuclear-stage zygotes is reportedly inactive. Recent evidence suggests that zygotic cytoplasm, if maintained at metaphase, can also support derivation of embryonic stem (ES) cells after SCNT, albeit at low efficiency. This led to the conclusion that critical oocyte reprogramming factors present in the metaphase but not in the interphase cytoplasm are 'trapped' inside the nucleus during interphase and effectively removed during enucleation. Here we investigated the presence of reprogramming activity in the cytoplasm of interphase two-cell mouse embryos (I2C). First, the presence of candidate reprogramming factors was documented in both intact and enucleated metaphase and interphase zygotes and two-cell embryos. Consequently, enucleation did not provide a likely explanation for the inability of interphase cytoplasm to induce reprogramming. Second, when we carefully synchronized the cell cycle stage between the transplanted nucleus (ES cell, fetal fibroblast or terminally differentiated cumulus cell) and the recipient I2C cytoplasm, the reconstructed SCNT embryos developed into blastocysts and ES cells capable of contributing to traditional germline and tetraploid chimaeras. Last, direct transfer of cloned embryos, reconstructed with ES cell nuclei, into recipients resulted in live offspring. Thus, the cytoplasm of I2C supports efficient reprogramming, with cell cycle synchronization between the donor nucleus and recipient cytoplasm as the most critical parameter determining success. The ability to use interphase cytoplasm in SCNT could aid efforts to generate autologous human ES cells for regenerative applications, as donated or discarded embryos are more accessible than unfertilized MII oocytes.

Genomic Instability and Cancer

Genomic instability is a characteristic of most cancer cells. It is an increased tendency of genome alteration during cell division. Cancer frequently results from damage to multiple genes controlling cell division and tumor suppressors. It is known that genomic integrity is closely monitored by several surveillance mechanisms, DNA damage checkpoint, DNA repair machinery and mitotic checkpoint. A defect in the regulation of any of these mechanisms often results in genomic instability, which predisposes the cell to malignant transformation. Posttranslational modifications of the histone tails are closely associated with regulation of the cell cycle as well as chromatin structure. Nevertheless, DNA methylation status is also related to genomic integrity. We attempt to summarize recent developments in this field and discuss the debate of driving force of tumor initiation and progression.