Maternal control of oocyte quality in cattle “a review”

Association between metabolic parameters and embryo production in superovulated dairy cattle

This study aims to investigate the relationship between metabolic parameters and the number of embryos produced in superovulated cows with high genetic characteristics in milk yield. Eighteen Holstein donors were treated with classic superovulation protocols, AI and flushing. During superovulation, decreasing doses of FSH (follicle-stimulating hormone) were administered at 12-h intervals for 4 days. Plasma insulin-like growth factor (IGF1), glucose (GLU), beta-hydroxybutyric acid (BHB), non-esterified fatty acid (NEFA), blood urea nitrogen (BUN) and total protein (TP) levels were determined by using an autoanalyzer. The mixed model analysis of variance was used for statistical analysis. As a result, plasma IGF1, BHB and BUN had significant interactions with both groups and days (p < .05). Additionally, plasma TP-days interactions were significant (p < .05). Furthermore, there was a negative correlation between the number of embryos and plasma BHB levels (p < .05). In conclusion, under appropriate environmental conditions, metabolic profile control of donors can contribute to the embryo production process and to the studies on the metabolic infrastructure.

Effect of maternal age on ATP content and distribution of mitochondria in bovine oocytes

Our objective was to understand how maternal age influences the mitochondrial population and ATP content of in vivo matured bovine oocytes. We hypothesized that in vivo matured oocytes from older cows would have altered mitochondrial number and distribution patterns and lower cytoplasmic ATP content compared to the oocytes obtained from younger cows. Follicles ≥5mm were ablated in old cows (13 to 22 yrs, Old Group, n = 7) and their younger daughters (4 to 10 years old, Young Group; n = 7) to induce the emergence of a new follicular wave. Cows were treated twice daily with eight doses of FSH starting 24 hr after ablation (Day 0, day of wave emergence). Prostaglandin F2alpha (PGF) was given on Days 3 and 3.5, LH on Day 4.5, and cumulus-oocyte-complexes were collected 18-20 hours post-LH by ultrasound-guided follicular aspiration. Oocytes were either processed for staining with MitoTracker Deep Red FM or for ATP assay. Stained oocytes were imaged with a Zeiss LSM 710 confocal microscope, and mitochondria were segmented in the oocyte volume sets using Imaris Pro 7.4. In vivo matured oocytes obtained from old cows were similar in morphological grades to those from young cows. However, the oocytes of COC from older cows had 23% less intracellular ATP (27.4±1.9 vs 35.7±2.2 pmol per oocyte, P = 0.01) than those of young cows. Furthermore, the average volume of individual mitochondria, indicated by the number of image voxels, was greater (P<0.05) in oocytes from older cows than in those from younger cows. Oocytes from older cows also tended to have a greater number of mitochondrial clusters (P = 0.06) and an increased number of clusters in the central region of the oocytes (P = 0.04) compared to those from younger cows. In conclusion, our study demonstrated that maternal age was associated with a decrease in the cytoplasmic ATP content of in vivo mature oocytes and an altered distribution of mitochondrial structures. These findings suggest that maternal age may negatively influence the developmental competence of oocytes from older cows.

Oocyte quality in adapted Bos taurus taurus cows

The objective of the current study was to determine the performance of creole cows of the Chino Santandereano breed in the ultrasound-guided follicular aspiration technique (OPU) and the quality of oocytes recovered. A total of 15 multiparous cows were selected from a herd located in the department of Santander with tropical climate. The cows were submitted to 5 sessions of follicular aspiration with an interval of 45 days. In each aspiration session, 7.9 ± 0.7 oocytes were recovered per cow, with a recovery rate of 64.9% ± 0.5 and a rate of viable and non-viable oocytes of 64.3% ± 0.6 and 35.7% ± 0.7, respectively. A difference (P < 0.05) in oocyte quality was presented for grades I, II and III (7.7 ± 0.4, 19.8 ± 0.5 and 36.8 ± 0.5, respectively). The results suggest that Chino Santandereano cows submitted to the OPU technique have a higher percentage of grade III oocytes recovered.

Use of equine chorionic gonadotropin in lactating dairy cattle: a rapid review

AIMS

To use an evidence-based approach to evaluate the available research data on the efficacy of equine chorionic gonadotropin (eCG) to improve reproductive performance of dairy cows when added to oestrus synchronisation programmes for the treatment of cows not detected in oestrus.

METHODS

A rapid literature review was conducted to summarise the existing trial data, primarily the effect of eCG on conception rate (CR) to fixed time artificial insemination (FTAI) from oestrus synchronisation programmes in lactating dairy cows. Relevant papers were identified via databases and auxiliary search strategies, then information was collected using a standardised data collection form. Similar studies were grouped together to create a descriptive summary of CR to FTAI and secondary outcome measures, with the creation of forest plots to visualise results.

RESULTS

A total of 15 studies were identified for review: nine examined the administration of 400-500 IU eCG as part of an oestrus synchronisation programme based on intra-vaginal progesterone-releasing devices, gonadotropin-releasing hormone and prostaglandin (P4-GPG programme). The variable methodologies in the trials evaluated posed difficulties in grouping studies for further analysis and meant that there was insufficient data for a full meta-analysis. A single study reported a statistically significant increase in CR to FTAI from the addition to eCG to a P4-GPG programme in cows with anovulatory anoestrous. Four studies evaluated the addition of eCG to P4-GPG programmes in cows without visible oestrous signs; risk differences for CR to FTAI were between -1.7% and 28.8%, with three out of four studies reporting a positive effect of eCG on CR to FTAI, but all 95% CI values crossed the line of no effect. Two studies reported on the effect of eCG on 42-day pregnancy rate following a P4-GPG programme; one reported a risk difference of -4.9% (95% CI = -10.6-0.8%), while the other reported a risk difference of 7.9% (95% CI = 0.8-15%).

CONCLUSIONS

The results of published studies describing the effect of eCG in P4-GPG programmes on CR to FTAI are inconsistent and further well-designed, adequately powered studies with standardised outcome measures are required to investigate its effect.

Tanshinone IIA enhances the ovarian reserve and attenuates ovarian oxidative stress in aged mice

Background

Tanshinone IIA (TSA), a major lipophilic component extracted from the roots of Salvia miltiorrhiza Bunge, has been widely used in China for its various biological activities. However, its effect on ovarian reserve in aged mice was not studied elsewhere.

Objectives

This study aimed to explore the effect of TSA on the ovarian reserve of aged mice as well as young mice. Forty weeks old mice (N = 40) were considered as aged group compared to 4 weeks old mice (N = 40), and these groups were subdivided into four subgroups (N = 10) to receive different doses of TSA (0, 10, 20, and 40 μg/g/day).

Methods

The effect of TSA was evaluated by counting follicular number by histological examination. Basal serum levels of FSH, LH, E2, and anti‐Mullerian hormone (AMH) were measured by ELISA. Moreover, the expression levels of antioxidant genes (CAT, Nrf2, GPX1), gap junction (Cx37), ERK1/2, and Smad5 family gene were examined at both mRNA (qPCR) and protein levels (western blot).

Results

Follicular number, level of AMH and E2, and the expression of CAT, Nrf2, and GPX1 genes increased significantly (p < 0.05) in aged mice administrated with medium (20 μg/g/day) and high (40 μg/g/day) doses of TSA, whereas FSH and LH levels were significantly low compared to low dose (10 μg/g/day) and control (0 μg/g/day) aged subgroups. However, we did not observe any effect of all doses of TSA on young mice.

Conclusions

Administration of TSA with medium and high doses up‐regulates the expression of antioxidative genes, reduces the oxidative injury, increases levels of AMH, and E2 levels that are relatively comparable to those in young mice, and consequently results in a healthy oocyte development.

Comparative transcriptome analysis identifies important maternal molecules and associated biological pathways for pig and human mature oocytes

Recent researches reveal that during oocyte maturation, species-specific molecular profile exists, and has important functional roles. However, molecular differences between pig (a larger animal model for human reproduction) and human mature oocytes remain unknown. Here, by comparative transcriptome analyses of single cell RNA-seq data, we aimed to identify the common and unique maternal factors and associated biological processes between in vivo and in vitro matured pig oocytes, and between in vitro matured human and pig oocytes. Annotated protein coding mRNAs were identified in pig in vivo (11147) and in vitro (11997), and human in vitro (14491) MII oocytes, respectively. For in vivo and in vitro derived pig MII oocytes, 10551 annotated maternal mRNAs were common, mainly enriched in signaling pathways such as cell cycle, oocyte meiosis, microtubule cytoskeleton, MAPK, RNA processing/binding. Besides, in vivo (596) and in vitro (1446) pig MII-specific mRNAs and their involved signaling pathways (in vivo: Bmp, calcium-mediated signaling, PI3K-Akt; in vitro: growth factor activity, JAK-STAT, cytokine-cytokine receptor interaction, calcium signaling pathway) were also found. As for in vitro derived human and pig MII oocytes, 10285 annotated mRNAs were common, enriched in a variety of signaling pathways (cell cycle, oocyte meiosis, microtubule, AMPK, RNA splicing, protein serine/threonine kinase activity, etc). In vitro MII-specific mRNAs were found for humans (4206) and pigs (1712), which were also enriched in species-specific signaling pathways (humans: golgi related terms, transcription repressor and hormone activity; pigs: ATP biosynthetic process, G protein-coupled peptide receptor activity, animoacyl-tRNA biosynthesis), respectively. These findings improve our understanding on oocyte maturation, and also the limitations of pig model for human oocyte maturation and fertilization.

Oocyte quality and aging

It is well known that female reproduction ability decreases during the forth decade of life due to age-related changes in oocyte quality and quantity; although the number of women trying to conceive has today increased remarkably between the ages of 36 to 44. The causes of reproductive aging and physiological aspects of this phenomenon are still elusive. With increase in the women's age, during Assisted Reproductive Technologies (ART) we have perceived a significant decline in the number and quality of retrieved oocytes, as well as in ovarian follicle reserves. This is because of increased aneuploidy due to factors such as spindle apparatus disruption; oxidative stress and mitochondrial damage. The aim of this review paper is to study data on the potential role of the aging process impacting oocyte quality and female reproductive ability. We present the current evidence that show the decreased oocyte quality with age, related to reductions in female reproductive outcome. The aging process is complicated and it is caused by many factors that control cellular and organism life span. Although the factors responsible for reduced oocyte quality remain unknown, the present review focuses on the potential role of ovarian follicle environment, oocyte structure and its organelles. To find a way to optimize oocyte quality and ameliorate clinical outcomes for women with aging-related causes of infertility.

Proteomic determinants of uterine receptivity for pregnancy in early and mid-postpartum dairy cows†

Dairy cow subfertility is a worldwide issue arising from multiple factors. It manifests in >30% early pregnancy losses in seasonal pasture-grazed herds, especially when cows are inseminated in the early post-partum period. Most losses occur before implantation, when embryo growth depends on factors present in maternal tract fluids. Here we examined the proteomic composition of early and mid-postpartum uterine luminal fluid in crossbred lactating dairy cows to identify molecular determinants of fertility. We also explored changes in uterine luminal fluid from first to third estrus cycles postpartum in individual cows, linking those changes with divergent embryo development. For this, we flushed uteri of 87 cows at day 7 of pregnancy at first and third estrus postpartum, recovering and grading their embryos. Out of 1563 proteins detected, 472 had not been previously reported in this fluid, and 408 were predicted to be actively secreted by bioinformatic analysis. The abundance of 18 proteins with roles in immune regulation and metabolic function (e.g. cystatin B, pyruvate kinase M2) was associated with contrasting embryo quality. Matched-paired pathway analysis indicated that, from first to third estrus postpartum, upregulation of metabolic (e.g. creatine and carbohydrate) and immune (e.g. complement regulation, antiviral defense) processes were related to poorer quality embryos in the third estrus cycle postpartum. Conversely, upregulated signal transduction and protein trafficking appeared related to improved embryo quality in third estrus. These results advance the characterization of the molecular environment of bovine uterine luminal fluid and may aid understanding fertility issues in other mammals, including humans.

Pyometra does not affect some molecular quality-related parameters of canine oocytes

Cystic endometrial hyperplasia-pyometra complex (CEH/P) significantly perturbs the reproductive performance of affected bitches and ovariohysterectomy (OHE) is a commonly applied treatment. Thus the only way to take advantage of the genetic potential of valuable females is application of assisted reproductive techniques (ART) mainly in vitro embryo production (IVP) or in some exceptional cases animal cloning by somatic cell nuclear transfer (SCNT). The aim of our study was to examine a potential effect of the CEH/P status on the quality of oocytes from females subjected to OHE. In total, 828 immature oocytes collected from ovaries of 33 bitches (21 control, 12 CEH/P) were subjected to genetic analyses (mRNA expression of two maternal-effect genes: GDF-9, OCT4 and mitochondrial DNA (mtDNA) content). Oocytes of CEH/P females were characterized by a higher mtDNA content (471 696) than gametes of their healthy counterparts (368 175; P<0.005). Transcripts for the two genes were detected in all samples and the mRNA level was not affected by the CEH/P status. In conclusion, the CEH/P complex does not exert a negative effect on oocyte quality reflected by the two parameters examined in this study.

Molecular characteristics of oocytes and somatic cells of follicles at different sizes that influence in vitro oocyte maturation and embryo production

During the last 10 to 15 yr, in vitro research to predict antral follicle growth and oocyte maturation has delivered interesting advances in the knowledge of processes regulating follicle growth and developmental competence of oocytes. This review discusses the contribution of cumulus and mural granulosa cells in the process of oocyte maturation and cumulus expansion in cumulus-oocyte complexes (COCs) from follicles of different sizes and shows that differences in gene expression in oocytes, granulosa, and theca cells of small and large follicles impact the success of in vitro blastocyst development. In addition, the molecular mechanisms by which COC metabolism and antioxidant defense provide oocyte competence are highlighted. Furthermore, new insights and perspectives on molecular and cellular regulation of in vitro oocyte maturation are emphasized.

Oocyte Selection for In Vitro Embryo Production in Bovine Species: Noninvasive Approaches for New Challenges of Oocyte Competence

Simple Summary

The efficiency of producing embryos using in vitro technologies in cattle species remains lower when compared to mice, indicating that the proportion of female gametes that fail to develop after in vitro manipulation is considerably large. Considering that the intrinsic quality of the oocyte is one of the main factors affecting embryo production, the precise identification of noninvasive markers that predict oocyte competence is of major interest. The aim of this review was to explore the current literature on different noninvasive markers associated with oocyte quality in the bovine model. Apart from some controversial findings, the presence of cycle-related structures in ovaries, a follicle size between 6 and 10 mm, a large slightly expanded investment without dark areas, large oocyte diameter (>120 microns), dark cytoplasm, and the presence of a round and smooth first polar body have been associated with better embryonic development. In addition, the combination of oocyte and zygote selection, spindle imaging, and the anti-Stokes Raman scattering microscopy together with studies decoding molecular cues in oocyte maturation have the potential to further optimize the identification of oocytes with better developmental competence for in vitro technologies in livestock species.

Abstract

The efficiency of producing embryos using in vitro technologies in livestock species rarely exceeds the 30–40% threshold, indicating that the proportion of oocytes that fail to develop after in vitro fertilization and culture is considerably large. Considering that the intrinsic quality of the oocyte is one of the main factors affecting blastocyst yield, the precise identification of noninvasive cellular or molecular markers that predict oocyte competence is of major interest to research and practical applications. The aim of this review was to explore the current literature on different noninvasive markers associated with oocyte quality in the bovine model. Apart from some controversial findings, the presence of cycle-related structures in ovaries, a follicle size between 6 and 10 mm, large number of surrounding cumulus cells, slightly expanded investment without dark areas, large oocyte diameter (>120 microns), dark cytoplasm, and the presence of a round and smooth first polar body have been associated with better competence. In addition, the combination of oocyte and zygote selection via brilliant cresyl blue (BCB) test, spindle imaging, and the anti-Stokes Raman scattering microscopy together with studies decoding molecular cues in oocyte maturation have the potential to further optimize the identification of oocytes with better developmental competence for in-vitro-derived technologies in livestock species.

Embryo development is impaired in goats that are treated for hydrometra and subsequently subjected to superovulation

BACKGROUND

Reproductive efficiency after hydrometra (HD) treatment is usually unsatisfactory.

METHODS

To identify mechanisms involved in low reproductive efficiency of HD-treated goats, pluriparous dairy goats treated for HD (n=10, HD) or with no reproductive disorders (n=11, control: CONT) were induced to oestrus and superovulated. Goats were mated with fertile bucks and seven days after oestrus, non-surgical embryo recovery was performed. Embryos were evaluated and gene expression was performed.

RESULTS

There were no differences (P>0.05) in sexual behaviour parameters, superovulation response, mean number of retrieved structures and viable embryos between groups; although embryo recovery rate was higher (P=0.01) in CONT group. Structures in delayed stage (8-16 cells) were more frequent (P<0.05) in HD (29 vs 1 per cent) goats, as well as the percentage of advanced embryos was greater (P<0.05) for CONT (59.3 vs 33.3 per cent) goats. However, the expression of genes related to apoptosis (BAX and Bcl-2), trophectoderm differentiation (CDX2) and pluripotency maintenance (NANOG) was not affected (P>0.05) in embryos that reached the morulae and blastocyst stages.

CONCLUSION

Although the HD embryos that developed to morula and blastocyst stages showed no change in the expression of genes related to their quality and implantation capacity, overall, embryo development was impaired in HD-treated goats.

The blueprint of RNA storages relative to oocyte developmental competence in cattle (Bos taurus)

From the time oocytes leave quiescence, there are constant microenvironmental influences contributing to development, thus acquiring developmental competence is not a simple, linear phenomenon. During folliculogenesis, oocytes experience many morphological and cytological changes that contribute toward the acquisition of developmental competence, a process defined by an oocyte’s ability to progress through folliculogenesis, be fertilized, undergo cleavage, and develop into an embryo. Many factors, such as ovarian follicle size, cow age, and the morphology of the cumulus–oocyte complex, have been extensively investigated to understand this process. In parallel to aiding in the understanding of oocyte biology, these features have been used to characterize an oocyte’s ability to achieve competence. In addition, oocytes undergo intense gene transcription and protein translation to accumulate the maternal stores. When the oocyte is fully grown, most genes are transcriptionally inactive, and the chromatin is densely compacted. More recently, RNA profiling has been used to further define the transcriptional parameters that are associated with oocyte development. Here, focusing on cattle, we provide an overview of the experimental models commonly used to understand the underlying biology related to oocyte developmental competence. We compiled public data and showed that cattle oocytes can express over 15 000 protein-coding genes, suggesting a complex transcriptome landscape. Surprisingly, less than 2% of the expressed genes have been linked to developmental competence. The identification of the gene products that contribute to oocyte development, and understanding their biological function, are a vital component of our quest toward defining oocyte developmental competence at the molecular level.

Coculture of porcine cumulus–oocyte complexes with porcine luteal cells during IVM: effect on oocyte maturation and embryo development

Coculture with somatic cells is an alternative to improve suboptimal invitro culture conditions. In pigs, IVF is related to poor male pronuclear formation and high rates of polyspermy. The aim of this study was to assess the effect of a coculture system with porcine luteal cells (PLCs) on the IVM of porcine cumulus–oocyte complexes (COCs). Abattoir-derived ovaries were used to obtain PLCs and COCs. COCs were matured invitro in TCM-199 with or without the addition of human menopausal gonadotrophin (hMG; C+hMG and C-hMG respectively), in coculture with PLCs from passage 1 (PLC-1) and in PLC-1 conditioned medium (CM). In the coculture system, nuclear maturation rates were significantly higher than in the C-hMG and CM groups, but similar to rates in the C+hMG group. In cumulus cells, PLC-1 coculture decreased viability, early apoptosis and necrosis, and increased late apoptosis compared with C+hMG. PLC-1 coculture also decreased reactive oxygen species levels in cumulus cells. After IVF, monospermic penetration and IVF efficiency increased in the PLC-1 group compared with the C+hMG group. After invitro culture, higher blastocysts rates were observed in the PLC-1 group. This is the first report of a coculture system of COCs with PLCs. Our model could be an alternative for the conventional maturation medium plus gonadotrophins because of its lower rates of polyspermic penetration and higher blastocysts rates, key issues in porcine invitro embryo production.

Alpine and lowland grazing differentially alter the reproductive tract redox milieu and amino acid composition in cattle

An alpine environment is unique due to pasture biodiversity, with an abundant content of natural antioxidant polyphenols. The present study investigated the effects of lowland and alpine grazing on the oviduct and uterine tissue redox status and amino acid concentrations in plasma and reproductive fluids. In the first experiment, heifers grazed on lowland (H-LOW: n = 13) and on alpine (H-ALP: n = 15) pastures. In the second experiment, heifers grazed on the same lowland (HS-LOW: n = 6) and on a different alpine (HS-ALP: n = 6) pasture. The abundance of mRNA transcripts for antioxidant enzymes in the oviduct (glutathione S-transferase alpha 2, glutathione synthetase (GSS)) and the endometrium (catalase, glutathione-disulfide reductase, GSS) was less (P <  0.05), and for glutathione peroxidase 4 in the endometrium greater (P =  0.006) in the H-LOW than in the H-ALP group. The abundance of mRNA transcript for catalase was less in the endometrium in the H-LOW than in the H-ALP (P =  0.001) group. Catalase and NAD(P)H quinone dehydrogenase 1 concentrations in the oviduct were greater in the HS-LOW than in the HS-ALP group (P <  0.05). Of 32 amino acids analysed, there were differences in concentrations in the H-LOW and H-ALP group of 13, seven and 15 in plasma, oviduct and uterine fluids, respectively (P <  0.05). Comparing the HS-LOW to the HS-ALP groups, there were 13, one and three amino acids in the plasma, oviduct and uterine fluids, respectively, that were differentially abundant (P <  0.05). The grazing systems had some effect on the redox status and amino acid patterns in reproductive tissues.

Novel ultrastructural findings in bovine oocytes matured in vitro

The ultrastructural morphology of the bovine oocyte at different maturation stages has been previously analyzed but without detailed structural observations at the mature stage. The objective of the present study was thus to establish the ultrastructural characteristics of the mature bovine oocyte in full detail. Oocytes from Bos taurus (Holstein-Friesian) cows were aspirated from ovaries collected after being slaughtered at a local abattoir. After in vitro culture for 24 h, some of them were processed for electron microscopy. We described the ultrastructure of the zona pellucida, which presented three different regions, and novel cytoplasmic findings. There were two types of electron-lucent vesicles (heterogeneous and striated), which were suggested to give rise to lipid droplets, and presence of receptor-mediated endocytosis. In conclusion, our results indicate that although the mature bovine oocyte is devoid of evident yolk, it might be filled with an extensive lipid factory. In addition, even before fertilization, the mature oocyte seemed to absorb nutrients through receptor-mediated endocytosis, indicating active energy use or storage.

Lipopolysaccharide and tumor necrosis factor-alpha alter gene expression of oocytes and cumulus cells during bovine in vitro maturation

Communication between the oocyte and cumulus facilitates oocyte growth, cell cycle regulation, and metabolism. This communication is mediated by direct contact between oocytes and cumulus cells, and soluble secreted molecules. Secreted molecules involved in this process are known inflammatory mediators. Lipopolysaccharide (LPS) is detected in follicular fluid and is associated with reduced fertility, whereas accumulation of inflammatory mediators in follicular fluid, including tumor necrosis factor-α (TNF-α), is associated with female infertility. Maturation of oocytes in the presence of LPS or TNF-α reduces meiotic maturation and the capacity to develop to the blastocyst. Here we evaluated the abundance of 92 candidate genes involved immune function, epigenetic modifications, embryo development, oocyte secreted factors, apoptosis, cell cycle, and cell signaling in bovine cumulus cells or zona-free oocytes after exposure to LPS or TNF-α during in vitro maturation. We hypothesize that LPS or TNF-α will alter the abundance of transcripts in oocytes and cumulus cell in a cell type dependent manner. Exposure to LPS altered abundance of 31 transcripts in oocytes (including ACVR1V, BMP15, DNMT3A) and 12 transcripts in cumulus cells (including AREG, FGF4, PIK3IP1). Exposure to TNF-α altered 1 transcript in oocytes (IGF2) and 4 transcripts in cumulus cells (GJA1, PLD2, PTGER4, STAT1). Cumulus expansion was reduced after exposure to LPS or TNF-α. Exposing COCs to LPS had a marked effect on expression of targeted transcripts in oocytes. We propose that altered oocyte transcript abundance is associated with reduced meiotic maturation and embryo development observed in oocytes cultured in LPS or TNF-α.

Distinct roles of cohesin acetyltransferases Esco1 and Esco2 in porcine oocyte meiosis I

In mammalian cells, cohesin acetyltransferases Esco1 and Esco2 acetylate cohesin subunit Smc3 to establish chromosome cohesion, ensuring the accurate chromosome segregation. However, we have previously documented that both Esco1 and Esco2 have unique substrates and roles in mouse oocyte meiosis I to orchestrate the meiotic progression, but whether these functions are conserved among species is still not determined. Here, we used porcine oocytes as a model to illustrate that Esco1 and Esco2 exerted conserved functions during oocyte meiosis. We observed that Esco1 and Esco2 exhibited different localization patterns in porcine oocytes. Esco1 was localized to the spindle apparatus while Esco2 was distributed on the chromosomes. Depletion of Esco1 by siRNA microinjection caused the meiotic arrest by showing the reduced frequency of first polar body extrusion and defective spindle/chromosome structure. In addition, Esco1 bound to α-tubulin and was required for its acetylation level to maintain the microtubule dynamics. By contrast, depletion of Esco2 by siRNA microinjection resulted in the accelerated meiotic progression by displaying the precocious polar body extrusion and inactivation of spindle assembly checkpoint. Notably, Esco2 was shown to be associated with histone H4 for the acetylation of H4K16 to modulate the kinetochore function. Collectively, our data reveal that Esco1 and Esco2 perform distinct and conserved functions in oocytes to drive the meiotic progression beyond their canonical roles in the cohesion establishment.

Applications of omics and nanotechnology to improve pig embryo production in vitro

An appropriate environment to optimize porcine preimplantation embryo production in vitro is required as genetically modified pigs have become indispensable for biomedical research and agriculture. To provide suitable culture conditions, omics technologies have been applied to elucidate which metabolic substrates and pathways are involved during early developmental processes. Metabolomic profiling and transcriptional analysis comparing in vivo- and in vitro-derived embryos have demonstrated the important role of amino acids during preimplantation development. Transcriptional profiling studies have been helpful in assessing epigenetic reprogramming agents to allow for the correction of gene expression during the cloning process. Along with this, nanotechnology, which is a highly promising field, has allowed for the use of engineered nanoplatforms in reproductive biology. A growing number of studies have explored the use of nanoengineered materials for sorting, labeling, and targeting purposes; which demonstrates their potential to become one of the solutions for precise delivery of molecules into gametes and embryos. Considering the contributions of omics and the recent progress in nanoscience, in this review, we focused on their emerging applications for current in vitro pig embryo production systems to optimize the generation of genetically modified animals.

Extracellular vesicles of follicular fluid from heat-stressed cows modify the gene expression of in vitro-matured oocytes

The effect of heat stress (HS) on cattle reproduction is deleterious with respect to ovarian follicular development and oocyte quality. The objective of this study was to investigate the effect of follicular fluid extracellular vesicles (EVs) obtained from cows maintained in thermoneutral (TN) or HS conditions on in vitro oocyte maturation. Nonlactating cows were estrous synchronized. Immediately after ovulation day (D1), the cows were randomly assigned to TN or HS environments. Follicular fluid from all follicles from each treatment was pooled, and EVs were obtained. Pools of 20 cumulus oocyte-complexes (COCs), were allocated to the following treatments: Control (n = 4 COC pools): matured in base medium; TN (n = 4 COC pools): matured in base medium supplemented with TN EV suspension; and HS (n = 4 COC pools): matured in base medium that was supplemented with the HS EV suspension. All treatments were conducted at 38.5 °C for 24 h in a humid atmosphere with 5% CO2. After maturation, the COCs were evaluated for meiotic progression, DNA integrity and oocyte quality-related gene expression. When the experimental groups were compared with the control group, a treatment effect was not observed for meiotic progression and DNA integrity. In the cumulus cells of TN group, there was relatively lesser expression of the IGFBP4 gene. In the oocytes of the TN as compared with the HS group, the IGFBP2, BMP15, GDF9, CDCA8, HAS2, RPL15, STAT3 and PFKP genes were expressed to a lesser extent. The findings indicated that oocytes matured in the presence of EVs from the follicular fluid of cows collected when there were TN conditions, however, there was a lesser expression of genes related to oocyte quality.

Quercetin influences in vitro maturation, apoptosis and metabolically active mitochondria of goat oocytes

SummaryThe present study aimed to investigate the effect of quercetin as an alternative antioxidant to cysteamine on in vitro maturation. Oocytes were collected from goat ovaries, destined for in vitro maturation and distributed into three groups: CIS group, oocytes were immersed in MIV base medium; in Groups Q4 and Q8, oocytes were immersed in the medium of the CIS group, adding 4 μM or 8 μM of quercetin, respectively, and cultured for 24 h at 38.5°C with 5% CO2. The CIS and Q4 groups presented the same percentage of expanded cumulus cells, but the per cent in the Q8 group was significantly lower than that of the other groups (P&lt;0.05). The oocyte retraction rate in the Q8 group was higher (P&lt;0.05) than in the CIS and Q4 groups. Treatment with 8 μM of quercetin presented a lower proportion of expanded oocytes than the CIS group and 4 μM of quercetin (P&lt;0.05). The percentage of MII oocytes was higher in the Q4 group than in the CIS group (P&lt;0.05), but the percentages in the CIS and Q8 groups were similar. The rate of apoptosis was higher in the CIS group than in the other groups (P&lt;0.05). In addition, oocytes matured with 4 μM quercetin showed higher mitochondrial activity than matured oocytes in the CIS and Q8 groups (P&lt;0.05). In conclusion, 4 μM of quercetin can be used as an alternative to cysteamine in the in vitro maturation of goat oocytes.

Single-cell transcriptome sequencing reveals that cell division cycle 5-like protein is essential for porcine oocyte maturation

The brilliant cresyl blue (BCB) test is used in both basic biological research and assisted reproduction to identify oocytes likely to be developmentally competent. However, the underlying molecular mechanism targeted by the BCB test is still unclear. To explore this question, we first confirmed that BCB-positive porcine oocytes had higher rates of meiotic maturation, better rates of cleavage and development into blastocysts, and lower death rates. Subsequent single-cell transcriptome sequencing on porcine germinal vesicle (GV)-stage oocytes identified 155 genes that were significantly differentially expressed between BCB-negative and BCB-positive oocytes. These included genes such as cdc5l, ldha, spata22, rgs2, paip1, wee1b, and hsp27, which are enriched in functionally important signaling pathways including cell cycle regulation, oocyte meiosis, spliceosome formation, and nucleotide excision repair. In BCB-positive GV oocytes that additionally had a lower frequency of DNA double-strand breaks, the CDC5L protein was significantly more abundant. cdc5l/CDC5L inhibition by short interference (si)RNA or antibody microinjection significantly impaired porcine oocyte meiotic maturation and subsequent parthenote development. Taken together, our single-oocyte sequencing data point to a potential new role for CDC5L in porcine oocyte meiosis and early embryo development, and supports further analysis of this protein in the context of the BCB test.

Addition of insulin-like growth factor I to the maturation medium of bovine oocytes subjected to heat shock: effects on the production of reactive oxygen species, mitochondrial activity and oocyte competence

This study was performed to investigate the effects of insulin-like growth factor-I (IGF-I) addition to in vitro maturation (IVM) medium on apoptosis, mitochondrial membrane potential, ROS production, and developmental competence of bovine oocytes subjected to heat shock. Two temperatures (conventional: 24 h at 38.5°C, or heat shock: 12 h at 41°C followed by 12 h at 38.5°C) and 3 IGF-I concentrations (0, 25, and 100 ng/mL) were tested during IVM. The oocytes were then fertilized in vitro, and the presumptive zygotes were cultured until reaching the blastocyst stage. There was no interaction between temperature and IGF-I concentration for any variable evaluated (P > 0.05). The addition of IGF-I did not alter the proportion of nuclear maturation, TUNEL-positive oocytes and caspase-3 activity, or blastocyst proportion on Days 7 and 8 post-fertilization. Furthermore, the total number of cells and the number of cells in the inner cell mass (ICM) in the blastocyst were not altered (P > 0.05). However, IGF-I increased (P < 0.05) the mitochondrial membrane potential and the production of ROS in oocytes and decreased (P < 0.05) the proportion of apoptotic cells in the ICM in blastocysts. Heat shock increased (P < 0.05) the proportion of TUNEL-positive oocytes and ROS production and reduced (P < 0.05) the mitochondrial membrane potential. Moreover, heat shock increased (P < 0.05) the apoptosis proportion in the ICM cells. In conclusion, supplementing IVM medium with IGF-I may increase the mitochondrial membrane potential and ROS production in oocytes and decrease apoptosis in the ICM in blastocysts. Heat shock for 12 h compromised oocyte developmental competence and increased apoptosis within the ICM cells of the blastocysts.

Feed restriction regime in a rabbit line selected for growth rate alters oocyte maturation manifested by alteration in MSY2 gene expression

Young rabbit females selected for growth rate may have nutritional needs, which may not be met with the common practice of feed restriction during rearing in commercial rabbit production. The aim of this study was to analyse whether two different feeding programmes: ad libitum or restricted (130 g/day) feeding, applied in young rabbit females for 1 month at the end of rearing, could modulate the origin of ovulation process and the quality of the oocytes. At 16 weeks of age, 34 females were randomly assigned to restricted or ad libitum feeding, maintaining these conditions for a month. Then, in an initial experiment, transcriptional profiling of hypothalamus-hypophysis tissue was performed to assess failure to ovulate. In the second experiment, the gene expression analysis of some candidate genes related to oocytes quality was performed. Our results demonstrated that neither of the two feeding programmes modified the transcription of hypothalamus-hypophysis tissue, while the only differences in MSYR expression were found in in vivo mature oocytes ready for successful fertilization. Specifically, MSYR was over-expressed in oocytes from females fed ad libitum. MSYR is one of the most abundant proteins in the oocyte and has proven to be a key regulator of maternal RNA transcription and translation. This finding suggests that MSYR gene is a promising gene in our understanding of the relationship between high growth rate and reproductive performance decline.

Logistics of large scale commercial IVF embryo production

The use of IVF in agriculture is growing worldwide. This can be explained by the development of better IVF media and techniques, development of sexed semen and the recent introduction of bovine genomics on farms. Being able to perform IVF on a large scale, with multiple on-farm experts to perform ovum pick-up and IVF laboratories capable of handling large volumes in a consistent and sustainable way, remains a huge challenge. To be successful, there has to be a partnership between veterinarians on farms, embryologists in the laboratory and animal owners. Farmers must understand the limits of what IVF can or cannot do under different conditions; veterinarians must manage expectations of farmers once strategies have been developed regarding potential donors; and embryologists must maintain fluent communication with both groups to make sure that objectives are met within predetermined budgets. The logistics of such operations can be very overwhelming, but the return can be considerable if done right. The present mini review describes how such operations can become a reality, with an emphasis on the different aspects that must be considered by all parties.

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

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

Exocannabinoids effect on in vitro bovine oocyte maturation via activation of AKT and ERK1/2

Endocannabinoids are known to mediate practically all reproductive events in mammals; however, little is known about their role in oocyte maturation. Through RT-PCR and immunocytochemistry, this study confirms the presence of CB1 and CB2 cannabinoid receptors in bovine oocytes and shows how exposure to the exogenous cannabinoids HU-210 and THC during their in vitro maturation (IVM) activates the phosphorylation of AKT and ERK1/2 proteins associated with the resumption of meiosis. Although supplementation with HU-210 or THC during IVM did not increase blastocyst yields, the expression of interferon tau (IFNτ) and gap junction alpha-1 protein (GJA1) was enhanced at the blastocyst stage. Our data suggest that cannabinoid agonists may be useful IVM supplements as their presence during oocyte maturation upregulates the expression in blastocysts of key genes for embryo quality.

DNA methylation and mRNA expression of developmentally important genes in bovine oocytes collected from donors of different age categories

Epigenetic changes are critical for the acquisition of developmental potential by oocytes and embryos, yet these changes may be sensitive to maternal ageing. Here, we investigated the impact of maternal ageing on DNA methylation and mRNA expression in a panel of eight genes that are critically involved in oocyte and embryo development. Bovine oocytes were collected from donors of three different age categories-prepubertal (9-12 months old), mature (3-7 years old), and aged (8-11 years old)-and were analyzed for gene-specific DNA methylation (bTERF2, bREC8, bBCL-XL, bPISD, bBUB1, bDNMT3Lo, bH19, and bSNRPN) and mRNA expression (bTERF2, bBCL-XL, bPISD, and bBUB1). A total of 1,044 alleles with 88,740 CpGs were amplified and sequenced from 362 bovine oocytes. Most of the detected molecules were either fully methylated or completely unmethylated. Only 9 out of 1,044 alleles (<1%) were abnormally methylated (>50% of CpGs with an aberrant methylation status), and seven of the nine abnormally methylated alleles were within only two candidate genes (bDNMT3Lo and bH19). No significant differences were detected with regard to mRNA expression between oocytes from the three groups of donors. These results suggest that genes predominantly important for early embryo development (bH19 and bDNMT3Lo) are less resistant to abnormal methylation than genes critically involved in oocyte development (bTERF2, bBCL-XL, bPISD, bBUB1, and bSNRPN). Establishment of DNA methylation in bovine oocytes seems to be largely resistant to changes caused by maternal ageing, irrespective of whether the genes are critical to achieve developmental competence in oocytes or early embryos. Mol. Reprod. Dev. 83: 802-814, 2016 © 2016 Wiley Periodicals, Inc.