203 Genome Modifications by Sleeping Beauty Transposition and CRISPR/Cas9 to Improve Cow Milk Composition for Human Consumption

Genome manipulation of cattle represents a powerful tool to increase the nutritional value and reduce allergenicity of cow milk for human consumption. This could be accomplished by improving the amount of polyunsaturated fatty acids (ω-3 and ω-6) and simultaneously abolishing β-lactoglobulin (BLG), a potent allergen for predisposed humans. The aim of this study was to introduce the sequence for a desaturase construct (mFAT-2, from C. elegans), which is able to catalyse the synthesis of ω-3 and ω-6 fatty acids, into the bovine genome by Sleeping Beauty (SB) transposition, and simultaneously knocking out the bovine β-lactoglubulin gene using CRISPR/Cas9 system. The sgRNA (AAGTGCCTCCTGCTTGCCC) targeted to BLG exon 1 was synthesised as an oligo linker and cloned into the px459-Cas9. The mutation activity of the designed sgRNA at the target locus was determined by T7 endonuclease assay I (T7EI) mismatch detection assay. Briefly, bovine fetal fibroblasts (BFF) were seeded at 0.5 × 105 cells per well of a 24-well plate in triplicate, when the cells reached 80% confluence (12–24 h), cultures were transfected with 1 μg of px459-Cas9::BLG plasmid co-expressing Cas9 and sgRNA using polyethylenimine reagent (PEI; 3 ng μL−1). After 3 days of puromycin selection, genomic DNA from transfected cells were extracted and the sequence of interest was PCR-amplified and digested by T7EI restriction enzyme. Digestion products showed a mutation efficiency at the target locus of 29%. Subsequently, we chemically cotransfected 0.5 × 105 BFF with 0.5 μg of knockout vector (px459-Cas9::BLG) and 0.5 μg of SB plasmids (carrying mFAT-2 cDNA for mammary gland-specific expression) using 3 ng μL−1 PEI in triplicate. At 48 h post-transfection, cell cultures were subjected to 3 days of puromycin and 21 days of neomycin selection. PCR analysis of antibiotic resistant colonies revealed the presence of mFAT-2 transgene in almost 70% of the analysed cells lines. Genotyping of BLG exon 1 was performed by direct sequencing of PCR amplicons using primers flanking the target site. Despite the appreciable gene mutation activity of the sgRNA sequence previously determined by T7EI assay (29%), none of the cell lines analysed showed modification in the BLG target locus. We speculate that the SB vector might have disrupted the activity of targeting vector. We are currently performing additional experiments to accomplish gene addition (mFAT) and gene knockout (BGL) in one step using these highly efficient and precise transgenic tools. Genetically modified cells will be used as nuclear donor to produce transgenic cows by somatic cells nuclear transfer. The financial support of CONICET, UNRC and FONCYT is gratefully acknowledged.

178 TRANSCRIPTIONAL DIFFERENCES IN GENES RELATED TO GLUCOSE METABOLISM BETWEEN COMPETENT AND INCOMPETENT BOVINE IMMATURE CUMULUS-OOCYTE COMPLEXES SELECTED BY BCB

In vitro maturation is a key step of in vitro embryo production, being the main factor responsible for the low blastocyst yield. In vitro maturation requires the selection of competent immature cumulus-oocytes complexes (COC), which is usually accomplished based on morphological criteria and follicle size. Competent immature COC have finished their growth phase and show decreased G6PDH activity. Brilliant cresol blue (BCB) is a dye that is degraded by G6PDH and, therefore, can be used to distinguish COC that have finished their growth phase (BCB+) from those that are still growing and are less competent (BCB-). The objective of this study was to determine the metabolic differences between BCB- and BCB+ COC by performing a transcriptional analysis of genes related to glucose metabolism. The COC obtained from slaughterhouse ovaries were selected based on BCB staining. The BCB+ and BCB- COC were fertilized and cultured in vitro to determine the differences in developmental ability. For gene expression analysis, BCB+ and BCB- COC were denuded by vortexing and 5 groups of 10 oocytes; their corresponding cumulus cells per group were snap-frozen until analysis. Messenger RNA was extracted by Dynabeads (Dynal Biotech, Lake Success, NY, USA) and relative mRNA abundance was analysed by quantitative PCR using PPIA1 as housekeeping. Statistical differences were determined based on ANOVA (P < 0.05). The genes analysed were G6PDH, its positive regulator SIRT2, 2 glucose transporters SLC2A1 and SLC2A5, 2 genes involved in anaerobic glycolysis GAPDH and LDHA, 2 genes related with Krebs cycle CS and ATP5A1, and 1 gene related to glutathione metabolism GPX1. As expected, the BCB+ group showed a higher cleavage rate (85.6 ± 1.8 v. 74.2 ± 1.3%, BCB+ v. BCB-; P < 0.05) and blastocyst yield (Day 9: 33.3 ± 3.8 v. 16.1 ± 1.4%, BCB+ v. BCB-; P < 0.05) compared with BCB-. Genes SIRT2, GAPDH, and LDHA were significantly up-regulated in BCB- cumulus cells (SIRT2: 1 ± 0.04 v. 1.45 ± 0.21; GAPDH: 1 ± 0.17 v. 1.46 ± 0.15; LDHA: 1 ± 0.22 v. 1.65 ± 0.12; BCB+ v. BCB-; P < 0.05), whereas no significant differences were found in the other genes and in oocytes. In conclusion, the differences in G6PDH activity between BCB+ and BCB- COC are not controlled by G6PDH transcript abundance, but seem to be mediated by SIRT2 regulation of G6PDH activity. The BCB- cumulus cells showed an up-regulation of GAPDH and LDHA, suggesting a higher activity of anaerobic glycolysis in BCB- COC compared with BCB+.

A novel antioxidant formulation designed to treat male infertility associated with oxidative stress: promising preclinical evidence from animal models

STUDY QUESTION

Does a novel antioxidant formulation designed to restore redox balance within the male reproductive tract, reduce sperm DNA damage and increase pregnancy rates in mouse models of sperm oxidative stress?

SUMMARY ANSWER

Oral administration of a novel antioxidant formulation significantly reduced sperm DNA damage in glutathione peroxidase 5 (GPX5), knockout mice and restored pregnancy rates to near-normal levels in mice subjected to scrotal heat stress.

WHAT IS KNOWN ALREADY

Animal and human studies have documented the adverse effect of sperm DNA damage on fertilization rates, embryo quality, miscarriage rates and the transfer of de novo mutations to offspring. Semen samples of infertile men are known to be deficient in several key antioxidants relative to their fertile counterparts. Antioxidants alone or in combination have demonstrated limited efficacy against sperm oxidative stress and DNA damage in numerous human clinical trials, however these studies have not been definitive and an optimum combination has remained elusive.

STUDY DESIGN, SIZE, DURATION

The efficacy of the antioxidant formulation was evaluated in two well-established mouse models of oxidative stress, scrotal heating and Gpx5 knockout (KO) mice, (n = 12 per experimental group), by two independent laboratories. Mice were provided the antioxidant product in their drinking water for 2-8 weeks and compared with control groups for sperm DNA damage and pregnancy rates.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In the Gpx5 KO model, oxidative DNA damage was monitored in spermatozoa by immunocytochemical detection of 8-hydroxy-2'-deoxyguanosine (8OHdG). In the scrotal heat stress model, male fertility was tested by partnering with three females for 5 days. The percentage of pregnant females, number of vaginal plugs, resorptions per litter, and litter size were recorded.

MAIN RESULTS AND ROLE OF CHANCE

Using immunocytochemical detection of 8OHdG as a biomarker of DNA oxidation, analysis of control mice revealed that around 30% of the sperm population was positively stained. This level increased to about 60% in transgenic mice deficient in the antioxidant enzyme, GPX5. Our results indicate that an 8 week pretreatment of Gpx5 KO mice with the antioxidant formulation provided complete protection of sperm DNA against oxidative damage. In mouse models of scrotal heat stress, only 35% (19/54) of female mice became pregnant resulting in 169 fetuses with 18% fetal resorption (30/169). This is in contrast to the antioxidant pretreated group where 74% (42/57) of female mice became pregnant, resulting in 427 fetuses with 9% fetal resorption (38/427). In both animal models the protection provided by the novel antioxidant was statistically significant (P < 0.01 for the reduction of 8OHdG in the spermatozoa of Gpx5 KO mice and P < 0.05 for increase in fertility in the scrotal heat stress model).

LIMITATIONS, REASONS FOR CAUTION

It was not possible to determine the exact level of antioxidant consumption for each mouse during the treatment period.

WIDER IMPLICATIONS OF THE FINDINGS

Recent clinical studies confirm moderate to severe sperm DNA damage in about 60% of all men visiting IVF centers and in about 80% of men diagnosed with idiopathic male infertility. Our results, if confirmed in humans, will impact clinical fertility practice because they support the concept of using an efficacious antioxidant supplementation as a preconception therapy, in order to optimize fertilization rates, help to maintain a healthy pregnancy and limit the mutational load carried by children.

STUDY FUNDING/COMPETING INTERESTS

The study was funded by the Clermont Université and the University of Madrid. P.G. is the Managing Director of CellOxess LLC, which has a commercial interest in the detection and resolution of oxidative stress. A.M. and A.P. are employees of CellOxess, LLC. J.R.D., A.G.-A. and R.J.A. are honorary members of the CellOxess advisory board.

Most regions of mouse epididymis are able to phagocytose immature germ cells

The role of the epididymis as a quality control organ in preventing infertile gametes entering the ejaculate has been extensively explored, and it has been suggested that a specific region of mammalian epididymis is able to phagocytose abnormal germ cells. This study examines whether the epithelium of certain zones of the mouse epididymis can act as a selection barrier by removing immature germ cells from the lumen by phagocytosis. To detect the presence of immature germ cells in the epididymis, we generated transgenic mice expressing enhanced green fluorescent protein under the deleted in azoospermia-like (mDazl) promoter to easily identify immature germ cells under fluorescence microscopy. Using this technique, we observed that during the first stage of spermatogenesis in prepuberal mice, a wave of immature germ cells is released into the epididymis and that the immature epididymis is not able to react to this abnormal situation. By contrast, when immature germ cells were artificially released into the epididymis in adult mice, a phagocytic response was observed. Phagosomes appeared inside principal cells of the epididymal epithelium and were observed to contain immature germ cells at different degradation stages in different zones of the epididymis, following the main wave of immature germ cells. In this paper, we describe how the epididymal epithelium controls sperm quality by clearing immature germ cells in response to their artificially induced massive shedding into the epididymal lumen. Our observations indicate that this phenomenon is not restricted to a given epididymis region and that phagocytic capacity is gradually acquired during epididymal development.

The role of prion protein in stem cell regulation

Cellular prion protein (PrP(C)) has been well described as an essential partner of prion diseases due to the existence of a pathological conformation (PrP(Sc)). Recently, it has also been demonstrated that PrP(C) is an important element of the pluripotency and self-renewal matrix, with an increasing amount of evidence pointing in this direction. Here, we review the data that demonstrate its role in the transcriptional regulation of pluripotency, in the differentiation of stem cells into different lineages (e.g. muscle and neurons), in embryonic development, and its involvement in reproductive cells. Also highlighted are recent results from our laboratory that describe an important regulation by PrP(C) of the major pluripotency gene Nanog. Together, these data support the appearance of new strategies to control stemness, which could represent an important advance in the field of regenerative medicine.

250 ALL REGIONS OF THE MOUSE EPIDIDYMIS ARE ABLE TO PHAGOCYTIZE IMMATURE SPERMATOGENIC CELLS

Successful mammalian fertilization requires gametes with an intact structure and functionality. Although it is well known that epididymal functions are sperm maturation, sustenance, transport, and storage, there is controversial information about its role in sperm quality control, and it has been suggested that some regions of the rat epididymis are able to phagocytize germ cells. Our objective was to analyse whether different segments of the mouse epididymal epithelium act as a selection barrier for abnormal spermatogenic cells by removing immature cells from the lumen by phagocytosis. To detect the presence of immature germ cells along the epididymis, transgenic mice expressing enhanced green fluorescent protein under a Deleted in Azoospermia-Like (mDazl) promoter were generated. The transgenic animals express specifically enhanced green fluorescent protein in spermatogonias, spermatocytes, and spermatids; thus, immature spermatogenic cells can be easily identified by fluorescence microscopy. Colchicine, a microtubule disruptor that leads to severe alterations in the architecture of the seminiferous tubules, was administered in the rete testis to induce the release of immature germ cells into the epididymis. Mice were killed daily, from Day 1 to 8 post-administration, and epididymides were collected and observed under a fluorescence stereoscope to determine the transit of immature germ cells along the epididymis. Epididymides from control mice without colchicine administration were also collected. Fluorescent immature germ cells were present in the caput epididymis 24 h after colchicine administration, and they progressed through the corpus and cauda, leaving the epididymis 7 days after colchicine administration. After fluorescence observation, epididymides were fixed, sectioned, and stained with hematoxylin solution. Immature germ cells and phagosomes were not observed in control epididymides. By contrast, the presence of phagosomes in the principal cells of the epididymal epithelium containing immature germ cells in different degrees of degradation was observed by light microscopy in mice injected with colchicine. Phagocytosis was observed along the epididymis following the main wave of fluorescent immature cells. Thus, when immature cells had reached the corpus epididymis, phagocytosis was detected in several segments of the caput epididymis. Later, once the immature cells had arrived to the cauda epididymis or had abandoned the epididymis, phagocytosis was observed in the corpus and cauda epididymis. The presence of phagosomes was observed in all epididymal tubules within a phagocytosis area. In conclusion, we demonstrated that the epididymal epithelium is engaged in sperm quality control by clearing immature germ cells after a massive shedding into the epididymal lumen, and that this phenomenon is not restricted to a specific segment of the epididymis.

Sex-specific embryonic origin of postnatal phenotypic variability

Preimplantation developmental plasticity has evolved in order to offer the best chances of survival under changing environments. Conversely, environmental conditions experienced in early life can dramatically influence neonatal and adult biology, which may result in detrimental long-term effects. Several studies have shown that small size at birth, which is associated with a greater risk of metabolic syndrome, is largely determined before the formation of the blastocysts because 70%–80% of variation in bodyweight at birth has neither a genetic nor environmental component. In addition, it has been reported that adult bodyweight is programmed by energy-dependent process during the pronuclear stage in the mouse. Although the early embryo has a high developmental plasticity and adapts and survives to adverse environmental conditions, this adaptation may have adverse consequences and there is strong evidence that in vitro culture can be a risk factor for abnormal fetal outcomes in animals systems, with growing data suggesting that a similar link may be apparent for humans. In this context, male and female preimplantation embryos display sex-specific transcriptional and epigenetic regulation, which, in the case of bovine blastocysts, expands to one-third of the transcripts detected through microarray analysis. This sex-specific bias may convert the otherwise buffered stochastic variability in developmental networks in a sex-determined response to the environmental hazard. It has been widely reported that environment can affect preimplantation development in a sex-specific manner, resulting in either a short-term sex ratio adjustment or in long-term sex-specific effects on adult health. The present article reviews current knowledge about the natural phenotypic variation caused by epigenetic mechanisms and the mechanisms modulating sex-specific changes in phenotype during early embryo development resulting in sex ratio adjustments or detrimental sex-specific consequences for adult health. Understanding the natural embryo sexual dimorphism for programming trajectories will help understand the early mechanisms of response to environmental insults.

New challenges in the analysis of gene transcription in bovine blastocysts

In the last years, enormous progress has been made in the analysis of gene transcription at the blastocyst stage. The study of gene expression at this early stage of development is challenging because of the very small amount of starting material, which limits the use of traditional mRNA analysis approaches such as Northern blot. Another problem is the difficulty for data normalization, particularly the identification of the best housekeeping gene with the lowest fluctuation under different developmental conditions. Moreover, the transcriptional analysis of embryo biopsies or individual embryos needs to take into consideration that the blastocyst is a transitional stage of development, which is composed of three different types of cells (trophoblast, epiblast and primitive ectoderm) with different patterns of gene expression, and that there are large differences between male and female blastocysts. In this review, we analyse the different specific and sensitive tools available to compare mRNA expression levels of specific genes at the blastocyst stage, and how the protocol and the analytical method used can influence the results dramatically. Finally, we describe future research challenges to identify candidate genes related to developmental competence of bovine blastocysts, not only in terms of pregnancy rates but also in relation to adverse long-term consequences in the adult animal.

Effect of long-term culture of mouse embryonic stem cells under low oxygen concentration as well as on glycosaminoglycan hyaluronan on cell proliferation and differentiation

OBJECTIVES

Maintaining undifferentiated stem cells in defined conditions is of critical importance to improve their in vitro culture. We have evaluated the effects of culturing mouse stem (mES) cells under physiological oxygen concentration as well as by replacing fibroblast feeder layer (mEF) with gelatin or glycosaminoglycan hyaluronan (HA), on cell proliferation and differentiation.

MATERIALS AND METHODS

After 3 days culture or after long-term cell culture under different conditions, levels of apoptotic cell death were determined by cell cycle and TUNEL (TdT-mediated dUTP nick end labelling) assays and levels of cell proliferation by CFSE (5-(and-6)-carboxyfluorescein diacetate succinimidyl ester) labelling. We assessed spontaneous differentiation into cardiomyocytes and mRNA expression of pluripotency and differentiation biomarkers.

RESULTS

After 3 days culture under hypoxic conditions, levels of proliferation and apoptosis of mES cells were higher, in correlation with increase in intracellular reactive oxygen species. However, when cells were continuously grown for 1 month under those conditions, the level of apoptosis was, in all cases, under 4%. Hypoxia reduced spontaneous differentiation of mES into cardiomyocytes. Long-term culture on HA was more effective in maintaining the pluripotent state of the mES cells when compared to that on gelatin. Level of terminal differentiation was highest on mEF, intermediate on HA and lowest on gelatin.

CONCLUSIONS

Our data suggest that hypoxia is not necessary for maintaining pluripotency of mES cells and appeared to be detrimental during ES differentiation. Moreover, HA may offer a valuable alternative for long-term culture of mES cells in vitro.

203 EFFECT OF OXYGEN TENSION AND SUBSTRATE ON GROWTH AND DIFFERENTIATION OF MOUSE EMBRYONIC STEM CELLS

Normally the majority of mammalian cells, including murine embryonic stem (mES) cells, are immersed in a low oxygen environment (hypoxia); however, mES are generally cultured in an atmosphere containing 21% O2 (normoxia). Such conditions may not be the most appropriate for mES propagation. We have tested the effects of hypoxia and culture on either feeder fibroblasts or gelatin substrate on mES cell growth and spontaneous differentiation. Two ES cell lines (R1 129/Sv from the laboratory of A. Nagy and MAR B6D2 F1 generated in our laboratory) were cultured under two different oxygen tensions (5 and 21%), and on two different substrates, 0.1% gelatin or murine embryonic fibroblasts (mEF). Cell cycle, cell proliferation, mRNA expression of pluripotency and differentiation markers, as well as spontaneous differentiation to cardiomyocytes, were monitored. For cell proliferation measurements, mES after 7 days of culture at the different conditions were labeled with 5-(and-6)-carboxyfluorescein diacetate succinimidyl ester, and cultured for up to three more days. Cells were then harvested for flow cytometry analysis every 24 h after labeling (Cell TraceTM CFSE Cell Proliferation Kit; Molecular Probes, Inc., Eugene, OR, USA). For cell cycle analysis, cells grown on mEF under the two different oxygen tensions were fixed after 10 days of culture, and then stained with propidium iodide/Triton-X-100 for flow cytometry analysis (Current Protocols in Cytometry, Chap. 7, 2001). The spontaneous differentiation of embryoid bodies [formed by ES cells in the absence of leukemia inhibitory factor (LIF)] to cardiomyocytes was also monitored. For mRNA expression of pluripotency (Nanog, Oct-3/4, Rex1, GENESIS, FGFR-4, TERF1, Cx43, and GLUT1) and differentiation markers (GATA4, GATA2, AFP, Msx-1, Brachyury, and Myf5), RT-PCR analysis was performed on mES cells from Day 0 to Day 10. Under hypoxia conditions, the proliferation of both types of mES cells was greater than under normoxia, independent of substrate used, and a higher number of apoptotic cells was detected. Moreover, only under normoxia conditions did mES cells lose the expression of pluripotency markers GENESIS and GLUT1. In addition, under lower oxygen tension, the rate of differentiation to beating cardiomyocytes was significantly lower on the feeder layer than that under normoxia (11.9% vs. 28.1%; P = 0.012). The feeder layer supported significantly higher cardiomyocyte formation when compared to 0.1% gelatin at 21% O2 (28.1% vs. 8.3%; P < 0.001). Our results show that normoxia may not be the most appropriate condition for mES cell propagation and that hypoxic culture may be necessary to maintain full pluripotency of mES cells.