Developmental capacity of Bos indicus oocytes after inhibition of meiotic resuption by 6-dimethylaminopurine

Approaches to oocyte meiotic arrest in vitro and impact on oocyte developmental competence

Oocytes are maintained in a state of meiotic arrest following the first meiotic division until ovulation is triggered. Within the antral follicle, meiotic arrest is actively suppressed in a process facilitated by the cyclic nucleotides cGMP and cAMP. If removed from this inhibitory follicular environment and cultured in vitro, mammalian oocytes undergo spontaneous meiotic resumption in the absence of the usual stimulatory follicular stimuli, leading to asynchronicity with oocyte cytoplasmic maturation and lower developmental competence. For more than 50 years, pharmacological agents have been used to attenuate oocyte germinal vesicle (GV) breakdown in vitro. Agents which increase intra-oocyte cAMP or prevent its degradation have been predominantly used, however agents such as kinase and protein synthesis inhibitors have also been trialled. Twenty years of research demonstrates that maintaining GV arrest for a period before in vitro maturation (IVM) improves oocyte developmental competence, and is likely attributed to maintenance of bidirectional communication with cumulus cells leading to improved oocyte metabolic function. However, outcomes are influenced by various factors including the mode of action of the modulators, dose, treatment duration, species, and the degree of hormonal priming of the oocyte donor. Cyclic GMP and/or cAMP modulation in a prematuration step (called pre-IVM) prior to IVM has shown the greatest consistency in improving oocyte developmental competence, whereas kinase and protein synthesis inhibitors have proven less effective at improving IVM outcomes. Such pre-IVM approaches have shown potential to alter current use of artificial reproductive technologies in medical and veterinary practice.

Effect of Rolipram on in vitro maturation, gene expression and embryonic development in bovines

ABSTRACT The aim of this work was to evaluate the effect of the Rolipram during the maturation of bovine oocytes and gene expression of embryos produced in vitro. Bovine ovaries were collected in slaughterhouse. The COCs were selected and divided into 5 groups: Control 0 time; Control: IVM for 24 hours; Rolipram treatments with IVM blocking for 24 hours in maturation medium containing (100, 150 and 200µM). After 24 hours all groups were reseated in IVM for another 24 hours. Subsequently COCs were subjected to the same IVM system and fertilized, being checked for cleavage post fertilization and for blastocyst. In addition, performed expression of the following genes: Mater, BMP15 and Bax. No difference was found in gene expression. Of oocytes evaluated shortly after follicular aspiration, 79.00% were in GV, GVBD, MI, while 13.40%, were in MII and 7.60%, D/NI. Significant difference was observed in different concentrations (T100, T200 and T150µM) in oocytes that have reached the MII phase compared to control treatments (P= 0.003). Differences were observed in cleavage rate (P< 0.05) between T150 and T200 when compared to the C/24 Group. A high difference was observed on blastocyst rate (P< 0.001) among treatments compared to the control group.

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.

Advances in in vitro production of sheep embryos

Sheep is an important livestock in the world providing meat, milk and wool for human beings. With increasing human population, the worldwide needs of production of sheep have elevated. To meet the needs, the assistant reproductive technology including ovine in vitro embryo production (ovine IVP) is urgently required to enhance the effective production of sheep in the world. To learn the status of ovine IVP, we collected some publications related to ovine IVP through PubMed and analyzed the progress in ovine IVP made in the last five years (2012-2017). We made comparisons of these data and found that the recent advances in ovine IVP has been made slowly comparable to that of ovine IVP two decades ago. Therefore, we suggested two strategies or approaches to tackle the main problems in ovine IVP and expect that the efficiency of ovine IVP could be improved significantly when the approaches would be implemented.

Meiotic arrest as an alternative to increase the production of bovine embryos by somatic cell nuclear transfer

This study aimed to evaluate the effect of meiotic arrest using phosphodiesterase type 3A (PDE 3A) inhibitors, cilostamide and C-type natriuretic peptide (NPPC), on pre-maturation (PM) of oocytes to be used in the production of cloned embryos. Nuclear maturation, in vitro embryo production (IVP), somatic cell nuclear transfer (SCNT) and parthenogenetic activation (PA), and total cells number of cloned embryos were evaluated. The results were analysed by chi-squared and Kruskal-Wallis test with a P-value 0.05) between control and PM, both for cleavage (78.2% and 76.9%) and blastocyst (35.5% and 29.3%) rates. After SCNT, cleavage rate was also similar (P > 0.05) between control and PM (66% and 51.9%) however, blastocyst rate was lower (P < 0.05) in the PM group than in the control group (7.4% and 30.2%). After 6 h of PM with 100 nM of NPPC, approximately 84.9% of the oocytes remained at GV. No difference was found between control and PM in cleavage (69.2% and 76.1%) and blastocyst rates (37,4% and 35%) after IVP. Similarly, no differences between PM and control groups were observed for cleavage (69.2% and 68.4%) and blastocyst (24.4% and 21.5%) rates. SCNT and PA embryos from control or PM oocytes had similar total cell number. It can be concluded that PM for 6 h with 100 nM NPPC is feasible for cloned embryo production without affecting embryo outcome.

Effect of insulin-transferrin-selenium (ITS) and l-ascorbic acid (AA) during in vitro maturation on in vitro bovine embryo development

The aim of this study was to evaluate the effect of adding a combination of insulin, transferrin and selenium (ITS) and l-ascorbic acid (AA) during in vitro maturation (IVM) and in vitro culture (IVC) on in vitro embryo production. To verify the effect of the supplements, cleavage and blastocyst rates, embryo size and total cell number were performed. Embryonic development data, embryo size categorization and kinetics of maturation were analyzed by chi-squared test, while the total cell number was analyzed by a Kruskal-Wallis test (P < 0.05). When ITS was present during IVM, IVC or the entire culture, all treatments had a cleavage and blastocyst rates and embryo quality, similar to those of the control group (P < 0.05). Supplementation of IVM medium with ITS and AA for 12 h or 24 h showed that the last 12 h increased embryo production (51.6%; n = 220) on D7 compared with the control (39.5%; n = 213). However, no improvement was observed in blastocyst rate when less competent oocytes, obtained from 1-3 mm follicles, were exposed to ITS + AA for the last 12 h of IVM, with a blastocyst rate of 14.9% (n = 47) compared with 61.0% (n = 141) in the control group. The results suggest that the addition of ITS alone did not affect embryo production; however, when combined with AA in the last 12 h of maturation, there was improvement in the quantity and quality of embryos produced. Furthermore, the use of ITS and AA during IVM did not improve the competence of oocytes obtained from small follicles.

The effect of pre-maturation culture using phosphodiesterase type 3 inhibitor and insulin, transferrin and selenium on nuclear and cytoplasmic maturation of bovine oocytes

This study aims to evaluate if a pre-maturation culture (PMC) using cilostamide as a meiotic inhibitor in combination with insulin, transferrin and selenium (ITS) for 8 or 24 h increases in vitro embryo production. To evaluate the effects of PMC on embryo development, cleavage rate, blastocyst rate, embryo size and total cell number were determined. When cilostamide (20 μM) was used in PMC for 8 or 24 h, 98% of oocytes were maintained in germinal vesicles. Although the majority of oocytes resumed meiosis after meiotic arrest, the cleavage and blastocyst rates were lower than the control (P 0.05) to the control. The deleterious effect of 20 μM cilostamide treatment for 24 h on a PMC was confirmed by lower cumulus cell viability, determined by trypan blue staining, in that group compared with the other groups. A lower concentration (10 μM) and shorter exposure time (8 h) minimized that effect but did not improve embryo production. More studies should be performed to determine the best concentration and the arresting period to increase oocyte competence and embryo development.

Bovine oocyte meiotic inhibition before in vitro maturation and its value to in vitro embryo production: does it improve developmental competence?

The efficiency of bovine in vitro embryo production has remained low despite extensive effort to understand the effects of culture conditions, media composition and supplementation. As bovine oocytes resume meiosis spontaneously when cultured, it was hypothesized that preventing meiosis in vitro before in vitro maturation (IVM) and in vitro fertilization (IVF) would allow more oocytes to acquire developmental competence. This article reviews some of the factors involved in meiotic arrest as well as the effects of meiotic inhibition before IVM on bovine oocytes developmental competence following IVF. Follicular components and cAMP-elevating agents can delay or inhibit meiosis in various proportions of oocytes; however, few studies have examined their effects on development following IVM and IVF because they are not practical (follicular components) or have a transient effect on meiosis (cAMP-elevating agents). Protein synthesis or phosphorylation inhibition prevented meiosis in high percentages of oocytes; however, these non-specific inhibitions led to lower developmental competence compared with non-arrested oocytes. Maturation promoting factor (MPF) inhibition with specific inhibitors has been examined in several studies. Despite faster maturation following removal from inhibition and some structural damage to the oocytes, MPF inhibition generally led to blastocyst rates similar to control, non-arrested oocytes. Future work will involve evaluating the effects on arrested oocytes of molecules that can improve developmental competence in non-arrested oocytes. It is also anticipated that new IVM systems that take into consideration new knowledge of the mechanisms involved in the control of meiosis will be developed. Moreover, global gene expression analysis studies will also provide clues to the culture conditions required for optimal expression of developmental competence.

Improved blastocyst development of single cow OPU-derived presumptive zygotes by group culture with agarose-embedded helper embryos

BACKGROUND

The in vitro culture of presumed zygotes derived from single cow ovum pick-up (OPU) is important for the production of quality blastocysts maintaining pedigree. The aim of the present study was to evaluate the agar chip-embedded helper embryo coculture system for single cow OPU-derived zygotes by assessing embryo quality.

METHODS

Cumulus oocyte complexes (COCs) were collected from Hanwoo cows with high genetic merit twice a week using the ultra-sound guided OPU technique and from slaughterhouse ovaries. The Hanwoo cow COCs and slaughterhouse ovaries were matured in vitro, fertilized in vitro with thawed Hanwoo sperm and cultured for 24 h. The presumed zygotes were subsequently placed in three different culture systems: (1) control OPU (controlOPU) with single cow OPU-derived presumed zygotes (2~8); (2) agar chip-embedded slaughterhouse helper embryo coculture (agarOPU) with ten presumed zygotes including all presumed zygotes from a cow (2~8) and the rest from agar chip-embedded slaughterhouse presumed zygotes (8~2); and (3) slaughterhouse in vitro embryo production (sIVP) with ten slaughterhouse ovary-derived presumed zygotes, each in 50 μL droplets. Day 8 blastocysts were assayed for apoptosis and gene expression using real time PCR.

RESULTS

The coculture system promoted higher blastocyst development in OPU zygotes compared to control OPU zygotes cultured alone (35.2 vs. 13.9%; P < 0.01). Genes predicted to be involved in implantation failure and/or embryo resorption were down-regulated (P < 0.05) in control OPU zygotes (CD9, 0.4-fold; AKRAB1, 0.3-fold) and in cocultured zygotes (CD9, 0.3-fold; AKRAB1, 0.3-fold) compared to sIVP blastocysts (1.0-fold). Moreover, genes involved in implantation and/or normal calf delivery were up-regulated (P < 0.05 to P < 0.01) in control OPU zygotes (PGSH2, 5.0-fold; TXN, 4.3-fold; PLAU, 1.7-fold) and cocultured zygotes (PGSH2, 14.5-fold; TXN, 3.2-fold; PLAU, 6.8-fold) compared to sIVP (1.0-fold) blastocysts. However, the expression of PLAC8, TGF-β1, ODC1, ATP5A1 and CASP3 did not differ between the three culture groups.

CONCLUSIONS

Results show that the agar chip-embedded helper embryo coculture system enhances developmental competence and embryo quality in cultures of limited numbers of high pedigree single cow OPU presumed zygotes.

Induction of reversible meiosis arrest of bovine oocytes using a two-step procedure under defined and nondefined conditions

The objective was to study the effect of a defined culture system, on nuclear and cytoplasmic maturation of bovine oocytes, using the two-step procedure of IVM to detect possible inhibition and subsequent resumption of meiosis arrest. In the first step, called the prematuration period (PMP), COCs were cultured in T1-non-defined medium (NDM), or T2-defined medium (DM), both for 24 h. In step 2, called the resumption period (RP), COCs were cultured in: NDM (T1); DM + NDM (T3); or DM+DM (T4) for 24 h in each medium. The NDM was composed of TCM-199 supplemented with FCS and FSH. The DM was composed of alpha-MEM supplemented with PVA, insulin, IGF-1, androstenedione, nonessential amino acids, transferrin, and sodium selenium. Oocytes from T2 had a lower (P < 0.05) rate of nuclear maturation (19.8%) than T1 oocytes (83.2%). Also, T2 COCs appeared to be in the process of cytoplasmic maturation, according to the distribution of organelles assessed by transmission electron microscopy (MET). These COCs had characteristics previously described as mature: erect microvilli on the plasmembrane, presence of cortical/evenly distributed mitochondria throughout the ooplasm, and presence of 50% aligned/cluster cortical granules. Immature characteristics such as small PvS, compact cumulus cells, and presence of 50% cortical granule clusters were also observed. The T1 COCs had only characteristics of maturation (P < 0.05). In step 2 (RP), meiosis arrest induced by DM was resumed after an additional 24 h of culture in NDM (T3) with 79.2% mature COCs, whereas in T4, meiosis arrest was maintained, resulting in almost 70% immature COCs (P < 0.05). At the end of RP, T3 COCs had the mature characteristics of mitochondria spread throughout the cytoplasm (P < 0.05), cumulus expansion, and alignment of cortical granules, whereas the T4 group had both immature and mature characteristics. We inferred that DM can be used in lieu of meiosis inhibitors and furthermore, it can provide extra time to study nuclear and cytoplasmic maturation synchrony of IVM.

Oocyte maturation: Emerging concepts and technologies to improve developmental potential in vitro

Oocyte in vitro maturation (IVM) is an important reproductive technology that generates mature oocytes that are capable of supporting preimplantation embryo development and full development to term. There is great clinical and commercial incentive to improve the efficiency of the technology, however, progress has been slow over the past decade. A critical challenge is to understand what constitutes oocyte developmental competence and the mechanisms governing it. We have taken the approach of studying in detail oocyte-somatic cell interactions; including, oocyte-cumulus cell (CC) gap-junctional communication, and bidirectional paracrine signalling between the two cell types. It is becoming clear that, compared to oocytes matured in vivo, IVM oocytes undergo maturation prematurely as they are still in the process of acquiring developmental competence in vivo, and the molecular cascade reinitiating meiosis differs entirely to that in vivo. Attempts to enhance oocyte developmental competence by attenuating the spontaneous meiotic resumption of oocytes in vitro have been met with mixed success. Kinase inhibitors that prevent maturation-promoting factor activity have, in general, been ineffectual on promoting oocyte developmental potential post-IVM. In contrast, agents that modulate oocyte cAMP during IVM show greater potential, possibly as these compounds extend oocyte-CC gap-junctional communication. An important concept that is now emerging is that the oocyte secretes potent growth factors that regulate fundamental aspects of CC function and thereby determine the distinctive phenotype of the cumulus-oocyte complex. The capacity of an oocyte to regulate its own microenvironment by oocyte-secreted factors (OSFs) may constitute an important component of oocyte developmental competence. In support of this notion, we have recently demonstrated that supplementing IVM media with exogenous OSFs improves oocyte developmental potential, as evidenced by enhanced pre- and post-implantation embryo development.