Consequences of bovine oocyte maturation, fertilization or early embryo development in vitro versus in vivo: implications for blastocyst yield and blastocyst quality

Effect of BMP15 and/or AMH during in vitro maturation of oocytes from involuntarily culled dairy cows

The high metabolic activity to which the dairy cattle are exposed to maintain milk production altered steroid metabolism that affects reproductive physiology and reduce oocyte competence. Our aims were (a) to characterize the competence of immature oocytes collected from dairy cattle based on the expression of genes in cumulus cells (CCs) and (b) to improve oocyte competence to support preimplantation embryo development by the supplementation of maturation medium with bone morphogenetic protein 15 (BMP15) and/or anti-mullerian hormone (AMH). Oocyte donors were identified at the moment of ovary collection and grouped by involuntarily culled dairy cows (Holstein breed) or beef cattle. The embryo development speed to blastocyst of the cull dairy cattle versus beef cattle (control group) was lower. Besides, <10% of oocytes (with CC biopsies) derived from dairy cattle were able to develop to the blastocyst stage. In addition, a higher level of expression and a positive correlation were observed in the expression of most of the genes evaluated (LUM, KRT18, KRT8, CLIC3, BMPR1B, and SLC38A3) in the cumulus-oocyte complexes that produced blastocysts versus those which did not develop correctly (arrested development). Further, use of BMP15 in the maturation of oocytes from dairy cattle seems to increase competence, modulating the expression of OCT4, SOX2, CDX2, GATA6, and TP1 in resulting blastocysts.

Supplementation of bovine follicular fluid during in vitro maturation increases oocyte cumulus expansion, blastocyst developmental kinetics, and blastocyst cell number

Bovine follicular fluid (bFF) is the natural milieu for oocyte growth and development. However, its value as supplementation to in vitro maturation medium is still questioned due to inconsistent results. In this study we hypothesized that adding 10% of follicular fluid as well as heat treating it to inhibit the complement system, would produce higher quality embryos. To do so, experiments were conducted to compare the effect of bFF and heat-treated bFF (bFFin) on oocyte competence assessed by different parameters such as nuclear and cytoplasmic maturation, IVF efficiency, in vitro embryo development and embryo survivability post-vitrification. No differences on nuclear maturation nor cortical granules migration were observed but differences were found on oocyte's cumulus cell expansion, with bFF group having the highest increase (79.0 ± 3.7%). bFFin had a negative impact on IVF efficiency (58.6 ± 3.2%), but no differences were found between bFF (62.9 ± 3.2%) and control (72.8 ± 3.0%). Although the cleavage and blastocyst rate were similar between groups, the day 6 embryo development rate was higher in bFFin group, suggesting an accelerated developmental kinetics. Hatched blastocysts from the bFF group showed a higher cell count than the control group (241.3 ± 20.1 and 185.8 ± 10.0, respectively), and bFFin embryos showed values in between (214.9 ± 14.0). No difference on survivability post-vitrification was found between groups, although the blastocyst stage had a significant impact on the survival rate across all groups. In conclusion, using bFF as supplementation to maturation medium showed a higher benefit when comparing to the standard supplementation by having oocytes with higher cumulus expansion rate, faster development of embryos and higher number of cells per embryo. Inactivation of bFF lowered IVF efficiency but didn't compromise blastocyst development and quality.

Embryonic maternal interaction in cattle and its relationship with fertility

Embryo mortality is a major contributor to poor reproductive efficiency and profitability in cattle production systems. While conception is achieved (i.e., the oocyte is fertilized) in the vast majority of cases if insemination is carried out correctly, a significant proportion of the resulting embryos fail to develop to term. Appropriate communication between the developing conceptus and the maternal endometrium is essential for the establishment and maintenance of pregnancy in all mammals. Up to the blastocyst stage, around Days 7-9, contact worth the female reproductive system is not required. However, the process of conceptus elongation after hatching and prior to implantation is entirely maternally driven and is essential to ensure that sufficient quantities of interferon-tau (IFNT) are secreted by the developing conceptus to abrogate the mechanisms that bring about luteolysis. While the importance of conceptus-derived IFNT in maternal recognition of pregnancy and prevention of luteolysis in cattle is unequivocal, many questions, such as the threshold level of IFNT required for pregnancy maintenance, remain unanswered. Furthermore, the precise role of IFNT-independent mechanisms in pregnancy establishment remains to be elucidated. Irrespective of this, failure of the conceptus to elongate undoubtedly results in embryonic loss and is thus believed to contribute greatly to reproductive failure in cattle. This review will address some of these answered questions and try to shed some light on those gaps in knowledge that could potentially contribute to improved embryo survival and reproductive efficiency.

The consequences of porcine IVM medium supplementation with follicular fluid become reflected in embryo quality, yield and gene expression patterns

Oocyte and embryo developmental competence are shaped by multiple extrinsic and intrinsic factors. One of the most extensive research areas in the last decade is the regulation of lipid metabolism in oocytes and embryos of different species. We hypothesized that differences in developmental competence of oocytes and embryos between prepubertal and cyclic gilts may arise due to distinct fatty acid profiles in follicular fluid. We found that supplementation of oocyte maturation media with follicular fluid from prepubertal pigs affected quality and development of embryos from prepubertal pigs while embryos of cyclic pigs were not affected. PLIN2, SCD and ACACA transcripts involved in lipid metabolism were upregulated in embryos originating from oocytes of prepubertal pigs matured with autologous follicular fluid. The surface occupied by lipid droplets tend to increase in oocytes matured with follicular fluid from prepubertal pigs regardless oocyte origin. The change into follicular fluid of cyclic pigs increased the efficiency of embryo culture and improved quality, while gene expression was similar to embryos obtained from cyclic gilts. We assume that the follicular fluids of prepubertal and cyclic pigs influenced the quality of oocytes and embryos obtained from prepubertal pigs which are more susceptible to suboptimal in vitro culture conditions.

The effects of aquarium culture on coral oocyte ultrastructure

As the world's oceans are currently threatened by anthropogenic pollution and climate change, coral breeding has become an important conservation method, since it can limit marine organisms' exposure to sub-optimal environment conditions. However, the aquarium environment is inherently different from the ocean, and this could manifest in physiological changes in the reared organisms, particularly with respect to their reproduction. Therefore, the aim of this study was to observe and compare the ultrastructure of the oocytes from wild Oxypora lacera and Echinopora gemmacea with the oocytes from cultured corals using transmission electron microscope. The oocytes from Wild O. lacera and E. gemmacea were larger than cultured ones, though their microvillus layers were significantly thiner. Internally, lipid granule areas and yolk material density in the oocytes of wild O. lacera and E. gemmacea were ~25% lower than in their cultured counterparts. Food availability and the presence and availability of symbiotic dinoflagellates (genus Symbiodinium) may have played a role in driving these lipid-based differences, in particular, as cultured corals had limited potential for heterotrophic feeding. These data will aid in future coral husbandry efforts.

Contributions from the ovarian follicular environment to oocyte function

The magnitude of oocyte's role for embryo development is categorical. This unique cell contains the machineries and cellular components necessary to remodel male and female chromatin, to sustain early development and to, ultimately, generate a complete and complex individual. However, to gain these competences before fertilization, the oocyte undergoes several morphological, cellular and molecular changes during its lifetime enclosed in the ovarian follicle. This review will briefly revisit how the oocyte orchestrate the follicular cells, and how molecules transit to the oocyte from the innermost (cumulus) and outermost (antrum and granulosa cells) layers surrounding the follicle-enclosed oocyte. Finally, we will discuss the interferences of in vitro culture conditions in the communication of the oocyte with its surrounding cells and the potential strategies to modulate these communication systems to increase oocyte competence.

Oocyte maturation with royal jelly increases embryo development and reduces apoptosis in goats

Royal jelly (RJ) was supplemented to goat oocyte in vitro maturation (IVM) medium at three different concentrations (2.5, 5, and 10 mg/ml). Maturation rate, embryo cleavage, and blastocyst rate were recorded. Gene expression of apoptosis-related transcripts was investigated in matured oocytes. Percentage of oocytes that reached MII-stage was increased in RJ-treated groups compared to the control group. Glutathione (GSH) content of mature oocytes was enhanced when RJ was added to IVM medium at any supplementation compared with control. Percentage of cleaved embryos and blastocysts was higher in the RJ-treated groups at a concentration of 5 than in the 2.5 mg/ml and control group. Total number of cells per blastocyst was not different in the control and RJ-treated group at 5 mg/ml. However, number of apoptotic cells per blastocyst was higher in the control group than in the RJ-treated group at 5 mg/ml. Expression profile of Bax, and p53 was down-regulated while Bcl-2 was up-regulated in oocytes treated with RJ at 5 and 10 mg/ml compared with the control group. Addition of RJ at concentrations of 5 mg/ml improved embryo production through increasing maturation rate. RJ seems to improve the IVM microenvironment by reducing expression of genes inducing apoptosis, enhancing GSH content, and reducing incidence of apoptosis in blastocysts.

Effects of recombinant OVGP1 protein on in vitro bovine embryo development

Previously, our group demonstrated that recombinant porcine oviductin (pOVGP1) binds to the zona pellucida (ZP) of in vitro-matured (IVM) porcine oocytes with a positive effect on in vitro fertilization (IVF). The fact that pOVGP1 was detected inside IVM oocytes suggested that this protein had a biological role during embryo development. The aim of this study was to evaluate the effects of pOVGP1 on bovine in vitro embryo development. We applied 10 or 50 µg/ml of pOVGP1 during IVF, embryonic in vitro culture (IVC), or both, to evaluate cleavage and embryo development. Blastocyst quality was assessed by analyzing the expression of important developmental genes and the survival rates after vitrification/warming. pOVGP1 was detected in the ZP, perivitelline space, and plasma membrane of blastocysts. No significant differences (P > 0.05) were found in cleavage or blastocyst yield when 10 or 50 µg/ml of pOVGP1 was used during IVF or IVC. However, when 50 µg/ml pOVGP1 was used during IVF + IVC, the number of blastocysts obtained was half that obtained with the control and 10 µg/ml pOVGP1 groups. The survival rates after vitrification/warming of expanded blastocysts cultured with pOVGP1 showed no significant differences between groups (P > 0.05). The use of pOVGP1 during IVF, IVC, or both, increased the relative abundance of mRNA of DSC2, ATF4, AQP3, and DNMT3A, the marker-genes of embryo quality. In conclusion, the use of pOVGP1 during bovine embryo in vitro culture does not affect embryo developmental rates but produces embryos of better quality in terms of the relative abundance of specific genes.

Effects of sex on response of the bovine preimplantation embryo to insulin-like growth factor 1, activin A, and WNT7A

BACKGROUND

Alterations in maternal environment can sometimes affect embryonic development in a sexually-dimorphic manner. The objective was to determine whether preimplantation bovine embryos respond to three maternally-derived cell signaling molecules in a sex-dependent manner.

RESULTS

Actions of three embryokines known to increase competence of bovine embryos to develop to the blastocyst stage, insulin-like growth factor 1 (IGF1), activin A, and WNT member 7A (WNT7A), were evaluated for actions on embryos produced in vitro with X- or Y- sorted semen from the same bull. Each embryokine was tested in embryos produced by in vitro fertilization of groups of oocytes with either pooled sperm from two bulls or with sperm from individual bulls. Embryos were treated with IGF1, activin A, or WNT7A on day 5 of culture. All three embryokines increased the proportion of cleaved zygotes that developed to the blastocyst stage and the effect was similar for female and male embryos. As an additional test of sexual dimorphism, effects of IGF1 on blastocyst expression of a total of 127 genes were determined by RT-qPCR using the Fluidigm Delta Gene assay. Expression of 18 genes was affected by sex, expression of 4 genes was affected by IGF1 and expression of 3 genes was affected by the IGF1 by sex interaction.

CONCLUSION

Sex did not alter how IGF1, activin A or WNT7A altered developmental competence to the blastocyst stage. Thus, sex-dependent differences in regulation of developmental competence of embryos by maternal regulatory signals is not a general phenomenon. The fact that sex altered how IGF1 regulates gene expression is indicative that there could be sexual dimorphism in embryokine regulation of some aspects of embryonic function other than developmental potential to become a blastocyst.

Profiling bovine blastocyst microRNAs using deep sequencing

MicroRNAs (miRNAs) are known to control several reproductive functions, including oocyte maturation, implantation and early embryonic development. Recent advances in deep sequencing have allowed the analysis of all miRNAs of a sample. However, when working with embryos, due to the low RNA content, miRNA profiling is challenging because of the relatively large amount of total RNA required for library preparation protocols. In the present study we compared three different procedures for RNA extraction and prepared libraries using pools of 30 bovine blastocysts. In total, 14 of the 15 most abundantly expressed miRNAs were common to all three procedures. Furthermore, using miRDeep discovery and annotation software (Max Delbrück Center), we identified 1363 miRNA sequences, of which bta-miR-10b and bta-miR-378 were the most abundant. Most of the 179 genes identified as experimentally validated (86.6%) or predicted targets (13.4%) were associated with cancer canonical pathways. We conclude that reliable analysis of bovine blastocyst miRNAs can be achieved using the procedures described herein. The repeatability of the results across different procedures and independent replicates, as well as their consistency with results obtained in other species, support the biological relevance of these miRNAs and of the gene pathways they modulate in early embryogenesis.

Blastocyst-induced changes in the bovine endometrial transcriptome

The objectives of this study were (i) to determine whether blastocyst-induced responses in endometrial explants were detectable after 6- or 24-h co-culture in vitro; (ii) to test if direct contact is required between embryos and the endometrial surface in order to stimulate endometrial gene expression; (iii) to establish the number of blastocysts required to elicit a detectable endometrial response; (iv) to investigate if upregulation of five interferon-stimulated genes (ISGs) in the endometrium was specific to the blastocyst stage and (v) to test if alterations in endometrial gene expression can be induced by blastocyst-conditioned medium. Exposure of endometrial explants to Day 8 blastocysts in vitro for 6 or 24 h induced the expression of ISGs (MX1, MX2, OAS1, ISG15, RSAD2); expression of IFNAR1, IFNAR2, NFKB1, IL1B, STAT1, LGALS3BP, LGALS9, HPGD, PTGES, ITGB1, AKR1C4, AMD1 and AQP4 was not affected. Culture of explants in the presence of more than five blastocysts was sufficient to induce the effect, with maximum expression of ISGs occurring in the presence of 20 blastocysts. This effect was exclusive to blastocyst stage embryos; oocytes, 2-cell embryos or Day 5 morulae did not alter the relative abundance of any of the transcripts examined. Direct contact between blastocysts and the endometrial surface was not required in order to alter the abundance of these transcripts and blastocyst-conditioned medium alone was sufficient to stimulate a response. Results support the notion that local embryo-maternal interaction may occur as early as Day 8 of pregnancy in cattle.

Short- and long-term outcomes of the absence of protein during bovine blastocyst formation in vitro

In cattle, individual in vitro embryo culture after Day 6 benefits development, allowing non-invasive analysis of culture medium. However, undefined supplements in culture reduce analytical reliability. In this study we assayed the short- and long-term performance of embryos after bovine serum albumin removal over a 24-h period in individual culture. The absence of protein decreased embryo development and cell counts in the inner cell mass without affecting blastocyst sex ratio. However, the absence of protein produced embryos with an improved tendency to survive vitrification after 24h in culture (P=0.07). After transfer to recipients, birth rates of embryos that had been cultured with protein tended to decrease (P<0.06) mostly as a result of a higher number of miscarriages (P<0.013), reflecting lower viability. Birthweight, gestation length, height and thorax circumference did not differ between embryos cultured with or without protein. In fresh blastocysts cultured without protein, gene expression analysis showed higher abundance (P<0.05) of insulin-like growth factor 2 receptor (IGF2R; imprinting) and activating transcription factor 4 (ATF4) and DNA-damage-inducible transcript 3 (DDIT3; endoplasmic reticulum stress) transcripts, with DNA methyltransferase 3A (DNMT3A; imprinting) tending to increase (P=0.062). However, in hatched blastocysts that survived cryopreservation, glucose-6-phosphate dehydrogenase (G6PD) was overexpressed in embryos cultured without protein (P<0.01). The absence of protein results in fewer blastocysts but improved long-term viability after cryopreservation.

Membrane lipid profile of in vitro-produced embryos is affected by vitrification but not by long-term dietary supplementation of polyunsaturated fatty acids for oocyte donor beef heifers

Dietary rumen-protected polyunsaturated fatty acids (PUFAs) rich in linoleic acid (LA) may affect embryo yield, and LA can modulate the molecular mechanisms of lipid uptake in bovine blastocysts produced in vitro. In embryos, membrane lipids, such as phosphatidylcholines (PCs) and sphingomyelins (SMs), affect cryopreservation success. The aim of the present study was to evaluate embryonic developmental rates after the IVF of oocytes retrieved from Nellore heifers fed for approximately 90 days with rumen-protected PUFAs rich in LA. In addition, we evaluated embryo cryotolerance and the membrane structure lipid composition using matrix-assisted laser desorption ionisation mass spectrometry of fresh and vitrified embryos. Embryo development to the blastocyst stage (mean 43.2%) and embryo survival after vitrification and warming (mean 79.3%) were unaffected by diet. The relative abundance of one lipid species (PC ether (PCe; 38:2, which means that this lipid has 38 carbon atoms and 2 double bonds in the fatty acyl residues) was increased after PUFAs supplementation. However, 10 ions were affected by cryopreservation; ions consistent with PC 32:0, PC 34:1, SM 24:1, PC 40:6 or PC 42:9, PC plasmalogen (PCp) 44:10 or PC 42:7, triacylglycerol (TAG) 54:9 and a not assigned ion (m/z 833.2) were lower in blastocysts that survived to the cryopreservation process compared with fresh blastocysts, whereas the abundance of the ions PC 36:3 or PC 34:0, PCe 38:2 or PC 36:6 and PC 36:5 or PCe 38:1 were increased after cryopreservation. Thus, the results demonstrate that the mass spectrometry profiles of PC, SM and TAG species differ significantly in bovine blastocysts upon cryopreservation. Because the lipid ion abundances of fresh and vitrified-warmed embryos were distinct, they can be used as potential markers of post-cryopreservation embryonic survival.

Sperm traits on in vitro production (IVP) of bovine embryos: Too much of anything is good for nothing

Sperm samples used on fertilization strongly influence the in vitro production (IVP) rates. However, sperm traits behind this effect are not stated consistently until now. This study aimed to evaluate the isolated and combined effect of some sperm traits (MB: total motility before Percoll^® gradient, MA: total motility after Percoll^® gradient, AI: acrosome integrity, MI: membrane integrity, MP: mitochondrial membrane potential, and CR: chromatin resistance) on IVP rates. This is the first study focusing on the isolated effect of distinct traits. For this purpose, the experiment was divided in three steps. In first step, to study behavior of traits sperm samples (n = 63 batches) were analyzed and ranked based on each trait. In second step, samples ranked were selected from target ranks regions and allocated in groups of four to five batches, creating Higher and Lower groups, according to two different approaches. One aimed to form groups that differed to all sperm traits simultaneously (effect of combined traits). The other aimed to form groups that differed only to a single sperm trait while no differences were observed for the remaining traits (effect of each isolated trait). In third step, for each group successfully formed in step 2, sperm samples were individually and prospectively used for IVP. Cleavage, embryo development and blastocyst rates were recorded and compared between Higher and Lower of respective trait groups. Surprisingly, evaluation of isolated effects revealed that lower levels of MB, AI and MP resulted in higher embryo development and blastocyst rates (p<0.05), which was not observed on cleavage rate. We conclude that sperm traits strongly influence embryo development after in vitro fertilization (IVF), affecting the zygote competence to achieve blastocyst stage. Individually, levels of MB, AI or MP could be some of the key traits that may define IVP efficiency on current systems of embryo production.

Effect of bovine oviductal fluid on development and quality of bovine embryos produced in vitro

To evaluate the effect of bovine oviductal fluid (OF) supplementation during in vitro culture of bovine embryos on their development and quality, in vitro-produced zygotes were cultured in synthetic oviductal fluid (SOF; negative control; C^-) supplemented with OF or 5% fetal calf serum (positive control; C⁺). Embryo development was recorded on Days 7-9 after insemination and blastocyst quality was assessed through cryotolerance, differential cell counting of the inner cell mass and trophectoderm, and gene expression. OF was added to the culture medium at concentrations ranging from 0.625% to 25%. The higher OF concentrations (5%, 10% and 25%) had a detrimental effect on embryo development. Lower OF concentrations (1.25% and 0.625%) supported embryo development until Day 9 (27.5%) and produced higher-quality blastocysts, as reflected by their cryotolerance (53.6% and 57.7% survival at 72h, respectively, vs 25.9% in C⁺) and total cell number (mean (± s.e.m.) 165.1±4.7 and 156.2±4.2, respectively, vs 127.7±4.9 in C^- and 143.1±4.9 in C⁺). Consistent with these data, upregulation of the water channel aquaporin 3 (AQP3) mRNA was observed in blastocysts supplemented with 1.25% OF compared with C^- and C⁺. Serum supplementation resulted in a reduction in the expression of glucose and lipid metabolism-related genes and downregulation of the epigenetic-related genes DNA methyltransferase 3A (DNMT3A) and insulin-like growth factor 2 receptor (IGF2R). In conclusion, in vitro culture with low concentrations of OF has a positive effect on the development and quality of bovine embryos.

N-octanoylated ghrelin peptide inhibits bovine oocyte meiotic resumption

BACKGROUND

Studies have shown that ghrelin plays an important role in the mammalian reproductive system, including the central, gonadal levels, and also during in vitro maturation of oocytes; however, the functions of ghrelin in bovine oocyte meiosis require further investigation.

OBJECTIVE

We aimed to evaluate the effects of an n-octanoylated ghrelin peptide on oocyte meiotic resumption and the developmental competence of mature oocytes in vitro.

EXPERIMENTAL

design: The expression of GHRL (encoding ghrelin) mRNA and its receptor (the growth hormone secretagogue receptor, GHSR) in the cumulus-oocyte complex (COCs), denuded oocytes (DOs), and cumulus cells (CCs) was assessed using quantitative real-time reverse transcription PCR (qRT-PCR), and the effects of the n-octanoylated ghrelin peptide on meiotic resumption were studied at four different doses (0, 10, 50, and 100 ng/mL) in a 6 h culture system.

RESULTS

qRT-PCR analysis showed that GHRL and GHSR mRNAs were expressed in all tested samples; however, GHRL was predominantly expressed in DOs, and GHSR was predominantly expressed in CCs. Germinal vesicle breakdown was inhibited significantly by 50 ng/mL ghrelin compared with that in the negative control (P < 0.05). Further studies showed that n-octanoylated ghrelin increased the levels of cAMP and cGMP in the CCs and DOs, which inhibited the meiotic resumption of bovine oocytes. And the inhibitory role in the developmental competence of mature oocytes were also included, ghrelin could significantly improve the cleavage rate (P < 0.05) and blastocyst rate (P < 0.05).

CONCLUSION

N-octanoylated ghrelin maintained bovine oocytes meiotic arrest and further improved their developmental competence; therefore, n-octanoylated ghrelin could be considered as a potential pharmaceutical inhibitor of meiosis for the in vitro maturation of bovine oocytes.

Genome stability of bovine in vivo-conceived cleavage-stage embryos is higher compared to in vitro-produced embryos

STUDY QUESTION

Is the rate and nature of chromosome instability (CIN) similar between bovine in vivo-derived and in vitro-cultured cleavage-stage embryos?

SUMMARY ANSWER

There is a major difference regarding chromosome stability of in vivo-derived and in vitro-cultured embryos, as CIN is significantly lower in in vivo-derived cleavage-stage embryos compared to in vitro-cultured embryos.

WHAT IS KNOWN ALREADY

CIN is common during in vitro embryogenesis and is associated with early embryonic loss in humans, but the stability of in vivo-conceived cleavage-stage embryos remains largely unknown.

STUDY DESIGN, SIZE, DURATION

Because human in vivo preimplantation embryos are not accessible, bovine (Bos taurus) embryos were used to study CIN in vivo. Five young, healthy, cycling Holstein Friesian heifers were used to analyze single blastomeres of in vivo embryos, in vitro embryos produced by ovum pick up with ovarian stimulation (OPU-IVF), and in vitro embryos produced from in vitro matured oocytes retrieved without ovarian stimulation (IVM-IVF).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Single blastomeres were isolated from embryos, whole-genome amplified and hybridized on Illumina BovineHD BeadChip arrays together with the bulk DNA from the donor cows (mothers) and the bull (father). DNA was also obtained from the parents of the bull and from the parents of the cows (paternal and maternal grandparents, respectively). Subsequently, genome-wide haplotyping and copy-number profiling was applied to investigate the genomic architecture of 171 single bovine blastomeres of 16 in vivo, 13 OPU-IVF and 13 IVM-IVF embryos.

MAIN RESULTS AND THE ROLE OF CHANCE

The genomic stability of single blastomeres in both of the in vitro-cultured embryo cohorts was severely compromised (P < 0.0001), and the frequency of whole chromosome or segmental aberrations was higher in embryos produced in vitro than in embryos derived in vivo. Only 18.8% of in vivo-derived embryos contained at least one blastomere with chromosomal anomalies, compared to 69.2% of OPU-IVF embryos (P < 0.01) and 84.6% of IVM-IVF embryos (P < 0.001).

LARGE SCALE DATA

Genotyping data obtained in this study has been submitted to NCBI Gene Expression Omnibus (GEO; accession number GSE95358).

LIMITATIONS REASONS FOR CAUTION

There were two main limitations of the study. First, animal models may not always reflect the nature of human embryogenesis, although the use of an animal model to investigate CIN was unavoidable in our study. Second, a limited number of embryos were obtained, therefore more studies are warranted to corroborate the findings.

WIDER IMPLICATIONS OF THE FINDINGS

Although CIN is also present in in vivo-developed embryos, in vitro procedures exacerbate chromosomal abnormalities during early embryo development. Hence, the present study highlights that IVF treatment compromises embryo viability and should be applied with care. Additionally, our results encourage to refine and improve in vitro culture conditions and assisted reproduction technologies.

STUDY FUNDING/COMPETING INTEREST(S)

The study was funded by the Agency for Innovation by Science and Technology (IWT) (TBM-090878 to J.R.V. and T.V.), the Research Foundation Flanders (FWO; G.A093.11 N to T.V. and J.R.V. and G.0392.14 N to A.V.S. and J.R.V.), the European Union's FP7 Marie Curie Industry-Academia Partnerships and Pathways (IAPP, SARM, EU324509 to J.R.V., T.V., O.T, A.D., A.S. and A.K.) and Horizon 2020 innovation programme (WIDENLIFE, 692065 to J.R.V., O.T., T.V., A.K. and A.S.). M.Z.E., J.R.V. and T.V. are co-inventors on a patent application ZL913096-PCT/EP2014/068315-WO/2015/028576 ('Haplotyping and copy-number typing using polymorphic variant allelic frequencies'), licensed to Cartagenia (Agilent Technologies).

Intragenic sequences in the trophectoderm harbour the greatest proportion of methylation errors in day 17 bovine conceptuses generated using assisted reproductive technologies

Background

Assisted reproductive technologies (ART) are widely used to treat fertility issues in humans and for the production of embryos in mammalian livestock. The use of these techniques, however, is not without consequence as they are often associated with inauspicious pre- and postnatal outcomes including premature birth, intrauterine growth restriction and increased incidence of epigenetic disorders in human and large offspring syndrome in cattle. Here, global DNA methylation profiles in the trophectoderm and embryonic discs of in vitro produced (IVP), superovulation-derived (SOV) and unstimulated, synchronised control day 17 bovine conceptuses (herein referred to as AI) were interrogated using the EmbryoGENE DNA Methylation Array (EDMA). Pyrosequencing was used to validate four loci identified as differentially methylated on the array and to assess the differentially methylated regions (DMRs) of six imprinted genes in these conceptuses. The impact of embryo-production induced DNA methylation aberrations was determined using Ingenuity Pathway Analysis, shedding light on the potential functional consequences of these differences.

Results

Of the total number of differentially methylated loci identified (3140) 77.3 and 22.7% were attributable to SOV and IVP, respectively. Differential methylation was most prominent at intragenic sequences within the trophectoderm of IVP and SOV-derived conceptuses, almost a third (30.8%) of the differentially methylated loci mapped to intragenic regions. Very few differentially methylated loci were detected in embryonic discs (ED); 0.16 and 4.9% of the differentially methylated loci were located in the ED of SOV-derived and IVP conceptuses, respectively. The overall effects of SOV and IVP on the direction of methylation changes were associated with increased methylation; 70.6% of the differentially methylated loci in SOV-derived conceptuses and 57.9% of the loci in IVP-derived conceptuses were more methylated compared to AI-conceptuses. Ontology analysis of probes associated with intragenic sequences suggests enrichment for terms associated with cancer, cell morphology and growth.

Conclusion

By examining (1) the effects of superovulation and (2) the effects of an in vitro system (oocyte maturation, fertilisation and embryo culture) we have identified that the assisted reproduction process of superovulation alone has the largest impact on the DNA methylome of subsequent embryos.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4818-3) contains supplementary material, which is available to authorized users.

Alpha-linolenic acid protects the developmental capacity of bovine cumulus-oocyte complexes matured under lipotoxic conditions in vitro

Elevated concentrations of free fatty acids (FFAs), predominantly palmitic, stearic, and oleic acids (PSO), exert detrimental effects on oocyte developmental competence. This study examined the effects of omega-3 alpha-linolenic acid (ALA) during in vitro oocyte maturation (IVM) in the presence of PSO on subsequent embryo development and quality, and the cellular mechanisms that might be involved. Bovine cumulus-oocyte complexes (COCs) were supplemented during IVM with ALA (50 μM), PSO (425 μM), or PSO+ALA. Compared with FFA-free controls (P < 0.05), PSO increased embryo fragmentation and decreased good quality embryos on day 2 postfertilization. Day 7 blastocyst rate was also reduced. Day 8 blastocysts had lower cell counts and higher apoptosis but normal metabolic profile. In the PSO group, cumulus cell (CC) expansion was inhibited with an increased CC apoptosis while COC metabolism was not affected. Mitochondrial inner membrane potential (MMP; JC-1 staining) was reduced in the CCs and oocytes. Heat shock protein 70 (HSP70) but not glucose-regulated protein 78 kDa (GRP78, known as BiP; an endoplasmic reticulum stress marker) was upregulated in the CCs. Higher reactive oxygen species levels (DCHFDA staining) were detected in the oocytes. In contrast, adding ALA in the presence of PSO normalized embryo fragmentation, cleavage, blastocyst rates, and blastocyst quality compared to controls (P > 0.05). Combined treatment with ALA also reduced CC apoptosis, partially recovered CC expansion, abrogated the reduction in MMP in the CCs but not in the oocytes, and reduced BiP and HSP70 expression in CCs, compared with PSO only (P < 0.05). In conclusion, ALA supplementation protected oocyte developmental capacity under lipotoxic conditions mainly by protecting cumulus cell viability.

Asynchronous embryo transfer as a tool to understand embryo-uterine interaction in cattle: is a large conceptus a good thing?

The aim was to examine the effect of embryo-uterine synchrony on conceptus elongation and pregnancy rate in cattle. In Study 1, crossbred beef heifers each received 10 Day-7 in vitro-produced blastocysts on either Day 5, 7 or 9 after oestrus. A proportion of Day 5 recipients were supplemented with progesterone, via a progesterone-releasing intravaginal device from Days 3-5 plus either 750IU equine chorionic gonadotrophin or 3000IU human chorionic gonadotrophin on Day 3. At embryo age Day 14, all heifers were slaughtered and the uterus was flushed. Fewer recipients yielded conceptuses (P<0.05) and fewer conceptuses were recovered (P<0.05) following transfer on Day 5 compared with Day 7 or 9. Supplementation with progesterone resulted in short cycles in approximately 50% of recipients. Mean conceptus length was greater (P<0.05) following transfer to an advanced uterus. In Study 2, overall pregnancy rate following the fresh transfer of a single in vitro-produced blastocyst was 43.5% (2065/4749). Transfer of a Day 7 embryo to a synchronous Day-7 uterus resulted in a pregnancy rate of 47.3%. Transfer to a Day-5 (40.8%) or a Day-8 (41.3%) uterus moderately impacted pregnancy rate (P<0.01) while transfer to a uterus 2 days in advance (Day-9, 24.4%) or 3 days behind (Day-4, 27.0%) reduced (P<0.001) pregnancy rate compared with synchronous transfers. In conclusion, transfer of an embryo into an advanced uterus results in an acceleration of conceptus development, but does not result in greater pregnancy rates.

Lactation-induced changes in metabolic status and follicular-fluid metabolomic profile in postpartum dairy cows

The aim was to investigate the effect of lactation on the composition of pre-ovulatory follicular fluid (FF). Forty in-calf primiparous heifers and 20 maiden heifers were enrolled. Immediately after calving, half of the cows were dried off while the remainder were milked twice daily. Serum samples were collected twice weekly from two weeks pre- to 84 days postpartum (dpp). FF was analysed by gas chromatography-mass spectrometry. Serum concentrations of non-esterified fatty acids and β-hydroxybutyrate were higher, while glucose, insulin and Insulin-like growth factor 1 (IGF1) concentrations were lower in lactating cows compared with non-lactating cows and heifers (P<0.01). Principal component analysis of FF metabolites revealed a clear separation of the lactating group from both non-lactating cows and heifers. The amino acids tyrosine, phenylalanine and valine and fatty acids heneicosanoic acid and docosahexaenoic acid were all lower in FF from lactating compared with dry cows (P<0.05). FF from lactating cows was higher in aminoadipic acid, α-aminobutyric acid, glycine and serine while histidine, leucine, lysine, methionine and ornithine were all lower than in dry cows and heifers (P<0.05). The ratio of n6:n3 was higher in lactating cows compared with both non-lactating cows and heifers, whereas total n3 polyunsaturated fatty acids, pentadecanoic, linolenic, elaidic and arachidonic acids were all lower in the FF of lactating cows than both non-lactating cows and heifers (P<0.05). In conclusion, lactation induces distinct changes in the overall metabolic status of postpartum lactating dairy cows which are associated with divergent metabolite profiles in FF.

Melatonin Improves The Developmental Competence of Goat Oocytes

Background

DNA methylation is one the epigenetic mechanisms, which is critically involved in gene expression. This phenomenon is mediated by DNA methyl-transferases and is affected by environmental stress, including in vitro maturation (IVM) of oocytes. Melatonin, as an antioxidant, may theoretically be involved in epigenetic regulation via reductions of reactive oxygen species. This study was performed to investigate DNA methylation and the possibility of goat oocyte development after treatment with different concentrations of melatonin.

MATERIALS AND METHODS

This experimental study was performed to investigate DNA methylation and the possibility of goat oocyte development after treatment with different concentrations of melatonin. For this purpose, oocytes with granulated cytoplasm were selected and co-cultured with at least two layers of cumulus cells in maturation medium with 10^-6 M, 10^-9 M, 10^-12 M and 0-M (as control group) of melatonin. Nucleus status, glutathione content and developmental competence of the oocytes in each experimental group were assessed. Also, expression of genes associated with DNA methylation, including DNA methyltransferase 1 (DNMT1), DNA methyltransferase 3b (DNMT3b) and DNA methyltransferase 3a (DNMT3a) was evaluated by quantitative real time-polymerase chain reaction (RT-PCR).

RESULTS

According to our findings, the percentage of oocytes that reached the M-II stage significantly increased in the 10-12 M group (P<0.05). Also, a significant elevation of glutathione content was observed in melatonin-treated oocytes (P<0.05). Analysis of blastocyst formation revealed that developmental competence of the oocytes was higher than the control group (P<0.05). It was observed that melatonin treatment decreased expression levels of DNA methyltransferases (DNMTs) and global DNA methylation (P<0.05). In addition, the expression of melatonin receptor1A (MTNR1A) was detected in both cumulus and oocyte by RT-PCR.

CONCLUSION

The results suggested that in goat model melatonin affects DNA methylation pattern, leading to an improvement in the developmental competence of the oocytes.

Sex Steroid-Mediated Control of Oviductal Function in Cattle

In cattle, the oviduct is a tubular organ that connects the ovary and the uterus. The oviduct lumen stages a dynamic set of cellular and molecular interactions to fulfill the noble role of generating a new individual. Specific anatomical niches along the oviduct lumen provide the appropriate microenvironment for final sperm capacitation, oocyte capture and fertilization, and early embryo development and transport. To accomplish such complex tasks, the oviduct undergoes spatially and temporally-regulated morphological, biochemical, and physiological changes that are associated with endocrine events of the estrous cycle. Specifically, elevated periovulatory concentrations of estradiol (E2) and progesterone (P4) influence gene expression and morphological changes that have been associated positively to fertility in beef cattle. In this review, we explore how E2 and P4 influence oviductal function in the beginning of the estrous cycle, and prepare the oviductal lumen for interactions with gametes and embryos.

Using RT-PCR and glutathione level to study the effect of follicular fluid on in vitro maturation and gene expression of sheep oocytes

The aim of this study is to evaluate the effect of sheep follicular fluid (SFF) supplementation of the in vitro maturation (IVM) media of sheep oocytes on the resumption of meiosis, glutathione (GSH) level, and expression of apoptosis (Bax, Bcl-2) as well as heat shock protein beta-1 (HSPB1) genes. Sheep ovaries were collected from the central slaughterhouse of Riyadh city, KSA. Oocytes were aspirated from 3 to 8 mm follicles. Sheep oocytes were cultured in maturation medium with different concentrations of sheep follicular fluid: 0% (control), 10%, 20% and 40% for 24 h. The results indicated that the maturation rate of oocytes was significantly (p ≤ .05) decreased in 40% SFF (36.87%) versus the control (61.3%), 10% SFF (63.95%) and 20% SFF (64.08%). The supplementation of the IVM medium with 10% SFF induced an intra-oocyte GSH concentration that was significantly higher than in sheep oocytes cultured with 20% and 40% SFF and similar to the GSH content in oocytes cultured without SFF. Real-time polymerase chain reaction analysis of gene expression revealed no significant differences in the Bax and HSPB1 genes between the control and 10% SFF, whereas they were significantly higher in 40% FF (p ≤ .05) compared to the control. The expression of Bax:Bcl-2 was significantly higher in 20% and 40% SFF compared to the control group. In conclusion, the addition of SFF to the IVM culture of sheep oocytes is recommended to support nuclear maturation and increase oocyte competence.

α-Tocopherol modifies the expression of genes related to oxidative stress and apoptosis during in vitro maturation and enhances the developmental competence of rabbit oocytes

The developmental competence of in vitro maturation (IVM) oocytes can be enhanced by antioxidant agents. The present study investigated, for the first time in the rabbit model, the effect of adding α-tocopherol (0, 100, 200 and 400 µM) during IVM on putative transcripts involved in antioxidant defence (superoxide dismutase 2, mitochondrial (SOD2), glutathione peroxidase 1 (GPX1), catalase (CAT)), cell cycle regulation and apoptosis cascade (apoptosis tumour protein 53 (TP53), caspase 3, apoptosis-related cysteine protease (CASP3)), cell cycle progression (cellular cycle V-Akt murine thymoma viral oncogene homologue 1 (AKT1)), cumulus expansion (gap junction protein, alpha 1, 43 kDa (GJA1) and prostaglandin-endoperoxide synthase 2 (prostaglandin G/H synthase and cyclo-oxygenase) (PTGS2)) and metabolism (glucose-6-phosphate dehydrogenase (G6PD)). Meiotic progression, mitochondrial reallocation, cumulus cell apoptosis and the developmental competence of oocytes after IVF were also assessed. Expression of SOD2, CAT, TP53, CASP3 and GJA1 was downregulated in cumulus–oocyte complexes (COCs) after IVM with 100 μM α-tocopherol compared with the group without the antioxidant. The apoptotic rate and the percentage of a non-migrated mitochondrial pattern were lower in COCs cultured with 100 μM α-tocopherol, consistent with better-quality oocytes. In fact, early embryo development was improved when 100 μM α-tocopherol was included in the IVM medium, but remained low compared with in vivo-matured oocytes. In conclusion, the addition of 100 μM α-tocopherol to the maturation medium is a suitable approach to manage oxidative stress and apoptosis, as well as for increasing the in vitro developmental competence of rabbit oocytes.

In vitro cultured bovine endometrial cells recognize embryonic sex

Endometrial cell co-culture (ECC) with single embryo may reflect endometrium responses in vivo. Bovine Day-6 in vitro-produced morulae were cultured until Day-8 in modified synthetic oviductal fluid (mSOF), or on the epithelial side of ECC. Expression of epithelial- and stromal-cell transcripts was analyzed by RT-PCR in ECC with one male (ME) or female embryo (FE). Concentrations of ARTEMIN (ARTN) and total protein were determined in epithelial cell-conditioned medium. ECCs yielded embryos with more cells in the inner cell mass than embryos cultured in mSOF. Embryos altered transcript expression only in epithelial cells, not in stromal ones. Thus, ME induced larger reductions than FE and controls (i.e., no embryos cultured) in hexose transporter solute carrier family 2 member 1 (SLC2A1) and member 5 (SLC2A5), connective tissue growth factor (CTGF), artemin (ARTN), and interferon alpha and beta receptors subunit IFNAR1 and IFNAR2. FE reduced SLC2A1 and SLC2A5, and increased ARTN expression with respect to controls. ME tended to reduce total protein concentration (P < 0.082) in ECC-conditioned medium, while ARTN protein and gene expressions strongly correlated (R > 0.90; P < 0.05) in the group of ME or FE, but not in controls (without embryo). Isolated male and female embryos may differentially release signaling factors that induce sexually dimorphic responses in endometrial cells.

Improvement of bovine in vitro embryo production by ovarian follicular wave synchronization prior to ovum pick-up

This study evaluated the effects of the synchronization of ovarian follicular wave emergence on the efficiency of in vitro embryo production. Bos indicus cows (n = 20) were divided into two groups (control vs. synchronization) and subjected to repeated ovum pick-up (OPU) sessions (8 replicates each, with an interval of 21 days in a 2 × 2 crossover design) and subsequent in vitro embryo production. Cows in the control group (n = 10) were submitted to OPU procedures without any stimulation every 21 days. Animals in the synchronization group received a protocol-based progesterone implant, estradiol benzoate and prostaglandin on a random day of the estrus cycle (Day 0) and the OPU was performed on Day 5. After in vitro production, embryos were transferred to recipients synchronized at a fixed time and the diagnosis was performed 60 days later. An evaluation of the parameters for each OPU session revealed that donors that received the synchronization protocol pre-OPU showed a greater number of embryos (5.9 ± 0.5 vs. 4.5 ± 0.4; P = 0.037), higher rate of embryo production (45.8% vs. 38.5%; P = 0.001) and higher mean number of conceptions per group (2.2 ± 0.2 vs. 1.6 ± 0.2; P = 0.07) in relation to the group that did not receive hormonal treatment. We concluded that synchronization of the follicular wave prior to OPU showed positive effects on in vitro embryo production as well as on pregnancy rates.

Melatonin Pretreated Blastocysts along with Calcitonin Administration Improved Implantation by Upregulation of Heparin Binding-Epidermal Growth Factor Expression in Murine Endometrium

Objective

Implantation failure is an obstacle in assisted reproduction techniques (ART). Calcitonin is a molecules involved in uterine receptivity and embryo implantation. Melatonin can promote embryo quality and improve implantation. This study examines the effect of pretreatment of blastocysts with melatonin and calcitonin on heparin binding-epidermal growth factor (HB-EGF) expression in murine endometrium.

Materials and Methods

In this experimental study, we collected 2-cell embryos from the oviducts of 1.5 day pregnant NMRI mice. Embryos were cultured to the blastocyst in G^TM medium with or without 10^-9 M melatonin. Pregnant and pseudo-pregnant mice received intraperitoneal (IP) injections of 2 IU calcitonin. After 24 hours, we transferred the cultured blastocysts into the uteri of pseudo-pregnant mice. Two days later, implantation sites were counted and we assessed the levels of HB-EGF mRNA and protein in the uteri of naturally pregnant and pseudo-pregnant mice by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Statistical analysis was performed with one-way ANOVA followed by the Tukey post hoc test. P<0.05 was considered statistically significant.

Results

Melatonin pretreatment of blastocysts along with calcitonin administration significantly increased HB-EGF mRNA and protein (P<0.001) in the endometrium of pseudo-pregnant mice. Administration of calcitonin in naturally pregnant mice significantly increased HB-EGF mRNA and protein levels (P<0.001). Compared with the control group (2.6 ± 0.5), the average number of implantation sites in the melatonin group (4.6 ± 0.5, P<0.05) and calcitonin group (7 ± 1, P<0.001) significantly increased. There was a significant increase in implantation sites in the combined melatonin and calcitonin group (8.6 ± 0.5, P<0.001). Calcitonin significantly enhanced calcitonin receptor mRNA (P<0.001) and protein (P<0.05) in the uteri of naturally pregnant and pseudo-pregnant mice.

Conclusion

Melatonin pretreated blastocysts along with calcitonin increased HB-EGF expression in the uteri of pseudo- pregnant mice. Calcitonin administration upregulated HB-EGF in uteri of naturally pregnant mice.

Three-step in vitro maturation culture of bovine oocytes imitating temporal changes of estradiol-17<i>β</i> and progesterone concentrations in preovulatory follicular fluid

Abstract. The objective of the article is to evaluate the effect of three-step in vitro maturation (IVM) culture system imitating estradiol-17β (E2) and progesterone (P4) concentrations in preovulatory follicles on in vitro bovine embryo production. The cumulus–oocyte complexes (COCs) were collected from follicles (2 to 8 mm in diameter) of bovine ovaries obtained from a local slaughterhouse. For IVM, the COCs were cultured for 22 h in a three-step system: (1) culture in medium 199, containing 700 ng mL−1 E2 and 50 ng mL−1 P4, for 5 h, followed by the medium containing 150 ng mL−1 E2 and 150 ng mL−1 P4 for 11 h, and then the medium containing 20 ng mL−1 E2 and 300 ng mL−1 P4 for 6 h (EP group); (2) culture in the medium containing 700 ng mL−1 E2 for 5 h, followed by the medium containing 150 ng mL−1 E2 for 11 h, and then the medium containing 20 ng mL−1 E2 for 6 h (E group); or (3) culture in the medium containing 50 ng mL−1 P4 for 5 h, followed by the medium containing 150 ng mL−1 P4 for 11 h, and then the medium containing 300 ng mL−1 P4 for 6 h (P group). The COCs were cultured in the medium containing 1000 ng mL−1 E2 for 22 h (control group). After IVM, the COCs were co-incubated with sperm and further cultured. At 48 h after insemination, the cleavage rate of embryos was not different among the groups. At 192 h after insemination, the blastocyst formation rate of EP group was significantly higher than that of the other groups. The total cell number of blastocysts did not differ among the groups. In conclusion, these results demonstrate that the three-step IVM culture system of bovine oocytes imitating temporal changes of E2 and P4 concentrations in preovulatory follicular fluid improves the developmental potential of embryos in vitro.

Effect of season on follicular population, quality and nuclear maturation of bovine oocytes under tropical conditions

The aim was to determine the effect of season of the year and the presence of a corpus luteum (CL) on follicular population (FP) and the quality of the oocytes, and of season on nuclear maturation of the bovine oocytes under tropical conditions. Three seasons were evaluated: hot-dry (March-June), hot-humid (July-October) and fresh-humid (November-February). In a first study, 1112 bovine ovaries were obtained from a local slaughterhouse. Follicles were classified as small (≤4mm), middle (4.1-8mm) and large (≥8.1mm); and the maximum diameter of the follicle (MDF) and CL (MDCL) were also recorded. The oocytes were collected by aspiration and classified as viable (grade I and II) and damaged (grade III and IV). In the second study, 2261 viable oocytes were matured in vitro, and then fixed and stained with Lacmoid to classify the stage of development as mature (metaphase II), immature or degenerate. Data were analyzed using analysis of variance and chi-square procedures. The largest FP of large follicles (0.67), MDF (1.18mm), MDCL (1.87mm), and the highest proportion of viable oocytes (34.19%) were obtained during the hot-humid season (P<0.05). The ovaries without CL had the greatest FP (10.34) with more viable oocytes (24.44%). The highest proportion of mature oocytes (76.92%) was also obtained in the hot-humid season. In conclusion, season influenced FP, MDF, MDCL, and the quality and nuclear maturation of oocytes. The presence of a CL in the ovary resulted in a decrease of FP and viability of oocytes.

Natriuretic peptide receptor 2 (NPR2) localized in bovine oocyte underlies a unique mechanism for C-type natriuretic peptide (CNP)-induced meiotic arrest

Meiosis is of prime importance for successful gametogenesis, and insufficient maintenance of oocyte meiotic arrest compromises oocyte developmental competence. Recent studies have demonstrated that the C-type natriuretic peptide (CNP)-Natriuretic peptide receptor 2 (NPR2) pathway can inhibit mammalian oocyte meiotic resumption. In mouse and porcine, the inhibitory effect of mural granulosa cell (MGC)-derived CNP on oocyte meiotic resumption is mediated by NPR2 localized in cumulus cells (CCs) surrounding the oocytes. However, in the present study, we identified a novel mechanism for CNP-induced meiotic arrest that appears to be unique to bovine oocytes. Unlike mouse and porcine, bovine NPR2 not only localizes in CCs, but also in oocyte membranes. We also showed that CNP can directly activate intra-oocyte cGMP production via NPR2 localized in oocyte membranes, in parallel with the CC-mediated pathway. Furthermore, we demonstrated that Npr2 expression in bovine CCs and oocytes were synergistically regulated by estradiol and oocyte-derived growth factors. Finally, based on the profound inhibitory effect of CNP on meiotic resumption, we established a natural factor synchronized in vitro oocyte maturation (NFSOM) system, which can significantly improve the developmental competence of matured oocytes, thereby resulting in higher in vitro embryo production efficiency. Taken together, our study not only provides new insight into understanding the crosstalk between oocytes and follicular somatic cells in mammals, but also presents a promising strategy for improving the in vitro oocyte maturation systems of assisted reproductive technology (ART).

The Role of Oocyte Organelles in Determining Developmental Competence

The ability of an oocyte to undergo successful cytoplasmic and nuclear maturation, fertilization and embryo development is referred to as the oocyte’s quality or developmental competence. Quality is dependent on the accumulation of organelles, metabolites and maternal RNAs during the growth and maturation of the oocyte. Various models of good and poor oocyte quality have been used to understand the essential contributors to developmental success. This review covers the current knowledge of how oocyte organelle quantity, distribution and morphology differ between good and poor quality oocytes. The models of oocyte quality are also described and their usefulness for studying the intrinsic quality of an oocyte discussed. Understanding the key critical features of cytoplasmic organelles and metabolites driving oocyte quality will lead to methods for identifying high quality oocytes and improving oocyte competence, both in vitro and in vivo.

Cholesterol added prior to vitrification on the cryotolerance of immature and in vitro matured bovine oocytes

This study examines whether incorporating cholesterol-loaded methyl-β-cyclodextrin (CLC) in the bovine oocyte plasma membrane improves oocyte tolerance to vitrification. In vitro matured oocytes were incubated with 2 mg/ml BODIPY-labeled CLC for different time intervals in FCS or PVA supplemented medium or exposed to different CLC concentrations to examine the subcellular localization of cholesterol by confocal microscopy live-cell imaging. Subsequently, the effects of optimized CLC concentrations and incubation times prior to vitrification on early embryo development were assessed. Then, we evaluated the effects of pretreatment with 2 mg/ml CLC for 30 min before the vitrification of immature (GV) and in vitro matured (MII) oocytes on developmental competence and gene expression. Our results indicate a high plasma membrane labeling intensity after 30 min of incubation with 2 mg/ml CLC for 30 min, regardless of the holding medium used. When oocytes were incubated with 1 mg/ml, 2 mg/ml and 3 mg/ml of CLC, intense labeling was observed at the plasma membrane after 40, 30 and 20 min, respectively. CLC pre-treatment before the vitrification of bovine oocytes did not affect subsequent cleavage and embryo development rates irrespective of CLC concentrations, incubation times or meiotic stage. However, pretreatment seems to improve the quality of embryos derived from vitrified oocytes, mainly when oocytes were vitrified at the GV stage.

Effect of GOLPH3 on cumulus granulosa cell apoptosis and ICSI pregnancy outcomes

Previous studies have shown that GOLPH3 mediates cell growth, proliferation and differentiation and inhibits cell apoptosis; however, the role of GOLPH3 in cumulus granulosa cells and the value of GOLPH3 in predicting ICSI pregnancy outcomes remain unknown until now. Our findings showed higher positive expression rate, score of staining intensity, and immunohistochemical score of GOLPH3 in the cumulus granulosa cells of the pregnant women relative to non-pregnant women, and a higher apoptotic rate of cumulus granulosa cells was detected in non-pregnant women than in pregnant women. Pearson correlation analyses revealed that pregnancy correlated negatively with GOLPH3 expression and apoptosis of cumulus granulosa cells, and positively with the number of follicles punctured, number of grade III oocytes, number of eggs retrieved for ICSI, number of zygotes, number of cleavage-stage embryos, number of top-quality embryos, number of blastocysts, number of top-quality blastocysts, and number of frozen embryos. GOLPH3 may be involved in the apoptosis of cumulus granulosa cells, which may correlate with oocyte maturation and egg development. GOLPH3 expression in cumulus granulosa cells may facilitate the selection of top-quality eggs and embryos, the prediction of the clinical pregnancy outcomes of ICSI, and the increase of the pregnancy rate.

Sex steroids modulate morphological and functional features of the bovine oviduct

In cattle, the oviduct plays a major role in the reproductive process; however, molecular control of oviduct receptivity to the embryo is poorly understood. A model for receptivity based on size of the pre-ovulatory follicle (POF) was used to compare oviductal morphology, cellular proliferation, and candidate transcript abundance. Growth of the POF of Nelore (Bos indicus) cows was manipulated to produce two groups: a large POF-large corpus luteum (CL) group (LF-LCL; greater receptivity) and a small POF-small CL group (SF-SCL). Samples of the ampulla and isthmus ipsilateral and contralateral to CL were collected 4 days after GnRH-induced ovulation. Tissues were either embedded in paraffin for Harris-Hematoxylin and Eosin and periodic acid-Schiff staining and KI67 immunostaining, followed by morphological analyses, or stored at -80 °C for RNA extraction, cDNA synthesis, and qPCR analyses. The effects of group (LF-LCL and SF-SCL), region (ampulla and isthmus), and side (ipsilateral and contralateral) were analyzed using three-way nested ANOVA. The ipsilateral ampulla of the LF-LCL group presented more primary mucosal folds, a greater mucosal-folding grade and luminal perimeter, and more secretory cells and proliferating cells when compared with the ampulla of the SF-SCL group and with the contralateral ampulla of both groups. There were no morphological differences in the isthmus between groups and sides. Changes in transcript abundance are suggestive of LF-LCL-stimulated secretory activity. In summary, ovulation of a larger POF generates a periovulatory endocrine milieu that modulates morphological and functional features of the bovine oviduct which may support embryo survival and development.

Effect of urokinase type plasminogen activator on in vitro bovine oocyte maturation

This study examines the impacts of the urokinase-type plasminogen activator (uPA) on the in vitro maturation (IVM) of bovine oocytes. Cumulus-oocyte complexes in IVM medium were treated with uPA, amiloride (an uPA inhibitor), dimethyl sulfoxide (DMSO) or left untreated (control group). After 24 h of IVM, oocytes were recovered for testing or were in vitro fertilized and cultured to the blastocyst stage. The factors examined in all groups were: (i) oocyte nuclear maturation (Hoëscht staining); (ii) oocyte cytoplasmic maturation (cortical granules, CGs, distribution assessed by LCA-FITC); (iii) oocyte and cumulus cell (CC) gene expression (RT-qPCR); and (iv) embryo development (cleavage rate and blastocyst yield). Oocytes subjected to uPA treatment showed rates of nuclear maturation and CG distribution patterns similar to controls (P > 0.05), whereas lower rates of oocyte maturation were recorded in the amiloride group (P < 0.05). Both in oocytes and CC, treatment with uPA did not affect the transcription of genes related to apoptosis, cell junctions, cell cycle or serpin protease inhibitors. In contrast, amiloride altered the expression of genes associated with cell junctions, cell cycle, oxidative stress and CC serpins. No differences were observed between the control and uPA group in cleavage rate or in blastocyst yield recorded on Days 7, 8 or 9 post-insemination. However, amiloride led to drastically reduced cleavage rate (28.5% vs 83.2%) and Day 9 embryo production (6.0% vs 21.0%) over the rates recorded for DMSO. These results indicate that the proteolytic activity of uPA is needed for successful oocyte maturation in bovine.