Selection of oocytes for in vitro maturation by brilliant cresyl blue staining: a study using the mouse model

Selection of Rattus norvegicus cumulus-oocyte complex for vitrification by brilliant cresyl blue

The influence of the method of evaluating developmentally competent oocytes on their viability after cryopreservation still needs to be better understood. The objective of this study was to determine the cleavage and embryo developmental rates after parthenogenetic activation of cumulus-oocyte complexes (COCs) selected by different concentrations of brilliant cresyl blue (BCB) and cryopreservation. In the first experiment, COCs were separated into groups and incubated for 1 h in medium containing BCB (13 μM, 16 μM, or 20 μM). The control group was not exposed to BCB staining. In the second experiment, COCs were divided into four groups: 13 μM BCB(+), 13 μM BCB(-), fresh control (selected by morphologic observation and immediately in vitro matured) and vitrified control (selected by morphologic evaluation, vitrified, and in vitro matured). In the first experiment, the 13 μM BCB group displayed greater development rates at the morula stage (65.45%, 36/55) when compared with the other groups. In the second experiment, cleavage (47.05%, 72/153) and morula development (33.55%, 51/153) of the control group of fresh COCs were increased compared with the other groups. However, when comparing morula rates between vitrified COC control and BCB(+) groups, the BCB(+) group had better results (19.23%, 5/26 and 64.7%, 11/17, respectively). Our best result in rat COC selection by BCB staining was obtained using a concentration of 13 μM. This selection could be a valuable tool to improve vitrification outcomes, as observed by the BCB(+) group that demonstrated better results compared with the vitrified COC control.

Brilliant Cresyl Blue Negative Oocytes Show a Reduced Competence for Embryo Development after In Vitro Fertilisation with Sperm Exposed to Oxidative Stress

The extent of oxidative damage transferred by the damaged sperm to the progeny is likely to be limited by the oocyte's repair and antioxidative capacity. We aimed to assess the association between Brilliant Cresyl Blue (BCB) staining in oocytes and their competence for embryo development after in vitro fertilisation (IVF) with damaged sperm. For this purpose, bovine sperm were incubated without (non-oxidised sperm, NOX S) or with 100 µM H2O2 (oxidised sperm, OX S) and were used to fertilise in-vitro-matured bovine oocytes (BCB-pos./BCB-neg.). Unstained oocytes served as controls (US). Development was assessed at 30, 46, 60 h and on Days (D) 7 and 8 after IVF. Total cell number and apoptotic index were analysed in D7 blastocysts. BCB-neg. oocytes showed lower cleavage rates and blastocyst rates than unstained oocytes after IVF with NOX S (p < 0.05). They showed the highest reduction in D7 blastocyst rate upon fertilisation with OX S and showed a delayed embryo development at 46 and 60 h after IVF compared to embryos produced with NOX S (p < 0.05). Total cell number in blastocysts produced with BCB-neg. oocytes was lower (p < 0.05) in the embryos produced with OX S than in embryos after IVF with NOX S. In conclusion, BCB-neg. oocytes have a lower competence to support embryo development after in vitro fertilisation with oxidised sperm.

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.

Electrophysiology and Fluorescence Spectroscopy Approaches for Evaluating Gamete and Embryo Functionality in Animals and Humans

This review has examined two of the techniques most used by our research group for evaluating gamete and embryo functionality in animal species, ranging from marine invertebrates to humans. Electrophysiology has given access to fundamental information on some mechanisms underpinning the biology of reproduction. This technique demonstrates the involvement of ion channels in multiple physiological mechanisms, the achievement of homeostasis conditions, and the triggering of profound metabolic modifications, often functioning as amplification signals of cellular communication. Fluorescence spectrometry using fluorescent probes to mark specific cell structures allows detailed information to be obtained on the functional characteristics of the cell populations examined. The simple and rapid execution of this methodology allowed us to establish a panel helpful in elucidating functional features in living cells in a simultaneous and multi-parameter way in order to acquire overall drafting of gamete and embryo functionality.

Tight gene co-expression in BCB positive cattle oocytes and their surrounding cumulus cells

BACKGROUND

Cytoplasmic and nuclear maturation of oocytes, as well as interaction with the surrounding cumulus cells, are important features relevant to the acquisition of developmental competence.

METHODS

Here, we utilized Brilliant cresyl blue (BCB) to distinguish cattle oocytes with low activity of the enzyme Glucose-6-Phosphate Dehydrogenase, and thus separated fully grown (BCB positive) oocytes from those in the growing phase (BCB negative). We then analyzed the developmental potential of these oocytes, mitochondrial DNA (mtDNA) copy number in single oocytes, and investigated the transcriptome of single oocytes and their surrounding cumulus cells of BCB positive versus BCB negative oocytes.

RESULTS

The BCB positive oocytes were twice as likely to produce a blastocyst in vitro compared to BCB- oocytes (P < 0.01). We determined that BCB negative oocytes have 1.3-fold more mtDNA copies than BCB positive oocytes (P = 0.004). There was no differential transcript abundance of genes expressed in oocytes, however, 172 genes were identified in cumulus cells with differential transcript abundance (FDR < 0.05) based on the BCB staining of their oocyte. Co-expression analysis between oocytes and their surrounding cumulus cells revealed a subset of genes whose co-expression in BCB positive oocytes (n = 75) and their surrounding cumulus cells (n = 108) compose a unique profile of the cumulus-oocyte complex.

CONCLUSIONS

If oocytes transition from BCB negative to BCB positive, there is a greater likelihood of producing a blastocyst, and a reduction of mtDNA copies, but there is no systematic variation of transcript abundance. Cumulus cells present changes in transcript abundance, which reflects in a dynamic co-expression between the oocyte and cumulus cells.

Higher quality rather than superior quantity of oocytes determine the amount of fertilizable oocytes in two outbred Dummerstorf high-fertility mouse lines

Dummerstorf fertility lines FL1 and FL2 represent two models of enhanced fertility characterized by the doubling of the litter size compared with an unselected control population (ctrl line, Dummerstorf FztDU). Both biodiverse FLs managed to reach this goal by increasing the ovulation rate per cycle, even showing decreased pregnancy rate and irregular oestrous cycle and metabolic hormone levels, compared with ctrl. The aim of the present study was to analyse oocytes in terms of quality and quantity by comparing the entire pool of oocytes per ovary, with those from the antral follicles within the same animal. We performed Brilliant Cresyl Blue staining as a non-invasive marker of oocyte quality in combination with an analysis of additional morphological indicators, e.g. cytoplasm clarity, cumulus cell layers, nuclear anatomy, size and shape. We compared our fertility lines with the unselected control population and with another independent line selected from the same founder population, showing lower litter size (DU6P). Our results suggest that fertility lines show decreased number of oocytes per ovary compared with DU6P but increased number of high-quality oocytes before ovulation. Hence, the raise in the ovulation rate and litter size of those super fertile mouse lines are not associated with an increased number of oocytes per ovary but rather with an increased number of higher quality fertilizable oocytes per cycle. In addition, the most conspicuous method to acquire oocytes with the highest quality in our lines is to assess their morphology, rather than their status after staining. All these discoveries together may be of fundamental importance for further studies in livestock farm animals showing some similar characteristics, e.g. irregular cycle or hormonal misbalances, to improve production while lowering costs, and in humans to increase the possibilities of successful pregnancies for couples undergoing in vitro fertilization (IVF).

Small-extracellular vesicles and their microRNA cargo from porcine follicular fluids: the potential association with oocyte quality

Background

Ovarian follicular fluids (FFs) contain several kinds of regulatory factors that maintain a suitable microenvironment for oocyte development. Extracellular vesicles (EVs) are among the factors that play essential roles in regulating follicle and oocyte development through their cargo molecules that include microRNAs (miRNAs). This study aimed to investigate small-EV (s-EV) miRNAs in porcine FFs and their potential association with oocyte quality.

Methods

Individual aspirated oocytes were stained with lissamine green B stain (LB), a vital stain for oocyte quality, and each oocyte was classified as high-quality (unstained; HQ) or low-quality (stained; LQ). FFs corresponding to oocytes were pooled together into HQ and LQ groups. Small-EVs were isolated from FFs, characterized, and their miRNA cargo was identified using the Illumina NovaSeq sequencing platform. Additionally, s-EVs from the HQ and LQ groups were utilized to investigate their effect on oocyte development after co-incubation during in vitro maturation.

Results

A total of 19 miRNAs (including miR-125b, miR-193a-5p, and miR-320) were significantly upregulated, while 23 (including miR-9, miR-206, and miR-6516) were downregulated in the HQ compared to the LQ group. Apoptosis, p53 signaling, and cAMP signaling were among the top pathways targeted by the elevated miRNAs in the HQ group while oocyte meiosis, gap junction, and TGF-beta signaling were among the top pathways targeted by the elevated miRNAs in the LQ group. The supplementation of small-EVs during maturation does not affect the oocyte developmental rates. However, LQ s-EVs increase the proportion of oocytes with homogeneous mitochondrial distribution and decrease the proportion of heterogeneous distribution.

Conclusion

Our findings indicated that FF-EVs contain different miRNA cargos associated with oocyte quality and could affect the mitochondrial distribution patterns during oocyte maturation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00723-1.

Strategies to Improve the Efficiency of Somatic Cell Nuclear Transfer

Mammalian oocytes can reprogram differentiated somatic cells into a totipotent state through somatic cell nuclear transfer (SCNT), which is known as cloning. Although many mammalian species have been successfully cloned, the majority of cloned embryos failed to develop to term, resulting in the overall cloning efficiency being still low. There are many factors contributing to the cloning success. Aberrant epigenetic reprogramming is a major cause for the developmental failure of cloned embryos and abnormalities in the cloned offspring. Numerous research groups attempted multiple strategies to technically improve each step of the SCNT procedure and rescue abnormal epigenetic reprogramming by modulating DNA methylation and histone modifications, overexpression or repression of embryonic-related genes, etc. Here, we review the recent approaches for technical SCNT improvement and ameliorating epigenetic modifications in donor cells, oocytes, and cloned embryos in order to enhance cloning efficiency.

Treatment of mouse cumulus-oocyte complexes with L-carnitine during vitrification and in vitro maturation affects maturation and embryonic developmental rate after parthenogenetic activation

The technique of oocyte vitrification remains a challenge in most animal species. The present study aimed to evaluate the effects of cumulus cell presence and L-carnitine (LC) treatment during vitrification of selected immature oocytes by brilliant cresyl blue (BCB) staining on maturation and embryonic developmental rate after parthenogenetic activation. Immature oocytes were obtained from C57BL/6 female mice ovaries and stained with BCB. The BCB⁺ cumulus-oocyte complexes (COCs) were then selected and random parts of COCs were denuded from cumulus cells (denuded oocytes: DOs). COCs and DOs were treated with/out LC (0.6 mg/ml) during vitrification and in vitro maturation (IVM) procedures. A number of non-vitrified COCs were also treated with LC during the IVM process (fresh group). Maturation rate, intracellular glutathione (GSH) contents, and developmental competence of oocytes were also examined. The GSH levels in vitrified DOs+LC and vitrified COCs+LC groups were significantly higher (p < 0.01) than untreated vitrified-warmed COCs and DOs. Maturation rate and blastocyst developmental rate were reduced after the vitrification-warming procedure compared with the fresh group. The vitrified COCs+LC group showed a higher percentage of mature oocytes and the ability to develop to blastocyst stage than the vitrified-warmed DOs group (p < 0.01). These data indicated that the presence of cumulus cells around the competent oocyte and LC treatment during vitrification and IVM procedure could improve parthenogenetic developmental competence of vitrified-warmed oocytes by increasing GSH levels and accelerating oocyte maturation.

Does maternal exposure to nicotine affect the oocyte quality and reproductive capacity in adult offspring?

Gonadal development begins in the intrauterine phase and females from most species are born with an established oocyte reserve. Exposure to drugs during gestation can compromise the offspring health, also affecting the gametes quality. Nicotine, the main component of cigarettes, is an oxidant agent capable of altering the fertility in men and women. As female gametes are susceptible to oxidative stress, this drug can damage the oolemma and affect oocyte maturation, induce errors during chromosomal segregation and DNA fragmentation. Oocyte mitochondria are particularly susceptible to injuries, contributing to the oocyte quality loss and embryonic development disruption. Thus, considering the high number of women who smoke during pregnancy, while significant events are occurring in the embryo for future fertility of offspring, we seek to verify the quality of the oocytes from adult rats exposed to nicotine during intrauterine phase and breastfeeding. Pregnant Wistar rats received nicotine by osmotic mini-pumps and the female progenies were evaluated in adulthood for oocyte quality (viability, lipid peroxidation, generation of reactive oxygen species and mitochondrial integrity) and reproductive capacity. Embryos (3dpc) and fetuses (20dpc) generated by these rats were also evaluated. The results showed that the dose of 2 mg/kg/day of nicotine through placenta and breast milk does not affect the number of oocytes and the fertility capacity of adult rats. However, it causes some morphological alterations in oocytes, mitochondrial changes, embryonic fragmentation and disruption of fetal development. The malformations in fetuses generated from these gametes can also indicate the occurrence of epigenetic modifications.

A novel lincRNA identified in buffalo oocytes with protein binding characteristics could hold the key for oocyte competence

Studying the maternal oocyte-specific genes, in farm animals is a significant step towards delineating the underlying mechanisms that regulate oocyte quality, early embryonic development and survival. With the creation of buffalo oocyte-specific subtracted cDNA library, it has raised new questions which need to be answered. The present study has characterized one of the ESTs selected from the library and highlighted its importance in the oocyte quality. The selected EST was made full length by RLM-RACE and four transcript variants were identified. Bioinformatics analysis indicated the novelty of full-length transcript along with conserved intergenic nature. The largest transcript was identified as long intergenic noncoding RNA based upon coding potential calculator output. The expression analysis at different hours of oocyte maturation showed a significant variation in developmentally competent oocytes to that of incompetent ones. Along with this, the transcript was also found to have protein binding ability which was confirmed by RNA electrophoretic mobility shift assay. The protein used in the experiment was isolated from oocyte and cumulus cells via sonication. A novel lincRNA has been reported here that might have an important role in maturation of oocytes, inferred from its relative gene expression study and protein binding characteristics.

Cellular and molecular alterations of buffalo oocytes cultured under two different levels of oxygen tension during in vitro maturation

This study was conducted to monitor the cellular and molecular changes of buffalo cumulus-oocytes complexes (COCs) cultured under high or low oxygen levels. Morphologically good quality COCs (n = 1627) were screened using brilliant cresyl blue (BCB) staining and placed into three groups (BCB+, BCB- and control). All groups of COCs were cultured under low (5%) or high (20%) oxygen tensions. Intracellular and molecular changes including oocyte ultrastructure, lipid contents, mitochondrial activity and transcript abundance of genes regulating different pathways were analyzed in the matured oocyte groups. The results revealed that oxygen tension did not affect cumulus expansion rates, however the BCB+ group had a higher (P ≤ 0.05) expansion rate compared with the BCB- group. BCB- oocytes recorded the lowest meiotic progression rate (P ≤ 0.05) under high oxygen levels that was linked with an increased level of reactive oxygen species (ROS) compared with the BCB+ oocytes. Ultrastructure examination indicated that BCB+ oocytes had a higher rate of cortical granules migration compared with BCB- under low oxygen tension. In parallel, our results indicated the upregulation of NFE2L2 in groups of oocytes cultured under high oxygen tension that was coupled with reduced mitochondrial activity. In contrast, the expression levels of MAPK14 and CPT2 genes were increased (P ≤ 0.05) in groups of oocytes cultured under low compared with high oxygen tension that was subsequently associated with increased mitochondrial activity. In conclusion, data from the present investigation indicated that low oxygen tension is a favourable condition for maintaining the mitochondrial activity required for nuclear maturation of buffalo oocytes. However, low-quality oocytes (BCB-) responded negatively to high oxygen tension by reducing the expression of gene-regulating metabolic activity (CPT2). This action was an attempt by BCB- oocytes to reduce the increased levels of endogenously produced ROS that was coupled with decreased expression of the gene controlling meiotic progression (MAPK14) in addition to nuclear maturation rate.

Selection of Immature Cat Oocytes with Brilliant Cresyl Blue Stain Improves In Vitro Embryo Production during Non-Breeding Season

Simple Summary

The domestic cat is commonly used as a model for the development of assisted reproductive technologies, including in vitro embryo production (IVEP) in felid species. Seasonal reproduction is a feature of domestic cats as well as of several species of wild feline. Likewise, the number and the quality of blastocysts produced in in vitro systems is linked to season. Maintaining stable in vitro embryo production throughout the year is crucial not only for research purposes but also for programs aimed at protecting endangered felines. We assess whether using Brilliant Cresyl Blue (BCB) selection in addition to the classical morphological selection could improve the IVEP outcomes during non-breeding season. Blastocyst yield and quality of the embryos (hatching rate and blastocyst cell numbers) were higher after IVM/IVF in oocytes defined as BCB+ (colored cytoplasm) based on the BCB test than in oocytes only morphologically selected. Furthermore, no adverse effects on bioenergetic/oxidative status were observed in oocytes subjected to BCB staining. In conclusion, BCB test implementation in IVEP programs might ensure a steady output of domestic cat blastocysts throughout the year.

Abstract

In domestic cats, the maturation, fertilization, and development potential in vitro decreases during the non-breeding season. This study aims at evaluating the efficacy of Brilliant Cresyl Blue (BCB) staining in selecting developmentally competent oocytes to be used in in vitro embryo production (IVEP) programs in order to overcome the season variability in blastocyst yield. Cumulus-oocytes complexes (COCs) collected from antral follicles of domestic cat ovaries during the anestrus phase (July to November) were selected by BCB staining and classified as BCB+ (colored cytoplasm) and BCB− (colorless cytoplasm). COCs not exposed to BCB staining were used as control. Before and after in vitro maturation mitochondrial activity and reactive oxygen species (ROS) were measured. Following in vitro fertilization, blastocyst rate, hatching rate, and blastocyst cell numbers were recorded. The results show that BCB staining did not alter the mitochondrial function and ROS production in cat oocytes. BCB+ oocytes presented a higher (p < 0.05) blastocyst rate, hatching rate, and blastocyst cell number than BCB− and control oocytes. In conclusion, BCB staining does not affect the bioenergetic/oxidative status of the oocyte while being a useful tool for selecting good quality oocytes to increase IVEP in domestic cats during non-breeding season.

Mechanistic insights into the reduced developmental capacity of in vitro matured oocytes and importance of cumulus cells in oocyte quality determination

In vitro maturation of oocytes is a promising assisted reproductive technology (ART) for infertility treatment, although it is still not a routine technique for human ART due to reduced embryonic development. The aim of the present study was to clarify the possible reasons for reduced capacity of in vitro matured oocytes. Our results showed that the oocytes matured in vitro displayed increased abnormal mitochondrial distribution, reduced mitochondrial membrane potential, and increased reactive oxygen species levels when compared to in vivo matured oocytes. These results were not different in oocytes matured in vitro with or without cumulus cells. Notably, in vitro matured oocytes displayed increased mitochondrial DNA numbers probably due to functional compensation. In vitro matured oocytes showed significantly lower activation and embryonic development rates, and their ability to produce Ca²⁺ oscillations was much lower in response to parthenogenetic activation, especially in oocytes matured in vitro without cumulus cells with nearly half of them failing to produce calcium waves upon strontium chloride stimulation. These data are important for understanding the reasons for reduced developmental potential of in vitro matured oocytes and the importance of cumulus cells for oocyte quality.

Genes regulating hormone stimulus and response to protein signaling revealed differential expression pattern during porcine oocyte in vitro maturation, confirmed by lipid concentration

Genes influencing oocyte maturation may be valuable for predicting their developmental potential, as well as discerning the mechanistic pathways regulating oocyte development. In the presented research microarray gene expression analysis of immature and in vitro matured porcine oocytes was performed. Two groups of oocytes were compared in the study: before (3 × n = 50) and after in vitro maturation (3 × n = 50). The selection of viable oocytes was performed using the brilliant cresyl blue (BCB) test. Furthermore, microarrays and RT-qPCR was used to analyze the transcriptome of the oocytes before and after IVM. The study focused on the genes undergoing differential expression in two gene-ontology groups: “Cellular response to hormone stimulus” and “Cellular response to unfolded protein”, which contain genes that may directly or indirectly be involved in signal transduction during oocyte maturation. Examination of all the genes of interest showed a lower level of their expression after IVM. From the total number of genes in these gene ontologies ten of the highest change in expression were identified: FOS, ID2, BTG2, CYR61, ESR1, AR, TACR3, CCND2, EGR2 and TGFBR3. The successful maturation of the oocytes was additionally confirmed with the use of lipid droplet assay. The genes were briefly described and related to the literature sources, to investigate their potential roles in the process of oocyte maturation. The results of the study may serve as a basic molecular reference for further research aimed at improving the methods of oocyte in vitro maturation, which plays an important role in the procedures of assisted reproduction.

Transmission of Dysfunctional Mitochondrial DNA and Its Implications for Mammalian Reproduction

Mitochondrial DNA (mtDNA) encodes proteins for the electron transport chain which produces the vast majority of cellular energy. MtDNA has its own replication and transcription machinery that relies on nuclear-encoded transcription and replication factors. MtDNA is inherited in a non-Mendelian fashion as maternal-only mtDNA is passed onto the next generation. Mutation to mtDNA can cause mitochondrial dysfunction, which affects energy production and tissue and organ function. In somatic cell nuclear transfer (SCNT), there is an issue with the mixing of two populations of mtDNA, namely from the donor cell and recipient oocyte. This review focuses on the transmission of mtDNA in SCNT embryos and offspring. The transmission of donor cell mtDNA can be prevented by depleting the donor cell of its mtDNA using mtDNA depletion agents prior to SCNT. As a result, SCNT embryos harbour oocyte-only mtDNA. Moreover, culturing SCNT embryos derived from mtDNA depleted cells in media supplemented with a nuclear reprograming agent can increase the levels of expression of genes related to embryo development when compared with non-depleted cell-derived embryos. Furthermore, we have reviewed how mitochondrial supplementation in oocytes can have beneficial effects for SCNT embryos by increasing mtDNA copy number and the levels of expression of genes involved in energy production and decreasing the levels of expression of genes involved in embryonic cell death. Notably, there are beneficial effects of mtDNA supplementation over the use of nuclear reprograming agents in terms of regulating gene expression in embryos. Taken together, manipulating mtDNA in donor cells and/or oocytes prior to SCNT could enhance embryo production efficiency.

Resveratrol supplementation during in vitro maturation improves embryo development of prepubertal goat oocytes selected by brilliant cresyl blue staining

This study aimed to investigate the effect of resveratrol supplementation in maturation medium on the developmental ability and bioenergetic\oxidative status of prepubertal goat oocytes selected by brilliant cresyl blue (BCB). Oocytes collected from slaughterhouse-derived ovaries were selected by 13 µM BCB staining and classified as grown BCB+ and growing BCB- oocytes. All oocytes were matured in vitro in our conventional maturation medium and supplemented with 1 µM (BCB+R and BCB-R) and without (Control groups: BCB+C and BCB-C) resveratrol. After 24 h, IVM-oocytes were fertilized with fresh semen and presumptive zygotes were in vitro cultured for 8 days. Oocytes were assessed for blastocyst development and quality, mitochondrial activity and distribution, and levels of GSH, ROS, and ATP. BCB+R (28.3%) oocytes matured with resveratrol presented significantly higher blastocyst development than BCB+C (13.0%) and BCB- groups (BCB-R: 8.3% and BCB-C: 4.7%). Resveratrol improved blastocyst development of BCB-R oocytes at the same rate as BCB+C oocytes. No differences were observed in blastocyst quality among groups. GSH levels were significantly higher in resveratrol groups (BCB+R: 36554.6; BCB-R: 34946.7 pixels/oocyte) than in control groups (BCB+C: 27624.0; BCB-C: 27655.4 pixels/oocyte). No differences were found in mitochondrial activity, ROS level, and ATP content among the groups. Resveratrol-treated oocytes had a higher proportion of clustered active mitochondria in both BCB groups (BCB+R: 73.07%; BCB-R: 79.16%) than control groups (BCB+C: 19.35%; BCB-C: 40%). In conclusion, resveratrol increased blastocyst production from oocytes of prepubertal goats, particularly in better quality oocytes (BCB+).

Brilliant cresyl blue staining allows the selection for developmentally competent immature feline oocytes

The outcome of in-vitro-maturation and in-vitro-fertilization of feline oocytes depends on the selection of high quality oocytes, and is often restricted to morphological criteria. The aim of this study was to test whether the Brilliant cresyl blue (BCB) staining is suitable for pre-selection of feline oocytes before in-vitro-maturation. Cumulus-oocytes-complexes (COC) were released from domestic cat ovaries obtained after ovariectomy and were subjected to BCB staining. BCB+ stained oocytes were characterized by a violet/pale blue staining of the ooplasma, BCB- oocytes remained unstained. Transmission electron microscopy indicated for a slightly advanced stage of BCB- oocytes within the maturation process. After 24 h in-vitro-maturation, almost 75% of BCB+ and 21.5% of BCB- oocytes were able to reach metaphase II. Also, after in-vitro-fertilization, significantly more oocytes developed to morulae (19.2%) if oocytes were preselected for BCB staining, although 8% of unstained COC still reached advanced embryo stages. Prolonged storage of ovaries before COC retrieval for 16-20 h at 4 °C was accompanied by reduced number of BCB+ oocytes (96 of 210, 45.7%) in comparison to freshly isolated COC (151 of 225, 67.1%), and impaired cleavage rate (19.8%) and morula rate (9.4%) of BCB+ oocytes but the rate of embryos which developed to advanced stages remained unchanged (∼50%). To conclude, BCB staining is a very useful tool to preselect immature COC of feline species ensuring higher developmental rates.

Propensity in low-grade oocytes for delayed germinal vesicle breakdown compromises the developmental ability of sub-optimal grade Bubalus bubalis oocytes

SummaryMaturing oocytes have diverse developmental potential and good quality oocytes exhibit a better ability to attain physiological milestones in a time-dependent manner. This situation necessitates the confirmation of oocyte developmental status more precisely under an in vitro embryo production (IVEP) regime. The aim of this study was to explain timely events in germinal vesicle breakdown (GVBD), an important milestone of oocyte nuclear maturation, to delineate the developmental capacity of Bubalus bubalis oocytes. In addition, the expression profile of genes responsible for GVBD was assessed in order to understand the molecular context responsible for GVBD. The chronology of GVBD events at different time intervals during in vitro maturation (IVM) suggests that the rate at which oocytes undergo GVBD was strikingly different in the brilliant cresyl blue (BCB)+ and BCB- groups. The expression of AKT and CDC25B genes for BCB+ oocytes was maximum at 8 h of IVM, and CCNB (cyclin B) peaked at around 10 h, which suggested that GVBD was finished after 10 h in BCB+ oocytes, whereas the expression of AKT and CDC25B was found to peak at around 12-14 h of IVM. This difference consequently delays the GVBD event by 2-4 h in BCB- oocytes. Poor abundance of gene transcripts was mainly implicated in delay and lower rate of GVBD in BCB- oocytes which in turn strongly affected the translational ability of oocytes to blastocysts. The findings of this study support the idea that there is a propensity in sub-optimal grade oocytes for delayed GVBD that compromises the developmental ability of low grade buffalo oocytes. The study highlights the very small, but importantly vital and separate, time window of the GVBD event during which the competence levels of buffalo oocytes are altered along with their translational ability to develop into the prospective embryos.

Simple separation of good quality bovine oocytes using a microfluidic device

We fabricated a simple microfluidic device for separation of bovine oocytes based on the oocyte quality to improve the conception rate of in vitro fertilization (IVF) by using good quality oocytes. The microfluidic device separates oocytes based on sedimentation rate differences in a sucrose buffer, which is dependent on oocyte quality. The microfluidic device has a 700 µm width, 1 mm height, and 10 mm long separation channel. Oocytes were injected from the upper half of the separation channel, and they flowed while sinking. The outlets of the separation channel were divided into upper and lower chambers. Good quality oocytes settled faster than poor quality oocytes in sucrose buffer; therefore, good quality oocytes were collected from the lower outlet. We performed IVF after the microfluidic separation of oocytes. The developmental rate to blastocysts of oocytes collected from the lower outlet was significantly higher than those collected from the upper outlet (36.0% vs. 14.1%). This result was comparable to that in the BCB staining method performed as a comparison method (BCB+ : 35.7%, BCB−: 15.4%). These findings indicate that our microfluidic device could be applied to oocyte separation and contribute to improvement of in vitro embryo production system.

Sucrose assists selection of high-quality oocytes in pigs

We investigated whether high‐quality in vitro matured (IVM) oocytes can be distinguished from poor ones based on the morphological changes after treatment with hyperosmotic medium containing 0.2 mol/L sucrose in pigs. We hypothesize that IVM oocytes maintaining round shape have higher quality than mis‐shapened oocytes following dehydration. Oocyte quality was verified by determining embryonic developmental competence using in vitro fertilization, nuclear transfer and parthenogenetic activation. In all cases, the round oocytes had greater (p < .05) developmental competence than that of mis‐shapened oocytes in terms of blastocyst rate and total cell number in blastocysts obtained after 6 days of in vitro culture. We also confirm that round aged oocytes are higher in quality than mis‐shapened aged oocytes. In an attempt to find out why high‐quality oocytes maintain a round shape whereas poorer oocytes become mis‐shapened following sucrose treatment, we examined the arrangement of actin microfilaments and microtubules. Abnormal organization of these cytoskeletal components was higher (p < .05) in mis‐shapened oocytes compared to round oocytes after 52 hr of IVM. In conclusion, sucrose treatment helps selection of high‐quality oocytes, including aged oocytes, in pigs. Abnormal cytoskeleton arrangements partly explain for low developmental competence of mis‐shapened oocytes.

With low ovarian reserve, Highly Individualized Egg Retrieval (HIER) improves IVF results by avoiding premature luteinization

Background

Highly Individualized Egg Retrieval (HIER), defined as age-specific early oocyte retrieval (ER), has been demonstrated to avoid premature luteinization in women ≥43. We here investigated whether HIER also applies to younger women with premature ovarian aging (POA), and what best lead follicle size should be for administration of ovulation-triggers.

Methods

Fifty-six women ≥43, and 37 POA patients underwent IVF cycles. Granulosa cells (GCs) were isolated, cultures were established, RNA was extracted and real-time PCR analyses performed, with gene expressions at mRNA level investigated for FSH receptor (FSHR), luteinizing hormone receptor (LHCPR), P450 aromatase (CYP19a1) and progesterone receptor (PGR). POA was defined by age < 40, FSH above 95%CI and/or AMH below 95%CI for age. Women ≥43 years were divided into very early retrieval (VER), with human chorionic gonadotropin (hCG) trigger at 13.5–15.5 mm, ER at 16.0–18.0 mm or standard retrievel (SR) at 18.5–20.5 mm; POA patients were divided into ER and SR. Pregnancy rates and and molecular markers of premature luteinization (PL) were main outcome measures.

Results

ER resulted in a significantly higher clinical pregnancy rate (16.7%) than VER (5.9%) or SR (6.7%; both P < 0.05). Molecular markers of PL were highest with SR and lowest with VER. In POA, ER improved pregnancy chances even more than in women ≥43 (7.7% with SR vs. 41.7% with ER), while also reducing molecular markers of PL. With low ovarian reserve (LOR), by avoiding PL, ER with hCG trigger at 16.0–18.0 mm, thus, improves clinical pregnancy rates at all ages. As VER demonstrated lowest molecular PL marker but equally poor pregnancy rates as SR, too early ovulation triggers, likely, result in cytoplasmatic immaturity.

Conclusions

HIER is even more effective in POA patients than women above age 43, demonstrating that HIER should be further investigated going into even more advanced ages.

Is there an association between PAWP/WBP2NL sequence, expression, and distribution in sperm cells and fertilization failures in ICSI cycles?

Successful fertilization in mammals depends on the sperm's ability to initiate intracellular Ca²⁺ oscillations in the egg, a phenomenon that is elicited by Sperm-oocyte activating factors (SOAFs), whose quantitative and/or qualitative defect might result in fertilization failure. One such proposed factor is Post-acrosomal WW domain-binding protein (PAWP/WBP2NL), although its ability to activate human oocytes has been questioned and its implication in human fertilization failure remains unknown. Here, we sought to determine if PAWP/WBP2NL expression and distribution in sperm cells associate with low/complete fertilization failure in males participating in intracytoplasmic sperm injection (ICSI) cycles. This prospective study was conducted on eight couples referred for elective ICSI with either the woman's own (n = 4) or a donor eggs (n = 4). Eight sperm donor samples used in ICSI, which resulted in normal fertilization rates, were used as the control group. For each male patient and donor sperm, PAWP/WBP2NL sequence, protein expression, and cellular distribution were analyzed by PCR amplification-sequencing, Western blot, and immunofluorescence, respectively. PAWP/WBP2NL was present in all samples, and no significant differences were detected between patients with fertilization failure and donors in sequence variants or mean protein expression, or in the proportion of PAWP/WBP2NL-positive sperm. In conclusion, no clear association between PAWP/WBP2NL protein expression in sperm and fertilization outcome in ICSI were observed from this cohort.

Developmental competence of Dromedary camel (Camelus dromedarius) oocytes selected using brilliant cresyl blue staining

The objectives of the present studies were to investigate the developmental capacity of dromedary camel oocytes selected by brilliant cresyl blue (BCB) staining and to investigate the expression of select transcripts in germinal vesicle (GV) stage oocytes. These transcripts included BMP15 and GDF9 as important transcripts for folliculogenesis and oocyte development, Zar1 and Mater as maternal transcripts required for embryonic development, Cyclin B1 and CDK1 as cell cycle regulators and Oct4 and STAT3 as transcription factors. Dromedary camel oocytes were retrieved from ovaries collected at a local slaughterhouse. After exposure to BCB staining, cumulus–oocyte complexes (COCs) from BCB+, BCB− and control (selected based on morphological criteria) groups were subjected toin vitromaturation,in vitrofertilization andin vitroculture. For gene expression studies, after BCB staining cumulus cells were stripped off and the completely denuded GV stage oocytes were used for RT-PCR analysis of selected transcripts. BCB+ oocytes showed higher maturation, and fertilization rates compared with BCB− and control groups. Indices of early embryonic development, namely, cleavage at 48 hours post insemination (hpi), and development to morula at day 5 and day 7 blastocyst rates were also significantly higher in the BCB+ group. RT-PCR revealed a higher expression of BMP15, GDF9, Zar1, Mater, Cyclin B1, CDK1, OCT4 and STAT3 in good quality oocytes that stained positively for BCB (BCB+). Collectively, results provide novel information about the use of BCB screening for selecting good quality oocytes to improvein vitroembryo production in the dromedary camel.

Dual mTOR inhibitor MLN0128 suppresses Merkel cell carcinoma (MCC) xenograft tumor growth

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin cancer. Pathologic activation of PI3K/mTOR pathway and elevated expression of c-Myc are frequently detected in MCC. Yet, there is no targeted therapy presently available for this lethal disease. Recently, MLN0128, a second-generation dual TORC1/2 inhibitor is shown to have therapeutic efficacy in preclinical studies. MLN0128 is currently in clinical trials as a potential therapy for advanced cancers. Here we characterize the therapeutic efficacy of MLN0128 in the preclinical setting of MCC and delineate downstream targets of mTORC1/2 in MCC cellular systems. MLN0128 significantly attenuates xenograft MCC tumor growth independent of Merkel cell polyomavirus. Moreover, MLN0128 markedly diminishes MCC cell proliferation and induces apoptosis. Further investigations indicate that senescence does not contribute to MLN0128-mediated repression of xenograft MCC tumor growth. Finally, we also observe robust antitumor effects of MLN0128 when administered as a dual therapy with JQ1, a bromodomain protein BRD4 inhibitor. These results suggest dual blockade of PI3K/mTOR pathway and c-Myc axis is effective in the control of MCC tumor growth. Our results demonstrate that MLN0128 is potent as monotherapy or as a member of combination therapy with JQ1 for advanced MCC.

Early germinal vesicle breakdown is a predictor of high preimplantation developmental competent oocytes in mice

The preselection of highly developmentally competent oocytes for in vitro maturation (IVM) is crucial for improving assisted reproductive technology. Although several intrinsic markers of oocyte quality are known to be closely related to the onset of nuclear maturation (germinal vesicle break down, GVBD), a direct comparison between GVBD timing and oocyte quality has never been reported. In this study, we established a non-invasive oocyte evaluation method based on GVBD timing for preselecting more developmental competent oocytes in mice. Because the O2 concentration during IVM may affect the nuclear kinetics, all experiments were performed under two distinct O2 concentrations: 20% and 5% O2. First, we determined the time course of changes in nuclear maturation and preimplantation developmental competence of in vitro-matured oocytes to estimate GVBD timing in high developmental competent oocytes. Two-thirds of oocytes that underwent GVBD in early IVM seemed to mainly contribute to the blastocyst yield. To confirm this result, we compared the preimplantation developmental competence of the early and late GVBD oocytes. Cleavage and blastocyst formation rates of early GVBD oocytes (80.2% and 52.7% under 20% O2, respectively, and 67.6% and 47.3% under 5% O2, respectively) were almost double those of late GVBD oocytes (44.8% and 26.0% under 20% O2, respectively, and 40.4% and 17.9% under 5% O2, respectively). With no observable alterations by checking the timing of GVBD in preimplantation developmental competence, oocyte evaluation based on GVBD timing can be used as an efficient and non-invasive preselection method for high developmental competent oocytes.

Oocytes from small and large follicles exhibit similar development competence following goat cloning despite their differences in meiotic and cytoplasmic maturation

Reduced developmental competence after IVF has been reported using oocyte derived from small follicles in several species including cattle, sheep, and goats. No information is currently available about the effect of follicle size of the cytoplast donor on in vivo development after somatic cell nuclear transfer (SCNT) in goats. Oocytes collected from large (≥3 mm) and small follicles (<3 mm) were examined for maturation and in vivo developmental competence after SCNT. Significantly greater maturation rate was observed in oocytes derived from large follicles compared with that of small follicles (51.6% and 33.7%, P < 0.05). Greater percent of large follicle oocytes exhibited a low glucose-6-phosphate dehydrogenase activity at germinal vesicle stage compared with small follicle oocytes (54.9% and 38.7%, P < 0.05). Relative mRNA expression analysis of 48 genes associated with embryonic and fetal development revealed that three genes (MATER, IGF2R, and GRB10) had higher level of expression in metaphase II oocytes from large follicles compared with oocytes from small follicles. Nevertheless, no difference was observed in pregnancy rates (33.3% vs. 47.1%) and birth rates (22.2% vs. 16.7%) after SCNT between the large and small follicle groups). These results indicate that metaphase II cytoplasts from small and large follicles have similar developmental competence when used in goat SCNT.

Improvements in IVF in women of advanced age

Women above age 40 years in the US now represent the most rapidly growing age group having children. Patients undergoing in vitro fertilization (IVF) are rapidly aging in parallel. Especially where egg donations are legal, donation cycles, therefore, multiply more rapidly than autologous IVF cycles. The donor oocytes, however, are hardly ever a preferred patient choice. Since with use of own eggs, live birth rates decline with advancing age but remain stable (and higher) with donor eggs, older patients always face the difficult and very personal choice between poorer chances with own and better chances with donor oocytes. Physician contribution to this decision should in our opinion be restricted to accurate outcome information for both options. Achievable pregnancy and live birth rates in older women are, however, frequently underestimated, thereby mistakenly biasing fertility providers, private insurance companies and even regulatory government agencies. Restriction on access to IVF for older women is then often the consequence. In this review, we summarize the limited published data on best treatments of 'older' ovaries, while also addressing treatment approaches that should be avoided in older women. This focused review, therefore, to a degree is subjective. Research addressing aging ovaries in IVF has been disappointingly sparse, and has in our opinion too heavily concentrated on methods of embryo selection (ES), which, especially in older women, not only fail to improve IVF outcomes, but actually, negatively affect live birth chances. We conclude that, aside from breakthroughs in gamete creation, only pharmacological interventions into early (small growing follicle stages) follicle maturation will offer new potential to positively impact oocyte and embryo quality and, therefore, IVF outcomes. Research, therefore, should be accordingly redirected.

Expressão gênica em ovócitos suínos de diferentes classificações morfológicas

A produção in vitro de embriões suínos tem alcançado resultados insatisfatórios: ovócitos maturados in vivo produzem uma porcentagem maior de embriões em relação aos maturados in vitro. O sucesso da maturação in vitro está diretamente relacionado com a competência ovocitária. Somente ovócitos competentes são capazes de serem fecundados e terem desenvolvimento embrionário normal. A competência ovocitária pode ser avaliada por vários parâmetros. Recentemente têm sido utilizados como parâmetro os estudos da expressão de genes associados com a competência. O presente trabalho teve por objetivo avaliar diferenças na expressão dos genes BMP15, RYBP, MATER e ZAR1 em ovócitos imaturos de diferentes classes morfológicas, sendo elas: 1, 2, 3 e 4, com a finalidade de proporcionar importantes marcadores moleculares relacionados com a capacidade ovocitária. O RNA total dos ovócitos foi extraído e utilizado como molde para a síntese da primeira fita de cDNA. Os resultados da expressão gênica foram analisados utilizando-se modelo misto, considerando os dados de expressão gênica variável dependente e as classes ovocitárias variáveis independentes. Os genes BMP15, ZAR1 e RYBP apresentaram expressão semelhante nas classes ovocitárias 1, 2 e 3; somente a categoria 4 diferiu na expressão desses genes (P<0,05). O gene MATER foi expresso de forma semelhante em todas as classes ovocitárias estudadas (P>0,05). A técnica de RT-qPCR foi eficiente para detecção desses transcritos em ovócitos de diferentes classes. No entanto, para melhor entendimento do envolvimento desses transcritos na aquisição da competência ovocitária, são necessários mais estudos avaliando ovócitos de diferentes classes morfológicas, em diferentes fases de desenvolvimento, e implicação de outros genes envolvidos com a competência ovocitária.

Isolation and Characterization of Mouse Antral Oocytes Based on Nucleolar Chromatin Organization

This protocol describes a simple and quick method to isolate and characterize mouse antral GV (Germinal Vesicle) oocytes as able (SN, Surrounded Nucleolus) or unable (NSN, Not Surrounded Nucleolus) to develop to the blastocyst stage after in vitro maturation (IVM) and in vitro fertilization (IVF). It makes use of Hoeschst33342 (or any other DNA intercalating dye) able to bind to the heterochromatin of the nucleolus showing a ring in the SN oocytes or not, like in the NSN oocytes. This represents the easiest and quickest way to sort both antral oocytes that can be eventually used for IVM or IVF procedures. Briefly, the protocol consists of the following steps: hormone injection to stimulate follicular growth; isolation of the oocytes at the GV stage from the antral compartment by puncturing the ovary with a sterile needle; preparation of thin glass pipettes for mouth pipetting of the oocytes; sorting of the oocytes with Hoechst33342 prepared at a supravital concentration; IVM, IVF or any other molecular/cellular analysis. Unfortunately there are still few evidences to sort SN and NSN oocytes using less invasive techniques. If and once they will be identified, they could be potentially applied to human assisted reproductive technologies, although with several aspects that should be modified. To date, this technique has potential implications to dramatically increase IVM and IVF successful procedures in both endangered and species with economic interest.

Subcellular Characterization of Porcine Oocytes with Different Glucose-6-phosphate Dehydrogenase Activities

The in vitro maturation (IVM) efficiency of porcine embryos is still low because of poor oocyte quality. Although brilliant cresyl blue positive (BCB+) oocytes with low glucose-6-phosphate dehydrogenase (G6PDH) activity have shown superior quality than BCB negative (−) oocytes with high G6PDH activity, the use of a BCB staining test before IVM is still controversial. This study aimed to shed more light on the subcellular characteristics of porcine oocytes after selection using BCB staining. We assessed germinal vesicle chromatin configuration, cortical granule (CG) migration, mitochondrial distribution, the levels of acetylated lysine 9 of histone H3 (AcH3K9) and nuclear apoptosis features to investigate the correlation between G6PDH activity and these developmentally related features. A pattern of chromatin surrounding the nucleoli was seen in 53.0% of BCB+ oocytes and 77.6% of BCB+ oocytes showed peripherally distributed CGs. After IVM, 48.7% of BCB+ oocytes had a diffused mitochondrial distribution pattern. However, there were no significant differences in the levels of AcH3K9 in the nuclei of blastocysts derived from BCB+ and BCB− oocytes; at the same time, we observed a similar incidence of apoptosis in the BCB+ and control groups. Although this study indicated that G6PDH activity in porcine oocytes was correlated with several subcellular characteristics such as germinal vesicle chromatin configuration, CG migration and mitochondrial distribution, other features such as AcH3K9 level and nuclear apoptotic features were not associated with G6PDH activity and did not validate the BCB staining test. In using this test for selecting porcine oocytes, subcellular characteristics such as the AcH3K9 level and apoptotic nuclear features should also be considered. Adding histone deacetylase inhibitors or apoptosis inhibitors into the culture medium used might improve the efficiency of IVM of BCB+ oocytes.

Safety of brilliant cresyl blue staining protocols on human granulosa and cumulus cells

The selection of human immature oocytes destined for in vitro maturation (IVM) is performed according to their cumulus-oocyte complex (COC) morphology. In animal models, oocyte pre-selection with brilliant cresyl blue (BCB) staining improves fertilization and blastocyst rates and even increases the number of calves born. As the granulosa cells and cumulus cells (GCs and CCs) have a close relationship with the oocyte and are available in in vitro fertilization (IVF) programs, applying BCB staining to these cells may help to elucidate whether BCB shows toxicity to human oocytes and to determine the safest protocol for this dye. GCs and CCs were isolated from 24 patients who underwent controlled ovarian stimulation. After 48 h, cells were exposed to: Dulbecco's Modified Eagle Medium (DMEM) with or without phenol red, DPBS and mDPBS for 60 min; 13, 20 and 26 μM BCB for 60 min; and 60, 90 or 120 min to 13 μM BCB. Cellular viability was tested using 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) and trypan blue assays. The 20 and 26 μM BCB exposures resulted in lower cell viability, similar to when cells were exposed to BCB for 90 or 120 min. GCs and CCs viabilities were equal among control group and 13 μM BCB group after 60 min. BCB staining was not toxic to GCs and CCs when the regime of 13 μM BCB for 60 min was used. Due to the close molecular/biochemical relationship between these cells and the gamete, we propose that it is unlikely that the use of BCB could interfere with the viability/health of human oocytes.

Expression of TGFβ superfamily components and other markers of oocyte quality in oocytes selected by brilliant cresyl blue staining: relevance to early embryonic development

Brilliant cresyl blue (BCB) is a super-vital stain that has been used to select competent oocytes in different species. One objective of the present study was to assess the relationship between BCB staining, which correlates with an oocyte's developmental potential, and the transcript abundance for select TGFβ-superfamily components, SMAD2/3 and SMAD1/5 phosphorylation levels, and oocyte (JY1) and cumulus-cell (CTSB, CTSK, CTSS, and CTSZ) transcript markers in bovine oocytes and/or adjacent cumulus cells. The capacity of exogenous follistatin or JY1 supplementation or cathepsin inhibitor treatment to enhance development of embryos derived from low-quality oocytes, based on BCB staining, was also determined. Cumulus-oocyte complexes (COCs) from abattoir-derived ovaries were subjected to BCB staining, and germinal-vesicle-stage oocytes and cumulus cells were harvested from control, BCB+, and BCB- (low-quality oocyte) groups for real-time PCR or Western-blot analysis. Remaining COCs underwent in vitro maturation, in vitro fertilization, and embryo culture in the presence or absence of the above exogenous supplements. Levels of FST, JY1, BMP15, and SMAD1, 2, 3, and 5 transcripts were higher in BCB+ oocytes whereas CTSB, CTSK, CTSS, and CTSZ mRNA abundance was higher in cumulus cells surrounding BCB- oocytes. Western-blot analysis revealed higher SMAD1/5 and SMAD2/3 phosphorylation in BCB+ than BCB- oocytes. Embryo-culture studies demonstrated that follistatin and cathepsin inhibitor treatment, but not JY-1 treatment, improve the developmental competence of BCB- oocytes. These results contribute to a better understanding of molecular indices of oocyte competence.

Developmental competence of equine oocytes: impacts of zona pellucida birefringence and maternally derived transcript expression

In the present study, equine oocytes were classified into groups of presumably high and low developmental competence according to cumulus morphology, as well as oocyte ability to metabolise brilliant cresyl blue (BCB) stain. All oocytes were evaluated individually in terms of morphometry, zona pellucida birefringence (ZPB) and relative abundance of selected candidate genes. Oocytes with an expanded cumulus (Ex), representing those with presumably high developmental competence, had a significantly thicker zona (18.2 vs 17.3µm) and a significantly higher ZPB (64.6 vs 62.1) than oocytes with a compacted cumulus (Cp). Concurrently, oocytes classified as highly developmentally competent (BCB+) had a significantly thicker zona (18.8 vs 16.1µm) and significantly higher ZPB (63.1 vs 61.3) compared with oocytes classified as having low developmental competence. Expression of TFAM, STAT3 and CKS2 was significantly higher in Ex compared with Cp oocytes, whereas expression of COX1, ATPV6E and DNMT1 was lower. Together, the data reveal that developmentally competent equine oocytes are larger in size, have higher ZPB values and exhibit a typical genetic signature of maternally derived transcripts compared with oocytes with lower in vitro developmental competence.

Association of glucose-6-phosphate dehydrogenase activity with oocyte cytoplasmic lipid content, developmental competence, and expression of candidate genes in a sheep model

PURPOSE

To evaluate associations of glucose-6-phosphate dehydrogenase (G6PDH) activity in sheep oocytes with cytoplasmic lipid content, maturational competence, developmental competence to the blastocyst stage, and gene expression of certain molecular markers.

METHODS

Before brilliant cresyl blue (BCB) staining test, oocytes were classified as high, middle, and low cytoplasmic lipid content (HCLC, MCLC, and LCLC) and after the test as having low or high G6PDH-activity (BCB(+) and BCB(-), respectively). After maturation in vitro, a group of oocytes were subjected to IVF followed by in vitro embryo culture and another group was used for evaluation of expression of candidate genes.

RESULTS

The cleavage and blastosyst rates were lowest (P < 0.05) in LCLC group, intermediate (P < 0.05) in MCLC group and highest (P < 0.05) in HCLC group. More (P < 0.05) oocytes in HCLC group were BCB(+), and higher (P < 0.05) maturation, cleavage, and blastocyst rates were seen for BCB(+) oocytes than the BCB(-) oocytes. Our gene expression data indicated that mRNA transcript abundance of ITGB2, pZP3, BMP15, and GDF9 genes was similar between BCB oocytes groups. However, the expression of ATP1A1 was higher (P < 0.05) for BCB(+) oocytes compared to BCB(-) oocytes. In addition, BAX transcript abundance was similar (P > 0.05) among BCB(+), BCB(-), and control groups, before and after maturation in vitro.

CONCLUSION

Activity of G6PDH in sheep oocytes is highly associated with lipid content, and compared with the morphological parameters might be a more precise and objective predictor for subsequent developmental competence in vitro.

Intracellular glutathione content, developmental competence and expression of apoptosis-related genes associated with G6PDH-activity in goat oocyte

PURPOSE

To associate glucose-6-phosphate dehydrogenase (G6PDH) activity in goat oocytes with intracellular glutathione (GSH) content, meiotic competence, developmental potential, and relative abundance of Bax and Bcl-2 genes transcripts.

METHODS

Goat oocytes were exposed to brilliant cresyl blue (BCB) staining test and categorized into BCB(+) (blue-cytoplasm), and BCB(-) (colorless-cytoplasm) groups. A group of oocytes were not exposed to BCB test and was considered as a control group. After maturation in vitro, a group of oocytes were used for determination of nuclear status and intracellular GSH content while another group was subjected to parthenogenetic activation followed by in vitro embryo culture.

RESULTS

We found that BCB(+) oocytes not only yielded higher rate of maturation, but also showed an increased level of intracellular GSH content than BCB(-) and control oocytes. Furthermore, BCB(+) oocytes produced more blastocysts than BCB(-) and control oocytes. Our data revealed that the expression of anti-apoptotic (Bcl-2) and pro-apoptotic (Bax) genes were interacted with G6PDH-activity in mature oocyte, their surrounding cumulus cells, and blastocyst-stage embryos.

CONCLUSIONS

The results of this study demonstrate that selection of goat oocytes based on G6PDH-activity through the BCB test improves their developmental competence, increases intracellular GSH content, and affects the expression of the apoptosis-related genes.

Differences in cytoplasmic maturation between the BCB+ and control porcine oocytes do not justify application of the BCB test for a standard IVM protocol

The Brilliant Cresyl Blue (BCB) test relies on G6PDH activity and a simple protocol for the selection of higher quality oocytes. Although the BCB+ oocytes of all the species that have been investigated are characterized by superior quality when compared to BCB- counterparts, application of the test for embryo production still remains an open issue. The aim of our study was to compare BCB+ and the control oocytes (not subjected to the BCB test) in terms of selected aspects of cytoplasmic maturation (mtDNA copy number, mitochondria distribution, relative transcript abundance of six marker genes). The results of our study revealed more relevant differences within the BCB+ and the control oocytes (before and after IVM) than between the two categories of oocytes. There was no difference in the transcript abundance of the BCB+ and the control oocytes in 5 out of 6 analyzed genes (BMP15, GDF9, ATP5A1, EEF1A, ZAR1) and in mtDNA content (pre-IVM 179609 vs. 176595 and post-IVM 187243 vs. 246984, respectively). With regard to mitochondria distribution in pre- and post-IVM oocytes, there was nonsignificant tendency for a more frequent occurrence of the expected patterns in the BCB+ group. The results of the present study do not support the application of BCB staining in a routine IVM protocol due to relatively high similarity in selected parameters characterizing cytoplasmic maturation of BCB+ and control oocytes. This high similarity may results from the limited amount of less competent BCB- oocytes (10%) still present among nonselected oocytes of proper morphology.

The role of mitochondria from mature oocyte to viable blastocyst

The oocyte requires a vast supply of energy after fertilization to support critical events such as spindle formation, chromatid separation, and cell division. Until blastocyst implantation, the developing zygote is dependent on the existing pool of mitochondria. That pool size within each cell decreases with each cell division. Mitochondria obtained from oocytes of women of advanced reproductive age harbor DNA deletions and nucleotide variations that impair function. The combination of lower number and increased frequency of mutations and deletions may result in inadequate mitochondrial activity necessary for continued embryo development and cause pregnancy failure. Previous reports suggested that mitochondrial activity within oocytes may be supplemented by donor cytoplasmic transfer at the time of intracytoplasmic sperm injection (ICSI). Those reports showed success; however, safety concerns arose due to the potential of two distinct populations of mitochondrial genomes in the offspring. Mitochondrial augmentation of oocytes is now reconsidered in light of our current understanding of mitochondrial function and the publication of a number of animal studies. With a better understanding of the role of this organelle in oocytes immediately after fertilization, blastocyst and offspring, mitochondrial augmentation may be reconsidered as a method to improve oocyte quality.

Developmental potential of prepubertal mouse oocytes is compromised due mainly to their impaired synthesis of glutathione

Although oocytes from prepubertal animals are found less competent than oocytes from adults, the underlying mechanisms are poorly understood. Using the mouse oocyte model, this paper has tested the hypothesis that the developmental potential of prepubertal oocytes is compromised due mainly to their impaired potential for glutathione synthesis. Oocytes from prepubertal and adult mice, primed with or without eCG, were matured in vitro and assessed for glutathione synthesis potential, oxidative stress, Ca²⁺ reserves, fertilization and in vitro development potential. In unprimed mice, abilities for glutathione synthesis, activation, male pronuclear formation, blastocyst formation, cortical granule migration and polyspermic block were all compromised significantly in prepubertal compared to adult oocytes. Cysteamine and cystine supplementation to maturation medium significantly promoted oocyte glutathione synthesis and blastocyst development but difference due to maternal age remained. Whereas reactive oxygen species (ROS) levels increased, Ca²⁺ storage decreased significantly in prepubertal oocytes. Levels of both catalytic and modifier subunits of the γ-glutamylcysteine ligase were significantly lower in prepubertal than in adult oocytes. Maternal eCG priming improved all the parameters and eliminated the age difference. Together, the results have confirmed our hypothesis by showing that prepubertal oocytes have a decreased ability to synthesize glutathione leading to an impaired potential to reduce ROS and to form male pronuclei and blastocysts. The resulting oxidative stress decreases the intracellular Ca²⁺ store resulting in impaired activation at fertilization, and damages the microfilament network, which affects cortical granule redistribution leading to polyspermy.

Zona pellucida birefringence correlates with developmental capacity of bovine oocytes classified by maturational environment, COC morphology and G6PDH activity

In the present study we aimed to analyse structural changes during in vitro maturation of the bovine zona pellucida (ZP) by scanning electron microscopy (SEM) ands zona pellucida birefringence (ZPB). Here we show that alterations during in vitro maturation invasively analysed by SEM are reflected in ZPB. In vivo-matured oocytes displayed significantly lower birefringence parameters and significantly higher blastocyst rates compared with in vitro-derived oocytes (39.1% vs 21.6%). The same was observed for in vitro-matured oocytes with cumulus-oocyte complex (COC) Quality 1 (Q1) compared with Q3-COCs with respect to zona birefringence and developmental capacity. Immature oocytes with Q1-COCs displayed higher ZPB values and a higher developmental capacity to the blastocyst stage (27.7% vs 16.9%) compared with immature Q3-COCs. Considering in vitro-matured oocytes, only those with Q1-COC showed a trend for ZPB similar to in vivo-matured oocytes. Therefore, a decreasing trend for ZPB during in vitro maturation seems to be typical for high-quality oocytes and successful cytoplasmic maturation. In accordance, fully-grown immature oocytes reached significantly higher blastocyst rates (32.0% vs 11.5%) and lower ZPB values compared with still-growing ones. In conclusion, we successfully evaluated the applicability of zona imaging to bovine oocytes: alterations during in vitro maturation invasively analysed by scanning electron microscopy were reflected in the birefringence of the zona pellucida of bovine oocytes affecting developmental capacity at the same value. Therefore ZPB measurement by live zona imaging has potential to become a new tool to assess correctness of in vitro maturation and to predict developmental competence.

Selection of ovine oocytes by brilliant cresyl blue staining

Sheep oocytes derived from the ovaries collected from the slaughterhouse are often used for research on in vitro embryo production, animal cloning, transgenesis, embryonic stem cells, and other embryo biotechnology aspects. Improving the in vitro culture efficiency of oocytes can provide more materials for similar studies. Generally, determination of oocyte quality is mostly based on the layers of cumulus cells and cytoplasm or cytoplasm uniformity and colors. This requires considerable experience to better identify oocyte quality because of the intense subjectivity involved (Gordon (2003), Madison et al. (1992) and De Loos et al. (1992)). BCB staining is a function of glucose-6-phosphate dehydrogenase (G6PD) activity, an enzyme synthesized in developing oocytes, which decreases in activity with maturation. Therefore, unstained oocytes (BCB−) are high in G6PD activity, while the less mature oocytes stains are deep blue (BCB+) due to insuffcient G6PD activity to decolorize the BCB dye.

Oocytes selected using BCB staining enhance nuclear reprogramming and the in vivo development of SCNT embryos in cattle

The selection of good quality oocytes is crucial for in vitro fertilization and somatic cloning. Brilliant cresyl blue (BCB) staining has been used for selection of oocytes from several mammalian species. However, the effects of differential oocyte selection by BCB staining on nuclear reprogramming and in vivo development of SCNT embryos are not well understood. Immature compact cumulus-oocyte complexes (COCs) were divided into control (not exposed to BCB), BCB+ (blue cytoplasm) and BCB- (colorless cytoplasm) groups. We found that BCB+ oocytes yielded a significantly higher somatic cell nuclear transfer (SCNT) blastocyst rate and full term development rate of bovine SCNT embryos than the BCB- and control oocytes. BCB+ embryos (embryos developed from BCB+ oocytes) showed increased acetylation levels of histone H3 at K9 and K18 (AcH3K9, AcH3K18), and methylation levels of histone H3 at K4 (H3K4me2) than BCB- embryos (embryos developed from BCB- oocytes) at the two-cell stage. Furthermore, BCB+ embryos generated more total cells, trophectoderm (TE) cells, and inner cell mass (ICM) cells, and fewer apoptotic cells than BCB- embryos. The expression of SOX2, CDX2, and anti-apoptotic microRNA-21 were up-regulated in the BCB+ blastocysts compared with BCB- blastocysts, whereas the expression of pro-apoptotic gene Bax was down-regulated in BCB+ blastocysts. These results strongly suggest that BCB+ oocytes have a higher nuclear reprogramming capacity, and that BCB staining can be used to select developmentally competent oocytes for nuclear transfer.

Effect of oocyte quality on blastocyst development after in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in a sheep model

OBJECTIVE

To compare blastocyst production, after IVF and ICSI, from sheep oocytes of various quality. Sham-injected oocytes and parthenogenetic activated oocyte groups were considered as control.

DESIGN

Prospective experimental study.

SETTING

University.

ANIMAL(S)

Three- to 6-month-old sheep.

INTERVENTION(S)

Oocyte quality was assessed with the use of brilliant cresyl blue (BCB) stain. Adenosine triphosphate content was measured. Intracytoplasmic sperm injection and IVF were performed and blastocyst development and cell numbers were analyzed.

MAIN OUTCOME MEASURE(S)

Adenosine triphosphate content, embryo development and blastomere numbers.

RESULT(S)

After IVF, BCB-stained (BCB+) oocytes developed up to the blastocyst stage at higher percentages and with more cells per embryo (24.1% vs 4.0% and 69.7 vs 43.9, respectively) than unstained (BCB-) oocytes. Using intracytoplasmic sperm injection, no differences were found in blastocyst production (14.3% vs 11.8%) and number of cells per embryo (71.1 vs 54.3) between BCB+ and BCB- oocytes. Adenosine triphosphate content was higher before in vitro maturation than after in both types of oocytes. Brilliant cresyl blue-stained oocytes had more adenosine triphosphate content than BCB- oocytes.

CONCLUSION(S)

Brilliant cresyl blue-stained oocytes show more adenosine triphosphate content than BCB- oocytes. Results from IVF were affected by the oocyte quality while ICSI did not produce differences in embryo development or blastomere numbers.