Prematuration of bovine oocytes with butyrolactone I: Effects on meiosis progression, cytoskeleton, organelle distribution and embryo development

Progress toward species-tailored prematuration approaches in carnivores

In the past four decades, the bovine model has been highly informative and inspiring to assisted reproductive technologies (ART) in other species. Most of the recent advances in ART have come from studies in cattle, particularly those unveiling the importance of several processes that must be recapitulated in vitro to ensure the proper development of the oocyte. The maintenance of structural and functional communications between the cumulus cells and the oocyte and a well-orchestrated chromatin remodeling with the gradual silencing of transcriptional activity represent essential processes for the progressive acquisition of oocyte developmental competence. These markers are now considered the milestones of physiological approaches to increase the efficiency of reproductive technologies. Different in vitro approaches have been proposed. In particular, the so-called "pre-IVM" or "prematuration" is a culture step performed before in vitro maturation (IVM) to support the completion of the oocyte differentiation process. Although these attempts only partially improved the embryo quality and yield, they currently represent a proof of principle that oocytes retrieved from an ovary or an ovarian batch shouldn't be treated as a whole and that tailored approaches can be developed for culturing competent oocytes in several species, including humans. An advancement in ART's efficiency would be desirable in carnivores, where the success is still limited. Since the progress in reproductive medicine has often come from comparative studies, this review highlights aspects that have been critical in other species and how they may be extended to carnivores.

A prematuration approach to equine IVM: considering cumulus morphology, seasonality, follicle of origin, gap junction coupling and large-scale chromatin configuration in the germinal vesicle

Several studies report that a two-step culture where mammalian oocytes are first kept under meiosis-arresting conditions (prematuration) followed by IVM is beneficial to embryo development. The most promising results were obtained by stratifying the oocyte population using morphological criteria and allocating them to different culture conditions to best meet their metabolic needs. In this study, horse oocytes were characterised to identify subpopulations that may benefit from prematuration. We investigated gap-junction (GJ) coupling, large-scale chromatin configuration and meiotic competence in compact and expanded cumulus-oocyte complexes (COCs) according to follicle size (<1, 1-2, >2cm) and season. Then we tested the effect of cilostamide-based prematuration in compact COCs collected from follicles <1 and 1-2cm in diameter on embryo development. Meiotic competence was not affected by prematuration, whereas COCs from follicles 1-2cm in diameter yielded embryos with a higher number of cells per blastocyst than oocytes that underwent direct IVM (P<0.01, unpaired Mann-Whitney test), suggesting improved developmental competence. Oocytes collected from follicles <1cm in diameter were not affected by prematuration. This study represents an extensive characterisation of the functional properties of immature horse oocytes and is the first report of the effects of cilostamide-based prematuration in horse oocyte IVM on embryo development.

Iloprost affects in vitro maturation and developmental competence of bovine oocytes

Prostacyclin (PGI2) is synthesised in oviductal fluid and enhance the embryo development during the preimplantation period. The objective of the present study was to determine the effect of an analogue of prostacyclin (iloprost) on the in vitro maturation (IVM) and the developmental competence of bovine oocytes. Cumulus oocyte complexes (COCs) were cultured in maturation medium with iloprost (0.5 μM) for 24 h. We found that iloprost assisted maturation rates and cumulus cell expansion of bovine oocytes, and it increased the mRNA expression of genes related to cumulus expansion: ADAM17, AREG, and TNFAIP6 and cathepsin genes (CTSK and CTSS). Moreover, iloprost reduced the occurrence of apoptosis in COCs and promoted an antiapoptotic balance in the transcription of genes involved in apoptosis (BAX and BCL2). COCs treatment with iloprost during IVM also reduced intracellular reactive oxygen species (ROS) levels, while glutathione (GSH) levels and the mRNA expression of antioxidant genes CAT and GPx4 were markedly increased. We also showed that an analogue of PGI2 influenced the mitochondrial status via distribution rates of mitochondria and mitochondrial membrane potential in oocytes. Although, iloprost-enhanced maturation had no direct effect on number of embryos cleaved, it increased blastocyst rates of bovine embryos as well as proportion of expanded blastocysts. These results indicate that the supplementation of maturation medium with iloprost is beneficial for the maturation efficiency and developmental competence of bovine oocytes.

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.

Oxidative homeostasis in oocyte competence for in vitro embryo development

The objective of this study was to evaluate the levels of reactive oxygen species (ROS) and glutathione (GSH) in oocytes from follicles of different diameters and their relevance in the in vitro production of embryos (IVPE). Bovine ovaries were aspirated according to the diameter of the follicle [2-8 (general), 4-8 (large), and 2 < 4 mm (small)]. The oocytes were evaluated for levels of ROS, GSH, in vitro maturation, and IVPE. Higher levels of ROS and GSH were observed (p < 0.05) in oocytes of the large group (85.6 ± 7.2 and 140.0 ± 9.6) followed by those in the general (81.1 ± 10.5 and 134.3 ± 7.8) and small (73.5 ± 10.1 and 125.0 ± 10.6) groups. However, the proportion of ROS/GSH did not differ (p > 0.05) between the general, large, and small groups. The maturation was higher (p < 0.05) in the large group (87.8 ± 3.0%) than in the small group (72.2 ± 5.8%), but both were similar (p > 0.05) to that in the general group (82.2 ± 2.5%), whereas the IVPE of the large group (57.3 ± 3.0%) was higher (p < 0.05) than those in the general (44.7 ± 4.4%) and small (34.0 ± 4.0%) groups. We report that oocytes from large follicles are more competent for IVPE, whereas higher levels of ROS and GSH appear to be correlated with oocyte competence, as long as oxidative homeostasis is retained.

Melatonin Improves the Quality of Inferior Bovine Oocytes and Promoted Their Subsequent IVF Embryo Development: Mechanisms and Results

The inferior oocytes (IOs), which are not suitable for embryo development, occupy roughly one-third or more of the collected immature bovine oocytes. The IOs are usually discarded from the in vitro bovine embryo production process. Improving the quality of the inferior oocytes (IOs) and make them available in in vitro embryo production would have important biological, as well as commercial, value. This study was designed to investigate whether melatonin could improve the quality of IOs and make them usable in the in vitro maturation (IVM) and subsequent (in vitro fertilization) IVF embryo development. The results indicated that: the maturation rate of IOs and their subsequent IVF embryo developments were impaired compared to cumulus-oocyte complexes and melatonin treatment significantly improved the quality of IOs, as well as their IVF and embryo developments. The potential mechanisms are that: (1) melatonin reduced reactive oxygen species (ROS) and enhanced glutathione (GSH) levels in the IOs, thereby protecting them from oxidative stress; (2) melatonin improved mitochondrial normal distribution and function to increase ATP level in IOs; and (3) melatonin upregulated the expression of ATPase 6, BMP-15, GDF-9, SOD-1, Gpx-4, and Bcl-2, which are critical genes for oocyte maturation and embryo development and downregulated apoptotic gene expression of caspase-3.

Role of insulin-like growth factor 1 on cross-bred Bos indicus cattle germinal vesicle oocytes exposed to heat shock

Germinal vesicle (GV) oocytes are susceptible to heat stress. However, neither the cellular mechanisms triggered by elevated temperature nor the thermoprotective effects of insulin-like growth factor (IGF) on GV oocytes are completely understood. Therefore, a series of experiments was conducted to determine the direct effects of IGF1 (0, 12.5, 25, 50 and 100 ng mL–1) on heat-treated GV oocytes. Butyrolactone-arrested GV oocytes were cultured at 38.5°C (control) or 41°C (heat shock; HS) for 14 h in the presence of different concentrations of IGF1. Exposure of GV oocytes to 41°C increased (P < 0.05) the number of terminal deoxyribonucleotidyl transferase-mediated fluorescein-dUTP nick end-labelling (TUNEL)-positive oocytes. At concentrations of 12.5 and 25 ng mL–1, IGF1 tended to minimise these negative effect of HS (P = 0.07). However, neither HS nor IGF1 had any effect on caspase activity. HS also decreased (P < 0.05) GV oocyte mitochondrial activity and developmental competence to the blastocyst stage. These deleterious effects of HS were alleviated (P < 0.05) by 12.5 ng mL–1 IGF1. This concentration of IGF1 did not affect cleavage rate, the percentage of TUNEL-positive blastomeres and total blastocyst cell number regardless of temperature. In conclusion, exposure of GV oocytes to HS triggered the apoptotic cascade and compromised oocyte developmental competence. Physiological concentrations of IGF1 had a beneficial effect on heat-shocked GV oocytes.

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.

Pretreatment of in vitro matured bovine oocytes with docetaxel before vitrification: Effects on cytoskeleton integrity and developmental ability after warming

The stabilization of spindle fibersis important for successful vitrification of bovine oocytes because microtubules and other cytoskeleton fibers (CSF) can be damaged during vitrification, resulting in failure of fertilization after thawing. Docetaxel, a stabilizing agent, could potentially reduce CSF damage of bovine oocytes induced during vitrification. However, there have been no reports on the effects of docetaxel on their vitrification. Experiment 1 was conducted to investigate the effects of various doses of docetaxel (0.0, 0.05, 0.5, 5.0 and 50 μM) in preincubation medium of in vitro matured (IVM) bovine oocytes on their developmental ability after in vitro fertilization (IVF). The results show that 0.05 μM docetaxel had no adverse effect on embryo development, while docetaxel at a concentration of ⩾0.5 μM inhibited development. Experiments 2 and 3 were conducted to investigate the effects of preincubation of IVM bovine oocytes with 0.05 μM docetaxel for 30 min prior to vitrification-warming on CSF integrity (Experiment 2), and on oocyte survival and viability after IVF (Experiment 3). When preincubated with 0.05 μM docetaxel for 30 min before vitrification, post-thawed oocytes had less CSF damage and higher survival rates compared with those untreated with docetaxel before vitrification. Surviving oocytes also had higher rates of cleavage and development to the blastocyst stage after IVF. In conclusion, preincubation of IVM bovine oocytes with 0.05 μM docetaxel for 30 min before vitrification was effective at preventing CSF damage during vitrification, and improving oocyte viability after warming and subsequent cleavage and blastocyst formation after IVF.

Developmental potential of in vitro or in vivo matured oocytes

This study compared the embryological features of mature and immature oocytes (different stages) collected from stimulated cycles of in vitro fertilization (IVF). Immature oocytes were identified, classified as PI (prophase I – germinal vesicle, GV) or MI (metaphase I), were matured in vitro and fertilized using the intra-cytoplasmic sperm injection (ICSI) technique. Fertilization potential, cleavage, and subsequent transfer/cryopreservation of the embryos derived from these in vitro matured oocytes were compared with those of in vivo matured oocytes (collected at the MII stage). The characteristics of embryos derived from gametes recovered in the MI and MII stages were similar. The fertilization rate of immature oocytes recovered in PI was significantly lower than that of MII oocytes (P = 0.031), and the cleavage rate of the PI group was also lower than that of the MI (P = 0.004) and MII (P < 0.001) groups. In vitro maturation of MI oocytes is a suitable alternative when immature oocytes are recovered, as their characteristics and development are similar to those of in vivo matured oocytes. Optimization of outcomes for PI oocytes will require development of techniques that can distinguish which of these gametes will mature and fertilize.

Differential effects of linoleic and alpha-linolenic fatty acids on spatial and temporal mitochondrial distribution and activity in bovine oocytes

Using specific stains and confocal microscope imaging, the patterns of mitochondrial distribution, mitochondrial inner membrane potential and reactive oxygen species (ROS) levels during bovine oocyte maturation were determined in the presence or absence of physiological concentrations of linoleic acid (LA; 100µM) or α-linolenic acid (ALA; 50µM). Mitochondrial distribution in control oocytes at 0h was mainly peripheral and changed to a diffused pattern after 1h of culture; this was maintained up to 24h. Mitochondrial clusters were observed during the early hours of maturation (1-4h); the majority of these were arranged in perinuclear fashion. LA supplementation resulted in: (1) delayed redistribution of the mitochondria from a peripheral to a diffuse pattern and a decreased percentages of oocytes showing perinuclear mitochondrial clusters, (2) decreased mitochondrial inner membrane potential at 1 and 24h compared with the control and (3) higher ROS levels, associated with a lower nuclear maturation rate. In contrast, ALA supplementation had no effect on mitochondrial distribution and activity and decreased ROS levels compared with the control; this was associated with an increased nuclear maturation rate. In conclusion, LA induced alterations in mitochondrial distribution and activity as well as increasing ROS levels, which mediate, at least in part, the inhibitory effect on oocyte maturation.

Selection of Rattus norvegicus oocytes for in vitro maturation by brilliant cresyl blue staining

The objective of this work was to evaluate the rate of meiosis resumption and nuclear maturation of rat (Rattus norvegicus) oocytes selected for in vitro maturation (IVM) after staining of cumulus–oocyte complexes (COCs) with blue cresyl brilliant (BCB) using different protocols: exposure for 30, 60 or 90 min at 26 μM BCB (Experiment 1), and exposure for 60 min at 13, 20 or 26 μM BCB (Experiment 2). In Experiment 1, the selection of oocytes exposed to BCB for 60 min was found to be the most suitable, as meiosis resumption rates in the BCB+ group (n = 35/61; 57.37%) were the closest to the observed in the control (not exposed) group (n = 70/90; 77.77%) and statistically higher than the values observed for the BCB− group (n = 3/41; 7.32%). Additionally, the more effective evaluation of diagnostic tests (sensitivity and negative predictive value 100%) was observed in COCs exposed for 60 min. In Experiment 2, the 13 μM BCB+ group presented rates of meiosis resumption (n = 57/72; 72.22%) similar to the control group (n = 87/105; 82.86%) and higher than other concentration groups. However, this results of the analysis between BCB− oocytes was also higher in the 13 μM BCB group (n = 28/91; 30.78%) when compared with BCB− COCs exposed to 20 μM (n = 3/62; 4.84%) or 26 μM (n = 3/61; 4.92%) BCB. The nuclear maturation rate in the 13 μM BCB group was similar between BCB+ or BCB− oocytes. The 20 μM BCB group had a lower rate of nuclear maturation of BCB− oocytes than other groups. Thus, our best results in the selection of Rattus norvegicus oocytes by staining with BCB were obtained using the concentration of 13 μM and 20 μM, and an incubation period of 60 min.

Meiotic inhibition of bovine oocytes in medium supplemented with a serum replacer and hormones: effects on meiosis progression and developmental capacity

Aiming to improve the developmental competence of bovine oocytes during meiotic block, this study evaluated the effects of a serum replacer (Knockout SR®) and hormones (gonadotropins and estradiol) supplementation of prematuration medium (TCM119 with 0.5 mM IBMX [IBMX group] or 25 μM roscovitine [ROSC group]) on the kinetics of oocyte nuclear maturation and embryo development. Most IBMX and ROSC oocytes prematured for 8 h culture remained in the GV stage (70.3% and 73.1%, respectively; p > 0.05) similar to Control 8 h (63.5%) and to control immature oocytes (Control 0 h, 92.5%). After prematuration for 16 h, no oocytes remained in the GV stage at similar rates to those recently aspirated (p < 0.05); GV rates in ROSC (32.4%) were higher (p < 0.05) than in the Control 16 h group (8.6%), but similar (p > 0.05) to IBMX (9.7%). After in vitro maturation (IMV) for 24 h, metaphase II (MII) rates for oocytes prematured during 8 h were similar (p > 0.05) between control and treatments (65.0–71.7%). Similarly, MII rates oocytes prematured during 16 h were similar (p > 0.05) between all groups (45.9–60.4%). Cleavage rates (67.8–78.2%), embryonic development in day-7 (25.0–35.6%) and hatching rates in day-8 (2.5–11.3%) oocytes blocked during 8 h were similar for all groups (p > 0.05). Results indicate that addition of Knockout SR® and hormones to meiotic block culture with IBMX and roscovitine negatively affected meiotic arrest, but did not impair oocyte nuclear maturation and acquisition of developmental competence.

Prematuration of bovine oocytes with butyrolactone I reversibly arrests meiosis without increasing meiotic abnormalities after in vitro maturation

OBJECTIVES

Asynchrony between nuclear and cytoplasmic maturation, and possibly damage to the oocyte meiotic spindle, limits the application of in vitro maturation (IVM) in assisted reproduction. Several studies have suggested that Prematuration with meiosis blockers may improve oocyte quality after IVM, favoring early embryogenesis. Thus, we investigated the effect of Prematuration with the nuclear maturation inhibitor butyrolactone I (BLI) on the meiotic spindle and chromosomal configuration of bovine oocytes.

STUDY DESIGN

Immature oocytes obtained from cows slaughtered in a slaughterhouse (n=840) were divided into the following groups: (1) control (n=325), submitted only to IVM in TCM199 for 24h; (2) BLI 18h (n=208) submitted to meiotic blockage with 100 microM BLI for 24h (Prematuration) and then induction of IVM in TCM199 for 18h; and (3) BLI 24h (n=307), pre-matured with 100 microM BLI for 24h followed by 24h of IVM in TCM199. The oocytes were then fixed, stained by immunofluorescence for morphological visualization of both microtubules and chromatin, and evaluated.

RESULTS

Meiotic arrest occurred in 90.2% of the oocytes cultured with BLI. Maturation rates were similar for all groups (80.3%, 73.6% and 82.7% for the control, BLI 18h and BLI 24h groups, respectively). We observed 81.3% normal oocytes in metaphase II in the control group, and 80.0% and 81.2% in the BLI 18h and BLI 24h groups, respectively. The incidence of meiotic anomalies did not differ between groups (18.7%, 20.0% and 18.8% for the control, BLI 18h and BLI 24h, respectively).

CONCLUSION

Prematuration with butyrolactone I reversibly arrests meiosis without damaging the meiotic spindle or the chromosome distribution of bovine oocytes after in vitro maturation.